بسم الله الرحمن الرحيم
ABG analysis &Acid-base  Imbalance By/Dr.Babiker Mohd. Ahmed DR/ALA ELDIN HASSN . SHAAB T.H .
What is an ABG Arterial Blood Gas Drawn from artery- radial, brachial, femoral It is an  invasive  procedure. Caution must...
Precautions <ul><ul><ul><ul><li>Excessive Heparin  Decreases bicarbonate and PaCO 2  </li></ul></ul></ul></ul><ul><ul><ul>...
ABG analysis <ul><li>Why do we care ? </li></ul><ul><ul><li>Critical care requires a good understanding  </li></ul></ul><u...
Normal Arterial Blood Gas Values* PH  7.35-7.45   35-45 mm Hg    PaCO 2     70-100 m Hg   PaO 2 SaO 2  95-100%     22-26 m...
COMPONENTS OF THE ABG   pH : Measurement of acidity or alkalinity, based on the hydrogen (H+)   7.35 – 7.45 Pao 2  The par...
Stepwise approach to ABG <ul><li>Step 1:  Acidemic or Alkalemic?   </li></ul><ul><li>Step 2:  Is the primary disturbance r...
Interpretation: pH <ul><ul><ul><ul><li>Normal arterial pH = 7.36 to 7.44 </li></ul></ul></ul></ul><ul><ul><ul><li>Determin...
EFFECTS OF pH <ul><li>The most general effect of pH changes are on enzyme function </li></ul><ul><ul><li>Also affect excit...
PH {Potential Hydrogen} <ul><li>The pH is a measurement of the acidity or alkalinity of the blood. </li></ul><ul><li>It is...
pH is inversely related to [H + ]; a pH change of 1.00 represents a 10-fold change in [H + ]   <ul><ul><ul><li>pH   [H + ]...
Assess the PaCO 2 <ul><li>In an uncompensated state  –  when the pH and paCO 2  moves in the same direction: the primary p...
Assess the HCO 3 <ul><li>The pH and the HCO 3  moving in the opposite directions, we would conclude that the primary disor...
<ul><li>HCO 3 -  (bicarbonate): </li></ul><ul><li>SB (standard bicarbonate) </li></ul><ul><li>AB (actual bicarbonate) </li...
<ul><li>AB and SB are parameters to reflect  </li></ul><ul><li>metabolism, regulated by kidney. </li></ul><ul><li>Differen...
Assessing Oxygenation <ul><li>Normal value for arterial blood gas 80-100mmHg decreased progressively with    age </li></u...
Acceptable PaO2 Values on Room Air 60 yrs    80 mm Hg       1mm Hg/yr Age Group Accepable PaO2 (mm Hg) Adults upto 60 y...
INDICATORS OF OXYGENATION <ul><li>Assessing the efficiency of oxygenation requires knowledge of </li></ul><ul><li>Ventilat...
P(A-a)O 2 <ul><li>P(A-a)O 2  is the alveolar-arterial difference in partial pressure of oxygen.  It is commonly called the...
  Compare  P A O 2  to P a O 2 <ul><li>Healthy people:  P A O 2  = P a O 2 </li></ul><ul><li>Two Approaches to Comparison ...
a/A  ratio <ul><li>Normally averages just over 0.8  (Am. Rev. Resp. Dis. 109: 142-145, 1974) . </li></ul><ul><li>a/A  rati...
<ul><li>A-a gradient =  PAO2 - PaO2 PaO2   (partial pressure of O2 in the artery) --obtained from the arterial blood gases...
Alveolar Gas Equation <ul><li>PAO 2  = PIO 2  - 1.2 (PaCO 2 ) where PIO 2   =  FIO 2  (P B  – 47 mm Hg)   </li></ul><ul><l...
Oxygen Saturation <ul><li>Oxygen Saturation ( SaO2 ) </li></ul><ul><ul><li>This refers to the amount of oxygen being carri...
Important points for assessing tissue oxygenation <ul><li>This is the O2 that’s really available at the tissue level. </li...
<ul><li>PvO 2 :   Oxygenic partial pressure of mixed venous blood. </li></ul><ul><li>Normal: 35-45mmHg </li></ul><ul><li>m...
<ul><li>CaO2:   The content of the oxygen of the arterial blood .  </li></ul><ul><li>Normal: 19-21mmol/L </li></ul><ul><li...
SaO 2  and Oxygen Content <ul><li>Tissues need a requisite amount of oxygen molecules for metabolism.  Neither the PaO 2  ...
SaO 2  – is it calculated or measured? <ul><li>SaO 2  is measured in a ‘co-oximeter’.  The traditional ‘blood gas machine’...
Carbon monoxide – an important cause of hypoxemia <ul><li>Normal %COHb in the blood is 1-2%, from metabolism and small amo...
Physiologic causes of low PaO 2   <ul><ul><li>Non-Respiratory  P[A-a]O2 </li></ul></ul><ul><ul><li>Cardiac Right to Left S...
Anion GAP <ul><li>Calculation of AG is useful approach to analyse metabolic acidosis </li></ul><ul><li>AG = (Na+ + K+)  – ...
<ul><li>Anion gap (AG) : </li></ul><ul><li>the difference of undetermined anion and undetermined cation in serum. </li></u...
ANION GAP <ul><li>The AG is estimated by substracting the sum of Cl and Hco3 concentration  from the plasma Na: Na+unmeasu...
ELEVATED AG ACIDOSIS <ul><li>Causes are best remembered by mnemonic  KULT: </li></ul><ul><li>K: K etoacidosis (DKA,alcohol...
<ul><li>  K  etoacidosis  </li></ul><ul><li>U remia  </li></ul><ul><li>  S  epsis </li></ul><ul><li>S alicylate & other dr...
BASE EXCESS <ul><li>Base Excess (BE)  </li></ul><ul><li>Rising levels of bicarbonate make the blood more alkaline and a de...
BASE EXCESS <ul><li>Base Excess can be used in the following </li></ul><ul><li>To interpretate change in Hco3 levels : </l...
BASES EXCESS <ul><li>2-  If the base excess is less than -2 {Base deficit} then there is metabolic acidosis which may be p...
BASE EXCESS <ul><li>3- If the base excess is greater than +2 then there is metabolic alkalosis which may be primary or com...
Formula <ul><li>With the base excess is -10 in a 50kg person with metabolic acidosis mM of Hco 3  needed for correction is...
Compensated or Uncompensated—what does this mean? <ul><li>Evaluate pH—is it normal?  Yes </li></ul><ul><li>Next evaluate p...
COMPENSATION <ul><li>A patient can be uncompensated or partially compensated or fully compensated </li></ul><ul><li>pH rem...
Partially compensated pH paco 2 Hco 3 Res.Acidosis Res.Alkalosis Met. Acidosis Met.Alkalosis
FULLY COMPENSATED pH paco2 Hco3 Resp.Acidosis Normal but <7.40 Resp.Alkalosis Normal but >7.40 Met. Acidosis Normal but <7...
Clinical Significance <ul><li>To evaluate respiratory failure </li></ul><ul><li>type 1 or type 2 </li></ul><ul><li>To eval...
Hypoxia <ul><li>Mild: 80-60mmHg </li></ul><ul><li>Mediate: 60-40mmHg </li></ul><ul><li>Severe: <40mmHg </li></ul>
Respiratory Failure <ul><li>PaO 2 <60mmHg  respiratory failure </li></ul><ul><li>Notice: sea level, quiet, inspire air  </...
Classification of Respiratory Failure <ul><li>Type 1  Type2  </li></ul><ul><li>PaO2 (mmHg)  <60  <60  </li></ul><ul><li>Pa...
Other Parameters <ul><li>SaO2 :  Saturation of arterial blood oxygen </li></ul><ul><li>Normal: 0.95-0.98 </li></ul><ul><li...
PH 2,3DPG temperature  CO 2 ODC to right deviation Oxygenated hemoglobin release oxygen to tissue, prevent hypoxia of the ...
SaO 2 % PO 2 Oxygen dissociation curve
Oxygen dissociation curve:  SaO 2  vs. PaO 2   Also shown are CaO 2  vs. PaO 2  for two different hemoglobin contents:  15...
ODC <ul><li>Oxygen Dissociation Curve  </li></ul><ul><li>The curve highlights the affinity of oxygen to haemoglobin </li><...
ODC <ul><li>Oxygen Dissociation Curve  </li></ul><ul><li>It can be seen from the shape of the oxygen dissociation curve th...
Classification of Acid-basic Disorder <ul><li>PH  PaCO2  HCO 3 -   </li></ul><ul><li>Rest. acidosis  </li></ul><ul><li>Res...
Respiratory Acid Base Disorders <ul><li>Respiratory alkalosis most common of all the 4 acid base disorders (23-46%) -follo...
RESPIRATORY ACIDOSIS
<ul><li>is defined as a pH less than 7.35 with a paco2 greater than 45 mmHg. </li></ul><ul><li>Acidosis  – accumulation of...
RESPIRATORY ACIDOSIS <ul><li>Caused by hyperkapnia due to hypoventilation </li></ul><ul><ul><li>Characterized by a pH decr...
RESPIRATORY ACIDOSIS <ul><li>The speed and depth of breathing control the amount of  CO 2  in the blood </li></ul><ul><li>...
RESPIRATORY ACIDOSIS <ul><li>Respiratory acidosis can also develop when diseases of the nerves or muscles of the chest imp...
RESPIRATORY ACIDOSIS <ul><li>The treatment of respiratory acidosis aims to improve the function of the lungs </li></ul><ul...
RESPIRATORY ACIDOSIS <ul><li>Decreased  CO 2  removal can be the result of: </li></ul><ul><ul><li>Obstruction of air passa...
Manifestations of Resp Acidosis <ul><li>NEUROMUSCULAR: Related to cerebral A  vasodilatation &    Cerebral BF </li></ul><...
<ul><li>CARDIOVASCULAR: Related to coronary    vasodilation </li></ul><ul><li>Tachycardia with    N BP </li></ul><ul><li>...
Homeostatic Response  to   Respiratory Acidosis <ul><li>Imm response to rise in CO2 (& H2CO3)    blood and tissue buffers...
<ul><li>predicts rise in PaCO2    obligatory hypoxemia in pts breathing R.A.  </li></ul><ul><li>Resultant fall in PaO2 li...
Causes of Chronic Respiratory Acidosis <ul><li>EXCRETORY COMPONENT PROBLEMS: </li></ul><ul><li>Ventilation: COPD </li></ul...
Treatment of Respiratory Acidosis <ul><li>Ensure adequate oxygenation - care to avoid inadequate oxygenation while prevent...
<ul><li>Alkali (HCO3) therapy rarely in ac and never in ch resp acidosis    only if acidemia directly inhibiting cardiac ...
RESPIRATORY ALKALOSIS
Manifestations of Resp Alkalosis <ul><li>NEUROMUSCULAR: Related to cerebral A  vasoconstriction &    Cerebral BF </li></u...
<ul><li>CARDIOVASCULAR: Related to coronary    vasoconstriction </li></ul><ul><li>Tachycardia with    N BP </li></ul><ul>...
RESPIRATORY ALKALOSIS <ul><li>Can be the result of: </li></ul><ul><ul><li>1) Anxiety, emotional disturbances </li></ul></u...
RESPIRATORY ALKALOSIS <ul><li>Anxiety  is an emotional disturbance </li></ul><ul><li>The most common cause of hyperventila...
RESPIRATORY ALKALOSIS <ul><li>Usually the only treatment needed is to slow down the rate of breathing </li></ul><ul><li>Br...
RESPIRATORY ALKALOSIS <ul><li>Respiratory center lesions </li></ul><ul><ul><li>Damage to brain centers responsible for mon...
RESPIRATORY ALKALOSIS <ul><li>F ever </li></ul><ul><ul><li>Rapid shallow breathing blows off too much  CO 2 </li></ul></ul>
RESPIRATORY ALKALOSIS <ul><li>Salicylate poisoning (Aspirin overdose) </li></ul><ul><ul><li>Ventilation is stimulated with...
RESPIRATORY ALKALOSIS <ul><li>Assisted Respiration </li></ul><ul><ul><li>Administration of  CO 2  in the exhaled air of th...
RESPIRATORY ALKALOSIS <ul><li>High Altitude </li></ul><ul><ul><li>Low concentrations of  O 2  in the arterial blood reflex...
RESPIRATORY ALKALOSIS <ul><li>Kidneys compensate by: </li></ul><ul><ul><li>Retaining hydrogen ions </li></ul></ul><ul><ul>...
RESPIRATORY ALKALOSIS <ul><li>Decreased  CO 2  in the lungs will eventually slow the rate of breathing </li></ul><ul><ul><...
Homeostatic Response to Resp Alkalosis <ul><li>In ac resp alkalosis, imm response to fall in CO2 (& H2CO3)    release of ...
METABOLIC ACIDOSIS
Metabolic Acidosis <ul><li>Bicarbonate less than 22mEq/L with a pH of less than 7.35. </li></ul><ul><li>Renal failure </li...
METABOLIC ACIDOSIS <ul><li>The causes of metabolic acidosis can be grouped into  five  major categories </li></ul><ul><ul>...
METABOLIC ACIDOSIS <ul><li>Unregulated diabetes mellitus causes  ketoacidosis </li></ul><ul><ul><li>Body metabolizes fat r...
METABOLIC ACIDOSIS <ul><li>This leads to excessive production of  ketones: </li></ul><ul><ul><li>Acetone </li></ul></ul><u...
METABOLIC ACIDOSIS <ul><li>2) Abnormal Metabolism </li></ul><ul><ul><li>The body also produces excess acid in the advanced...
METABOLIC ACIDOSIS <ul><li>3) Kidney Insufficiencies </li></ul><ul><ul><li>Even the production of normal amounts of acid m...
METABOLIC ACIDOSIS <ul><li>3) Kidney Insufficiencies </li></ul><ul><ul><li>Kidneys may be unable to rid the plasma of even...
METABOLIC ACIDOSIS <ul><li>3) Kidney Insufficiencies </li></ul><ul><ul><li>This type of kidney malfunction is called  rena...
METABOLIC ACIDOSIS <ul><li>Treating the underlying cause of metabolic acidosis is the usual course of action </li></ul><ul...
METABOLIC ACIDOSIS <ul><li>Metabolic acidosis may also be treated directly </li></ul><ul><ul><li>If the acidosis is mild, ...
METABOLIC ALKALOSIS
Metabolic alkalosis <ul><li>Bicarbonate more than 26m Eq /L with a pH more than 7.45 </li></ul><ul><li>Excess of base /los...
METABOLIC ALKALOSIS <ul><li>A reduction in  H +  in the case of metabolic alkalosis can be caused by a deficiency of non-c...
METABOLIC ALKALOSIS <ul><li>Treatment of metabolic alkalosis is most often accomplished by replacing water and electrolyte...
METABOLIC ALKALOSIS <ul><li>Can be the result of: </li></ul><ul><ul><li>1) Ingestion of Alkaline Substances </li></ul></ul...
METABOLIC ALKALOSIS <ul><li>Baking soda ( NaHCO 3 ) often used as a remedy for gastric hyperacidity </li></ul><ul><ul><li>...
METABOLIC ALKALOSIS <ul><li>Bicarbonate neutralizes high acidity in stomach (heart burn) </li></ul><ul><li>The extra bicar...
METABOLIC ALKALOSIS <ul><li>Commercially prepared alkaline products for gastric hyperacidity are not absorbed from the dig...
METABOLIC ALKALOSIS <ul><li>2) Vomiting (abnormal loss of HCl) </li></ul><ul><ul><li>Excessive loss of  H + </li></ul></ul...
METABOLIC ALKALOSIS   <ul><li>Reaction of the body to alkalosis is to lower  pH  by: </li></ul><ul><ul><li>Retain  CO 2  b...
MIXED DISORDERS <ul><ul><ul><ul><ul><li>. </li></ul></ul></ul></ul></ul>
Mixed Acid-Base Disorders <ul><li>Patients may have two or more acid-base disorders at one time </li></ul><ul><li>Delta Ga...
Mixed Acid-base Disorders are Common <ul><li>In chronically ill respiratory patients, mixed disorders are probably more co...
Tips to Diagnosing Mixed  Acid-base Disorders <ul><li>TIP 1.   Do not interpret any blood gas data for acid-base diagnosis...
Tips to Diagnosing Mixed Acid-base Disorders  (cont.) <ul><li>TIP 2.   Single acid-base disorders do not lead to normal bl...
Tips to Diagnosing Mixed Acid-base Disorders  (cont) <ul><li>TIP 3 .  Simplified rules predict the pH and HCO 3 -  for a g...
Expected changes in pH and HCO 3 -  for   a 10-mm Hg change   in PaCO 2  resulting from either primary   hypoventilation (...
Predicted changes in HCO 3 -  for a directional change in PaCO 2  can help uncover mixed acid-base disorders.  <ul><li>A n...
<ul><li>TIP 4.   In maximally-compensated metabolic acidosis, the numerical value of PaCO 2  should be the same (or close ...
RESPONSES TO: ACIDOSIS AND ALKALOSIS <ul><li>Mechanisms protect the body against life-threatening changes in hydrogen ion ...
<ul><li>Buffer Systems   2) Respiratory Responses 3) Renal Responses 4) Intracellular Shifts of Ions </li></ul>
BUFFERS <ul><li>A buffer is a combination of chemicals in solution that resists any significant change in  pH </li></ul><u...
BUFFERS <ul><li>Buffering systems provide an immediate response to fluctuations in  pH:  1) Phosphate </li></ul><ul><ul><l...
BUFFERS <ul><li>Chemical buffers are able to react immediately (within milliseconds) </li></ul><ul><li>Chemical buffers ar...
<ul><li>Regulates  pH  within the cells and the urine </li></ul><ul><ul><li>Phosphate concentrations are higher intracellu...
<ul><li>1) Phosphate buffer system </li></ul><ul><li>Na 2 HPO 4  + H +  NaH 2 PO 4   + Na +   </li></ul><ul><ul><li>Most i...
PROTEIN BUFFER SYSTEM <ul><li>2) Protein Buffer System </li></ul><ul><ul><li>Behaves as a buffer in both plasma and cells ...
PROTEIN BUFFER SYSTEM <ul><li>Proteins are excellent buffers because they contain both acid and base groups that can give ...
PROTEIN BUFFER SYSTEM <ul><li>Hemoglobin buffers  H +  from metabolically produced  CO 2  in the plasma only </li></ul><ul...
BICARBONATE BUFFER SYSTEM <ul><li>3) Bicarbonate Buffer System </li></ul><ul><ul><li>Predominates in extracellular fluid (...
BICARBONATE BUFFER SYSTEM <ul><li>This system is most  important because the concentration of both components can be regul...
BICARBONATE BUFFER SYSTEM <ul><li>H 2 CO 3   <=>  H +  + HCO 3 - </li></ul><ul><ul><li>Hydrogen ions  generated   by metab...
BICARBONATE BUFFER SYSTEM <ul><li>Equilibrium shifts toward the formation of  acid </li></ul><ul><ul><li>Hydrogen ions tha...
BICARBONATE BUFFER SYSTEM Loss of HCl Addition of lactic acid H + HCO 3 - H 2 CO 3 H 2 O CO 2 + + Exercise Vomiting
RESPIRATORY RESPONSE <ul><li>Neurons in the medulla oblongata and pons constitute the   Respiratory Center </li></ul><ul><...
CHEMOSENSITIVE AREAS <ul><li>Chemosensitive areas of the respiratory center are able to detect blood concentration levels ...
CHEMOSENSITIVE AREAS <ul><li>The effect of stimulating the respiratory centers by increased  CO 2  and  H +  is weakened i...
CHEMORECEPTORS <ul><li>Chemoreceptors are also present in the  carotid  and  aortic  arteries which respond to changes in ...
CHEMORECEPTORS <ul><li>Overall compensatory response is: </li></ul><ul><ul><li>Hyperventilation  in response to increased ...
RENAL RESPONSE <ul><li>The kidney compensates for  Acid - Base  imbalance within 24 hours and is responsible for long term...
Intracellular Shifts of Ions
HYPERKALEMIA <ul><li>Hyperkalemia  is generally associated with acidosis </li></ul><ul><ul><li>Accompanied by a shift of  ...
HYPOKALEMIA <ul><li>Hypokalemia   is generally associated with reciprocal exchanges of  H +  and  K +  in the opposite dir...
ELECTROLYTE SHIFTS Acidosis Compensatory Response Result -  H +  buffered intracellularly - Hyperkalemia Alkalosis Compens...
Arterial Blood Gases:  Test Your Overall Understanding <ul><li>Case 1.   A 55-year-old man is evaluated in the pulmonary l...
Arterial Blood Gases:  Test Your Overall Understanding Case 1 - Discussion OXYGENATION :   The PaO 2  and SaO 2  are both ...
Arterial Blood Gases:  Test Your Overall Understanding <ul><li>Case 2.   A 46-year-old man has been in the hospital two da...
Arterial Blood Gases:  Test Your Overall Understanding Case 2 - Discussion   OXYGENATION:   The PaO 2  is lower than expec...
Arterial Blood Gases:  Test Your Overall Understanding <ul><li>Case 3.   A 58-year-old woman is being evaluated in the eme...
Arterial Blood Gases:  Test Your Overall Understanding Case 3 - Discussion   OXYGENATION:   The patient's PaO 2  is reduce...
  END   ACID - BASE BALANCE
<ul><li>] </li></ul>END THANK YOU
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  • 单位容积的动脉血液中所含氧的总量。包括与血红蛋白结合的氧和物理溶解的氧两个部分。
  • 动脉血氧与血红蛋白结合的程度
  • Abg&acid base balance

    1. 1. بسم الله الرحمن الرحيم
    2. 2. ABG analysis &Acid-base Imbalance By/Dr.Babiker Mohd. Ahmed DR/ALA ELDIN HASSN . SHAAB T.H .
    3. 3. What is an ABG Arterial Blood Gas Drawn from artery- radial, brachial, femoral It is an invasive procedure. Caution must be taken with patient on anticoagulants. Arterial blood gas analysis is an essential part of diagnosing and managing the patient’s oxygenation status, ventilation failure and acid base balance.
    4. 4. Precautions <ul><ul><ul><ul><li>Excessive Heparin Decreases bicarbonate and PaCO 2 </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Large Air bubbles not expelled from sample PaO 2 rises, PaCO 2 may fall slightly. </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Fever or Hypothermia, Hyperventilation or breath holding (Due to anxiety) may lead to erroneous lab results </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Care must be taken to prevent bleeding </li></ul></ul></ul></ul>
    5. 5. ABG analysis <ul><li>Why do we care ? </li></ul><ul><ul><li>Critical care requires a good understanding </li></ul></ul><ul><ul><li>Helps in the differential and final diagnosis </li></ul></ul><ul><ul><li>Helps in determining treatment plan </li></ul></ul><ul><ul><li>Treating acid/base disorders helps medications work better (i.e. antibiotics, vasopressors, etc.) </li></ul></ul><ul><ul><li>Helps in ventilator management </li></ul></ul><ul><ul><li>Severe acid/base disorders may need dialysis </li></ul></ul><ul><ul><li>Changes in electrolyte levels in acidosis (increased K+ and Na+, and decreases in HCO3) </li></ul></ul>
    6. 6. Normal Arterial Blood Gas Values* PH 7.35-7.45 35-45 mm Hg PaCO 2 70-100 m Hg PaO 2 SaO 2 95-100% 22-26 mEq/L - HCO3- % MetHb <2.0% <3.0% %COHb 16-22 ml O 2 /dl CaO 2 * At sea level, breathing ambient air ** Age-dependent
    7. 7. COMPONENTS OF THE ABG pH : Measurement of acidity or alkalinity, based on the hydrogen (H+) 7.35 – 7.45 Pao 2 The partial pressure oxygen that is dissolved in arterial blood. 80-100 mm Hg. PCO 2 : The amount of carbon dioxide dissolved in arterial blood. 35– 45 mmHg HCO 3 : The calculated value of the amount of bicarbonate in the blood 22 – 26 mmol/L B.E: The base excess indicates the amount of excess or insufficient level of bicarbonate. -2 to +2mEq/L (A negative base excess indicates a base deficit in blood) SaO 2 : The arterial oxygen saturation. >95%
    8. 8. Stepwise approach to ABG <ul><li>Step 1: Acidemic or Alkalemic? </li></ul><ul><li>Step 2: Is the primary disturbance respiratory or metabolic? </li></ul><ul><li>Step 3. Asses to Pa O 2. A value below 80mm Hg indicates Hypoxemia. For a respiratory disturbance, determine whether it is acute or chronic. </li></ul><ul><li>Step 4 . For a metabolic acidosis, determine whether an anion gap is present. </li></ul><ul><li>Step 5 . Assess the normal compensation by the respiratory system for a metabolic disturbance </li></ul>
    9. 9. Interpretation: pH <ul><ul><ul><ul><li>Normal arterial pH = 7.36 to 7.44 </li></ul></ul></ul></ul><ul><ul><ul><li>Determine Acidosis versus Alkalosis </li></ul></ul></ul><ul><ul><ul><ul><li>1. pH <7.35: Acidosis </li></ul></ul></ul></ul><ul><ul><ul><ul><li>2. pH >7.45: Alkalosis </li></ul></ul></ul></ul><ul><ul><ul><li>Metabolic Conditions are suggested if </li></ul></ul></ul><ul><ul><ul><ul><li>pH changes in the same direction as pCO2/HCO3- </li></ul></ul></ul></ul><ul><ul><ul><ul><li>pH is abnormal but pCO2 remains unchanged </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Respiratory Conditions are suggested if: </li></ul></ul></ul></ul><ul><ul><ul><ul><li>pH changes in the opp direction as pCO2/HCO3- </li></ul></ul></ul></ul><ul><ul><ul><ul><li>pH is abnormal but HCO3- remains unchanged </li></ul></ul></ul></ul>
    10. 10. EFFECTS OF pH <ul><li>The most general effect of pH changes are on enzyme function </li></ul><ul><ul><li>Also affect excitability of nerve and muscle cells </li></ul></ul>pH pH Excitability Excitability
    11. 11. PH {Potential Hydrogen} <ul><li>The pH is a measurement of the acidity or alkalinity of the blood. </li></ul><ul><li>It is inversely proportional to the no. of (H+) in the blood. </li></ul><ul><li>The normal pH range is 7.35-7.45. </li></ul><ul><li>Changes in body system functions that occur in an acidic state decreases the force of cardiac contractions, decreases the vascular response to catecholamines, and a diminished response to the effects and actions of certain medications. </li></ul><ul><li>An alkalotic state interferes with tissue oxygenation and normal neurological and muscular functioning. </li></ul><ul><li>Significant changes in the blood pH above 7.8 or below 6.8 will interfere with cellular functioning, and if uncorrected, will lead to death. </li></ul>
    12. 12. pH is inversely related to [H + ]; a pH change of 1.00 represents a 10-fold change in [H + ] <ul><ul><ul><li>pH [H + ] in nanomoles/L </li></ul></ul></ul><ul><ul><ul><li>7.00 100 </li></ul></ul></ul><ul><ul><ul><li>7.10 80 </li></ul></ul></ul><ul><ul><ul><li>7.30 50 </li></ul></ul></ul><ul><ul><ul><li>7.40 40 </li></ul></ul></ul><ul><ul><ul><li>7.52 30 </li></ul></ul></ul><ul><ul><ul><li>7.70 20 </li></ul></ul></ul><ul><ul><ul><li>8.00 10 </li></ul></ul></ul>
    13. 13. Assess the PaCO 2 <ul><li>In an uncompensated state – when the pH and paCO 2 moves in the same direction: the primary problem is metabolic. </li></ul><ul><li>The decreasing paco 2 indicates that the lungs acting as a buffer response (blowing of the excess CO 2 ) </li></ul><ul><li>If evidence of compensation is present but the pH has not been corrected to within the normal range, this would be described as metabolic disorder with the partial respiratory compensation. </li></ul>
    14. 14. Assess the HCO 3 <ul><li>The pH and the HCO 3 moving in the opposite directions, we would conclude that the primary disorder is respiratory and the kidneys acting as a buffer response: are compensating by retaining HCO 3 to return the pH to normal range . </li></ul>
    15. 15. <ul><li>HCO 3 - (bicarbonate): </li></ul><ul><li>SB (standard bicarbonate) </li></ul><ul><li>AB (actual bicarbonate) </li></ul><ul><li>SB: the contents of HCO 3 - of serum of arterial </li></ul><ul><li>blood in 38℃, PaCO2 40mmHg, SaO 2 100%. </li></ul><ul><li>Normal: 22-27mmol/L </li></ul><ul><li>mean: 24mmol/L </li></ul><ul><li>AB: The contents of HCO 3 - in actual condition. </li></ul><ul><li>In normal person: AB=SB </li></ul>
    16. 16. <ul><li>AB and SB are parameters to reflect </li></ul><ul><li>metabolism, regulated by kidney. </li></ul><ul><li>Difference of AB-SB can reflect the </li></ul><ul><li>respiratory affection on serum HCO 3 - . </li></ul><ul><li>Respiratory acidosis: AB>SB </li></ul><ul><li>Respiratory alkalosis: AB<SB </li></ul><ul><li>Metabolic acidosis: AB = SB<Normal </li></ul><ul><li>Metabolic alkalosis: AB=SB>Normal </li></ul>
    17. 17. Assessing Oxygenation <ul><li>Normal value for arterial blood gas 80-100mmHg decreased progressively with  age </li></ul><ul><li>Normal value for venous blood gas 40mmHg </li></ul><ul><li>Normal SaO2 </li></ul><ul><ul><li>Arterial: 97% </li></ul></ul><ul><ul><li>Venous: 75% </li></ul></ul><ul><ul><li>Hypoxemia is PaO2 < 80 mm Hg at RA </li></ul></ul>
    18. 18. Acceptable PaO2 Values on Room Air 60 yrs  80 mm Hg   1mm Hg/yr Age Group Accepable PaO2 (mm Hg) Adults upto 60 yrs & Children > 80 Newborn 40-70 70 yrs > 70 80 yrs > 60 90 yrs > 50
    19. 19. INDICATORS OF OXYGENATION <ul><li>Assessing the efficiency of oxygenation requires knowledge of </li></ul><ul><li>Ventilation is the mechanical movement of air. Oxygenation is the process of transporting oxygen from the alveolus across capillary membranes into pulmonary circulation.  A-a gradient (Alveolar to arterial gradient): </li></ul><ul><li>Provides an assessment of alveolar-capillary gas exchange. To calculate you need the alveolar PO2 (PAO2) and arterial pO2 (paO2). The larger the gradient, the more serious the respiratory compromise </li></ul>
    20. 20. P(A-a)O 2 <ul><li>P(A-a)O 2 is the alveolar-arterial difference in partial pressure of oxygen. It is commonly called the “A-a gradient,” though it does not actually result from an O 2 pressure gradient in the lungs. Instead, it results from gravity-related blood flow changes within the lungs (normal ventilation-perfusion imbalance). </li></ul><ul><li>PAO 2 is always calculated based on FIO 2 , PaCO 2, and barometric pressure. </li></ul><ul><li>PaO 2 is always measured on an arterial blood sample in a “blood gas machine.” </li></ul><ul><li>Normal P(A-a)O 2 ranges from 5 to 25 mm Hg breathing room air (it increases with age). A higher than normal P(A-a)O 2 means the lungs are not transferring oxygen properly from alveoli into the pulmonary capillaries. Except for right to left cardiac shunts, an elevated P(A-a)O 2 signifies some sort of problem within the lungs . </li></ul>
    21. 21. Compare P A O 2 to P a O 2 <ul><li>Healthy people: P A O 2 = P a O 2 </li></ul><ul><li>Two Approaches to Comparison </li></ul><ul><ul><li>(P A O 2 - P a O 2 ) difference </li></ul></ul><ul><ul><li>P a O 2 / P A O 2 ratio </li></ul></ul>. A-a difference increases with pulmonary disease
    22. 22. a/A ratio <ul><li>Normally averages just over 0.8 (Am. Rev. Resp. Dis. 109: 142-145, 1974) . </li></ul><ul><li>a/A ratio falls with pulmonary disease. </li></ul><ul><li>Lower limit normal: </li></ul><ul><ul><li>young (room air) : 0.74 </li></ul></ul><ul><ul><li>older ( room air) : 0.78 </li></ul></ul><ul><ul><li>Both groups (100% O 2 ): 0.82 </li></ul></ul>
    23. 23. <ul><li>A-a gradient =  PAO2 - PaO2 PaO2 (partial pressure of O2 in the artery) --obtained from the arterial blood gases. PAO2  (partial pressure of O2 in the alveoli)-- obtained from the Alveolar Gas equation. </li></ul>
    24. 24. Alveolar Gas Equation <ul><li>PAO 2 = PIO 2 - 1.2 (PaCO 2 ) where PIO 2 = FIO 2 (P B – 47 mm Hg) </li></ul><ul><li>Except in a temporary unsteady state, alveolar PO 2 (PAO 2 ) is always higher than arterial PO 2 (PaO 2 ). As a result, whenever PAO 2 decreases, PaO 2 also decreases. Thus, from the AG equation: </li></ul><ul><li>If FIO 2 and P B are constant, then as PaCO 2 increases both PAO 2 and PaO 2 will decrease (hypercapnia causes hypoxemia). </li></ul><ul><li>If FIO 2 decreases and P B and PaCO 2 are constant, both PAO 2 and PaO 2 will decrease (suffocation causes hypoxemia). </li></ul><ul><li>If P B decreases (e.g., with altitude), and PaCO 2 and FIO 2 are constant, both PAO 2 and PaO 2 will decrease (mountain climbing leads to hypoxemia). </li></ul>
    25. 25. Oxygen Saturation <ul><li>Oxygen Saturation ( SaO2 ) </li></ul><ul><ul><li>This refers to the amount of oxygen being carried by the haemoglobin (Hb) molecules </li></ul></ul><ul><ul><ul><li>The Hb molecule is divided into two portionsGlobin - made of protein </li></ul></ul></ul><ul><ul><ul><li>Haem - made of iron </li></ul></ul></ul><ul><ul><ul><li>There are 4 groups of haem on each molecule of Hb </li></ul></ul></ul><ul><ul><ul><li>Each haem group can bind 1 O2 molecule </li></ul></ul></ul>
    26. 26. Important points for assessing tissue oxygenation <ul><li>This is the O2 that’s really available at the tissue level. </li></ul><ul><li>Is the THb normal? </li></ul><ul><ul><li>Low THb means the ability of the blood to carry the O2 to the tissues is decreased </li></ul></ul><ul><li>Is perfusion normal? </li></ul><ul><ul><li>Low perfusion means the blood isn’t even getting to the tissues </li></ul></ul>
    27. 27. <ul><li>PvO 2 : Oxygenic partial pressure of mixed venous blood. </li></ul><ul><li>Normal: 35-45mmHg </li></ul><ul><li>mean: 40mmHg </li></ul><ul><li>Significance: Pa-vO 2 is to reflect the tissue absorbing oxygen. </li></ul>
    28. 28. <ul><li>CaO2: The content of the oxygen of the arterial blood . </li></ul><ul><li>Normal: 19-21mmol/L </li></ul><ul><li>Significance: a comprehensive parameter to evaluate arterial oxygen. </li></ul>
    29. 29. SaO 2 and Oxygen Content <ul><li>Tissues need a requisite amount of oxygen molecules for metabolism. Neither the PaO 2 nor the SaO 2 tells how much oxygen is in the blood. How much is provided by the oxygen content, CaO 2 (units = ml O 2 /dl). CaO 2 is calculated as: CaO 2 = quantity O 2 bound + quantity O 2 dissolved to hemoglobin in plasma CaO 2 = (Hb x 1.34 x SaO 2 ) + (.003 x PaO 2 ) </li></ul><ul><li>Hb = hemoglobin in gm%; 1.34 = ml O 2 that can be bound to each gm of Hb; SaO 2 is percent saturation of hemoglobin with oxygen; .003 is solubility coefficient of oxygen in plasma: .003 ml dissolved O 2 /mm Hg PO 2 . </li></ul>
    30. 30. SaO 2 – is it calculated or measured? <ul><li>SaO 2 is measured in a ‘co-oximeter’. The traditional ‘blood gas machine’ measures only pH, PaCO 2 and PaO 2, , whereas the co-oximeter measures SaO 2 , carboxyhemoglobin, methemoglobin and hemoglobin content. Newer ‘blood gas’ consoles incorporate a co-oximeter, and so offer the latter group of measurements as well as pH, PaCO 2 and PaO 2 . </li></ul><ul><li>Always make sure the SaO 2 is measured, not calculated. If it is calculated from the PaO 2 and the O 2 -dissociation curve, it provides no new information, and could be inaccurate -- especially in states of CO intoxication or excess methemoglobin. CO and metHb do not affect PaO 2 , but do lower the SaO 2 . </li></ul>
    31. 31. Carbon monoxide – an important cause of hypoxemia <ul><li>Normal %COHb in the blood is 1-2%, from metabolism and small amount of ambient CO (higher in traffic-congested areas) </li></ul><ul><li>All smokers have excess CO in their blood. </li></ul><ul><li>CO binds @ 200x more avidly to hemoglobin than O 2 , displacing O 2 from the heme binding sites. </li></ul><ul><li>CO : 1) decreases SaO 2 by the amount of %COHb present, and 2) shifts the O 2 -dissociation curve to the left, retarding unloading of oxygen to the tissues . </li></ul><ul><li>CO does not affect PaO 2 , only SaO 2 . To detect CO poisoning, SaO 2 and/or COHb must be measured (requires co-oximeter). In the presence of excess CO, SaO 2 (when measured) will be lower than expected from the PaO 2 . </li></ul>
    32. 32. Physiologic causes of low PaO 2 <ul><ul><li>Non-Respiratory P[A-a]O2 </li></ul></ul><ul><ul><li>Cardiac Right to Left Shunt Increased </li></ul></ul><ul><ul><li>Decreased Pio2 Normal </li></ul></ul><ul><ul><li>Respiratory </li></ul></ul><ul><ul><li>Pulmonary Right to Left Shunt Increased </li></ul></ul><ul><ul><li>V/Q Imbalance Increased </li></ul></ul><ul><ul><li>Diffussion barrier Increased </li></ul></ul><ul><ul><li>Hypoventilatio [increased CO2] Normal </li></ul></ul>
    33. 33. Anion GAP <ul><li>Calculation of AG is useful approach to analyse metabolic acidosis </li></ul><ul><li>AG = (Na+ + K+) – (cl- + Hco3-) </li></ul><ul><li>* A change in the pH of 0.08 for each 10 mm Hg indicates an ACUTE condition. * A change in the pH of 0.03 for each 10 mm Hg indicates a CHRONIC condition. </li></ul>
    34. 34. <ul><li>Anion gap (AG) : </li></ul><ul><li>the difference of undetermined anion and undetermined cation in serum. </li></ul><ul><li>AG={Na + K}-(Cl - + HCO 3 - ) </li></ul><ul><li>Normal: 8-16mmol/L Significance: </li></ul><ul><li>AG = acidosis: ketoacidosis, kidney failure </li></ul><ul><li>AG normal acidosis: Cl , diarrhea, fixed </li></ul><ul><li>acid decrease </li></ul><ul><li>to evaluate mix acid-basic disorder </li></ul>
    35. 35. ANION GAP <ul><li>The AG is estimated by substracting the sum of Cl and Hco3 concentration from the plasma Na: Na+unmeasured cations=Cl +Hco3 +unmeasured anions: </li></ul><ul><li>AG={Na} – {Cl} +{Hco3} </li></ul><ul><li>The major unmeasured cations are calcium,magnesium and potassium. </li></ul><ul><li>The major unmeasured anions are albumin,sulphate, phosphate,lactate. </li></ul>
    36. 36. ELEVATED AG ACIDOSIS <ul><li>Causes are best remembered by mnemonic KULT: </li></ul><ul><li>K: K etoacidosis (DKA,alcoholic ketoacidosis,starvation) </li></ul><ul><li>U: U raemia </li></ul><ul><li>L: L actic acidosis </li></ul><ul><li>T; T oxins (Ethylene glycol,methanol,salicylates,paraldehyde,INH} </li></ul>
    37. 37. <ul><li> K etoacidosis </li></ul><ul><li>U remia </li></ul><ul><li> S epsis </li></ul><ul><li>S alicylate & other drugs </li></ul><ul><li> M ethanol </li></ul><ul><li> A lcohol (Ethanol) </li></ul><ul><li>L actic acidosis </li></ul><ul><li> E thylene glycol </li></ul>REMEMBER
    38. 38. BASE EXCESS <ul><li>Base Excess (BE) </li></ul><ul><li>Rising levels of bicarbonate make the blood more alkaline and a depletion of bicarbonate makes it more acidic </li></ul><ul><li>Base excess refers to the amount of base (alkali) which needs to be added or taken away from the blood to return the pH to 7.4 </li></ul>
    39. 39. BASE EXCESS <ul><li>Base Excess can be used in the following </li></ul><ul><li>To interpretate change in Hco3 levels : </li></ul><ul><li>1- If the base excess is between -2 and +2 then there is no metabolic acidosis or alkalosis based on observed Hco3 change. </li></ul>
    40. 40. BASES EXCESS <ul><li>2- If the base excess is less than -2 {Base deficit} then there is metabolic acidosis which may be primary or compensatory process. </li></ul>
    41. 41. BASE EXCESS <ul><li>3- If the base excess is greater than +2 then there is metabolic alkalosis which may be primary or compensatory process. </li></ul><ul><li>=BASE EXCESS alone cannot differentiate between primary or compensatory process. </li></ul>
    42. 42. Formula <ul><li>With the base excess is -10 in a 50kg person with metabolic acidosis mM of Hco 3 needed for correction is: </li></ul><ul><li>= 0.3 X body weight X BE </li></ul><ul><li>= 0.3 X 50 X10 = 150 mM </li></ul>
    43. 43. Compensated or Uncompensated—what does this mean? <ul><li>Evaluate pH—is it normal? Yes </li></ul><ul><li>Next evaluate pCO2 & HCO3 </li></ul><ul><ul><li>pH normal + increased pCO2 + increased HCO3 = compensated respiratory acidosis </li></ul></ul><ul><ul><li>pH normal + decreased HCO3 + decreased pCO2 = compensated metabolic acidosis </li></ul></ul>
    44. 44. COMPENSATION <ul><li>A patient can be uncompensated or partially compensated or fully compensated </li></ul><ul><li>pH remains outside the normal range </li></ul><ul><li>pH has returned within normal range- fully compensated though other values may be still abnormal </li></ul><ul><li>Be aware that neither the system has the ability to overcompensate </li></ul>
    45. 45. Partially compensated pH paco 2 Hco 3 Res.Acidosis Res.Alkalosis Met. Acidosis Met.Alkalosis
    46. 46. FULLY COMPENSATED pH paco2 Hco3 Resp.Acidosis Normal but <7.40 Resp.Alkalosis Normal but >7.40 Met. Acidosis Normal but <7.40 Met. Alkalosis Normal but >7.40
    47. 47. Clinical Significance <ul><li>To evaluate respiratory failure </li></ul><ul><li>type 1 or type 2 </li></ul><ul><li>To evaluate acid-basic disorder </li></ul>
    48. 48. Hypoxia <ul><li>Mild: 80-60mmHg </li></ul><ul><li>Mediate: 60-40mmHg </li></ul><ul><li>Severe: <40mmHg </li></ul>
    49. 49. Respiratory Failure <ul><li>PaO 2 <60mmHg respiratory failure </li></ul><ul><li>Notice: sea level, quiet, inspire air </li></ul><ul><li>rule off other causes ( heart </li></ul><ul><li>disease) </li></ul>
    50. 50. Classification of Respiratory Failure <ul><li>Type 1 Type2 </li></ul><ul><li>PaO2 (mmHg) <60 <60 </li></ul><ul><li>PaCO2 (mmHg) ≤50 >50 </li></ul>
    51. 51. Other Parameters <ul><li>SaO2 : Saturation of arterial blood oxygen </li></ul><ul><li>Normal: 0.95-0.98 </li></ul><ul><li>Significance: a parameter to evaluate hypoxia, but not sensitive </li></ul><ul><li>ODC ( Dissociation curve of oxygenated hemoglobin): “S” shape </li></ul>
    52. 52. PH 2,3DPG temperature CO 2 ODC to right deviation Oxygenated hemoglobin release oxygen to tissue, prevent hypoxia of the tissue. But absorbed oxygen of hemoglobin is decreased from the alveoli. Bohr effect : movement of ODC place is induced by PH.
    53. 53. SaO 2 % PO 2 Oxygen dissociation curve
    54. 54. Oxygen dissociation curve: SaO 2 vs. PaO 2 Also shown are CaO 2 vs. PaO 2 for two different hemoglobin contents: 15 gm% and 10 gm%. CaO 2 units are ml O 2 /dl. P 50 is the PaO 2 at which SaO 2 is 50%.
    55. 55. ODC <ul><li>Oxygen Dissociation Curve </li></ul><ul><li>The curve highlights the affinity of oxygen to haemoglobin </li></ul><ul><li>When PO2 is high, oxygen is strongly affiliated to haemoglobin, so oxygen saturation will be high </li></ul><ul><li>When PO2 is low there is less affinity of oxygen to haemoglobin, so oxygen saturation drops </li></ul>
    56. 56. ODC <ul><li>Oxygen Dissociation Curve </li></ul><ul><li>It can be seen from the shape of the oxygen dissociation curve that initially there is a slight drop in SaO2 when there is a reduced PO2 </li></ul><ul><li>However, at a certain point there is a sudden drop in saturation as indicated by the steep decline in the curve </li></ul><ul><ul><li>Therefore, SaO2 normally only drops sharply if the PO2 is at a very low level8 kPa is the point at which the patient is hypoxaemic and is in respiratory failure </li></ul></ul>
    57. 57. Classification of Acid-basic Disorder <ul><li>PH PaCO2 HCO 3 - </li></ul><ul><li>Rest. acidosis </li></ul><ul><li>Rest. alkalosis </li></ul><ul><li>Meta. Acidosis </li></ul><ul><li>Meta. Alkalosis </li></ul>
    58. 58. Respiratory Acid Base Disorders <ul><li>Respiratory alkalosis most common of all the 4 acid base disorders (23-46%) -followed by met alkalosis - review of 8289 ABG analysis in ICU pts </li></ul><ul><li>Kaehny WD, MCNA 67(4), 1983 p 915-928 </li></ul><ul><li>Resp acidosis seen in 14-22% of pts </li></ul><ul><li>Attention to possibility of hypoxemia and its correction always assumes priority in analysis of pts with a possible respiratory acid-base disorder </li></ul>
    59. 59. RESPIRATORY ACIDOSIS
    60. 60. <ul><li>is defined as a pH less than 7.35 with a paco2 greater than 45 mmHg. </li></ul><ul><li>Acidosis – accumulation of co 2 , combines with water in the body to produce carbonic acid, thus lowering the pH of the blood. </li></ul><ul><li>Any condition that results in hypoventilation can cause respiratory acidosis. </li></ul>Res. Acidosis
    61. 61. RESPIRATORY ACIDOSIS <ul><li>Caused by hyperkapnia due to hypoventilation </li></ul><ul><ul><li>Characterized by a pH decrease and an increase in CO 2 </li></ul></ul>
    62. 62. RESPIRATORY ACIDOSIS <ul><li>The speed and depth of breathing control the amount of CO 2 in the blood </li></ul><ul><li>Normally when CO 2 builds up, the pH of the blood falls and the blood becomes acidic </li></ul><ul><li>High levels of CO 2 in the blood stimulate the parts of the brain that regulate breathing, which in turn stimulate faster and deeper breathing </li></ul>
    63. 63. RESPIRATORY ACIDOSIS <ul><li>Respiratory acidosis can also develop when diseases of the nerves or muscles of the chest impair the mechanics of breathing </li></ul><ul><li>In addition, a person can develop respiratory acidosis if overly sedated from narcotics and strong sleeping medications that slow respiration </li></ul>
    64. 64. RESPIRATORY ACIDOSIS <ul><li>The treatment of respiratory acidosis aims to improve the function of the lungs </li></ul><ul><li>Drugs to improve breathing may help people who have lung diseases such as asthma and emphysema </li></ul>
    65. 65. RESPIRATORY ACIDOSIS <ul><li>Decreased CO 2 removal can be the result of: </li></ul><ul><ul><li>Obstruction of air passages </li></ul></ul><ul><ul><li>Decreased respiration (depression of respiratory centers) </li></ul></ul><ul><ul><li>Decreased gas exchange between pulmonary capillaries and air sacs of lungs </li></ul></ul><ul><ul><li>Collapse of lung </li></ul></ul>
    66. 66. Manifestations of Resp Acidosis <ul><li>NEUROMUSCULAR: Related to cerebral A vasodilatation &  Cerebral BF </li></ul><ul><li>Anxiety </li></ul><ul><li>Asterixis </li></ul><ul><li>Lethargy, Stupor, Coma </li></ul><ul><li>Delirium </li></ul><ul><li>Seizures </li></ul><ul><li>Headache </li></ul><ul><li>Papilledema </li></ul><ul><li>Focal Paresis </li></ul><ul><li>Tremors, myoclonus </li></ul>
    67. 67. <ul><li>CARDIOVASCULAR: Related to coronary vasodilation </li></ul><ul><li>Tachycardia with  N BP </li></ul><ul><li>Ventricular arrythmias (related to hypoxemia and not hypercapnia per se) </li></ul><ul><li>Senstivity to digitalis </li></ul><ul><li>BIOCHEMICAL ABNORMALITIES: </li></ul><ul><li>  tCO2 </li></ul><ul><li>  Cl - </li></ul><ul><li>  PO 4 3- </li></ul>
    68. 68. Homeostatic Response to Respiratory Acidosis <ul><li>Imm response to rise in CO2 (& H2CO3)  blood and tissue buffers take up H+ ions, H2CO3 dissociates and HCO3- increases with rise in pH. </li></ul><ul><li>Steady state reached in 10 min & lasts for 8 hours. </li></ul><ul><li>PCO2 of CSF changes rapidly to match PaCO2. </li></ul><ul><li>Hypercapnia that persists > few hours induces an increase in CSF HCO3- that reaches max by 24 hr and partly restores the CSF pH. </li></ul><ul><li>After 8 hrs, kidneys generate HCO3- </li></ul><ul><li>Steady state reached in 3-5 d </li></ul>
    69. 69. <ul><li>predicts rise in PaCO2  obligatory hypoxemia in pts breathing R.A. </li></ul><ul><li>Resultant fall in PaO2 limits hypercapnia to  80 to 90 mm Hg </li></ul><ul><li>Higher PaCO2 leads to PaO2 incompatible with life. </li></ul><ul><li>Hypoxemia, not hypercapnia or acidemia, that poses the principal threat to life. </li></ul><ul><li>Consequently, oxygen administration represents a critical element in the management </li></ul>
    70. 70. Causes of Chronic Respiratory Acidosis <ul><li>EXCRETORY COMPONENT PROBLEMS: </li></ul><ul><li>Ventilation: COPD </li></ul><ul><li>Advanced ILD </li></ul><ul><li>Restriction of thorax/chest wall: </li></ul><ul><li>Kyphoscoliosis, Arthritis </li></ul><ul><li>Fibrothorax </li></ul><ul><li>Hydrothorax </li></ul><ul><li>Muscular dystrophy </li></ul><ul><li>Polymyositis </li></ul>
    71. 71. Treatment of Respiratory Acidosis <ul><li>Ensure adequate oxygenation - care to avoid inadequate oxygenation while preventing worsening of hypercapnia due to supression of hypoxemic resp drive </li></ul><ul><li>Correct underlying disorder if possible </li></ul><ul><li>Avoid rapid decrease in ch elevated PCO2 to avoid post hypercapnic met alkalosis (arrythmias, seizures  adequate intake of Cl-) </li></ul>
    72. 72. <ul><li>Alkali (HCO3) therapy rarely in ac and never in ch resp acidosis  only if acidemia directly inhibiting cardiac functions </li></ul><ul><li>Problems with alkali therapy: </li></ul><ul><li>Decreased alv ventilation by decrease in pH mediated ventilatory drive </li></ul><ul><li>Enhanced carbon dioxide production from bicarbonate decomposition </li></ul><ul><li>Volume expansion. </li></ul><ul><li>COPD pts on diuretics who develop met alkalosis often benfefited by acetazolamide </li></ul>
    73. 73. RESPIRATORY ALKALOSIS
    74. 74. Manifestations of Resp Alkalosis <ul><li>NEUROMUSCULAR: Related to cerebral A vasoconstriction &  Cerebral BF </li></ul><ul><li>Lightheadedness </li></ul><ul><li>Confusion </li></ul><ul><li>Decreased intellectual function </li></ul><ul><li>Syncope </li></ul><ul><li>Seizures </li></ul><ul><li>Paraesthesias (circumoral, extremities) </li></ul><ul><li>Muscle twitching, cramps, tetany </li></ul><ul><li>Hyperreflexia </li></ul><ul><li>Strokes in pts with sickle cell disease </li></ul>
    75. 75. <ul><li>CARDIOVASCULAR: Related to coronary vasoconstriction </li></ul><ul><li>Tachycardia with  N BP </li></ul><ul><li>Angina </li></ul><ul><li>ECG changes (ST depression) </li></ul><ul><li>Ventricular arrythmias </li></ul><ul><li>GASTROINTESTINAL: Nausea & Vomitting (cerebral hypoxia) </li></ul><ul><li>BIOCHEMICAL ABNORMALITIES: </li></ul><ul><li> tCO2  PO 4 3- </li></ul><ul><li> Cl -  Ca 2+ </li></ul>
    76. 76. RESPIRATORY ALKALOSIS <ul><li>Can be the result of: </li></ul><ul><ul><li>1) Anxiety, emotional disturbances </li></ul></ul><ul><ul><li>2) Respiratory center lesions </li></ul></ul><ul><ul><li>3) Fever </li></ul></ul><ul><ul><li>4) Salicylate poisoning (overdose) </li></ul></ul><ul><ul><li>5) Assisted respiration </li></ul></ul><ul><li>6) High altitude (low P O 2 ) </li></ul>
    77. 77. RESPIRATORY ALKALOSIS <ul><li>Anxiety is an emotional disturbance </li></ul><ul><li>The most common cause of hyperventilation, and thus respiratory alkalosis, is anxiety </li></ul>
    78. 78. RESPIRATORY ALKALOSIS <ul><li>Usually the only treatment needed is to slow down the rate of breathing </li></ul><ul><li>Breathing into a paper bag or holding the breath as long as possible may help raise the blood CO 2 content as the person breathes carbon dioxide back in after breathing it out </li></ul>
    79. 79. RESPIRATORY ALKALOSIS <ul><li>Respiratory center lesions </li></ul><ul><ul><li>Damage to brain centers responsible for monitoring breathing rates </li></ul></ul><ul><ul><ul><li>Tumors </li></ul></ul></ul><ul><ul><ul><li>Strokes </li></ul></ul></ul>
    80. 80. RESPIRATORY ALKALOSIS <ul><li>F ever </li></ul><ul><ul><li>Rapid shallow breathing blows off too much CO 2 </li></ul></ul>
    81. 81. RESPIRATORY ALKALOSIS <ul><li>Salicylate poisoning (Aspirin overdose) </li></ul><ul><ul><li>Ventilation is stimulated without regard to the status of O 2 , CO 2 or H + in the body fluids </li></ul></ul>
    82. 82. RESPIRATORY ALKALOSIS <ul><li>Assisted Respiration </li></ul><ul><ul><li>Administration of CO 2 in the exhaled air of the care - giver </li></ul></ul>Your insurance won’t cover a ventilator any longer, so Bob here will be giving you mouth to mouth for the next several days
    83. 83. RESPIRATORY ALKALOSIS <ul><li>High Altitude </li></ul><ul><ul><li>Low concentrations of O 2 in the arterial blood reflexly stimulates ventilation in an attempt to obtain more O 2 </li></ul></ul><ul><ul><li>Too much CO 2 is “blown off” in the process </li></ul></ul>
    84. 84. RESPIRATORY ALKALOSIS <ul><li>Kidneys compensate by: </li></ul><ul><ul><li>Retaining hydrogen ions </li></ul></ul><ul><ul><li>Increasing bicarbonate excretion </li></ul></ul>H + HCO 3 - HCO 3 - HCO 3 - HCO 3 - HCO 3 - HCO 3 - HCO 3 - HCO 3 - HCO 3 - HCO 3 - H + H + H + H + H + H + H + H + H + H +
    85. 85. RESPIRATORY ALKALOSIS <ul><li>Decreased CO 2 in the lungs will eventually slow the rate of breathing </li></ul><ul><ul><li>Will permit a normal amount of CO 2 to be retained in the lung </li></ul></ul>
    86. 86. Homeostatic Response to Resp Alkalosis <ul><li>In ac resp alkalosis, imm response to fall in CO2 (& H2CO3)  release of H+ by blood and tissue buffers  react with HCO3-  fall in HCO3- (usually not less than 18) and fall in pH </li></ul><ul><li>Cellular uptake of HCO3- in exchange for Cl- </li></ul><ul><li>Steady state in 15 min - persists for 6 hrs </li></ul><ul><li>After 6 hrs kidneys increase excretion of HCO3- (usually not less than 12-14) </li></ul><ul><li>Steady state reached in 1 1/2 to 3 days. </li></ul><ul><li>Timing of onset of hypocapnia usually not known except for pts on MV. Hence progression to subac and ch resp alkalosis indistinct in clinical practice </li></ul>
    87. 87. METABOLIC ACIDOSIS
    88. 88. Metabolic Acidosis <ul><li>Bicarbonate less than 22mEq/L with a pH of less than 7.35. </li></ul><ul><li>Renal failure </li></ul><ul><li>Diabetic ketoacidosis </li></ul><ul><li>Anaerobic metabolism </li></ul><ul><li>Starvation </li></ul><ul><li>Salicylate intoxication </li></ul>
    89. 89. METABOLIC ACIDOSIS <ul><li>The causes of metabolic acidosis can be grouped into five major categories </li></ul><ul><ul><li>1) Ingesting an acid or a substance that is metabolized to acid </li></ul></ul><ul><ul><li>2) Abnormal Metabolism </li></ul></ul><ul><ul><li>3) Kidney Insufficiencies </li></ul></ul><ul><ul><li>4) Strenuous Exercise </li></ul></ul><ul><ul><li>5) Severe Diarrhea </li></ul></ul>
    90. 90. METABOLIC ACIDOSIS <ul><li>Unregulated diabetes mellitus causes ketoacidosis </li></ul><ul><ul><li>Body metabolizes fat rather than glucose </li></ul></ul><ul><ul><li>Accumulations of metabolic acids (Keto Acids) cause an increase in plasma H + </li></ul></ul>
    91. 91. METABOLIC ACIDOSIS <ul><li>This leads to excessive production of ketones: </li></ul><ul><ul><li>Acetone </li></ul></ul><ul><ul><li>Acetoacetic acid </li></ul></ul><ul><ul><li>B-hydroxybutyric acid </li></ul></ul><ul><li>Contribute excessive numbers of hydrogen ions to body fluids </li></ul>Acetone Acetoacetic acid Hydroxybutyric acid H + H + H + H + H + H + H +
    92. 92. METABOLIC ACIDOSIS <ul><li>2) Abnormal Metabolism </li></ul><ul><ul><li>The body also produces excess acid in the advanced stages of shock, when lactic acid is formed through the metabolism of sugar </li></ul></ul>
    93. 93. METABOLIC ACIDOSIS <ul><li>3) Kidney Insufficiencies </li></ul><ul><ul><li>Even the production of normal amounts of acid may lead to acidosis when the kidneys aren't functioning normally </li></ul></ul>
    94. 94. METABOLIC ACIDOSIS <ul><li>3) Kidney Insufficiencies </li></ul><ul><ul><li>Kidneys may be unable to rid the plasma of even the normal amounts of H + generated from metabolic acids </li></ul></ul><ul><ul><li>Kidneys may be also unable to conserve an adequate amount of HCO 3 - to buffer the normal acid load </li></ul></ul>
    95. 95. METABOLIC ACIDOSIS <ul><li>3) Kidney Insufficiencies </li></ul><ul><ul><li>This type of kidney malfunction is called renal tubular acidosis or uremic acidosis and may occur in people with kidney failure or with abnormalities that affect the kidneys' ability to excrete acid </li></ul></ul>
    96. 96. METABOLIC ACIDOSIS <ul><li>Treating the underlying cause of metabolic acidosis is the usual course of action </li></ul><ul><ul><li>For example, they may control diabetes with insulin or treat poisoning by removing the toxic substance from the blood </li></ul></ul><ul><ul><li>Occasionally dialysis is needed to treat severe overdoses and poisonings </li></ul></ul>
    97. 97. METABOLIC ACIDOSIS <ul><li>Metabolic acidosis may also be treated directly </li></ul><ul><ul><li>If the acidosis is mild, intravenous fluids and treatment for the underlying disorder may be all that's needed </li></ul></ul>
    98. 98. METABOLIC ALKALOSIS
    99. 99. Metabolic alkalosis <ul><li>Bicarbonate more than 26m Eq /L with a pH more than 7.45 </li></ul><ul><li>Excess of base /loss of acid can cause </li></ul><ul><li>Ingestion of excess antacids, excess use of bicarbonate, or use of lactate in dialysis. </li></ul><ul><li>Protracted vomiting, gastric suction,hypchoremia,excess use of diuretics, or high levels of aldesterone. </li></ul>
    100. 100. METABOLIC ALKALOSIS <ul><li>A reduction in H + in the case of metabolic alkalosis can be caused by a deficiency of non-carbonic acids </li></ul><ul><li>This is associated with an increase in HCO 3 - </li></ul>
    101. 101. METABOLIC ALKALOSIS <ul><li>Treatment of metabolic alkalosis is most often accomplished by replacing water and electrolytes ( sodium and potassium ) while treating the underlying cause </li></ul><ul><li>Occasionally when metabolic alkalosis is very severe, dilute acid in the form of ammonium chloride is given by IV </li></ul>
    102. 102. METABOLIC ALKALOSIS <ul><li>Can be the result of: </li></ul><ul><ul><li>1) Ingestion of Alkaline Substances </li></ul></ul><ul><ul><li>2) Vomiting ( loss of HCl ) </li></ul></ul>
    103. 103. METABOLIC ALKALOSIS <ul><li>Baking soda ( NaHCO 3 ) often used as a remedy for gastric hyperacidity </li></ul><ul><ul><li>NaHCO 3 dissociates to Na + and HCO 3 - </li></ul></ul>
    104. 104. METABOLIC ALKALOSIS <ul><li>Bicarbonate neutralizes high acidity in stomach (heart burn) </li></ul><ul><li>The extra bicarbonate is absorbed into the plasma increasing pH of plasma as bicarbonate binds with free H + </li></ul>
    105. 105. METABOLIC ALKALOSIS <ul><li>Commercially prepared alkaline products for gastric hyperacidity are not absorbed from the digestive tract and do not alter the pH status of the plasma </li></ul>
    106. 106. METABOLIC ALKALOSIS <ul><li>2) Vomiting (abnormal loss of HCl) </li></ul><ul><ul><li>Excessive loss of H + </li></ul></ul>Gastric juices contain large amounts of HCl During HCl secretion, bicarbonate is added to the plasma <ul><li>The bicarbonate is neutralized as HCl is reabsorbed by the plasma from the digestive tract </li></ul><ul><li>During vomiting H+ is lost as HCl and the bicarbonate is not neutralized in the plasma </li></ul><ul><ul><li>Loss of HCl increases the plasma bicarbonate and thus results in an increase in pH of the blood </li></ul></ul>
    107. 107. METABOLIC ALKALOSIS <ul><li>Reaction of the body to alkalosis is to lower pH by: </li></ul><ul><ul><li>Retain CO 2 by decreasing breathing rate </li></ul></ul><ul><ul><li>Kidneys increase the retention of H + </li></ul></ul>CO 2 CO 2 H + H + H + H +
    108. 108. MIXED DISORDERS <ul><ul><ul><ul><ul><li>. </li></ul></ul></ul></ul></ul>
    109. 109. Mixed Acid-Base Disorders <ul><li>Patients may have two or more acid-base disorders at one time </li></ul><ul><li>Delta Gap </li></ul><ul><ul><li>Delta HCO 3 = HCO 3 + Change in anion gap </li></ul></ul><ul><ul><li>>24 = metabolic alkalosis </li></ul></ul>
    110. 110. Mixed Acid-base Disorders are Common <ul><li>In chronically ill respiratory patients, mixed disorders are probably more common than single disorders, e.g., RAc + MAlk, RAc + Mac, Ralk + MAlk. </li></ul><ul><li>In renal failure (and other conditions) combined MAlk + MAc is also encountered. </li></ul><ul><li>Always be on the lookout for mixed acid-base disorders. They can be missed! </li></ul>
    111. 111. Tips to Diagnosing Mixed Acid-base Disorders <ul><li>TIP 1. Do not interpret any blood gas data for acid-base diagnosis without closely examining the serum electrolytes: Na + , K + , Cl - , and CO 2 . </li></ul><ul><ul><li>A serum CO 2 out of the normal range always represents some type of acid-base disorder (barring lab or transcription error). </li></ul></ul><ul><ul><li>High-serum CO 2 indicates metabolic alkalosis &/or bicarbonate retention as compensation for respiratory acidosis. </li></ul></ul><ul><ul><li>Low-serum CO 2 indicates metabolic acidosis &/or bicarbonate excretion as compensation for respiratory alkalosis. </li></ul></ul><ul><ul><li>Note that serum CO 2 may be normal in the presence of two or more acid-base disorders. </li></ul></ul>
    112. 112. Tips to Diagnosing Mixed Acid-base Disorders (cont.) <ul><li>TIP 2. Single acid-base disorders do not lead to normal blood pH. Although pH can end up in the normal range (7.35 - 7.45) with a single mild acid-base disorder, a truly normal pH with distinctly abnormal HCO 3 - and PaCO 2 invariably suggests two or more primary disorders. </li></ul><ul><ul><li>Example: pH 7.40, PaCO 2 20 mm Hg, HCO 3 - 12 mEq/L in a patient with sepsis. Normal pH results from two co-existing and unstable acid-base disorders - acute respiratory alkalosis and metabolic acidosis. </li></ul></ul>
    113. 113. Tips to Diagnosing Mixed Acid-base Disorders (cont) <ul><li>TIP 3 . Simplified rules predict the pH and HCO 3 - for a given change in PaCO 2 . If the pH or HCO 3 - is higher or lower than expected for the change in PaCO 2 , the patient probably has a metabolic acid-base disorder as well. </li></ul><ul><li>The next slide shows expected changes in pH and HCO 3 - (in mEq/L) for a 10-mm Hg change in PaCO 2 resulting from either primary hypoventilation (respiratory acidosis) or primary hyperventilation (respiratory alkalosis). </li></ul>
    114. 114. Expected changes in pH and HCO 3 - for a 10-mm Hg change in PaCO 2 resulting from either primary hypoventilation (respiratory acidosis) or primary hyperventilation (respiratory alkalosis): <ul><ul><ul><li> ACUTE CHRONIC </li></ul></ul></ul><ul><ul><ul><li>Resp Acidosis </li></ul></ul></ul><ul><ul><ul><ul><li>pH ↓ by 0.07 pH ↓ by 0.03 </li></ul></ul></ul></ul><ul><ul><ul><ul><li>HCO 3 - ↑ by 1* HCO 3 - ↑ by 3 - 4 </li></ul></ul></ul></ul><ul><ul><ul><li>Resp Alkalosis </li></ul></ul></ul><ul><ul><ul><ul><li>pH ↑ by 0.08 pH ↑ by 0.03 </li></ul></ul></ul></ul><ul><ul><ul><ul><li>HCO 3 - ↓ by 2 HCO 3 - ↓ by 5 </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Units for HCO 3 - are mEq/L </li></ul></ul></ul></ul>
    115. 115. Predicted changes in HCO 3 - for a directional change in PaCO 2 can help uncover mixed acid-base disorders. <ul><li>A normal or slightly low HCO 3 - in the presence of hypercapnia suggests a concomitant metabolic acidosis, e.g., pH 7.27, PaCO 2 50 mm Hg, HCO 3 - 22 mEq/L. Based on the rule for increase in HCO 3 - with hypercapnia, it should be at least 25 mEq/L in this example; that it is only 22 mEq/L suggests a concomitant metabolic acidosis. </li></ul><ul><li>b) A normal or slightly elevated HCO 3 - in the presence of hypocapnia suggests a concomitant metabolic alkalosis, e.g., pH 7.56, PaCO 2 30 mm Hg, HCO 3 - 26 mEq/L. Based on the rule for decrease in HCO 3 - with hypocapnia, it should be at least 23 mEq/L in this example; that it is 26 mEq/L suggests a concomitant metabolic alkalosis. </li></ul>
    116. 116. <ul><li>TIP 4. In maximally-compensated metabolic acidosis, the numerical value of PaCO 2 should be the same (or close to) as the last two digits of arterial pH. This observation reflects the formula for expected respiratory compensation in metabolic acidosis: </li></ul><ul><li>Expected PaCO 2 = [1.5 x serum CO 2 ] + (8 ± 2) </li></ul><ul><li>In contrast, compensation for metabolic alkalosis (by increase in PaCO 2 ) is highly variable, and in some cases there may be no or minimal compensation. </li></ul>Tips to Diagnosing Mixed Acid-base Disorders (cont.)
    117. 117. RESPONSES TO: ACIDOSIS AND ALKALOSIS <ul><li>Mechanisms protect the body against life-threatening changes in hydrogen ion concentration </li></ul><ul><ul><li>1) Buffering Systems in Body Fluids </li></ul></ul><ul><ul><li>2) Respiratory Responses </li></ul></ul><ul><ul><li>3) Renal Responses </li></ul></ul><ul><li>4) Intracellular Shifts of Ions </li></ul>
    118. 118. <ul><li>Buffer Systems 2) Respiratory Responses 3) Renal Responses 4) Intracellular Shifts of Ions </li></ul>
    119. 119. BUFFERS <ul><li>A buffer is a combination of chemicals in solution that resists any significant change in pH </li></ul><ul><li>Able to bind or release free H + ions </li></ul>
    120. 120. BUFFERS <ul><li>Buffering systems provide an immediate response to fluctuations in pH: 1) Phosphate </li></ul><ul><ul><li>2) Protein </li></ul></ul><ul><ul><li>3) Bicarbonate Buffer System </li></ul></ul>
    121. 121. BUFFERS <ul><li>Chemical buffers are able to react immediately (within milliseconds) </li></ul><ul><li>Chemical buffers are the first line of defense for the body for fluctuations in pH </li></ul>
    122. 122. <ul><li>Regulates pH within the cells and the urine </li></ul><ul><ul><li>Phosphate concentrations are higher intracellularly and within the kidney tubules </li></ul></ul><ul><ul><li>Too low of a concentration in extracellular fluid to have much importance as an ECF buffer system </li></ul></ul>PHOSPHATE BUFFER SYSTEM
    123. 123. <ul><li>1) Phosphate buffer system </li></ul><ul><li>Na 2 HPO 4 + H + NaH 2 PO 4 + Na + </li></ul><ul><ul><li>Most important in the intracellular system </li></ul></ul>PHOSPHATE BUFFER SYSTEM
    124. 124. PROTEIN BUFFER SYSTEM <ul><li>2) Protein Buffer System </li></ul><ul><ul><li>Behaves as a buffer in both plasma and cells </li></ul></ul><ul><ul><li>Hemoglobin is by far the most important protein buffer </li></ul></ul>
    125. 125. PROTEIN BUFFER SYSTEM <ul><li>Proteins are excellent buffers because they contain both acid and base groups that can give up or take up H + </li></ul><ul><li>Proteins are extremely abundant in the cell </li></ul><ul><li>The more limited number of proteins in the plasma reinforce the bicarbonate system in the ECF </li></ul>
    126. 126. PROTEIN BUFFER SYSTEM <ul><li>Hemoglobin buffers H + from metabolically produced CO 2 in the plasma only </li></ul><ul><li>As hemoglobin releases O 2 it gains a great affinity for H + </li></ul>Hb O 2 O 2 O 2 O 2
    127. 127. BICARBONATE BUFFER SYSTEM <ul><li>3) Bicarbonate Buffer System </li></ul><ul><ul><li>Predominates in extracellular fluid ( ECF ) </li></ul></ul><ul><ul><li>HCO 3 - + added H + H 2 CO 3 </li></ul></ul>H +
    128. 128. BICARBONATE BUFFER SYSTEM <ul><li>This system is most important because the concentration of both components can be regulated: </li></ul><ul><ul><li>Carbonic acid by the respiratory system </li></ul></ul><ul><li>Bicarbonate by the renal system </li></ul>
    129. 129. BICARBONATE BUFFER SYSTEM <ul><li>H 2 CO 3 <=> H + + HCO 3 - </li></ul><ul><ul><li>Hydrogen ions generated by metabolism or by ingestion react with bicarbonate base to form more carbonic acid </li></ul></ul>
    130. 130. BICARBONATE BUFFER SYSTEM <ul><li>Equilibrium shifts toward the formation of acid </li></ul><ul><ul><li>Hydrogen ions that are lost (vomiting) causes carbonic acid to dissociate yielding replacement H + and bicarbonate </li></ul></ul>
    131. 131. BICARBONATE BUFFER SYSTEM Loss of HCl Addition of lactic acid H + HCO 3 - H 2 CO 3 H 2 O CO 2 + + Exercise Vomiting
    132. 132. RESPIRATORY RESPONSE <ul><li>Neurons in the medulla oblongata and pons constitute the Respiratory Center </li></ul><ul><li>Stimulation and limitation of respiratory rates are controlled by the respiratory center </li></ul><ul><li>accomplished by responding to CO 2 and H + concentrations in the blood </li></ul>
    133. 133. CHEMOSENSITIVE AREAS <ul><li>Chemosensitive areas of the respiratory center are able to detect blood concentration levels of CO 2 and H + </li></ul><ul><li>Increases in CO 2 and H + stimulate the respiratory center </li></ul><ul><ul><li>The effect is to raise respiration rates </li></ul></ul><ul><ul><ul><li>But the effect diminishes in 1 - 2 minutes </li></ul></ul></ul>
    134. 134. CHEMOSENSITIVE AREAS <ul><li>The effect of stimulating the respiratory centers by increased CO 2 and H + is weakened in environmentally increased CO 2 levels </li></ul><ul><li>Symptoms may persist for several days </li></ul>
    135. 135. CHEMORECEPTORS <ul><li>Chemoreceptors are also present in the carotid and aortic arteries which respond to changes in partial pressures of O 2 and CO 2 or pH </li></ul><ul><li>Increased levels of CO 2 (low pH ) or decreased levels of O 2 stimulate respiration rates to increase </li></ul>
    136. 136. CHEMORECEPTORS <ul><li>Overall compensatory response is: </li></ul><ul><ul><li>Hyperventilation in response to increased CO 2 or H + (low pH ) </li></ul></ul><ul><ul><li>Hypoventilation in response to decreased CO 2 or H + (high pH ) </li></ul></ul>
    137. 137. RENAL RESPONSE <ul><li>The kidney compensates for Acid - Base imbalance within 24 hours and is responsible for long term control </li></ul><ul><li>The kidney in response: </li></ul><ul><ul><li>To Acidosis </li></ul></ul><ul><ul><ul><li>Retains bicarbonate ions and eliminates hydrogen ions </li></ul></ul></ul><ul><ul><li>To Alkalosis </li></ul></ul><ul><ul><ul><li>Eliminates bicarbonate ions and retains hydrogen ions </li></ul></ul></ul>
    138. 138. Intracellular Shifts of Ions
    139. 139. HYPERKALEMIA <ul><li>Hyperkalemia is generally associated with acidosis </li></ul><ul><ul><li>Accompanied by a shift of H + ions into cells and K + ions out of the cell to maintain electrical neutrality </li></ul></ul>
    140. 140. HYPOKALEMIA <ul><li>Hypokalemia is generally associated with reciprocal exchanges of H + and K + in the opposite direction </li></ul><ul><ul><li>Associated with alkalosis </li></ul></ul><ul><li>Hypokalemia is a depressed serum K + </li></ul>
    141. 141. ELECTROLYTE SHIFTS Acidosis Compensatory Response Result - H + buffered intracellularly - Hyperkalemia Alkalosis Compensatory Response Result - Tendency to correct alkalosis - Hypokalemia cell H + K + H + K + cell
    142. 142. Arterial Blood Gases: Test Your Overall Understanding <ul><li>Case 1. A 55-year-old man is evaluated in the pulmonary lab for shortness of breath. His regular medications include a diuretic for hypertension and one aspirin a day. He smokes a pack of cigarettes a day. </li></ul><ul><li>FIO 2 .21 HCO 3 - 30 mEq/L </li></ul><ul><ul><ul><li>pH 7.53 %COHb 7.8% </li></ul></ul></ul><ul><ul><ul><li>PaCO 2 37 mm Hg Hb 14 gm% </li></ul></ul></ul><ul><ul><ul><li>PaO 2 62 mm Hg CaO 2 16.5 ml O 2 /dl SaO 2 87% </li></ul></ul></ul><ul><ul><ul><li>How would you characterize his state of oxygenation, ventilation, and acid-base balance? </li></ul></ul></ul>
    143. 143. Arterial Blood Gases: Test Your Overall Understanding Case 1 - Discussion OXYGENATION : The PaO 2 and SaO 2 are both reduced on room air. Since P(A-a)O 2 is elevated (approximately 43 mm Hg), the low PaO 2 can be attributed to V-Q imbalance, i.e., a pulmonary problem. SaO 2 is reduced, in part from the low PaO 2 but mainly from elevated carboxyhemoglobin, which in turn can be attributed to cigarettes. The arterial oxygen content is adequate. VENTILATION : Adequate for the patient's level of CO 2 production; the patient is neither hyper- nor hypo-ventilating. ACID-BASE : Elevated pH and HCO 3 - suggest a state of metabolic alkalosis, most likely related to the patient's diuretic; his serum K + should be checked for hypokalemia.
    144. 144. Arterial Blood Gases: Test Your Overall Understanding <ul><li>Case 2. A 46-year-old man has been in the hospital two days with pneumonia. He was recovering but has just become diaphoretic, dyspneic, and hypotensive. He is breathing oxygen through a nasal cannula at 3 l/min. </li></ul><ul><ul><ul><ul><ul><li>pH 7.40 </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>PaCO 2 20 mm Hg </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>%COHb 1.0% </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>PaO 2 80 mm Hg </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>SaO 2 95% </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Hb 13.3 gm% </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>HCO 3 - 12 mEq/L </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>CaO 2 17.2 ml O 2 /dl </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><li>How would you characterize his state of oxygenation, ventilation, and acid-base balance? </li></ul></ul></ul></ul>
    145. 145. Arterial Blood Gases: Test Your Overall Understanding Case 2 - Discussion OXYGENATION: The PaO 2 is lower than expected for someone hyperventilating to this degree and receiving supplemental oxygen, and points to significant V-Q imbalance. The oxygen content is adequate. VENTILATION: PaCO 2 is half normal and indicates marked hyperventilation. ACID-BASE : Normal pH with very low bicarbonate and PaCO 2 indicates combined respiratory alkalosis and metabolic acidosis. If these changes are of sudden onset, the diagnosis of sepsis should be strongly considered, especially in someone with a documented infection .
    146. 146. Arterial Blood Gases: Test Your Overall Understanding <ul><li>Case 3. A 58-year-old woman is being evaluated in the emergency department for acute dyspnea. </li></ul><ul><li>FIO 2 .21 </li></ul><ul><li>pH 7.19 </li></ul><ul><li>PaCO 2 65 mm Hg </li></ul><ul><li>%COHb 1.1% </li></ul><ul><li>PaO 2 45 mm Hg </li></ul><ul><li>SaO 2 90% </li></ul><ul><li>Hb 15.1 gm% </li></ul><ul><li>HCO 3 - 24 mEq/L </li></ul><ul><li>CaO 2 18.3 ml O 2 /dl </li></ul><ul><ul><ul><ul><li>How would you characterize her state of oxygenation, ventilation, and acid-base balance? </li></ul></ul></ul></ul>
    147. 147. Arterial Blood Gases: Test Your Overall Understanding Case 3 - Discussion OXYGENATION: The patient's PaO 2 is reduced for two reasons - hypercapnia and V-Q imbalance - the latter apparent from an elevated P(A-a)O 2 (approximately 27 mm Hg). VENTILATION : The patient is hypoventilating . ACID-BASE : pH and PaCO 2 are suggestive of acute respiratory acidosis plus metabolic acidosis; the calculated HCO 3 - is lower than expected from acute respiratory acidosis alone.
    148. 148. END ACID - BASE BALANCE
    149. 149. <ul><li>] </li></ul>END THANK YOU

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