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  • 1. Arterial Blood GasArterial Blood Gas Analysis & interpretationAnalysis & interpretation Mohammed A. El-haj MPH 07/12/2011
  • 2. What is an ABG?What is an ABG?  The Components – pH / PaCO2 / PaO2 / HCO3 / O2sat / BE  Desired Ranges – pH - 7.35 - 7.45 – PaCO2 - 35-45 mmHg – PaO2- 80-100 mmHg – HCO3 - 21-27 – O2sat - 95-100% – Base Excess - +/-2 mEq/L
  • 3. Why Order an ABG?Why Order an ABG? Aids in establishing a diagnosis Helps guide treatment plan Aids in ventilator management Improvement in acid/base management allows for optimal function of medications Acid/base status may alter electrolyte levels critical to patient status/care
  • 4. LogisticsLogistics  When to order an arterial line -- – Need for continuous BP monitoring – Need for multiple ABGs  Where to place -- the options – Radial – Femoral – Brachial – Dorsalis Pedis – Axillary
  • 5. Acid Base BalanceAcid Base Balance The body produces acids daily – 15,000 mmol CO2 – 50-100 mEq Nonvolatile acids The lungs and kidneys attempt to maintain balance
  • 6. Acid Base BalanceAcid Base Balance Assessment of status via bicarbonate-carbon dioxide buffer system  CO2 + H2O <--> H2CO3 <--> HCO3 - + H+  pH = 6.10 + log ([HCO3] / [0.03 x PCO2])
  • 7. Normal valuesNormal values Uncompensated acidosis pH .7 35–.7 45 Uncompensated alkalosis Respiratory alkalosis CO2 35-45 Respiratory acidosis Metabolic acidosis HCO3 23-27 Metabolic alkalosis
  • 8. CompensationCompensation 7.4 7.35 7.45 Partial compensated Partial
  • 9. Respiratory AcidosisRespiratory Acidosis ↓pH, ↑CO2,↓Ventilation Causes – CNS depression – Pleural disease – COPD/ARDS – Musculoskeletal disorders – Compensation for metabolic alkalosis
  • 10. Respiratory AcidosisRespiratory Acidosis Acute vs Chronic – Acute - little kidney involvement. Buffering via titration via Hb for example  pH ↓by 0.08 for 10mmHg ↑ in CO2 – Chronic - Renal compensation via synthesis and retention of HCO3 (↓Cl to balance charges hypochloremia)  pH ↓by 0.03 for 10mmHg ↑in CO2
  • 11. Respiratory AlkalosisRespiratory Alkalosis  ↑pH, ↓CO2, ↑Ventilation  ↓ CO2 ↓ HCO3 (↑Cl to balance charges hyperchloremia)  Causes – Intracerebral hemorrhage – Salicylate and Progesterone drug usage – Anxiety ↓lung compliance – Cirrhosis of the liver – Sepsis
  • 12. Respiratory AlkalosisRespiratory Alkalosis Acute vs. Chronic – Acute - ↓HCO3 by 2 mEq/L for every 10mmHg ↓ in PCO2 – Chronic - Ratio increases to 4 mEq/L of HCO3 for every 10mmHg ↓ in PCO2 – Decreased bicarb reabsorption and decreased ammonium excretion to normalize pH
  • 13. Metabolic AcidosisMetabolic Acidosis ↓pH, ↓HCO3 12-24 hours for complete activation of respiratory compensation ↓PCO2 by 1.2mmHg for every 1 mEq/L ↓HCO3  The degree of compensation is assessed via the Winter’s Formula PCO2 = 1.5(HCO3) +8 ± 2
  • 14. The CausesThe Causes Metabolic Gap Acidosis – M - Methanol – U - Uremia – D - DKA – P - Paraldehyde – I - INH – L - Lactic Acidosis – E - Ehylene Glycol – S - Salicylate Non Gap Metabolic Acidosis – Hyperalimentation – Acetazolamide – RTA (Calculate urine anion gap) – Diarrhea – Pancreatic Fistula
  • 15. Metabolic AlkalosisMetabolic Alkalosis  ↑pH, ↑HCO3  ↑PCO2by 0.7 for every 1mEq/L ↑ in HCO3  Causes – Vomiting – Chronic diarrhea – Hypokalemia – Renal Failure
  • 16. Mixed Acid-Base DisordersMixed Acid-Base Disorders Patients may have two or more acid-base disorders at one time Delta Gap Delta HCO3 = HCO3 + Change in anion gap >24 = metabolic alkalosis
  • 17. The six steps to ABGs analysisThe six steps to ABGs analysis Look at the pH if it is normal/acidotic/alkalotic Look at the PaCO2 if it is normal/acidotic/alkalotic Look at the HCO3 if it is normal/acidotic/alkalotic If the pH match with the PCO2 or with the HCO3  If the value goes opposite direction of the pH (determine the compensation). Look at the Po2 and oxygen saturation
  • 18. Sample problemSample problem pH 7.49 PCO2 40 HCO3 28 Uncompensated metabolic alkalosis  Vomiting/dearrhea  In this example the Bicarb is matching the pH  No compensation (Partial)
  • 19. Sample problemSample problem pH 7.10 PCO2 25 HCO3 7 Uncompensated metabolic acidosis  DKA/Dearrhea/shock/bleeding /sepsis  In this example the Bicarb is matching the pH  No compensation (Partial)  Severe metabolic acidosis
  • 20. Sample problemSample problem pH 7.42 PCO2 18 HCO3 11 PO2 150 O2 sat 99% compensated respiratory alkalosis  This pt is hyperventilated for too long (blowing off CO2)
  • 21. Sample problemSample problem pH 7.35 PCO2 60 HCO3 32 PO2 92 O2 sat 96%  No need for correction or treatment because pH is normal  Compensation is bringing the pH to the side of 7.4 but doesn't to the opposite side (stop in 7.4)
  • 22. Sample problemSample problem pH 7.37 PCO2 33 HCO3 18  Metabolic acidosis  Fully compensated
  • 23. Sample problemSample problem pH 7.36 PCO2 62 HCO3 34 PO2 70 O2 sat. 90%  Respiratory acidosis  Fully compensated  E.g. COPD
  • 24. Respiratory AlkalosisRespiratory Alkalosis Most common causes of respiratory alkalosis are: 1. Hypoxemia ( PaO2< 60mmHg and O2 sat. <90% ). A low PO2 drives increased breathing in spite of CO2 levels. 2. Anxiety 3. Pain
  • 25. hypoxemiahypoxemia Conditions causing V/Q (Ventilation perfusion) miss match 1. Shunt: loss of alveolar surface area 2. Dead space 3. Diffusion defect
  • 26. Danger a headDanger a head Hypoxemia Respiratory alkalosis Increased W.O.B Muscle fatigue Respiratory Acidosis
  • 27. Danger a headDanger a head ( Hypoxemia causing fatigue and respiratory acidosis) In the path from respiratory alkalosis to respiratory acidosis, the acid/base will temporarily appear normal, however the Ve (minute ventilation) will be increased (and probably the W.O.B) Respiratory Alkalosis Normal ABG Respiratory Acidosis
  • 28. Case 1Case 1 A 26 year old man with unknown past medical history is brought in to the ER by ambulance, after friends found him unresponsive in his apartment. He had last been seen at a party four hours prior. ABG: pH 7.25 Chem : Na+ 137 PCO2 60 K+ 4.5 HCO3 - 26 Cl- 100 PO2 55 HCO3 - 25
  • 29. Case 2Case 2 A 67 year old man with diabetes and early diabetic nephropathy (without overt renal failure) presents for a routine clinic visit. He is currently asymptomatic. Because of some abnormalities on his routine blood chemistries, you elect to send him for an ABG. ABG: pH 7.35 Chem : Na+ 135 PCO2 34 K+ 5.1 HCO3 - 18 Cl- 110 PO2 92 HCO3 - 16 Cr 1.4 Urine pH: 5.0
  • 30. Case 3Case 3 A 68 year old woman with metastatic colon cancer presents to the ER with 1 hour of chest pain and shortness of breath. She has no known previous cardiac or pulmonary problems. ABG: pH 7.49 Chem : Na+ 133 PCO2 28 K+ 3.9 HCO3 - 21 Cl- 102 PO2 52 HCO3 - 22
  • 31. DefinitionsDefinitions  Acidemia: Blood pH < 7.35  Alkalemia: Blood pH > 7.45  Acidosis:is a process that will result in acidemia if left unopposed.  Alkalosis:is a process that will result in alkalemia if left unopposed  Metabolic refers to a disorder that results from a primary alteration in [H+] or [HCO3-].  Respiratory refers to a disorder that results from a primary alteration in PCO2 due to altered CO2 elimination.  Normal HCO3- 24 meq/L; Normal PCO2 40 mm Hg ; Normal pH 7.35-7.45
  • 32. Definitions (Continued)Definitions (Continued) PH: - is a negative logarithm of Hydrogen ion concentration; and it is the initials of these two wards (puiessence Hydrogen) that mean the power of hydrogen
  • 33. Definitions (Continued)Definitions (Continued) An acid: - is a hydrogen ion or proton donor, and a substance which causes a rise in H+ concentration on being added to water. A base: - is a hydrogen ion or proton acceptor, and a substance which causes a rise in OH- concentration when added to water. Strength of acids or bases refers to their ability to donate and accept H+ ions respectively.
  • 34. Importance of acid-base balanceImportance of acid-base balance • The hydrogen ion (H+)concentration must be precisely maintained within a narrow physiological range • Small changes from normal can produce marked changes in enzyme activity & chemical reactions within the body
  • 35. Acidosis - CNS depression, coma (pH ~ 6.9) Alkalosis - CNS excitability, tetany, siezures Hydrogen ion concentration is most commonly expressed as pH (= negative logarithm of the H+ concentration)
  • 36. ACID-BASE CALCULATIONSACID-BASE CALCULATIONS The Henderson equation is easier to use, but only applies when pH is between 7.2 and 7.6. For this equation, one must calculate [H+] from pH. [H+] = 40 nEq/L when pH is 7.4. The [H+] increases 10 nEq/L for a 0.1 unit drop in pH. Henderson Eq. [H+] = 24 × PCO2 / [HCO3-]
  • 37. ph H+ (nmol/l) 7 100 7.1 80 7.2 63 7.3 50 7.36 44 7.4 40 7.44 36 7.5 32 7.6 25 7.7 20
  • 38. Normal pH: Arterial blood: 7.35 - 7.45 Venous blood, interstitial fluid: 7.35 Intracellular: 6.0-7.4 (average 7.0)
  • 39. Regulation of pHRegulation of pH • *Buffer systems - very rapid (seconds), incomplete • *Respiratory responses - rapid (minutes), incomplete • *Renal responses - slow (hours to days), complete
  • 40. BackgroundBackground H+ + H+ CO3 - ⇔ H2CO3 ⇔ H2O + CO2 -Metabolic Disorders: Affect HCO3 -: (Normal 22-26 meq/L) -Metabolic Acidosis ↑ Acid neutralizes HCO3 - ⇒ ↓H+ CO3 - , ↓ pH -Metabolic Alkalosis ↑ H+ CO3 - Production Drives Rxn to Right ⇒ ↓ H+ ⇒ ↑ pH
  • 41. Primary Abnormality in AcidPrimary Abnormality in Acid Base DisordersBase Disorders Acidosis Alkalosis Respiratory ↑ pCO2 Metabolic H+ + H+ CO3 - ⇔ H2CO3 ⇔ H2O + CO2
  • 42. Primary Abnormality in AcidPrimary Abnormality in Acid Base DisordersBase Disorders Acidosis Alkalosis Respiratory ↑ pCO2 ↓ pCO2 Metabolic H+ + H+ CO3 - ⇔ H2CO3 ⇔ H2O + CO2
  • 43. Primary Abnormality in AcidPrimary Abnormality in Acid Base DisordersBase Disorders Acidosis Alkalosis Respiratory ↑ pCO2 ↓ pCO2 Metabolic ↓ H+ CO3 - H+ + H+ CO3 - ⇔ H2CO3 ⇔ H2O + CO2
  • 44. Primary Abnormality in AcidPrimary Abnormality in Acid Base DisordersBase Disorders Acidosis Alkalosis Respiratory ↑ pCO2 ↓ pCO2 Metabolic ↓ H+ CO3 - ↑ H+ CO3 - H+ + H+ CO3 - ⇔ H2CO3 ⇔ H2O + CO2
  • 45. Simple Acid-Base Disorders: Type of Disorder pH PaCO2 [HCO3] Metabolic Acidosis ↓ ↓ ↓ Metabolic Alkalosis Acute Respiratory Acidosis Chronic Respiratory Acidosis Acute Respiratory Alkalosis Chronic Respiratory Alkalosis
  • 46. Simple Acid-Base Disorders: Type of Disorder pH PaCO2 [HCO3] Metabolic Acidosis Metabolic Alkalosis ↑ ↑ Acute Respiratory Acidosis Chronic Respiratory Acidosis Acute Respiratory Alkalosis Chronic Respiratory Alkalosis
  • 47. Simple Acid-Base Disorders: Type of Disorder pH PaCO2 [HCO3] Metabolic Acidosis Metabolic Alkalosis ↑ ↑ ↑ Acute Respiratory Acidosis Chronic Respiratory Acidosis Acute Respiratory Alkalosis Chronic Respiratory Alkalosis
  • 48. Simple Acid-Base Disorders: Type of Disorder pH PaCO2 [HCO3] Metabolic Acidosis Metabolic Alkalosis Acute Respiratory Acidosis ↓ ↑ Chronic Respiratory Acidosis ↓ ↑ Acute Respiratory Alkalosis Chronic Respiratory Alkalosis
  • 49. Simple Acid-Base Disorders: Type of Disorder pH PaCO2 [HCO3] Metabolic Acidosis Metabolic Alkalosis Acute Respiratory Acidosis ↓ ↑ ↑ Chronic Respiratory Acidosis ↓ ↑ ↑↑ Acute Respiratory Alkalosis Chronic Respiratory Alkalosis
  • 50. Simple Acid-Base Disorders: Type of Disorder pH PaCO2 [HCO3] Metabolic Acidosis Metabolic Alkalosis Acute Respiratory Acidosis Chronic Respiratory Acidosis Acute Respiratory Alkalosis ↑ ↓ Chronic Respiratory Alkalosis ↑ ↓
  • 51. Simple Acid-Base Disorders: Type of Disorder pH PaCO2 [HCO3] Metabolic Acidosis Metabolic Alkalosis Acute Respiratory Acidosis Chronic Respiratory Acidosis Acute Respiratory Alkalosis ↑ ↓ ↓ Chronic Respiratory Alkalosis ↑ ↓ ↓↓
  • 52. Simple Acid-Base Disorders: Type of Disorder pH PaCO2 [HCO3] Metabolic Acidosis ↓ ↓ ↓ Metabolic Alkalosis ↑ ↑ ↑ Acute Respiratory Acidosis ↓ ↑ ↑ Chronic Respiratory Acidosis ↓ ↑ ↑↑ Acute Respiratory Alkalosis ↑ ↓ ↓ Chronic Respiratory Alkalosis ↑ ↓ ↓↓
  • 53. CompensationCompensation For each acid-base disorder , there is a compensatory response mediated by the kidneys or the lungs that tends to bring the pH back towards normal. Compensation is never complete (i.e. pH never returns to 7.4). Therefore if the pH < 7.4, the primary process is an acidosis. If the pH > 7.4 the primary process is an alkalosis
  • 54. Compensated Abnormality in AcidCompensated Abnormality in Acid Base DisordersBase Disorders Acidosis Alkalosis 1° Respiratory Compensation ↑ pCO2 ↓ pCO2 1° Metabolic Compensation ↓ H+ CO3 - ↑ H+ CO3 - ↑ H+ CO3 - ↓ H+ CO3 - ↑ pCO2 ↓ pCO2 H+ + H+ CO3 - ⇔ H2CO3 ⇔ H2O + CO2
  • 55. Compensation (Continued)Compensation (Continued) Formulas predict normal compensation in both acute and chronic conditions. Inadequate compensation tells you that something else is wrong! Metabolic compensation takes time and is more complete in chronic conditions than acutely
  • 56. Buffer Systems A substance that can prevent major changes in the pH of body fluids by removed or releasing hydrogen ions ,they can act quickly to prevent excessive changes in hydrogen ion concentration Bicarbonate, phosphate and protein buffering systems are the three major buffering systems
  • 57. Bicarbonate buffer system *Primary extracellular buffer system (>50% of extracellular buffering) *Accurate assessment - readily calculated from PCO2 and pH using available blood gas machines *Consists of carbonic acid (weak acid) and bicarbonate
  • 58. *CO2 regulated by the lungs - rapidly *HCO3- is regulated by the kidneys – slowly *Not powerful *pKa = 6.1)the pK of a buffer system identifies the pH at which the concentration of acid and base in that system is equal) 33222 HCOHCOHCOOH +↔↔+ +
  • 59. Protein buffer system *Most powerful *75 % of all intracellular buffering *Hemoglobin -important extracellular buffer due to large concentration of hemoglobin in blood -buffering capacity varies with oxygenation -reduced hemoglobin is a weaker acid than oxyhemoglobin -dissociation of oxyhemoglobin results in more base available to combine w/ H+
  • 60. Plasma protein *acid buffer *important intracellular buffer system
  • 61. Phosphate buffer system *H2PO4- and HPO42- *important renal buffering system *extracellular concentration, 1/12 that of bicarbonate *pKa = 6.8 *phosphate is concentrated in the renal tubules
  • 62. Respiratory Responses  occurs within minutes of alteration in pH due to stimulation/depression of respiratory centers in the CNS  H+ acts directly on respiratory center in Medulla Oblongata  alveolar ventilation increases/decreases in response to changes in CO2  alveolar ventilation is inversely proportional to PaCO2 *2 x ventilation pH 7.4 to 7.63 *¼ ventilation pH 7.4 to 7.0  incomplete response because as the change in alveolar ventilation brings pH back towards normal, the stimulus responsible for the change in ventilation decreases .
  • 63. Renal Responses  the kidneys regulate pH by either acidification or alkalinization of the urine  complex response that occurs primarily in the proximal renal tubules  with acidosis, rate of H+ secretion exceeds HCO3- filtration  with alkalosis, rate of HCO3- filtration exceeds H+ secretion  occurs over hours/days, and is capable of nearly complete restoration of acid/base balance
  • 64. Renal & Respiratory CompensationRenal & Respiratory Compensation Primary Disorder Primary change Predicted Compensatory Response Metabolic acidosis ↓ HCO3 1.2 ↓ PaCO2 per 1 meg ↓ HCO3 Metabolic Alkalosis ↑ HCO3 .7 ↑ PaCO2 per 1meq ↑ HCO3 Respiratory acidosis: Acute ↑PaCO2 1 meq ↑ HCO3 per 10 mm ↑PaCO2 Respiratory acidosis: Chronic ↑PaCO2 3.5 meq ↑ HCO3 per 10 mm ↑PaCO2 Respiratory alkalosis: Acute ↓PaCO2 2 meq ↓HCO3 per 10mm ↓ PaCO2 Respiratory alkalosis: Chronic ↓PaCO2 4 meq ↓HCO3 per 10mm ↓ PaCO2
  • 65. SUMMARY OF SIMPLE ACID-BASE DISORDERS ANDSUMMARY OF SIMPLE ACID-BASE DISORDERS AND COMPENSATIONCOMPENSATION Primary Acid- Base Disorder Primary Defect Effect on pH Compensatory Response Expected Range of Compensation Limits of Compensatio n Respiratory Acidosis Hypoventilati on (↑PCO2) ↓ HCO3- Generation ↑ [HCO3-] = 1-4 mEq/L for each 10 mm Hg ↑ PCO2 [HCO3-] = 45 mEq/L Respiratory Alkalosis Hyperventilati on (↓PCO2) ↑ HCO3- Consumption ↓ [HCO3-] = 2-5 mEq/L for each 10 mm Hg ↓ PCO2 [HCO3-] = 12-15 mEq/L Metabolic Acidosis Loss of HCO3- or gain of H+(↑ HCO3-) ↓ Increase in Ventilation (↓PCO2) PCO2 = 1.5[HCO3-] + 8 PCO2 = 12-14 mm Hg Metabolic Alkalosis Gain of HCO3- or loss of H+ (↓ HCO3-) ↑ Decrease in Ventilation (↑PCO2 ( ↑ PCO2 = 0.6 mm Hg for each 1 mEq/L ↑ [HCO3-] PCO2 = 55 mm Hg
  • 66. GENERAL ASPECTS OFGENERAL ASPECTS OF ACID-BASE DISORDERSACID-BASE DISORDERS  A primary alteration in [H+], [HCO3-] or PCO2 results in abnormal pH.  The body has several mechanisms to correct pH towards the normal range. -In the acute phase (minutes to hours), the extra- and intra- cellular buffer systems (most importantly the bicarbonate system) minimize the pH changes. - In the chronic phase (hours to days), renal or respiratory compensation partially or completely restore pH towards normal.  There are limits to both types of compensation.  Compensation does not result in over correction of pH.
  • 67. DATA REQUIRED TO DIAGNOSEDATA REQUIRED TO DIAGNOSE ACID-BASE DISORDERSACID-BASE DISORDERS  An arterial blood gas shows the blood pH, PCO2 and [HCO3-].  A chemistry panel shows the [total CO2], [Cl-], [K+] and [Na+], [glucose], [BUN] and [creatinine].  The [total CO2] is the sum of the measured [CO2] + [HCO3-]. Thus the [HCO3-] from the blood gas and the [total CO2] from the electrolyte panel usually are within 2 mEq/L. Otherwise the measurements are in error or were taken at different times.
  • 68. NORMAL LABORATORYNORMAL LABORATORY VALUESVALUES Arterial Blood Gas: pH 7.35-7.45 [H+] 35-45 nmol/L or neq/L PCO2 35-45 mm Hg [HCO3-] 22-26 mmol/L or mEq/L Plasma Electrolytes [Na+] 135-145 mEq/L [K+ ] 3.5-5.0 mEq/L [Cl-] 96-109 mEq/L [total CO2] 24-30 mEq/L
  • 69. SIMPLE ACID-BASE DISORDERSSIMPLE ACID-BASE DISORDERS  Simple acid-base disorders have one primary abnormality.  The four primary disorders are respiratory acidosis, respiratory alkalosis, metabolic acidosis and metabolic alkalosis.  Mixed acid-base disorders have more than one abnormality. Two to three primary disorders can be combined together to result in a mixed disorder.
  • 70. Metabolic AcidosisMetabolic Acidosis Secondary to ↑ Acid production or ↑ H+ CO3 - loss Characterized by low serum H+ CO3 - ( by hyperventilation  ↓ PCO2 ⇒ ↓ HCO3- ) Divided into two categories: – Anion gap metabolic acidosis (High anion gap) – NonAnion gap metabolic acidosis (Normal anion gap)
  • 71. Anion GapAnion Gap The anion gap (AG) represents the difference between the major plasma cations and anions ,and reflects usually unmeasured anions such as sulfate. Anion Gap = [Na+ ] - ( [H+ CO3 - ]+ [Cl- ] ) Normal 14 +/- 2
  • 72.  Why does this help us in patients with metabolic acidosis? – Secondary to  ↑ Acid production or  ↑ H+ CO3 - loss – In disorders associated with ↑ acid production there anions accumulate  ↑ anion gap whereas – In disorders associated with ↑ H+ CO3 - loss, there is no accumulation of unmeasured anions and the anion gap is normal
  • 73. Unmeasured anions whichUnmeasured anions which accumulateaccumulate  Anion Gap AcidosisAnion Gap Acidosis Lactate Ketones Sulfates and phosphates Other organic acids
  • 74. Lactic AcidosisLactic Acidosis Fundamentally what causes a lactic acidosis? Answer: Anaerobic metabolism
  • 75. The differential diagnosis ofThe differential diagnosis of Lactic AcidosisLactic Acidosis Lactic acidosis occurs whenever the cells are unable to utilize aerobic respiration: i.e. whenever the cells are unable to obtain or utilize oxygen Consider Murphy’s law: “Whatever can go wrong will go wrong!” (i.e. take each step in oxygen absorption and distribution—any one of them can go away and cause lactic acidosis.)
  • 76. The differential diagnosis ofThe differential diagnosis of Lactic Acidosis (2)Lactic Acidosis (2)  Low environmental O2  Inability to absorb O2  O2 unable to bind Hg  Unable to pump O2  Tissues unable to utilize O2  High altitude  Lung Disease  CO poisoning  Shock (cardiogenic)  Septic shock  Focal vascular obstruction  Cyanide poisoning
  • 77. KetoAcidosisKetoAcidosis Occurs whenever the cells are unable to utilize glucose
  • 78. KetoAcidosisKetoAcidosis Three etiologies – Diabetic Ketoacidosis  Primarily in type 1 diabetes mellitus  Severe, life threatening  Often associated with precipitating illness – Starvation ketoacidosis  Mild acidosis – Alcoholic ketoacidosis  Mild acidosis
  • 79. Metabolic Acidosis Anion Gap Acidosis NonAnion Gap Acidosis Ketoacidosis Uremic Acidosis Lactic Acidosis Organic Acidosis Lung Disease CO poisening Shock (cardiogenic) Septic shock Focal vascular obstruction Cyanide poisening DKA (Type 1) Starvation Alcoholic
  • 80. Other anion gap acidosisOther anion gap acidosis Uremia – Failure to excrete daily metabolic acid load – Accumulation of phosphates and sulfates Organic acidosis – Methanol – Ethylene Glycol – Salicylates
  • 81. Metabolic Acidosis Anion Gap Acidosis NonAnion Gap Acidosis Ketoacidosis Uremic Acidosis Lactic Acidosis Organic Acidosis Lung Disease CO poisening Shock (cardiogenic) Septic shock Focal vascular obstruction Cyanide poisening DKA (Type 1) Starvation Alcoholic Methanol Ethylene Glycol Salicylate intoxication
  • 82. Non-anion gap metabolicNon-anion gap metabolic acidosisacidosis ↑ Bicarbonate loss  Diarrhea  Severe Burns  Urinary loss (renal tubular acidosis)
  • 83. Metabolic Acidosis Anion Gap Acidosis NonAnion Gap Acidosis Ketoacidosis Uremic Acidosis Lactic Acidosis Organic Acidosis Lung Disease CO poisening Shock (cardiogenic) Septic shock Focal vascular obstruction Cyanide poisening DKA (Type 1) Starvation Alcoholic Methanol Ethylene Glycol Salicylate intoxication Diarrhea Burns (severe) RTA
  • 84. Clinical ManifestationClinical Manifestation  Headache  Confusion  Drowsiness  ↑ RR and depth  Nausea and vomiting  Peripheral vasodilation and decreased Cardiac output (pH ↓7 )  ↓BP  Hyperkalemias
  • 85. Metabolic Acidosis: TreatmentMetabolic Acidosis: Treatment Treat underlying cause Alkali replacement – Acute metabolic acidosis  indicated when is pH less than ~7.15  goal is to raise serum [HCO3] to ~15mmol/L  bicarbonate dose = 0.5 x BW (kg) x{[HCO3]desired - [HCO3]actual} – Chronic metabolic acidosis  goal of treatment is to prevent long term sequelae  serum [HCO3] should be normalized
  • 86. Metabolic AlkalosisMetabolic Alkalosis Generation Maintenance
  • 87. Metabolic Alkalosis:Metabolic Alkalosis: GenerationGeneration Acid loss – renal acid losses  diuretic therapy  mineralocorticoid excess  Cushing’s syndrome  severe potassium depletion  Bartter’s syndrome  Liddle’s syndrome – gastrointestinal losses  gastric acid loss  chloride diarrhea
  • 88. Metabolic Alkalosis:Metabolic Alkalosis: GenerationGeneration Alkali gain – bicarbonate administration – milk alkali syndrome – infusion of organic anions  citrate  acetate  lactate – rapid correction of chronic hypercapnia
  • 89. Metabolic Alkalosis: MaintenanceMetabolic Alkalosis: Maintenance Decreased GFR – renal failure Increased proximal HCO3 - reabsorption – chloride depletion Increased distal tubular H+ secretion – hypokalemia
  • 90. Metabolic Alkalosis: TreatmentMetabolic Alkalosis: Treatment Saline responsive – intravascular volume expansion with normal saline – potassium repletion Saline resistant – potassium repletion – mineralocorticoid antagonists – acetazolamide
  • 91. Respiratory AcidosisRespiratory Acidosis Think “Murphy’s Law” again From Brain to alveolus, many problems can cause hypoventilation  ↑ PaCO2  ↓pH (Respiratory acidosis)
  • 92. Respiratory AcidosisRespiratory Acidosis  Brain  Spinal Cord  Peripheral Nerve  NeuroMuscular Junction  Lung and Pleural disease  Stroke  Drug Intoxication  C spine injury,  Guillan Barre  Myasthenia Gravis  Asthma, COPD, ARDS, etc
  • 93. Clinical ManifestationClinical Manifestation  Hypercapnia  ↑Pulse  ↑RR  ↑BP  Mental cloudiness  Feeling of fullness in the head  ↑ICP  Headache  Hyperkalemia
  • 94. Respiratory AlkalosisRespiratory Alkalosis Hyperventilation  ↓PaCO2  ↑ pH Etiologies – Fever – Pain – Anxiety – Pulmonary disease – Sepsis – Salicylate intoxication – Neurologic disorders
  • 95. MIXED ACID-BASE DISORDERSMIXED ACID-BASE DISORDERS Mixed acid-base disorders include all combinations of 2-3 simple acid base disorders. One must be able to recognize mixed acid- base disorders. This can be accomplished by examining the degree of compensation and calculating an anion gap. If the pH, PCO2 and [HCO3-] do not fit the rules of compensation for a simple disorder, one must hypothesize that there is a mixed acid-base disorder (or hypothesize that there is an error in the data).
  • 96. If there is extreme acidemia or alkalemia, one could hypothesize multiple acid-base disorders that that are additive. • If there is a mild acidemia or alkalemia, or pH is normal, particularly with an anion gap one could hypothesize multiple acid-base disorders that cancel each other out.
  • 97. Summary of the Approach toSummary of the Approach to ABGsABGs 1. Check the pH 2. Check the pCO2 3. Select the appropriate compensation formula 4. Determine if compensation is appropriate 5. Check the anion gap 6. If the anion gap is elevated, check the delta-delta 7. If a metabolic acidosis is present, check urine pH 8. Generate a differential diagnosis
  • 98. Putting it TogetherPutting it Together
  • 99. What is the clinical picture? Generate hypothesis! What is the pH? Acidemia Alkalemia Check HCO3- & PaCO2 Is it respiratory or metabolic? Check: Is compensation appropriate? Check Anion Gap Reach Final Diagnosis Step 1 Step 2 Step 3 Step 4 Step 5 Step 6
  • 100. Case 1Case 1 A 26 year old man with unknown past medical history is brought in to the ER by ambulance, after friends found him unresponsive in his apartment. He had last been seen at a party four hours prior. ABG: pH 7.25 Chem 7: Na+ 137 PCO2 60 K+ 4.5 HCO3 - 26 Cl- 100 PO2 55 HCO3 - 25
  • 101. Case 2Case 2 A 67 year old man with diabetes and early diabetic nephropathy (without overt renal failure) presents for a routine clinic visit. He is currently asymptomatic. Because of some abnormalities on his routine blood chemistries, you elect to send him for an ABG. ABG: pH 7.35 Chem 7: Na+ 135 PCO2 34 K+ 5.1 HCO3 - 18 Cl- 110 PO2 92 HCO3 - 16 Cr 1.4 Urine pH: 5.0
  • 102. Case 3Case 3 A 68 year old woman with metastatic colon cancer presents to the ER with 1 hour of chest pain and shortness of breath. She has no known previous cardiac or pulmonary problems. ABG: pH 7.49 Chem 7: Na+ 133 PCO2 28 K+ 3.9 HCO3 - 21 Cl- 102 PO2 52 HCO3 - 22
  • 103. pH7.34pH7.34, PaCO2 60 , HCO3- 31, PaCO2 60 , HCO3- 31 Primary Disorder Primary change Predicted Compensatory Response Metabolic acidosis ↓ HCO3 1.2 ↓ PaCO2 per 1 meg ↓ HCO3 Metabolic Alkalosis ↑ HCO3 .7 ↑ PaCO2 per 1meq ↑ HCO3 Respiratory acidosis: Acute ↑PaCO2 1 meq ↑ HCO3 per 10 mm ↑PaCO2 Respiratory acidosis: Chronic ↑PaCO2 3.5 meq ↑ HCO3 per 10 mm ↑PaCO2 Respiratory alkalosis: Acute ↓PaCO2 2 meq ↓HCO3 per 10mm ↓ PaCO2 Respiratory alkalosis: Chronic ↓PaCO2 4 meq ↓HCO3 per 10mm ↓ PaCO2
  • 104. Case 1Case 1  A 52 y.o. man with COPD is admitted to the hospital with a lower extremity cellulitis.  Hypothesis  Labs: Na+ 139, K+ 4.9, Cl- 98, HCO3- 31  ABG: pH 7.34, PaCO2 60, PaO2 69  Is he acidemic or alkalemic?  Is this metabolic (from sepsis) or respiratory (from COPD)?  Is this acute or chronic? Why does that matter?
  • 105. Case 1: AnswerCase 1: Answer  A 52 y.o. man with COPD is admitted to the hospital with a lower extremity cellulitis.  Labs: Na+ 139, K+ 4.9, Cl- 98, HCO3- 31  ABG: pH 7.34, PaCO2 60, PaO2 69  Why is he acidemic?  Is this metabolic (from sepsis) or respiratory (from COPD)?  Is this acute or chronic? Why does that matter?  Dx: Chronic Respiratory Acidosis – Not from sepsis – No need for intubation or ICU care – Note AG 10
  • 106. Case 2Case 2  A 45 y.o. man reports 6 days of persistent nausea and vomiting. PE  supine BP 100/60 pulse 105; Standing BP 85/55 pulse 125. Neck veins are flat  Hypotheses?  Labs: – Na+ 140, K+ 2.2, Cl- 86, HCO3 42 BUN 80, Cr 1.9 – ABG: pH 7.53, PaCO2 53, PaO2 82 – Urine Na+ 2 meg/L  Acidemic or Alkalemic?  Metabolic or Respiratory?  What is his acid base disorder?  Why is he alkalemic?  How would you fix it? What’s with the urine sodium?  Answer: Metabolic alkalosis. Correct with NaCL
  • 107. Case 3Case 3 79 y.o. woman with CC of abdominal pain Patient c/o abdominal pain for 2 days. Pain is moderately severe & diffuse, associated with vomiting. She reports passing no bowel movements or flatus for 2 days. PE: Elderly appearing woman in moderate distress; Vital signs T 38.5, RR 20, BP 115/60, HR 95. Abdominal exam: absent bowel sounds, diffusely distended, mild tenderness, without rebound or guarding. Rectal FOBT negative
  • 108. Case 3 (continuedCase 3 (continued)) Labs: – WBC 18K, 82% neutrophils, 10% bands – HCT 37 – Na 138, K 4.2 HCO3 - 6 CL 106 BUN 45 Cr. 1.0 Glucose 110 – ABG: pH 7.10, PaCO2 20mm Hg, PaO2 90 What is her acid base disorder? What does it tell you?
  • 109. Metabolic Acidosis Anion Gap Acidosis NonAnion Gap Acidosis Ketoacidosis Uremic Acidosis Lactic Acidosis Organic Acidosis Lung Disease CO poisening Shock (cardiogenic) Septic shock Focal vascular obstruction Cyanide poisening DKA (Type 1) Starvation Alcoholic Methanol Ethylene Glycol Salicylate intoxication Diarrhea Burns (severe) RTA
  • 110. Who gets your last ICU bed?Who gets your last ICU bed? ♦♦ 75 y.o. WF with COPD with CC cough & SOB R.A. ABG  7.35, PaC02 60, Pa02 48. ♦♦ 70 y.o. WM with COPD with CC purulent sputum, SOB. ABG on 4L  7.2, PaC02 60, Pa02 of 70
  • 111. What is the clinical picture? Generate hypothesis! What is the pH? Acidemia Alkalemia Check HCO3- & PaCO2 Is it respiratory or metabolic? Check: Is compensation appropriate? Check Anion Gap Reach Final Diagnosis Step 1 Step 2 Step 3 Step 4 Step 5 Step 6
  • 112. Arterial punctureArterial puncture
  • 113. Problems of taking arterialProblems of taking arterial blood samplesblood samples Bleeding Vessel obstruction Infection
  • 114. Allen's test. The radial and ulnar arteries are occluded by firm pressure while the fist is clenched. The hand is opened and the arteries released one at a time to check their ability to return blood flow to the hand
  • 115. ‫لحسن‬ ‫را‬ً ‫شك‬ ‫استماعكم‬