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![Body Buffer system
Hydrogen Ion Homeostasis
-About 50 to100 m mol of hydrogen ions are
released from cells into extracellular fluid each
day
*Hydrogen ion concentration [H+] is maintained
between about 35 and 45 nano molL.
40nmol/L=pH 7.4))](https://image.slidesharecdn.com/hanaaarterialbloodgasanalysis-171209212614/75/arterial-blood-gas-analysis-13-2048.jpg)
![What is PH?
PH is –ve log of H+ concentration.
P=protenz (strength-power), H=H+ concentration.
Relationship between pH & [H+]
pH [H+]
(nanomoles/l)
6.8 158
6.9 125
7.0 100
7.1 79
7.2 63
7.3 50
7.4 40
7.5 31
7.6 25
7.7 20
7.8 15
or more simply: The Henderson
equation:
[H+] = 24 x ( pCO2 / [HCO3] )
Henderson-Hasselbalch Equation
pH = pK’a + log ([HCO3] / 0.03 x pCO2)
The PKa of an acid is the PH at which
it is exactly half-dissociated](https://image.slidesharecdn.com/hanaaarterialbloodgasanalysis-171209212614/75/arterial-blood-gas-analysis-15-2048.jpg)
![The Anion Gap
[(Na+) + (K+)] – [(Cl-) + (HCO3
-)]
The normal anion gap is 12meq ± 4.
Causes ofHyperchloremic Acidosis
↑ GIT loss of HCO3 as in: diarrhea, high output fistula
(pancreatic, biliary or small intestinal).
↑ renal HCO3 loss as in: RTA(I, II), CAIs, hypoaldosteronism.
TPN.
Large amount of HCO3 free fluid
↑ CL containing acids.
Wide Anion Gap Acidosis
Keto Acidosis
Uremia
Lactic Acidosis
Salicylism
Toxins : Methanol,Paraldehyde,Ethylene glycol](https://image.slidesharecdn.com/hanaaarterialbloodgasanalysis-171209212614/75/arterial-blood-gas-analysis-47-2048.jpg)
More Related Content
Similar to arterial blood gas analysis
arterial blood gas analysis
- 1. Hanaa A. ElGendy Associate Professor of Anesthesia and ICU ASUH
- 2. The normal rangesfor arterial blood gas values Approach to arterial blood gas interpretation Arterial blood gas abnormalities in special circumstances
- 3. •Oxygenation Represented by PaO2 •Ventilation Represented by Pa Co2 • Acid Base Status Represented by pH, HCO3 and base deficit.
- 4. What information doesABG provide about the patient? FIRST: ABG provide an assessment of the following: 1)PaO2: Amount of o dissolved in the blood, it give initial information on efficiency of oxygenation. 2)PaCO2: Adequacy of ventilation is inversely proportional to Paco2 (when ventilation increase PaCO2 decrease and vice verse). 3) Acid base status (pH, HCO3, base deficit, anion gap). 4) Hb, Hct, oxygen saturation. 5) Electrolyte e.g. Na+, K+.
- 5. SECOND: Calculation of AlveolarGas Equation and A-a Gradient: PAO2 = FiO2×(Bp-pH2O)-PaCO2/R. = 21×(760-47)-40/0.8 = 100 mmHg. A-a Gradient is alvealo-arterial O2 gradient. A-a Gradient = PAO2 -PaO2 Ventilation-Perfusion abn Affected by -Age -Fio2 ( A-a increase 5-7 mmHg/10 % ↑Fio2) -PPV A normal A–a gradient for a young adult non-smoker breathing air, is between 5–10 mmHg.
- 6. 1) Arterial/alveolar ratio(a/A) PaO2/PAO2 PAO2 iscalculated by the alveolar air equation: PAO2 = FIO2 (PB – PH2O) – PaCO2/0.8 Normal value for the a/A ratio is 0.8, meaning that 80% of the alveolar oxygen is reaching the arterial system 2) PaO2/ FIO2 ratio A person breathing FIO2 of 1.0 at sea level should have a PaO2 of 550 to 600 mmHg) 3) A-a gradient (on 100% oxygen) PAO2 - PaO2 Where PAO2 is calculated by the alveolar air equation previously presented FIO2x500
- 7. Arterial/alveolar PCO2 Gradient(a-A PCO2) Arterial PCO2 - Alveolar PCO2 Where Alveolar PCO2 is measured by means of end–tidal PCO2 Normal gradient is an alveolar PCO2 2 mmHg less than arterial, Acute increase reflects increase in physiologic dead space
- 8. Sample source andcollection:- •Arterial blood sample is common utilized clinically but venous blood may be useful in determining acid base status. (Except in CHF and shock). •Blood sample should be in heparin coated syringe. •The sample should be analyzed as soon as possible. •Air bubble should be eliminated. •The syringe should be capped and placed in ice.
- 9. Problem associated withobtaining ABG: Arterial puncture may result in acute hyperventilation. To minimize that: we should use local anesthetic with small needle. When would you withdraw ABG sample after beginning or stopping O2 supplementation? In absence of significant lung disease we should wait from 5-7 minutes before withdraw ABG sample while patient with obstructive lung disease we should wait 25 min. The blood sample should be analyzed within 15 minutes and be stored at either room temperature 24-26 degree C or ice
- 10. Measurement Arterial blood Mixed venous Venous PH 7.36-7.44 7.30-7.407.30-7.40 PO2 80-100 35-40 30-50 PCO2 36-44 40-50 40-50 O2 saturation >95% 60%-80% 60%-85% HCO3 22-26 22-26 22-28 Base difference (deficit excess) -2 to 2
- 11. What isbase deficit ? The base deficit is the amount of acid or base needed to titrate a serum PH back to normal at 37 degree while the Paco2 is held constant at 40 mmHg, thus eliminating the respiratory component therefore the base deficit represent only the metabolic component of acid base disorders. Its +ve value indicate metabolic alkalosis, While –ve value indicate metabolic acidosis.
- 12. The basic Bronnsteddefinition of acids and bases are: An acid is a species having a tendency to lose proton A base is a species having a tendency to accept proton .
- 13. Body Buffer system HydrogenIon Homeostasis -About 50 to100 m mol of hydrogen ions are released from cells into extracellular fluid each day *Hydrogen ion concentration [H+] is maintained between about 35 and 45 nano molL. 40nmol/L=pH 7.4))
- 14. Is a processby which a strong acid (or base) is replaced by a weaker one, with a consequent reduction in the number of free hydrogen ions and therefore the change in PH HCl + NaHCO3 = H2CO3 + NaCl Strong acid buffer weak acid neutral salt
- 15. What is PH? PHis –ve log of H+ concentration. P=protenz (strength-power), H=H+ concentration. Relationship between pH & [H+] pH [H+] (nanomoles/l) 6.8 158 6.9 125 7.0 100 7.1 79 7.2 63 7.3 50 7.4 40 7.5 31 7.6 25 7.7 20 7.8 15 or more simply: The Henderson equation: [H+] = 24 x ( pCO2 / [HCO3] ) Henderson-Hasselbalch Equation pH = pK’a + log ([HCO3] / 0.03 x pCO2) The PKa of an acid is the PH at which it is exactly half-dissociated
- 16. Compensation is thebody’s way of restoring a normal blood pH (7.36-744) Remember: Acid + Base Neutrality Compensation DOES NOT treat the root of the problem – the reason for the acid-base imbalance is STILL THERE!!!
- 17. The body hasthree means to try to compensate for an acid-base imbalance (( Seconds-least efficient•Chemical • Respiratory 15 min-mod efficient – HCO3/CO2 ≈ 20)-3( • Renal 5 d-max efficient – HCO3/CO2 ≈ 20)–12 hs)
- 18. Chemicals within theblood act within seconds to correct respiratory or metabolic imbalances Used up quickly – not effective long-term Chemical buffers in the blood include Bicarbonate Phosphate Proteins
- 19. Used to compensatefor metabolic imbalances only Chemoreceptors respond to changes in H+ concentrations alters respiratory rate and depth Remember CO2 is an acid
- 20. Used to compensatefor respiratory imbalances Remember: HCO3 - is a base Kidneys respond to changes in blood pH Excrete H+ and retain HCO3 - when acidemia is present Retain H+ and excrete HCO3 - when alkalemia is present
- 21. The body isvery smart and will not overcompensate for an imbalance
- 22. An acid-base imbalancewill be compensated for in one of three ways Uncompensated Partially compensated Fully compensated
- 23. Uncompensated Body has madeno attempt to correct the acid-base imbalance Partially compensated Body is attempting to correct the imbalance Blood pH remains abnormal in spite of the attempt
- 24. Fully compensated The bodyis correcting the imbalance Blood pH is normal Other blood gas values remain abnormal until the root cause is treated and corrected
- 25. PH abnormal Either PaCO2OR HCO3 - abnormal All other values normal If PaCO2 is abnormal Problem is respiratory If HCO3 - is abnormal Problem is metabolic
- 26. Uncompensated respiratory acidosis PH <7.36 PaCO2> 44 HCO3 -WNL Uncompensated respiratory alkalosis PH ˃ 7.44 PaCO2˂ 36 HCO3 -WNL Remember that CO2 is an acid and that the more of it there is the worse is the acidemia. Notice that with uncompensated respiratory, the HCO3 is normal – this is because the body has not began to compensate for the alterations in CO2
- 27. Uncompensated metabolic acidosis pH ˂7.36 PaCO2WNL HCO3 - ˂ 22 Uncompensated metabolic alkalosis pH > 7.44 PaCO2WNL HCO3 - > 26 Remember that HCO3 is a base and that the more of it there is the more alkalotic you will be. Notice that in the case of uncompensated metabolic the PaCO2 is normal indicating that the body has not began to compensate.
- 28. Occur when compensationmechanisms are activated, but have not had sufficient time to normalize the blood pH NOTE: Some people say that there is no such thing as “partially” compensated – but it is indicative of a part of the process called compensation
- 29. pH is abnormal BothPaCO2 and HCO3 - are abnormal in the same direction (increased or decreased from normal) If PaCO2 is high (↑ acid), HCO3 - will also be high (↑ alkaline) to neutralize the environment If PaCO2 is low (↓ acid), HCO3 - will also be low (↓ alkaline) to neutralize the environment
- 30. Partially Compensated Respiratory Acidosis pH<7.36 PaCO2> 44 HCO3 -> 26 Partially Compensated Respiratory Alkalosis pH˃7.44 PaCO2˂ 36 HCO3 -˂ 22 In the case of Partially Compensated Resp Acidosis, the pH is low, indicating an acid environment…when you look at the PaCO2, it too is acidic, which is how you know that you have a respiratory acidosis. With the HCO3 being high, you can deduce that the body is raising its base to counteract the acid represented by the pH; therefore, partially compensated respiratory acidosis.
- 31. Partially Compensated Metabolic Acidosis pH<7.36 PaCO2˂ 36 HCO3 -˂ 22 Partially Compensated Metabolic Alkalosis pH˃7.44 PaCO2> 44 HCO3 -> 26 With partially compensated metabolic acidosis, you notice first that the pH is low (acidosis).Ask yourself, which number is representative of an acid condition. In this case it is the low base (HCO3), so you know you have a metabolic acidosis. You know it is partially compensated because the PaCO2 is low indicating that CO2 (an acid) is being lost from the body to correcfor the low pH.
- 32. Compensated Respiratory Acidosis WNLPH closerto 7.36 PaCO2> 44 HCO3-> 26 Compensated Respiratory Alkalosis PH closer to 7.44 WNL PaCO2< 36 HCO3-˂ 22 In compensated respiratory acidosis, the pH tends to range between 7.35 and 7.39 – still acidic,But in the normal pH range. When you look at the PaCO2, you notice that it is high (acidic), butThe HCO3 is also high, indicating that the body has compensated and normalized the low pH.
- 33. Compensated Metabolic Acidosis PH closerto 7.36 WNL PaCO2< 36 HCO3-˂ 22 Compensated Metabolic Alkalosis PH closer to 7.44 PaCO2> 44 HCO3-> 26
- 34. Occur when patienthas both metabolic and respiratory disorders that cause an acid-base imbalance Examples: Diabetic KetoAcidosis (metabolic acidosis) with decreased respiratory drive (respiratory acidosis) Severe vomiting (metabolic alkalosis) with high fever (respiratory alkalosis)
- 35. pH will benear normal PaCO2 and HCO3 - will be abnormal PaCO2 will be high with low HCO3 - (both tend toward acid side) PaCO2 will be low with high HCO3 - (both tend toward base side)
- 36. Mixed acidosis pH˂7.36 PaCO2> 44 HCO3 -˂ 22 Mixed alkalosis pH˃7.44 PaCO2< 36 HCO3 -> 26 Notice with the mixed acidosis that you have an acidic pH (less than 7.35, with other Parameters indicating an acid environment. High PaCO2 (too much acid). Low HCO3 (too little base – an acidic environment). This is classic mixed acidosis.
- 37. How is thepatient? Will provide useful clues to help with interpretation of the results TEN Steps for interpretation of ABG STEP 1 STEP 2 Assess oxygenation The PaO2 should be > 10 kPa (75 mmHg) breathing air inspired concentration Assessed by FiO2, SaO2, PaO2, Hb Ideal to keep FiO2 < .4/.5, PaO2 60-90 mmHg, The SpO2 can be used to titrate FiO2; goal is >90% Desired FiO2 = PaO2 desired X FiO2 known PaO2 known
- 38. STEP 3 Determine if: Acidemia(PH<7.36) OR Alkalemia(PH >7.44) is present.
- 39. Identify primary disturbance: PHIncreaseDecrease Alkalosis Acidosis Look at PCO2 Increased Decrease Increased Decreased Metabolic Alkalosis Respiratory Alkalosis Respiratory acidosis Metabolic acidosis STEP 4
- 40. STEP 5: Look atthe direction of the change of HCO3/PCO2: •If it is in the same direction it is either partial or compensated change. •But if it is in the opposite direction so it is mixed change. STEP 6: Calculate rate of change of Hco3 and co2 (Expected compensation) Disturbance Response Expected change Metabolic acidosis ↓Paco2 1.2×(24-HCO3 measured) Metabolic alkalosis ↑Paco2 0.7×(HCO3-24) Acute respiratory acidosis ↑Hco3 0.1×(PaCO2-40) Chronic respiratory acidosis ↑ Hco3 0.4×(PaCO2-40) Acute respiratory alkalosis ↓ Hco3 0.2×(40-PaCO2) Chronic respiratory alkalosis ↓ Hco3 0.4×(40-PaCO2)
- 41. N.B.: There is noover correction or compensation in acid base balance → if the compensatory response is more or less than expected → it is mixed acid base disorder N.B.: • In respiratory disturbance arterial pH change 0.08 for every 10 mmHg change in PCO2. • In metabolic disturbance arterial pH change 0.1 for every 6 meq /l change in HCO3.
- 42. Disturbance Primary AbnormalityCompensation Cause Metabolic Acidosis Excess endogenous acid depletes bicarbonate Hyperventilation lowers pCO2, Kidney excretes excess H+ and forms more HCO3 - Renal failure Ketosis Increased lactic acid Diarrhea Respiratory Acidosis Inefficient excretion of CO2 by the lungs Formation of excess HCO3 - by kidney Chronic pulmonary Diseases (COPD), such as emphysema Acute problems, such as pneumonia, airway obstruction, drugs such as opiates, congestive heart failure Metabolic Alkalosis Excess plasma bicarbonate Kidneys excrete excess HCO3 - and form less HCO3 - and NH4, Lungs hypoventilate Loss of gastric juice Chloride depletion Hypokalemia Increased corticosteroid Increased ingestion of antacids Respiratory Alkalosis Hyperventilation lowers pCO2 Increased excretion of bicarbonate by kidney Hyperventilation, such as with severe anxiety, fever, head injuries Stimulation of resp. center by drugs Central nervous system diseases
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- 47. The Anion Gap [(Na+)+ (K+)] – [(Cl-) + (HCO3 -)] The normal anion gap is 12meq ± 4. Causes ofHyperchloremic Acidosis ↑ GIT loss of HCO3 as in: diarrhea, high output fistula (pancreatic, biliary or small intestinal). ↑ renal HCO3 loss as in: RTA(I, II), CAIs, hypoaldosteronism. TPN. Large amount of HCO3 free fluid ↑ CL containing acids. Wide Anion Gap Acidosis Keto Acidosis Uremia Lactic Acidosis Salicylism Toxins : Methanol,Paraldehyde,Ethylene glycol
- 49. If there ismetabolic acidosis calculate the anion gap Anion Gap = Na+ - (Cl- + HCO3 -) = 12meq ± 4. • Corrected anion gap = observed anion gap + 2.5 (normal albumin - measured albumin). • If the anion gap ↑ proceed to step 8. STEP 7
- 50. If the aniongap metabolic acidosis is present we should evaluate for additional metabolic disorder because the elevation of anion gap above normal ∆ AG = (AG-12) should be buffered by HCO3. Adding ∆AG to current HCO3 will yield the corrected Hco3 which should be normal value 24 meq/l unless there is another disorder present. Corrected HCO3 = current HCO3 (measured) +∆A.G (Normal value 24 meq/l) •If corrected HCO3 >24 → metabolic alkalosis is also present •If corrected HCO3 <24 → a non gap metabolic acidosis is also present •If corrected HCO3 = 24 → it is pure gap metabolic acidosis. STEP 8
- 51. In case ofmetabolic alkalosis: measure urinary Cl- concentration Final step: Be sure that the interpretation of blood gas is consistent and correlated with the clinical picture of the patient. STEP 9 (CL responsive ( UC < 15 mEq/L CL resistant ( UC ˃ 25 mEq/L)