Sandbox: sadaf
Acid Base Disorders
Approach
Normal range
Blood gas analysis | Vessel | Range | Interpretation |
---|---|---|---|
Oxygen Partial Pressure (pO2) | Arterial | 80 to 100 mmHg (10.6 to 13.3 kPa) | Normal |
<80 mmHg | Hypoxia | ||
Venous | 35 to 40 mmHg | Normal | |
Oxygen Saturation (SO2) | Arterial | >95% | Normal |
<95% | Hypoxia | ||
Venous | 70 to 75% | Normal | |
pH | Arterial | <7.35 | Acidemia |
7.35 to 7.45 ([H+] 35 to 45 nmol/L) | Normal | ||
>7.45 | Alkalemia | ||
Venous | 7.26 to 7.46 | Normal | |
Carbon Dioxide Partial Pressure (pCO2) | Arterial | <35 mmHg | Low |
35 to 45 mmHg (4.7 to 6.0 kPa) | Normal | ||
>45 mmHg | High | ||
Venous | 40 to 45 mmHg | Normal | |
[HCO3−] | Arterial | <22 mmol/L | Low |
22 to 26 mmol/L | Normal | ||
>26 mmol/L | High | ||
Venous | 19 to 28 mmol/L | Normal | |
Base Excess (BE) | Arterial | <−3.4 | Acidemia |
−3.4 to +2.3 mmol/L | Normal | ||
>2.3 | Alkalemia | ||
Venous | −2 to −5 mmol/L | Normal | |
Osmolar gap
(Osmolality – Osmolarity) |
>10 | Abnormal | |
Anion gap
[Na+] – {[Cl−]+[HCO3−]} |
<8 | Low | |
8 to 16 | Normal | ||
>16 | High |
Compensation formula
Primary disorder | pH | PaCO2 | [HCO3−] | Compensation |
---|---|---|---|---|
Metabolic acidosis | ↓ | ↓ | ↓ | Respiratory |
Metabolic alkalosis | ↑ | ↑ | ↑ | Respiratory |
Respiratory acidosis | ↓ | ↑ | ↑ | Renal |
Respiratory alkalosis | ↑ | ↓ | ↓ | Renal |
Approach to acid–base disorders
Check pH on ABG | |||||||||||||||||||||||||||||||||||||||||
pH < 7.35= Acidosis | pH > 7.45= Alkalosis | ||||||||||||||||||||||||||||||||||||||||
Check PaCO2 | |||||||||||||||||||||||||||||||||||||||||
PaCO2 > 45mm Hg = Respiratory acidosis | PaCO2 Normal or < 35mm Hg = Metabolic acidosis | Check PaCO2 | |||||||||||||||||||||||||||||||||||||||
PaCO2 > 45mm Hg = Metabolic alkalosis | PaCO2 < 35mm Hg = Respiratory alkalosis | ||||||||||||||||||||||||||||||||||||||||
[HCO3-] > 29 | Check [HCO3-] | ||||||||||||||||||||||||||||||||||||||||
Normal or slight decrease = Acute respiratory alkalosis | Decreased < 24 = Chronic respiratory alkalosis | ||||||||||||||||||||||||||||||||||||||||
Management of Acidosis
pH < 7.35 | |||||||||||||||||||||||||||||||||||||||||||||||||||
Acidosis | |||||||||||||||||||||||||||||||||||||||||||||||||||
Determine the primary disorder Metabolic or respiratory? | |||||||||||||||||||||||||||||||||||||||||||||||||||
Check [HCO3-] and PaCO2 | |||||||||||||||||||||||||||||||||||||||||||||||||||
Low [HCO3-] and Low to normal PaCO2 | High PaCO2 and High to normal [HCO3-] | ||||||||||||||||||||||||||||||||||||||||||||||||||
Metabolic acidosis | Respiratory acidosis | ||||||||||||||||||||||||||||||||||||||||||||||||||
Check for respiratory compensation Calculate expected PCO2 | Check for renal compensation Calculate expected [HCO3-] | ||||||||||||||||||||||||||||||||||||||||||||||||||
Decrease in PaCO2=1.25 x (24- measured HCO3-)? | Acute acidosis? Increase [HCO3-]=0.1 x (measure PaCO2-40)? | Chronic acidosis? Increase [HCO3-]=0.1 x (measure PaCO2-40)? | |||||||||||||||||||||||||||||||||||||||||||||||||
PaCO2 too low? Mixed metabolic acidosis with respiratory alkalosis | PaCO2 too high? Mixed metabolic acidosis with respiratory acidosis | [HCO3-] too low? Mixed respiratory acidosis with metabolic acidosis | [HCO3-] too high? Mixed respiratory acidosis with metabolic alkalosis | [HCO3-] too low? Mixed respiratory acidosis with metabolic acidosis | E04=[HCO3-] too high? Mixed respiratory acidosis with metabolic alkalosis | ||||||||||||||||||||||||||||||||||||||||||||||
Measured PaCO2 is equal to expected value? Compensated metabolic acidosis | Measured [HCO3-] is equal to expected value? Compensated respiratory acidosis | Measured [HCO3-] is equal to expected value? Compensated respiratory acidosis | |||||||||||||||||||||||||||||||||||||||||||||||||
Click here for the management of metabolic acidosis | Click here for the management of respiratory acidosis | ||||||||||||||||||||||||||||||||||||||||||||||||||
Approach to Metabolic Acidosis
pH<7.35 And [HCO3-]<24 meq/L | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Metabolic acidosis | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Calculate the anion gap (AG) Na+ - Cl- - HCO3- | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Low AG AG<8 | Normal AG 8<AG<16 | High AG AG>16 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
Check albumin Correct the AG if albumin is low For every decrease of 1 g/dl of albumin, AG is decreased by 2.5 meg/L | Check Ca2+, Mg2+, K+, immunoglobulins High levels of these unmeasured cations decrease the AG | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Check urine AG Na+ + K+ - Cl- | Check ΔAG/ΔHCO3- | R/O low Ca2+, Mg2+, K+ | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
Negative urine AG GI causes RTA type II | Positive urine AG Renal failure RTA type I RTA type IV | ΔAG/ΔHCO3-<1 High AG metabolic acidosis combined with normal AG metabolic acidosis | 1<ΔAG/ΔHCO3-<2 Pure high AG metabolic acidosis | ΔAG/ΔHCO3->2 High AG metabolic acidosis combined with metabolic alkalosis | |||||||||||||||||||||||||||||||||||||||||||||||||||||
Metabolic Acidosis
Category | Disease | pH | Serum AG | Urine AG | Urine chloride | Volume depletion | HTN | Loss of consciousness | Fever | |||||
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Toxin/Medication | Methanol | ↓ | ↑ | |||||||||||
Paraldehyde | ↓ | ↑ | ||||||||||||
Propylene glycol | ↓ | ↑ | ||||||||||||
Ethylene glycol | ↓ | ↑ | ||||||||||||
Ethanol | ↓ | ↑ | ||||||||||||
Isopropyl alcohol | ↓ | ↑ | ||||||||||||
Toluene | ↓ | Nl | ||||||||||||
Pyroglutamic acid (5-oxoproline) | ↓ | ↑ | ||||||||||||
Salicylates | ↓↑ | ↑ | ||||||||||||
Metformin | ↓ | ↑ | ||||||||||||
Isoniazid | ↓ | ↑ | ||||||||||||
Acetazolamide | ↓ | Nl | ||||||||||||
Ammonium chloride | ↓ | Nl | ||||||||||||
Amphotericin B | ↓ | Nl | ||||||||||||
Cholestyramine | ↓ | Nl | ||||||||||||
Lactic acidosis | ↓ | ↑ | ||||||||||||
Uremia | ↓ | ↑ | ||||||||||||
Ketoacidosis | Diabetic | ↓ | ↑ | |||||||||||
Starvation | ↓ | ↑ | ||||||||||||
Alcoholic | ↓ | ↑ | ||||||||||||
Infection | ↓ | ↑ | ||||||||||||
Ischemia | ↓ | ↑ | ||||||||||||
Diarrhea | ↓ | Nl | ||||||||||||
Ureteral diversion | ↓ | Nl | ||||||||||||
Renal failure | ↓ | ↑ | ||||||||||||
Renal tubular acidosis | Type I | ↓ | Nl | ↑ | ||||||||||
Type II | ↓ | Nl | ↓ | |||||||||||
Type IV | ↓ | Nl | ↑ | |||||||||||
Hyperalimentation | ↓ | Nl | ||||||||||||
Addison's disease | ↓ | Nl | ||||||||||||
Post hypocapnea | ↓ | Nl | ||||||||||||
Vomiting | ↑ | ↓ | + | |||||||||||
Nasogastric tube suction | ↑ | ↓ | + | |||||||||||
Over-diuresis | ↑ | ↓ | + | |||||||||||
Cushing's syndrome | ↑ | Nl | + | |||||||||||
Hyperaldosteronism | ↑ | Nl | + | |||||||||||
Renal artery stenosis | ↑ | Nl | + | |||||||||||
Hypomagnesemia | ↑ | Nl | - | |||||||||||
Hypokalemia | ↑ | Nl | - | |||||||||||
Bartter's syndrome | ↑ | Nl | - | |||||||||||
Licorice ingestion | ↑ | Nl | - | |||||||||||
Category | Disease | pH | Serum AG | Urine AG | Urine chloride | Volume depletion | HTN | Loss of consciousness | Fever |
Metabolic Alkalosis
Respiratory Acidosis
Respiratory Alkalosis
Mixed Acid-Base Disorders
Disorder | Key features | Examples | |
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Metabolic acidosis—respiratory alkalosis | High- or normal-AG metabolic acidosis; prevailing Paco2 below
predicted value |
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Metabolic acidosis—respiratory acidosis | High- or normal-AG metabolic acidosis; prevailing Paco2 above
predicted value |
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Metabolic alkalosis—respiratory alkalosis | Paco2 does not increase as predicted; pH higher than expected |
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Metabolic alkalosis—respiratory acidosis | Paco2 higher than predicted; pH normal |
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Metabolic acidosis—metabolic alkalosis | Only detectable with high-AG acidosis; ∆AG >> ∆HCO3-diarrhea and lactic acidosis, toluene toxicity, treatment of diabetic
ketoacidosis |
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Metabolic acidosis—metabolic acidosis | Mixed high-AG—normal-AG acidosis; ∆HCO3- accounted for by
combined change in ∆AG and ∆Cl |
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