Acid Base Status
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The document provides guidance on evaluating acid-base disorders by assessing whether there is a primary respiratory or metabolic component, determining if there is an anion gap and investigating compensatory responses. It outlines approaches for characterizing different types of acidosis and alkalosis based on pH, pCO2, HCO3 and anion gap measurements and urine anion gap.
![ [anions] = [cations]
Cl + HCO3 + unmeas anions = Na + unmeas cations
Na - Cl- HCO3 = unmeas anions – unmeas cations
Normal anion gap = 12](https://image.slidesharecdn.com/acidbase2-121105173321-phpapp01/85/Acid-Base-Status-7-320.jpg)
![ Metabolic acid-base disorder almost immediate
ventilatory response
Winter’s Formula:
Expected pCO2 = 1.5 x [HCO3] + 8 +/- 2
Appropriate compensation measured pCO2 = exp pCO2
Respiratory alkalosis measured pCO2 < exp pCO2
Respiratory acidosis measured pCO2 > exp pCO2](https://image.slidesharecdn.com/acidbase2-121105173321-phpapp01/85/Acid-Base-Status-11-320.jpg)
![2.Check for respiratory compensation with Winter’s
formula:
Expected pCO2 = 1.5 x [HCO3] + 8 +/- 2
3.GI loss verses renal loss of HCO3?
Urine anion gap](https://image.slidesharecdn.com/acidbase2-121105173321-phpapp01/85/Acid-Base-Status-17-320.jpg)
![ Metabolic acid-base disorder almost immediate
ventilatory response
Expected pCO2 = 0.7 x [HCO3] + 21 +/- 2
Appropriate compensation measured pCO2 = exp pCO2
Respiratory alkalosis measured pCO2 < exp pCO2
Respiratory acidosis measured pCO2 > exp pCO2](https://image.slidesharecdn.com/acidbase2-121105173321-phpapp01/85/Acid-Base-Status-21-320.jpg)
Acid Base Status
- 1. Brad Bemiss, MD Chief Resident. Department of Medicine Loyola University Medical Center 2012.
- 2. Acidemia = pH<7.36 Alkalemia = pH>7.44 Change in pCO2 = Primary respiratory disorder Change in HCO3 = Primary metabolic disorder
- 3. Primary Disorder pH Primary Compensator Change Change y Change Respiratory Acidosis pCO2 HCO3 Respiratory Alkalosis pCO2 HCO3 Metabolic Acidosis HCO3 pCO2 Metabolic Alkalosis HCO3 pCO2
- 4. Acidosis Alkalosis Metabolic Respiratory Metabolic Respiratory 1. Gap or no gap? 1. Acute or chronic? 1. Check for 1. Acute or chronic? respiratory compensation High AG Normal AG Acute Chronic Acute Chronic 2. Measure 2a. Winters 2b. Winters 10 ∆pCO2: 10 ∆pCO2: urine 10 ∆pCO2: 10 ∆pCO2: chloride 3a. ∆/∆ 3b. Urine - pH ↓ by - pH ↓ by - pH ↑ by - pH ↑ by anion gap 0.08 0.03 0.08 0.03 4a. Osmol. gap - HCO3 ↑ - HCO3 ↑ - HCO3 ↓ - HCO3 ↓ by 1 by 4 by 2 by 5 2. If expected pH does 2. If expected pH does not equal actual pH, not equal actual pH, superimposed metabolic superimposed metabolic process process
- 5. Acidosis Alkalosis Metabolic Respiratory Metabolic Respiratory 1. Gap or no gap? High AG 2a. Winters 3a. ∆/∆ 4a. Osmol. gap
- 6. Caused by loss of HCO3 or accumulation of acid (e.g. lactate) in the ECF 1. Calculate anion gap 2. Check for respiratory compensation 3. Check for co-existing non-gap acidosis or metabolic alkalosis 4. If gap acidosis and no clear reason for gap, measure osmolar gap
- 7. [anions] = [cations] Cl + HCO3 + unmeas anions = Na + unmeas cations Na - Cl- HCO3 = unmeas anions – unmeas cations Normal anion gap = 12
- 8. Most of anion gap made up of albumin Low albumin smaller anion gap i.e., albumin 2g/dL “normal gap” = 7 For every 1g/dL below 4g/dL (nl albumin), add 2.5 to the gap or Adj gap = calc gap + 2.5 (4-meas albumin)
- 9. Methanol (formic acid) Uremia (ESRD impaired H+ secretion) DKA Paraldehyde INH, Inborn errors of metabolism Lactic acid Ethylene glycol (oxalic acid) Salicylates (salicylic acid)
- 10. Circulatory shock Sepsis Thiamine deficiency Meds (metformin, nitroprusside, NRTIs, tylenol) Propylene glycol toxicity (used in ativan drips) Hepatic insufficiency Seizures Acute asthma attacks
- 11. Metabolic acid-base disorder almost immediate ventilatory response Winter’s Formula: Expected pCO2 = 1.5 x [HCO3] + 8 +/- 2 Appropriate compensation measured pCO2 = exp pCO2 Respiratory alkalosis measured pCO2 < exp pCO2 Respiratory acidosis measured pCO2 > exp pCO2
- 12. Assess for non-gap metabolic acidosis or metabolic alkalosis ∆anion gap meas AG - 12 ∆HCO3 24 – meas HCO3 ◦ <1 = non gap acidosis ◦ >1 = metabolic alkalosis Measured HCO3 + ∆gap = 24 ◦ <24 = non gap acidosis ◦ >24 = metabolic alkalosis
- 13. If no clear explanation for high anion gap metabolic acidosis, check osmolar gap Osm gap = measured osm – calc osm Calc osm = 2(Na) + Gluc + BUN 18 28 Normal Osm gap = 10-15 >25 suggests methanol or ethylene glycol poisoning
- 14. Acidosis Alkalosis Metabolic Respiratory Metabolic Respiratory 1. Gap or no gap? High AG Normal AG 2a. Winters 2b. Winters 3a. ∆/∆ 3b. Urine 4a. Osmol. anion gap gap
- 15. U reterostomy S mall bowel fistula E ndocrine (adrenal insufficiency) D iarrhea C arbonic anhydrase inhibitors A limentation (TPN) R TA S aline
- 16. Renal (RTA, early renal insufficiency) Acetazolamide, ammonium chloride, hyperal (TPN) Gastrointestinal (diarrhea, fistulas) Endocrine (adrenal insufficiency) S aline
- 17. 2.Check for respiratory compensation with Winter’s formula: Expected pCO2 = 1.5 x [HCO3] + 8 +/- 2 3.GI loss verses renal loss of HCO3? Urine anion gap
- 18. Urine Na + K – Cl Normal gap is zero or slightly positive Negative urine anion gap (-20 to -50) indicates GI losses (ne-GUT-ive) ◦ Diarrhea ◦ Fistulas
- 19. Acidosis Alkalosis Metabolic Respiratory Metabolic Respiratory 1. Gap or no gap? 1. Check for respiratory compensation High AG Normal AG 2. Measure 2a. Winters 2b. Winters urine chloride 3a. ∆/∆ 3b. Urine anion gap 4a. Osmol. gap
- 20. Volume contraction ◦ Vomiting ◦ Diuretics ◦ Dehydration NGT suction Hypokalemia Post-hypercapnia Glucocorticoid excess
- 21. Metabolic acid-base disorder almost immediate ventilatory response Expected pCO2 = 0.7 x [HCO3] + 21 +/- 2 Appropriate compensation measured pCO2 = exp pCO2 Respiratory alkalosis measured pCO2 < exp pCO2 Respiratory acidosis measured pCO2 > exp pCO2
- 22. Chloride Responsive Chloride Unresponsive Urine Cl<15 Urine Cl >25
- 23. Chloride Responsive Chloride Unresponsive Urine Cl<15 Urine Cl >25 • Vomiting • Diuretics • Dehydration • Continuous NG suction • Post-hypercapnia
- 24. Chloride Responsive Chloride Unresponsive Urine Cl<15 Urine Cl >25 • Vomiting • Pure hypokalemia • Diuretics • Mineralocorticoid excess • Dehydration • Continuous NG suction • Post-hypercapnia
- 25. Acidosis Alkalosis Metabolic Respiratory Metabolic Respiratory 1. Gap or no gap? 1. Acute or chronic? 1. Check for 1. Acute or chronic? respiratory compensation High AG Normal AG Acute Chronic Acute Chronic 2. Measure 2a. Winters 2b. Winters 10 10 urine 10 10 ∆pCO2: ∆pCO2: chloride ∆pCO2: ∆pCO2: 3a. ∆/∆ 3b. Urine anion gap - pH ↓ by - pH ↓ by - pH ↑ by - pH ↑ by 4a. Osmol. 0.08 0.03 0.08 0.03 gap - HCO3 ↑ - HCO3 ↑ - HCO3 ↓ - HCO3 ↓ by 1 by 4 by 2 by 5 2. If expected pH 2. If expected pH does not equal actual does not equal actual pH, superimposed pH, superimposed metabolic process metabolic process
- 26. Lung disease ◦ Asthma/COPD ◦ Pulmonary edema/Pneumonia ◦ ARDS Depression of respiratory center ◦ Drug overdose ◦ Obesity Hypoventilation Nerve or muscular disorders ◦ Guillain-Barre ◦ Myasthenia gravis
- 27. Anxiety Drugs ◦ Salicylate overdose ◦ Progesterone Pregnancy Liver disease Head injury
- 28. ∆ pCO2 ∆ pH Acute ↑ 10 ↓ 0.08 Respiratory Acidosis Chronic ↑ 10 ↓ 0.03 Acute ↓ 10 ↑ 0.08 Respiratory Alkalosis Chronic ↓ 10 ↑ 0.03
- 29. ∆ pCO2 ∆ HCO3 Acute ↑ 10 ↑1 Respiratory Acidosis Chronic ↑ 10 ↑4 Acute ↓ 10 ↓2 Respiratory Alkalosis Chronic ↓ 10 ↓5
- 30. IfpH is lower than expected pH, metabolic acidosis ◦ Don’t forget to measure the gap! If pH is higher than expected pH, metabolic alkalosis
- 31. Acidosis Alkalosis Metabolic Respiratory Metabolic Respiratory 1. Gap or no gap? 1. Acute or chronic? 1. Check for 1. Acute or chronic? respiratory compensation High AG Normal AG Acute Chronic Acute Chronic 2. Measure 2a. Winters 2b. Winters 10 ∆pCO2: 10 ∆pCO2: urine 10 ∆pCO2: 10 ∆pCO2: chloride 3a. ∆/∆ 3b. Urine - pH ↓ by - pH ↓ by - pH ↑ by - pH ↑ by anion gap 0.08 0.03 0.08 0.03 4a. Osmol. gap - HCO3 ↑ - HCO3 ↑ - HCO3 ↓ - HCO3 ↓ by 1 by 4 by 2 by 5 2. If expected pH does 2. If expected pH does not equal actual pH, not equal actual pH, superimposed metabolic superimposed metabolic process process
- 32. Metabolic alkalosis 2/2 7.58/49/80 hypokalemia 145 86 8 1.9 40 0.7 Albumin 3.8 Urine Chloride = 74
- 33. • Acute respiratory 7.52/19/244 alkalosis • Anion gap metabolic 140 112 10 acidosis 2.8 19 0.7 Albumin 1.1 Lactate 4.6
- 34. • Anion gap metabolic 7.12/19/92 acidosis • Non-gap metabolic 140 108 35 acidosis 3.8 6 2.1 Urine Na = 55 Albumin 3.9 Urine K = 5 Urine Cl = 110
- 35. Chronic respiratory 7.35/60/146 acidosis 145 102 50 3.8 33 1.8 Albumin 2.3
- 36. • Anion gap metabolic 7.14/45/86 acidosis • Respiratory acidosis 140 98 50 3.0 17 2.6 • Metabolic alkalosis Albumin 3.7
- 37. • Acute respiratory 7.59/21/154 alkalosis • Anion gap metabolic 127 79 12 acidosis 3.7 20 0.5 • Metabolic alkalosis Albumin 4.1
Editor's Notes
- #4: If pH, HCO3 and pCO2 all change in the same direction, it is a primary metabolic disorder Compensatory change will not completely correct the pH, just limits the severity of the change in PH
- #12: Degree of elevated lactate directly correlates with mortality in shock used in ativan, valium, esmolol, NTG and dilantin drips In asthma, there is increased lactate produced by resp muscles)
- #13: - (mediated by chemoreceptors in carotid body inc or dec ventilation to affect pCO2)
- #15: Can also be seen in AKA, DKA, lactic acidosis and CRF
- #17: Loss of HCO3 is counterbalance by gain of Cl = normal anion gap Ureterostomy is fistula between ureter and GI tract Saline - saline increased [Cl] in ECF increased loss of HCO3 in urine
- #24: Contraction alkalosis Kidneys increase Na reabsorption accompanied by HCO3 reabsorption increased aldo increased H+ secretion Post-hypercapnia During respiratory acidosis, the kidneys reabsorb bicarbonate and secrete chloride to compensate for the acidosis. In the posthypercapnic state, urine chloride is high and can lead to chloride depletion. Once the respiratory acidosis is corrected, the kidneys cannot excrete the excess bicarbonate because of the low luminal chloride. Acids in infusions (lactate, acetate and citrate) converted to bicarbonate
- #25: Contraction alkalosis Kidneys increase Na reabsorption accompanied by HCO3 reabsorption increased aldo increased H+ secretion Post-hypercapnia During respiratory acidosis, the kidneys reabsorb bicarbonate and secrete chloride to compensate for the acidosis. In the posthypercapnic state, urine chloride is high and can lead to chloride depletion. Once the respiratory acidosis is corrected, the kidneys cannot excrete the excess bicarbonate because of the low luminal chloride. Acids in infusions (lactate, acetate and citrate) converted to bicarbonate
- #26: Contraction alkalosis Kidneys increase Na reabsorption accompanied by HCO3 reabsorption increased aldo increased H+ secretion Post-hypercapnia During respiratory acidosis, the kidneys reabsorb bicarbonate and secrete chloride to compensate for the acidosis. In the posthypercapnic state, urine chloride is high and can lead to chloride depletion. Once the respiratory acidosis is corrected, the kidneys cannot excrete the excess bicarbonate because of the low luminal chloride. Acids in infusions (lactate, acetate and citrate) converted to bicarbonate