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)
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
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
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
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
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
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)
- (mediated by chemoreceptors in carotid body inc or dec ventilation to affect pCO2)
Can also be seen in AKA, DKA, lactic acidosis and CRF
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
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
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
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
