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592 SeCTIOn III Renal ` RENAL—PhysioLogy Renal ` RENAL—PhysioLogy
Acid-base physiology
ph Pco [hCo ] ComPENsAtoRy REsPoNsE
–
2 3
Metabolic acidosis Hyperventilation (immediate)
Metabolic alkalosis Hypoventilation (immediate)
Respiratory acidosis renal [HCO ] reabsorption (delayed)
–
3
Respiratory alkalosis renal [HCO ] reabsorption (delayed)
–
3
Key: = compensatory response.
[HCO ]
−
Henderson-Hasselbalch equation: pH = 6.1 + log 3
0.03 P 2
Predicted respiratory compensation for a simple metabolic acidosis can be calculated using the
Winters formula. If measured Pco > predicted Pco concomitant respiratory acidosis; if
2
2
measured Pco < predicted Pco concomitant respiratory alkalosis:
2 2
Pco = 1.5 [HCO ] + 8 ± 2
–
3
2
Acidosis and alkalosis
Check arterial pH
pH < 7.35 pH > 7.45
Acidemia Alkalemia
–
Pco > 44 mm Hg HCO < 20 mEq/L Pco < 36 mm Hg HCO > 28 mEq/L
–
3
3
2 2
Respiratory Metabolic acidosis Respiratory Metabolic alkalosis
acidosis alkalosis
Hypoventilation Check anion gap Hyperventilation H loss/HCO excess
–
+
3
–
= Na – (CI + HCO _ )
+
Airway obstruction 3 Anxiety/panic attack Loop diuretics
Acute lung disease Hypoxemia (eg, high altitude) Vomiting
Chronic lung disease Salicylates (early) Antacid use
Opioids, sedatives Tumor Hyperaldosteronism
Weakening of respiratory Pulmonary embolism
muscles
> 12 mEq/L 8–12 mEq/L Pco =
2
45 Metabolic 40 mm Hg
alkalosis
40 Respiratory
Anion gap Normal anion gap 35 acidosis Mixed
MUDPILES: HARDASS: 30 alkalosis
Methanol (formic acid) Hyperchloremia/hyperalimentation –
Uremia Addison disease Plasma [HCO 3 ] (mmol/L) 25 Bu er line
Diabetic ketoacidosis Renal tubular acidosis 20 Mixed
Propylene glycol Diarrhea acidosis
Iron tablets or INH Acetazolamide 15
Lactic acidosis Spironolactone 10 Respiratory
Ethylene glycol (oxalic acid) Saline infusion 5 Metabolic alkalosis
acidosis
Salicylates (late)
6.97.0 7.17.2 7.37.4 7.57.6 7.77.8 7.9
pH
FAS1_2019_14-Renal.indd 592 11/7/19 5:42 PM
