Acid-Base Disorders

Arash Safaie, MDEmergency Physician

pH

↓7.36: Acidemia ↑7.44: Alkalemia

Physiologic Buffers Bicarbonate Carbonic Acid Systems (RBCs) Phosphate Buffers (Bone)

Basic Concepts

Useful Knowledge

ABG vs. VBG

VBG pH: 0.03↓ PCO2: 6.6↑ HCO3: 1.4↑

Role of TemperatureTemperatu

re (°C)

pHPaco2 (mm Hg)

Pao2 (mm Hg)

20 7.65 19 27

30 7.50 30 51

35 7.43 37 70

37 7.40 40 80

39 7.37 44 91

Acute

Intracellular Buffering CO2 Narcosis ↑PCO2: 10 ↑HCO3: 1 ↑PCO2: 10 ↓pH: 0.08

Chronic Beyond 6-12h starts 5d completes Hypochloremia ↑PCO2: 10 ↑HCO3: 4 ↑PCO2: 10 ↓pH: 0.03

Respiratory Acidosis

Acute

Intracellular Buffering ↓PCO2: 10 ↓HCO3: 2 ↓PCO2: 10 ↑pH: 0.08

Chronic Beyond 6-36h starts 14d completes Hyperchloremia ↓PCO2: 10 ↓HCO3: 3.5 ↓PCO2: 10 ↑pH: 0.03

Respiratory Alkalosis

Pregnancy

pH: 7.46-7.50 PaCO2: 31-35 HCO3: 18-22

Childhood (7-19y) PaCO2: 37

Pregnancy & Childhood

Compensation

↓HCO3: 1 ↓PCO2: 1.2 PCO2: (1.5 x HCo3) + 8 12-24h for Max. Respiratory Response Compensation Limit PCO2: 10-15

Normal AG Urine AG: (Urine Na + Urine K) – Urine Cl Positive Urine AG: Altered Urinary Acidification Negative Urine AG: GI Loss

Role of NaHCO3 in Rx

Metabolic Acidosis

AG: Na – (Cl + HCO3)

> 15 High < 3 Low

ΔG: (AG – 12) – (24 – HCO3) >+6: concurrent Metabolic Alkalosis or

Respiratory Acidosis <-6: concurrent Normal AG Metabolic

Acidosis or Respiratory Alkalosis

Anion Gap & ΔGap

Compensation

↑HCO3: 1 ↓PCO2: 1.2 Compensation Limit PCO2: 55-75

Saline Responsiveness Saline-Responsive: Urine Cl <10 Saline-Resistant: Urine Cl >10

Rx Saline-Responsive: NaCl + KCl

Severe: IV Mineral Acids Edematous: Acetazolamide, Dialysis

Saline-Resistant: KCl + Mineralocorticoid Antagonist

Metabolic Alkalosis

ASK ME

pH: 7.37 PCO2: 50 HCO3: 28 Na: 139 Cl: 102

1

pH: 7.44 PCO2: 46 HCO3: 34 Na: 140 Cl: 100

2

pH: 7.35 PCO2: 28 HCO3: 14 Na: 140 Cl: 110

3

pH: 7.32 PCO2: 50 HCO3: 25 Na: 140 Cl: 110

4

pH: 7.43 PCO2: 30 HCO3: 22 Na: 140 Cl: 108

5

pH: 7.30 PCO2: 40 HCO3: 20 Na: 140 Cl: 110

6

pH: 7.37 PCO2: 16 HCO3: 4 Na: 140 Cl: 96

7

pH: 7.30 PCO2: 16 HCO3: 4 Na: 140 Cl: 106

8

pH: 7.30 PCO2: 28 HCO3: 14 Na: 140 Cl: 111

9

pH: 7.42 PCO2: 50 HCO3: 29 Na: 140 Cl: 105

10