Respiratory Acidosis

Report
Arash Safaie, MD
Emergency Physician
Basic Concepts

 pH
 ↓7.36: Acidemia
 ↑7.44: Alkalemia
 Physiologic Buffers
 Bicarbonate
 Carbonic Acid Systems (RBCs)
 Phosphate Buffers (Bone)
Useful Knowledge

ABG vs. VBG
 VBG
 pH: 0.03↓
 PCO2: 6.6↑
 HCO3: 1.4↑
Role of Temperature
Tempe
rature
(°C)
pH
Paco2
(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
Respiratory Acidosis

 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 Alkalosis

 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
Pregnancy & Childhood

 Pregnancy
 pH: 7.46-7.50
 PaCO2: 31-35
 HCO3: 18-22
 Childhood (7-19y)
 PaCO2: 37
Metabolic Acidosis

 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
Anion Gap & ΔGap

 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
Metabolic Alkalosis

 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
1

 pH:
 PCO2:
 HCO3:
 Na:
 Cl:
7.37
50
28
139
102
2

 pH:
 PCO2:
 HCO3:
 Na:
 Cl:
7.44
46
34
140
100
3

 pH:
 PCO2:
 HCO3:
 Na:
 Cl:
7.35
28
14
140
110
4

 pH:
 PCO2:
 HCO3:
 Na:
 Cl:
7.32
50
25
140
110
5

 pH:
 PCO2:
 HCO3:
 Na:
 Cl:
7.43
30
22
140
108
6

 pH:
 PCO2:
 HCO3:
 Na:
 Cl:
7.30
40
20
140
110
7

 pH:
 PCO2:
 HCO3:
 Na:
 Cl:
7.37
16
4
140
96
8

 pH:
 PCO2:
 HCO3:
 Na:
 Cl:
7.30
16
4
140
106
9

 pH:
 PCO2:
 HCO3:
 Na:
 Cl:
7.30
28
14
140
111
10

 pH:
 PCO2:
 HCO3:
 Na:
 Cl:
7.42
50
29
140
105

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