acid-base and blood gas analysis zsolt molnar 2009
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Acid-base and blood gas analysis
Zsolt Molnar
2009
• H+ potency: pH (pondus Hydrogenii)
Søren Sørensen, 1909
• pH = -lg H+
• -lg 40 = 7.40
Potency of H+
Molnár ‘99
H+ nmol/L
40
• H+ potency: pH (pondus Hydrogenii)
Søren Sørensen, 1909
• pH = -lg H+
• -lg 40 = 7.40
Potency of H+
Molnár ‘99
H+ nmol/L
40
100
16
• H+ potency: pH (pondus Hydrogenii)
Søren Sørensen, 1909
• pH = -lg H+
• -lg 40x10-9 = 7.40• -lg 100x10-9 = 7.00• -lg 16x10-9 = 7.80
Molnár ‘99
H+ nmol/L
40
100
16
Potency of H+
• H+ potency: pH (pondus Hydrogenii)
Søren Sørensen, 1909
• pH = -lg H+
• -lg 40x10-9 = 7.40• -lg 100x10-9 = 7.00• -lg 16x10-9 = 7.80• Henderson-Hasselbalch:
Molnár ‘99
H+ nmol/L
40
100
16
Potency of H+
Blood gas analysis
• pH• PaCO2
• actHCO3-
• stHCO3-
• BE• BB
What does an ABG tell us?
Molnár ‘99
- measured: 7.35-7.45- measured: 35-45 Hgmm - calc: 22-24 mmol/L
- calc: (T, CO2) 21-28 mmol/L
- c: (T, CO2, pH) 3 mmol/L- c: (össz puffer) ~48 mmol/l
• Skandinavian school• Sörensen, Astrup, Siggaard-Andersen• BE, BB
• Boston school• Henderson, Hasselbalch• Use what is measured• pH, CO2, HCO3
-
Skandinavian vs. Boston school
Molnár ‘99
1. H+ concentration: pHa. > 7.45 = alkalosis
b. < 7.35 = acidosis
c. 7.35 < pH < 7.45 = normal v. compensated
2. Respiratory component: PaCO2
a. > 45 Hgmm = respiratory acidosis
b. < 35 Hgmm = respiratory alkalosis
3. Metabolic component: HCO3-
a. > 25 mmol/L = metabolic alkalosis
b. < 20 mmol/L = metabolic acidosis
4. Compensated changesa. 1/c + 2/a + 3/a = respiratory acidosis
b. 1/c + 2/b + 3/b = metabolic acidosis
Analysing algorhythm
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Concept of electroneutrality + = 154 - = 154 mmol/L
HCO3 = 26
Organic acids = 6
Protein = 16HPO4 = 2SO4 = 1
Cl- = 109Na+ = 142
K+ = 4
Mg2+ = 2
Ca2+ = 5Misc = 1
anions = kations
• Anion-gap=(Na+K)-(Cl+HCO3)
Metabolic acidosis + = 154 - = 154 mmol/L
HCO3 = 26
Organic acids = 6
Protein = 16HPO4 = 2SO4 = 1
Cl+ = 109Na+ = 142
K+ = 4
Mg2+ = 2
Ca2+ = 5Misc = 1
• High AG
Metabolic acidosis + = 154 - = 154 mmol/L
HCO3 = 16
Organic acids = 14
Protein = 16HPO4 = 2SO4 = 1
Cl+ = 109Na+ = 142
K+ = 4
Mg2+ = 2
Ca2+ = 5Misc = 1
• High AG
AG
Metabolic acidosis + = 154 - = 154 mmol/L
HCO3 = 16
Organic acids = 14
Protein = 16HPO4 = 2SO4 = 1
Cl+ = 109Na+ = 142
K+ = 4
Mg2+ = 2
Ca2+ = 5Misc = 1
• High AG
• AG = 26 mmol/L
AG
Metabolic acidosis + = 154 - = 154 mmol/L
HCO3 = 26
Organic acids = 6
Protein = 16HPO4 = 2SO4 = 1
Cl+ = 109Na+ = 142
K+ = 4
Mg2+ = 2
Ca2+ = 5Misc = 1
• Normal AG
Metabolic acidosis + = 154 - = 154 mmol/L
HCO3 = 16
Organic acids= 6
Proteins = 16HPO4 = 2SO4 = 1
Cl+ = 119Na+ = 142
K+ = 4
Mg2+ = 2
Ca2+ = 5Egyéb = 1
• Normal AG
Reasons
• High AG a. Lactate acidosis: shock, sepsis, liver failure, etcb. Ketoacidosisc. Acid intake: salicilate toxicity
• Normal AGa. Intestinal HCO3
- loss: diarrhea, fistula stb.
b. Renal HCO3- loss: RTA
Metabolic acidosis
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• Acid lossa. NG aspirate
b. Diuretics - hypokalemia
• Excessive alkalinizationa. HCO3
-
b. Citrate, lactate (Ringer), acetate
Metabolic alkalosis
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• Altered level of consciousness• Overdose: opiates, sedatives• Trauma: head, i.c. bleeding
• Muscle weakness• Guillain-Barré, myastenia, muscle relaxant effect
• Type II respiratory failure• COPD, acute exacerbation• Inadequate IPPV
Respiratory acidosis
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• Pulm. emb.• CNS excitation
• Meningitis, encephalitis
• I.c. bleeding
• Asthma• Iatrogen
• Inadekvate IPPV
Respiratory alkalosis
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• Acidosisa. Shock: septic, cardiogen+pulm oedema
b. St. post CPR
• Alkalosisa. Hyperventilation + NG aspirate (vomiting)
b. Liver failure + diuretics
Mixed disorders
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Examples
• 48 y old woman, admitted with shock: BP 90/50, HR 130, Dg: UTI
• pH: 7.36
• CO2: 29
• HCO3-: 16
• Na+: 134
• K+: 4.8
• Cl-: 98
• AG: 34.8
• Dg: compensated metabolic acidosis• Treatment:
• O2, fluid, vasopressors, AB
Practice – case 1
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• 53 y old man, cirrhotic, bleeding from eoph. varices: BP 70/.., HR 130
• pH: 7.28
• CO2: 33
• HCO3-: 17
• Na+: 134
• K+: 5.4
• Cl-: 103
• AG: 19.4
• Dg: decompensated metabolic acidosis• Treatment:
• O2, fluid, blood, endoscopy+ligation
Practice – case 2
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• 53 y old man, IDDM, admitted with coma• pH: 7.05
• CO2: 23
• HCO3-: 6.5
• Na+: 139
• K+: 5.4
• Cl-: 104
• AG: 34.4
• Dg: severe decompensated metabolic acidosis• Treatment:
• ETT-O2, fluid (NS+bicarb), insulin i.v. bolus+cont.
Practice – case 3
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• 68 y old man, colon cancer, postop day 3, unwell, GCS: 12
• pH: 7.60
• CO2: 43
• HCO3-: 43
• Na+: 144
• K+: 2.8
• Cl-: 102
• AG: 1.8
• Dg: decompensated metabolic alkalosis• Treatment:
• O2, fluid (NS, RL), K+ (max: 50 mmol/h)
Practice – case 4
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• 70 y old man, COPD, admitted with acute flareup of cold
• pH: 7.48
• CO2: 72
• HCO3-: 54
• Na+: 148
• K+: 3.4
• Cl-: 96
• AG: 1.4
• Dg: compensated respiratory acidosis• Treatment:
• O2, fluid (NS, RL), observation on medical ward, ?AB
Practice – case 5
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• 75 y old man, COPD, admitted with vomiting+diarrhoea for days
• pH: 7.24
• CO2: 72
• HCO3-: 28
• Na+: 148
• K+: 5.7
• Cl-: 96
• AG: 29.7
• Dg: decompensated metabolic acidosis• Treatment:
• O2, fluid (NS, RL), ?dialysis, ?AB
Practice – case 6
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• 62 y old woman, post op acute gastric perforation• pH: 7.57
• CO2: 26
• HCO3-: 24
• Na+: 148
• K+: 3.8
• Cl-: 104
• AG: 23.8
• Dg: decompensated respiratory alkalosis• Treatment:
• O2, morphine+ whatever
Practice – case 7
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• 17 y old girl, admitted from a disco in coma, otherwise stable:
• pH: 7.06
• CO2: 80
• HCO3-: 25
• Na+: 148
• K+: 4.4
• Cl-: 105
• AG: 22.4
• Dg: decompensated respiratory acidosis• Treatment:
• ETT, ?antidote, …give her time
Practice – case 8
Molnár ‘99
• Differentiate between fact (measurement) and fiction (calculation)!
• Look at the whole picture not just the „deep picture”
• Treat the patient not the figures!
Summary
Molnár ‘99