ARTERIAL BLOOD GASES for starters… Jean D. Alcover, M.D. 2nd year resident UP-PGH Department of Medicine

 Normal Values at Normal Physiologic State pH 7.4pCO2 40 mmHg HCO3 24 mmolpO2 FiO2 x 5

DisorderpHPrimary Disturbance Compensatory Response Metabolic Acidosis DecreasedDec HCO3Dec pCO2 Metabolic Alkalosis IncreasedInc HCO3Inc pCO2 Respiratory Acidosis DecreasedInc pCO2Inc HCO3 Respiratory Alkalosis IncreasedDec pCO2Dec HCO3

pCO 2 + H 2 O  H 2 CO 3  HCO 3 + H  Respiratory DisorderPrimary Abnormality Secondary Response AcidosisHypoventilationHCO3 generation by kidneys AlkalosisHyperventilationHCO3 consumption

pCO 2 + H 2 O  H 2 CO 3  HCO 3 + H  Metabolic DisorderPrimary Abnormality Secondary Response AcidosisLoss of HCO3 or gain of H+ Hyperventilation AlkalosisGain HCO3 or lose H+ Hypoventilation

Compensatory Mechanisms DisorderPrimary AbnormalitySecondary Response Metabolic AcidosisLoss of HCO3 or gain of H+ 1.2 mmHg dec in pCO2 for every 1 mEq fall in HCO3 Metabolic AlkalosisIncrease in HCO3 or loss of H+ 0.7 mmHg inc in pCO2 for every 1 meq rise in HCO3 Respiratory AcidosisIncrease in pCO21 meq inc in HCO3 for every 10 mm Hg rise in pCO2 Respiratory AlkalosisDecrease in pCO22 meq dec in HCO3 for every 10 mmHg fall in pCO2

 Sample Problem #1 pH 7.14 HCO3 9 pCO2 25

 Sample Problem #1 pH 7.14 HCO3 9 pCO2 25 Metabolic acidosis with respiratory acidosis

 Sample Problem #2 pH 7.2 HCO3 15 pCO2 40

 Sample Problem #2 pH 7.2 HCO3 15 pCO2 40 Metabolic acidosis with respiratory acidosis

 Sample Problem #3 pH 7.5 HCO3 15 pCO2 20

 Sample Problem #3 pH 7.5 HCO3 15 pCO2 20 Respiratory alkalosis with metabolic acidosis

 Sample Problem #4 pH 7.36 HCO3 26 pCO2 65

 Sample Problem #4 pH 7.36 HCO3 26 pCO2 65 Respiratory acidosis, compensated

 Sample Problem #5 pH HCO3 15 pCO2 25.1

 Sample Problem #5 pH HCO3 15 pCO Metabolic Acidosis with Respiratory Alkalosis

ANION GAP Na + K = Cl + HCO3 + unmeasured anions Unmeasured anions: Sulfates, phosphates, organic anions, anionic proteins

ANION GAP  Na + K = Cl + HCO3 + unmeasured anions  Na + K = Cl + HCO3 + anion gap

ANION GAP  Thus… AG = (Na + K) – (Cl + HCO3) Or…

ANION GAP  Thus… AG = Na – (Cl + HCO3) Normal AG = 12 +/- 2

ANION GAP NORMAL ANION GAP METABOLIC ACIDOSIS 1.GI losses as in diarrhea 2.Renal loss of HCO3 as in RTA Type 2 3.Ingestion of ammonium chloride 4.Acetazolamide therapy

ANION GAP HIGH ANION GAP METABOLIC ACIDOSIS 1.Lactic acidosis (lactate) 2.Ketoacidosis (B-hydroxybutyrate) 3.Renal failure (sulfates, phosphate, etc.) 4.Ingestions A.Salicylates B.Methanol C.Ethylene glycol

ANION GAP MUDPILESMUDPILES

Methanol ingestion Uremia Diabetic ketoacidosis Paraldehyde poisoning Isoniazid poisoning Lactic acidosis Ethanol ingestion Salicylate ingestion

ANION GAP Delta Values ΔHCO3 = HCO3 – 24 ΔAG = AG – 12 ΔCl = Cl - 105

ANION GAP NORMAL ANION GAP METABOLIC ACIDOSIS ΔHCO3 = ΔClpure NAGMA ΔHCO3 < ΔClNAGMA with metabolic alkalosis ΔHCO3 > ΔClNAGMA plus HAGMA HIGH ANION GAP METABOLIC ACIDOSIS ΔHCO3 = ΔAGpure HAGMA ΔHCO3 < ΔAGHAGMA with metabolic alkalosis ΔHCO3 > ΔAGHAGMA plus NAGMA

PROBLEMS Sample Problem #1… 54/M, 75 kgs, who underwent femoral popliteal bypass surgery under GA. 24-hours later, he develops oliguria, with cold, clammy extremities. BP was only 70 palp. ABGs… pH 7.0Na 147 pCO2 32K 6.4 HCO3 8Cl 108 S Crea 220

PROBLEMS Primary Problem? Metabolic Acidosis Compensation? No. There is respiratory acidosis. Anion Gap? AG = 31. HAGMA. Mixed Metabolic Problem? ΔAG = 31 – 12 = 19 ΔHCO3 = 24 – 8 = 16 ΔHCO3< ΔAG. Thus, HAGMA + Metabolic Alkalosis HIGH ANION GAP METABOLIC ACIDOSIS WITH RESPIRATORY ACIDOSIS WITH METABOLIC ALKALOSIS

PROBLEMS Sample Problem #2… 25/M presenting at the ER with status epilepticus ABGs… pH 7.14Na 140 pCO2 45K 5.0 HCO3 14Cl 98

PROBLEMS Primary Problem? Metabolic Acidosis Compensated? No. There is respiratory acidosis Anion Gap? AG = 28. HAGMA. Mixed Metabolic Problem? ΔHCO3 = 10 ΔAG = 16 ΔHCO3 < ΔAG… Thus, HAGMA with metabolic alkalosis HIGH ANION GAP METABOLIC ACIDOSIS WITH RESPIRATORY ACIDOSIS WITH METABOLIC ALKALOSIS

PROBLEMS Sample Problem #3… 45/F with persistent diarrhea of 2 days, tachypneic with an RR of 28 ABGs… pH 7.2Na 140 pCO2 19K 4.7 HCO3 7Cl 122

PROBLEMS Primary Problem? Metabolic Acidosis Compensated? Yes. Anion Gap? AG = 11 Mixed Metabolic Disorder? ΔHCO3 = 17 ΔCl = 17 ΔHCO3 = ΔCl… PURE NAGMA PURE NAGMA, WITH FULL RESPIRATORY COMPENSATION

PROBLEMS Sample Problem #4… 50/F, known diabetic on insulin, presenting at ER with vomiting and eventual decrease in sensorium ABGs… pH 7.0Na 139 pCO2 38K 4.7 HCO3 7Cl 122 CBG 450

PROBLEMS Primary Problem? Metabolic Acidosis Compensated? No. There is respiratory acidosis. Anion Gap? AG = 10. NAGMA???? However… Corrected Na = (CBG – 100) x Na = (450 – 100) x = Anion Gap (corrected) = 15.6 … HAGMA

PROBLEMS Mixed Metabolic Problem? ΔHCO3 = 17 ΔAG = 3.6 ΔHCO3 > ΔAG… HAGMA plus NAGMA HIGH ANION GAP METABOLIC ACIDOSIS WITH SECONDARY NORMAL ANION GAP METABOLIC ACIDOSIS WITH RESPIRATORY ACIDOSIS

PROBLEMS Patient with CKD unable to comply with twice-weekly hemodialysis pH pCO pO HCO3 9.7 Sats 97.3% Na 147 K 4.7 Cl 99

ANION GAP NORMAL ANION GAP METABOLIC ACIDOSIS ΔHCO3 = ΔClpure NAGMA ΔHCO3 < ΔClNAGMA with metabolic alkalosis ΔHCO3 > ΔClNAGMA plus HAGMA HIGH ANION GAP METABOLIC ACIDOSIS ΔHCO3 = ΔAGpure HAGMA ΔHCO3 < ΔAGHAGMA with metabolic alkalosis ΔHCO3 > ΔAGHAGMA plus NAGMA

PROBLEMS High anion gap metabolic acidosis, with full respiratory compensation and secondary metabolic alkalosis, with good oxygenation

PROBLEMS 48 year old male with jaundice, ascites and dyspnea. On chest X-ray: massive pleural effusion R>L pH 7.13 pCO2 52 pO2 64 HCO3 30 Na 145 K 4.8 Cl 102

PROBLEMS Respiratory acidosis with metabolic alkalosis, with moderate hypoxemia