Blood gases

Question	Answer
Winter's formula	Calc's compensation in metabolic acidosis pCO2 = (1.5 x bic) +8
Anion gap calculation	AG = (Na + K) minus (Cl + bic) Normal is 12 to 15
Delta gap calculation	Calc's if mixed or pure acid/base disorder = Delta AG/delta bic = Calc AG minus 12/(24 minus bic)
Delta gap values Interpretation	>2: met acid AND met alk/preexisting resp acidosis 1 to 2 pure HAGMA 0.4 to 0.8 NAGMA + HAGMA <0.4 pure NAGMA (hyperchloraemic)
NAGMA and K	Most a/w hypokalaemia except hyperchloraemia, adrenal insufficiency, ARF
Low AG Causes	Lithium Hypoalbuminaemia
Respiratory acidosis Compensation	Bic: CO2 rise Acute 1:10 Chronic 4:10
Respiratory alkalosis Compensation	Bic:CO2 fall Acute 2:10 Chronic 5:10
Osmolar gap	(2xNa) + urea + glucose + EtOH Normal is 10
High osmolar gap Causes	Alcohols Glucose Osmotic diuretics (mannitol, sorbitol)
Alveolar gas equation At sea level	PAO2 minus PaO2 where PAO2= (FiO2x713) minus (1.25xPaCO2) In room air, FiO2x713 = 150
Alveolar gas equation Normal values for age	(Age/4) + 4
K correction for pH	For every decrease pH 0.1, K increases 0.5 eg if pH 7.2, expect K to be 6 (reverse applies if pH increases)
Ca corrected for pH	For every pH decrease 0.1, Ca increase 0.05
HAGMA Causes	MUDPILES (methanol, ureamia, DKA, paraldehyde/paracetamol, isoniazid, lactic acidosis, EtOH, salicylates)
NAGMA Causes	USED CARP Renal/GI loss of bicarb OR gain acid (ureterosigmoidostomy, saline admin, endo, diarrhoea, carbonic anhydrase inhibitor, ammonium, RTA, pancreatititis)

Resource summary

	Created by snough about 10 years ago