Blood gases Flashcards
Discuss PF ratio
The ratio of inspired air to arterial o2
should be greater than 200mmhg
Discuss Assessing o2 content
Determined by HB concentration and saturation
Assess function of HB is the measured saturation what you would expect for the Pao2 if not there is a shift in the curve
Measure your P50 – partial pressure at which o2 sat is 50%
increase means a rightward shift (hyperthermia, hypercapnia, acidosis, increase 23 DPG)
decrease means a leftward shift (hypothermia, hypocapnia, alkalsosi, decrease 23 DPG
Discuss Anion Gap
NA - (CL+HCO2)
normal 8-16
Discuss causes of high anion gap metabolic acidosis (KUSMAL)
Ketoacidosis Ureamia salicylates methanol alcoholic ketoacidosis lactic acidossis
Discuss causes of normal anion gap metabolic acidosis
Gi hco3 loss -diarrhoea -pancreatic or biliary drainage -urinary diversion Renal bicarb loss -type 2 rneal tubular acidosis -ketoacidosis
Discuss lactic acidosis
Without clear evidence to the contrary lactic acidosis should be assumed to be secondary to inadequate tissue perfusion
Discuss classes of lactic acidosis
Type 1 (inadequate tissue perfusion) -shock -severe hypoxaemia -aneamia -post convulsions -sever exercise sepsis
Type B (no evidence of inadequate perfusion) B1 -- associated with udnerlying disease (leukaemia, lymphoma) B2- Drugs -metformin -salicylates -sorbitol -paracetamol B3 - inborn metabolic errors
Discuss respiratory compensation for metabolic acidosis
Complete respiratory compensation for acidosis does not occur and normal PH in a patient with metabolic acidosis should raise suspicion of co-current alkolosis
Discuss metabolic alkalosis
Usually initiated by increase loss of acid from the stomach or kidney. Excretion of high hco3 is usually so high that metabolic acid is not sustained
Sustained metabolic acidosis is usually due to volume deficit. In volume deficit kidney re-absorbs NA over other homeostatic mechanisms. HCO3 is combined in reabsorption of NA through carbonic acid
Another mechanisms is hyperadrenocorticoidism (conns, cushings)
Discuss respiratory alkalosis
Can be caused by hypoxia or non hypoxic respiratory center stimulation
Non hypoxic include
- anxiety
- stress
- pregnancy
- sepsis
- salicylates
- hepatic cirrhosis
Can cause tetany probably due to direct increase in neuromuscular excitability rather then modest decrease in ionized calcium, sever may also cause confusion or loss of consciousness
Discuss Mixed
Common causes
- salicylate
- sepsis
- DKA
- alcohol (metabolic acidosis with hyperventilation from DT)