assessment of acid-based balance part 2 W3

Question 1

practical aspects of blood gas samples?

Answer 1

usually collect from radial artery
painful, risk of damage (can compromise blood sup to hand)
collect from femoral artery in arrest situation

Question 2

interpretation of ABGs

Answer 2

is the patient adequately oxygenated?
what is their pH/H+?
is there pCO2 or bicarbonate disturbance

Question 3

base excess?

Answer 3

concentration of hydrogen ions required to return pH to reference range if if pCO2 were in reference range (~5.3kPa)

Question 4

when should base excess be deranged, and when is it positive/negative?

Answer 4

should only be deranged in a metabolic disorder
negative in metabolic acidosis
positive in metabolic alkalosis

Question 5

what is standardised bicarbonate?

Answer 5

what we would expect the bicarbonate to be if pCO2 were in reference range (~5.3kPa)

Question 6

standardised bicarbonate values in resp/met disorder?

Answer 6

in ref range in purely resp disorder.
should be same as actual bicarbonate concentration in metabolic disorder.

inboth respirartory and metabolic, quite different from actual bicarbonate

Question 7

case: 19 yr-old female. confused, restless, tachypnoeic.
high H+, slightly high O2, low bicarbonate.

Answer 7

not hypoxic
acidaemia
respiratory alkalosis - compensation from body (partial)
metabolic acidosis (low bicarb, high H+) - primary disorder

Question 8

metabolic acidosis - causes of increased acid formation? (different to last slide in last lecture idk why)

Answer 8

ketoacidosis (diabetic, starvation, alcoholic)
lactic acidosis (tissue hypoxia)
poisoning (salicylate, methanol)
inherited metabolic disorders (early infancy)

Question 9

metabolic acidosis - causes of reduced excretion? (also different?)

Answer 9

renal failure (AKI, CKD, AKI ON CKD)
renal tubular acidosis (types 1 and 4)

Question 10

metabolic acidosis - causes of loss of bicarbonate?

Answer 10

gastrointestinal (diarrhoea, high-output small bowel fistula)
renal (renal tubular acidosis type 2)

Question 11

what is the anion gap used for

Answer 11

narrowing differential of metabolic acidosis

Question 12

what is the anion gap?

Answer 12

theoretical: difference between most abundant cations and anions

Question 13

which causes of metabolic acidosis have a normal anion gap?

Answer 13

severe diarrhoea
high intestinal fistula output
renal tubular acidosis

Question 14

which causes of metabolic acidosis have an elevated anion gap?

Answer 14

DKA
lactic acidosis
salicylate (aspirin) overdose
ethylene glycol / methanol poisoning
renal failure

Question 15

what type of acidosis is found with a normal anion gap? what does this mean?

Answer 15

hyperchloremic acidosis - bicarbonate ions are replaced with chloride ions

Question 16

what is occurring in acidosis with elevated anion gap?

Answer 16

bicarbonate ions are replaced with anions corresponding to lactate, keto-acids etc

Question 17

clinical effects of metabolic acidosis?

Answer 17

cardiovascular - negative inotropic effect (if severe)

O2 delivery - acutely, H+ causes R-shift of oxyHb dissociation curve (facilitates O2 delivery). after several hrs, H+ reduces 2,3-DPG causing L-shift of curve (impairs O2 delivery)

nervous system - impaired consciousness (little correlation with H+)

potassium homeostasis - leakage from cells causing high plasma K+, may also be lost renally

bone - choric acidosis then buffering by bone, leads to decalcification

Question 18

case - male, 55, cough, wheeze, breathless
low O2 and high CO2

Answer 18

primary disorder - resp acidosis
compensation - metabolic alkalosis. know its chronic as kidneys take a while to compensate.

not vice versa because of resp symptoms.

Question 19

causes of acute respiratory acidosis?

Answer 19

airway obstruction, cardioresp arrest
infective exacerbation of COPD
neuro - opiate toxicity, GB syndrome, MA

Question 20

causes of chronic respiratory acidosis?

Answer 20

COPD
obstructive - obesity
restrictive - pulmonary fibrosis
neuro - MND, myopathy

Question 21

effects of respiratory acidosis?

Answer 21

hypercapnia (high CO2):
-shortness of breath
-raised respiratory rate
-neuro effects (anxiety, coma, headache, extensor plantares, myoclonus)
-systemic vasodilatation