workup and treatment of acid base disorders

Question 1

order lab studies

Answer 1

ABG: To assess pH, PCO2, HCO3-, and oxygenation; alternatively, venous blood gas
metabolic panel: To assess changes in sodium, chloride, bicarbonate, other electrolytes, and renal function, and to calculate the anion gap

Question 2

a mixed acid base disorder is when

Answer 2

The expected compensatory response differs from the laboratory findings.

Question 3

anion gap

Answer 3

the difference between the concentration of measured cations and measured anions

Question 4

high anion gap means

Answer 4

increased concentration of organic acids such as lactate, ketones (e.g., beta-hydroxybutyrate, acetoacetate), oxalic acid, formic acid, or glycolic acid, with no compensatory increase in Cl-.

Question 5

general principles of metabolic acidosis

Answer 5

Calculation of the anion gap is the first step in the evaluation of metabolic acidosis.

Question 6

concommitant acid-base disturbances

Answer 6

Calculation of the delta gap can help determine if another acid-base disturbance is present in addition to a high anion gap metabolic acidosis. Cut-off values may vary depending on the source.
delta gap: a ratio of the change in anion gap to the change in bicarbonate

Question 7

deltaa gap values

Answer 7

Delta gap < 1 : Hyperchloremic or normal anion gap metabolic acidosis is present in addition to high anion gap metabolic acidosis. [10]
Delta gap 1–2 : Only high anion gap metabolic acidosis is present.
Delta gap > 2 : A metabolic alkalosis is present in addition to high anion gap metabolic acidosis. [11]

Question 8

urine anion gap

Answer 8

The difference between the concentration of measured anions and the concentration of measured cations in the urine.

Question 9

workup of normal anion gap metabolic acidosis

Answer 9

Calculate the urine anion gap
Negative urine anion gap: Acidosis is likely due to loss of bicarbonate.
Positive urine anion gap: Acidosis is likely due to decreased renal acid excretion.

Question 10

loss of bicarbonate

Answer 10

negative urine anion gap
causes:
- diarhhoea
- GI fistulas
- toluene ingestion
- meds
- type 2 renal tubular acidosis

Question 11

decreased renal acid excretion

Answer 11

positive urine anion gap
causes:
- hyperchloraemia
- renal failure
- addison disease
- renal tubular acidosis

Question 12

compensation in metabolic disorders

Answer 12

rapid within minutes through respiratory compensation

Question 13

compensation in respiratory disorders

Answer 13

slow over several hours through changes in urine pH

Question 14

calculating the expected compensation in metabolic acidosis

Answer 14

winter formula
expected pCO2 = 1.5 x HCO3 +8 +/- 2

Question 15

what is the first step in metabolic acidosis

Answer 15

calculation of the anion gap
determines whether the loss of HCO3 is being compensated by an increase in Cl

Question 16

high anion gap metabolic acidosis approach

Answer 16

exclude accumulation of endogenous acids eg. ketoacidosis (measure ketone levels in urine or serum, lactic acidosis, uraemia (measure BUN and creatinine)
consider accumulation of exogenous organic acids (ingestion) as the cause: serum or urine toxicology screen.
calculate the delta gap to exclude concommittant acid base disturbnaces

Question 17

causes of lactic acidosis

Answer 17

related to hypoxia eg. by septic shock, hypovolaemic shock, hopoxaemia
or not relted to hypoxia eg. caused by liver failure, metformin

Question 18

causes of accumulation of exogenous organic acids

Answer 18

ingestion of methanol
ingestion of etylene glycol (antifreeze)
ingestion of propylene glycol
toluene
salicylate toxicity
iron overdose
isoniazid overdose

Question 19

workup of normal anion gap metabolic acidosis

Answer 19

calculate the urine anion gap
negative urine anion gap: acidosis is likely due to the los of bicarbonate
positive urine anion gap: acidosis is. likely due to the decreased renal acid excretion

Question 20

when. to. calculate the urine osmolol gapp

Answer 20

ppreferred over. the urine anion gap if the urine pH is >6.5
decreased urine osmolol gap suggests impairment in the excretion of urinary ammonium

Question 21

appraoch of metabolic alkalosis

Answer 21

assess blood pressure and volume status
evaluate for exogenous ingestion (eg. laxatives, calcium, alkali load, diuretics
obtin BMP and serum calcium, urinary chloride, urinary potassium levels

Question 22

if there is low urine potassium

Answer 22

consider laxative abuse as a potential cause

Question 23

testing urinary chloride in metabolic alkalosis

Answer 23

chloride resposive alkalosis: hypovolaemia (Gi lossess due to vomiting, NG. tube, diarrhoea), renal losses, cystic fibrosis, dietary chloride deficiency
chloride resistant metabolic alkalosis: severe magnesium deficiency, extreme hypercalcaemia or hypokalaemia, loop. or thiazide diuretics,

Question 24

respiratory acidosis workup

Answer 24

establish chronicity based on severity of presentation: is it acute or chornic

Question 25

acute respiratory acidosis

Answer 25

acute lung disease
acute exacerbation of COPD
CNS depression due to head trauma, postictal state, drug toxicity, central sleep apnoea

Question 26

chronic respiratory acidosis

Answer 26

COPD, asthma
respiratory muscle weakness ego myasthenia gravis, ALS, GBS, poliomyelitis, MS, severe hypokalaemia

Question 27

HCO3- is

Answer 27

alkaline

Question 28

CO2 is

Answer 28

acidic

Question 29

kidney compensation of respiratory aklalosis

Answer 29

proximal convoluted tubule secreetes more HCO3

Question 30

respiratory alkalosis is seen in

Answer 30

hyperventilation

Question 31

causes of acute respiratory alkalosis

Answer 31

pulmonary disease eg. pneumonia, pulmonary embolism, pulmonary oedema, ppulmonary oedema, aspiration pneumonitis, interstitial firbosis
pain, anxiety, panic attacks
fever
drug toxicity
CNS infections
stroke
severe anaemia
congestive heart fialure
sepsis
hypoxaemia
hyperventilation while on mechanical ventilation

Question 32

chronic respiratory alkalosis

Answer 32

pulmonary. embolism
liver failure
hyperthyroidism
brainstem tumour