Evaluation of Acid-Base Disorders

Question 1

2 things you do whenever evaluating acid-base

Answer 1

determine if primary process if acidosis or alkalosis

calculate anion gap

Question 2

Always calculate an anion gap:

why?

Answer 2

acidsosis may be occuring even with normal pH

may have concurrent alkalosis that covers the acidosis in pH

if anion gap is present, may have anion gap metabolic acidosis

Question 3

When to calculate osm gap

Answer 3

if anion gap is present

Question 4

Elevated osm gap may indicate

Answer 4

ingestion of ethylene glycol, methanol, ethanol

Question 5

When to calculate excess anion gap

Answer 5

when calculated anion gap is elevated

Question 6

Formula for calculating osm

Answer 6

2 [Na⁺] + [Glc]/18 + [BUN]/2.8 = calculated osms

usually ~285

Question 7

Formula for calculating excess anion gap

Answer 7

calculated anion gap - 12

add this to measured bicarb

this should equal normal bicarb (24-26)

Question 8

Elevated excess anion gap indicates

Answer 8

underlying metabolic alkalosis

Question 9

Primary etiology of elevated anion gap metabolic acidosis

Answer 9

retention of acid

lactate, ketones, etc

Question 10

Lab findings in metabolic acidosis

Answer 10

pH < 7.35

low HCO₃

low pCO₂ (due to respiratory compensation)

anion gap > 15 (8-12)

Question 11

DDx in elevated anion gap metabolic acidosis

Answer 11

MUD PILES

M = methanol

U = uremics

D = DKA and AKA

P = paraldehyde

I = iron or isoniazid

L = lactic acid

S = salicylates

Question 12

Etiology of normal anion gap metabolic acidosis

Answer 12

loss of HCO₃^-

Question 13

Causes of normal anion gap metabolic acidosis

Answer 13

HARD UP

loss of HCO₃^-

H = post-hyperventilation, hyperalimentation

A = acid ingestion (CA inhibitor, HCl)

R = RTA

D = diarrhea

U = urethral and ileal diversion

P = pancreatic fistula

Question 14

Normal anion gap acisosis also called

Answer 14

hyperchloremic metabolic acidosis

Question 15

Etiology of metabolic alkalosis

Answer 15

hypoventilation

increased HCO₃^-

Question 16

Two types of metabolic alkalosis

Answer 16

chloride responsive

kidney is holding onto Cl^-

chloride unresponsive

Question 17

Chloride-responsive metabolic alkalosis causes

Answer 17

emesis

diuretics

NG suction

diarrhead causing dehydration, Cl^- wasting

*low urine Cl^- indicates kidney is holding onto NaCl (not valid if on diuretic)

Question 18

Chloride-Unresponsive Metabolic Alkalosis

Answer 18

elevated aldosterone

increased H⁺ and K⁺ secretion

increase reabsorption of Na⁺ and HCO₃^-

Question 19

Respiratory acidosis etiology

Answer 19

hypoventilation

COPD

venilator settings

Question 20

Respiratory acidosis

acute compensation

and

chronic compensation

Answer 20

acute:

HCO₃^- rises 1 mEq for each 10 in pCO₂

chronic:

HCO₃^- rises 3 mEq for each 10 in pCO₂

Question 21

Respiratory alkalosis

etiology

Answer 21

hyperventilation

anxiety

aspirin, cocaine, progesterone

tachypnea 2˚ to sepsis, fever, PE, pneumonia, hypoxia

alcohol or narcotic withdrawl

many others

Question 22

Respiratory alkalosis

acute compensation

chronic compensation

Answer 22

acute:

HCO₃^- falls 2 mEq for each 10 in pCO₂

chronic:

HCO₃^- falls 4 mEq for each 10 in pCO₂

Question 23

A patient in respiratory acidosis that does not get supplemental O₂, or is at least closely monitored is…

Answer 23

COPD retainer

Question 24

Why does O₂ create even more respiratory acidosis in COPD retainers?

Answer 24

when hypoxic, they vasoconstrict capillaires to poorly perfused areas where their alveoli are damaged

giving O₂ tricks these alveli into thinking they are better functioning than they actually are

now they get perfusion and better alveoli don’t get perfusion as much

overall, you get less perfusion to well-oxgenatable areas of the lungs