Acid base disorders

Question 1

Effects of metabolic acidosis

Answer 1

• O2 curve shifts to right = increased O2 delivery to tissues
• CNS depression
• arrhythmias
• decreased cardiac contractility
• hyperkalemia –> due to intracellular buffering
• decreased pulmonary blood flow

Question 2

Causes of metabolic acidosis

Answer 2

1. H gain
   - -> Increased H production = multiple causes
   - -> Decreased H secretion = Chronic kidney disease, RTA
2. HCO3 loss
   - -> diarrhea
   - -> RTA

Differential dx for metabolic diagnosis should ALWAYS start by calculating the anion gap!

Question 3

Causes of high anion gap metabolic acidsosis

Answer 3

MUDPILES

• Methanol (diethylene glycol)
• Uremia –> build up of sulfates
• Diabetic ketoacidosis
• Propylene glycol
• Ingestions/INH/Infections
• Lactic acidosis
• Ethylene glycol
• Salicylates (late)

Question 4

Causes of non-anion gap metabolic acidosis

Answer 4

Primarily renal and GI causes

• Renal = RTA –> urine pH is NOT maximally acidic except for late proximal RTA
• GI = diarrhea

HEARTCCU

• Hyperalimentation
• Expansion
• Acetazolimide
• RTA
• Turds –> diarrhea
• Cholestyramine
• Carbonic anhydrase increase
• Uterersigmoidostomy

Question 5

Effects of metabolic alkalosis

Answer 5

• O2 curve shifts to the left –> decreased O2 delivery to tissues
• decreased cerebral blood flow
• tetany
• seizures
• arrhythmias

Question 6

Causes of metabolic alkalosis

Answer 6

Gain of HCO3

• citrate –> repeated blood transfusions
• bicarbonate

Loss of H+

• renal –> diuretics
• non-renal
• -> GI = vomiting, NG tube suctioning, HCO3 infestion
• -> hypokalemia –> H+ transcellular shift

Contraction alkalosis
- diuretics –> cause loss of Na, K and Cl and water, but not HCO3 = decreased ECF but same concentration of HCO3- = increased HCO3 concentration

Question 7

Transient metabolic alkalosis

Answer 7

Metabolic alkalosis resolves after the increased HCO3 load has stopped –> extra HCO3 load lost by the kidney is not reclaimed

Causes

• NaHCO3 loading to prevent tumor lysis syndrome
• Upon correction of acute hypercapnia (hypoventilation) without Cl depletion
• Recovery from organic anion metabolic acidosis

Question 8

Maintained metabolic alkalosis

Answer 8

Persists after the increased HCO3- load has stopped

• extra HCO3 load is retained by the kidney and H secretion is increased
• occurs because K or Cl depletion occurs simultaneously with HCO3 loading = stimulus that maintains the continued secretion of H in the face of metabolic alkalosis
• K/Cl depletion must be corrected to rectify the metabolic alkalosis

Question 9

Causes of maintained metabolic alkalosis

Answer 9

Cl/volume depletion

• vomiting, NG tube suctioning (also mild K loss)
• diuretics –> prevent reabsorption of Na,Cl and K, cause volume depletion (mild K loss)
• post hypercapneic alkalosis –> chronic resp acidosis causes a compensatory metabolic alkalosis = increased H + Cl loss by the kidney –> causes Cl depletion –> following correction of the resp acidosis, metabolic alk is maintained by by Cl- depletion

K depletion

• hypokalemia –> transcellular shift = H excretion
• diuretics –> hypokalemia –> transcellular shift
• mineralocorticoid excess –> increased H/K secretion by the kidneys
• -> primary/secondary hyperaldo
• -> apparent mineralocorticoid excess syndrome (licorice)
• renal failure

Cl and K depletion –> Liddles, Barters and Gittlemans

Decreased GFR –> effective volume depletion

Question 10

Causes of respiratory acidosis

Answer 10

• CNS depressants
• resp muscle dysfunction
• airway obstruction
• poor gas exchange

Question 11

Causes of respiratory alkalosis

Answer 11

• hypoxemia
• lung disease
• sepsis
• salicylates (early)
• CNS stimulants