S3C19 - Acid-base disorders

Question 1

Metabolic Alkalosis - classification

Answer 1

• either chloride sensitive or insensitive

- results from either gain of bicarb or loss of acid

Question 2

Chloride-sensitive metabolic alkalosis - pathophys

Answer 2

• conditions that cause Cl- loss tend to decrease ECV, which increases mineralocorticoid activity enhancing Na+ reabsorption and K+ and H+ secretion in the distal tubule leading to increased bicarb generation
• increase in serum bicarb, resulting in a hypokalemic, hypochloremic alkalosis to responds to normal saline

Question 3

Chloride-Insensitive metabolic alkalosis - pathophys

Answer 3

• these disease states cause excess mineralocorticoid activity in the face of normovolemia or hypovolemia the urine chloride is normal or elevated
• usually associated with HTN
• can not be reversed with normal saline
• causes: Bartter and Gitelman syndrome
• compensation: PCO2 should rise by 0.7mmHg for every milliequivalent increase in HCO3- (PCO2 will rarely rise >55)

Question 4

Alkalosis - sequelae

Answer 4

• tetany
• neuromuscular instability
• seizures
• shifts O2 dissociation curve to the left making O2 less available to tissues

Question 5

Alkalosis - treatment

Answer 5

• if severe then consider hydrochloric acid IV (0.1 normal solution (100mmol/L) infused at 0.1mmol/kg/h through a central line)
• Dose = (delta [HCO3-])(wt in kg)(0.5)

Question 6

Metabolic Alkalosis - chloride insensitive causes

Answer 6

• renal artery stenosis
• renin-secreting tumors
• adrenal hyperplasia
• hyperaldosteronism
• cushing syndrome
• liddle syndrome
• exogenous mineralocorticoids - licorice, fludrocortisone

Question 7

Respiratory Acidosis - pathophys and causes

Answer 7

• alveolar hypoventilation
• dx: rise in PCO2
• inadequate ventilation from: head trauma, chest trauma, lung disease, excess sedation
• each 1mmHg increase in PC)2 should produce a 0.01 decrease in pH
• if pH is lower or higher than expected when compared to the PCO2 then a mixed disorder is present

Question 8

Ratios for acute/chronic/mixed Resp Acidosis

Answer 8

=delta [H+]/delta PCO2

> 0.8 then metabolic acidosis also present
=0.8 then acute respiratory acidosis
0.3-0.8 mixed
=0.3 chronic respiratory acidosis

Question 9

Respiratory Acidosis - treatment

Answer 9

• improve ventilation
• COPD - bronchodilators, anticholinergics, O2
• if pH

Question 10

Respiratory Alkalosis - pathophys

Answer 10

• hyperventilation
• findings: higher PCO2 than expected
• causes: dz that stimulate respiratory centers
• eg. tumor, stroke, infxn, pregnancy, hypoxia, toxins, anxiety, pain, overventilation
• acute decrease in PCO2 causes decrease in H+ resulting in an increase in negative ions which then bind calcium leading to tetany and paresthesias
• chronic resp alk seen at altitudes due to decreased PO2, tx = acetazolamide or descent