What common conditions decrease pCO2 and cause respiratory alkalosis?
Some causes --> hyperventilation --> alkalosis
What is the mechanism of respiratory alkalosis?
CO2 deficit --> decreased pCO2 --> increased ratio of base/acid --> increased pH
Causes of hyperventilation:
- hypoxic conditions
- psychological disturbances
- pulmonary embolus
- CNS disorders/lesions - meningitis, CVA
- epinephrine --> stimulates chemoreceptors --> hyperventilation
- salicylate intoxication
- = initially respiratory alkalosis from chemoreceptor stimulation
- = then metabolic acidosis from salicylate accumulation
Causes of metabolic acidosis due to increased H+ ion.
- lactic acidosis (increased plasma volume, increased O2)
- ingestion (ASA, methanol, ethylene glycol)
Causes of metabolic acidosis due to HCO3- loss
- diarrhea (pooping base) - pancreatic, biliary, intestinal fistulas
- renal tubular acidosis (does not generate bicarb)
- = type I - distal, decreased ability to secrete H+ and decreased NH4 excretion
- = type II - proximal, decreased ability to reabsorb HCO3-
Mechanism of metabolic acidosis
HCO3- deficit --> decreased ratio of base/acid --> decreased pH
Mechanism of metabolic alkalosis.
HCO3- excess --> increased ratio of base/acid --> increased pH and usually compensatory hypoventilation --> increased pCO2
Compensation for metabolic acidosis.
increased metabolic acidosis --> increased respirations --> decreased pCO2
Kidneys directed to reclaim all filtered HCO3- plus generate new HCO3- by forming titratable acid and ammonium (NH4)
Compensation for metabolic alkalosis.
- increased pH --> stimulates chemoreceptors --> decreased ventilation --> increased pCO2
- Respiratory compensation:
- - not as effective in metabolic alkalosis as in metabolic acidosis
- - with decreased ventilation, may also decrease pO2
- Renal response:
- - decreased HCO3- reabsorption and H+ ion retention by decreasing Na+/H+ exchange
- - decreases ammonium formation and new HCO3-
Clinical effects of metabolic acidosis.
dilation of arterioles (contribute to increased respiration for pulmonary response of hyperventilation) --> vascular collapse, systemic venous constriction, decreased cardiac output --> pulmonary congestion and edema
Clinical effects of metabolic alkalosis
- if pH = 7.5 or greater may have:
- - tetany with cramping
- - convulsions
- - neuromuscular irritability
- - confusion
- - stupor
- - coma