Question

explain the pathology of respiratory acidoisis, respiratory alkalosis,metabolic acidosis and metabolic alkalosis. what are the medical management in each conditions?

Answer 1

Ans) Acid- Base disorders are a group of conditions characterized by changes in the concentration of hydrogen ions (H+) or bicarbonate(HCO3-), which lead to changes in the arterial blood pH. These conditions can be categorized as acidoses or alkaloses and have a respiratory or metabolic origin, depending on the cause of the imbalance. Diagnosis is made by arterial blood gas (ABG) interpretation. In the setting of metabolic acidosis, calculation of the anion gap is an important resource to narrow down the possible causes and reach a precise diagnosis. Treatment is based on identifying the underlying cause.

Pathophysiology:

Respiratory acidosis	Respiratory alkalosis	Metabolic acidosis		Metabolic alkalosis
Mechanism	Alveolar hypoventilation→ CO2 retention	↑ In respiratory rate and/or tidal volume→ alveolar hyperventilation→ CO2 washout	↑ Production/ingestionof H+ or loss of HCO3-		Loss of H+ or ↑ production/ingestionof HCO3-
Common causes	Airway obstruction: COPDexacerbation, bronchial asthma Respiratory muscle weakness CNS depression Head trauma Post-ictal state Drug toxicity(opiates, barbiturates, and benzodiazepines)	Pain, anxiety, panic attacks Pregnancy High altitude Drug toxicity (theophylline, progesterone, salicylate toxicity) Hyperventilation while on mechanical ventilation	High anion gap metabolic acidosis Lactic acidosis: severe tissue hypoxia, liver failure, metformin use Ketoacidosis: diabetes mellitus, starvation, alcoholism Renal insufficiency, uremia Accumulation ofexogenous organic acids (methanol, ethylene glycol, toluene, salicylate toxicity) Normal anion gap metabolic acidosis Renal tubular acidosis GI loss of HCO3-(e.g., diarrhea, GI fistulas, intestinal stomas)		Chloride-responsive(urinary chloridenormal [< 25 mmol/L]) Vomiting ornasogastric suction Hypovolemia(contraction alkalosis) Loop or thiazide diuretics Chloride-resistant(urinary chlorideelevated [> 40 mmol/L]) Hyperaldosteronism Cushing syndrome Bartter syndrome Gitelman syndrome Liddle syndrome
pH*	↓	↑	↓		↑
PCO2	↑	↓	↓ (compensation)		↑ (compensation)
HCO3-	↑ (compensation)	↓ (compensation)	↓		↑
*pH values may be within the reference range in the case of complete compensation. However, it still is referred to as compensated alkalosis or acidosis.

Treatment of acid-base disorders should always address the underlying cause. Some steps in urgent management are listed below.

• Respiratory acidosis: treat underlying cause (see “Treatment” of COPD, opioid intoxication, benzodiazepine overdose)
• Respiratory alkalosis: treat underlying cause; in the event of hyperventilation syndrome, patients benefit from reassurance and rebreathing into a paper bag.

• Metabolic acidosis
  • Acute severe metabolic acidosis (pH < 7.1): intravenous sodium bicarbonate
  • Chronic metabolic acidosis: oral sodium bicarbonate along with treatment of the underlying cause (e.g., diarrhea, renal tubular acidosis)
  • Electrolyte disturbances: correct (e.g., hyperkalemia; see “Treatment” of potassium disorders)
  • See individual learning cards for the management of diabetic ketoacidosis, salicylate toxicity.
• Metabolic alkalosis
  • Volume depletion: isotonic saline to increase urinary bicarbonate excretion and correct extracellular volume loss
  • Bicarbonate excess: acetazolamide
  • Electrolyte disturbances: correct (e.g., see “Treatment” of potassium disorders)