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Acid-Base Imbalances Overview

Jul 2, 2025

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Overview

This lecture reviews acid-base imbalances, focusing on their key lab values, causes, and basic treatments, emphasizing respiratory and metabolic disorders.

Normal Acid-Base Lab Values

  • Normal pH: 7.35–7.45; <7.35 is acidosis, >7.45 is alkalosis.
  • Normal PaCO₂ (carbon dioxide): 35–45 mmHg; higher is acidic, lower is basic.
  • Normal HCO₃⁻ (bicarbonate): 21–28 mEq/L; less than 21 is acidic, more than 28 is alkalotic.

Respiratory Acid-Base Imbalances

  • Respiratory alkalosis: pH > 7.45, PaCO₂ < 35 mmHg; caused by hyperventilation (e.g., anxiety, pain, neurologic injury).
  • Respiratory alkalosis treatment: calm the patient, have them breathe into cupped hands or a paper bag.
  • Respiratory acidosis: pH < 7.35, PaCO₂ > 45 mmHg; caused by retaining CO₂ (e.g., COPD, oversedation, opioid overdose, ventilator missettings).
  • Respiratory acidosis treatment: stimulate breathing, adjust ventilator, give antidotes (naloxone for opioids, flumazenil for benzodiazepines).
  • COPD patients often have chronic respiratory acidosis due to persistent air trapping.

Metabolic Acid-Base Imbalances

  • Metabolic alkalosis: pH > 7.45, HCO₃⁻ > 28 mEq/L; commonly from antacid overdose, vomiting, or excessive GI suctioning.
  • Metabolic acidosis: pH < 7.35, HCO₃⁻ < 21 mEq/L; caused by diabetic ketoacidosis (DKA), kidney failure, or excessive diarrhea.
  • Treatment for metabolic imbalances depends on the cause: stop antacids, give antiemetics for vomiting, insulin for DKA.

Key Terms & Definitions

  • pH — a measure of blood acidity or alkalinity.
  • PaCO₂ — partial pressure of carbon dioxide in arterial blood, reflects respiratory function.
  • HCO₃⁻ — bicarbonate, a metabolic buffer produced and regulated by the kidneys.
  • Respiratory Alkalosis — high pH, low CO₂ due to hyperventilation.
  • Respiratory Acidosis — low pH, high CO₂ from hypoventilation or air trapping.
  • Metabolic Alkalosis — high pH, high bicarbonate from acid loss or excess base.
  • Metabolic Acidosis — low pH, low bicarbonate from base loss or acid excess.

Action Items / Next Steps

  • Review and memorize normal pH, PaCO₂, and HCO₃⁻ values.
  • Practice interpreting acid-base imbalances based on lab results.
  • Prepare for next lecture on macronutrients, micronutrients, and BMI.

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