Inhalational Anesthetic Agents

Halothane, CF3-CHBrCl

halothane

Introduced in 1956, our most cost-effective inhalational agent.

Physical Properties

  • halogenated ethrane
  • vapor pressure = 243 mmHg at 20 deg C
  • spontaneous oxidative decomposition retarded by
    • thymol preservative
    • amber-colored bottle
  • least expensive volatile anesthetic agent

Organ System Effects

Cardiovascular
  • direct myocardial depressant and coronary artery vasodilator
    • interfers with Na-Ca exchange and
    • intracellular Ca utilization
    • depresses cardiac output and lowers arterial BP
    • depresses myocardial O2 demand so that
    • myocardial O2 delivery is adequate
  • depresses SA-node function
    • bradycardia
    • AV nodal rhythm
  • depresses baroreflex
  • enhances myocardial sensitivity to the dysrhythmogenic effects of epinephrine
    • limit epi to < 1.5 mcg/kg
Respiratory
  • fast, shallow breathing, with
  • increased paCO2 (during spontaneous ventilation) that
  • partly reverses cardiovascular depression
  • severe depression of hypoxic ventilatory drive (even at 0.1 MAC)
  • potent bronchodilator (inhibits intracellular Ca mobilization)
  • depresses mucocilliary function
CNS
  • general anesthesia, MAC = 0.75
  • cerebral vasodilator
  • increases CBF
  • blunts cerebrovascular autoregulation
  • hyperventilation prior to halothane may prevent the expected rise in ICP

Biotransformation and Toxicity

  • oxidized in liver by cytochrome P-450 2EI to trifluroacetic acid
  • absent O2, hepatotoxic reduction products may arise
  • halothane hepatitis
    • extremely rare (1:35,000 cases)
    • factors that increase risk:
      • multiple exposures to halothane over a short interval
      • middle-aged, obese women
      • familial predisposition
      • personal history of toxicity
    • centrilobular necrosis
    • antibody that binds to halothane-exposed hepatocytes may be isolated

Contraindications/Precautions

  • malignant hyperthermia susceptibility
  • unexplained liver dysfunction after previous halothane exposure
  • intracranial mass lesion
  • hypovolemia
  • aortic stenosis
  • pheochromocytoma
  • with aminophylline has been associated with severe ventricular dysrhythmias




Send Comments to Greg Gordon MD, gjg@po.cwru.edu
Department of Anesthesiology
The MetroHealth System
2500 MetroHealth Drive
Cleveland, Ohio 44109-1998
Phone: (216) 778-4801
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