Closed-circuit halothane and enflurane using an in-circle Goldman vaporizer

Area of Science:

• Anesthesiology
• Respiratory Physiology
• Medical Engineering

Background:

• Accurate delivery of volatile anesthetics is crucial for patient safety.
• Understanding anesthetic gas dynamics in closed-circuit systems is essential for optimizing delivery and minimizing waste.
• Previous studies have not fully elucidated the performance of specific vaporizer systems under varying respiratory conditions.

Purpose of the Study:

• To quantify inspired and end-tidal concentrations of halothane and enflurane delivered via a closed-circle absorber system with an in-circle Goldman vaporizer.
• To assess the impact of spontaneous respiration versus intermittent positive-pressure ventilation (IPPV) on anesthetic gas concentrations.
• To evaluate nitrogen accumulation in the breathing circuit during minimal pre-oxygenation.

Main Methods:

• Utilized a closed-circle absorber system with an in-circle Goldman vaporizer for anesthetic administration.
• Administered halothane and enflurane in oxygen to adult patients.
• Measured inspired and end-tidal concentrations using mass spectrometry after stabilization at each vaporizer setting.
• Compared gas concentrations during spontaneous respiration and IPPV (maintained at 5% end-tidal carbon dioxide).
• Assessed nitrogen accumulation with minimal pre-oxygenation.

Main Results:

• Halothane inspired concentrations ranged from 0.5-0.9% (setting 1), 1.4-2.4% (setting 1.5), and 3.3-4.5% (setting 2).
• Enflurane inspired concentrations ranged from 0.8-1.4% (setting 1), 1.9-2.8% (setting 1.5), and 3.7-5.0% (setting 2).
• IPPV led to slight increases in inspired concentrations but significant increases in end-tidal concentrations.
• Maximum nitrogen concentration reached 56% in the circuit.

Conclusions:

• The Goldman vaporizer system demonstrates variable delivery of halothane and enflurane, influenced by vaporizer settings and respiratory patterns.
• Intermittent positive-pressure ventilation significantly impacts end-tidal anesthetic concentrations compared to spontaneous respiration.
• Nitrogen accumulation can be substantial in closed-circuit systems with minimal pre-oxygenation, necessitating careful monitoring.