Comparing the priming methods of anesthesia circuits using passive and ventilator-assisted techniques-An exploratory study.

Background and aims: Priming the breathing circuit with a volatile agent plays a major role in inhalational induction. It depends on the fresh gas flow rate (FGF), concentration setting of the volatile agent, and time taken to attain the desired end-tidal concentration. The aim of the study is to compare ventilator-assisted priming (VAP) and a passive priming technique using different fresh gas flows (FGFs) in neonatal, pediatric, and adult anesthetic circuits with sevoflurane vaporizer.

Methodology: An exploratory study was conducted on a single Datex ohmeda GE Inc. workstation using three different circuits. In both techniques, FGF with 100% oxygen and 8% sevoflurane vaporizer concentration was set at 2 L/min, 4 L/min, and 8 L/min corresponding to their three groups FGF-2, FGF-4, and FGF-8, respectively. The time taken to achieve 6% sevoflurane concentration at the patient end of the circuit was measured. In this study, we have explored various combinations of tidal volumes, respiratory rates with three different fresh gas flows, and their priming time with sevoflurane consumption.

Results: The minimum time required to prime neonate, pediatric, and adult circuits using the ventilator-assisted technique to attain end-tidal sevoflurane 6% is 29 seconds, 39 seconds, and 61 seconds with 2 L/min FGF. Their corresponding sevoflurane consumptions are 0.25 ml for the neonate circuit, 0.78 ml for the pediatric circuit, and 2 ml for the adult circuit.

Conclusion: The ventilator-assisted priming technique is an effective and quick method to attain end-tidal sevoflurane 6% with low FGF (2 L/min), low tidal volume (100 ml), maximum respiratory rate (20), and minimal sevoflurane consumption when compared to the passive priming technique.