Ventilator-assisted priming of an anaesthesia circuit (VAP technique): An exploratory study

BACKGROUND AND AIMS: The speed of inhalational induction depends on a variety of factors, of which priming the breathing circuit with volatile anaesthetics plays a vital role. This study compared ventilator-assisted priming (VAP) and a passive priming technique using different fresh gas flows (FGFs) in neonatal, paediatric, and adult anaesthetic circuits. METHODS: In both techniques, FGF with 100% oxygen and 8% sevoflurane vaporiser concentration were set at 2 Lmin(-1), 4 Lmin(-1), and 8 Lmin(-1), representing 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 addition to this, we explored various combinations of tidal volumes and respiratory rates in the VAP technique and recorded the priming time with each combination. The amount of sevoflurane consumed for priming in both techniques was also calculated. RESULTS: VAP was three times faster than passive priming in all the FGF groups in the three circuits. In the VAP technique, the shortest priming times were similar for FGF-4 and FGF-8 (P > 0.05) but were significantly higher for FGF-2 (P = 0.001) in the three circuits. Sevoflurane consumption did not differ in FGF-2 and FGF-4 groups, whereas it doubled in the FGF-8 group using the VAP technique in all three circuits. CONCLUSION: The VAP technique provides a quick and effective method for priming to achieve a high anaesthetic concentration within the breathing circuit for inhalational induction.