Maxima and Bain Breathing Systems Compared in Controlled Ventilation

The Maxima is a new universal breathing system, which, despite its being valveless, functions with near maximal efficiency in spontaneous and controlled ventilation. It was compared to the Bain system in controlled ventilation by adjusting fresh gas flows (V̇F) to achieve an endtidal CO2 of 5% in 40 patients aged from one to seventy-six years. They received a combined regional and general anaesthetic technique. The overall V̇F requirement of the Maxima system was: weight in kg x 35 ml.min−1 .kg−1 + 1160 ml.min−1; the Bain system required V̇F of: weight in kg x 42 ml.min-1 .kg-1 + 2070 ml.min−1. The mean V̇F requirement for the Bain system was greater by 45%. Of these forty patients, the results from the twenty-four adult patients weighing 50 kg or more gave the respective V̇F requirements for the Maxima and Bain systems of 52 and 71 ml.min−1 .kg−1. In a separate study using twenty-nine patients, the fractional utilization of fresh gas (FU) (or VAe/VF where VAe = effective alveolar ventilation) in the Maxima and Bain systems was shown to be 0.94 and 0.71 respectively.