A clinical evaluation of the ‘mini parallel Lack’ breathing system in cats and comparison with a modified Ayre's T‐piece

Abstract

ObjectiveTo evaluate the suitability of a ‘mini parallel Lack’ (MPL) breathing system for use in spontaneously breathing cats and to compare the fresh gas flow requirement with that of a modified Ayre's T‐piece (MATP). AnimalsTwenty client‐owned cats, ASA I and II, presented for elective procedures requiring anaesthesia. Materials and methodsPre‐anaesthetic medication and induction of anaesthesia were carried out using several techniques commonly used in our teaching hospital. Anaesthesia was maintained with halothane or isoflurane vaporized in either oxygen or with a mixture of oxygen and nitrous oxide. Both breathing systems were evaluated in each cat, with the order of use randomized. Initial fresh gas flows were 300 mL kg−1 minute−1 for the MPL and 500 mL kg− 1 minute−1 for the MATP. After a 20‐minute stabilization period, fresh gas flow was reduced by 200 mL minute−1 every 5 minutes until re‐breathing – defined as an increase in the inspired partial pressure of carbon dioxide to 0.3 kPa (2 mm Hg) – was detected. The fresh gas flow was then increased in 100 mL minute−1 increments until re‐breathing was no longer detectable, and this value was recorded as the minimum fresh gas flow requirement for the breathing system in use. The procedure was then repeated for the second breathing system. Minimum fresh gas flow requirements were compared using a paired Students t‐test. Cardiopulmonary variables were compared using anova. Valve opening pressure was measured in the MPL using a manometer. ResultsThe mean (±SD) fresh gas flow that prevented re‐breathing with the MPL (510 ± 170 mL minute−1; equivalent to 142 ± 47 mL kg−1 minute−1) was significantly lower than that required for the MATP (1430 ± 560 mL minute−1; equivalent to 397 ±155 mL kg−1 minute−1). There were no significant differences in cardiopulmonary variables attributable to the use of the two breathing systems. The MPL valve opening pressure was 1.1 cm H2O. ConclusionsThe MPL breathing system used lower gas flows than the MATP without affecting cardiovascular or respiratory function. Clinical relevanceIn spontaneously breathing cats, the MPL offers the advantages of a reduction in cost and atmospheric pollution because less volatile agent is vaporized.