Respiratory mechanics during nitrous oxide and xenon anesthesia with and without metacholine-induced bronchoconstriction
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KeywordsNitrous Oxide Respiratory Mechanic Peak Airway Pressure Differential Pressure Transducer Airway Occlusion
The use of xenon (Xe) as inhalative anesthetic agent might impair respiratory mechanics because of the relatively high density of this gas (5.897 g/l) when compared to nitrogen (N2, 1.250 g/l) or nitrous oxide (N2O, 1.964 g/l). The aim of this study was to compare inspiratory airway resistance (Raw) as well as mean and peak airway pressure (Paw) in pigs under normal conditions and with metacholine-induced bronchoconstriction during Xe versus N2O anesthesia.
Two groups of anesthetized and paralysed pigs (N2O n = 5, Xe n = 6) were ventilated with constant inspiratory flow provided by a semi-closed anesthesia circuit (CICERO, Drägerwerk AG, Germany) with a fresh gas supply correspondoing to half-minute ventilation. Ventilator settings were: tidal volume (VT) = 12 ml/kg, respirtory rate (f) = 12/min, duration of inspiration (TI) = 1.5 s, inspiratory breath hold (iBH) = 1 s and PEEP = 0 cmH2O. Paw was measured through a port proximal to the endotracheal tube with a differential pressure transducer (140PC, Honeywell Inc., Plymouth, MN) and airflow (V) by a heated pneumotachograph (Fleisch No. 2, Fleisch, Switzerland) connected with a differential pressure transducer. Animals were ventilated for three sequential periods of 45 min with a (control) mixture of 70% N2 and 30% O2 (period 1 and 3) and a testgas mixture of 70% Xe or N2O and 30% O2 (period 2). At the end of each period we performed three series of end-inspiratory airway occlusions in order to calculate Raw and determined peak Paw as well as mean Paw (for a period of 2 min). For the second part of the study we induced a bronchoconstriction by a continuous metacholine infusion (16-32 μg/kg per min) during ventilation with the control gas mixture and repeated the same study protocol once again.
In contrast to the marked increase in Raw, changes in Paw during Xe anesthesia were less impressive but should be individually considered whenever using this gas as inhalative anesthetic agent.
We thank Drägerwerk AG for kindly providing the CICERO EM.