Respiratory mechanics during nitrous oxide and xenon anesthesia with and without metacholine-induced bronchoconstriction

Introduction

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 (R_aw) as well as mean and peak airway pressure (P_aw) in pigs under normal conditions and with metacholine-induced bronchoconstriction during Xe versus N₂O anesthesia.

Methods

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. P_aw 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 R_aw and determined peak P_aw as well as mean P_aw (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.

Results

X = P < 0.05. Friedman ranks signed ANOVA, followed, when significant, by the Student-Newman-Keuls method.

Results

X =P < 0.05. Friedman ranks signed ANOVA, followed, when significant, by the Student-Newman-Keuls method.

Conclusions

In contrast to the marked increase in R_aw, changes in P_aw during Xe anesthesia were less impressive but should be individually considered whenever using this gas as inhalative anesthetic agent.