Effects of 20% nitrous oxide on the ventilatory response to hypercapnia and sustained isocapnic hypoxia in man

Abstract

To examine the effects of a sub-anaesthetic concentration of nitrous oxide on ventilation, we have studied the ventilatory response to carbon dioxide and isocapnic hypoxia (FIN2O 0.2). In five subjects, we performed step decreases in PE'O2 to 6.7 kPa for 15 min and step increases in PE'CO2 (delta PE'CO2 1.5 kPa). The carbon dioxide responses were partitioned into a fast peripheral and slow central component. All control oxygen responses were biphasic: the acute hypoxic response was 7.2 (4.6) litre min-1 and the subsequent decline 4.2 (2.6) litre min-1. With nitrous oxide, the acute hypoxic response was 10.3 (6.7) litre min-1, but was followed by a nonsignificant decline of 3.8 (3.0) litre min-1 because of a progressive increase in breathing frequency in the hypoxic period. None of the variables obtained from the carbon dioxide responses differed between groups. Our data indicate that a sub-anaesthetic concentration of nitrous oxide did not affect the peripheral chemoreflex loop. The hyperventilatory response to prolonged hypoxia was sustained better with nitrous oxide compared with control.

Effects of N2O narcosis on breathing and effort sensations during exercise and inspiratory resistive loading

“…This supports the findings of other investigators (39,42) who have found that the load-compensating respiratory reflexes important in maintaining ventilation during inspiratory resistive loading are not impaired by breathing mixtures containing up to 50% N 2 O. Moreover, in a recent study (13) in which the effects of 20% N 2 O on the ventilatory responses to hypercapnia were studied in five subjects, it was concluded that this subanesthetic concentration of N 2 O did not affect the peripheral chemoreflex loop.…”

The variable effect of low‐dose volatile anaesthetics on the acute ventilatory response to hypoxia in humans: a quantitative review

“…In one article, the anaesthetic dose was uncontrolled [28], whereas in another, the anaesthetic (nitrous oxide) dose was 0.4 MAC [29]. The single articles referring to methoxyflurane [30], ether [30], desflurane [31] and nitrous oxide [32] were not included in the analysis. Finally, one article was excluded as it provided no data for a control group (i.e.…”

Effect of low dose inhaled anaesthetic agents on the ventilatory response to carbon dioxide in humans: a quantitative review

“…3). This analysis could be criticised for including the results of methoxyflurane and ether studies (neither of which are now in use) [10], and also for including two studies using N 2 O (which some might argue is not a true 'anaesthetic') [10,11]. However, excluding this data does not change the conclusions of the analysis.…”

“…One of the suggested reasons for the difference in results was that Knill et al [1,2] had used Read's rebreathing method to induce hypercapnia (the end-tidal PCO 2 rises progressively over several minutes as air, or oxygenenriched air, is rebreathed from a large bag), whereas Dahan et al [3] used step hypercapnia (end-tidal PCO 2 rises rapidly to the desired level within seconds). Subsequent studies have explored these observations [4][5][6][7][8][9][10][11][12][13][14]. The original studies of Knill et al [1,2,5,10] found that some agents (N 2 O, enflurane and isoflurane) did indeed depress the ventilation-CO 2 response, but other agents (ether and methoxyflurane), like halothane, had no effect.…”