Nitrous Oxide Elimination Research Articles

Effects of N2 O elimination on the elimination of second gases in a two-step mathematical model of heterogeneous gas exchange.

We have investigated the elimination of inert gases in the lung during the elimination of nitrous oxide (N2 O) using a two-step mathematical model that allows the contribution from net gas volume expansion, which occurs in Step 2, to be separated from other factors. When a second inert gas is used in addition to N2 O, the effect on that gas appears as an extra volume of the gas eliminated in association with the dilution produced by N2 O washout in Step 2. We first considered the effect of elimination in a single gas-exchanging unit under steady-state conditions and then extended our analysis to a lung having a log-normal distribution of ventilation and perfusion. A further increase in inert gas elimination was demonstrated with gases of low solubility in the presence of the increased ventilation-perfusion mismatch that is known to occur during anesthesia. These effects are transient because N2 O elimination depletes the input of that gas from mixed venous blood to the lung, thereby rapidly reducing the magnitude of the diluting action.

Diffusion Hypoxia

ABSTRACTThe aim of this study was to see if we could improve our practice in theatres for the benefit of the patient thus preventing diffusion hypoxia. When a patient continues to breathe from an anaesthetic circuit at the end of anaesthesia, there is a risk of delayed recovery, both by rebreathing and by the presence of anaesthetic vapour emerging from the tubes and other components of the anaesthetic equipment. It has been recommended that nitrous oxide be discontinued early in the recovery period, to monitor the patient during the first elimination phase. As hyperventilation does not influence the elimination of nitrous oxide largely, but increases the risk of subsequent hypoventilation during transport to the recovery room, hyperventilation should be avoided. It is also recommended that oxygen therapy should be used, during transport from theatre to the recovery room, regardless of the duration of nitrous oxide anaesthesia. There has proven to be a risk of Diffusion Hypoxia for at least 30 minutes after discontinuation of nitrous oxide administration in the presence of hypoventilation. The practitioner should always be cautious with heavy smokers, as they present a much greater risk of respiratory problems, and careful observation is needed for the first 5 minutes of breathing room air. Diffusion Hypoxia has proven to be avoided by administration of oxygen for 10 minutes from cessation of nitrous oxide anaesthesia.

Nitrous oxide elimination by the newborn.

The elimination of nitrous oxide by ten infants whose mothers had received 50% nitrous oxide in oxygen and enflurane 0.6-1% during general anaesthesia for Caesarean section was studied. The concentration of nitrous oxide detected in end-expired gas ranged from 1 to 4 vol% (mean 1.9 vol%). These levels are too low to produce significant diffusion hypoxia in vigorous neonates. However, a minority of infants may be adversely affected and it is recommended that oxygen-enriched air be administered to infants whose mothers have received nitrous oxide.

EXPERIMENTS DEMONSTRATING THE UPTAKE, DISTRIBUTION AND ELIMINATION OF NITROUS OXIDE IN THE CONTEXT OF OUT-PATIENT ANAESTHESIA : PART I: REBREATHING EXPERIMENTS

SUMMARY A series of experiments is described which was designed to illustrate the fundamentals of the uptake, distribution and elimination of nitrous oxide in the context of out-patient anaesthesia. The experiments are grouped under three main headings: (1) Rebreathing experiments (Part I); (2) Non-rebreathing experiments (Part II); and (3) Experiments using the jerkin plethysmograph (Part II). More emphasis is placed upon the practical demonstration of the essential features of the subject than upon precision in measurement, but a comparison with a previous study of the uptake of nitrous oxide using pneumotachography is made (see Part II). The experiments indicate the influence of inspired gas mixture, pulmonary ventilation and cardiac output, upon the alveolar tension and the uptake of nitrous oxide: but they hint that there is more to the induction of anaesthesia than the uptake of anaesthetic and the rise in its arterial tension, and the contributions of cerebral perfusion and narcotic threshold are mentioned. They indicate a potential hazard of respiratory obstruction. They also demonstrate how redistribution of nitrous oxide may speed immediate recovery, yet delay elimination; and how elimination is also dependent upon total uptake.