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.

Induction of anaesthesia with halothane and isoflurane in the rabbit: a comparison of the use of a face-mask or an anaesthetic chamber

The effects of induction of anaesthesia with halothane or isoflurane were studied in rabbits. The anaesthetic agents were delivered either via a face-mask, or the animals were placed in an anaesthetic induction chamber. All rabbits had periods of apnoea during induction, lasting 30-120s, resulting in moderate hypercapnia and acidosis. Periods of apnoea were associated with a marked bradycardia. The combination of bradycardia and hypercapnia during induction may represent an increased risk of anaesthetic associated mortality. Animals in all groups tried to avoid inhaling anaesthetic vapour, and this behaviour, together with the occurrence of breath-holding suggests that induction was aversive.

A modified anaesthetic induction chamber for rats

The anaesthetic induction chamber for rats described in this paper has been designed for use in conjunction with a controlled delivery of halothane/O2 mixture and an anaesthetic scavenger system. Using this system rapid induction of anaesthesia is achieved using low levels of anaesthetic vapour without risk to the operator.

A modified anaesthetic vapour extraction system

A number of design modifications have been made to an extraction system for use with inhalation anaesthesia techniques in rats and other small laboratory animals. These changes necessitated a re-evaluation of the effectiveness of this equipment in limiting the operator's exposure to the anaesthetic vapours used. With a given fresh gas flow. the halothane vapour concentration in the operator's breathing zone was dependent on the design of the oronasal mask. With the optimum configuration the atmospheric concentration of halothane was less than 1 ppm.