Arterial oxygen saturation during induction of anaesthesia

Abstract

Three groups of 10 ASA 1 patients were studied to determine the incidence of hypoxaemia (oxygen saturation less than or equal to 90%) using pulse oximetry during induction of 'mask' anaesthesia, and whether simple oxygenation techniques could prevent its occurrence. We also surveyed all anaesthetists in three major hospitals to ascertain their techniques for this method of anaesthesia. Anaesthesia was induced in all patients with thiopentone and maintained with nitrous oxide and isoflurane. The first group received 33% oxygen in nitrous oxide as carrier gases, a second group a few normal breaths of 100% oxygen during thiopentone administration followed by 33% oxygen in nitrous oxide, while a third group received 100% oxygen after loss of eyelash reflex until spontaneous breathing was established. No patient received positive pressure ventilation before spontaneous breathing was established. Six of the 10 patients in the first group became hypoxaemic compared to none in the second group, and three patients became hypoxaemic in the third group. Thirty-seven percent of anaesthetists who responded to the survey either did not apply positive pressure ventilation before establishment of spontaneous breathing, or only did so if apnoea was prolonged. Only one anaesthetist fully pre-oxygenated patients lungs. We conclude that to avoid the likely occurrence of hypoxaemia during induction of mask anaesthesia, a minimum of a few breaths pre-oxygenation is necessary.

Preoxygenation with 20º head-up tilt provides longer duration of non-hypoxic apnea than conventional preoxygenation in non-obese healthy adults

“…Preoxygenation, which is the routine administration of 100% oxygen to the conscious individual before induction of general anesthesia, has now become an integral part of the safe conduct of general anesthesia [1,2]. It is now described as a new ''minimum standard of care'' because the benefits incurred by it far outweigh the disadvantages [3].…”

A prospective, randomised controlled trial comparing the efficacy of pre‐oxygenation in the 20° head‐up vs supine position*

“…Pre‐oxygenation, the routine administration of 100% oxygen to the conscious individual before general anaesthesia, has become an integral part of safe conduct at induction of general anaesthesia. Apnoea following administration of an induction agent or neuromuscular blocking drugs can lead to a fall in arterial oxygen saturation ( S p o 2 ) to 80% within 1 min in healthy subjects breathing air before induction [1, 2]. Pre‐oxygenation in adults increases total body oxygen stores from an estimated 1.2 l before oxygenation to 3.2 l at 1 min and 4.8 l at 3 min [3, 4].…”

Präoxygenierung mit NasOral ® -System oder herkömmlicher Gesichtsmaske?

“…So zeigten Thorpe u. Gauntlett, dass ohne Präoxygenierung Hypoxämien bereits nach einer Apnoedauer von 10 s signifikant häufiger auftreten als nach suffizienter Präoxygenierung[26].Sitz der Maske zu achten ist. Undichter Sitz führt zu signifikant schnellerer Desaturierung des Patienten in Apnoe [7].…”