The 1959 Frumin study on apneic oxygenation is a classic. It is an elegant demonstration of apnoeic oxygenation. Ie how patients can maintain oxygenation despite total apnea. Elegant, but I’m not so sure the ethical committees that are available to me today would approve of the study protocol.
The theory is that as oxygen is pulled from the lungs into the blood, a oxygen gradient is created between the lungs and upper airway. Oxygen is now constantly forced down this gradient, thus passively oxygenating the patient. During optimal conditions the patient will remain oxygenated indefinitely. The limiting factor is CO2 build-up.
Eight healthy subjects due for minor operations were selected as test subjects. They were given induction with thiopental and Succinylcholin and intubated. Then the subjects breathed 100% oxygen for 30 minutes to achieve complete denitrogenation. Anesthesia was maintained with repeated thiopental boluses. and if any movement was noticed, the patient was given more relaxant.
After denitrogenation the endotracheal tubes remained connected to the circle apparatus filled with 100% oxygen. Then they basically just waited. The patients weren’t ventilated and apnoea was allowed to persist during a set period of time. Arterial blood was regularly sampled and SaO2 was monitored.
Apnea lasting 30-55 minutes was tolerated in all subjects without desaturation. In 6 out of 8 patients the apneic period was terminated after 50 minutes, which was planned prior to the study as the researchers assumed PaCO2 levels by then would be high. In the remaining two the experiment was terminated prematurely after the ECGs showed VES or other ectopic beats.
Under optimal conditions apnoeic oxygenation can ´indefinitely´ (for my purposes) oxygenate a patient. The problem is the ‘optimal conditions’ part. Perfect apnoeic oxygenation requires a hemodynamically stable patient, denitrogenation, an open airway and a FiO2 of 100%. Then there is the CO2 build-up that most sick patients can’t afford.
There are also a few studies showing apneic oxygenation may prolong apnea time without desat in healthy patients with around 2 minutes, using a nasopharyngeal catheter or nasal cannulas with pure O2 at 5 L/min. As far I know there are no studies proving apnoeic oxygenation is effective in the real world of intubating the crashing patient or in anaesthesia gone bad. Still, it probably works to some degree and I am aware of trying to maintain an open airway and keep the oxygen flowing during airway management, even when I am not ventilating the patient.
The study is available for free here.
This post is a translation and a reworking of a post in Scandinavian that was originally posted about a year ago.