Oxygen - Benefit and Risks

The following article contains the lectures of an equally named symposium, held at Hanover Medical School on September 1^st 2001. The meeting was held in tradition of 200 discussion meetings of local anaesthesists and marked the 100^th platform “anaesthesiology, intensive care medicine, emergency medicine, pain therapy”. The aim was to examine more closely the most common and apparently well known molecule in anaesthesiology from various sites.

As well as the anaesthetists are aware of oxygen as an indispensable part of life, as less the specific physical and chemical risks are known. E. Schwanbom from Luebeck technical college has therefore named his report „Oxygen - a vital hazard”. In his lecture he specifies the most important technical and historical data. He lists the importance of oxygen for the biosphere and human life and its toxic effects. Further he emphasizes the technical dangers when using oxygen and explains the application of safety precautions to minimize the risks.

R. Zander, department of physiology and pathophysiology, Johannes-Gutenberg-university, Mainz, illustrates in his report “The pulmonary oxygen-store - physiology and clinical benefit” the physiological background of important measures as preoxygenation and apnoeic oxygenation. He adds the differences when dealing with pregnant women and prematures. Moreover he explains the use and limits of the pulsoximetric monitoring. In an adult one can tolerate an apnoea for about ten minutes after accurate preoxygenation without risking relevant hypoxaemia.

K. Jaeger and B. Juettner, department of anaesthesiology, Hanover Medical School, and W. Fanko, hyperbaric medical center Hanover, illustrate in their report “Hyperbaric oxygen therapy - possibilities and limits” the hyperbaric oxygenation (HBO) to increase the amount of physically soluted oxygen in the tissues. Evidence based indications are decompression illness, arterial gaseous emboli, carbon-monoxide intoxication and muscle necrosis in Clostridia infection. The risks and side-effects are barotrauma of the lungs and possible toxic effects of the oxygen on the central nervous system.

The “risks of oxygen in laser surgery” are presented by H. Gehring, department of anaesthesiology, university hospital Luebeck. The punctual high amount of energy of the laser can lead to burnings or explosion. This is a relevant hazard with FiO₂ > 0,3, which can achieved by nasal application of oxygen during spontaneous breathing. Ignition of tissues, hair or material is possible. During laser surgery in the upper airways non inflammable airway tubes are used and the FiO₂ should be 0,3 or less. Nitrous oxide (N₂O) can replace oxygen as an oxidant and therefore should be avoided. While performing intra-abdominal or intra-vesical laser surgery explosive gaseous compounds of hydrogen or methane can develop by diffusion of nitrous oxide.

Another common problem is examined by W. Karzai, department of anaesthesiology and intensive care medicine, Central Hospital Bad Berka, and U. Klein, department of anaesthesiology and intensive care medicine, Suedharz Hospital Nordhausen, in their report “Avoidance of hypoxaemia during one-lung-ventilation”. While switching from two-lungs-ventilation to one-lung-ventilation during thoracic surgery a decrease in arterial oxygen pressure and hypoxaemia can be observed. Possible reasons are pre-existent disorders in gas exchange or unequal ventilation-perfusion-relations of the lungs with reduced hypoxic pulmonary vessel constriction, the patient’s position and special difficulties in separating the airways, while the mode of anaesthesia has no effect on the oxygenation. As prophylactics and therapy of hypoxaemia sufficient airway separation, optimized ventilation, apnoeic oxygenation of the non ventilated lung and increasing FiO₂ are used.

E.-P. Horn, department of anaesthesiology, university hospital Hamburg-Eppendorf presents in his report “Halving of post surgery wound infections after colon surgery by increasing inspiratory oxygen fraction from 30 to 80 % during and after surgery” a formerly less regarded aspect. The increase of the inspiratory oxygen fraction from 30 to 80 % during surgery and the first two hours after colon surgery decreases significantly the rate of wound infections. A possible risk in increasing FiO2 is the occurrence of atelectases which was not observed in the presented study.

Benefit and risk of oxygen is an important topic for the daily routine. Basic sciences can be as helpful as clinical studies and the clinical routine. The following article will help answering some essential questions.

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