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health advisory Hospital Doctor Yu 2007-11-8 19:08:10

Answers:

Oxygen is needed by the body all the time, during anesthesia you have been breathing slowly. You need more oxygen to help tissues heal and to help get the anesthesia out.

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The causes of increased venous admixture (ventilation/perfusion mismatch, shunt and airway closure) and the abnormal response to hypoxia continue into the postoperative period for a number of days following major surgery. Postoperative hypoventilation is common and may be due to the residual effect of anaesthesia, the use of opioid analgesia, pain or airway obstruction. Shivering in the immediate postoperative period causes an increase in oxygen consumption. Additional oxygen should therefore be given to all unconscious patients in recovery and to those awake patients who either shiver, hypoventilate, desaturate or who are considered to be at special risk (eg. ishaemic heart disease).

Postoperatively, on the ward, episodes of airway obstruction during sleep are common and may aggravate borderline oxygenation due to the above factors. This is due to the use of opioid analgesia and a change in sleep pattern that occurs on the second and third postoperative nights. It is clear that after major surgery the risk of hypoxaemia extends well into the postoperative period. Small degrees of cyanosis are not easy to detect clinically, especially in anaemic patients, and therefore oxygen should be given to these patients wherever possible. It is especially important to give it overnight to patients at special risk (ischaemic heart disease). Postoperative pain should be effectively treated (see Update 7) as patients in pain following abdominal or thoracic surgery will be reluctant to breathe deeply. If opioid analgesics are indicated, hypoventilation should be anticipated, and oxygen given

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Because we all need a certain minimum amount of oxygen to be delivered to our blood every minute.