Oxygen therapy can be normobaric or hyyperbaric. During oxygen therapy, ventilation and airway maintenance should be adequate so that oxygen reaches the lung for gas exchange. Reserve of oxygen in the body is 1.5 litres, which lasts for about 6 minutes in circulatory arrest assuming a consumption of 250 ml/min. Hb contains 800 ml and alveoli contains about 400 ml of oxygen. Pre-oxygenation prior to induction of anaesthesia leads to denitration and increase in the alveolar oxygen content, enabling tolerance of longer period of apnea.
Circulatory gradient of oxygen: Oxygen …

Oxygen pressure guage attached to a Boyle’s machine for general anaesthesia.

Nitrous oxide pressure guage attached to a Boyle’s machine for general anaesthesia.

Isoflurane delivery device attached to a Boyle’s machine used for general anaesthesia using inhalational agents.

Halothane delivery device used for delivering metered dose of halothane for general anaesthesia. The device can be attached on the Boyle’s machine and halothane vapour delivered along with oxygen through the endotracheal tube. Halothane is an inhalational anaesthetic agent like nitrous oxide and isoflurane.

Boyle’s machine used for delivering oxygen and anaesthetic gases for general anaesthesia. Flow meters for nitrous oxide and oxygen as well as delivery device for isoflurane are seen attached to the top bar. Pressure guages for nitrous oxide with blue screens are seen on the left side and those for oxygen with white screens are seen on the right side.

Nitrous oxide and oxygen flow meters as part of a Boyle’s apparatus used for anaesthesia. The position of the float in the graduated tubing goes up as the flow increases.