Intended for healthcare professionals

Student Education

Anaesthesia explained

BMJ 2001; 322 doi: (Published 01 April 2001) Cite this as: BMJ 2001;322:010494
  1. Nina Ruth Lewis, Surgical house officer1,
  2. Jo Fitz-Henry, consultant anaesthetist1
  1. 1King's Mill Hospital, Mansfield

Hypoxia kills.

As the house officer, you must prevent your patients from turning blue. Having to manage the patient with acute hypoxia causes anxiety among many doctors. We hope that this article will dispel common misconceptions that you may have about hypoxia and its treatment and give you the confidence to carefully prescribe oxygen (yes it's a drug) for those in need.

Box 1: Some definitions

  • Hypoxia: low level of oxygen in the air, blood or tissues.

  • Hypoxaemia: low level of oxygen in the blood.

  • Cyanosis: descriptive term for the blue discolouration of the skin and mucous membranes that accompanies hypoxaemia, usually evident when the oxygen free haemoglobin (deoxyhaemoglobin) exceeds 5g per litre of blood.

  • Partial pressure: directly proportional to the number of molecules of gas in a given environment. The higher the partial pressure of oxygen, the greater the driving pressure from air to lungs to haemoglobin and ultimately to the cell. Often abbreviated to PO2 (pressure of oxygen) with other letters inserted to show at what position the pressure is being measured—for example, PaO2 means the pressure of arterial oxygen

Oxygen–one of life's little necessities

All metabolising cells in carbon based life forms need oxygen to metabolise energy rich substrates to maintain cellular integrity and function. Without it, the cell turns from aerobic to the vastly inefficient anaerobic metabolism. Only one eighth of the energy is produced at the expense of producing a lot of lactic acid. Cells do notfunction well in an acidic environment and tend to die. Our dependence on oxygen has its own inherent problems. Firstly, most of our cells are far away from a reliable source (the air). It is also fairly insoluble in water. To help overcome these problems, we have a transport network (the cardiovascular system) for getting the oxygen from the air to the cells via the lungs. Unfortunately, the liquid that …

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