Discuss the physiological causes of early post operative hypoxaemia.
For a good mark it was expected that candidates define hypoxaemia and, in a structured manner,
discuss the physiological causes of early postoperative hypoxaemia. Candidates should always try
and begin their answer with a definition of the term that is to be discussed. Many candidates
invoked clinical disease related causes and not physiological. This did not score marks. Similarly,
factors leading to tissue hypoxia, such as anaemia or low 2,3-dpg were not given marks.
Candidates may have done so because they confused “hypoxaemia” with “hypoxia”.
Better answers addressed different physiological causes of hypoxaemia, including areas of low
V/Q; hypoventilation; increased oxygen consumption; loss of hypoxic pulmonary vasoconstriction
and closing capacity exceeding functional residual capacity.
Syllabus: B1a2b, B1e,f,g
References: Nunn’s respiratory physiology – various sections
Definitions of hypoxaemia and hypoxia:
Causes of post-operative hypoxaemia:
Jones, J. G., D. J. Sapsford, and R. G. Wheatley. "Postoperative hypoxaemia: mechanisms and time course." Anaesthesia 45.7 (1990): 566-573.
Treacher, D. F., and R. M. Leach. "Oxygen transport—1. Basic principles." Bmj 317.7168 (1998): 1302-1306.
Tipping, Robert, Robin Berry, and Ian Nesbitt. "Mechanisms of hypoxaemia and the interpretation of arterial blood gases." Surgery (Oxford) 30.10 (2012): 505-511.