A validation and feasibility study of the non-invasive measurement of oxygen delivery and consumption after elective major abdominal surgery.
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Major surgery triggers a physiological stress response that results in an increase in post-operative metabolic demand and oxygen consumption (V̇O2), which must be met by an increased oxygen delivery (DO2). Historical studies described the increase in V̇O2 in patients after major surgery and presented evidence that the inability to meet this increase oxygen demand and the temporal pattern of this oxygen deficit appears to differ according to whether patients survive, or develop complications or not. The survival and complication profile of patients in modern practice is different from that previously described, And the methods employed in these historical studies were invasive and inconsistent with contemporary practice. V̇O2 can be measured non-invasively with indirect calorimetery, and DO2 calculated from non-invasive cardiac output monitors, and haemoglobin and oxygen saturation measurement devices. This thesis describes two prospective observational studies which1) validate and 2) assess the feasibility of non-invasive measurements of V̇O2 and DO2 and explore their temporal patterns after contemporary abdominal surgery. These techniques demonstrate moderate to good trending ability when measuring changes in V̇O2 and DO2. The non-invasive measurement of V̇O2 and DO2 is feasible in patients after major abdominal surgery. There appear to be distinct patterns of V̇O2 and DO2 after contemporary abdominal surgery in those who develop complications or not. Contemporary patterns of net cumulative oxygen debt appear to differ from those previously described.