Medicine (St Vincent's) - Theses
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ItemThe role of cardiac output and fluid responsive measurements in improving outcomes after major abdominal surgery in adults( 2021)Adequate delivery of oxygen to tissues is essential to tissue healing and preserving organ function following major surgery which is characterised by an increased oxygen demand. Cardiac output (CO), the flow out of the heart, can now be measured with monitors using technology that allows them to be used safely during the perioperative period. This thesis explores the monitors used to target CO, the effect of targeting CO, goal-directed therapy (GDT), and haemodynamic differences between restrictive and liberal fluid therapy. The CO technology of focus in this thesis is the oesophageal Doppler with arterial pressure waveform devices and plethysmography also assessed for their ability for agreement to clinical events. Two prospective observational studies assessed the ability of the monitors to track the clinical events of fluid and vasopressor administration. Compared to each other, the Doppler monitor and arterial pressure waveform monitor had reduced concordance to track CO changes following fluid boluses with even poorer concordance to vasopressor administration. Compared to the reference standard of thermodilution, both technologies displayed reduced precision but the Doppler tracked fluid boluses more consistently. A randomised control trial was conducted with patients having colorectal resection surgery targeting an optimal CO using fluid bolus therapy. Importantly, it was conducted within a contemporary enhanced recovery after surgery (ERAS) framework to demonstrate whether GDT can have a benefit in addition to optimal perioperative care. There was no difference in hospital length of stay or proportion of patients with major complications. A meta-analysis of other studies shows that the benefit to GDT with a Doppler technology device is effective in reducing complications but the results are less applicable with lower perioperative risk, such as patients within an ERAS framework. Finally, the haemodynamic effect of a restrictive fluid therapy compared to a modestly liberal fluid therapy was observed with CO monitoring and fluid responsive parameters. Fluid restriction resulted in a reduced CO and stroke volume which may explain a finding of increased kidney injury and surgical site infection observed in this group. In summary, targeting an increased CO in major abdominal surgery may show reductions in complications but this is not seen in low-risk patients. A Doppler CO monitor has a better ability to detect changes after a fluid bolus but measurement of CO clinically is still challenging with reduced precision observed. The demonstration of reduced CO with fluid restriction supports the importance of avoiding the harmful effects of hypovolaemia and the utility of the measurement and targeting of CO.