[Truncated abstract] Introduction: The early and accurate detection of hypovolaemia in patients is important but challenging. Traditional clinical signs such as heart rate and blood pressure are poor predictors. The use of more invasive monitoring modalities such as central venous or pulmonary artery pressures is of limited benefit and associated with rare but serious risks. There is growing evidence that accurate assessment and management of fluid status is associated with better patient outcome. Intravenous fluids are no longer considered benign drugs. Commercially available minimally invasive cardiac output monitors can reliably and quickly detect hypovolaemia in ventilated patients but their performance in conscious, spontaneously ventilating subjects is uncertain and has not been widely investigated. Aims: The focus of this thesis is to determine whether minimally invasive cardiac output monitoring methods are more accurate than clinical signs in detecting hypovolaemia in conscious subjects. Specifically, it will characterise the performance of four commercially available monitors: Vigileo FloTrac ™ (FloTrac), LiDCOrapid™ (LiDCO), USCOM 1A (USCOM) and CardioQ Oesophageal Doppler (CardioQ) in detecting blood loss in conscious subjects. The adult volunteer haemorrhage model constructed for this thesis is rare and provides an opportunity to perform additional work characterising oxidative stress in controlled haemorrhage. Methods: Eight healthy volunteer anaesthetists were venesected 20% of their blood volume in 2.5% aliquots with concurrent recording of clinical hemodynamic parameters and cardiac output monitor readings. At each level of blood loss a passive leg raise was performed as a dynamic circulatory challenge with the central redistribution of blood. This manoeuvre functions as a potential marker of fluid responsiveness. Each monitor functions in a different way but all give an estimate of stroke volume. This estimate of stroke volume allows a direct comparison of their ability to detect blood loss. The degree of blood loss detected by a 10% change in monitored parameters (for each of the monitors and clinical signs) from baseline values was determined. The performance of each monitor in detecting a known 10% blood loss was assessed by constructing receiver operator characteristic (ROC) curves and determining positive and negative predictive values for both the monitors and clinical signs. The utility of a passive leg raise in detecting blood loss and the response to blood reinfusion of venesected blood was also assessed. Blood samples for the detection of oxidative stress measured using Isofurans and Isoprostanes were taken at baseline and at each five percent blood volume venesected and reinfused (nine samples in total). Results: Changes in heart rate and blood pressure associated with the venesection and reinfusion of blood were not clinically significant. A 10% change in stroke volume from baseline was observed at 7.5% blood loss with the USCOM, at 12.5% blood loss with FloTrac and CardioQ...
|Publication status||Unpublished - 2013|