Acta Anaesthesiol Scand 2014; 58: 495–500 Printed in Singapore. All rights reserved

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Letters to the Editor Undercalibrating in goal-directed therapy?

ment using arterial pulse power analysis during aortic aneurysm repair. Anaesthesia 2010; 65: 1194–9.

doi: 10.1111/aas.12186 Sir, We read with interest, the investigations of Bisgaard et al.1 Benefits of goal-directed therapy continue to be discussed, along with the methods by which it should be assessed. Bisgaard et al. concluded that perioperative individualised goal-directed therapy does not affect post-operative complications, or length of intensive care unit and hospital stay, in open elective abdominal aortic surgery. The study protocol states that LiDCOplus (LiDCO Group plc, London, UK) recalibration occurred twice in the study period; firstly, prior to induction of general anaesthesia, and secondly, following unclamping of the aorta. The findings from this recalibration suggest that there was no significant change in calibration factor (CF) between these two times. However, the findings from Beattie et al. suggest that recalibration is necessary throughout non-cardiac surgery as CF varies during the procedure.2 This study protocol had six points of recalibration, following the initial baseline calibration prior to induction: after establishing epidural anaesthesia, following induction of general anaesthesia, following aortic crossclamping, after aortic unclamping, at skin closure, and following return of spontaneous ventilation and removal of endotracheal tube. The findings indicate that there is a significant fall in CF on aortic cross-clamping, leading to an overestimation of stroke volume and cardiac output unless recalibration is undertaken. Conversely, CF was significantly higher following epidural and general anaesthesia compared with the CF prior to induction. This would underestimate the stroke volume and cardiac output if recalibration did not occur. Beattie et al. concluded in order to obtain absolute values of cardiac output, recalibration of the LiDCOplus monitor is necessary during abdominal aortic surgery as the magnitude of changes in CF varies between patients, and this cannot be predicted. Potential errors such as the administration or withholding of fluid or drug therapy could occur as a result of this over- or underestimation when frequent recalibration does not occur. It would appear that before dismissing the potential advantages of goal-directed therapy in abdominal aortic aneurysm patients, a further study, including the calibration outlined by Beattie et al., should be performed. Conflict of interest: None. M. Cockroft J. Mann M. McSwiney

References 1. Bisgaard J, Gilsaa T, Rønholm E, Toft P. Optimising stroke volume and oxygen delivery in abdominal aortic surgery: a randomised controlled trial. Acta Anaesthesiol Scand 2013; 57: 178–88. 2. Beattie C, Moores C, Thomson AJ, Nimmo AF. The effect of anaesthesia and aortic clamping on cardiac output measure-

Address: Melanie Cockroft Department of Anaesthesia Cheltenham General Hospital Sandford Road Cheltenham GL53 7AN UK e-mail: [email protected]

Intraoperative goal-directed fluid therapy – which goals should we choose? Reply* doi: 10.1111/aas.12275 Sir, We thank you and Dr Cockroft et al. for the opportunity to discuss the relevant subject of under-calibrating in goal-directed therapy (GDT). The LiDCOplus system (LiDCO Ltd., Cambridge, UK) uses pulse power analysis and requires initial calibration. It is well validated with an acceptable accuracy and precision.1–3 The in-built algorithm calculating stroke volume (SV) and cardiac output is affected by aortic compliance. The LiDCOplus monitor calculates a correction factor (CF) when calibrated. In intensive care patients, this CF has been shown to be stable so that recalibration is not needed for at least 8 h.4 In the perioperative scene of frequent and rapid haemodynamic changes (anaesthetics, vasopressors, haemorrhage and aortic cross-clamping), recalibration may be required after each intervention. An underestimated CF would lead to an overestimation of cardiac output, which could lead to withholding of fluids and vasopressors, possibly compromising the circulation. Beattie et al.5 showed a significant change in CF after induction of anaesthesia and after aortic cross-clamping during abdominal aortic aneurysm surgery. Using GDT in high-risk surgery has, in several studies, proved to be superior to predefined volume-restrictive or liberal fluid protocols in improving outcome.6 The concept of GDT, however, is not well defined and may be performed in various ways. The pioneers, Shoemaker et al., used predefined, absolute haemodynamic measures (oxygen delivery index, DO2I).7 Pearse et al. used a combination of absolute, predefined goals (DO2I) and relative measures (changes in SV) to guide a more individualised therapy.8 The current tendency in daily clinical practice is to recommend individualised GDT, based on relative haemodynamic measures, such as percentage change in SV. *Response to letter by Dr. Cockroft, AAS 12186.

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Undercalibrating in goal-directed therapy?

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