Br. J. Surg. 1991, Vol. 78, February, 237-241
D. P. Taggart, D. C. McMillan*, T. Preston?, R. Richardson*, H. J. G. Burns* and D. J. Wheatley Departments of Cardiac Surgery and *Surgery. Royal Infirmary, and ?Scottish Universities Research and Reactor Centre, East Kilbride, Glasgow, UK Correspondence to: Dr D. P. Taggart, Lecturer in
Cardiac Surgery, Royal Infirmary, Glasgow G 4 OSF, UK
Effects of cardiac surgery and intraoperative hypothermia on energy expenditure as measured by doubly labelled water Total energy expenditure ( T E E ) was measured over two 10-day periods, before and after operation in 16 patients undergoing coronary artery surgery and randomized to have cardiopulmonary bypass with an intraoperative blood temperature of either 28 or 20°C. T E E was measured with doubly labelled water containing stable isotopes of hydrogen and o.qvgen to allow calculation of T E E over fixed periods from the differential rate of excretion of the two isotopes. Results were available f o r eight patients in the 28°C group but f o r onl-v seven in the 20°C group (one patient in this group was excluded as the temperature allocated was not achieved). The groups were similar with respect to body-weight and lean body mass. The 20°C group received more grafts than the 28°C group, resulting in an increase in cross-clamp and bypass times. Mean preoperative T E E was similar in both groups. The mean difference in fractional turnover rates of hydrogen and oxygen was not significantly different in the postoperative period. There was a non-significant increase in the mean 10-day postoperative TEE, calculated in total calories, of 4.7per cent in the 28°C and 5.1 per cent in the 20°C group. When changes in postoperative T E E were calculated according to lean body mass, the mean increases were respectively 3.7 and 3.2 per cent. Cardiac surgery utilizing cardiopulmonary bypass and intraoperative hypothermia results in only a modest increase in postoperative TEE. In this study a more profound level of intraoperative hypothermia did not influence the change in postoperative TEE.
The effect of surgical trauma on total energy expenditure (TEE) is controversial. Some groups have reported little postoperative change',2 while others have reported variable increases of up to 25 per cent3-'. Cardiac surgery combines cardiopulmonary bypass and intraoperative hypothermia with conventional surgical injury. Intraoperative hypothermia during cardiac surgery modifies the endocrine'.' and protein turnover" responses to surgery, but changes in TEE after cardiac surgery have not been reported and it is not known whether intraoperative hypothermia can modify any such changes. The doubly labelled water technique permits measurement of TEE by administration of stable isotopes of hydrogen and oxygen ( 2 H , 0 and H2'80)'1-'8. The technique is based on the observation that oxygen atoms in respired carbon dioxide are in eqilibrium with oxygen atoms in body water through the action of carbonic anhydrase". After mixing with body water, 'H is lost as water whereas I8O is lost both as water and as carbon dioxide. The difference in the rate of excretion of the two isotopes from the body is therefore due to carbon dioxide production from which TEE can be calculated' I . The technique can provide an integrated assessment of TEE over 1 day in contrast to the factorial computations of daily energy expenditure derived from short periods of indirect calorimetry. The aims of this study were threefold: to examine the effects of uncomplicated cardiac surgery on energy expenditure; to investigate whether changes in energy expenditure could be modified with a more profound level of intraoperative hypothermia; and to determine the applicability and suitability of the doubly labelled water technique in surgical patients.
0007-1323/91/02023745
ip 1991 Butterworth-Heinemann Ltd
Patients and methods Protocol
Patients presented 10 days before surgery and, after passing a baseline urine sample to determine background enrichment, drank a tumbler of water containing 75 mg ''0 per kg body-weight (8.7 atom per cent l80,Delta Isotopes, Crewe, UK) mixed with dueterium (25 mg 'H per kg body-weight, 99.8 atom per cent, MSD Isotopes, Montreal, Canada). Patients then went home and collected daily urine samples (20 ml) until surgery. A second identical dose of doubly labelled water was administered 6 h after surgery as an intravenous infusion after microfiltration. Residual levels of oxygen and hydrogen enrichment were calculated from the presurgery isotope decay curves. After surgery, 20 ml morning urine samples were collected for a further 10 days. Patients and methods Sixteen male patients undergoing elective coronary artery surgery were prospectively randomized to an intraoperative blood temperature of 28 or 20°C. The age range of the patients was 4G62 years and all required at least two coronary artery grafts using saphenous vein and/or internal mammary artery. No patient was unstable or in cardiac failure or known to have diabetes mellitus, hyperlipidaemia, endocrine disorders, or renal or hepatic impairment. All patients were nutritionally replete, judged by typical biochemical and anthropometric parameters. Informed consent was obtained from all patients and the study was approved by the Hospital Ethical Committee. Anaesthetic regimen A standard anaesthetic regimen was followed; 20 mg temazepam was administered on the night before surgery, anaesthesia was induced with
237
Energy expenditure during surgery and hypothermia: D. P. Taggart et al.
midazolam and and fentanyl. and intubation was performed after the administration of a muscle relaxing agent latracurium or pancuronium). During surgery, anaesthesia was maintained with a combination of morphine, fentanyl and midazolam and boluses of atracurium or pancuronium. The total anaesthetic dose of morphine was < 2 mg/kg body-weight and of fentanyl ~ 2 pg/kg 0 body-weight. Curdiopulnionary b.vpass Bypass was performed using pulsatile perfusion, bubble oxygenation, a 40 pm pore size arterial filter and 2 litres of crystalloid prime. The intraoperative blood temperature was continuously recorded in the extracorporeal circuit (Therm-A, Edwards CVS Division, Berkshire, UK) while the core temperature was simultaneously measured in the nasopharynx (Yellow Springs series 401 temperature probe, Siemens Ltd., Cumbernauld, UK). The perfusion flow rate was calculated from the formula that at normothermia full flow is equivalent to 2.4 I/m2 per min. During intraoperative hypothermia the flow rate was reduced but did not fall below 1.5 I/m2 per min. One litre of 4'C cardioplegic solution (St, Thomas' Hospital formula) was administered in divided doses during the cross-clamp period and the heart was topically cooled with physiological saline at 4°C. Acid-base status during bypass was controlled by pH-STAT management. On the patient's return to the cardiac intensive care unit, boluses of morphine (1-2 mg), midazolam (1-2 mg) and vecuronium (2 mg) were used to maintain analgesia and permit mechanical ventilation until the patient was fully rewarmed, haemodynamically stable and ready for extubation.
''0 andqsi.~ All urine samples were analysed for " 0 enrichment by continuous flow isotope ratio mass spectrometry (CF-IRMS)I9. 1.5 ml samples of urine were equilibrated with carbon dioxide (18.5 ml 10 per cent carbon dioxide) in a vacutainer at 25°C for 72 h. 1 mi gas samples (100 pl carbon dioxide) were then injected into a CF-IRMS (Roboprep-CN Sample Convertor, Europa Scientific, Crewe, UK) interfaced to an MM602 IRMS (VG Isogas, Middlewich, UK) via a septum inlet where the gas was in turn dried, purified by gas chromatography and bled into the mass spectrometer. The mass ratio 46/44+45 was measured aulomaticaly and the instrument was calibrated against distilled water standards of known " 0 enrichment. The coefficient of variation for replicate urine samples was
D. P. Taggart, D. C. McMillan*, T. Preston?, R. Richardson*, H. J. G. Burns* and D. J. Wheatley Departments of Cardiac Surgery and *Surgery. Royal Infirmary, and ?Scottish Universities Research and Reactor Centre, East Kilbride, Glasgow, UK Correspondence to: Dr D. P. Taggart, Lecturer in
Cardiac Surgery, Royal Infirmary, Glasgow G 4 OSF, UK
Effects of cardiac surgery and intraoperative hypothermia on energy expenditure as measured by doubly labelled water Total energy expenditure ( T E E ) was measured over two 10-day periods, before and after operation in 16 patients undergoing coronary artery surgery and randomized to have cardiopulmonary bypass with an intraoperative blood temperature of either 28 or 20°C. T E E was measured with doubly labelled water containing stable isotopes of hydrogen and o.qvgen to allow calculation of T E E over fixed periods from the differential rate of excretion of the two isotopes. Results were available f o r eight patients in the 28°C group but f o r onl-v seven in the 20°C group (one patient in this group was excluded as the temperature allocated was not achieved). The groups were similar with respect to body-weight and lean body mass. The 20°C group received more grafts than the 28°C group, resulting in an increase in cross-clamp and bypass times. Mean preoperative T E E was similar in both groups. The mean difference in fractional turnover rates of hydrogen and oxygen was not significantly different in the postoperative period. There was a non-significant increase in the mean 10-day postoperative TEE, calculated in total calories, of 4.7per cent in the 28°C and 5.1 per cent in the 20°C group. When changes in postoperative T E E were calculated according to lean body mass, the mean increases were respectively 3.7 and 3.2 per cent. Cardiac surgery utilizing cardiopulmonary bypass and intraoperative hypothermia results in only a modest increase in postoperative TEE. In this study a more profound level of intraoperative hypothermia did not influence the change in postoperative TEE.
The effect of surgical trauma on total energy expenditure (TEE) is controversial. Some groups have reported little postoperative change',2 while others have reported variable increases of up to 25 per cent3-'. Cardiac surgery combines cardiopulmonary bypass and intraoperative hypothermia with conventional surgical injury. Intraoperative hypothermia during cardiac surgery modifies the endocrine'.' and protein turnover" responses to surgery, but changes in TEE after cardiac surgery have not been reported and it is not known whether intraoperative hypothermia can modify any such changes. The doubly labelled water technique permits measurement of TEE by administration of stable isotopes of hydrogen and oxygen ( 2 H , 0 and H2'80)'1-'8. The technique is based on the observation that oxygen atoms in respired carbon dioxide are in eqilibrium with oxygen atoms in body water through the action of carbonic anhydrase". After mixing with body water, 'H is lost as water whereas I8O is lost both as water and as carbon dioxide. The difference in the rate of excretion of the two isotopes from the body is therefore due to carbon dioxide production from which TEE can be calculated' I . The technique can provide an integrated assessment of TEE over 1 day in contrast to the factorial computations of daily energy expenditure derived from short periods of indirect calorimetry. The aims of this study were threefold: to examine the effects of uncomplicated cardiac surgery on energy expenditure; to investigate whether changes in energy expenditure could be modified with a more profound level of intraoperative hypothermia; and to determine the applicability and suitability of the doubly labelled water technique in surgical patients.
0007-1323/91/02023745
ip 1991 Butterworth-Heinemann Ltd
Patients and methods Protocol
Patients presented 10 days before surgery and, after passing a baseline urine sample to determine background enrichment, drank a tumbler of water containing 75 mg ''0 per kg body-weight (8.7 atom per cent l80,Delta Isotopes, Crewe, UK) mixed with dueterium (25 mg 'H per kg body-weight, 99.8 atom per cent, MSD Isotopes, Montreal, Canada). Patients then went home and collected daily urine samples (20 ml) until surgery. A second identical dose of doubly labelled water was administered 6 h after surgery as an intravenous infusion after microfiltration. Residual levels of oxygen and hydrogen enrichment were calculated from the presurgery isotope decay curves. After surgery, 20 ml morning urine samples were collected for a further 10 days. Patients and methods Sixteen male patients undergoing elective coronary artery surgery were prospectively randomized to an intraoperative blood temperature of 28 or 20°C. The age range of the patients was 4G62 years and all required at least two coronary artery grafts using saphenous vein and/or internal mammary artery. No patient was unstable or in cardiac failure or known to have diabetes mellitus, hyperlipidaemia, endocrine disorders, or renal or hepatic impairment. All patients were nutritionally replete, judged by typical biochemical and anthropometric parameters. Informed consent was obtained from all patients and the study was approved by the Hospital Ethical Committee. Anaesthetic regimen A standard anaesthetic regimen was followed; 20 mg temazepam was administered on the night before surgery, anaesthesia was induced with
237
Energy expenditure during surgery and hypothermia: D. P. Taggart et al.
midazolam and and fentanyl. and intubation was performed after the administration of a muscle relaxing agent latracurium or pancuronium). During surgery, anaesthesia was maintained with a combination of morphine, fentanyl and midazolam and boluses of atracurium or pancuronium. The total anaesthetic dose of morphine was < 2 mg/kg body-weight and of fentanyl ~ 2 pg/kg 0 body-weight. Curdiopulnionary b.vpass Bypass was performed using pulsatile perfusion, bubble oxygenation, a 40 pm pore size arterial filter and 2 litres of crystalloid prime. The intraoperative blood temperature was continuously recorded in the extracorporeal circuit (Therm-A, Edwards CVS Division, Berkshire, UK) while the core temperature was simultaneously measured in the nasopharynx (Yellow Springs series 401 temperature probe, Siemens Ltd., Cumbernauld, UK). The perfusion flow rate was calculated from the formula that at normothermia full flow is equivalent to 2.4 I/m2 per min. During intraoperative hypothermia the flow rate was reduced but did not fall below 1.5 I/m2 per min. One litre of 4'C cardioplegic solution (St, Thomas' Hospital formula) was administered in divided doses during the cross-clamp period and the heart was topically cooled with physiological saline at 4°C. Acid-base status during bypass was controlled by pH-STAT management. On the patient's return to the cardiac intensive care unit, boluses of morphine (1-2 mg), midazolam (1-2 mg) and vecuronium (2 mg) were used to maintain analgesia and permit mechanical ventilation until the patient was fully rewarmed, haemodynamically stable and ready for extubation.
''0 andqsi.~ All urine samples were analysed for " 0 enrichment by continuous flow isotope ratio mass spectrometry (CF-IRMS)I9. 1.5 ml samples of urine were equilibrated with carbon dioxide (18.5 ml 10 per cent carbon dioxide) in a vacutainer at 25°C for 72 h. 1 mi gas samples (100 pl carbon dioxide) were then injected into a CF-IRMS (Roboprep-CN Sample Convertor, Europa Scientific, Crewe, UK) interfaced to an MM602 IRMS (VG Isogas, Middlewich, UK) via a septum inlet where the gas was in turn dried, purified by gas chromatography and bled into the mass spectrometer. The mass ratio 46/44+45 was measured aulomaticaly and the instrument was calibrated against distilled water standards of known " 0 enrichment. The coefficient of variation for replicate urine samples was
