Manual versus target-controlled infusions of propofol

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1 Manual versus target-controlled s of propofol D. S. Breslin, 1 R. K. Mirakhur, 2 J. E. Reid 3 and A. Kyle 4 1 Research Fellow, 2 Professor, 3 SpR, 4 Research Nurse, Department of Anaesthetics and Intensive Care Medicine, The Queen s University of Belfast, 97 Lisburn Road, Belfast, BT9 7BL, UK Summary Target-controlled systems have been shown to result in the adistration of larger doses of propofol, which may result in delayed emergence and recovery from anaesthesia. The aim of this study was to investigate if this was due to a difference in the depth of hypnosis (using the bispectral index monitoring) between the manual and target controlled systems of adistration. Fifty unpremedicated patients undergoing elective surgery were randomly allocated to have their anaesthesia maintained with manual or target-controlled propofol schemes. In both groups, the rate of propofol adistration was adjusted according to standard clinical criteria while bispectral index scores were recorded by an observer not involved in the delivery of anaesthesia. The total dose of propofol used was higher in the target controlled group (mean 9.9 [standard deviation 1.6] compared with 8.1 [1.0] mg.kg )1.h )1 in the manual group [p <0.0001]). The times to emergence and recovery end-points were comparable between the two groups. The difference in the total dosage of propofol was mainly due to higher rate of propofol adistration in the first 30 in the target controlled group. The bispectral index scores were lower in the target controlled group during this time, being significantly so over the first 15 of anaesthesia. We conclude that propofol adistration by a target controlled system results in the adistration of higher doses of propofol and lower bispectral index values mainly in the initial period of anaesthesia. Keywords Anaesthetics, intravenous; propofol. Monitoring, intraoperative; bispectral index.... Correspondence to: R. Mirakhur r.mirakhur@qub.ac.uk Accepted: 10 May 2004 Traditionally propofol s have been adistered by a manually controlled regimen involving a bolus dose followed by a continuous. A popular scheme is that of Roberts et al. [1] where the rate of is stepped down at 10- intervals for 30. More recently, target-controlled (TCI) systems have become available which allow easy alteration of depth of anaesthesia with improved cardiovascular and respiratory stability [2,3]. However it has been shown that, while both the target-controlled and manually, adistered propofol s provide adequate anaesthesia, TCI is associated with the adistration of greater doses of propofol possibly resulting in a longer recovery time [4,5]. It is possible that the higher propofol dose and prolonged recovery may be due to a non-standardised depth of anaesthesia between the two techniques. The bispectral index (BIS) is a processed electroencephalographic monitor designed to give information on the depth of anaesthesia, or more specifically a quantitative measurement of the patient s hypnotic state [6,7]. This index provides an objective means of adjusting anaesthetic depth. Target levels of between 45 and 60 during anaesthesia are required to prevent awareness or recall of intra-operative events [8]. The purpose of this study was to compare the amount of propofol used by the manual and the TCI schemes using the standard monitoring while also recording the BIS values without the anaesthetist in charge of the patient being aware of these values. Patients and Methods Fifty ASA grade I or II patients, aged 18 65, scheduled for elective orthopaedic or body surface surgery lasting more than 30 were enrolled in the study after informed consent and Research Ethics Committee approval. Patients on regular sedative or narcotic Ó 2004 Blackwell Publishing Ltd 1059

2 D. S. Breslin et al. Æ Manual versus target-controlled s of propofol Anaesthesia, 2004, 59, pages medications were excluded from the study. No sedative premedication was adistered. The patients were allocated using a computer generated randomisation scheme to have their anaesthesia maintained with either target-controlled or a manual scheme. An intravenous cannula was sited in a forearm vein in all patients and an of Ringer s lactate commenced prior to the induction of anaesthesia. Minimum standard monitoring was used throughout the procedure. All patients received fentanyl 1.5 lg.kg )1 intravenously prior to induction of anaesthesia. In the manual group, anaesthesia was induced with propofol 1.0 mg.kg )1 and a propofol commenced at 10 mg.kg )1.h )1, being reduced to 8 and 6 mg.kg )1.h )1 at 10- intervals according to a standard regimen [1]. Further boluses or alterations in the propofol s were dictated by clinical signs. Anaesthesia in the TCI group was induced with initial target plasma concentration set at 5 lg.ml )1, further changes in the target concentration then being made as detered clinically as in the manual group. The propofol s were adistered using a Graseby 3500 pump (Graseby Medical Limited, Watford, UK) in either the TCI or the manual modes. In both groups anaesthesia was maintained with propofol and 65% nitrous oxide in oxygen. Adequacy of anaesthesia was based on absence of haemodynamic changes (heart rate and arterial blood pressure within 20% of baseline values), and somatic (movement, grimacing) and autonomic (lacrimation, sweating) responses. No patients received neuromuscular blocking agents. Further boluses of fentanyl were adistered as required. A laryngeal mask airway was inserted and ventilation assisted as required. Morphine 0.1 mg.kg )1 was adistered about 15 before the anticipated end of surgery along with wound infiltration with bupivacaine for postoperative pain relief. Bispectral index was monitored using two channel referential montage and the 3.31 version software (Aspect Medical Systems, Natick, MA, USA). The scores were monitored continuously and recorded by an observer not involved in the adistration of the anaesthetic. The attending anaesthetist was unaware of the BIS values throughout the study period. The total dose of propofol in both groups was recorded at 5- intervals. Nitrous oxide and propofol were stopped at the end of surgery and the times to eye opening, laryngeal mask airway removal and orientation were recorded. The times to achieve an Aldrete score [9] of 9 or greater and to discharge from the recovery ward were also recorded. Five different parameters are assessed in the Aldrete score (activity, respiration, circulation, consciousness and oxygen saturation) each being rated as 0, 1 or 2 giving a maximum possible score of 10 (appendix). The number of patients in this study was based on the results of a previous study [4] where 23 patients were required in each group, to show a difference of 6 in the time to emergence from anaesthesia (80% power, a = 0.05, two tailed). The data were analysed using Student t-tests and Welch s correction as appropriate. A p-value of less than 0.05 was considered to be statistically significant. Results Fifty-three patients were recruited as three patients were excluded due to unanticipated short duration of anaesthesia and surgery (< 30 ). The analysis of results is based on the 50 patients who met all the inclusion criteria. The two groups were comparable with regard to patient characteristics, duration of anaesthesia and the dosage of fentanyl (Table 1). The total dose (mean and standard deviation (SD)) of propofol adistered was significantly higher in the TCI group (9.9 (1.6) vs. 8.1 (1.0) mg.kg )1.h )1 in the manual group, p < ). This higher rate of adistration occurred mainly during the initial 30 and was associated with lower BIS values during this time, being significantly so over the first 15 of anaesthesia (Fig. 1). The times to emergence and recovery from anaesthesia including the times to attain Aldrete scores of 9 10 were not significantly different (Table 2). Mean systolic arterial pressures and heart rates were also similar in both groups throughout the study period (Fig. 2). The number of patients requiring morphine and the mean morphine requirements in the recovery ward also did not differ significantly between the groups and the times to discharge from the recovery ward were similar (Table 3). No patients had any recall of any intra-operative events at the postoperative visit. Table 1 Patient characteristics, duration of anaesthesia and fentanyl dose. Values given are means (standard deviations) and [ranges]; *p < Age; year 41 (13) [18 62] 41 (11) [21 63] Weight; kg 77 (17) 77 (14) Height; cm 174 (11) 172 (9) Male Female Duration; 78 (30) 78 (31) Fentanyl; lg.kg )1 3.2 (0.8) 3.1 (0.8) Total propofol adistered; mg.kg )1.h )1 8.1 (1.0) 9.9 (1.6)* 1060 Ó 2004 Blackwell Publishing Ltd

3 D. S. Breslin et al. Æ Manual versus target-controlled s of propofol Infusion rate (mg.kg 1.h 1 ) Heart rate (beats. 1 ) or systolic arterial pressure (mmhg) Preop Figure 2 Heart rate (beats. )1 ) (broken line) and systolic arterial pressures (mmhg) (continuous line) (mean and standard deviation) in patients given propofol by manual (m) and target controlled (j) systems. 0 5* 10* 15* 20 30* Table 3 Discharge times and morphine requirements. Values are mean (standard deviation). Bispectral index Discussion 5* 10* 15* Figure 1 Propofol rates (mg.kg )1.h )1 ) (top graph) and the bispectral index values (bottom graph) (mean and standard deviation) in patients given propofol by manual (m) and target controlled (j) systems. *p <0.05. Table 2 Recovery times in utes. Values are mean (standard deviation). Eye opening 9.5 (5.0) 10.3 (4.2) Laryngeal mask airway removal 10.6 (5.3) 11.2 (4.2) Orientation 13.5 (6.2) 13.3 (4.8) Aldrete score = (8) 18 (6) Recovery room discharge; 85 (17) 86 (20) Patients requiring morphine; n Dosage of morphine; mg 15 (6) 16 (8) The use of intravenous anaesthesia has increased in recent years due to availability of propofol, which has the desirable characteristics for induction and maintenance of anaesthesia. Previous studies have shown that both TCI and manual schemes are suitable for the adistration of propofol; however, the TCI method is usually preferred [2,5]. In this study, we have shown that the use of the TCI system was associated with higher propofol usage but that this occurred mostly during the initial 30. Thereafter the propofol dosage used in both groups was comparable. Propofol s were titrated to achieve an adequate depth of anaesthesia using standard clinical parameters. It appears that even though the rate was initially higher in the TCI group, the haemodynamic responses, indicating adequate anaesthesia, were similar in the two groups. Russell et al. and Servin both showed the total dose of propofol was higher in the TCI compared to the manual groups when titrated to haemodynamic responses [2,5]. In a study by Lehmann et al. comparing propofol s during insertion of cardioverter-defibrillators, haemodynamic parameters were also similar between the TCI and the manual groups despite a larger mean dose of propofol being used in the TCI group [10]. This may imply that relatively fit and healthy patients can safely tolerate a wider range of propofol doses. Previous studies have shown that BIS is a satisfactory index of hypnosis when using propofol anaesthesia [7,11]. In our study the BIS values were significantly lower in Ó 2004 Blackwell Publishing Ltd 1061

4 D. S. Breslin et al. Æ Manual versus target-controlled s of propofol Anaesthesia, 2004, 59, pages the TCI group during the initial phase of anaesthesia suggesting that this group had a greater depth of anaesthesia, consistent with the higher propofol rate during this period. The mean total doses of propofol adistered 9.9 (1.6) vs. 8.1 (1.0) mg.kg )1.h )1 in the TCI and manual groups, respectively, were lower than that in earlier studies [2,5]. This may be due to factors such as anaesthesia being adistered by anaesthetists experienced with both methods, anaesthesia being carefully titrated to the clinical endpoints, use of 65% nitrous oxide, and patients receiving on average 3.1 lg.kg )1 of fentanyl. Both nitrous oxide and fentanyl have been shown to reduce the propofol requirements during anaesthesia [12,13]. These lower mean rates of of propofol in both groups may explain the faster rate of emergence and recovery from anaesthesia compared to these previous studies [2,5]. Despite the total dose of propofol adistered in the TCI group being higher, both groups had comparable times to emergence, orientation, achieving an Aldrete score of 9 and discharge from the recovery ward. This is probably due to the similar propofol rates after 30 in both groups in a relatively young healthy patient population with a mean duration of anaesthesia of 78. The results from this study also indicate that the recovery using TCI systems may be delayed in comparison to the manual schemes for shorter surgery. Despite proper skin preparation and impedance checks, three patients in the TCI group and five patients in the manual group had BIS values above 70 at some stage during maintenance of anaesthesia despite no clinical signs of light anaesthesia. Previous authors have highlighted that a high BIS score may not always indicate inadequate anaesthesia [14], because of using nitrous oxide [15], interference from electrocautery and other sources [16], and electromyographic activity [17,18] (although more recent software revisions including the 3.31 version have improved the filtering of electromyographic activity). While patients had a mean time to Aldrete scores of greater than 9 of less than 20 in both groups, the mean time to actual discharge from the recovery ward was about 85. The recovery profile of agents such as propofol is only one factor which influences the actual discharge time from recovery wards [19,20]. However, it shows that patients after relatively short surgery could be discharged earlier from the recovery ward. In conclusion the use of TCI system was associated with the adistration of significantly more propofol. This higher rate occurred during the initial 30 of anaesthesia and was associated with lower BIS values during this period. References 1 Roberts FL, Dixon J, Lewis GTR, Tackley RM, Prys- Roberts C. Induction and maintenance of propofol anaesthesia. A manual scheme. Anaesthesia 1988; 43: 14S 17S. 2 Russell D, Wilkes MP, Hunter SC, Glen JB, Hutton P, Kenny GN. Manual compared with target-controlled of propofol. British Journal of Anaesthesia 1995; 75: Engbers FHM. in practice. European Journal of Anaesthesiology 1995; 12 (Suppl. 10): O Hare RA, Mirakhur RK. Intravenous anesthesia: Manual or target controlled systems. Anesthesiology 1999; 91: A Servin FS. TCI compared with manually controlled of propofol: a multicentre study. Anaesthesia 1998; 53 (Suppl. 1): Todd MM. EEGs, EEG processing, and the bispectral index. Anesthesiology 1998; 89: Struys M, Versichelen L, Byttebier G, Mortier E, Moerman A, Rolly G. Clinical usefulness of bispectral index for titrating propofol target effect-site concentration. Anaesthesia 1998; 53: Vernon JM, Lang E, Sebel PS, Manberg P. Prediction of movement using bispectral electroencephalographic analysis during propofol alfentanil or isoflurane alfentanil anesthesia. Anesthesia and Analgesia 1995; 80: Aldrete JA. The post-anesthesia recovery score revisited. Journal of Clinical Anesthesia 1995; 7: Lehmann A, Boldt J, Thaler E, Piper S, Weisse U. Bispectral index in patients with target controlled or manuallycontrolled of propofol. Anesthesia and Analgesia 2002; 95: Bonhomme V, Plourde G, Meuret P, Fiset P, Backman SB. Auditory steady-state response and bispectral index for assessing level of consciousness during propofol sedation and hypnosis. Anesthesia and Analgesia 2000; 91: Davidson JAA, MacLeod AD, Howie JC, White M, Kenny GNC. Effective concentration 50 for propofol with and without 67% nitrous oxide. Acta Anaesthesiologica Scandinavica 1993; 37: Smith C, McEwan AI, Jhaveri R et al. The interaction of fentanyl on the CP 50 of propofol for loss of consciousness and skin incision. Anesthesiology 1994; 81: Guignard B, Chauvin M. Bispectral index increases and decreases are not always signs of inadequate anesthesia. Anesthesiology 2000; 92: Puri GD. Paradoxial changes in bispectral index during nitrous oxide adistration. British Journal of Anaesthesia 2001; 86: Hemmerling TM, Migneault B. Falsely elevated bispectral index during endoscopic shoulder surgery attributed to interferences with the endoscopic shaver device. Anesthesia and Analgesia 2002; 95: Bruhn J, Bouillon TW, Shafer SL. Electromyographic activity falsely elevates the bispectral index. Anesthesiology 2000; 92: Ó 2004 Blackwell Publishing Ltd

5 D. S. Breslin et al. Æ Manual versus target-controlled s of propofol 18 Vivien B, Di Maria S, Ouattara A, Langeron O, Coriat P, Riou B. Overestimation of bispectral index in sedated intensive care unit patients revealed by adistration of muscle relaxant. Anesthesiology 2003; 99: O Hare RA, Mirakhur RK, Reid JE, Breslin DS, Hayes AH. Recovery from propofol anaesthesia when supplemented with remifentanil. British Journal of Anaesthesia 2001; 86: Breslin DS, Reid JE, Mirakhur RK, Hayes AH, McBrien ME. Sevoflurane-nitrous oxide anaesthesia supplemented with remifentanil: effect on recovery and cognitive function. Anaesthesia 2001; 56: Appendix The parameters and their scores used in the Aldrete Score Activity (voluntary or on command) Moves all extremities 2 Moves two extremities 1 Unable to move 0 Respiration Breathes deeply and coughs freely 2 Dyspnoea, shallow or limited breathing 1 Apnoea 0 Circulation Arterial blood pressure within 20 mmhg of baseline 2 Arterial blood pressure within mmhg of baseline 1 Arterial blood pressure outside 50 mmhg of baseline 0 Consciousness Fully awake 2 Arousable on calling 1 Not responsive 0 Oxygen saturation SpO 2 > 92% (on room air) 2 SpO 2 > 90% (on oxygen) 1 SpO 2 < 90% (on oxygen) 0 Ó 2004 Blackwell Publishing Ltd 1063