University Department of Anaesthesia, Critical Care and Pain Management, University Hospitals of Leicester, Leicester Royal Infirmary, Leicester LE1 5WW, UK*Corresponding author
Accepted for publication: November 13, 2001
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Abstract |
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Methods. Patients received either remifentanil 0.5 µg kg1 over 30 s, followed by an infusion of 0.1 µg kg min1 (group R) or alfentanil 10 µg kg1 over 30 s, followed by an infusion of saline (group A). Anaesthesia was then induced with propofol, rocuronium, and 1% isoflurane with 66% nitrous oxide in oxygen.
Results. Systolic arterial pressure (SAP) and mean arterial pressure (MAP) decreased after the induction of anaesthesia (P<0.05) and increased for 3 min after intubation in both groups (P<0.05), but remained below baseline values throughout. Heart rate remained stable after induction of anaesthesia but increased significantly from baseline after intubation for 1 and 4 min in groups R and A, respectively (P<0.05). There were no significant between-group differences in SAP, MAP, and heart rate. Diastolic pressure was significantly higher in group A than group R at 4 and 5 min after intubation (P<0.05). Hypotension (SAP <100 mm Hg) occurred in four patients in group R and three patients in group A.
Conclusions. Remifentanil and alfentanil similarly attenuate the pressor response to laryngoscopy and intubation, but the incidence of hypotension confirms that both drugs should be used with caution in elderly patients.
Br J Anaesth 2002; 88: 4303
Keywords: age factors, cardiovascular responses; analgesics opioid, remifentanil; analgesics opoid, alfentanil; intubation tracheal, responses; heart, heart rate; arterial pressure
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Introduction |
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Few studies of the haemodynamic responses to intubation have been performed in the elderly, and none have used remifentanil. The aim of this study was to compare the effects of remifentanil and alfentanil in modifying the haemodynamic response to intubation in elderly patients.
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Methods and results |
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All patients received i.v. Hartmanns solution 5 ml kg1 over 510 min before the induction of anaesthesia. Routine monitoring was instigated and heart rate and arterial pressure were recorded at 1 min intervals throughout the study. Arterial pressure was measured non-invasively using an automatic oscillometer (Datex Cardiocap II) and ECG was monitored with electrodes in the CM5 position. Three readings of heart rate and arterial pressure were taken before the start of the study and the mean of these three values defined as each individuals baseline data. All patients received i.v. glycopyrrolate 0.2 mg immediately followed by a bolus of either remifentanil (0.5 µg kg1 in 10 ml saline over 30 s) followed by a remifentanil infusion at 0.1 µg kg1 min1 (group R), or a bolus of alfentanil (10 µg kg1 in 20 ml saline over 30 s) followed by an infusion of saline (group A). Immediately after the study drug, anaesthesia was induced with propofol (0.5 mg kg1 followed by 10 mg every 10 s until loss of verbal contact) and rocuronium 0.6 mg kg1 was administered to produce neuromuscular block. Patients lungs were ventilated manually with 1% isoflurane and 66% nitrous oxide in oxygen, to an end-tidal carbon dioxide tension of 4.04.5 kPa. Neuromuscular block was confirmed with a nerve stimulator and laryngoscopy, and tracheal intubation were then performed 3 min after loss of verbal contact.
Ephedrine (3 mg increments) was administered for hypotension (systolic arterial pressure (SAP) <100 mm Hg, or a decrease of >30% from baseline values for >60 s) and atropine, in 300 µg increments, for bradycardia (heart rate <45 beats min1). For hypertension (SAP >200 mm Hg, or an increase of >30% above baseline for >60 s) or tachycardia (heart rate >130 beats min1 for >60 s), the inspired isoflurane concentration was increased in increments of 0.5%. Power calculations based on previous data,7 suggested that 20 patients per group would detect a 15% difference in SAP or heart rate between the groups after intubation (=0.05, ß=0.2).
Statistical analysis was performed using a general linear model analysis of variance for repeated measures for continuous variables (with treatment group and time as between- and within-group factors, and Bonferroni adjustment for multiple comparisons). All analyses were performed using SPSS for Windows computer software (release 9.0).
One patient in the remifentanil group was excluded because of a procedural violation (unanticipated difficult tracheal intubation with duration of laryngoscopy >2 min). Patient characteristics are given in Table 1. Baseline arterial pressure and heart rate were similar in both groups (Table 2). Mean arterial pressure (MAP) decreased significantly after induction of anaesthesia in both groups (P<0.05 compared with baseline values) and increased for 3 min after intubation (P<0.05 compared with pre-intubation), but remained below baseline throughout the study period. It was significantly lower than baseline at 45 min after intubation in both groups (P<0.05). Changes in SAP and diastolic arterial pressure (DAP) followed a similar pattern but DAP was significantly higher in group A at 4 and 5 min post-intubation (P<0.05). However, there were no differences between groups in MAP or SAP at any time point.
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One patient in group R and two patients in group A experienced marked hypotension (SAP <80 mm Hg for >1 min). Four patients in group R and three in group A required ephedrine for hypotension. However, nine patients in group R and eight in group A had transient hypotension (SAP <100 mm Hg for <1 min) which did not require ephedrine. One patient in group R and two in group A received an increased inspired concentration of isoflurane to treat hypertension. There were no incidences of bradycardia, tachycardia, arrhythmias, ST segment, or other ECG changes observed during the study.
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Comment |
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Mild hypotension (SAP <100 mm Hg for <1 min) after induction of anaesthesia occurred in almost 50% of patients despite i.v. fluid pre-loading and glycopyrrolate pre-treatment, but marked hypotension (SAP <80 mm Hg for >1 min) occurred in only three patients. There was also large variation in response to laryngoscopy and tracheal intubation, with the maximum mean heart rate and arterial pressure occurring 2 min after intubation. Mean SAP, 2 min after tracheal intubation, was 140.6 (range 100193) and 143.5 (range 92196) mm Hg in groups R and A, respectively.
These findings suggest that the elderly are susceptible to marked fluctuations in arterial pressure and heart rate at induction of anaesthesia and that attenuation of cardiovascular responses was sometimes incomplete, with large variations between individual patients. However, the overall incidence and degree of hypotension in this study is likely to have been greater, had higher doses of remifentanil or alfentanil been used. Although studies in younger adults have used higher doses of alfentanil, 10 µg kg1 was found to be optimal in elderly patients.7 The potency of remifentanil compared with alfentanil is approximately 20:1,8 which corresponds to the remifentanil dose of 0.5 µg kg1 used here. A previous study showed these dose regimens to have similar cardiovascular effects in hypertensive patients.9
In another study in elderly patients, the cardiovascular response to tracheal intubation was attenuated by fentanyl 3 µg kg1 but with a 35% incidence of marked hypotension (SAP <80 mm Hg).10 The incidence of hypotension in the present study may also have stemmed from the use of propofol, despite careful titration of dose to effect. The elderly are known to be sensitive to the effects of propofol,11 but it has been suggested to be the preferred i.v. anaesthetic agent to attenuate the cardiovascular response to intubation.12 However, severe hypotension was rare in this study.
Although the drug combinations and doses were reasonable in this group of elderly patients, no patients in this study had significant cardiovascular disease. Few data are available on the effects of remifentanil in patients with impaired cardiac function, although hypotension is more likely to occur, and further studies should investigate the optimum dose of remifentanil in these high-risk patients.
In summary, remifentanil 0.5 µg kg1 over 30 s followed by an infusion of 0.1 µg kg1 min1 was as effective as alfentanil 10 µg kg1 in attenuating the pressor response to tracheal intubation in elderly patients. It is an acceptable alternative to alfentanil at induction of anaesthesia when a remifentanil infusion is used during surgery.
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References |
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