mg, 1 h before operation. On arrival in the anaesthetic room a peripheral i.v. infusion of. Hartmann's solution was commenced and an extra- dural catheter was ...
British Journal of Anaesthesia 1998; 80: 7–10
CLINICAL INVESTIGATIONS
Comparison of continuous and intermittent administration of extradural bupivacaine for analgesia after lower abdominal surgery L. A. DUNCAN, M. J. FRIED, A. LEE AND J. A. W. WILDSMITH Summary We have compared intermittent bolus and continuous infusion of extradural local anaesthetic for pain relief in a randomized, doubleblind study of 48 patients who underwent major abdominal gynaecological surgery. Each patient received 5 ml of 0.375% bupivacaine hourly, either as a bolus over 5 min or as a constant infusion. Patients who received the intermittent administration technique maintained a more extensive sensory block, reported marginally better analgesia and had a lower requirement for rescue medication. The intermittent bolus technique was not associated with an increase in side effects. (Br. J. Anaesth. 1998; 80: 7–10) Keywords: analgesic techniques, extradural; local, bupivacaine; surgery, gynaecological
anaesthetics
Extradural administration of local anaesthetic is now well established in the management of acute pain. Constant rate infusion from an electromechanical pump is generally used, mainly to minimize medical and nursing workload. In addition, there is a perception that constant infusion produces an unchanging block to maintain analgesia and minimize cardiovascular disturbance.1 With constant infusions of local anaesthetic, sensory block has been shown to regress with time resulting in a requirement for supplementary analgesia,2 3 and even in the presence of an apparently effective extradural block there may be a need for additional medication (usually an opioid) in as many as 50% of patients.4 Intermittent injections of extradural local anaesthetic may provide more reliable analgesia than that obtained by continuous infusion,5 but the lack of suitable pumps implied that this method could not be used widely. The development of devices which can deliver bolus injections at regular intervals has now made this method of administration practicable. This study was designed to compare constant infusion and intermittent injection of extradural bupivacaine after major gynaecological surgery.
Hartmann’s solution was commenced and an extradural catheter was inserted at a lower thoracic or upper lumbar spinal interspace. A test dose of 4 ml of 2% lidocaine was administered to exclude intravascular or intrathecal catheter placement and was followed by 16 ml of 2% lidocaine with epinephrine 1:200 000. General anaesthesia was induced with either thiopental 250–375 mg or propofol 100–200 mg i.v. and maintained by inhalation of either enflurane or isoflurane (1–2%) and 70% nitrous oxide in oxygen. Patients breathed spontaneously via a laryngeal mask or a tracheal tube, and succinylcholine 1 mg kg91 was used to facilitate intubation if required. At 1 h or skin closure, whichever occurred first, 0.5% bupivacaine 10 ml was injected extradurally. Patients were then allocated randomly to one of two postoperative extradural regimens. Every patient received 0.375% bupivacaine 5 ml hourly, either at a constant rate infusion (control group) or as an hourly bolus delivered at 1 ml min91 (study group). A Medfusion 2001 syringe pump (Medex Medical) was used in all patients and was programmed by an anaesthetist who was not one of the investigators, all of whom were unaware of the mode of administration until the end of the study. All patients received i.v. patient-controlled analgesia from an Abbott Lifecare PCA system set to deliver a 1-mg bolus doses of morphine with a lockout time of 5 min. As soon as the patient was able to co-operate after recovery of consciousness, the upper and lower levels of block to pinprick and the degree of motor block (Bromage scale) in the legs were assessed, together wtih pain (10-cm visual analogue scale (VAS)) at rest, on coughing after deep inspiration and on moving from the supine to the sitting position. These assessments were repeated 2, 4, 6, 9, 12, 21 and 24 h after surgery. At 4, 9 and 24 h, cumulative morphine consumption was recorded and patients were asked to rate pain control to date using a four-point verbal rating scale (VRS: 1:poor, 2:fair, 3:good, 4: excellent). Routine measurements of heart rate, arterial pressure, ventilatory frequency (hourly) and volume of extradural solution infused were carried
Patients and methods After obtaining approval from the area Ethics Committee and informed consent, we studied 48 ASA I, II or III patients. All were undergoing major gynaecological surgery via a lower abdominal incision and were premedicated with temazepam 10–30 mg, 1 h before operation. On arrival in the anaesthetic room a peripheral i.v. infusion of
L. A. DUNCAN*, FRCA, M. J. FRIED†, BSC(HONS), MRCGP, FFARCSI, A. LEE, BSC(HONS), FRCA, J. A. W. WILDSMITH*, MD, FRCA, FRCPED, Department of Anaesthetics, Royal Infirmary, Edinburgh EH3 9YW. Accepted for publication: August 21, 1997. Present addresses: *University Department of Anaesthesia, Ninewells Hospital and Medical School, Dundee DD1 9SY. †Department of Anaesthetics, St John’s Hospital at Howden, Livingston EH54 6PP. Correspondence to L. A. D.
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British Journal of Anaesthesia
Table 1 Patient details (mean (SD or range) or number)
Age (yr) Weight (kg) Height (cm) ASA (I/II/III) Extradural site T10–11 T11–12 T12–L1 L2–L3 Incision Transverse Mid-line Duration of surgery (min)
Bupivacaine 0.375% intermittently (n:19)
Bupivacaine 0.375% continuously (n:21)
43.5 (21–66) 67.9 (13.7) 163.5 (6.3) 12/5/2
45.9 (29–85) 63.9 (9.9) 161.6 (6.3) 13/7/1
7 9 3
3 15 2 1
16 3 60.7 (20.3)
17 4 53.6 (14.4)
Table 2 Requirements for rescue medication. Morphine consumption is shown as median (interquartile range). Extradural top-ups were of 0.5% bupivacaine as a 5-ml bolus dose Time
Morphine consumption (mg)
No. of extradural top ups
Intermittent group Continuous group Intermittent group Continuous group
0–4 h
4–9 h
9–24 h
4 (0–9)
4 (2–6)
11 (4–14)
3 (1–6) 1 in 1 patient 3 in 3 patients
6 (3–10) 1 in 1 patient 6 in 4 patients
12 (6–15) 1 in 1 patient 10 in 4 patients
sensory or motor block, but those patients who received intermittent boluses had, as a group, more extensive sensory (pinprick) blocks thereafter. The difference was significant at 2, 4, 6, 9 and 24 h (fig. 1), but there was no difference in the degree of motor block at any time (fig. 2). An obviously unilateral block developed in two patients in the intermittent bolus group and five in the continuous infusion group. Three patients in the intermittent group (including one with a unilateral block) received a single bolus injection of 0.5% bupivacaine 5 ml because of poor analgesia. In the continuous group, six such patients (including one with unilateral block) required a total of 19 single bolus injections for breakthrough pain (table 2). Unilateral blocks were treated only if pain relief was poor. Mean bupivacaine consumption for the 24-h study period was 456 mg in the intermittent bolus group and 473 mg in the infusion group (P:0.001). Morphine consumption tended to be lower in the group receiving intermittent bolus administration, but the difference was not significant (table 2). Both VRS and VAS results (figs 3–5) suggested that the quality of analgesia was somewhat better in the intermittent bolus group. If a VRS score of good or excellent is taken as satisfactory then 74%, 89% and 84% of patients in the intermittent group had acceptable pain relief at 4, 9 and 24 h compared with 55%, 71% and 67% of patients in the continuous group. The difference between the groups in VRS was significant at 24 h (P:0.05). VAS results at rest and during movement were significantly better in the intermittent group at 4 and 6 h, but there was no difference in pain during coughing at any time (figs 4 and 5). There were no differences in cardiovascular variables between the groups, and there were no episodes of hypotension requiring treatment in any patient.
Discussion
Figure 1 Upper and lower level of block to pinprick in the intermittent bolus and continuous infusion groups (median). *P :0.05 between groups.
out by the nursing staff according to normal ward practice. Comparisons between groups were made using chi-square and Mann–Whitney with Bonferroni correction tests, as appropriate.
Results Eight patients were excluded from the study, two as a result of technical problems with either the extradural or the infusion pump, and six as a result of design violations by the ward nursing staff. In patients who completed the study, there were minimal differences between the two groups in patient characteristics, level of extradural catheter insertion, type of incision and duration of surgery (table 1). At the first assessment after surgery there were no differences between groups in the degree of
Extradural administration of local anaesthetic drugs provides useful analgesia after surgery, but supplementary analgesia (usually an opioid) is often required.6 This study confirms these findings, with patients in both groups reporting low pain scores while consuming moderate amounts of morphine. Median VAS pain scores were less than 30 mm in the intermittent group at all times and, although higher, were still satisfactory in the continuous group. Patient satisfaction was assessed using a four-point VRS and was greater in the intermittent bolus group (fig. 3). Previous investigators have suggested that continuous extradural local anaesthetic infusion is associated with less hypotension, less motor block and uninterrupted analgesia compared with intermittent bolus injection.7 Similar results have been obtained when extradural block was used to provide analgesia in labour.8 However, in those studies the bolus injection was administered only when the patient had developed pain and requested relief. The advantage of constant infusion techniques is that the level of block does not change acutely and the aim of this study was to see if a similarly constant block could be produced by intermittent, but regular, bolus injection. In a previous study, Scott, Schweitzer and Thorn found that this method of extradural local
Extradural bupivacaine for analgesia after lower abdominal surgery anaesthetic injection produced more predictable analgesia than continuous infusion without any increase in side effects.5 However, the injections were made by nursing staff and it was not always possible to give them frequently enough to maintain analgesia. In this study a modern electromechanical pump was used to deliver regular hourly bolus doses of bupivacaine and the findings confirm those of the earlier study. Heart rate and arterial pressure were recorded hourly by the ward staff and there was no cause for concern with either intermittent or continuous injection. However, these were relatively healthy patients who were assessed by routine clinical methods after straightforward lower abdominal surgery. A more definitive comparison of the cardiovascular effects of the two modes of extradural administration is in progress in older patients undergoing upper abdominal surgery. In both groups the sensory level of analgesia regressed progressively during the first 6 h after operation and then remained relatively stable, a feature of continuous extradural block noted previously.2 9 10 The initial regression has been ascribed to either tachyphylaxis or changes in local blood flow altering the uptake of local anaesthetic, but it is most likely that this represents regression of the larger bolus doses used for surgery. The block remained more extensive in the intermittent group and this is consistent with the latter interpretation.
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Figure 4 Visual analogue scores (VAS) at rest (median, interquartile range) in the intermittent bolus and continuous infusion groups.
Figure 5 Visual analogue scores (VAS) on movement (median, interquartile range) in the intermittent bolus and continuous infusion groups.
Figure 2 Degree of motor block (Bromage scale) in the intermittent bolus (Int.) and continuous infusion (Con.) groups. Most dense block recorded when motor block differed between legs. RR:Recovery room.
Figure 3 Verbal rating score (VRS) of overall satisfaction with pain control in the intermittent bolus (Int.) and continuous infusion (Con.) groups.
The faster bolus injection may create a higher pressure in the extradural space and cause the solution to spread further. In contrast, a low volume continuous infusion may be less likely to spread far from the extradural catheter, so that regression of block is more likely. All patients in the study received opioid analgesia in addition to extradural local anaesthetic. This was by i.v. PCA, although there may be advantage in administering the opioid extradurally with the local anaesthetic.11 One of the advantages claimed for mixtures is that reduced local anaesthetic dosage decreases the incidence of lower limb motor block. However, lower limb paralysis was minimal by 4 h in both groups (fig. 2), perhaps reflecting the level of catheter insertion as much as local anaesthetic dose. Motor block may be more of a problem with continuous lumbar extradural block after lower limb surgery. The addition of opioid to an extradural infusion also carries the risk of producing profound respiratory depression and the underlying theme of this project was to see if modification of the technique of administration produces better quality analgesia with local anaesthetic alone, and so minimize the need for opioid supplementation. PCA with morphine was used primarily to provide another method of comparing the effectiveness of the two techniques. The supervision of both extradural and PCA infusion pumps caused no practical problems, although it may be difficult to provide both in the routine clinical setting. This is one of the reasons for
10 trying to minimize opioid requirements by developing the method of extradural injection. It may seem surprising that there was little difference between the groups in morphine consumption, despite lower pain scores and better patient satisfaction with the intermittent technique, but there are two possible explanations. First, a recent study has cast doubt on the reliability of PCA as an assessment technique, noting that patients use it for reasons other than pain relief.12 Second, the aim was to provide good analgesia for all patients in the study. As a result, several patients in pain, despite the use of PCA, received supplementary bolus injections of bupivacaine from investigators who did not know which method was in use. Nineteen such injections were administered to those in the continuous group, in comparison with only three to the intermittent group and this almost certainly masked any potential increase in morphine requirement in the continuous group. An increased local anaesthetic requirement has also been shown when continuous infusion is compared with intermittent injection by patientcontrolled extradural analgesia in labour.13 We conclude that regular, intermittent extradural administration of local anaesthetic provided better quality analgesia after surgery and reduced the need for supplementary medication compared with constant infusion of local anaesthetic. This study only compared two specific injection techniques and a wide range of combinations of volume, drug concentration and infusion rate is possible. However, the results suggest that a reappraisal of intermittent injection techniques for extradural analgesia using modern devices to ensure fixed time intervals of administration is merited. Variations in the volume, concentration and time interval of injection might reduce further the need for supplementary medication and for a separate PCA device.
Acknowledgement We thank Medex Medical for providing the Medex 2001 syringe pump, and Astra Pain Control UK for financial support for L. A. D.
British Journal of Anaesthesia
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