1 Department of Obstetric Anaesthesia, St James' University Hospital, Leeds, UK. 2 Intensive Care Unit, South Manchester University Hospital, Wythenshawe, UK
* Corresponding author. E-mail: nik_lucy{at}hotmail.com
Accepted for publication March 6, 2005.
![]() |
Abstract |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Method. Eighty ASA I and II women of at least 37 weeks gestation and planned for elective Caesarean section under combined spinalepidural anaesthesia were recruited. They were randomized into two groups to receive intrathecal hyperbaric bupivacaine 0.5% at an initial dose of 13 mg, with the next dose determined by the response of the previous patient (dose interval 1 mg). One group also received diamorphine 400 µg intrathecally. If a block height of T5 to blunt light touch had been achieved after 20 min, the block was deemed effective. A difference in the ED50 for hyperbaric bupivacaine between the groups would indicate that diamorphine influenced block height. Intraoperative patient discomfort and need for analgesic supplementation was noted.
Results. The median effective dose (ED50) to achieve a T5 block to light touch for Caesarean section using hyperbaric bupivacaine 0.5% was 9.95 mg [95% confidence interval (CI) 9.010.90] and with the addition of diamorphine it was 9.3 mg (95% CI 8.1510.40), while the ED95 was 13.55 mg (95% CI 10.1017.0) and 13.6 mg (95% CI 9.1518.05), respectively. Five women who had received intrathecal diamorphine and 13 who had not received diamorphine needed intraoperative supplementation (not significant).
Conclusion. The addition of intrathecal diamorphine does not appear to influence block height.
Keywords: anaesthetic techniques, epidural ; anaesthetics, local, bupivacaine ; analgesics, opioid, diamorphine ; surgery, Caesarian section
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
Method |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Technique
Patients were randomized according to a computer-generated code (Microsoft MS Excel, Richmond, VA, USA) into two groups. The anaesthetic management of the women was standardized. Premedication consisted of lansoprazole 30 mg given orally at least 90 min before the operation, and 30 ml of 0.3 M sodium citrate in the anaesthetic room. Standard maternal monitoring included continuous electrocardiography, pulse oximetry and non-invasive blood pressure monitoring (Philips, Boeblingen, Germany). An infusion of saline 0.9% (500 ml) was administered via a 16 gauge intravenous cannula over approximately 15 min. A two-space combined spinalepidural technique was used. An epidural catheter was placed in the second lumbar interspace in the sitting position using an 18 gauge Tuohy needle and loss of resistance to saline. No test dose was given. Spinal anaesthesia was performed via the third lumbar interspace using a 27 gauge Whitacre spinal needle. All the patients were given hyperbaric bupivacaine intrathecally at the predetermined dose.
Women in Group 1 received intrathecal hyperbaric bupivacaine 0.5% (AstraZeneca) with diamorphine 400 µg (Evans Vaccine Limited) dissolved in 0.4 ml saline 0.9%.3 The initial dose of hyperbaric bupivacaine was 2.6 ml (13 mg). Subsequently the dose of hyperbaric bupivacaine depended on the response of the previous woman in terms of block height. Group 2 was the same as Group 1, except that 0.4 ml of saline 0.9% was substituted for the diamorphine solution.
After the procedure, the women were helped to lie supine with a 715° left lateral tilt.9 Ephedrine 30 mg in 500 ml of saline 0.9% was connected to the intravenous cannula and titrated against the mean arterial blood pressure to keep it >80% of the baseline recording. This was measured using a non-invasive blood pressure monitoring machine (Philips, Boeblingen, Germany) at 5-min intervals. Three outcomes were possible: effective, ineffective and repeat.
In the effective outcome, anaesthesia (loss of blunt light touch sensation) reached the T5 level (between the xiphisternum and the nipple line) or higher bilaterally. This indicates the end of the study and directs a reduction in the local anaesthetic dose by 1 mg (0.2 ml) for the next woman in that group.
In the ineffective outcome, if the level of anaesthesia had failed to reach T5 after 20 min, rescue anaesthesia using increments of plain bupivacaine 0.5% (AstraZeneca) was administered into the epidural space until a level of T5 anaesthesia was achieved. The study ends and directs an increase in intrathecal local anaesthetic dose for the next woman in that group.
In the repeat outcome, a successful dural puncture and subsequent intrathecal injection was defined as visible cerebrospinal fluid at the hub of the spinal needle and the ability to aspirate it freely before and after intrathecal injection of the anaesthetic. Failure to achieve this indicated a failure of technique. The woman was withdrawn from the study and managed according to our established practice for failed spinal. In terms of the study, withdrawal of a patient because of technical failure or protocol violation required that the same local anaesthetic dose be repeated for the next woman in that group.
Women were encouraged to report any episodes of discomfort during the procedure. If this occurred, supplementary analgesia was offered either intravenously or epidurally, or both. At the delivery of the baby, 10 IU of oxytocin was given slowly intravenously, and an umbilical cord blood sample was taken for gas analysis. The placebo group, who had not received intrathecal diamorphine, were given diamorphine 3 mg in 10 ml of saline 0.9% via the epidural catheter, while the remainder were given 10 ml of saline 0.9%. All patients who had consented to rectal diclofenac were given 100 mg at the end of the operation. The procedure was timed from skin incision to the last abdominal suture. All women were observed in the postanaesthetic care unit on the delivery suite for a period of 23 h, and then on a general postnatal ward with monitoring of vital signs as for any other routine operation. A combination of oral paracetamol 1 g with codeine phosphate 60 mg every 4 h, to a maximum of four times in 24 h, and diclofenac 50 mg every 8 h, to a maximum of 150 mg in 24 h, was given for analgesia.
A researcher, who played no clinical role in the anaesthetic, prepared the syringes under sterile conditions. The syringes used for intrathecal injection were made up to a fixed volume of 0.4 ml, while those for epidural use were at a fixed volume of 10 ml. All observations were made by an independent anaesthetist, who was blinded as to what was in the additional syringes used either intrathecally or epidurally. It was not possible to disguise syringe volume.
Age, height, weight, parity, gestation and duration of procedure were recorded. After intrathecal injection of bupivacaine with or without diamorphine, the following were recorded: intraoperative analgesic supplementation, number of women who experienced mean arterial pressure <80% baseline and umbilical blood gas analysis.
Statistical analysis
A previous study confirmed that 15 mg of hyperbaric bupivacaine will produce anaesthesia to the T5 level to pinprick in 62% of parturients.10 The standard deviation was 3.33 mg and, assuming 3 mg as the minimum clinically significant difference between the groups, we required 40 women per group to give the study a power of more than 0.8.
Patient and obstetric data were collected and presented as mean (SD) and median (interquartile range) and compared using Student's t-test, the MannWhitney U-test and Fisher's exact test as appropriate. The median effective doses (ED50) were estimated from the updown sequences using the Dixon and Massey formula, which enabled mean local anaesthetic dose with 95% confidence intervals (95% CI) to be derived.11 The ED95 was derived using doseresponse curves. The results were subjected to Wilcoxon and Litchfield probit analysis as a test of sensitivity.
Block height data were presented as median (interquartile range) and compared using Student's t-test and the MannWhitney U-test. They were subjected to robust regression using Huber's method.
The software used was MS Microsoft Excel XP (Richmond, VA, USA) and SPSS version 10.0 (SPSS, Chicago, IL, USA). The PC hardware was from Delfino, Leeds, UK.
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
|
|
|
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Opioid analgesics have been shown to influence block height, but only in relation to block regression. Several studies have shown the benefits of opiate analgesics in prolonging sensory blocks when given by a variety of routes.8 12 13 Intrathecal fentanyl can prolong a sensory block to pinprick,8 12 and Henderson and colleagues13 showed that intravenous diamorphine, when given after prostatectomy under spinal anaesthesia, halted the regression of sensory block level to cold sensation. These studies also showed that there was no effect on motor block. It appears that when diamorphine is given systemically, or fentanyl is given intrathecally, it is possible to detect changes in A (pinprick) and C nerve fibres (cold), but this is only apparent during block regression. They appear to have no effect on A
fibres which control muscle function. In contrast, Gormley and colleagues14 showed that alfentanil, added to lidocaine for axillary brachial plexus anaesthesia prolonged both the sensory block to pinprick and motor block. Whether the alfentanil is acting systemically or locally is not known.
The precise mechanism for slowing of sensory block regression is unclear, but three possibilities have been proposed.13 Morphine is known to reduce spinal blood flow, and this would slow the rate of local anaesthetic absorption and thus prolong block duration. Modulation of central transmission of sensory input at a supraspinal level (in the substantia gelatinosa), where there is opioid receptor stimulation, may alter appreciation of peripheral stimuli. The opioid analgesics may have altered the recognition of peripheral sensation by an effect on conscious level.
We also know that narcotics improve intraoperative comfort for the patient3 8 when given intrathecally for Caesarean section. This can be assessed with intraoperative visual analogue pain scores and bupivacaine-sparing effects.
Åkerman and colleagues15 investigated the addition of morphine spinally in an animal model, and showed that morphine combined with bupivacaine or lidocaine produced significantly greater antinociceptive effects than when morphine or the local anaesthetic was injected alone. There was still an enhanced effect even when the morphine dose was sub-therapeutic. They proposed that there was a synergistic action with local anaesthetic that potentiated the analgesic effects of morphine, the precise mechanisms of which are still unknown. The addition of intrathecal diamorphine will improve intraoperative comfort at Caesarean section,3 and in the same role fentanyl has also been shown to have bupivacaine-sparing effects.8 Although there was a dose reduction, there was little effect on block height. Fentanyl might be expected to differ from diamorphine because of its weak local anaesthetic action,6 7 but an orthopaedic lower limb study suggests that this is not the case.16 It is not clear whether fentanyl is narcotic or local anaesthetic based. For a block of a given height, the addition of a narcotic will improve comfort compared with pure local anaesthetic without necessarily producing a change in block height. Intrathecal narcotics are more effective at C-fibre blockade,17 and any difference of this nature would not have been detected by a test of block height to light touch that is probably closer to the Aß fibre.18
Amongst other weaknesses of our study design is the subjective nature of the determination of block height. We used blunt light touch to T5 to assess whether the block was effective. Assessing with blunt light touch has been shown to improve the chance of a pain-free Caesarean section.4 The T5 dermatome is the upper level of entry into the spinal cord of the greater splanchnic nerve, which innervates the peritoneum covering the uterus.19 Every precaution was taken to make sure block height was accurately determined using a neurotip (Owen Mumford) and, although subjective influences must be acknowledged, all researchers used the definition of the T5 dermatome as between the xiphisternum and the nipple line. There is no proven best method of assessing blunt light touch. By using a large number of patients in each group any subjective influences would be spread equally and so suppress the problem.
Although the anaesthetist performing the spinal block was blind to the dose of hyperbaric bupivacaine 0.5% used, and to the use of intrathecal or epidural diamorphine, we were unable to blind the anaesthetist to the actual volume of local anaesthetic used. This was a potential source of bias when assessing the block, but only if recognized and if the anaesthetist knew which group the patient was in. The sequential difference within each group was 0.2 ml, which was too small to be a problem. In addition, only the researcher knew the full order of sequences in each limb of the study until it was complete.
Our study established that the ED50 for hyperbaric bupivacaine 0.5% with and without 400 µg diamorphine was clinically and statistically insignificant. We conclude that intrathecal diamorphine provides no benefit on block height for Caesarean section. The clinical significance of this is that the addition of diamorphine does not permit any reduction in hyperbaric bupivacaine dose that might threaten the goal of T5 for block height.
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
2 Geranscher JC, Floyd H, Eisenach J. Determination of an effective dose of intrathecal morphine for pain relief after Caesarean delivery. Anesth Analges 1999; 88: 34651
3 Saravanan S, Robinson APC, Dar AQ, Columb M, Lyons GR. Minimum dose of intrathecal diamorphine required to prevent intraoperative supplementation of spinal anaesthesia for Caesarean section. Br J Anaesth 2003; 91: 36872
4 Russell IF. Levels of anaesthesia and intra-operative pain at Caesarean section under regional block. Int J Obstet Anesth 1995; 4: 717[CrossRef][Medline]
5 Aitkenhead A. The pattern of litigation against anaesthetists. Br J Anaesth 1994; 73: 1021[ISI][Medline]
6 Power I, Brown DT, Wildsmith JA. The effect of fentanyl, meperidine and diamorphine on nerve conduction in vitro. Reg Anesth 1991; 16: 2048[ISI][Medline]
7 Gissen AJ, Gugino LD, Datta S, Miller J, Covino BG. Effects of fentanyl and sufentanil on peripheral mammalian nerves. Anesth Analges 1987; 66: 12726[Abstract]
8 Choi DH, Ahn HJ, Kim MH. Bupivacaine sparing effect of fentanyl in spinal anesthesia for Caesarean section. Reg Anesth Pain Med 2000; 25: 2405[CrossRef][ISI][Medline]
9 Jones SJ, Kinsella SM, Donald FA. Comparison of measured and estimated angles of table tilt at Caesarean section. Br J Anaesth 2003; 90: 867
10 Norris MC. Patient variables and the subarachnoid spread of hyperbaric bupivacaine in the term parturient. Anesthesiology 1990; 72: 478[ISI][Medline]
11 Dixon WJ, Massey FJ. Introduction to Statistical Analysis, 4th edn. Boston, MA: McGraw-Hill, 1983; 42641
12 Singh H, Yang J, Thornton K, Giesecke AH. Intrathecal fentanyl prolongs sensory bupivacaine spinal block. Can J Anesth 1995; 42: 98791.[Abstract]
13 Henderson DJ, Jones G. Effect of IV diamorphine on the regression of spinal block. Br J Anaesth 1995; 74: 61011
14 Gormley WP, Murray JM, Fee JPH, Bower S. Effect of the addition of alfentanil to lignocaine during axillary brachial plexus anaesthesia. Br J Anaesth 1996; 76: 8025
15 Åkerman B, Arweström W, Post C. Local anesthetics potentiate spinal morphine antinociception. Anesth Analges 1988; 67: 9438[Abstract]
16 Patterson L, Avery N, Chan P, Parlow JL. The addition of fentanyl does not alter the extent of spread of intrathecal isobaric bupivacaine in clinical practice. Can J Anesth 2001; 48: 76872
17 Sosnowski M, Yaksh TL. Spinal administration of receptor-selective drugs as analgesics: new horizons. J Pain Symptom Manage 1990; 5: 20413[CrossRef][Medline]
18 Liu S, Kopacz DJ, Carpenter RL. Quantitative assessment of differential sensory nerve block after lidocaine spinal anesthesia. Anesthesiology 1995; 82: 603[CrossRef][ISI][Medline]
19 Snell RS. The thorax: Part II. The thoracic cavity. In: Clinical Anatomy for Medical Students, 4th edn. Boston, MA: Little, Brown, 1992; 1245
|