EPIDURAL ANALGESIA FOR THE SURGICAL INDUCTION OF LABOUR

Br. J. Anaesth. (1974), 46, 747 EPIDURAL ANALGESIA FOR THE SURGICAL INDUCTION OF LABOUR N. G. CASEBY SUMMARY Surgical induction of labour was performed on 80 patients under epidural analgesia and on 73 patients without any analgesia. The difference between the two groups, with respect to the patient's assessment of discomfort, is highly significant (P<0.0001). Epidural analgesia blocked perineal skin sensation in only one case. Unilateral block occurred in 17 patients (21%) after the initial dose of bupivacaine but this was corrected by the use of an extra dose of bupivacaine and positioning of the patient. Hypotension, which occurred in 10 patients after epidural analgesia (12%), was due to caval compression in 6 patients and to sympathetic blockade in 4 patients. 22% of women find surgical induction without analgesia a painful and distressing procedure. The elective surgical induction of labour is a commonplace event in many modern labour suites. Pawson and Simmons (1970) quote a 12.7% incidence of routine surgical induction, while Macdonald (1970) induced 27% of all labours and O'Driscoll, Stronge and Minogue (1973) induced labour in 26.7% of a series of 1,000 primigravidae. The incidence of routine amniotomy in the Birmingham Maternity Hospital for 1972 was 36% out of a total of 5,000 deliveries. Whilst the majority of patients do not find the surgical induction of labour too distressing, there remains a considerable minority who approach the procedure with great apprehension and for them it becomes a major psychological ordeal. Little information is available in the medical literature regarding the provision of analgesia for amniotomy. Some patients are premedicated with narcotic analgesics or analgesic-sedative combinations (Pawson and Simmons, 1970; Patterson, 1971) and others are encouraged to inhale Entonox, trichloroethylene or methoxyflurane from the appropriate apparatus. Many are provided with no analgesia. When labour is to be conducted under continuous epidural analgesia it is logical to extend the use of the epidural block to provide analgesia for the artificial rupture of membranes as advocated by Crawford (1972a). Crawford states that "the administration of 6-8 ml 0.25% bupivacaine (Marcain) has consistently provided satisfactory NIGEL G. CASEBY, M.B., CH.B., F.F.A.R.C.S.. The United Birmingham Hospitals, Queen Elizabeth Medical Centre, Edgbaston, Birmingham, B15 2TH. analgesia for the operation", but he does not support this statement with statistical evidence. It was felt that a more critical appraisal of the efficacy of epidural block in providing satisfactory analgesia for surgical induction was indicated, and that, in addition, an assessment of the frequency of associated side effects should be made. This study also attempts to ascertain the incidence of, and some of the factors contributing to unpleasant experiences in women subjected to artificial rupture of membranes without any analgesia. PATIENTS AND METHODS Patients, selected by obstetricians for the elective surgical induction of labour, were grouped according to whether or not they were going to have continuous epidural analgesia throughout labour. Group I consisted of 80 patients who chose to have an epidural block (about 80% of the group) and those for whom the technique was indicated for medical or obstetrical reasons. In each patient a vein was cannulated and an epidural catheter was inserted, usually in the L2-L3 interspace, with the patient in the left lateral position. The catheter was introduced to a depth of 10 cm from the skin or occasionally to a depth of 15 cm in obese patients. A test dose of 2 ml of 0.5% plain lignocaine (Xylocaine) was administered. The patient then sat upright and 5 min later a standard dose of 10 ml of 0.25 % plain bupivacaine (Marcain) was injected. The patient remained sitting, and after 20 min the extent of loss of skinprick appreciation using a 21-

748 BRITISH JOURNAL OF ANAESTHESIA gauge needle was assessed and recorded. She was then placed in the lithotomy position for the operation. Shordy after the surgical induction the patient was asked to describe the procedure as "painful", "painless" or as producing "some discomfort". Meticulous recordings of maternal arterial pressure and pulse rate and foetal heart rate were made throughout the preparation for surgical induction and during the procedure itself. Readings were taken with the patient in the lateral position before the insertion of the epidural catheter, after the test dose, after sitting upright for 5 min, at 5-min intervals following the main dose of bupivacaine for at least 20 min and, lastly, after die surgical induction had been performed with the patient still in the lithotomy position. The subsequent progress of the epidural block throughout labour and delivery was recorded Group II consisted of 73 patients who either refused or were deliberately not given an epidural block. These patients, who were not given any form of analgesia, were placed in the lithotomy position for the surgical induction of labour. A few minutes after the operation each patient was asked to describe the procedure as "painful", "painless" or as producing "some discomfort". At the same time, a question was put to her: "If the surgical induction had to be repeated, would you prefer some form of pain relief next time?" Maternal arterial pressure and pulse rate and foetal heart rate were recorded before the surgical induction with the patient in the lateral position, and again immediately after the induction with the patient still in the lithotomy position. In respect of both groups additional factors were noted: the age, height, weight and parity of the patient; whether or not she had been attending relaxation classes; whether or not she had received an oral premedication of chlordiazepoxide 20 mg (Librium); the status of the obstetrical operator, and his assessment of the degree of discomfort suffered by the patient during surgical induction. A pelvic score (Bishop, 1964) was charted for each patient and this included the degree of cervical dilatation. Any symptoms or side effects occurring in the patient during surgical induction (and also during preparation for it in Group I) were recorded. RESULTS Epidural analgesia was provided for 80 patients as described. On testing for loss of skinprick appreciation 20 min after the injection of bupivacaine, a unilateral block was detected in 17 patients of whom 9 were given an extra volume of 5 ml of either 0.25 or 0.50% plain bupivacaine while in the lateral position with the unblocked side dependent. In each patient the block became bilateral, and the surgical induction was then performed. No attempt was made to alter the sensory block in the remaining 8 patients with unilateral block, and the obstetrician proceeded with the surgical induction. Efficacy of epidural analgesia (table I). Out of a total of 80 patients who were given epidural analgesia before the surgical induction (Group I), 4 patients found the operation "painful", 62 found it "painless" and 14 had "some discomfort". These figures include 8 patients with untreated unilateral block. If these patients are excluded, only 1 patient out of 72 found the operation "painful", 60 found it "painless" and 11 had "some discomfort". Of the 73 patients who had a surgical induction performed without any form of analgesia (Group II), 16 found it "painful", 13 found it "painless" and 44 had "some discomfort". TABLE I. Patient assessment of the degree of discomfort during surgical induction (percentages in brackets). No analgesia Epidural analgesia (including unilateral blocks) Epidural analgesia (excluding unilateral blocks) Painful Some discomfort Painless 16(21.9) 44(60.3) 13(17.8) 4 (5.0) 14 (17.5) 62 (77.5) 1(1.3) 11(15.3) 60(83.3) The difference in distribution between "no analgesia" and either category of epidural block is statistically significant (P < 0.0001). The application of suitable chi-squared tests, or Fisher's exact test where small frequencies made this necessary, reveals a highly significant difference with respect to the patient's assessment of discomfort in the two groups (P<0.0001). This is true whether or not the untreated unilateral block patients are included. Unilateral block. A unilateral block occurred in 17 patients in Group I (21%). In the 9 patients given an extra volume of bupivacaine the subsequent surgical induction was a "painless" procedure. In the remaining 8 patients, only 2 found the procedure

EPIDURAL ANALGESIA FOR THE SURGICAL INDUCTION OF LABOUR 749 "painless", 3 found it "painful" and 3 had "some discomfort". In 14 of the 17 patients the catheter was inserted at the L2-L3 interspace and at L1-L2 in the remaining 3. The depth of the epidural catheter from the skin was 10 cm in every case except one where it was introduced to a depth of 15 cm in a 97.5-kg patient. The catheter was always inserted whilst the patient was on her left side but the side that remained unblocked appeared to be related to the person who administered the block. One anaesthetist produced 8 unilateral blocks, all of which were of the left side. Another produced 3, all of which were of the right side. A third anaesthetist produced 4 unilateral blocks, 3 of the left side and 1 of the right. The epidural blocks in the remaining 2 patients were performed by two different operators. In the 8 patients not given an extra volume of bupivacaine for the surgical induction, bilateral spread occurred in each case following the subsequent "top-up" doses and positioning of the patient the patient lay on the "unblocked" side for the first 4-5 min after a top-up, then lay on the other side. In one patient the block regularly wore off more quickly on one side, and in all patients satisfactory analgesia was effected for both labour and delivery. In no patient was the catheter withdrawn. Side effects in the epidural group (Group I). The number of patients in Group I who had no untoward effects during the interval of about 40 min between insertion of the epidural catheter and completion of the surgical induction was 54 (67%). Some patients had multiple apparently related side effects (hypotension, nausea and faintness). All side effects were transient, the majority lasting a few minutes only and none had any detectable adverse effect on either foetus or mother. Hypotension, defined as a decrease in arterial systolic pressure of more than 10 mm Hg and occurring during the interval between an injection of bupivacaine and completion of surgical induction of labour, occurred in 10 patients (12%). When hypotension occurred the patient was placed immediately in the lateral position and this restored the arterial pressure to normal in 6 patients. Thus there was a 7% incidence of hypotension as a result of vena caval compression. The remaining 4 patients required further therapeutic measures in the form of elevation of the legs plus a rapid intravenous infusion of Hartmann's solution (0.5-1 1.) to restore the arterial pressure. No major changes in foetal heart rate occurred in any patient. On further questioning a history of supine hypotensive syndrome was elicited in one patient. Transient faintness occurred in 14 patients being associated with hypotension on ten occasions, but there was no loss of consciousness. Nine patients had nausea and one vomited. Nine complained of weakness of the legs, in four of whom this was unilateral. One patient complained of shivering and two patients experienced transient pain down one leg on insertion of the epidural catheter. Dural puncture by the catheter occurred in one case. Non-epidural patients (Group II). Of the patients who had surgical induction without analgesia 16 (22%) said that they would like some form of analgesia if the procedure had to be repeated. The patients in this group were remarkably free from side effects during surgical induction. One had hypotension and faintness because of caval compression and two others felt faint. Parity and pain at surgical induction. The differing responses to surgical induction between primigravidae and multigravidae in Group II are shown in table II. Although there is a slight preponderance of primigravidae over multigravidae in the "painful" column and the opposite in the "painless" column, the difference is not statistically significant when suitable chi-squared tests are applied. TABLE II. Patient assessment of the degree of discomfort during surgical induction of labour without analgesia with reference to parity (percentages in brackets). Primigravidae Multigravidae Painful 10 (27.8) 6 (16.2) Some discomfort 22(61.1) 22 (59.5) Painless 4(11.1) 9 (24.3) The difference between primigravidae and multigravidae is not statistically significant. DISCUSSION This study reveals that 22% of women find surgical induction of labour a painful procedure and would like the provision of some form of analgesia for it. The study also shows that epidural block can provide satisfactory analgesia for the operation. Thus it is beneficial to commence the epidural block before the surgical induction in patients who are to have

750 BRITISH JOURNAL OF ANAESTHESIA labour conducted under continuous epidural analgesia. Loss of perineal skin sensation following epidural block was detected in only one case despite the patients' sitting up for 20 min following an injection of bupivacaine. The fact that epidural block is so effective in providing analgesia for surgical induction, while not producing perineal anaesthesia, confirms the widely held belief that the painful part of the procedure is the dilatation of the cervix. It would appear that it is essential to block spinal segments Til and T12 only for effective analgesia, and that the sitting position is probably unnecessary. On the other hand, where perineal pathology exists or vaginismus is present, an effort should be made to achieve perineal anaesthesia and this will involve giving a larger dose of local anaesthetic if the lumbar approach is used. Alternately, the caudal approach can be employed. A comparison of the patients in Group II who found the surgical induction "painful" with those who found it "painless" does not reveal any factor to account for the difference in response. There is equal distribution in both subgroups of factors such as age, attendance at relaxation classes, and premedication with oral chlordiazepoxide. The corresponding average degree of cervical dilatation and the average pelvic scores in both subgroups are almost identical. The status of the operator is equally distributed. The difference in response between primigravidae and multigravidae is not statistically significant. Thus selection of patients who will probably require analgesia for surgical induction is clearly not possible. Perhaps personality factors such as neuroticism and lie score (Dalrymple, Parbrook and Steel, 1973) should have been measured. A surprisingly high incidence of unilateral block (21%) following the initial dose of bupivacaine was encountered. None of the unilateral blocks was persistent. In a retrospective analysis of 920 patients with continuous lumbar epidural analgesia, Ducrow (1971) reports an incidence of 1.5% of unilateral block after bupivacaine with adrenaline of which 0.54% remained persistent. She mentions that the catheter was inserted with the patient in the left lateral position and that there was a marked preference for the right side to remain unblocked. There was a similar tendency in this present series for the right side to remain unanaesthetized (70%), but more significant was the fact that the side remaining unblocked varied with the person who performed the epidural. The mechanism of unilateral block can be explained by the hypothesis put forward by Usubiaga, Dos Reis and Usubiaga (1970), who suggested that if the catheter tip is positioned in the ventrolateral part of the epidural space then deposition of local anaesthetic in this area, because of anterior midline trabeculations, is usually confined to that side with the subsequent development of unilateral anaesthesia. They explain that contralateral spread will occur with backfiow of local anaesthetic solution into the posterior epidural area (in which there are no trabeculations), and that this is favoured by increasing the volume of local anaesthetic, or by positioning the patient on the non-anaesthetized side, or by withdrawing the catheter a few centimetres into the posterior epidural area. The fact that each of the 17 patients with unilateral block in the present study developed bilateral spread following subsequent doses of bupivacaine and positioning is in keeping with the hypothesis. The observation that the unblocked side in this study varied with the operator is presumably due to individual variations in technique. The epidural needle is probably slightly angulated to one side of the midline when the catheter is introduced, the side varying with the operator. The existence of such a high incidence of unilateral block in this study emphasizes the need for routine testing for pinprick skin analgesia before proceeding to surgical induction. Hypotension occurred in 12% of patients who had surgical induction under epidural analgesia and was due to caval compression in 7% and to sympathetic blockade in 5%. Crawford (1972b), who defines hypotension as a fall of systolic blood pressure in excess of 10 mm Hg occurring within 20 min of the injection of a dose of bupivacaine, quotes an incidence of 1.4% of hypotension occurring in almost 6,000 top-up doses and states that caval occlusion contributed to most. The higher incidence in the present study can be rationalized on two accounts. Firstly, the lithotomy position predisposed the patient to caval compression as half of the patients were in this position when hypotension occurred. Secondly, it must be emphasized that the initial response to a moderately large dose of bupivacaine is recorded in this study. After realizing that a patient was susceptible to hypotension and after intravenous fluids had been

EPIDURAL ANALGESIA FOR THE SURGICAL INDUCTION OF LABOUR 751 given where necessary, subsequent top-up doses resulted in few problems. Indeed, further hypotension in these patients was conspicuous by its absence. Complete analgesia for surgical induction was achieved in 77% of all patients having epidural block. Failure to provide absolute analgesia for the operation can be accounted for by unilateral block in 6 patients and by failure to block spinal segments Til or T12 completely in 4 patients; 1 patient had a very tender perineum; and 2 patients were extremely apprehensive. There remain 5 patients (6.25%) complaining of "some discomfort" for which no rational explanation can be found. One can only speculate that these patients may have an additional cervical innervation via the parasympathetic nervi erigentes as suggested by Moir (1971) when considering the sensory nerve supply of the birth canal, or that the discomfort arose from the lower birth canal. ACKNOWLEDGEMENTS I am most grateful to Dr J. S. Crawford for his advice and encouragement. I would also like to thank the nurses and obstetricians of the Birmingham Maternity Hospital who co-operated in the study; Dr K. J. Banton, Dr E. Evans and Dr S. Hylton who performed some of the epidural blocks; and Dr P. Davies, Department of Mathematical Statistics of the University of Birmingham, who analysed the data. REFERENCES Bishop, E. H. (1964). Pelvic scoring for elective induction. Obstet. Gynecol, 24, 266. Crawford, J. S. (1972a). Principles and Practice of Obstetric Anaesthesia, 3rd edn, p. 125. Oxford: Blackwell. (1972b). The second thousand epidural blocks in an obstetric hospital practice. Br. J. Anaesth., 44, 1277. Dalrymple, D. G., Parbrook, G. D., and Steel, D. F. (1973). Factors predisposing to postoperative pain and pulmonary complications: a study of female patients undergoing elective cholecystectomy. Br. J. Anaesth., 45, 589. Ducrow, M. (1971). The occurrence of unblocked segments during continuous lumbar epidural analgesia for pain relief in labour. Br. J. Anaesth., 43, 1172. Macdonald, D. (1970). Surgical induction of labor. Am. J. Obstet. Gynecol, 107, 908. Moir, D. D. (1971). Recent advances in pain relief in childbirth. II: Regional anaesthesia. Br. J. Anaesth., 43, 849. O'Driscoll, K., Stronge, J. M., and Minogue, M. (1973). Active management of labour. Br. Med. J., 3, 135. Patterson, W. M. (1971). Amniotomy, with or without simultaneous oxytocin infusion. J. Obstet. Gynaecol. Br. Commonw., 78, 310. Pawson, M. E., and Simmons, S. C. (1970). Routine induction of labour by amniotomy and simultaneous syntocinon (synthetic oxytocin) infusion. Br. Med. J., 3, 191. Usubiaga, J. E., Dos Reis, A. jr, and Usubiaga, L. E. (1970). Epidural misplacement of catheters and mechanisms of unilateral blockade. Anesthesiology, 32, 158.