A SIMPLE SAFE METHOD FOR CONTINUOUS INFUSION EPIDURAL ANALGESIA IN OBSTETRICS A.O. DAVIES AND I.W. FETTES ABSTRACT Continuous infusion epidural anaesthesia may reduce the risks of hypotension, high spinal block and intravenous injection associated with repeated bolus injections. However, controlling the rate of a simple infusion is difficult and infusion pumps are expensive and bulky. We describe a method for continuous infusion epidural anesthesia using a 6ml/hr capillary infusion device (lntraflo CFS-06F Sorenson Research Co., Salt Lake City, Utah) and bupivicaine 0.25 per cent. In a study of 50 patients, 35 (70 per cent) had adequate pain relief with the infusion alone for a mean time untildelivery of 5 hours (range 2 to 13 hours). A further I I patients (22 per cent) required only one top-up for the second stage of labour after a mean pain-free time of 5.4 hours (range 1.5 to 9.7 hours). There were no maternal or foetal complications related to the technique of continuous infusion used. No block went higher than the ninth thoracic dermatome at any time. KEY WORDS: ANAESTHESIA, obstetrical; ANAESTHESIA TECHNIQUES, epidural, continuous infusion. THE FIRST EPIDURAL ANAESTHETIC may have fast or too slow. 4 Patients have even attempted to been administered by James Coming in 18857 In adjust their own drips, leading to excessive the intervening 95 years, the practice of epidural block, s The use of a mechanical infusion pump ''6 anaesthesia has become widespread, especially solves some of these problems, but the pumps are in obstetrics. expensive, bulky and may break down. The flow For long term use, the common technique is rate may also be increased inadvertently. repeated bolus injection through an epidural We felt that a capillary tube device (lntraflo, catheter. Thc bolus injections all carry some CFS-06F, Sorenson Research Co., Salt Lake risks. Sudden increases in sympathetic block can City, Utah) designed to deliver a constant slow summate with aorto-caval compression to pro- flow infusion of 5-7 ml/hr could be adopted for duce maternal hypotension and foetal distress. use in continuous infusion epidural anaesthesia, Bolus injection of local anaesthetic intrathecally since we found that we were using about 12 ml of may produce "total spinal" anaesthesia with bupivicaine 0.25 per cent injected every two hypotension and apnoea leading to loss of con- hours. The technique requires inexpensive, sciousness. A large volume of drug injected into readily available, disposible equipment and the an epidural vein can cause systemic toxicity due chance of accidental overdose is negligible. A to high blood levels manifested by convulsions, preliminary study confirmed that the Intraflo de- coma, or circulatory collapse. vices did deliver between 5 and 7 ml/hr of fluid Therefore slow continuous infusion of local when the pressure infusion bags were inflated to anaesthetic through the epidural catheter follow- 300 torr. ing an initial bolus injection, as first described by We therefore designed a study to ascertain Dawkins, z is theoretically safer 3 than intermit- whether our technique was effective in practice, tent injection and can provide more consistent and institutional approval was obtained. pain relief. However, using gravity drip alone may result METHODS AND MATERIALS in flow rates that vary with time and become too Informed consent was obtained from each of a A.O. Davies, M.D., F.R.C.P.(C), StaffAnaesthetist; series of 50 consecutive patients admitted to the I.W. Fettes, M.B., Ch.B., F.R.C.P.(C), Anaesthetist- delivery suite who wished to have an epidural in-Chief; North Bay Civic and St. Joseph's General anaesthetic and whose labour was likely to last Hospitals. more than three hours. The epidurals were com- From The Department of Anaesthesia, St. Joseph's menced when cervical dilatation was 3 to 5 cm. General Hospital, 720 McLaren Street, North Bay, Ontario, Canada. After an intravenous infusion of at least 500 ml 484 Canad. Anaesth. Soc. J., vol. 28, no. 5, September 1981 DAVIES & FETTES. METHOD FOR CONTINUOUS INFUSION 485 of crystalloid solution, epidural anaesthesia was induced with the patient in the left lateral decu- bitus position, using a # 16 Touhy needle in the L3-4 interspace. A Portex epidural catheter was d advanced 2 to 4 cm into the epidural space. After negative aspiration for cerebrospinal fluid or blood, a test dose of 2 to 3 ml of bupivicaine 0.25 per cent was given and, if there were no untoward sequelae, l0 ml of bupivicaine 0.25 per cent was injected. After securing the catheter to the skin, ,O the patient was then turned onto her right side and the blood pressure was checked every 5 minutes for 20 minutes. MILL.IPORE FILTER ., ' ' During this period 10ml of normal saline was removed fi'om a 50 ml polyvinylchloride (P.V.C.) / -FLUS,SVSTtM \ -- - intravenous solution bag and 40 ml of bupivicaine 0.5 per cent was added, using sterile precau- tions, to give a total of 80 ml of bupivicaine 0.25 per cent. This was run through a standard intra- venous infusion set and the P.V.C. bag was then inserted next to the bladder of a pneumatic blood infusion pump which was inflated to 300tort. An Intraflo device (CFS-06F, Sorenson Research FIGURE I The setup of blood infusion pump, Company, Salt Lake City, Utah) designed to Intraflo, and epidural catheter. Note the red rubber deliver 5-7 ml/hr was attached to the intravenous bypass valve has been cut off the lntraflo Io prevent excessive flow rate. infusion set. After filling the dead space of the lntraflo, the red rubber bypass valve was cut off the episiotomy and the patient was satisfied with to prevent any bypass of the capillary tube. The the block at the post-partum interview. The Intraflo device, which incorporates a micropore epidural was a failure if the patient was dissatis- bacteriological filter, was then attached to the fied with the pain relief or needed other analge- epidural catheter as illustrated in Figure I. sics for labour and delivery. To check that the Intraflo was functioning Only two patients in this series went on to normally, the drip rate from the intravenous in- Caesarian Section and their perineal analgesia fusion set was observed to ensure that it was was assessed before injecting additional bupivi- about 6 microdrops/min or 1 big drop/min. caine to allow intra-abdominal surgery. Twenty minutes after the injection, the upper level of analgesia on each side was determined. RESULTS The patients were encouraged to spend approxi- mately equal lengths of time on their right and left The volume of local anaesthetic used for these sides. Their blood pressures and levels of epid- patients was noted, and the flow rates produced ural block were assessed every thirty minutes. by the Introflo in this clinical study were in the The pressure bag was kept inflated to 300 tort. range expected (between 5 and 7 ml/hr). If there was any question of the location of the The quality and duration of analgesia with the catheter, aspiration could be accomplished by continuous infusion is reported in Table 1. This attaching a syringe to the transducer port of the shows that thirty-five patients (70 per cent) Intraflo. Similarly, additional local anaesthetic needed only the initial injection and the continu- could be injected through the same site, if neces- ous infusion for labour and delivery with a mean sary. pain-free duration of 5 hours (range 2 to 13 On the day following delivery, the patients hours). A further I I patients (22 percent) needed were reassessed to determine the subjective only one top-up for the second stage, so that 92 effectiveness of the epidural block. This was per cent of patients had adequate analgesia with, scored as complete if the patient felt no pain from at most, one top-up. the time of insertion of the epidural. The block The two failed epidural blocks in this series was adequate if the patient felt some discomfort included one single nerve root block and one at delivery but did not need other analgesics for block which was initially successful but which 486 CANADIAN ANAESTHETISTS' SOCIETY JOURNAL TABLE I QUALITY OF ANALGESIAWITH CONTINUOUS[NFUSION EPIDURAL Duration (hr) before Supplement Duration to Necessary Delivery (hr) Result Number Per cent Mean Range Mean Range 1. Complete Analgesia - with infusion alone 26 52 -- -- 5.2 2-13 2. Adequate Analgesia - with infusion alone 9 18 -- -- 4.7 2.5-7.5 - one top-up for delivery II 22 5.4 1.5-9.7 -- -- - more than one top-up 2 4 8 7-9 -- -- 3. Failure of Analgesia 2 4 .... could not be reinforced thereafter by any the level of block would be expected, since method. 10-15 mg of isobaric bupivicaine have been used Only four patients (8 per cent) needed addi- for spinal anaesthesia. 7 tions to the original bolus to achieve complete If an obstetrical nurse is concerned about any analgesia. Twenty minutes after the initial dose, feature of the infusion, he or she has only to turn 17 per cent of the blocks were at TI2 level, 43 per it off and call the anaesthetist to assess the cent at TI 1 level, 32 per cent at T[0, and 7 per situation. The bypass valve of the Intraflo was cent at Tg. During the continuous infusion, 24 per cut off in this study as a safety precaution. cent of blocks increased one or two segments, 45 However, even if this is pulled out on purpose, per cent stayed the same and 30 per cent dropped only 1 to 3ml/min flow through the device, one or two segments.