Postoperative Analgesia After Lumbar Laminectomy

Epidural Fentanyl Infusion Versus Patient-Controlled Intravenous Morphine

Abstract

We compared the efficacy and safety of continuous epidural fentanyl infusion with intravenous morphine via a patient-controlled analgesia system (IV-PCA) in the management of postoperative pain after lumbar laminectomy. Twenty patients undergoing elective lumbar laminectomy were randomly allocated to one of two groups. The epidural group (n = 10) received an epidural fentanyl infusion (2 micro gram/mL at 4-10 mL/h) while the IV-PCA group (n = 10) received IV morphine through a PCA system. The general anesthetic technique was standardized. Visual analog pain scores were recorded at 12, 24, and 48 h after the operation. The amount of morphine (or its equivalent in fentanyl) used over the 48-h postoperative period was documented. The postoperative pain scores were significantly lower in the epidural group than in the IV-PCA group throughout the study period. The total consumption of morphine (or its fentanyl equivalent) over the 48-h period was significantly lower (P < 0.001) in the epidural group compared to the IV-PCA group. Although more patients in the IV-PCA group required urinary catheterization and had somnolence than the epidural group, there was no difference in the incidence of vomiting or pruritus. No patient developed respiratory depression or wound infection. We conclude that continuous epidural infusion of fentanyl is superior to IV-PCA morphine in the management of pain after lumbar laminectomy.

(Anesth Analg 1995;80:511-4)

In recent years, the management of postoperative pain has improved with the use of continuous epidural analgesia and intravenous patient-controlled analgesia (IV-PCA). Both epidural opioids and IV-PCA opioids provide effective postoperative analgesia and their use has become widespread in the past decade ^[1,2]. Patients undergoing lumbar laminectomy (LL) experience severe pain in the postoperative period which may increase postoperative morbidity and complications. Pain after LL is usually treated with intramuscular or IV-PCA opioids.

The degree of postoperative analgesia achieved with epidural opioids is superior to that achieved by intramuscular and IV-PCA opioids ^[3-5]. However, placement of an epidural catheter after LL raises the concerns of increased infection and absorption of drugs from the surgical site. We, therefore, designed a randomized study to compare the efficacy and safety of opioids administered by continuous epidural infusion and IV-PCA in providing analgesia after LL.

Methods

After Institutional Ethical Committee approval and informed consent, 20 (ASA physical status I or II) patients scheduled for elective multilevel LL were studied at the Cappagh Orthopaedic Hospital, Dublin, Ireland. Patients with previous back surgeries and receiving opioid analgesic medications in the preoperative period were excluded. In each case, the surgery was performed by the same surgeon. Patients were randomly assigned, using a computer-generated random number sequence, to receive either continuous epidural fentanyl infusion (Group E) or IV-PCA morphine (Group P) for postoperative analgesia.

Prior to premedication, all patients were instructed in the use of the 10-cm visual analog scale (VAS) with zero and 10 labeled as "no pain" and "worst pain imaginable," respectively, and a baseline VAS pain score was recorded. Patients were premedicated with 0.15 mg/kg diazepam orally 2 h before the surgery. A standardized, general anesthetic protocol was followed. General anesthesia was induced with IV fentanyl (1 micro gram/kg) and thiopentone (3-5 mg/kg). Tracheal intubation was facilitated by vecuronium, and ventilation was controlled. Anesthesia was maintained with isoflurane (1%-1.5%) in a mixture of 70% N₂ O in oxygen. Supplemental doses of IV fentanyl (25-50 micro gram) were administered as required. Usual monitoring was used. Residual paralysis at the end of the surgery, as detected by a nerve stimulator, was reversed with IV neostigmine and glycopyrrolate.

In Group E, after surgery but before the closure of the surgical incision, the surgeon passed a Tuohy needle through the skin approximately 2-3 cm caudad to the incision and positioned the tip under direct vision into the epidural space in the middle of the surgical field. An epidural catheter (18-gauge, multiple pore) was threaded through the Tuohy needle and placed under direct vision in the exposed epidural space and the needle was removed. The surgical wound was then closed after ensuring that the field was dry and the catheter was not in the subarachnoid space. After this, 10 mL fentanyl (2 micro gram/mL) was injected through the epidural catheter.

In the recovery room, patients were given IV morphine (2-5 mg every 5 min) until they were pain free. After this initial dose either an epidural infusion of fentanyl (2 micro gram/mL at 4-10 mL/h; Group E) or IV-PCA morphine (Group P) was started. In Group P, patients were able to self-administer 1 mg of morphine every 6 min (lockout time). If analgesia was inadequate the incremental dose was increased to 1.5 mg and/or lockout time decreased to 5 min. The epidural and PCA adjustments were made by the nurse taking care of the patient. Total consumption of opioid was also recorded at these times and the total amount of fentanyl used was converted to analgesic equivalents of morphine (1 mg of morphine is equivalent to 10 micro gram of fentanyl). The incidence of side effects, such as vomiting, pruritus, urinary retention, excessive somnolence (asleep with difficulty in responding to verbal commands), and respiratory depression were recorded. Postoperative pain was evaluated using a VAS scale at 12, 24, and 48 h after the surgery. The site of the catheter insertion was examined daily for signs of infection. The epidural catheter was removed 48-72 h after the surgery.

Results are expressed as mean +/- SD. Demographic data and analgesic requirements were analyzed using the unpaired t-test. Comparison of pain scores was performed using the Mann-Whitney U-test. A P value of less than 0.05 was considered statistically significant.

Results

The two groups were similar with respect to age, weight, baseline pain scores, amount of fentanyl used intraoperatively, and duration of anesthesia Table 1. The intraoperative course in all patients was uneventful, and at no point was the subarachnoid space breached during the surgery. The postoperative pain scores were lower in Group E as compared to Group P throughout the study period Figure 1. The total consumption of morphine over the 48-h study period (this includes the morphine used in the recovery room) was significantly higher (P < 0.001) in Group P (mean 182.4 +/- 26.2 mg) as compared to the morphine equivalent of fentanyl used in Group E (mean 58.4 +/- 16.1 mg). No patient developed respiratory depression or infection at the catheter site. There was no difference between the two groups with regard to vomiting or pruritus Table 2.

Table 1: Demographic and Clinical Data of Patients Undergoing Lumbar Laminectomy

Figure 1: Visual analog pain scores (VAS) (mean +/- SD) after the lumbar laminectomy. fill square Epidural group; open square intravenous patientcontrolled analgesia (IV-PCA) group. *P < 0.05.

Table 2: Incidence of Opioid-Related Adverse Effects in the Two Study Groups

Discussion

We have demonstrated that epidural fentanyl infusion provides greater analgesia after LL with fewer side effects than IV-PCA morphine. The catheter placed under direct vision should prevent inadvertent subarachnoid placement and also decrease the possibility of neurologic damage.

Direct application of 3 mg morphine to the dura before the closure of the laminectomy wound has been shown to provide superior postoperative analgesia for 12-24 h, as compared to conventional intramuscular opioid analgesics ^[6]. In similar studies, a single injection of morphine injected either before or after the closure of the laminectomy wound, through a catheter placed in the epidural space and then withdrawn, provided excellent analgesia after spinal surgery ^[7,8].

A retrospective study by Ozuna et al. ^[9] compared the analgesic efficacy of intermittent injections of epidural morphine with conventional intramuscular and oral analgesics. Patients receiving epidural morphine required fewer parenteral and oral analgesics. Similarly, in an uncontrolled study Ray and Bagley ^[10] reported excellent analgesia with intermittent injections of morphine through an indwelling epidural catheter. Continuous epidural opioid infusion has not been compared previously with IV-PCA opioid administration for the management of postlaminectomy pain.

In contrast to previous studies, we used epidural fentanyl because lipophilic opioids such as fentanyl provide a rapid onset of analgesia and decrease the incidence of severe respiratory depression ^[11]. Furthermore, the incidence of nausea, vomiting, and pruritus are also lower with the use of epidural fentanyl as compared to epidural morphine ^[12]. The high lipid solubility of fentanyl leads to increased systemic uptake and limited ability to spread within the cerebrospinal fluid. Thus, the analgesic effects of epidural fentanyl are reported to be mediated by systemic absorption ^[13]. However, placement of the epidural catheter in the area of maximum nociceptive input should decrease the requirements of fentanyl.

It is alleged that epidural infusions of combinations of opioids and low-dose local anesthetics are more effective than either drug alone and thus have become increasingly popular ^[14]. However, we did not combine a local anesthetic with fentanyl because the former occasionally produce undesirable effects such as numbness and motor weakness which may interfere with the evaluation of occasional temporary numbness and weakness that may occur during the first 24-48 h after lumbar spine surgery ^[10]. Furthermore, despite the alleged synergy between opioids and local anesthetics clinical studies often have failed to demonstrate a benefit of adding bupivacaine to fentanyl ^[15]. In addition, there is the concern of increased systemic toxicity of local anesthetics because of increased absorption from the raw surgical surface.

In accordance with Ray and Bagley ^[10], we passed the epidural catheter cephalad, because the direction of the catheter tip in the epidural space influences the cephalad spread of analgesics with the catheters in the cephalad direction requiring significantly less volume than the catheters in the caudad direction ^[16].

Although epidural opioids are effective for postoperative pain relief, these are not without an element of risk and side effects, such as nausea, vomiting, pruritus, urinary retention, and respiratory depression ^[17,18]. Respiratory depression, although rare, may be severe and requires vigilance and monitoring in the postoperative period ^[19]. The incidence of respiratory insufficiency has been reported to be between 1.9% and 2.3% ^[18]. Thus, there is concern that epidural opioids may not be the standard of care because of the cost of postoperative monitoring. However, postoperative pain can be safely and effectively treated with epidural opioids on surgical wards without expensive monitoring ^[20].

Intramuscular or IV-PCA opioids are currently used techniques to treat pain after LL. Compared to opioids given intramuscularly, IV-PCA provides better analgesia with lower opioid requirements, less sedation, fewer nocturnal sleep disturbances, earlier ambulation, fewer pulmonary complications, and higher patient satisfaction ^[2,21]. IV-PCA is an effective technique for administration of parenteral opioids and has greatly improved management of postoperative pain. However, IV-PCA is expensive and is subject to mechanical failure and human error ^[22]. Patients using an IV-PCA system may experience narcotic-induced side effects, especially when treating severe pain. Because the consumption of opioids with IV-PCA is significantly more than with epidural administration, patient tolerance for the doses of opioids necessary to attain profound analgesia may be limited by opioidrelated side effects ^[23].

The opioid administered by an IV-PCA system should be potent with rapid onset and moderate duration of action, should not accumulate or produce tolerance, and should have no "ceiling effect." Although many opioids can be used in the IV-PCA technique, morphine is the most widely used. Fentanyl and its newer analogs have short duration of action and thus will require higher frequency of demands when administered as incremental bolus doses ^[2]. Although background infusion to PCA is reported to improve the quality of analgesia, we did not use a background infusion because it may decrease the safety of this technique and does not reduce the number of demands or the analgesic requirements ^[24,25]. Finally, it must be noted that although no patient in our study developed infection at the catheter site, the number of patients studied is small and the period of observation was short.

In conclusion the present findings suggest that, compared to IV-PCA morphine, epidural fentanyl infusion provides significantly superior analgesia after LL. Epidural placement after LL is a safe and simple technique which improves patient comfort and does so with minimal adverse effects.

The authors thank the surgical and nursing staff of Cappagh Orthopaedic Hospital for their cooperation and support in making this study possible.