Epidural pethidine for post-operative pain relief after upper abdominal surgery.
The site and nature of operation along with individual patient response largely governs the incidence and severity of postoperative pain.
The pain following upper abdominal and intrathoracic operations, is known to be the most severe and to result in marked functional restriction of the respiratory system. In addition, fear and anxiety, associated with this post-operative suffering, cause rigid muscle contraction in an attempt to splint the operative site. This self perpetuating cycle of pain, fear and muscle spasm can be interrupted by active measures for post-operative pain relief.
The discovery of opiate receptors in the spinal cord has led to the use of opiates intrathecally or epidurally for this purpose.,,, In this study, a comparison of the effect of a single dose of epidural pethidine with that of a single intramuscular administration of this drug, has been carried out.
Fifty patients undergoing upper abdominal surgery were selected for this study. The surgical procedures included 15 gastrectomies, 22 vagotomy and gastrojejunostomies and 13 cholecystectomies.
The patients were randomly divided into two groups. Grout) I of 25 patients received epidural pethidine and group II of 25 patients received intramuscular pethidine. The patient characteristics in both the groups were comparable [Table - 1]
Before the operation, patients in group I consented to receive epidural pethidine for post-operative pain relief.
Premedication consisted of inj. atropine (0.5 mg) and inj. diazepam (0.2 mg/Kg body wt.) half an hour before induction of anaesthesia. The anaesthesia was maintained with 30% oxygen, 70% nitrous oxide, non-depolarizing muscle relaxant (d-tubocurarine 0.5 mg/kg body wt.) and intermittent halothane following the induction dose of thiopentone (4 mg/kg. body wt.) and suxamethonium (1 mg/kg. body wt.). The intra-operative use of opiates was avoided. After reversal with atropine (0.02 mg,/kg. body wt.) and neostigmine (0.08 mg/kg. body wt.) post-operatively, when they first complained of pain and demanded analgesia, patients in group I received a single epidural injection of 0.5 mg /kg body wt pethidine diluted in 10 ml isotonic saline at T8-T9 intervertebral space. Group II patients received a single injection of 1 mg/kg body wt pethidine by intramuscular route.
All patients were observed in the recovery room for a period of 24 hours. The analgesic effect was rated with the aid of subjective and objective tests. The subjective tests were quality of analgesia (no pain, mild pain, moderate pain and severe pain), duration of analgesia and ability to cough, breathe deeply and turn in bed. The objective tests consisted of vital capacity (VC) and forced expiratory volume at one minute (FEV1). They were studied with a portable vitallograph and the observations were carried out in all patients, first at the time of pre-operative visit and then post-operatively at the time of pain and thereafter at 2, 6, 12, and 24 hours after the administration of pethidine by either route. The results were subjected to statistical analysis.
I. Subjective analysis of pain [Table - 2] In group I, significantly greater percentage of patients had complete pain relief than that in group II, throughout the observation period. The onset of action was earlier in the epidural group than in the intramuscular group.
II. Manoeuvres for physiotherapy: Ability to cough, deep breathe and turn in bed [Table - 2]
With regard to various manoeuvres for physiotherapy, significantly greater percentage of patients in group I could cough, breathe deeply and turn in bed at all times of observations as compared to the percentage of patients in group II.
II. Vital capacity and FEV1 [Table - 3]: There was significant reduction in vital capacity and FEV1 at the time of pain, the extent of reduction being comparable in both the groups.
After the administration of pethidine, the restoration of vital capacity or FEV1 was significantly greater in group I than in group II at all times of observation. Even in group I, the restoration of vital capacity and FEV1 at the time of peak pain relief. i.e. at 2 hours, did not reach the pre-operative values.
III. Side effects [Table - 4]: Thirty-two per cent of patients in group I had difficulty in passing urine. There was greater incidence of nausea, hypotension and drowsiness in group II.
In the present day situation, offering post-operative rain relief has become an integral part of anaesthesia practice. In the early period after an operation a `standard' dose of an opiate, given intramuscularly, is frequently found to be either excessive or inadequate. It is the discovery of opiate receptors in substantia gelatinosa which raised hopes of a new way to exploit narcotic analgesics. Various studies have shown that the narcotics produced an unusually intense and segmental analgesia when injected into epidural or sub-archnoid space of animal and man.,,,
This study was undertaken to get an idea of the analgesic efficacy of epidural injection of pethidine following upper abdominal surgery. The patients undergoing upper abdominal operations are known to have severe pain,, and hence these patients were selected for the study. The pain and distress due to this type of surgery is usually associated with increased incidence of post-operative respiratory complications and post-operative hypoxaemia.
Pethidine was chosen as it has lipophilic property in addition to a weak local anaesthetic action, as opposed to morphine. Ruttar found that pethidine is more effective than morphine when given epidurally, probably due to the use of larger dosages. Cousins and colleagues-, measured blood and C.S.F. concentrations of pethidine after epidural administration and found that the onset of pain relief coincided with high C.S.F. concentration, while the blood pethidine concentration was below the analgesic level.
In our study, out of 25 patients, 84-92% had complete pain relief for a period of 6 hours after epidural administration of pethidine in a dose of 0.5 mg/kg body wt. Cousins and colleagues, reported similar effects with 100 mg pethidine injected epidurally.
The most serious side effect of epidural opiates is respiratory depression. Studies have reported severe respiratory depression and coma following epidurally administered opiates, though the onset of depression, quoted, appears to vary anywhere between 45 minutes, to 4-7 hours after the administration of the narcotic. Glynn and colleagues commented that this depression could have been due to the use of narcotic premedication given earlier. Kitahata reported a slight sedation, of short duration of 10-15 minutes with 100 mg epidural pethidine, whereas Scot used 60, mg epidural pethidine arbitraraily and found respiratory depression in two of his patients. Torda reported hypotension with a similar dose of pethidine in one patient.
In this study, during the 24 hours of the observation period, there was no evidence of respiratory depression or hypotension; infact, there was an improvement in the respiratory parameters.
The lack of respiratory depression and hypotension in our study may be because of tailoring the dose of pethidine to the body weight and hence usage of comparatively smaller dose of the drug. In addition, we have completely avoided the use of narcotic drugs for premedication or as intra-operative adjuvant.
Simpson used continuous epidural block for post-operative pain relief with restoration of 69% of vital capacity compared to that of pre-operative value, following upper abdominal surgery. We found the vital capacity being restored to 70% of preoperative values following similar type of surgery with epidural pethidine. Bromage reported the restoration of FEV1 to 68% of the control value after epidural narcotics. Our results are comparable to this [Table - 3]. This improvement in the respiratory parameters, though not to 100% of pre-operative values, enabled the patients to effectively cough, deep breathe and turn in bed. It is interesting to note that the restoration to 60-70% of pre-operative values of these parameters is sufficient to enable the patient to co-operate for respiratory physiotherapy, while anything less than this, does not achieve this end.
The advantage of our analgesic technique perhaps lies in the margin of safety provided between the effects of pain relief and restoration of function on one hand and the negative effect of respiratory depression on the other hand.
This margin is narrowed with systemic administration of pethidine. Most of the patients in group II were not co-operative for physiotherapy. This may be either due to the inadequate pain relief or the drowsiness caused by central nervous system depression.
However, the routine administration of epidural opiates demands the availability of skilled personnel, maintenance of strict asepsis and a special area where these patients can be observed for a period of 24 hours. When these requirements are fulfilled, the practice of epidural blockade of appropriate segments with narcotics relieves both somatic and visceral pain and abolishes reflex muscle spasm, while still leaving the patient alert and co-operative.