Epidural opiate and perioperative analgesia

Epidural sufentanil for intra- and postoperative analgesia in thoracic surgery: a comparative study with intravenous sufentanil

A comparative study was undertaken to evaluate the effectiveness of epidural sufentanil in providing intra- and postoperative analgesia during thoracic surgery. Sufentanil was chosen on the basis of its high lipid solubility and its potent opiate receptor binding. Epidural sufentanil was compared with intravenous sufentanil as the major intraoperative analgetic agent in an anesthesia regimen with midazolam and nitrous oxide. Epidural sufentanil significantly decreased the need for supplementary intravenous analgesia. In the epidural sufentanil group the immediate postoperative analgesia was found to be better, with a longer duration of action, compared with the intravenous sufentanil group. Postoperatively epidural sufentanil was compared with epidural morphine. Sufentanil provided good analgesia with a very fast onset and a mean duration of almost 7 h. Severe respiratory depression was observed in one patient within 1 h of extubation, probably due to the combined effects of the narcotic administration and residual midazolam. It is concluded that 50 micrograms of sufentanil administered in the thoracic epidural space provides valuable intraoperative analgesia which can easily be extended into the postoperative period, although all necessary precautions for epidural opiate administration should be taken.

Changes in micturition volume thresholds in conscious dogs following spinal opiate administration

Micturition difficulties appear as an often-reported side effect of the clinical use of opiates for spinal analgesia. Only a few experimental studies have focused specifically on this problem, especially in an unanesthetized animal model where chronic pharmacological studies can be carried out. The changes in micturition volume thresholds that occurred following spinal intrathecal injections of 1 mg of morphine sulphate were measured in 11 conscious dogs and compared with threshold changes produced in these same dogs by i.v. injections of various doses of morphine sulphate and by intrathecal and i.v. injections of naloxone HCl. In all cases, intrathecal or systemic morphine at doses of 1.0 mg or greater significantly (P less than 0.05) increased the bladder volume at which micturition took place. Naloxone, injected intrathecally to reverse the effects of intrathecal morphine, significantly reduced the micturition volume threshold, in most cases to below control volumes. A 400 microgram dose of naloxone, injected intrathecally without prior injection of morphine, significantly lowered the volume threshold in 9 dogs, even though two of these dogs had elevated thresholds following naloxone injection. The reduction in volume thresholds by i.v. naloxone not preceded by morphine injection was not statistically significant over that of control. These results are interpreted in light of recent findings concerning localization of endogenous opiate receptors within the micturition reflex pathway.

Epidural fentanyl counteracts sympathetic gastric inhibition

Postoperative paralytic ileus is in part mediated by the sympathetic gastrointestino-gastrointestinal (GI-GI) reflex. The modulation of this reflex by epidural fentanyl (50 micrograms) was studied in chloralose-anesthetized, ventilated cats. The vagi were cut in the neck but could be efferently stimulated. Gastric volume, arterial pressure and heart rate were followed and the GI-GI reflex was elicited by intestinal distension, mesenteric afferent nerve stimulation or heating or capsaicin administered intra-arterially to an intestinal loop. Epidural fentanyl enhanced the gastric contraction response to efferent vagal stimulation and considerably counter-acted the GI-GI reflex inhibition of vagally induced tone. These effects were reversed by epidural naloxone (10 micrograms). In contrast, 50 micrograms of fentanyl i.v. only enhanced the effect of vagal stimulation but had no influence on the inhibitory GI-GI reflex responses. Apparently, epidural fentanyl may inhibit the GI-GI reflex by a spinal point of action.

Epidural morphine prophylaxis of postoperative pain: report of a double-blind multicentre study

In a double-blind placebo-controlled trial, 154 subjects, having intraperitoneal surgery or Caesarean section, and 53 patients undergoing lower limb orthopaedic surgery, received epidural morphine, 5 mg in 10 ml 0.9 per cent NaCl, or placebo, 10 ml 0.9 per cent NaCl, intraoperatively to determine duration of action and efficacy in preventing postoperative pain. Epidural morphine gave significantly longer postoperative analgesia (greater than 11 h) than placebo (3-6 h) in both groups (p less than 0.05) and patients who received morphine required less postoperative analgesic. Obstetric subjects experienced longer pain relief (18.3 +/- 1.3 h) than patients undergoing non-obstetric intraperitoneal surgery (9.2 +/- 1.2 h) (p less than 0.001). Generally mild pruritus affected more than 40 per cent of those receiving morphine, but over 90 per cent of obstetric patients receiving morphine. Respiratory depression occurred in 2-7 per cent of subjects who received morphine; unpredictable in onset, it responded rapidly to naloxone. Epidural bupivacaine, if employed for the surgical procedure, appeared to prolong epidural morphine analgesia. We consider epidural morphine useful in preventing postoperative pain, but its use demands close observation of respiratory rate in a high density nursing area.

The relevance of cholinergic transmission at the spinal level to opiate effectiveness

Rats chronically implanted with intrathecal catheters displayed a dose-dependent increase in the hot-place and tail-flick response latencies following the injection of morphine or nicomorphine into the subarachnoid space through the indwelling catheter. Naloxone inhibited the antinociceptive effect of both opiate drugs, but the inhibition of nicomorphine-induced antinociception was incomplete. To evaluate the importance of cholinergic mechanisms in opiate effectiveness, the interactions with atropine or physostigmine were evaluated. Atropine reduced the effects of morphine and abolished the effects of nicomorphine at the doses used. Physostigmine markedly potentiated morphine effectiveness, but had a negligible effect on nicomorphine effectiveness. It is proposed that these differences relate to a specific cholinergic mechanism involved in antinociception after intrathecal nicomorphine. The data indicate that at a spinal level cholinergic mechanisms are relevant to opiate effectiveness.

Epidural analgesia and anticoagulant therapy. Experience with one thousand cases of continuous epidurals

One thousand lumbar epidural blocks in 950 patients undergoing vascular surgery are reported. All patients were receiving oral anticoagulants pre-operatively. Mean thrombotest (TT) was 19.3% (normal range 70-130%). During surgery intravascular heparin was administered. At the end of surgery, the kaolin cephalin clotting time (KCCT) was 68 (+/- 0.8) seconds (normal range 35-60 seconds), and partial thromboplastin time (PTT) was 536 (77.9%, normal control of 100%). Despite the anticoagulant therapy, no side effects were observed in any patient which could be related to haemorrhage or haematoma formation in the epidural space. It is concluded that, provided adequate precautions are taken, epidural analgesia can be safely used in patients receiving anticoagulant therapy.

Effect of prophylactic epidural morphine or bupivacaine on postoperative pain after upper abdominal surgery

Morphine 2 mg and 4 mg or bupivacaine 50 mg (another 50 mg 4 h later) was administered into the epidural space prior to general anaesthesia of 40 patients undergoing upper abdominal surgery. During anaesthesia, additional analgesics were not given. In the recovery room (4 h) the pain score (0-10) was lowest in the bupivacaine group (mean 2.4) followed by the 4 mg-morphine group (4.1), 2 mg-morphine group (5.3) and control group (5.7). Half of the patients of the bupivacaine group and those of the 4 mg-morphine group needed no analgesics in the recovery room. Later, in the ward (until next morning 7 am), only morphine patients (5/20) managed without postoperative analgesics. The mean number of requests for analgesics during that time was: 4 mg-morphine 1.3, 2 mg-morphine 1.9, bupivacaine 2.7, and control 2.9. Episodes of hypotension and nausea were most frequent in the bupivacaine group. No serious respiratory complications occurred; 4 h after anaesthesia three patients in the 4 mg-morphine group and two in the bupivacaine group had capillary PCO2 values above 6.65 kPa (50 mmHg), the highest being 7.1 kPa. In two additional patients with choledochal drainage (T-tube), the intracholedochal pressure was shown to rise about 2 kPa 915 mmHg) and 2.7 kPa after epidural injection of 2 mg and 4 mg, respectively. A pressure peak was reached within 10 min and at 75 min the pressure was still 0.7-1.3 kPa above the initial level.

Influence of epidural morphine on postoperative pain, endocrine-metabolic, and renal responses to surgery. A controlled study

In order to assess the analgesic properties of epidural low-dose morphine and its possible influence on the adrenocortical, hyperglycemic, renal, electrolyte and leukocyte responses to surgery and nitrogen excretion, a double-blind randomized study was undertaken in 14 otherwise healthy patients admitted for hysterectomy under halothane, N2O/o2 anesthesia. Before induction of anesthesia, an epidural catheter was introduced into the lumbar epidural space. After induction of anesthesia, either morphine 4 mg in 10 ml saline or 10 ml saline was injected into the epidural space, according to the allocation. Postoperatively, the degree of pain was evaluated by mean of a visual analogue scale (0-10). When pain score exceeded 5 points during the 24 -h trial, either 4 mg morphine in saline or saline was given epidurally. If the pain score did not decrease more than 2 points after an epidural injection, morphine was given parenterally (5 mg i.v. +5 mg i.m.). The results showed that pain scores, duration of pain relief and doses of morphine differed significantly between groups (P less than 0.05). Plasma concentration of cortisol and glucose, plasma-and urine electrolytes, 24-h creatinine and free-water clearances, diuresis, fluid balance, leukocyte count and nitrogen excretion differed insignificantly between groups. In conclusion, epidural low-dose morphine is a superior alternative to conventional postoperative pain treatment because of greater and longer lasting pain relief, without apparent side-effects. The measured endocrine-metabolic and renal response did not differ between groups, indicating that low-dose epidural morphine does not inhibit afferent neurogenic stimuli from the site of surgical trauma.