Evaluation of a pilot regimen for postoperative pain control in patients receiving oral morphine pre-operatively

Postoperative analgesia in patients who receive regular oral opioids pre-operatively is frequently suboptimal. To improve management we introduced a regimen using subcutaneous diamorphine infusions with incremental doses. Infusion doses were calculated as half the daily pre-operative dose of oral morphine with the increments as one-sixth of the infusion dose. Results were recorded on the first two postoperative days before (n = 13) and after (n = 23) commencing the new regimen. The percentage of patients reporting severe pain at rest and on movement were significantly reduced by the new regimen (54% and 69% vs. 13% and 40%, respectively) since the opioid dose as a percentage of the pre-operative dose was significantly higher (160% vs. 352%). There were no instances of excessive sedation or slow respiratory rate in any patient. The use of the regimen has resulted in greater doses of opioids being administered with fewer patients in severe pain without significant complications.     

Stability of premixed syringes of diamorphine and hyperbaric bupivacaine

BACKGROUND: It is common clinical practice to add diamorphine to heavy bupivacaine when performing spinal anaesthesia for either obstetric or general surgical procedures. If pre-filled syringes were available potential problems arising due to the wrong mixture being administered could be reduced, whilst also providing greater assurances of sterility and accuracy of dosage. It is therefore necessary to establish whether diamorphine 100 microg/mL is stable in solution with 0.5% hyperbaric bupivacaine, to allow production of pre-filled syringes for use in spinal anaesthesia. METHOD: Diamorphine hydrochloride was dissolved in water for injection, and added to hyperbaric bupivacaine then stored in 5-mL plastic syringes. Eleven syringes were stored at 40 degrees C/75% relative humidity, 25 degrees C/60% relative humidity and 7 degrees C for 90 days. Samples were taken at five time points for measurement of diamorphine and bupivacaine concentrations using high performance liquid chromatography. RESULTS: Diamorphine concentrations fell over the study period. No significant changes were observed the bupivacaine content of the samples. There was 10% degradation of diamorphine after 4 days at 40 degrees C, after 7 days at 25 degrees C, and after 26 days at 7 degrees C. CONCLUSION: Diamorphine is stable in hyperbaric bupivacaine at 7 degrees C for long enough to allow preparation of pre-filled syringes in advance (by hospital pharmacy aseptic units) for use in spinal anaesthesia.     

Epidural infusion of bupivacaine and diamorphine for postoperative analgesia

An audit of postoperative epidural analgesia in a District General Hospital is presented. Three hundred and forty-eight patients received epidural infusions of a bupivacaine and diamorphine mixture, and were managed on general surgical wards using a standard protocol of observations and instructions. Good analgesia was achieved in 339 (97%) patients. Respiratory depression, defined as a respiratory rate of eight breaths.min-1 or less, occurred in 22 (6%) patients, was of gradual onset, and was simply and successfully managed without morbidity. There were no respiratory arrests. Other complications, and the significance of catheter insertion level are discussed.     

High-dose intrathecal diamorphine for analgesia after Caesarean section

Forty women undergoing elective Caesarean section under spinal anaesthesia using hyperbaric 0.5% bupivacaine were randomly allocated to receive either 0.5 mg or 1 mg intrathecal diamorphine. All women received diclofenac 100 mg at the end of surgery and morphine via a patient-controlled analgesia system. Oral analgesics were not used. Postoperative analgesia was more prolonged and more reliable in the 1-mg group. Mean time to first analgesia was 10.2 h in the 1-mg group and 6.9 h in the 0.5-mg group, and 45% in the 1-mg group used no morphine, compared with 10% in the 0.5-mg group. Mean morphine consumption over 24 h was 5.2 mg in the 1-mg group and 10.6 mg in the 0.5-mg group. Pain scores all tended to be lower in the 1-mg group but this was only significant at 4 h. There were no serious side-effects. Minor side-effects were common but well tolerated, and the incidence did not differ between the groups. If intrathecal diamorphine is used in combination with rectal diclofenac and without oral analgesia, then 1 mg provides superior analgesia to 0.5 mg without any worsening of the side-effects.     

A comparison of patient-controlled analgesia administered by the intravenous or intranasal route during the early postoperative period

Intranasal administration of lipophilic opioids has been shown to be an effective method of administration which is devoid of major side-effects. Whether it is as effective as intravenous administration for patient-controlled analgesia (PCA) has been investigated for fentanyl and pethidine, but not for diamorphine. This study reports a randomised controlled trial designed to compare the effectiveness of diamorphine administered as PCA utilising either the intranasal or intravenous routes. We investigated 52 consecutive patients undergoing primary lower limb joint replacement surgery. Patients were randomly allocated to receive PCA diamorphine, administered either intravenously (0.5 mg bolus, 3 min lockout) or intranasally (1.0 mg bolus, 3 min lockout). Pain was assessed using a Visual Analogue Score (VAS) at rest and on movement on five occasions over the first 36 h postoperatively. The results demonstrated that patients in the intranasal PCA group had significantly higher VAS scores than the intravenous group, both at rest (intranasal median 35.5 vs. intravenous median 20; p = 0.030) and on movement (intranasal median 64 vs. intravenous median 50; p = 0.016). However, significantly fewer patients in the intranasal group compared with the intravenous group suffered episodes of vomiting (intranasal 0/24 vs. intravenous 6/24 patients; p = 0.022). We suggest that if a maximal reduction in pain score is considered the goal of PCA management, the intravenous route is preferable to the intranasal route.