Intranasal fentanyl for postoperative analgesia after elective Caesarean section (2003)

There are many methods for providing postoperative analgesia, but each have certain disadvantages. Patient-controlled analgesia (PCA) requires intravenous access; epidural insertion may be difficult or contraindicated; intramuscular injections are painful, relatively inconvenient to administer, and have a risk of infection and nerve damage. We tested fentanyl administered as patient-controlled intranasal analgesia (PCINA). In this study, we used a nasal pump by Go Medical from Anaesthetic Medical Systems Ltd. The pump is a spray bottle with flow-control tubing that, after activating a spray, takes 3 min for the reservoir to refill. This serves as a lockout mechanism and prevents continuous and over-administration of fentanyl. The volume of the bolus is 0.18 ml. Striebel et al. [1, 2] used a 27-µg fentanyl dose for non-obstetric surgical procedures but side-effects included mild respiratory depression. We opted for a 4.5-µg dose. The efficacy of nasal fentanyl is comparable to intravenous administration, because opioids are well absorbed from the nasal mucosa, it avoids first-pass metabolism and results in a high bioavailability (71%) [1, 2]. Following Research Ethics Committee approval, we compared analgesia for pain relief for 8 h after elective Caesarean section under a standard spinal anaesthetic. We administered fentanyl via PCINA (a maximum of 90 µg of fentanyl per hour) to 10 patients (Group I), and intramuscular morphine 10 mg on a 4-hourly PRN basis to 11 patients (Group II). Physiological parameters were measured at 30-min intervals, including sedation, pulse oximetry, heart rate, blood pressure, respiratory rate and time for three-segment regression of the spinal block. Rescue analgesia of 2–2.5 mg intravenous morphine was provided to patients in both groups. Pain relief was assessed every 30 min using a 10-cm visual analogue scale (VAS). All patients recorded pain scores by 4 h. In Group I, there was a mean of four fentanyl dosages per 30-min interval. The lowest number of dosages was 17 (76.5 µg) and the highest was 71 (319.5 µg) during the 8 h. Two patients had nine dosages in 30-min intervals, i.e. the highest possible number of intranasal sprays allowed by the lockout time; neither required rescue analgesia. In Group II, most patients received one intramuscular morphine dose during the 8 h. Two patients received two intramuscular doses. One patient did not request any analgesia. The mean of the highest VAS scores was 4.5 for Group I and 5.1 for Group II. Rescue analgesia was given as 2–2.5 mg intravenous morphine PRN every 15 min if VAS scores were greater than 5, or if the patient was too distressed by pain. This occurred in six patients: one in Group I (6 mg) and five in Group II (6–20 mg). No side-effects were reported from any Group I patients. One patient from Group II reported mild to moderate pruritus. Mean analgesic plasma concentration of fentanyl ranges from 0.6 to 3 ng.ml−1 following intravenous administration [3]. Blood samples from patients in Group I were taken at 0, 5, 15, 30, 60 and 120 min after the first administration of intranasal fentanyl. However, no fentanyl was detected in any of the serum samples. We found no clinically relevant intergroup difference in the measured sedation scores, oxygen saturation, heart rate, systolic blood pressure and respiratory rate (unpaired t-test with two-sample equal variance test), VAS scores, or amount of rescue analgesia (Fisher's exact test, p = 0.149). However, for this small sample of patients, the power of this study was only 0.23. In conclusion, we think that our results are encouraging. The ease of intranasal administration, the safety of a controlled dose and the high patient acceptability of this method of pain relief deserve more attention. The lack of clinical significance between the two groups' VAS scores suggests that PCINA may be as effective as intramuscular morphine, or may be superior in terms of the number of patients requiring rescue analgesia. The high patient satisfaction with the intranasal pain relief was also remarkable. However, the PCINA patients had a much more frequent rate of analgesic administration at their disposal. This may contribute to a placebo effect. Further work needs to be done with this novel but, as yet, less established tool of providing analgesia to determine optimum dose without increasing side-effects. This work was supported by funds from The Friends of Guy's Hospital, Guy's Hospital, London. The spray bottles (manufactured by Go Medical) were provided by Dr Tim Craft (Royal United Hospital, Bath).