RESPIRATORY CHANGES DURING TREATMENT OF POSTOPERATIVE PAIN WITH HIGH-DOSE TRANSDERMAL FENTANYL

This study made a longterm (72 hours) evaluation of the efficacy and p ossible side-effects of transdermal delivery of fentanyl (TTS-system) for post-operative pain relief. The study was double-blind, placebo-co ntrolled with either a TTS-system delivering fentanyl 100 mu g . h(-1) and rescue analgesic on demand or a placebo system and analgesic on d emand. Analgesic consumption, pain, general satisfaction, respiratory race, and levels of SpO(2) and tcCO(2) (pulse oximetry and transcutane ous CO2 measuring) were evaluated. Recruitment was stopped after enrol ment of 24 patients, on safety grounds. The Fentanyl group was more sa tisfied with postoperative pain relief(P=0.008); they had a lower anal gesic demand (P<0.05) but also a lower respiratory rate (P<0.05) and a higher level of tcCO(2) 23 hours after application (P<0.05). There we re three cases (25%) of increased PaCO2 (>6.5 kPa) in the Placebo grou p but without, low PaO2 levels, sedation or bradypnoea. Conversely, th ere were three cases (33%) in the Fentanyl group with bradypnoea (<10 breaths/minute), two without influence on PaO2 or PaCO2, but one (no. 24) with bradypnoea, heavy sedation, a marked decrease in PaO2 (5.8 kP a) and increased PaCO2 (7.5 kPa). These findings terminated the study. The 100 mu g transdermal fentanyl system is agreeable to the patients , but apparently too potent for routine postoperative pain relief due to a risk of respiratory depression. Respiratory frequency can not be relied upon as sole indicator of insufficient respiration.