Background
The number of patients chronically treated with opioids has increased with the crescent use of opioids to treat chronic pain.1
The transdermal delivery systems (TDDS) allow the desired systemic effect to take place by administrating medication through transcutaneous route at a predetermined rate. During perioperative period, fluid and temperature changes can lead to erratic medication absorption.2,3
We describe a clinical case of buprenorphine overdose.

Case Report
A 91-year-old female patient, 70Kg, chronically medicated with buprenorphine TDDS 35μg/hour for bowel cancer, presented with bowel occlusion and was admitted for urgent exploratory laparotomy under general anaesthesia. We decided to maintain the TDDS in the perioperative period.
We administered propofol 80mg, fentanyl 0,1mg, rocuronium 60mg and maintained anaesthesia with sevoflurane.
We administered 2000ml of crystalloids. The patient lost about 1000ml of gastric content, 500ml of urine and 500ml of blood.
As analgesic medication, we administered paracetamol 1000mg and morphine 4mg, titrated in 2mg boluses.
The procedure took 2 hours. In the end, we administered ondansetron 4mg and sugammadex 150mg. After 30 minutes, there wasn’t any expired anaesthetic gas and the patient didn’t respond to verbal nor painful stimulus and hadn’t returned spontaneous ventilation.
We administered naloxone 80μg and the patient initiated spontaneous ventilation afterwards. She was extubated and transferred to the recovery unit.

Discussion
The acute and chronic pain teams should assess chronically opioid treated patients before surgery, and elaborate an ideal analgesic plan for those patients.
Since it was an urgent surgery, we decided to keep the TDDS on the patient.
Although we avoid any heating systems, the fluid shift in the intraoperative period led to increased buprenorphine absorption, with a consequent overdose in an opioid tolerant patient.

References
1. Contin Educ Anaesth Crit Care Pain 2005;5(4):127-129
2. Best Pract Res Clin Anaesthesiol 2005;19(1):59-76
3. Contin Educ Anaesth Crit Care Pain 2007;7(5):171-176

Learning points
1. Anaesthesiologists must be aware of the influence of perioperative period on the TDDS absorption rate.
2. In surgeries with anticipated blood volume changes or fluid shift, the TDDS should be removed and equianalgesic doses of opioid should be administered to the patients.

Transdermal delivery systems: Is there overdose risk? A case report