Impact of Opioid Free Anesthesia on Outcome After DIEPflap Surgery

The investigators included all patients in the hospital database.belgium who underwent DIEPflap surgery between Jan 2014 and April 2019. All patients entering the hospital provided consent to allow retrospective data analysis without patient identification.

Because patient assignment to an operating day was determined without knowing who would perform the anesthesia on a few exceptions, the choice of opioid free anesthesia (OFA) or opioid anesthesia (OA) in most cases was random. Patients were classified as receiving OFA when no opioids were given pre- or intra- operatively until wound closure. Opioids given after wound closure were counted as post-operative opioids. Patients who received a lower dose of intra-operative opioids by using additives were still classified as OA. Post-operative opioid free analgesia was classified as receiving no opioids after wound closure until discharge from hospital in patients not receiving medium- or long-acting opioids, pre- or intra-operatively.

The method of reaching OFA remained stable since 2014. Dexmedetomidine was given in a first loading dose of 0.3 mcg/kg 15 minutes before induction, a second loading dose of 0.1 mcg/kg at induction followed by an infusion of 0.1 mcg/kg/h for maintenance. Lidocaine is given as a loading dose of 1 mg/kg at induction followed by 1 mg/kg/h for maintenance. A Ketamine loading dose of 0.1 mg/kg is given at induction with an extra bolus of 0.7 mg/kg (or max 50 mg) before incision followed by an infusion of 0.1mg/kg/h.

Post-operative analgesia was further improved by continuing very low doses of dexmedetomidine (0.05 mcg/kg/h), ketamine (0.05 mg/kg/h), and lidocaine (0.5 mg/kg/h) for the first hours (maximum 5 hours) with the possibility of giving a bolus of 10 mg lidocaine, 1 mg ketamine and 1 mcg dexmedetomidine every 15 minutes.

OA was induced with sufentanil (0.1 - 0.3 mcg/kg) and continued with extra boli (0.1 - 0.2 mcg/kg) or a continuous infusion of remifentanil (0.20 - 0.35 mcg/kg/h). Since 2014 more and more additives like clonidine, dexmedetomidine, ketamine and lidocaine were given as a single additive at the induction to reduce the total dose of intraoperative opioid use. Nevertheless these patients were still counted as OA.

All patients getting OFA got a strict goal directed fluid therapy with an average amount of fluids between 600 and 1200 ml. Patients on OA got a more liberal fluid therapy resulting in total amounts between 3000 and 5000 ml. For each patient the total amount of fluids given intra operative and the duration of the surgical procedure is calculated.

Following demographic data was retrieved: age, body mass index (BMI), American society of anesthesiology (ASA) score, incidence of hypertension, smoking or history of recent smoking, motion sickness or previous PONV. A bilateral DIEPflap is noted as bilat versus unilat and depending on the use of opioids postoperative an Apfel score is calculated. The number of anti emetic drugs given before any PONV took place and the number given after PONV is calculated, the incidence of nausea and the incidence of vomiting is measured. The maximum visual analog score (VAS) during the first 24 hours and the total equivalent dose of morphine used in the first 24 hours is measured.

Postoperative flap skin temperature was measured every hour in the first 24 hours and compared to a reference skin temperature close by.

Perioperative complications during the first post-operative month were graded according to a score (CLAVIEN), (DINDOO).

DIEPflap failure was defined as the need for a revision procedure that fails in preserving the flap and requires a new or other flap procedure.

The investigators calculated length of hospital stay (LOS) as the total number of nights in hospital after surgery.

The investigators retrieved all measured factors potentially related to complications of grade I to grade V or healthcare utilization outcomes from the database and medical records. Post-operative opioids were defined as the total dose of opioids used during the first 24 hours post-operatively, calculated as iv morphine equivalents. The following were considered equivalent to 1 mg iv morphine: 1 mg iv or subcutaneous piritramide, 10 mg iv tramadol, or 2 mg sublingual oxycodone.