Introduction It is known that nociceptive stimuli, triggered by surgery and tissue inflammation can cause peripheral sensitization and primary hyperalgesia, increases spinal responsiveness to stimuli, whether harmful or not, due to the wind-up phenomenon, and other mechanisms, with induction central sensitization. Additionally, opioids commonly employed during general anesthesia may activate, both, the antinociceptive system and the pro-nociceptive system which can lead to acute tolerance and hyperalgesia. There is evidence that NMDA receptors are involved in the development of these changes and that low doses of ketamine (\< 1mg/kg) may control of postoperative pain to bind to the receptor phencyclidine the NMDA channel and inhibit the activation of the channel by glutamate non-competitively. Recently, there has been a change in pain management, which includes the observation of non-traditional variables such as those related to the concepts of satisfaction and quality of life related to health. To this end, a growing number of authors went on to assess the opinion of patients as a way to determine the quality of recovery from anesthesia, meaning the observation not only of pain intensity, but also aspects related to emotional state, comfort and independence physical. The QoR-40 questionnaire (Quality of recovery-40), a validated instrument for this purpose, allows an objective approach of these factors that can influence the perception of the patient and allows you to compare different therapeutic ways. There are no recent data on the application of this instrument to assess the effects of giving, or not, of low doses of ketamine on the quality of recovery of patients undergoing total intravenous anesthesia.

Methods After arrival in the operating room, standard American Society of Anesthesiologists (ASA) monitors will be applied. Midazolam 0.06 mg/kg and 1% lidocaine (30 mg) will be administered intravenously immediately after venoclysis. After anesthesia induction, capnographic monitoring will be added and the neuromuscular blockade will be evaluated using acceleromyography (TOF Watch). Induction and maintenance of anesthesia will be performed as follows: remifentanil, induction dose 0.5 μg/kg/min, followed by a maintenance dose of 0.3 μg/kg/min. Propofol, initial bolus (2.0 mg/kg) followed by infusion at 4 to 6 mg/kg/h. Each patient will receive rocuronium (0.6 mg/kg) before tracheal intubation. Ventilation will be controlled by adjusting the flow volume and respiratory rate to keep the end-tidal carbon dioxid (CO2) level between 30 and 40 mmHg. In the case of inadequate depth of anesthesia (movements, sweating, tachycardia, blood pressure increase \>10% of the pre-induction value), propofol infusion or sevoflurane rate will be increased (by 1%); if this was not sufficient, the remifentanil infusion rate will be also increased (by 0,1 μg/kg/min). Patients who exhibit reductions in systolic arterial pressure (SAP) greater than 30% or heart rate (HR) reductions to less than 50 bpm will be given ephedrine (10 mg) and atropine (0.5 mg), respectively. After induction patients will receive one of three intravenous solutions: ketamine 0.2 mg/kg - diluted in saline until the volume of 5 mililiters (mL) (k2 group); ketamine 0.4 mg/kg diluted in saline until the volume of 5 ml (k4 group) or 5mL of 0.9% normal saline (K0 group). Hydration will be maintained with 0.9% normal saline 2 ml/kg/h. All of the participants were given dexamethasone (8 mg) and ketoprofen (100 mg) at the onset of surgery and dimenhydrinate (30 mg), dipyrone (1 g) and morphine (0.1 mg/kg) 15 minutes prior the end of the procedure. Atropine (0.01 mg/kg) and neostigmine (0.05 mg/kg) were used to achieve T4/T1\>0.9 on the TOF monitor. Extubation was performed after awakening. When stable vital signs and respiration was confirmed, all patients were transferred to the postanesthesia care unit (PACU). Data related to the occurrence of pain, nausea, vomiting, dizziness or hallucinations at the PACU will be recorded as will be the length of stay in the PACU. Pain will be assessed every 15 minutes using a 0-10 numeric pain rating scale, where zero meant no pain and 10 the worst imaginable pain. Morphine (1 to 2 mg) will be administered intravenously every 10 minutes to maintain the pain score below 4 (1 mg when the pain score was \<7 and 2 mg when it was ≥7). Following discharge from the PACU (minimum stay 60 minutes and Aldrete \& Kroulik index \>9), all of the participants will be given ketoprofen (100 mg) every 12 hours and dipyrone (30 mg/kg, maximum 1 g) every six hours intravenously. Whenever patients judged that their analgesia was insufficient, tramadol (100 mg) will be administered intravenously at eight-hour minimum intervals as needed. Postoperative nausea and vomiting (PONV) will be treated with dimenhydrinate (30 mg) intravenously. Pain score, use of analgesics, and the occurrence of nausea, vomiting, and other complications during the hospital ward stay will be recorded.

QoR40 The quality of postoperative functional recovery will be assessed by the QoR40 questionnaire, which assesses five dimensions of recovery (physical comfort - 12 items; emotional state - 7 items; physical independence - 5 items; physiological support - 7 items; and pain - 7 items). Each item is rated on a five-point Likert scale: none of the time, some of the time, usually, most of the time, and all the time. The total score on the QoR40 ranges from 40 (poorest quality of recovery) to 200 (best quality of recovery). The QoR40 will be administered by a blind investigator 24 hours after surgery.