Three Different Doses of Neostigmine on the Reversal of Cisatracurium-induced Moderate Neuromuscular Blockade

METHODS

After the approval of the Research Ethics Committee of the Faculty of Medical and Health Sciences of Pontificia University Catholic of Sao Paulo (PUC-SP), patients submitted to nose or ear surgeries at Santa Lucinda Hospital and able to participate in this clinical, prospective, and randomized trial will be evaluated. The following will be included: patients aged between 18 and 65 years old, physical status according to the American Society of Anesthesiologists I and II, submitted to general anesthesia. Exclusion criteria will be: (i) refusal to participate in the study; (ii) presence of kidney, liver or neuromuscular disease; (iii) contraindication to the use of any of the drugs used in the study or (iv) body mass index (BMI) ≥ 30. Patients will be randomly distributed into one of 6 groups according to the type of anesthesia (inhalational or venous) and the dose of neostigmine used to reverse NMB:

• Group I-30: inhalational anesthesia and reversal with neostigmine 30 mcg/kg and atropine 15 mcg/kg
• Group I-50: inhalational anesthesia and reversal with neostigmine 50 mcg/kg and atropine 25 mcg/kg
• Group I-70: inhalational anesthesia and reversal with neostigmine 70 mcg/kg and atropine 35 mcg/kg
• Group V-30: intravenous anesthesia and reversal with neostigmine 30 mcg/kg and atropine 15 mcg/kg
• Group V-60: intravenous anesthesia and reversal with neostigmine 50 mcg/kg and atropine 25 mcg/kg
• Group V-70: intravenous anesthesia and reversal with neostigmine 70 mcg/kg and atropine 35 mcg/kg.

For each patient, an opaque envelope will be prepared, sealed and numbered sequentially containing the group to which the patient will be allocated. A list of randomized computer-generated numbers (www.random.org) will be used for this purpose. No surgeon, members of the nursing team, anesthesiologist involved in anesthesia or data collection will be aware of the dose of neostigmine to be administered. The type of anesthesia (inhalation or venous) will not be covered. An anesthesiologist not involved in the study will be responsible for preparing the solution containing neostigmine and atropine (diluted with saline solution until complete 20 mL) according to the group to which each patient belongs. Syringes (20 mL) will be similar and identified only with a label with the word "reversal".

STUDY SEQUENCE

Anesthesia

After entry into the operating room, all patients will be monitored with cardioscopy, noninvasive blood pressure, pulse oximetry and, after tracheal intubation, with capnography. Venous access will be obtained on one of the upper limbs. After pre-oxygenation, anesthetic induction and maintenance will be as follows:

1. Group I-30, I-50 and I-70 - Induction with remifentanil at a dose of 0.5 mcg/kg/min for 3 minutes, followed by a maintenance dose of 0.3 mcg/kg/min. Propofol bolus (2.0 mg/kg) followed by maintenance with sevoflurane 2% diluted in O2/air flow (60%) 2L/min.
2. Group V-30, V-50 and V-70 - Induction with remifentanil at a dose of 0.5 mcg/kg/min for 3 minutes, followed by maintenance dose of 0.3 mcg/kg/min. Bolus propofol (2.0 mg/kg) followed by infusion at the rate of 4 to 6 mg/kg/h.

For both groups, cisatracúrio (0.1 mg/kg) will be administered before tracheal intubation, which will be performed when T1 was less than 5%. Ventilation will be controlled, with tidal volume and respiratory rate adjusted for the maintenance of PETCO2 between 30 and 40 mmHg. When there is a suspect of inadequate anesthesia plan, the infusion rate of propofol or sevoflurane will be increased and if adequacy is not sufficient, the infusion rate of remifentanil will be increased. Patients who have a decrease in systolic blood pressure (SBP) greater than 30% or heart rate (HR) less than 50 bpm will be treated with ephedrine (10 mg) and atropine (0.5 mg), respectively. Hydration will be performed with 0.9% saline solution (500 ml in the first 30 minutes and 2 mL/kg/min the following hours). The central temperature will be maintained above 35oC and peripheral (tenar eminence of the monitored palm) above 32o C. Reversal of NMB will be performed when TOFc 3 by administration of the previously prepared solution.

Monitoring of neuromuscular blockade NMB will be monitored by acceleromyography method (TOF Watch SX®;¬ Schering-Plough) as recommended for use in clinical research. 9 The acceleration transducer will be fixed on the volar side of the distal phalanx of the thumb. Venous access and blood pressure cuff will be positioned on the opposite arm to the limb used for NMB monitoring. After cleaning the skin in the path of the ulnar nerve in the forearm, the electrodes will be positioned at the height of the wrist with a distance between 3 to 6 cm between them. Calibration will be performed after automatically after a 50 Hz tetanus stimulus for 5 seconds. The stimulation (Train-of-Four-TOF) will be applied every 15 seconds for 2 minutes before cisatracúrio is given. No additional doses of NMB will be administered. Once the third response to the TOF is obtained, a dose of neostigmine (30, 50 or 70 mcg/kg) will be administered and the time for until the TOF reaches values equal to 0.9 and 1.0 will be recorded. The primary outcome will be the time required for the reversal of moderate NMB (TOF=3) up to TOF = 0.9 and TOF = 1.0. In addition, the probability of reversion of NMB will be evaluated in less than 10 minutes or 15 minutes after the administration of different doses of neostigmine in patients undergoing intravenous or inhalational anesthesia. The sample size will be based on a previous study that determined the need for 12 patients per group to detect with a power of 90% and alpha error of 5% a difference between groups equal to or greater than 1.3 standard deviations. 10 Considering possible losses, 90 patients will be included.