Assessment of requirement of Atracurium based on Neuromuscular monitoring compared to clinical assessment parameters in patients undergoing Laparoscopic Cholecystectomy under General Anaesthesia

Neuromuscular blocking agents (NMBA) are routinely administered during anaesthesia to facilitate endotracheal intubation, to provide good muscle relaxation for optimal surgical conditions. The degree of muscle relaxation required depends on the surgical procedure, the patient, the depthof anaesthesia, and the skill of the surgeon. The optimal depth of neuromuscular (NM) blockade during general anaesthesia should be a balance between immobility during the operative procedure and complete recovery at the end of the operation.

In most clinical settings, intubating time after administration of NMBA is determined by clinical feel of the patient (ease of ventilation, jaw and upper airway tone) or time of onset of action of the NMBA. Intraoperative dosages of NMBA are based on predetermined fixed time after administration of the last dose of NMBA, changes displayed on capnography, the ventilatory graphs or on request of operating surgeon. This may often lead to over-dosage of the NMBA thereby delaying administration of reversal agent i.e. cholinesterase inhibitors (Neostigmine), delaying extubation and shifting from the operating room with increased risk of residual paralysis in the recovery room.

Literature recommends neuromuscular block should be monitored for all patients who receive NMBAs during anaesthesia, to guide appropriate NMBA dosing and appropriate timing for administration of reversal agents.

Perioperative neuromuscular monitoring has multiple benefits – on induction of anaesthesia it indicates optimal time for laryngoscopy and intubation, intra-operatively it guides the need of NMBA and at the end of surgery it signals readiness for pharmacological antagonism.

Neuromuscular monitoring can be done by Qualitative or Quantitative assessment. Qualitative (subjective) assessment is done using peripheral nerve stimulator(PNS) device which provides nerve stimulation without measuring the evoked muscular response. The estimated strength of muscle contractions inresponse to train-of-four (TOF) stimulation are by visual or tactile means hence prone for errors. The anaesthesiologist is the monitor who makes a subjective evaluation of the strength of the muscle response.1

Quantitative monitoring is an objective real-time measurement of the evoked muscle response to nerve stimulation. It measures, analysis and displays Train-of-Four Ratio (TOFR -calculated by dividing the amplitude of the fourth response (T4) by the amplitude of the first response (T1)) in real time. With the wide variability of patient response to NMBA, quantitative monitoring can be used to guide the intraoperative use of NMBA, to ensure effective antagonism and to prevent residual neuromuscular weakness and its complications.

Recent studies reveal that Qualitative assessment using nerve stimulators is performed in less than 40% of patients and objective monitoring in only used for 17% of patients.

Hence, we hypothesize that intra-operative requirement of Atracurium (NMBA) guided by Quantitative Neuromuscular monitoring is decreased as compared to the clinical assessment in patients undergoing Laparoscopic Cholecystectomy.

STUDY DESIGN : Prospective observational study

STUDY SETTING: surgery operation theater in a Tertiary care hospital.

SAMPLING METHOD: Convenient consecutive consenting sample.

METHODOLOGY:

This observational prospective longitudinal study will be performed after approval . All the patients satisfying the inclusion criteria will be enrolled for the study. Written informed consent will be obtained from all patients.

Routine anaesthesia protocol of monitoring will be followed i.e. applying monitors and noting baseline parameters of heart rate, blood pressure and saturation.

Routine protocol of providing balanced general anaesthesia using premedication i.e. Inj. Glycopyrrolate 4 mcg/kg IV; Inj. Midazolam 0.02 mg/kg IV; Inj. Fentanyl 1 mcg/kg IV is given.

Induction of General anaesthesia is done using intravenous Propofol 1.5 – 2 mg/kg till the loss of consciousness and centralization of

Pupils. After confirming ventilation Inj. Atracurium 0.75 mg/kg iv is administered. Intermittent positive pressure ventilation is continued with gas mixture of O2 + air + Sevoflurane.Laryngoscopy and intubation is performed by an experienced anaesthesiologist on clinical signs of adequate relaxation ( or 3 minutes after Atracurium administration).

The quality of relaxation for intubation will be noted on a scale of 1 to 3 where 1 being best grade relaxation, 2 – average relaxation and 3 being poor relaxation.

Intra-operatively, mechanical lung ventilation is carried out using Sevoflurane/ Desflurane in Oxygen and Air (40:60) mixture to maintain a MAC of 0.7 – 0.8. The Minute ventilation is adjusted to maintain End Tidal Carbon dioxide (ETCO2) ranging from 35 to 45 mm Hg.

If Neuro-muscular monitor is available in the operating room, it will be an additional monitor attached to the patient. These patients will be included in Group A. All the other patients in whomNeuro-muscular monitor will not be available and basis for administering NMBA is on clinical basis will be included in Group B.

In Group A - After the centralization of pupil, Neuro-muscular monitor is calibrated to obtain the supra-maximal stimulus (using automatic calibration) and baseline TOF ratio and Twitch percentage (T1%) will be noted. Following this, Inj Atracurium 0.75 mg/kg IV is administered. TOF stimulation (2 Hz current lasting 0.2 ms) is performed every 30 seconds till the complete loss of responses to TOF stimulation (i.e TOF count =0).

Time taken to achieve TOF =0 will be noted followed by laryngoscopy and endotracheal intubation is done.

TOF Monitoring is done every 5 minutes intra-operatively.inj. Atracurium top-up (0.25 mg/kg iv) is administered when TOF Count is ≥ 2 or T1% is > 25% whichever is early.

In Group B – Intraoperatively, Atracurium doses (0.25 mg/kg iv) is given based upon the clinical signs, capnogram pattern indicating patients respiratory attempt, patient movement.

Peri-procedurally, if surgeon perceives inadequate relaxation or if there are clinical signs of inadequate muscle relaxation, additional Atracurium will be administered as per the discretion of the involved anaesthesiologist.

Time interval between the Atracurium doses (top ups) and total dose of Atracurium required for the procedure will be noted in both the groups.

At the end of surgery, the residual neuromuscular blockade is reversed by administering Inj. Neostigmine 0.06 mg/kg andInj. Glycopyrrolate 8 mcg/kg IV.

Trachea is extubated on obtaining TOF ratio >0.9 in Group A orwhen clinical criteria of extubation are met, in Group B.

The time to extubate (i.e time from beginning of reversal till extubation) will be noted in both groups