The Feasibility Of Measuring Evoked Twitch Response Of Laryngeal Adductors With Dual-cuff Endotracheal Tube Technique

BackgroundDuring anesthesia, it is highly desirable to facilitate tracheal intubation by paralyzing vocal cord using muscle relaxant, and, the neuromuscular transmission recovery of laryngeal muscles is important to airway protection at the time of extubation. The most commonly used conventional method for monitoring the potency and duration of muscle relaxant is evoked twitch response of adductor pollicis. However, the nondepolarizing muscle relaxant effects on laryngeal muscles differ from those on adductor pollicis. This necessitate the monitoring of evoked twitch response of laryngeal muscles.The presently available technique of single-cuff endotracheal tube indirectly reflects the contraction strength of laryngeal adductors by recording the cuff pressure at the time of evoked twitch response of the muscle. This method yields unstable results. Therefore, this study was conducted to investigate the feasibility of measuring evoked twitch response of laryngeal adductors with dual-cuff endotracheal tube technique.Materials and methodsTwenty female patients, ASA physical statusⅠandⅡ, aged 20~50, scheduled for elective surgical procedure were enrolled. Normal cardiopulmonary function was verified in all patients. No drug may influence neuromuscular transmission was used within a week. Patients with electrolyte disorders, acid-base imbalance, fever and any other diseases or metabolic abnormality known to alter neuromuscular transmission were excluded. The intubation condition assessment according to Mallampatis classification showed grade I or II in all patients. Intramuscular midazolam 0.05 mg/kg and atropine 0.01 mg/kg were used 30 min before anesthesia. The operation room temperature was maintained at 24 ~26℃.After entrance of operating room, supine position was assumed, left median cubital vein was cannulated and lactated ring's solution was infused at a rate of 10ml·kg-1·h-1. Systolic blood pressure (SBP), mean arterial pressure(MAP)and diastolic blood pressure(DBP)were recorded at right upper arm with Mindray PM 9000 monitor, and leadⅡelectrocardiogram, heart rate (HR) and pulsatile oxygen saturation (SpO2) were monitored. Anesthesia induction was initiated after stabilization of the above parameters. Target-controlled infusion (TCI) of propofol at a target concentration of 5μg/ml was initiated using ALARIS infusion pump. Sufentanil 0.4μg/kg was administered intravenously when an effect compartment of 5μg/ml attained. After loss of consciousness, the lungs were ventilation via face mask. Topical anesthesia of pharyngolaryngeal area was performed by 2% lidocaine spray with the aid of laryngoscopy. After one minute the tracheal was intubation, then intermittent positive pressure ventilation was applied to maintain a PETCO2 value of 35～40 mmHg. Anesthesia was maintained by intermittent boluses of sufentanil 0.1μg/kg and propofol TCI at the above effect compartment concentration. MAP, HR and SpO2 value were recorded before, after anesthesia induction and during the period of drug effect monitoring.After anesthesia induction, an dual-cuff endotracheal tube of ID 7.0mm was intubated, the tip of the tube was situated at a distance of 2～3cm distal to carina of trachea with the aid of bronchofibroscope, with the middle one-third of the pressure-monitoring cuff astride the fissure of glottis. Then the seal cuff was inflated, and the lungs were ventilated mechanically. The inflation tube of the pressure-monitor cuff was connected to a calibrated transduser (PT-100, TME Technology Co., China) through a three-way stopcock to facilitate pressure measurement. Monitoring the laryngeal adductorsA negative surface electrode were placed on the superior thyroid notch, and the positive one the sterna angle or the forehead. The pressure-monitoring cuff was inflated through the stopcock, and the cuff pressure was measured using a Data Acquisition & Analysis System (BL-420S, TME Technology Co., China) with a stable baseline pressure of 10～20mmHg. Percutaneous supramaximal train-of-four stimulation (frequency 2 Hz, and wave width of 0.2ms) were applied to the recurrent laryngeal nerve at an interval of 12 s using a TOF-Guard neuromuscular monitor.Monitoring the adductor pollicisLeft upper limb was abducted 30°and fixed on a hand–rest plate. The stimulation electrode was placed on the body surface projection of the ulnar nerve, the acceleration sensor the palm side of thumb end, and the shell temperature sensor the thenar eminence. A TOF-Guard neuromuscular monitor was used to percutaneously stimulate the ulnar nerve and record the induced twitchs of adductor pollicis.Two TOF-Guard neuromuscular monitor were used to simultaneously stimulate the recurrent laryngeal nerve and the ulnar nerve, and the baseline twitchs of adductor pollicis and laryngeal adductors were recorded. The amplitude of T1 baseline of laryngeal adductors was defined as 100%. The relative magnitude of T1 during the monitoring period was calculated using the formula: T1(%)=(The amplitude of T1 during the period of monitoring/ T1 baseline)×100%.After intubation and 5min of stable recording of all parameters, intravenous rocuronium 0.3mg/kg was given in 5s through a three-way stopcock. Inhibition and recovery of the laryngeal adductors and the adductor pollicis were recorded, including lag time, onset time, the maximum inhibition of T1(Tmax.), the time for T1 to recover to 25%, 50%, 75%, 90% and 95% of baseline value and time for TOFr to recover to 0.75. The observation was finished when T1 recover to 100% of baseline value and TOFr recover to 0.75. The change of skin temperature was recorded. The data were analyzed with SPSS 10.0. for windows. Measurement data were expressed as mean±standard deviation. T test and ANOVA were used to compare baseline value and measured value of blood pressure, heart rate, skin temperature and induced twitch of the laryngeal adductors and the adductor pollicis before and after rocuronium administration. Significance was decided when P<0.05.ResultsAverage age, height, weight and body weight index were (34.5±8.8) years, (159.7±5.4) cm, (52.4±7.4) kg and( 20.5±2.3) kg/m2, respectively. Average skin temperature before rocuronium administration, when T1 attained maximum inhibition and TOFr =0.75 and the average skin temperature acquired at the thenar eminence were (33.3±1.0)℃, (33.2±1.0)℃and (33.1±1.0)℃,respectively (P>0.05). The changes in MAP and HR were below 5% in 5 min after rocuronium administration.After infusion of rocuronium 0.3 mg/kg, the lag time and onset time in laryngeal adductors ( 35.3±7.3 s and 3.3±0.8 min) were shorter than those in adductor pollicis (39.8±12.2 s and 4.3±1.5 min ) (P< 0.01), and Tmax in the former (73.3%±10.6%) is apparently little than that in the latter (95.7%±3.7%) (P<0.01). Time for T1 to recover to 50%, 75% of baseline value and for TOFr to recover to 0.75 in laryngeal adductors (12.3±5.4 min, 21.3±5.3 min and 21.5±6.2 min) were significantly shorter than those in adductor pollicis (20.4±4.1min, 26.0±5.3 min and 27.7±7.5 min) (P<0.01), and time for T1 to recover to 90% of baseline value in the former (25.5±7.0) min was shorter than that in the latter (31.5±7.2) min (P<0.05).ConclusionsWhen rocuronium 0.3 mg/kg was given in young and middle-aged female patients, the maximum inhibition of laryngeal adductors is little than that of adductor pollicis, and the onset of the paralysis is earlier and the time for neuromuscular effect to fade is shorter in the former than in the latter.Dual-cuff technique for monitoring evoked twitch response in laryngeal adductors is safe and yields stable and secure data. It is a feasible application in this situation.