Postoperative neuromuscular function in pediatric day-care patients.

After anesthesia employing nondepolarizing muscle relaxants, 30%-40% of adult patients demonstrate residual paralysis with a train-of-four ratio less than 70%, but it is not known if the same is true for children. This study was designed to investigate neuromuscular transmission in 91 ASA physical status I or II day-care children (aged 0-10 yr) after halothane anesthesia in which pancuronium (n = 34), atracurium (n = 32), or vecuronium (n = 25) was administered. Peripheral nerve stimulation was used clinically to assess neuromuscular blockade during surgery. In the recovery room, the evoked response of the adductor pollicis muscle was measured by train-of-four stimulation of the ulnar nerve. This measurement was made (mean +/- SEM) at 18.0 +/- 1.5, 15.0 +/- 1.3, and 15.0 +/- 1.7 min after pharmacologic antagonism with 0.02 mg/kg atropine and 0.06 mg/kg neostigmine in the pancuronium, atracurium, and vecuronium groups, respectively. There were no differences in the ages of the patients in the three groups at 4.3 +/- 0.4, 4.0 +/- 0.4, and 5.0 +/- 0.5 yr, with 17 children less than 2 yr. Recovery from neuromuscular blockade in all three groups was almost complete. The train-of-four ratio (height of fourth twitch compared with the first) was similar in patients who had received pancuronium (96.7% +/- 0.9%), atracurium (95.5% +/- 0.9%), or vecuronium (96.3% +/- 1.3%). Therefore, postoperative muscle weakness or respiratory impairment is unlikely in pediatric day-care surgical patients more than 2 yr old when these anesthetic techniques are used.     

Postoperative residual block after intermediate-acting neuromuscular blocking drugs

The frequency and duration of postoperative residual neuromuscular block on arrival of 150 patients in the recovery ward following the use of vecuronium (n = 50), atracurium (n = 50) and rocuronium (n = 50) were recorded. Residual block was defined as a train-of-four ratio of <0.8. An additional group of 10 patients received no neuromuscular blocking drugs during anaesthesia. The incidence of postoperative residual neuromuscular block was 64%, 52% and 39% after the use of vecuronium, atracurium and rocuronium, respectively. Similar numbers of patients were not able to maintain a sustained head or leg lift for 5 s on arrival in the recovery ward. The mean [range] times to attaining a train-of-four ratio of > or =0.8 after arrival in the recovery ward were 9.2 [1-61], 6.9 [1-24] and 14.7 [1.5-83] min for vecuronium, atracurium and rocuronium, respectively. None of the 10 patients who did not receive neuromuscular blocking drugs had train-of-four ratios <0.8 on arrival in the recovery ward. It is concluded that a large proportion of patients arrive in the recovery ward with a train-of-four ratio <0.8, even with the use of intermediate-acting neuromuscular blocking drugs. Although the residual block is relatively short lasting, it may occasionally be prolonged, requiring close observation and monitoring of such patients in the recovery ward.     

Monitoring of neuromuscular function

Clinical monitoring of neuromuscular function can be accomplished by either measuring the evoked mechanical or EMG response of a skeletal muscle via an accessible motor nerve. The pattern of motor nerve stimulation varies from supramaximal single repeated stimuli at a specified frequency to tetanic stimulation, posttetanic single stimuli at the pretetanic frequency, and train-of-four stimuli at 2 Hz. The response to relaxants is unpredictable in the population at large and more so in pathologic states. This makes monitoring of the muscle response to motor nerve stimulation extremely valuable and helpful. The train-of-four technique of measurement has proved to be valuable not only as a reliable clinical tool to measure the response to relaxants and monitoring recovery, but also as a research tool for studies of old and new neuromuscular blocking drugs. Evoked responses and clinical criteria for adequate recovery from muscle relaxants should complement each other. The more criteria fulfilled, the better and safer the conclusion that the patient has recovered from clinical neuromuscular blockade.     

Postoperative residual neuromuscular block: a survey of management

Background. To avoid postoperative residual neuromuscular blockthere is a need for a change in clinician's attitude towardsmonitoring and reversal. This study aims to evaluate changesof perioperative neuromuscular block management during the lastdecade in our institution and to quantify the incidence of postoperativeresidual neuromuscular block. Methods. Patients receiving intermediate-acting neuromuscularblocking agents for scheduled surgical procedures during 3-monthperiods in 1995 (n=435), 2000 (n=130), 2002 (n=101), and in2004 (n=218) were prospectively and successively enrolled inour study. The management of neuromuscular block in the operatingroom and the adequacy of the recovery were at the discretionof the anaesthesiologist. An attempt was made between each studyperiod to promote a change in the management of neuromuscularblock. In the post-anaesthesia care unit, train-of-four (TOF)stimulations were used to assess the presence of a residualneuromuscular block. Results. Between 1995 and 2004 quantitative measurement andreversal of neuromuscular block in the operating room increasedfrom 2 to 60% and from 6 to 42%, respectively (P<0.001).During the same time, the incidence of residual neuromuscularblock defined as a TOF ratio less than 0.9 decreased from 62to 3% (P<0.001). Use of objective neuromuscular monitoringand/or anticholinesterase drugs was less likely in patientswith an inadequate recovery (P<0.001). Conclusions. During the last decade the incidence of residualneuromuscular block strongly decreased in our institution. Itconfirms the positive impact of neuromuscular monitoring andreversal of neuromuscular block in routine anaesthetic practice.     

Postoperative neuromuscular block following atracurium or alcuronium in children

Postoperative neuromuscular block (NMB) was evaluated in 60 children who received randomly either atracurium or alcuronium to induce and maintain an 85-95 per cent NMB during balanced anaesthesia. The EMG-monitor was turned away from the anaesthetist 10-15 min before the end of surgery. The average NMB was comparable between the groups at the time of reversal with neostigmine 50 micrograms.kg-1 (84 +/- 9 per cent, mean +/- SD) as were the NMB and the train-of-four ratio when the tracheas were extubated on a clinical basis (32 +/- 20 per cent and 50 +/- 18 per cent, respectively). Patients who had been paralyzed with atracurium arrived at the recovery room earlier and on arrival had greater train-of-four ratios than the patients paralyzed with alcuronium (P less than 0.01). Time to a train-of-four ratio of greater than 90 per cent was significantly shorter in the atracurium group (10 +/- 5 min vs 26 +/- 15 min, P less than 0.001). Thus, an intermediate-acting muscle relaxant offers a safer recovery profile of the NMB than a long-acting muscle relaxant in paediatric patients.     

Assessment of neuromuscular function in infants

This study was conducted to measure neuromuscular transmission in newborn infants. Age-dependent differences in neuromuscular transmission and the effect of nitrous oxide anesthesia upon neuromuscular function were assessed in pediatric surgical patients following induction of anesthesia with methohexital by the use of the frequency sweep electromyogram (FS-EMG). Children older than 12 weeks' chronologic age usually had FS-EMG responses similar to those of adults, whereas infants less than 12 weeks old had significantly less pronounced FS-EMG responses at high stimulation frequencies (>50 Hz). Administration of 70 per cent nitrous oxide induced 11-38 per cent reductions in the amplitudes of the FS-EMG responses at all frequencies of stimulation in the younger group. A positive correlation was found between inability to sustain a tetanic contracture (FS-EMG fade) in the 50-100-Hz region of stimulation and percentage depression of the FS-EMG response induced by nitrous oxide.     

Postoperative hypophosphataemia and muscle function

Muscle function tests of the triceps brachii muscle were performed before operation and on the third postoperative day in ten patients undergoing elective cholecystectomy. Electromyograms (EMGs) were recorded by surface electrodes during sustained isotonic and isometric muscle contraction with a constant force of 20 per cent of the preoperative maximal voluntary contraction. Root-mean-square of the EMG was calculated together with the neuromuscular efficiency and measures of the fatiguability. These parameters were compared with changes in the simultaneously measured serum phosphate concentrations. Mean (s.e.m.) neuromuscular efficiency measured after 32-40 s of muscle contraction decreased 14(5) per cent after operation (P less than 0.01), whereas the mean fatiguability of the muscle was unchanged. Mean serum phosphate concentration was 0.87(0.06) mmol/l before operation and 0.79(0.06) mmol/l 3 days after the operation (P greater than 0.05). Two patients developed severe postoperative hypophosphataemia (serum phosphate concentration less than 0.50 mmol/l). Postoperative muscle function deterioration was not associated with changes in the serum phosphate level (P greater than 0.10; r = 0.03). We conclude that patients undergoing cholecystectomy develop postoperative deterioration in skeletal muscle function, which is not associated with serum phosphate concentration.     

Postoperative disorders of cardiovascular function

Cardiovascular instability is the cause of almost 50% of postoperative complications and raises postoperative mortality far above that intraoperatively. The aged patient with pre-existing heart disease represents a high postoperative risk. These patients are very susceptible to hypoxia, anemia, hypovolemia, the negative inotropic effects of certain anesthetics, and increased oxygen consumption due to shivering. The reversal of anesthetic agents is also rather debatable in these cases. Hypertension and arrhythmias are common phenomena in the recovery room. They may be aggravated by a number of factors such as metabolic and respiratory imbalances, incorrect fluid substitution, pain, or excitation. The frequency of postoperative myocardial infarction (MI) depends upon pre-existing coronary artery disease and hypertension. A medical history of heart failure or previous MI also plays an important role hemodynamic course as do the surgical procedure and the intraoperative. Postoperative hemodynamic monitoring should be performed according to the standards suggested by the American Society of Anesthesiologists. Medical treatment basically consists of symptomatic therapy and the avoidance of risk factors. Specific treatment is rarely required.     

Effects of tourniquet compression on neuromuscular function

Neuromuscular function in New Zealand White rabbits was evaluated after thigh tourniquet compression in the directly compressed quadriceps muscles and the distal tibialis anterior by measuring isometric contractile function after supramaximal stimulation of the motor nerve. Tourniquet compression resulted in markedly decreased force production beneath and distal to the tourniquet. Two days after compression, maximal quadriceps force production was decreased to 46% of control values with 125 mm Hg compression and 21% of control values after 350 mm Hg compression. Maximum tibialis anterior force production declined to 70% of control values after 125 mm Hg thigh compression and 24% of control values after 350 mm Hg thigh compression. Functional deficits were greater in the directly compressed quadriceps muscles, but the quadriceps and tibialis anterior had significantly increased impairment when the tourniquet inflation pressure was increased from 125 mm Hg to 350 mm Hg. Three weeks after compression, quadriceps function had returned to 94% of control value after 125 mm Hg compression and 83% after 350 mm Hg. Tibialis anterior function returned to 88% of control values after 125 mm Hg thigh compression and 83% after 350 mm Hg. Clinically, the use of lower inflation pressures may minimize the complications of tourniquet use and enhance postoperative recovery.