Masseter Muscle Rigidity After Initiating Monitored Anaesthesia Care of Propofol and Remifentanil

Masseter muscle rigidity can be seen following administration of opioids, succinylcholine, and nondepolarizing muscle relaxants. We report a case of a 56-year-old male patient in a “Cannot Intubate Cannot Ventilate Situation” due to masseter muscle rigidity after initiating monitored anaesthesia care (MAC) with remifentanil and propofol using target-controlled infusion in procedural cardiology. For rapid effect and equilibrium between plasma-concentration and effect site-concentration using target-controlled infusion, remifentanil overdose is possible during the induction period of MAC. Moreover, the presence of propofol could result in a significantly greater remifentanil concentration. To manage masseter muscle rigidity, muscle relaxants and emergent ventilation systems should be prepared to secure airway maintenance. In addition, alternative airway management devices and techniques should be on hand even if no airway difficulties are expected.

Management of Residual Neuromuscular Blockade Recovery: Age-Old Problem with a New Solution

Neostigmine has been traditionally used as the agent of choice to reverse Neuromuscular Blockade (NMB) after muscle paralysis during general anesthesia. However, the use of neostigmine has not been without untoward events. Sugammadex is a novel drug that selectively binds to aminosteroid nondepolarizing muscle relaxants and reverses even a deep level of NMB. Controversy exists regarding the optimal dose of sugammadex that is effective in reversing the NMB after the incomplete reversal with neostigmine and glycopyrrolate. We discuss a case where sugammadex reduced the time of the recovery from NMB in a patient who had incomplete antagonisms following adequate treatment with neostigmine, aiding timely extubation without persistent residual NMB, and hence prevented the requirement of postoperative ventilation and the improvement in patient care. More randomized control studies are needed in order to conclude the appropriate dose of sugammadex in cases of incomplete reversal.

The Use of Intravenous Neostigmine in Palliation of Severe Ileus

Neostigmine is a parasympathomimetic drug that acts as a reversible acetylcholinesterase inhibitor. Clinically it is used in patients with acute colonic pseudo-obstruction (ACPO or Ogilvie’s syndrome, which is a gastrointestinal motility disorder characterized by marked dilatation of the colon in the absence of mechanical obstruction), postoperative ileus, urinary retention, myasthenia gravis, and in anesthesia to reverse the effects of nondepolarizing muscle relaxants. Both bolus and infusion are noted to be effective and lead to prompt evacuation of flatus or stool with a reduction in abdominal distention on physical examination. Median duration is noted to be 4–30 minutes in some trials. Here we present our experience of using 2 mg of intravenous neostigmine to help relieve the severe abdominal distention and ileus in a patient with severe fecal impaction when all conservative measures had been futile. The most frequent side effect of the drug is abdominal pain/cramping, which was noted in our patient as well. Other complications include bradycardia which is very infrequently symptomatic to require atropine. Overall, the drug is a simple, safe, and effective strategy; and as pointed out in the previous studies, the drug appears to be underused in patients who do not have a true contraindication to its use.

Onset–potency relationship of nondepolarizing muscle relaxants: a reexamination using simulations

Nondepolarizing muscle relaxants (MRs) display an inverse onset–potency relationship, that is, less potent MRs display a more rapid onset. We have conducted the current investigation to estimate the impact of variable pharmacokinetic or pharmacodynamic properties of the MRs on potency and onset time, and on the onset–potency relationship. Using a model of neuromuscular transmission, we changed either the affinity of MRs for the postsynaptic receptors or the pharmacokinetic properties of the MRs. The elimination rate constant, k10, which defines the systemic clearance, was assigned one of 9 values and the transport rate constant, k12, one of 5 values. The transport rate constant into the effect compartment was constant (ke1 = 0.2 min–1). Only one parameter was altered at a time. With constant pharmacokinetics, a 100-fold decrease in affinity caused a proportional decrease in potency, but little change (0.02 min) in onset time. With constant affinity, increasing the clearance from 1 to 250 mL·kg–1·min–1 shortened the onset time from 7.2 to 0.7 min and decreased the potency 12-fold. In a double logarithmic plot, the onset–potency relationship was linear. Lesser affinities produce a nearly parallel rightward shift of the regression lines. The inverse onset–potency relationship may be explained by the pharmacokinetic factors producing changes in both the potency and onset times.