Hironori Itoh

Left-molar Approach Improves the Laryngeal View in Patients with Difficult Laryngoscopy

Background The molar approach of laryngoscopy is reported to improve glottic view in sporadic cases of difficult laryngoscopy. The authors studied the effect of molar approaches and optimal external laryngeal manipulation (OELM) using the Macintosh blade. Methods A series of 1,015 adult patients who underwent general anesthesia and tracheal intubation was studied. Laryngoscopy was carried out using a Macintosh no. 3 or 4 standard blade. Three consecutive trials of direct laryngoscopy using the midline and left- and right-molar approaches were carried out under full muscle relaxation with optimal head and neck positioning. The best glottic views were recorded for each approach with and without OELM. Results Difficult laryngoscopy with a midline approach accounted for 6.5% (66 cases) before OELM and 1.97% (20 cases) after OELM. A left-molar approach with OELM further reduced difficult laryngoscopy to seven cases (P < 0.001 vs. midline approach with OELM); a right-molar approach with OELM reduced difficult laryngoscopy to 18 cases (P = 0.48). Conclusions The left-molar approach with OELM improves the laryngeal view in patients with difficult laryngoscopy.

Sensitivity to vecuronium in seropositive and seronegative patients with myasthenia gravis.

Patients with myasthenia gravis (MG) are hypersensitive to nondepolarizing neuromuscular blocking drugs. Although antibodies to the acetylcholine receptor (AChR) often are observed in MG patients, 10% to 30% of patients do not show an anti-AChR antibody. Little is known about differences in sensitivity to nondepolarizing neuromuscular blocking drugs between MG patients with and without anti-AChR antibody. Hypothesizing that seronegative patients are as sensitive to vecuronium as seropositive patients, we assessed sensitivity in seropositive and seronegative MG patients and in non-MG patients (n = 8 each). During anesthesia with sevoflurane (2.5%) and nitrous oxide (60%) in oxygen, neuromuscular transmission was monitored by measuring the twitch tension of the adductor pollicis muscle with supramaximal stimulation. After baseline measurements, 10 &mgr;g/kg IV dose increments of vecuronium were administered sequentially until blockade exceeded 90%. The degree of blockade and onset time after the initial 10 &mgr;g/kg of vecuronium were assessed, and doses required to exceed 90% blockade were recorded. In addition, effective doses of 50% and 95% for vecuronium were calculated from a single data point. Both types of MG patients showed increased sensitivity to vecuronium compared with non-MG patients.

Neuromuscular monitoring at the orbicularis oculi may overestimate the blockade in myasthenic patients.

BackgroundIn most publications about myasthenia, monitoring neuromuscular blockade during anesthesia is recommended. In healthy patients, the relation of blockade between muscles has been established, but there is little information about the relation in myasthenic patients. Our objective was to investigate whether the relation between the orbicularis oculi and adductor pollicis muscles is the same in healthy patients and myasthenic patients. MethodsAfter anesthesia was induced with 4–6 mg/kg thiopental and 2 &mgr;g/kg fentanyl, followed by 2% sevoflurane and 60% nitrous oxide in oxygen, 10 healthy patients and 10 myasthenic patients received 0.025 and 0.01 mg/kg vecuronium, respectively. Neuromuscular monitoring was performed with use of accelerometry at the orbicularis oculi and the adductor pollicis muscles by stimulating the temporal branch of the facial nerve and the ulnar nerve. ResultsThe relation of blockade between these two muscles was not the same in healthy patients and myasthenic patients: in healthy patients, the maximum neuromuscular blockade with 0.025 mg/kg vecuronium was less in the orbicularis oculi than in the adductor pollicis (median 72%vs. 91%;P < 0.05); in contrast, in myasthenic patients, the blockade with 0.01 mg/kg vecuronium was greater in the orbicularis oculi than in the adductor pollicis (median 96%vs. 62%;P < 0.05). ConclusionNeuromuscular monitoring at the orbicularis oculi may overestimate blockade in myasthenic patients. Extubation must be performed when the muscle most sensitive to neuromuscular blocking agents is recovered. Therefore, neuromuscular monitoring at the orbicularis oculi is recommended to avoid persistent neuromuscular blockade in patients with myasthenia gravis.

Train-of-four fade and neuromuscular block in rats: a comparison between pancuronium, vecuronium, and rocuronium

Purpose: To darify the relationship between neuromoscular block and train-of-four fade and to investigate the causes of these drugs-dependent differences, we compared the neuromuscular block and TOF fade after pancuronium, vecuronium and rocuronium.Methods: In 24 anesthetized rats, the sciatic nerve was stimulated, and the twitch of left tibialis anterior muscle was recorded. After T1 (first twitch response) was kept constant at 90% block by administration of pancuronium, vecuronium, or rocuronium (n=8, in each), the TOF fade was measured when T1 block was decreased to 40% and 20%. In addition using 24 phrenic nerve-diaphragm preparations, the fade was measured when the T1 block increased to 20% and 40% by titrating of either one of the three drugs (n=8, in each).Results: Inin vivo experiments, the fade produced by pancuronium was greater than that by vecuronium or rocuronium when T1 block was at 40% (81±9 vs 63±15 and 63±6%, respectively) and at 20% (66±13 vs 34±17 and 40±6%, respectively). In contrast, inin vitro experiments, the differences did not reach significant levels among the three drugs either at 20% (32±19 vs 33±10 and 32±17%) or 40% of block (62±29 vs 65±14 and 55±14%).Conclusions: For vecuronium and rocuronium, the results were similarin vivo and in vitro. For pancuronium, fade was greaterin vivo. These results suggest that different neuromuscular blocking agent have different relationships between the fade and the block.In vitro results might not be the same asin vivo, possibly due to pharmacokinetic differences.RésuméObjectif: Clarifier la relation entre le blocage neuromusculaire et l’affaiblissement de la réaction aux stimulations musculaires en train-de-quatre. De plus, comparer le bloc et l’affaissement du TDQ obtenu avec le pancuronium, le vécuronium et le rocuronium, et rechercher les causes des différences.Méthode: On a stimulé le nerf sciatique chez 24 rats anesthésiés et on a enregistré la contraction (twitch T) du muscle jambier antérieur gauche. Après avoir atteint un T1 constant (réponse à la première stimulation) avec un bloc à 95% en administrant du pancuronium, du vécuronium ou du rocuronium (n=8 dans chaque cas), l’affaissement du TDQ a été mesurée lorsque le bloc était réduit à 40% et à 20%. De plus, en utilisant 24 préparations de diaphragme-nerf phrénique, l’affaissement a été mesuré lorsque le bloc à T1 a été augmenté à 20% et à 40% en dosant l’un des trois médicaments (n=8 dans chaque cas).Résultats: Dans les expériencesin vivo, l’affaissement produit par le pancuronium a été plus grand que celui qui a été provoqué par le vécuronium ou le rocuronium lorsque le bloc à T1 était à 40% (81±9 vs 63±15 et 63±6%, respectivement) et à 20% (66±13 vs 34±17 et 40±6%, respectivement). Par ailleurs, dans les expériencesin vitro, les différences n’étaient pas significatives entre les trois médicaments, que ce soit un bloc à 20% (32±19 vs 33±10 et 32±17%) ou un bloc à 40% (62±29 vs 65±14 et 55±14%).Conclusion: Les résultats d’expériencesin vivo etin vivo ont été similaries avec le vécuronium et le rocuronium. L’affaissement du TDQ a été plus important avec le pancuronium lors d’expériencesin vivo. Ces résultats suggèrent que différents myorelaxants présentent des liens différents entre l’affaissement du TDQ et le bloc. Les résultats différents entre les expériencesin vitro etin vivo peuvent provenir de différences pharmacocinétiques.

Effects of neuromuscular‐blocking drugs in rats in vivo: Direct measurements in the diaphragm and tibialis anterior muscle

Background:  Effects of neuromuscular‐blocking drugs are often investigated in rodents using both the diaphragm in vitro and the tibialis anterior muscle in vivo. Differences in the properties of these muscles cannot be neglected. We evaluated the neuromuscular effects of drugs on the rat diaphragm in vivo in comparison with the tibialis anterior muscle, directly measuring twitch tension with a force transducer.

Cardiovascular Responses to the Induction of Mild Hypothermia in the Presence of Epidural Anesthesia

BackgroundThe combining of epidural anesthesia with general anesthesia impairs central and peripheral thermoregulatory control and therefore is often accompanied by unintended intraoperative hypothermia. However, little is known about the cardiovascular response to hypothermia during combined epidural and general anesthesia. The authors assessed the effects of hypothermia during such combined anesthesia. MethodsThe authors randomly assigned 30 mongrel dogs anesthetized with isoflurane (1.0%) to three groups of 10: control, receiving general anesthesia alone; thoracic injection, additionally receiving thoracic epidural anesthesia; and lumbar injection, additionally receiving thoracolumbar epidural anesthesia. Core temperature was lowered from 38.5°C to approximately 34°C (mild hypothermia) using a femoral arteriovenous shunt in an external cool water bath. During hypothermia, the authors measured heart rate, cardiac output, and plasma catecholamine concentrations in each group. Ejection fraction was also measured using echocardiography. ResultsCompared with measurements during baseline conditions (general anesthesia alone with no epidural injection and no hypothermia) in the control, thoracic, and lumbar injection groups, the injections followed by hypothermia produced 17, 32, and 41% decreases in heart rate; 22, 32, and 47% reductions in cardiac output; 66, 85, and 92% decreases in the epinephrine concentrations; and 27, 44, and 85% decreases in the norepinephrine concentrations. In contrast, ejection fraction did not change in any group. ConclusionMild hypothermia during combined epidural anesthesia and general anesthesia markedly reduced cardiac output in dogs, mainly by decreasing heart rate.

Comparison of Respiratory Sparing Effect on Pancuronium, Vecuronium and Rocuronium in Rats in Vivo

Respiratory muscles are more resistant to the action of muscle relaxants (MRs) such as pancuronium (PAN) than peripheral muscles, and this concept has been called respiratory sparing effect (RSE). Regarding to vecuronium (VEC) and rocuronium (ROC), however, the RSE has not been clearly elucidated yet. The aim of the present study was to compare the magnitude of RSE in rats on three steroidal MRs: PAN, VEC and ROC.