Control of breathing in patients with limb girdle dystrophy: a controlled study.

BACKGROUND--In patients with limb girdle dystrophy the relative contribution of peripheral factors (respiratory muscle weakness, and lung and/or airway involvement) and central factors (blunted and/or inadequate chemoresponsiveness) in respiratory insufficiency has not yet been established. To resolve this, lung volumes, arterial blood gas tensions, respiratory muscle strength, breathing pattern and neural respiratory drive were investigated in a group of 15 patients with limb girdle dystrophy. An age-matched normal group was studied as a control. METHODS--Respiratory muscle strength was assessed as an arithmetic mean of maximal inspiratory (MIP) and expiratory (MEP) pressures. Breathing pattern was evaluated in terms of volume (ventilation VE, tidal volume VT) and time (respiratory frequency Rf, inspiratory time TI, expiratory time TE) components of the respiratory cycle. Neural respiratory drive was assessed as the mean inspiratory flow (VT/TI), mouth occlusion pressure (P0.1) and electromyographic activity (EMG) of the diaphragm (EMGd) and the intercostal parasternal (EMGp) muscles. In 10 of the 15 patients the responses to carbon dioxide (PCO2) stimulation were also evaluated. RESULTS--Most patients exhibited a moderate decrease in vital capacity (VC) (range 37-87% of predicted), MIP (range 23-84% of predicted), and/or MEP (range 13-41% of predicted). The arterial carbon dioxide tension (PaCO2) was increased in three patients breathing room air, while PaO2 was normal in all. Compared with the control group Rf was higher, and VT, TI and TE were lower in the patients. EMGd and EMGp were higher whilst VT/TI and P0.1 were normal in the patients. Respiratory muscle strength was inversely related to EMGd and EMGp. PaCO2 was found to relate primarily to VC and duration of illness, but not to respiratory muscle strength. During hypercapnic rebreathing delta VE/delta PCO2, delta VT/delta PCO2, and delta P0.1/delta PCO2 were lower than normal, whilst delta EMGd/delta PCO2 and delta EMGp/delta PCO2 were normal in most patients. A direct relation between respiratory muscle strength and delta VT/delta PCO2 was found. CONCLUSIONS--The respiratory muscles, especially expiratory ones, are weak in patients with limb girdle dystrophy. Reductions in respiratory muscle strength are associated with increased neural drive and decreased ventilatory output (delta VT/delta PCO2). The decrease in VC, together with the duration of disease, influence PaCO2. VC is a more useful test than respiratory muscle strength for following the course of limb girdle dystrophy.     

Effets ventilatoires d’une hypothermic modérée (36° C–28° C) chez le chien anesthésie à l’halothane

Changes in systemic haemodynamic variables (mean arterial pressure, MAP; heart rate, HR; cardiac output, Qc), in oxygen consumption, VO2, and in ventilation (minute ventilation, V; respiratory frequency, f; tidal volume, VT; and arterial blood gases) with particular attention to respiratory times (duration of inspiration, TI; duration of expiration, TE; duration of the breathing cycle, TTOT), to respiratory timing (TI/TTOT) and respiratory drive (VT/TI) were studied during moderate progressive hypothermia (36 degrees C to 28 degrees C) during stable halothane anaesthesia (MAC = 1.5) in six dogs. MAP, HR and Qc decreased; V and f decreased, the decrease in f being correlated with that in temperature (r = 0.66; P < 0.01). Tidal volume did not change. The PaO2 and pHa decreased while PaCO2 increased slightly. The decrease in ventilation was related to changes in respiratory times (TI and TE) which increased (TE more than TI) and in respiratory drive (VT/TI which decreased due to the increase in TI). The relation between VT/TI and TI/TTOT changes was not constant during cooling. Changes in respiratory times and drive could be due to the effect of cold on medullar respiratory control.     

Evaluation of respiratory muscle strength by randomized controlled trial comparing thoracoscopy, transaxillary thoracotomy, and posterolateral thoracotomy for lung biopsy.

OBJECTIVE: The aim of this study was to demonstrate that the postoperative recovery of respiratory muscle strength is better in patients who undergo video-thoracoscopy than in patients who undergo transaxillary thoracotomy or posterolateral thoracotomy. DESIGN: Randomized controlled trial with three parallel groups. Study population: Eligible patients had undergone wedge resection for lung biopsy in interstitial lung disease or in pulmonary nodule. Twenty-four patients were randomly assigned to one of the three thoracic procedures: eight in the video-thoracoscopy (VT) group, eight in the transaxillary thoracotomy (TT) group, and eight in the posterolateral thoracotomy (PLT) group. MEASUREMENTS: The postoperative respiratory muscle strength was assessed by maximum inspiratory pressure (MIP) and maximum expiratory pressure (MEP) measured by mouth pressure. Measurements were made the day before the operation and 2, 4, and 30 days after the operation. Changes in postoperative MIP and MEP were expressed as a percentage of preoperative values. RESULTS: The three groups were comparable with respect to age, gender, comorbidity, preoperative spirometry, preoperative MIP, MEP and peak flow, and volume of lung tissue. At 2, 4, and 30 days after the operation, mean MIP were, respectively, 111+/-22%, 119+/-22%, and 124+/-22% in the VT group, 76+/-22%, 109+/-22%, and 127+/-22% in the TT group, and 51+/-22%, 50+/-22%, and 77+/-22% in the PLT group (p<0.0001). At 2, 4, and 30 days after the operation, mean MEP were, respectively, 94+/-15%, 103+/-15%, and 105+/-15% in the VT group, 61+/-15%, 98+/-15%, and 126+/-15% in the TT group, and 62+/-15%, 75+/-15%, and 87+/-15% in the PLT group (p<0.05). CONCLUSIONS: Video-thoracoscopy allows better recovery of respiratory muscle function after surgery than posterolateral thoracotomy. However, at 4 and 30 days after surgery, video-thoracoscopy and transaxillary thoracotomy gave similar results of impairment of respiratory muscle strength.     

Evaluation of amplified spontaneous pattern ventilation in postoperative patients. Comparison with pressure support]

HYPOTHESIS: Amplified spontaneous pattern (ASP) ventilation is a new method for giving partial support by reproducing, in an amplified manner, the patients' own spontaneous flow wave form, thereby optimizing patient adaptation to support. OBJECTIVES: To study clinical use of ASP ventilation for the first time in terms of flow wave form, patient synchronization, ventilation pattern, work of breathing (WOB), and inspiratory effort by transpulmonary pressure (TPP) and to compare ASP and pressure support ventilation applied in a similar clinical setting. PATIENTS AND METHOD: We studied 20 patients after heart surgery during weaning from controlled ventilation. Each patient was ventilated during 4 phases of 15 min each with two similar levels of support using ASP and PS applied successively and randomly. Maximum support (ASPmax and PSmax) was that which was set to give the same respiratory frequency (F) and tidal volume (VT) as that recorded during the earlier period of controlled ventilation. Half support (PEA1/2 and PS1/2) was set for half the aforementioned levels. At the end of each phase we obtained gas measurements and flow (V) curves and VT and pressure in airways and esophagus (Pes) to measure F, VT, the ratio of inspiratory to total time (TI/TTOT and TPP, as well as the VT/Pes loop with a mechanical ventilation monitor. The WOB was determined by measuring area under the curve (Campbell's method). RESULTS: We observed no significant differences between the two modes, with similar levels of support, with regard to ventilation (PaCO2) or ventilatory pattern (F, VT, TI/TTOT). De-adaptation occurred, however, eight times with PS (25%) but never with ASP. WOB and TPP decreased with PS when level of support increased, whereas with ASP these variables were constant regardless of level of amplification within the normal range. CONCLUSIONS: Adaptation to support is better with ASP than with PS during postoperative weaning and causes no significant respiratory work overload.     

Myasthenic crisis

Opinion statement Myasthenia gravis is the most common disorder of the neuromuscular junction. Myasthenia crisis, defined as respiratory failure requiring mechanical ventilation in myasthenia gravis, is a common life-threatening complication that occurs in approximately 15% to 20% of patients with myasthenia gravis. The advent of effective mechanical ventilation, specialized neurointensive care units, and the widespread use of immunotherapies have substantially altered the prognosis of myasthenic crisis. The authors recommend more liberal intubation of patients with myasthenia gravis crisis; early intubation and mechanical ventilation is perhaps the most important step in the management of myasthenia gravis crisis. The authors favor an orotracheal approach for intubation, and placement of small bore duodenal tubes that may help decrease the risk of aspiration and may be more comfortable than regular nasogastric tubes for the patient. Plasma exchange is more effective than intravenous immunoglobulin in the treatment of myasthenia gravis involving respiratory failure. A randomized trial is required to confirm the superior efficacy of plasma exchange compared with intravenous immunoglobulin. In the acute setting, the role of immunosuppression and intravenous or intramuscular pyridostigmine remains limited and at times controversial. The therapy should be tailored on an individual basis using the best clinical judgment.     

Ventilatory changes during nitrous oxide isoflurane anaesthesia in children

The changes in ventilatory variables under nitrous oxide isoflurane anaesthesia were studied in 10 children (mean age 46 +/- 13.4 months, mean weight 16.2 +/- 2.1 kg). Measurements of flow and volume were performed by pneumotachography. PE'CO2 was measured by capnography. The following variables (VE, VT, TI/TTOT, VI, PE'CO2) were measured or calculated under three increasing inspired isoflurane concentrations (0.75%, 1.5%, 2.25%). At each level of anaesthesia, ventilatory changes during exposure to an inspired CO2 fraction of 2% were studied. The increase in the inspired concentration of isoflurane was associated with a decrease in alveolar ventilation. PE'CO2 increased significantly with increasing depth of anaesthesia. The respiratory rate was slightly increased under light nitrous oxide isoflurane anaesthesia, but no further changes were observed with increasing depth of anaesthesia, although the children were breathing a mixture of nitrous oxide and oxygen. The ventilatory response to a raised inspired CO2 is markedly decreased under light nitrous oxide isoflurane anaesthesia, and decreases significantly with increasing depth of anaesthesia. In response to a raised CO2, VE, VT and VI increase, but respiratory rate decreases or remains constant and TI/TTOT is unchanged.     

Breathing pattern and central ventilatory drive in mild and moderate generalised myasthenia gravis.

BACKGROUND--Myasthenia gravis is a specific autoimmune disease characterised by weakness and fatigue. Respiratory muscle weakness has been studied using the determination of maximal respiratory pressures, but the response of respiratory centres is not well characterised. This study was undertaken to determine the breathing pattern and the central ventilatory drive in patients with mild and moderate generalised myasthenia gravis. METHODS--Twenty four patients with myasthenia gravis were studied, divided into two groups. Group 1 included 13 subjects (eight women and five men aged 23-64) with mild generalised myasthenia gravis, and group 2 was composed of 15 patients (11 women and four men aged 23-69) with moderate generalised myasthenia gravis. A control group comprised 15 healthy persons with a similar age and sex distribution. Spirometric measurements and maximal respiratory pressures were performed under basal conditions in all subjects, and the rate and depth of breathing and the inspiratory occlusion pressure in the mouth in the first 0.1 second (P0.1) were measured. RESULTS--No difference was detected for parameters of breathing pattern between patients in group 1 and control subjects, although P0.1 was higher in those in group 1. Subjects in group 2 had a lower tidal ventilation, shorter inspiratory time, and a higher frequency with a higher P0.1 than control subjects. CONCLUSIONS--Mild myasthenia gravis causes increased neuromuscular drive with a normal breathing pattern. Moderate myasthenia gravis is characterised by a more rapid shallow breathing pattern.     

Effect of Analgesia on Respiratory Muscle Function after Upper Abdominal Surgery

The effects of three methods of analgesia (intravenous morphine, epidural lidocaine and epidural morphine) on vital capacity (VC), forced expiratory volume in 1 s (FEV₁) and maximal expiratory and inspiratory pressures (MEP and MIP) at the mouth were studied in 12 high respiratory risk patients following upper abdominal surgery. VC, FEV¹, MEP and MIP markedly decreased following laparotomy. VC and FEV₁, were partially restored by epidural analgesia and remained unchanged following intravenous morphine. MEP and MIP remained unchanged after each of the three methods of analgesia. This suggests the existence of a non-analgesic dependent dysfunction of inspiratory and expiratory muscles following upper abdominal surgery.     

疼痛对上腹部术后呼吸肌功能不全的影响

目的　观察疼痛在上腹部手术后呼吸肌功能不全中所起的作用。方法　ASAⅠ～Ⅱ级择期腹腔镜胆囊切除术患者 30例 ,随机分为病人自控镇痛 (PCA)组与对照组 ,每组 15例。用最大吸气压 (MIP)和最大呼气压 (MEP)来评估呼吸肌功能。两组于术前 ,术后 2 4、4 8h分别测定MIP、MEP ,并用视觉模拟疼痛评分法 (VAS)评估疼痛程度。结果　术后对照组的MIP与MEP比术前显著下降 (P <0 0 5 )。VAS评分两组均增加 ,与术前相比 ,对照组有显著差异 (P <0 0 5 )。两组相比 ,PCA组的VAS增加明显少于对照组 (P <0 0 5 )。MIP、MEP和疼痛在统计学上有显著相关 (P <0 0 1)。结论　疼痛是导致上腹部术后呼吸肌功能不全的一个重要因素 ,而PCA则能部分地改善术后呼吸肌功能不全     

Effects of scoliosis on respiratory muscle strength in patients with neuromuscular disorders

Background contextNeuromuscular disorders (NMD) are characterized by loss of lung volume and respiratory muscle weakness, but the effects of scoliosis on lung function are unclear.PurposeTo compare pulmonary function and respiratory muscle strength in patients with NMD with and without scoliosis as well as in healthy controls.Study design/settingProspective comparison of pulmonary function testing and respiratory muscle strength were made at the pediatric pulmonology and cardiopulmonary rehabilitation units of a university hospital.Patient sampleTwenty-two patients with NMD and scoliosis, 17 patients with NMD without scoliosis, and 24 age- and sex-matched healthy controls. Outcome measures were compared in patients with NMD with and without scoliosis and healthy subjects using Student t test, Mann-Whitney U test, chi-square test, one-way analysis of variance (ANOVA), Kruskal-Wallis one-way ANOVA, Pearson correlation coefficients, and Spearman rank correlation, as appropriate.Outcome measures1) Pulmonary function: forced vital capacity (FVC), forced expiratory volume in 1 second (FEV₁), peak expiratory flow rate (PEF), forced expiratory flow between 25% and 75% of FVC (FEF_25–75%), and maximum expiratory flows at 75%, 50%, and 25% of FVC (MEF₇₅, MEF₅₀, and MEF₂₅, respectively); 2) oxygen saturation: pulse oxymeter reading; and 3) respiratory muscle strength: maximal inspiratory mouth pressure (MIP) and maximal expiratory mouth pressure (MEP).MethodsPulmonary function, oxygen saturation, MIP, and MEP were measured and compared in patients with NMD, patients with and without scoliosis, and in healthy subjects.ResultsThe patients with NMD, both with and without scoliosis, had significantly lower PEF, MIP, MEP, % predicted MIP (%MIP), and % predicted MEP (%MEP) than those of healthy subjects (p<.05). The patients with NMD and scoliosis had significantly lower values than those with NMD without scoliosis and controls (p<.05) for FVC, FEV₁, and FEF_25–75%.ConclusionBoth inspiratory and expiratory muscle strength were diminished in patients with NMD compared with healthy controls. Significant differences were also noted in pulmonary function in patients with NMD with or without scoliosis. This suggests that NMD may impact respiratory function independently of the effects of scoliosis. Clinicians treating patients with NMD should be aware of the possibility of compromised respiratory function in these patients to address possible complications.     

Breathing pattern and carbon dioxide retention in severe chronic obstructive pulmonary disease.

BACKGROUND: The factors leading to chronic hypercapnia and rapid shallow breathing in patients with severe chronic obstructive pulmonary disease (COPD) are not completely understood. In this study the interrelations between chronic carbon dioxide retention, breathing pattern, dyspnoea, and the pressure required for breathing relative to inspiratory muscle strength in stable COPD patients with severe airflow obstruction were studied. METHODS: Thirty patients with COPD in a clinically stable condition with forced expiratory volume in one second (FEV1) of < 1 litre were studied. In each patient the following parameters were assessed: (1) dyspnoea scale rating, (2) inspiratory muscle strength by measuring minimal pleural pressure (PPLmin), and (3) tidal volume (VT), flow, pleural pressure swing (PPLsw), total lung resistance (RL), dynamic lung elastance (ELdyn), and positive end expiratory alveolar pressure (PEEPi) during resting breathing. RESULTS: Arterial carbon dioxide tension (PaCO2) related directly to RL/PPLmin, and ELdyn/PPLmin, and inversely to VT and PPLmin. There was no relationship between PaCO2 and functional residual capacity (FRC), total lung capacity (TLC), or minute ventilation. PEEPi was similar in eucapnic and hypercapnic patients. Expressing PaCO2 as a combined function of VT and PPLmin (stepwise multiple regression analysis) explained 71% of the variance in PaCO2. Tidal volume was directly related to inspiratory time (TI), and TI was inversely related to the pressure required for breathing relative to inspiratory muscle strength (PPLsw, %PPLmin). There was an association between the severity of dyspnoea and both the increase in PPLsw (%PPLmin) and the shortening in TI. CONCLUSIONS: The results indicate that, in stable patients with COPD with severe airflow obstruction, hypercapnia is associated with shallow breathing and inspiratory muscle weakness, and rapid and shallow breathing appears to be linked to both a marked increase in the pressure required for breathing relative to inspiratory muscle strength and to the severity of the breathlessness.     

Maternal myasthenia gravis complicated by fetal arthrogryposis multiplex congenita

We report the management of a 24-year-old primigravid woman who was diagnosed with myasthenia gravis at 20 weeks of gestation. Maternal symptoms improved with therapeutic plasma exchange, steroids, immunoglobulin therapy and pyridostigmine. Despite this, the fetus had arthrogryposis multiplex congenita due to trans-placental transfer of anti-acetylcholine receptor antibodies. The baby was delivered by elective caesarean section at 34 weeks of gestation but died in the immediate postpartum period. The mother underwent thymectomy within five weeks of delivery. The implications of myasthenia gravis for both the mother and baby are discussed.     

An analysis of the ventilatory response to carbon dioxide during halothane, isoflurane, or enflurane anesthesia in humans

To analyze the effects of halothane, isoflurane, or enflurane on the ventilatory response to CO2, minute volume (VE), respiratory rate (f), occlusion pressure, mean inspiratory flow rate (VT/TI), and effective elastance (Pmax/VT) were measured in 26 patients during quiet breathing and when the respiratory system was stressed by CO2. Comparison was made at equipotent anesthetic concentration (1 MAC) and all measurements were made in the absence of surgical stimulation. Respiratory rate and Pmax/VT were unchanged in all groups after end-tidal CO2 was elevated. By contrast, VE, VT/TI, and occlusion pressure increased in all the groups when the respiratory system was stressed by CO2. Among the parameters tested delta VE/delta PaCO2 and delta VT/TI/delta PaCO2 were significantly (P less than 0.05) greater during halothane anesthesia than during isoflurane or enflurane anesthesia. We conclude that, at equipotent anesthetic concentrations, isoflurane and enflurane depress CO2 chemosensitivity more than halothane does, and that such effect is primarily related to the greater depressant effects of isoflurane and enflurane on the respiratory driving mechanisms.     

Neonatal pattern of breathing following cesarean section: epidural versus general anesthesia

We tested the hypothesis that different anesthetic techniques for elective cesarean section would be reflected in the pattern of breathing and its control after birth. The pattern of breathing, including tidal volume, total breath duration (TTOT), minute ventilation, inspiratory (TI) and expiratory times, TI/TTOT ratio, and mouth occlusion pressure, was measured in 27 infants delivered by elective cesarean section during maternal epidural (lidocaine-carbon dioxide-epinephrine, n = 19) or general anesthesia (66% oxygen in N2O and 0.5% halothane, n = 8) at 10, 60, and 90 min and 3-5 days of age. Neonatal acid-base values and Apgar scores were within normal limits in both groups of infants. In general, at any given age the values of the respiratory parameters measured and their variability were similar between the two groups of infants. These findings indicate that the pattern of breathing after birth is not different following epidural or general anesthesia, and on the basis of our measurements, both epidural or general anesthesia appeared equally suitable for elective cesarean section.     

Preanesthetic train-of-four fade predicts the atracurium requirement of myasthenia gravis patients

BACKGROUND: The most sensitive diagnostic criterion of myasthenia gravis is a decrement in the muscular response to repetitive stimulation. The authors hypothesized that myasthenia gravis patients who show a train-of-four ratio (T4/T1) < 0.9 in the preanesthetic period will have increased sensitivity to nondepolarizing neuromuscular blocking agents compared with myasthenia gravis patients with preanesthetic T4/T1 > or = 0.9. METHODS: After institutional review board approval was obtained, 20 electrophysiologically documented myasthenia gravis patients were studied. Current pyridostigmine therapy was continued until the morning of surgery. Before induction of anesthesia, neuromuscular transmission was recorded from the hypothenar muscles using electromyography with train-of-four stimulation of the ulnar nerve. According to the T4/T1 ratio, patients were assigned to the "normal" group (T4/T1 > or = 0.9) or the "decrement" group (T4/T1 < 0.9). After induction of intravenous anesthesia, the effective dose to achieve a 95% neuromuscular blockade (ED95) for atracurium was assessed with a cumulative bolus technique. Postoperatively, pyridostigmine was titrated to obtain a T4/T1 > 0.75 and to treat residual myasthenic symptoms. RESULTS: In 14 patients, preanesthetic T4/T1 was > or = 0.9 (normal), whereas 6 patients presented with T4/T1 < 0.9 (decrement). Decrement patients had a lower ED95 of 0.07 +/- 0.03 mg/kg atracurium (mean +/- SD) compared with normal patients with an ED95 of 0.24 +/- 0.11 mg/kg atracurium (P = 0.002). All patients were extubated within 30 min after surgery. Postoperative pyridostigmine infusion did not differ significantly between groups. CONCLUSIONS: The requirement for atracurium is significantly reduced in myasthenia gravis patients with a T4/T1 ratio < 0.9 before anesthesia. This study indicates that routine neuromuscular monitoring in myasthenia gravis patients should be extended into the preinduction period to identify patients who require less atracurium.     

Repeated Abdominal Exercise Induces Respiratory Muscle Fatigue

Prolonged bouts of hyperpnea or resisted breathing are known to result in respiratory muscle fatigue, as are primarily non respiratory exercises such as maximal running and cycling. These exercises have a large ventilatory component, though, and can still be argued to be respiratory activities. Sit-up training has been used to increase respiratory muscle strength, but no studies have been done to determine whether this type of non-respiratory activity can lead to respiratory fatigue. The purpose of the study was to test the effect of sit-ups on various respiratory muscle strength and endurance parameters. Eight subjects performed pulmonary function, maximum inspiratory pressure (MIP) and maximum expiratory pressure (MEP) measurements, and an incremental breathing test before and after completing a one-time fatiguing exercise bout of sit-ups. Each subject acted as their own control performing the same measurements 3-5 days following the exercise bout, substituting rest for exercise. Following sit-up induced fatigue, significant decreases were measured in MIP [121.6 ± 26 to 113.8 ± 23 cmH₂O (P <0.025)], and incremental breathing test duration [9.6 ± 1.5 to 8.5 ± 0.7 minutes (P <0.05)]. No significant decreases were observed from control pre-test to control post-test measurements. We conclude that after a one-time fatiguing sit-up exercise bout there is a reduction in respiratory muscle strength (MIP, MEP) and endurance (incremental breathing test duration) but not spirometric pulmonary function.

Key points

• Exercise that is primarily abdominal in nature can lead to inspiratory muscle fatigue.
• This exercise also can cause expiratory muscle fatigue, which would be expected.
• This study shows a link between a predominantly non-respiratory exercise and decreases in both respiratory muscle strength and endurance.

Key words: Maximal inspiratory pressure, endurance breathing test, inspiratory muscles, sit-ups     

Preanesthetic Train-of-four Fade Predicts the Atracurium Requirement of Myasthenia Gravis Patients

Background: The most sensitive diagnostic criterion of myasthenia gravis is a decrement in the muscular response to repetitive stimulation. The authors hypothesized that myasthenia gravis patients who show a train-of-four ratio (T4/T1) < 0.9 in the preanesthetic period will have increased sensitivity to nondepolarizing neuromuscular blocking agents compared with myasthenia gravis patients with preanesthetic T4/T1 >= 0.9.

Methods: After institutional review board approval was obtained, 20 electrophysiologically documented myasthenia gravis patients were studied. Current pyridostigmine therapy was continued until the morning of surgery. Before induction of anesthesia, neuromuscular transmission was recorded from the hypothenar muscles using electromyography with train-of-four stimulation of the ulnar nerve. According to the T4/T1 ratio, patients were assigned to the "normal" group (T4/T1 >= 0.9) or the "decrement" group (T4/T1 < 0.9). After induction of intravenous anesthesia, the effective dose to achieve a 95% neuromuscular blockade (ED95) for atracurium was assessed with a cumulative bolus technique. Postoperatively, pyridostigmine was titrated to obtain a T4/T1 > 0.75 and to treat residual myasthenic symptoms.

Results: In 14 patients, preanesthetic T4/T1 was >= 0.9 (normal), whereas 6 patients presented with T4/T1 < 0.9 (decrement). Decrement patients had a lower ED95 of 0.07 +/- 0.03 mg/kg atracurium (mean +/- SD) compared with normal patients with an ED95 of 0.24 +/- 0.11 mg/kg atracurium (P = 0.002). All patients were extubated within 30 min after surgery. Postoperative pyridostigmine infusion did not differ significantly between groups.     

Asystole during electroconvulsive therapy in a patient with depression and myasthenia gravis

A 44-yr-old woman presented with major depression. She was scheduled to receive electroconvulsive therapy under anesthetic care because of drug-induced leukopenia. Her significant past medical history was myasthenia gravis. She had been treated with thymectomy and pyridostigmine. She showed no evidence of muscle weakness while receiving the medication. After preanesthetic assessment, pyridostigmine was continued and routine anesthetics were chosen. Under 100% oxygen inhalation, thiamylal and suxamethonium were administered intravenously. Alternate current was delivered for 5 seconds, which induced seizure satisfactorily. However, asystole lasted for 10 seconds during the procedure. Spontaneous beating appeared followed by tachycardia and bigemina. Normal sinus rhythm returned four minutes later. She recovered smoothly, and showed no evidence of confusion nor muscle weakness. We speculated that pyridostigmine potentiated the ECT-induced vagal reflex and provoked asystole. In the following session, we pretreated her with intravenous atropine prior to thiamylal and suxamethonium. Although the current delivery increased RR-interval up to 1.2 seconds, neither asystole nor serious tachyarrhythmia occurred. Seven sessions of ECT relieved her psychiatric symptoms uneventfully. We presented a case of depression for which ECT was applied. Asystole with ECT seems associated with administration of pyridostigmine for the treatment of myasthenia gravis. Pretreatment with atropine can prevent asystole without inducing hazardous tachyarrhythmia.     

Autoimmune myasthenia gravis: Recommendations for treatment and immunologic modulation

Opinion statement Treatment for myasthenia gravis should be individualized to each patient based on the clinical characteristics of myasthenia including the distribution, duration, and severity of weakness and resulting functional impairment; the risks for treatment complications related to age, gender, and medical comorbidities; and the presence of thymoma. Acetylcholinesterase inhibitors provide temporary, symptomatic treatment for all forms of myasthenia gravis. Immune modulators address the underlying autoimmune process in myasthenia gravis, but are associated with potential complications and side effects. Most patients with generalized myasthenia who have significant weakness beyond the ocular muscles and who remain symptomatic, despite treatment with cholinesterase inhibitors, are candidates for immune modulation. Although corticosteroids are effective for long-term immune modulation in myasthenia gravis, several more contemporary immunomodulators including azathioprine, cyclosporine, and mycophenolate mofetil have shown efficacy in myasthenia gravis and are used increasingly as first-line treatments and as steroid-sparing agents. Plasma exchange is used to achieve rapid improvement in patients with myasthenic crisis or exacerbation, to improve strength before a surgical procedure or thymectomy, and to minimize steroid-induced exacerbation in patients with oropharyngeal or respiratory muscle weakness. Intravenous immunoglobulin represents an alternative to plasma exchange in patients requiring relatively rapid short-term improvement in the setting of poor venous access. Because of a lack of controlled trials, the role of thymectomy in nonthymomatous myasthenia gravis is unclear, although evidence suggests that thymectomy increases the probability for myasthenic remission or improvement.     

Anesthesia and myasthenia gravis

Myasthenia gravis (MG) is a disease affecting the nicotinic acetylcholine receptor of the post-synaptic membrane of the neuromuscular junction, causing muscle fatigue and weakness. The myasthenic patient can be a challenge to anesthesiologists, and the post-surgical risk of respiratory failure has always been a matter of concern. The incidence and prevalence of MG have been increasing for decades and the disease is underdiagnosed. This makes it important for the anesthesiologist to be aware of possible signs of the disease and to be properly updated on the optimal perioperative anesthesiological management of the myasthenic patient. The review is based on electronic searches on PubMed and a review of the references of the articles. The following keywords were used: myasthenia gravis AND neuromuscular blocking agents, myasthenia gravis AND sevoflurane, myasthenia gravis AND epidural, myasthenia gravis AND neuromuscular blockade reversal and myasthenia gravis AND pyridostigmine. The articles included were from reviews and clinical trials written in English. MG patients can easily be anesthetized without need for post-surgery mechanical ventilation whether it is general anesthesia or peripheral nerve block. Volatile anesthesia or the use of an epidural for the patient makes it possible to avoid the use of neuromuscular blocking agents, and when used, it should be in smaller doses and the patient should be carefully monitored. This review shows that with thorough pre-operative evaluation, continuing the daily pyridostigmine and careful monitoring the MG patient can be managed safely.