Efficacy of preoxygenation with non-invasive low positive pressure ventilation in obese patients: crossover physiological study.

OBJECTIVE: The impact of non-invasive positive pressure ventilation (NIPPV), which is a combination of inspiratory positive airway pressure (IPAP) and positive end expiratory pressure (PEEP), on the effectiveness of preoxygenation in obese patients was evaluated. DESIGN: Randomized, controlled, double blinded, crossover study comparing NIPPV vs. tidal volume breathing (TVB) with regard to the expiratory O(2) fraction (FeO(2)). PATIENTS AND METHODS: Thirty participants with body mass index (BMI) greater or equal to 30 kg/m(2) scheduled for elective surgery were included. Patients with facial hair, and airway anomalies were excluded. Each patient underwent 3 minutes 100% O(2) preoxygenation with the two following methods in a random order: 1: TVB; 2: NIPPV (4 cmH(2)O IPAP+4 cmH(2)O PEEP). Primary outcome was FeO(2) after 3 minutes. Secondary outcomes were the number of patients reaching FeO(2) greater or equal to 90%, tidal volume, respiratory rate, and patient comfort on a 4-point scale. RESULTS: No differences between methods were found regarding the FeO(2) change with time or after 3 minutes (89 ± 6% with TBV vs. 91 ± 4% with NIPPV). FeO(2) greater or equal to 90% was reached more frequently with NIPPV (80%) than with TVB (60%) (P=0.008). Tidal volume (m ± SD) was larger throughout preoxygenation with TBV (837 ± 440 mL) than with NIPPV (744 ± 368 mL), (P=0.0005). Respiratory rate did not differ between regimens. Patient comfort was good and similar. CONCLUSION: This study suggests that providing a positive pressure of 4 cmH(2)O throughout inspiration and expiration during preoxygenation in obese patients provided benefits with regard to the FeO(2).

[Inspiratory support versus spontaneous breathing during preoxygenation in healthy subjects. A randomized, double blind, cross-over trial]. / Intérêt de la ventilation non invasive en pression positive au masque facial pour la préoxygénation chez le sujet sain : étude randomisée, en double insu, croisée.

OBJECTIVE: Applying an inspiratory support (AI) and a positive end expiratory pressure (PEP) could increase the effectiveness of the preoxygenation. STUDY DESIGN: This randomized double blinded controlled study compares the impact on the expiratory oxygen fraction (FEO(2)) of two levels of AI with PEP to a traditional preoxygenation. PATIENTS AND METHODS: Twenty healthy volunteers were studied. The criteria of exclusion were a body mass index >30, the presence of beard or moustache and the claustrophobia. Each subject went through three modes of preoxygenation during 3 minutes each in a random order: 1-spontaneous ventilation (VS), 2-preoxygenation with AI with 4 cmH(2)O/PEP 4 cmH(2)O (AI-4/PEP-4), 3-preoxygenation with AI with 6 cmH(2)O/PEP 4 cmH(2)O (AI-6/PEP-4). Subject's tolerance and leaks were also noted. RESULTS: The FEO(2) at the end of the 3 minutes of preoxygenation was higher (p<0,001) with AI-4/PEP-4 (94+/-3%) and AI-6/PEP-4 (94+/-4%) than with technique VS (89+/-6%). One hundred percent and 90% of the participants reached one FEO(2)=90% with AI-4/PEP-4 and AI-6/PEP-4 respectively vs 65% with VS (p=0.0013). The participants tolerated better the VS and the AI-4/PEP-4 than the AI-6/PEP-4. More leaks were noted with the AI-6/PEP-4 than with the VS and the AI-4/PEP-4. CONCLUSION: This study shows applying AI plus PEP during preoxygenation improves its effectiveness in the healthy subjects. It also suggests that, in a population of healthy volunteers, combination AI-4/PEP-4 is preferable to AI-6/PEP-4 because so effective, but better tolerated.

Anaesthetic management of an adolescent for scoliosis surgery with a Fontan circulation.

Advances in the treatment of congenital heart disease have led to a new group of adolescents or adults patients with cardiac anomalies. The anaesthetic management of these patients can be challenging especially when they are scheduled for major noncardiac surgery inducing haemodynamic instability. We report the case of a 14-year-old boy scheduled for posterior spinal fusion for idiopathic scoliosis who underwent a Fontan operation in infancy for pulmonary atresia with right ventricle hypoplasia. The preoperative investigations and the anaesthetic management are described.

Increased sensitivity to depolarization and nondepolarizing neuromuscular blocking agents in young rat hemidiaphragms.

BACKGROUND: Newborn neuromuscular junctions are more sensitive to d-tubocurarine than more mature preparations. It is unclear whether the same modifications occur with newer nondepolarizing agents and depolarizing agent succinylcholine. The purpose of this study was to determine the relative sensitivity of newborn neuromuscular junctions to succinylcholine and five nondepolarizing agents. METHODS: The phrenic nerve-hemidiaphragm preparation from 60 rats was used, 30 aged 9-12 days (newborn) and 30 aged 27-33 days (adult). Five rats from each group were exposed to one of six neuromuscular blocking agents (d-tubocurarine, cisatracurium, atracurium, vecuronium, rocuronium, and succinylcholine). Indirectly elicited twitch tension was measured during control conditions in the absence of blocking agent, followed by four concentrations of one of the six agents. Concentration-response curves were constructed and the EC50 (concentration required to produce 50% depression of twitch tension) was obtained. Potency ratios (EC50adult/EC50newborn) were derived for each agent. RESULTS: Newborn preparations were significantly (P < 0.001) more sensitive than their adult counterparts for all six agents tested. For nondepolarizing agents, the potency ratio was in the 6-12 range. The EC50adult/EC50newborn were as follows, in decreasing potency order: d-tubocurarine, 1.68/0.23 microM; cisatracurium, 2.73/0.47 microM; vecuronium, 5.47/0.59 microM; rocuronium, 9.7/0.78 microM; and atracurium, 12.3/1.9 microM. Succinylcholine was three times as potent in newborn rats, with an EC50adult/EC50newborn of 21.3/7.3 microM. The ratio for succinylcholine was significantly less than for all nondepolarizing drugs (P < 0.02). CONCLUSION: The newborn neuromuscular junction of the rat shows an increased sensitivity to all neuromuscular blocking agents tested, including succinylcholine. However, the potency ratio was greater for nondepolarizing than depolarizing drugs. The optimal dose of these agents for certain situations such as cesarean section and anesthesia in neonates should be reassessed.

Massive gastrointestinal hemorrhage after transoesophageal echocardiography probe insertion.

PURPOSE: To describe a case of a massive gastric bleeding following emergency coronary artery bypass surgery associated with transoesophageal echocardiographic (TEE) examination. CLINICAL FEATURES: A 50-yr-old man was referred for an acute myocardial infarction and pulmonary edema (Killip class 3). Twelve hours after his myocardial infarction, he was still having chest pain despite an i.v. heparin infusion. Coronary angiography revealed severe three-vessel disease with multifocal stenosis of the left anterior descending, circumflex and total occlusion of the right coronary artery. The patient was transferred to the operating room for emergency coronary artery bypass graft surgery. After total systemic heparinization (3 mg.kg-1) was obtained for cardiopulmonary bypass, a multiplane TEE probe was inserted without difficulty to monitor myocardial contractility during weaning from CPB. During sternal closure, the TEE probe was removed and an orogastric tube was inserted with immediate drainage of 1,200 ml red blood. Endoscopic examination demonstrated a mucosal tear near the gastro-oesophageal junction and multiple erosions were seen in the oesophagus. These lesions were successfully treated with submucosal epinephrine injections and the patient was discharged from the hospital eight days after surgery. CONCLUSION: This is a report of severe gastrointestinal hemorrhage following TEE examination in a fully heparinized patient. This incident suggest that, if the use of TEE is expected, the probe should preferably be inserted before the administration of heparin and the beginning of CPB.

A light and electron microscopic study of dystrophin localization at the mouse neuromuscular junction.

Duchenne muscular dystrophy (DMD) is characterized by a lack of dystrophin expression. Dystrophin is a 420 Kd protein localized in the muscle sarcolemma that most likely provides stability to the muscle plasma membrane. Neuromuscular junctions (NMJs) were localized by revealing either the acetylcholine receptors (AChRs) with alpha-bungarotoxin coupled with cascade blue or by revealing desmin, a protein found in higher concentration at the NMJs using immunochemistry. An accumulation of dystrophin was observed in normal mice by immunoperoxidase labelling at NMJs identified with these markers. Dystrophin was pinpointed on the postjunctional folds of NMJs by electron microscopy and was more abundant on the postjunctional membrane than on the remaining muscle membrane. Our observations are similar to previous observations suggesting that dystrophin may interact with the AChRs.

Is dystrophin present in the nerve terminal at the neuromuscular junction? An immunohistochemical study of the heterozygote dystrophic (mdx) mouse.

Neuromuscular junctions (NMJs) were identified by revealing the presence of cholinergic receptors (AChR) with alpha-bungarotoxin coupled to the fluorescent dye cascade blue in 9- and 60-day-old normal and heterozygote mdx mice. Dystrophin was detected by an immunoperoxidase technique. All the muscle fibers of the normal animals observed in cross sections were immunoreactive for dystrophin and an accumulation of dystrophin was observed at all NMJs identified by alpha-bungarotoxin. In the 9-day-old mdx heterozygote animals, dystrophin positive, negative, and partially positive muscle cross sections were observed. Four different observations were made in these heterozygote animals on the coexistence of AChR and dystrophin. First, alpha-bungarotoxin sites (i.e., NMJs) were observed on dystrophin positive muscle fiber cross sections with an accumulation of dystrophin at these sites. Second, alpha-bungarotoxin sites were observed on dystrophin positive fibers without a dystrophin accumulation at NMJs. Third, there was a coexistence of alpha-bungarotoxin and dystrophin labelling at NMJs of muscle fibers with perimeters labelling negative for dystrophin. Fourth, NMJs, identified by alpha-bungarotoxin, were observed on muscle fibers negative for dystrophin even at the NMJ. These observations suggest that dystrophin is present not only in the muscle membrane but also in the presynaptic nerve terminals.

A monoclonal antibody to conotoxin reveals the distribution of a subset of calcium channels in the rat cerebellar cortex.

Voltage-sensitive calcium channels (VSCC) are a family of ionophores having different electrical and pharmacological properties. The omega-conotoxin GVIA (omega-CgTX) is a specific blocker of one subset of VSCCs. Because of the specificity of this toxin, a monoclonal anti-omega-CgTX antibody was generated against a omega-CgTX-key hole limpet hemocyanin conjugate and used as a specific marker to study VSCC distributions. This mab was shown to recognize omega-CgTX on Western blots and to display omega-CgTX-dependent immunoperoxidase staining of rat cerebellum. Incubation of fresh, unfixed sections of adult rat cerebellum in omega-CgTX followed by light fixation and peroxidase immunocytochemistry with mab anti-omega-CgTX revealed a specific pattern of labelling. All principal classes of cerebellar neurons were immunoreactive, but in general glial cells were not stained. Most interestingly, strong focal immunoreactivity was encountered at branching points of Purkinje cell dendrites. This characteristic staining pattern implies that a subset of VSCC is specifically concentrated in these regions and suggests that these channels may play a role in the functional integration of dendritic signals.

Postsynaptic structure may account for variations in miniature endplate current shapes along frog neuromuscular junctions.

Intracellular recordings were made in the presence of 6-9 microM neostigmine with an electrode placed halfway between the distal end and the proximal region of a long simple branch of a frog neuromuscular junction. During the intracellular recording period, an extracellular electrode was placed alternatively at a distal and at a proximal site. The temporal correspondence between the extracellular miniature endplate current and intracellular miniature endplate potential permitted us to identify two miniature endplate potential (MEPP) populations originating, respectively, from the distal and proximal regions. The frequency and intracellular amplitude of MEPPs were higher in the proximal than in the distal region. The rise time and the decay time of the extracellularly recorded MEPC were longer in the proximal region. A significant correlation was observed between the amplitude (in mV) and surface (in mV.ms) of MEPCs. The slope of this regression line was steeper for the proximal region. Furthermore, the correlation coefficient was lower for that region owing to variations of MEPC shape. Our observations suggest that in the presence of anticholinesterase, ACh rebinds more often to acetylcholine receptors in the proximal region because of the presence of longer postjunctional folds.