Nadine Kawkabani

Preoxygenation: Comparison of Maximal Breathing and Tidal Volume Breathing Techniques

BACKGROUND Preoxygenation with tidal volume breathing for 3-5 min is recommended by Hamilton and Eastwood. This report compares tidal volume preoxygenation technique with deep breathing techniques for 30-60 s. METHODS The study was conducted in two parts on patients undergoing elective coronary bypass grafting. In the first group (n = 32), each patient underwent all of the following preoxygenation techniques: the traditional technique consisting of 3 min of tidal volume breathing at an oxygen flow of 5 l/min; four deep breaths within 30 s at oxygen flows of 5 l/min, 10 l/min, and 20 l/min; and eight deep breaths within 60 s at an oxygen flow of 10 l/min. The mean arterial oxygen tensions after each technique were measured and compared. In the second group (n = 24), patients underwent one of the following techniques of preoxygenation: the traditional technique (n = 8), four deep breaths (n = 8), and eight deep breaths (n = 8). Apnea was then induced, and the mean times of hemoglobin desaturation from 100 to 99, 98, 97, 96, and 95% were determined. RESULTS In the first group of patients, the mean arterial oxygen tension following the tidal breathing technique was 392+/-72 mm Hg. This was significantly higher (P<0.05) than the values obtained following the four deep breath technique at oxygen flows of 5 l/min (256+/-73 mm Hg), 10 l/min (286+/-69 mm Hg), and 20 l/min (316+/-67 mm Hg). In contrast, the technique of eight deep breaths resulted in a mean arterial oxygen tension of 369+/-69 mm Hg, which was not significantly different from the value achieved by the traditional technique. In the second group of patients, apnea following different techniques of preoxygenation was associated with a slower hemoglobin desaturation in the eight-deep-breaths technique as compared with both the traditional and the four-deep-breaths techniques. CONCLUSION Rapid preoxygenation with the eight deep breaths within 60 s can be used as an alternative to the traditional 3-min technique.

Cisatracurium in a myasthenic patient undergoing thymectomy.

PurposeThe report investigates cisatracurium neuromuscular block in a myasthénic patient undergoing thymectomy.Clinical FeaturesA myasthénie patient (Osserman II B) was prepared preoperatively with 240 mg·day−1 pyridostigmine. The neuromuscular block produced by 0.05 mg·kg−1 cisatracurium was monitored by Datex electromyography. The electromyographic response was compared with that in a control group of five non-myasthenic patients. In the myasthenic patient, cisatracurium resulted in a rapid onset of complete (97–98%) neuromuscular block, while a slow onset of partial (80–90%) block was achieved in the control group. Also, administration of 0.05 mg·kg−1 neostigmine at the end of surgery reversed the neuromuscular block of cisatracurium in the non-myasthenic patients, but did not change the rate of spontaneous recovery in the myasthenic patient.ConclusionThe myasthenic patient is sensitive to cisatracurium, as evidenced by a more rapid onset and more marked neuromuscular block compared with the control non-myasthenic patients. This may be attributed to the decreased number of functional endplate acetylcholine receptors in the myasthenic patient, with a consequent decrease of the safety margin of neuromuscular transmission. Also, in contrast with the control group, the rate of recovery from neuromuscular block in the myasthenic patient was not enhanced by neostigmine at the end of surgery. This may be attributed to the prior inhibition of acetylcholinesterase by the preoperative pyridostigmine, as well as by possible desensitization of the cholinergic receptors secondary to prolonged pyridostigmine therapy.RésuméObjectifÉtudier le blocage neuromusculaire produit par le cisatracurium chez un patient myasthénique subissant une thymectomie.Éléments cliniquesUn patient myasthénique (Osserman II B) a été préparé à l’opération avec 240 mg·jour−1 de pyridostigmine. On a surveillé le blocage neuromusculaire produit par 0,05 mg·kg−1 de cisatracurium à l’aide de l’électromyographie Datex. La réponse électromyographique a été comparée à celle de cinq patients non myasthéniques d’un groupe témoin. Chez le patient myasthénique, le cisatracurium a provoqué un début d’action rapide du blocage neuromusculaire complet (97–98%), tandis qu’un bloc partiel s’est lentement installé (80–90%) chez les patients témoins. De plus, l’administration de 0,05 mg·kg−1 de néostigmine à la fin de l’intervention a renversé le bloc chez les patients non myasthéniques, mais n’a pas changé la vitesse de la récupération spontanée chez le patient myasthénique.ConclusionLe patient myasthénique est sensible au cisatracurium comme l’ont mis en évidence la rapidité d’action et le blocage neuromusculaire plus marqué que chez les patients témoins. On peut expliquer cette situation par la baisse du nombre de récepteurs fonctionnels d’acétylcholine de la plaque motrice chez le patient myasthénique et par une baisse consécutive de la marge de sécurité de la transmission neuromusculaire. Par ailleurs, dans le groupe témoin, la vitesse de la récupération du blocage neuromusculaire n’est pas améliorée par la néostigmine administrée à la fin de l’opération. Ce qui pourrait relever de l’inhibition antérieure de l’acétylcholinestérase liée à l’administration préopératoire de pyridostigmine aussi bien qu’à la désensibilisation possible des récepteurs cholinergiques secondaire à la thérapie prolongée avec la pyridostigmine.

Magnesium therapy for refractory ventricular fibrillation

THE MAGNESIUM ION has a distinct influence on cardiac activity.1 The value of magnesium in correcting lethal arrhythmias in hypomagnesemic patients has been well established.2,3 Its antiarrhythmic effect has also been reported in the absence of known magnesium (Mg++) deficiency, or hypomagnesemia.4 A search of the medical literature, however, revealed no controlled studies of the efficacy of magnesium in the treatment of sustained ventricular fibrillation (VF), and only a few cases of intractable ventricular tachyarrhythmias or refractory VF responsive to magnesium therapy have been reported.4–7 The VF algorithm suggested by the American Heart Association recommends the use of magnesium in hypomagnesemia, torsades de pointes, digitalis toxicity, and as a last resort when other antiarrhythmic drugs, such as lidocaine and bretylium, fail to control the fibrillation.8 The authors report five cardiac patients who developed refractory VF, secondary to different causes, who were successfully treated by a single countershock after the administration of a bolus of magnesium sulfate (Table 1). The rationale behind the use of magnesium for management of refractory VF is the well-known benefit of magnesium in the management of intractable tachyarrhythmias4–7 as well as its myocardial protective action in the setting of ischemia-reperfusion injury.9

Neuromuscular interaction of sevoflurane — cisatracurium in a myasthenic patient

Purpose: To describe the influence of sevoflurane anesthesia on cisatracurium neuromuscular block in a myasthenic patient undergoing thymectomy.Clinical features: A myasthenic patient (Osserman IIB) was managed for one year before surgery with 60 mg pyridostigmine qid, 50 mg immuran tid and 30 mg prednisone therapy. Pyridostigmine was interrupted three months before surgery, and five sessions of plasmapheresis were done within 13 days before surgery. The neuromuscular response was monitored by Datex electromyographic response to train-of-four stimulation of the ulnar nerve. Sevoflurane 4% decreased the T1/C ratio by 20%. Administration of 0.025 mg·kg−1 cisatracurium, during sevoflurane anesthesia, was followed by complete neuromuscular block for 45 min. Discontinuation of sevoflurane resulted, after 10 min, in recovery of the T1 which reached T1/C ratio of 50% after 30 min.Conclusion: The marked sensitivity of this myasthenic patient to 0.5 × ED95 of cisatracurium can be attributed to potentiation of cisatracurium neuromuscular block by sevoflurane, as evidenced by the reappearance of the first twitch of the train-of-four response 10 min after sevoflurane was discontinued.RésuméObjectif: Décrire l’influence de l’anesthésie au sévoflurane sur le blocage neuromusculaire avec cisatracurium chez un patient myasthénique qui doit subir une thymectomie.Éléments cliniques: Un patient myasthénique (Osserman IIB) a été traité pendant un an avant l’intervention chirurgicale avec 60 mg de pyridostigmine qid, 50 mg d’imuran tid et 30 mg de prednisone die. La prise de pyridostigmine a été interrompue trois mois avant l’opération et cinq sessions de plasmaphérèse ont été réalisées pendant les 13 jours qui ont précédé l’opération. La réponse neuromusculaire a été suivie par la réponse électromyographique Datex à une stimulation en train-de-quatre du nerf cubital. Le sévoflurane à 4 % a fait baisser le ratio T1/C de 20 %. L’administration de 0,025 mg·kg−1 de cisatracurium, pendant l’anesthésie au sévoflurane a été suivie d’un blocage neuromusculaire complet pendant 45 min. L’arrêt du sévoflurane a amené, après 10 min, la récupération de T1 qui a atteint le ratio T1/C de 50 % après 30 min.Conclusion: La sensibilité marquée de ce patient myasthénique à la dose de 0,5 × ED95 de cisatracurium peut être attribuée à la potentialisation, par le sévoflurane, du blocage neuromusculaire avec cisatracurium, comme l’a mis en évidence la réapparition de la première contraction de la réponse en train-de-quatre 10 min après l’arrêt du sévoflurane.

Apnea-induced hemoglobin desaturation during one-lungvs two-lung ventilation

PurposeTo compare the rate of apnea-induced hemoglobin desaturation during one-lung ventilation (OLV) vs two-lung ventilation (TLV) in patients undergoing thoracic surgery.MethodsSix patients undergoing thoracotomy or thoracoscopy were included. Each patient served as his/her own control. The lungs were ventilated with oxygen 100% using TLV, followed after 20–30 min by OLV and the resultant PaO2 was measured. Apnea was then induced following the two techniques of ventilation, and the times for every 1% decrease in hemoglobin saturation from 100% to 95%, as monitored by pulse oximetry, were recorded. The times for every 1 % decrease in the saturation were compared in the two groups.ResultsThe mean PaO2 value following TLV (445 ± 99 mmHg) was higher than the mean PaO2 following OLV (156 ± 18 mmHg). Also, the mean time for subsequent apnea induced hemoglobin desaturation from SpO2 100% to 95% following TLV was twice the time of desaturation following OLV (6.3 ± 1.2 min vs 3.2 ± 0.5 min,P < 0.05).ConclusionHemoglobin desaturation occurs more rapidly during apnea following OLV than TLV. The rapid desaturation may be attributed to the decrease of FRC, associated with an increased transpulmonary shunting. The results suggest that two-lung ventilation with oxygen 100% provides a greater safety margin than one-lung ventilation with oxygen 100% whenever ventilation is interrupted.RésuméObjectifComparer la vitesse de désaturation de l’hémoglobine induite par l’apnée pendant la ventilation unilatérale (VUL) vs bilatérale (VBL) chez des patients qui subissent une intervention chirurgicale thoracique.MéthodeSix patients devant subir une thoracotomie ou une thoracoscopie ont participé à l’étude. Chaque patient était son propre témoin. La VBL a été réalisée avec 100 % d’oxygène et a été suivie, 20–30 min après, par la VUL. On a mesuré la PaO2 qui en a résulté. L’apnée a été ensuite induite selon les deux techniques de ventilation et le temps nécessaire à la diminution de chaque 1 % de saturation de l’hémoglobine, de 100 % à 95 % démontrée par l’oxymétrie puisée, a été enregistrée. On a fait une comparaison intergroupe du temps de chaque baisse de 1%.RésultatsLa valeur moyenne de la PaO2 à la suite de la VBL (445 ± 99 mmHg) a été plus élevée que la PaO2 moyenne qui a suivi la VUL (156 ± 18 mmHg). De plus, le temps moyen nécessaire à la désaturation subséquente de l’hémoglobine, induite par l’apnée, passant d’une SpO2 de 100 % à 95 %, à la suite d’une VBL a été deux fois plus long que le temps de désaturation après la VUL (6,3 ± 1,2 min vs 3,2 ± 0,5 min,P < 0,05).ConclusionLa désaturation de l’hémoglobine survient plus rapidement pendant l’apnée qui suit une VUL qu’une VBL. La désaturation rapide peut relever de la baisse de la CRF, associée à une augmentation du shunt transpulmonaire. Les résultats suggèrent que la ventilation bilatérale avec 100 % d’oxygène fournit une plus grande marge de sécurité que la ventilation unilatérale de même nature chaque fois que la ventilation est interrompue.

Rocuronium in the myasthenic patient

IIIII Rocuronium is a new aminosteroid muscle relaxant, which is characterised by a rapid onset and an intermediate duration of nondepolarising neuromuscular block [I]. The present report investigates the neuromuscular blocking effect of rocuronium in a myasthenic patient undergoing trans-sternal thymectomy. The patient was a 22-year-old, 65 kg, female, scheduled for trans-sternal thymectomy. She was suffering from generalised myasthenia, which was classified as IIA according to Osserman classification [2]. One year prior to surgery, the patient was started on pyridostigmine 60 mg orally, four times daily, which improved significantly muscle power. Neuromuscular transmission was monitored by a Datex Relaxograph. The ulnar nerve was stimulated supramaximally at the wrist every 2 0 s and the resulting electromyographic response displayed. Anaesthesia was induced with propofol 2.5 mg.kg’ and the electromyographic response was recorded. Rocuronium 0.15 mg.kg I was injected intravenously and when maximal neuromuscular block was achieved, the trachea was intubated and anaesthesia maintained with 65% nitrous oxide in oxygen supplemented by fentanyl 3 pg.kgI. This dose of rocuronium resulted in complete neuromuscular block within 120s. After 20min, 25% recovery of neuromuscular transmission occurred (upper trace, Fig. 1). The neuromuscular block of rocuronium in the myasthenic patient was compared to that achieved in a control group of five normal female patients of a comparable age and body weight who were scheduled for laparoscopy and who were anaesthetised with the same technique. In the normal patients, rocuronium 0.15 mg.kgonly produced 30-50% neuromuscular block within 240 s. Also, recovery of neuromuscular transmission was more rapid in the control patients as compared to the myasthenic patient (lower trace, Fig. I) . The present report shows that the myasthenic patient is sensitive to rocuronium, similar t o other intermediate-acting nondepolarising muscle relaxants such as atracurium [3,4] and vecuronium [5,6]. The reduction of the number of functional acetylcholine receptors at the neuromuscular junction of the myasthenic patient and the consequent reduction of the safety margin, make myasthenic patients extremely sensitive to nondepolarising muscle relaxants [7]; the speed of onset of neuromuscular block is accelerated [8], the degree of block is potentiated and the rate of recovery is decreased. Thus, neuromuscular transmission must be monitored carefully intra-operatively and postoperatively in order to titrate the ROClJRONlUM 035 mg.Kp”