Desynchronization of daily rest-activity rhythm in the days following light propofol anesthesia for colonoscopy.

Anesthesia and surgery are associated with fatigue and sleep disorders, suggestive of disturbance of the circadian rest-activity rhythm. Previous studies on circadian rhythm disturbance were focused on patients undergoing general anesthesia associated with surgery. This does not permit one to draw valid conclusions about the effects of general anesthesia per se on circadian rhythms. Our study was set up to determine the impact of a hypnotic dose of propofol on the circadian rest-activity rhythm in humans under real-life conditions. Seventeen healthy subjects scheduled to receive light propofol anesthesia for ambulatory colonoscopy were investigated. Their rest-activity rhythms were assessed using actigraphic monitoring. Diurnal rest was increased, whereas nocturnal sleep was unchanged in the days following anesthesia. Nonparametric analyses showed a decrease in the strength of coupling of the rhythm to stable environmental zeitgebers and increase of fragmentation of the rhythm after anesthesia. Light general anesthesia itself impairs synchronization of the circadian rest-activity rhythm to local time in patients by acting directly on the circadian clock.

Mixed venous oxygen saturation monitoring during liver transplantation.

High mixed venous oxygen saturation (SVO2) values due to limited oxygen extraction capacities are reported in some patients with severe liver disease. The aim of this study was to evaluate the usefulness of SVO2 monitoring to assess adequate oxygen supply in such patients scheduled for liver transplantation. Nineteen patients with oxygen extraction ratio below 12% were analysed and compared to 20 patients with a pre-operative ratio over 17%. The two groups were comparable with regard to initial pathology, preload and haemoglobin levels. SVO2 values measured discontinuously by co-oximetry were unaffected by the first part of surgery and the clamping period in patients with low oxygen extraction ratio. In these patients, SVO2 was never correlated to oxygen supply during the whole procedure whereas good correlation was noted before and after unclamping in the other group. Tissue hypoxia detected by a dependent oxygen consumption-oxygen supply relationship occurred at clamping and unclamping in patients with initial low oxygen extraction capacities. It is concluded that expensive SVO2 continuous monitoring may not be effective in reflecting changes in oxygen supply in anaesthetized patients with initial severely impaired oxygen extraction capacity.

[Difficult intubation managed by laryngeal mask and fibroscopy]. / Intubation difficile réglée par un masque laryngé et un fibroscope.

A case is reported of a patient due to undergo a combined kidney and pancreas transplant who proved to be difficult to intubate. This diabetic hypertensive 35-year-old male patient also had ankylosing spondylitis. Mouth opening was normal (more than fingers' breadth), the chin-sternum distance was 4 cm on full cervical flexion, and cervical extension was only slightly impaired. The Mallampati score was 1. Anaesthesia was induced with thiopentone, fentanyl and 6 mg of pancuronium. Mask ventilation was quite satisfactory. However, on laryngoscopy, the vocal cords could not be seen. Several attempts to carry out endotracheal intubation, including with a stylet, failed. A laryngeal mask (LM) was therefore applied to ventilate the patient correctly. It was not possible to pass a small endotracheal tube (6 mm diameter) through the LM tube, probably because of a small malposition of this latter. A paediatric fibroscope, passed through the LM tube, served as guide for the endotracheal tube. The mask was not removed, although its cushion was slightly deflated, so as not to extubate the patient. The benefits and usefulness of a laryngeal mask in predictable and unpredictable cases of difficult intubation are discussed.

[General anesthesia in the elderly]. / Anesthésie générale du sujet âgé.

Physiologic and pathologic changes due to ageing should be taken in account for the preoperative evaluation and peroperative management of geriatric patients. Pharmacokinetic changes ed to reduce the doses of intravenous agents by 50%. MAC of inhalational agents is decreased by 25 to 75%. Pharmacodynamic deleterious effects are limitative in the choice of some drugs. Cardiocirculatory and pulmonary functions need specific, if possible non invasive monitoring, during surgery, recovery and the early postoperative days.

[Retrograde orotracheal intubation]. / L'intubation oro-trachéale par voie rétrograde.

Four different techniques of retrograde tracheal intubation were studied in 77 cadavers (patients who had died less than 4 h before). None had any laryngeal disease or a previous intubation. Following techniques were evaluated: cricothyroid membrane puncture; infracricoid puncture; catheter guide inserted through the endotracheal tube; catheter guide only inserted through the distal lateral eye (Murphy eye) of the endotracheal tube. An epidural catheter was used as a guide. Success rate was low (5 out of 17 attempts) when cricothyroid puncture was used, and the guide passed through the whole length of the tube. All 20 attempts were successful when infracricoid puncture was used and the guide passed through the distal lateral eye of the endotracheal tube. The different techniques and equipment needed are discussed in the light of the available literature. Retrograde tracheal intubation seems to be an easy and useful technique, which all anaesthetists should know, in case of difficult intubation.

[Expiratory blockage of a Monnal S respirator caused by rupture of the capsule of a pneumatic Bennett valve]. / Blocage expiratoire d'un respirateur Monnal S par rupture du ballonnet de la valve pneumatique Bennett.

In the recovery room, a ventilated patient suddenly developed bradycardia and severe cardiovascular collapse due to increased airway pressure. The cause of this life-threatening complication was continuous occlusion of the expiratory valve by a ruptured diaphragm in a Bennett's valve. When the rupture is located within the circular contact area with the expiratory port, the valve occludes normally during insufflation. On expiration, the expiratory gas under pressure penetrates the ruptured capsule, maintaining the valve occluded. A small part of the expired gas escapes through the small-bore connecting tube of the diaphragm.