IntroductionComputed tomography of the lung has shown that ventilation shifts from dependent to nondependent lung regions. In this study, we investigated whether, at the bedside, electrical impedance tomography (EIT) at the cranial and caudal thoracic levels can be used to visualize changes in ventilation distribution during a decremental positive end-expiratory pressure (PEEP) trial and the relation of these changes to global compliance in mechanically ventilated patients.MethodsVentilation distribution was calculated on the basis of EIT results from 12 mechanically ventilated patients after cardiac surgery at a cardiothoracic ICU. Measurements were taken at four PEEP levels (15, 10, 5 and 0 cm H2O) at both the cranial and caudal lung levels, which were divided into four ventral-to-dorsal regions. Regional compliance was calculated using impedance and driving pressure data.ResultsWe found that tidal impedance variation divided by tidal volume significantly decreased on caudal EIT slices, whereas this measurement increased on the cranial EIT slices. The dorsal-to-ventral impedance distribution, expressed according to the center of gravity index, decreased during the decremental PEEP trial at both EIT levels. Optimal regional compliance differed at different PEEP levels: 10 and 5 cm H2O at the cranial level and 15 and 10 cm H2O at the caudal level for the dependent and nondependent lung regions, respectively.ConclusionsAt the bedside, EIT measured at two thoracic levels showed different behavior between the caudal and cranial lung levels during a decremental PEEP trial. These results indicate that there is probably no single optimal PEEP level for all lung regions.

Electrical impedance tomography (EIT) is a non-invasive, radiation-free functional imaging technique, which allows continuous bedside measurement of regional lung ventilation. Pneumothorax is an uncommon but nevertheless potentially dangerous incident that may arise unexpectedly. We report an incident of an accidental tension pneumothorax during an experimental ventilation study in a pig that was continuously monitored by EIT. The early sign of the occurring pneumothorax, prior to all clinical signs, was a fast increase of end-expiratory impedance in the ventral part of the right lung indicating that non-ventilated air entered this part, followed by a disappearance of ventilation in this region. At the same time the ventilation-related impedance changes of the left lung remained almost unchanged. The pneumothorax onset was localized using a newly introduced pneumothorax dynamics map directly derived from dynamic EIT data. We conclude that non-invasive EIT may be helpful as a tool to detect the development of a pneumothorax, which could be of particular interest during invasive procedures such as insertion of a central venous catheter.

886CAN J ANESTH 2000 / 47: 9 / pp [886][887][888][889] Purpose: To report failure of insertion of #5 and #4 intubating laryngeal mask airways (ILMAs) in a patient with a mouth opening of just under 25 mm, and the variances among same-size ILMAs.Clinical features: A 53-yr-old man with obstructive sleep apnea underwent elective ENT surgical repair. His mouth opening was just under 25 mm. Ventilation by mask was easy. Direct laryngoscopy failed after induction of anesthesia and neuromuscular block. Neither a #5 nor a #4 ILMA could be passed between the patient's teeth, despite different twisting maneuvres. A #4 LMA was thus prepared as a conduit for fibreoptic intubation. Placement of the LMA was easy, as was fibreoptic-guided intubation. The LMA was removed over the tracheal tube (TT) to enable ENT surgery, and the further course was uneventful. Manual examination showed that, unlike others of the same type, the failed ILMAs were not sufficiently compressible either to allow insertion in this patient or to the 20 mm reported as the maximal outer dimension of the device. Radiological examination revealed that, at the point of the device where it is intended to be compressible, the silicone layer was thicker in the failed devices than in stock compressible ILMAs, and the end of the steel tube was not so sharply beveled.Conclusion: Our inability to insert an ILMA in a patient with an interdental distance of just under 25 mm was because the device was not sufficiently compressible although the manufacturer states the maximal outer dimension to be 20 mm.Objectif : Rapporter l'échec de l'insertion de masques laryngés d'intubation n os 5 et 4 (MLI) chez un patient dont l'ouverture de la bouche était d'un peu moins de 25 mm et préciser les différences entre les MLI de même taille.Éléments cliniques : Un homme de 53 ans, souffrant d'apnée du sommeil d'origine obstructive, a subi une réparation ORL. L'ouverture de sa bouche était d'à peine 25 mm. La ventilation par masque a été facile. La laryngoscopie directe a échoué après l'induction de l'anesthésie et le blocage neuromusculaire. Ni le MLI 5, ni le 4 n'ont pu être insérés entre les dents du patient en dépit de différentes manoeuvres de torsion. Le ML 4 a alors été préparé comme un tube pour l'intubation fibroscopique. La mise en place du ML et l'intubation avec guidage fibroscopique ont été faciles. Le ML a été retiré du tube trachéale (TT) pour permettre l'intervention ORL qui s'est déroulée sans incident. L'examen manuel a d'abord montré, comparativement à d'autres du même type, que les MLI inefficaces n'étaient pas suffisamment compressibles pour permettre l'insertion ou mesuraient plus que les 20 mm reconnus comme la dimension extérieure maximale. L'examen radiologique a révélé qu'à la pointe de l'appareil, dans sa partie compressible, la couche de silicone était plus épaisse sur les dispositifs inefficaces à l'intubation que sur les autres MLI souples et que l'extrémité du tube d'acier comportait un biseau plus court. Conclusion :Notre incapacité à insérer un MLI ch...