Postoperative pulmonary complications are common, but severe complications are infrequent. Their reduction requires measures to prevent infection and mechanical ventilation-associated lung injury through the use of low tidal volumes and early extubation. Noninvasive ventilation after extubation can be utilized to avoid reintubation and the associated increased morbidity and mortality. However, noninvasive ventilation should be done under rigorous conditions and by following strict criteria.

This study analyses characteristics of lung injuries produced by alveolar overdistension in three animal species. Mechanical ventilation at normal tidal volume (10 mL/Kg) and high tidal volume (50 mL/Kg) was applied for 30 min in each species. Data were gathered on wet/dry weight ratio, histological score, and area of alveolar collapse. Five out of six rabbits with high tidal volume developed tension pneumothorax, and the rabbit results were therefore not included in the histological analysis. Lungs from the pigs and rats showed minimal histological lesions. Pigs ventilated with high tidal volume had significantly greater oedema, higher neutrophil infiltration, and higher percentage area of alveolar collapse than rats ventilated with high tidal volume. We conclude that rabbits are not an appropriate species for in vivo studies of alveolar overdistension due to their fragility. Although some histological lesions are observed in pigs and rats, the lesions do not appear to be relevant.

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During mechanical ventilation high fluctuations of introthoracic pressures occur. No data have been presented as to the effects of positive pressure ventilation in patients with chronic obstructive pulmonary disease on the assessment of cardiac output from thoracic electrical bioimpedance. In order to evaluate a thoracic electrical bioimpedance system for the measurement of cardiac output, 40 paired values of cardiac output in 12 mechanically ventilated patients with chronic obstructive pulmonary disease were measured simultaneously with the standard thermodilution method. The data were plotted as the mean for the two measurement techniques versus the difference. The chosen acceptable difference for limits of agreement (mean difference +-2SD) was set at 22%. The mean difference was 0,1 liter per minute and standard deviation 0,7 liter per minute (12,2%). 92% of differences for two measurement techniques did not exceed the chosen acceptable difference.The two methods ore therefore considered to be in agreement. The continous and noninvasive nature of impedance method and its simplicity of use makes this technology very useful for the titration of drug and fluid therapy. It provides warning from impending problems which might require immediate treatment.

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