Acute tracheal trauma in sheep caused by percutaneous tracheostomy.

The aim of our study was to compare dilation forceps tracheostomy and sequential dilator tracheostomy in anaesthetized live adult sheep with respect to the characteristics of the stoma formed and the associated injury. We performed percutaneous tracheostomy on adult sheep randomly allocated to receive either dilation forceps or sequential dilators. Sheep were sacrificed immediately after insertion of the percutaneous tracheostomy and the tracheas dissected. Specimens were examined for site, shape and size of stoma, mucosal lacerations, and posterior wall trauma. Ten sheep had dilation forceps tracheostomy and ten had sequential dilator tracheostomy. All of the specimens were found to have cephalo-caudal mucosal tears, usually crossing tracheal rings. The dilation forceps technique was found to have a larger stoma (28.8 mm vs 24.0 mm, P=0.023). The incidence of posterior needle trauma and mucosal lacerations were common (35% and 50% respectively), but they were not statistically different between the two groups. The role of the mucosal tears in the development of tracheal stenosis is reviewed in the discussion.

Respiratory and cardiovascular responses to PEEP in artificially ventilated patients after cardiopulmonary bypass surgery.

The respiratory and haemodynamic effects of incremental levels of positive and expiratory pressure (PEEP) to 9 cm H2O were studied in ten adult patients 3--6 hours after uneventful cardiopulmonary bypass surgery. Functional residual capacity was increased and deadspace-tidal volume ratio tended to fall, the latter approaching significance at +6 and +9 cm PEEP. Thus lung volume was increased and there was a tendency to improved gas distribution to the alveoli. However there was no significant change in PaO2, alveolar-arterial oxygen tension difference or venous admixture. Cardiac index, and left ventricular strokework index were marginally depressed at 6 cm PEEP and further at 9 cm, while right atrial pressure and pulmonary artery occlusion pressure were raised at 9 cm PEEP. It would appear that low levels (3--6 cm) of PEEP do not improve gas exchange in the lungs to any worthwhile degree, and levels (6--9 cm) may impair cardiac performance.

Needle tracheostomy: a laboratory study.

Percutaneous needle tracheostomy and transtracheal ventilation continues to be advocated for the management of upper airway obstruction. Recent studies recommend the use of artificial ventilation. However, as apparatus for this is not always available and because there remains some doubt regarding conditions for successful use of needle tracheostomy during spontaneous respiration, we undertook such a study in dogs. Pressure-flow characteristics of short hollow needles 18-10 SWG were first determined. The smallest of these (14 SWG Bardic Intracath) that would deliver flow sufficient (by calculation) to meet the respiratory requirement of 10-13 kg laboratory dogs was selected for further study. Respiration was possible by spontaneous or artificial methods in the presence of complete tracheal occlusion. Little or no deterioration was noted in an hour of such breathing. Artificial ventilation by machine and by hand could considerably lower PaCO2. We conclude that the technique is possible provided appropriate needles are selected and care is given to their method of use.

The effect of positive end expiratory pressure on rebreathing and gas dilution in the Ayre's T-piece system--a laboratory study.

The effect of positive end expiratory pressure on the function of the Ayre's T-Piece System was studied using a simple lung model. Positive end expiratory pressure did not effect end tial CO2 during "controlled breathing" but caused an increase during "spontaneous breathing" when fresh gas flow was less than 3 times the minute volume. Gas dilution did not occur under any of the test conditions.