1776 HIGH FREQUENCY EXTERNAL OSCILLATION WITHOUT INTUBATION

Abstract

High frequency ventilation with a jet or oscillator requires either a tracheotomy or intubation. A method of external oscillation in a cat model was developed which does not require either tracheotomy or intubation. Twelve mongrel, mature cats, (2.0 - 3.80 kg) were placed in a specially made thoracoabdominal plexiglass chamber connected to a high frequency oscillator (Metrex) and a vacuum source to create different levels of negative pressure, the mouth being held open with a retractor. The chamber was then oscillated at an initial frequency of 3 Hz with mean pressure excursions of 6.3 cm H2O (range 2-14 cm) while varying the mean chamber pressure (MCP) with the vacuum source. Following an initial blood gas after commencing oscillation the animals were given pancuronium bromide 200 mcg/kg PRN throughout the remainder of the experiment while being maintained in the oscillated chamber for a minimum of 4 hours. Oscillation was associated with a significant fall in PCO2 (p=.006) and pH (p=.006) and increase in pO2 (p=.03). PCO2 and A-aDO2 were minimal between 1 & 3 Hz and increased with higher frequencies (p<.01). Increasing negative MCP resulted in decreased A-aDO2 and increased FRC (p <.001). Tidal volume fell with increasing frequency from 1-9 Hz (p <.01). Blood pressure was well maintained throughout the experiment. External negative pressure oscillation without intubation is an effective form of ventilation in paralyzed normal cats and may be applicable to apneic infants.