Ie. Smith et al., CHOOSING A NEGATIVE-PRESSURE VENTILATION PUMP - ARE THERE ANY IMPORTANT DIFFERENCES, The European respiratory journal, 8(10), 1995, pp. 1792-1795
Five negative pressure ventilator pumps were assessed to determine whe
ther there were any differences in performance which were likely to be
of clinical importance. The pumps tested were the NEV-100 (Lifecare I
nc), the Negavent Respirator DA-1 (Dima Italia), the Thompson Maxivent
(Puritan Bennett), the CCP-001 and Newmarket pumps (Si-Pian Electroni
cs Research Ltd). A patient model was employed to investigate the rela
tionship between the pressure waveform of each pump and the tidal volu
me generated, the stability of performance on a continuous 8 h test, a
nd the response to a change in leak. On the continuous tests, the stab
ility was better than +/-1% for the inspiratory/expiratory (I:E) ratio
and rate, and better than +/-10%, for the peak negative pressure for
all of the pumps. The Negavent and NEV-100 pumps generated a square wa
ve of pressure and for the same peak negative pressure produced a tida
l volume up to 30% greater than the CCP-001 and the Newmarket pumps, w
hich produced a half sine wave. The Maxivent produced an intermediate
waveform, with a plateau at peak negative pressure but a curved decay
back to atmospheric pressure. It is argued that if the pressure of the
pumps producing a half sine wave is made more negative to compensate
and produce an equivalent tidal volume, they are more likely to induce
upper airway obstruction. The leak compensation of the NEV-100 and Ne
gavent pumps was nearly complete but took several breaths to develop,
the CCP-001 and Newmarket pumps had a very rapid compensation but this
was less complete, whilst the Maxivent has no mechanism for leak comp
ensation. From these results, it seems that in patients liable to uppe
r airway obstruction the NEV-100 and Negavent pumps would be advantage
ous, whilst when rapidly changing leaks impair the efficiency of negat
ive pressure ventilation the CCP-001 and Newmarket pumps would be pref
erable. The Maxivent pump seems to offer no advantages.