Patient-ventilator interaction during hypercapnic chemoreceptor
stimulation: pressure support vs proportional assist ventilation.
Ranieri, V. Marco, Rocco Giuliani, Luciana Mascia, Salvatore Grasso,
Vito Petruzzelli, Nuccia Puntillo, Gaetano Perchiazzi, Tommaso Fiore,
and Antonio Brienza.
ISTITUTO DI ANESTESIOLOGIA E RIANIMAZIONE, UNIVERSIT[grave]a DI
BARI, OSPEDALE POLICLINICO, 70100 BARI, ITALIA
APStracts 3:0155A, 1996.
Objective of this study was to compare patient-ventilator interaction
during pressure support ventilation (PSV) and proportional assist
ventilation (PAV) in the course of increased ventilatory requirement
obtained by adding a dead space in twelve patients on weaning from
mechanical ventilation. With PSV, the level of unloading was provided
by setting the inspiratory pressure at 20 and 10 cmH2O, whereas with
PAV the level of unloading was at 80 and 40 % of the elastic and
resistive load. Hypercapnia increased (p<0.001) tidal swing of
esophageal pressure (_Pes) and pressure time product per breath
(PTP/b) at both levels of PSV and PAV. During PSV, application of
dead space increased ventilation (VE) during PSV (67+/-4 and 145+/-5
% during PSV 20 and 10 respectively, p<0.001). This was due to a
relevant increase in respiratory rate (Fr) (48+/-4 and 103+/-5 %
during PSV 20 and 10 respectively, p<0.001), while the increase
in tidal volume (VT) played a little role (13+/-1 and 21+/-2 % during
PSV 20 and 10 respectively, p<0.001). With PAV, the increase in
VE consequent to hypercapnia (27+/-3 and 64+/-4 % during PAV 80 and
40% respectively, p<0.001) was related to the increase in VT
(32+/-1 and 66+/-2 % during PAV 80 and 40% respectively,
p<0.001) remaining Fr unchanged. The increase in PTP per minute
(PTP/min) and per liter (PTP/L) consequent to acute hypercapnia and
the sense of breathlessness were significantly (p<0.001) higher
during PSV than during PAV. Our data show that, following hypercapnic
stimulation of the respiratory drive, the capability to increase VE
through changes in VT modulated by variations in inspiratory muscle
effort is preserved only during PAV; the compensatory strategy used
to increase VE during PSV requires greater muscle effort and causes
more pronounced patient discomfort than during PAV.
Received 21 September 1995; accepted in final form 9 February
1996.
APS Manuscript Number A1026-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 27 March 96