Respiratory load compensation during mechanical ventilation--proportional assist ventilation with load-adjustable gain factors versus pressure support.
BACKGROUND
In mechanically ventilated patients respiratory system impedance may vary from time to time, resulting, with pressure modalities of ventilator support, in changes in the level of assistance. Recently, implementation of a closed-loop adjustment to continuously adapt the level of assistance to changes in respiratory mechanics has been designed to operate with proportional assist ventilation (PAV+).


OBJECTIVE
The aim of this study was to assess, in critically ill patients, the short-term steady-state response of respiratory motor output to added mechanical respiratory load during PAV+ and during pressure support (PS).


METHODS
In 10 patients respiratory workload was increased and the pattern of respiratory load compensation was examined during both modes of support.


RESULTS
Airway and transdiaphragmatic pressures, volume and flow were measured breath by breath. Without load, both modes provided an equal support as indicated by a similar pressure-time product of the diaphragm per breath, per minute and per litre of ventilation. With load, these values were significantly lower (p<0.05) with PAV+ than those with PS (5.1+/-3.7 vs 6.1+/-3.4 cmH2O.s, 120.9+/-77.6 vs 165.6+/-77.5 cmH2O.s/min, and 18.7+/-15.1 vs 24.4+/-16.4 cmH2O.s/l, respectively). Contrary to PS, with PAV+ the ratio of tidal volume (VT) to pressure-time product of the diaphragm per breath (an index of neuroventilatory coupling) remained relatively independent of load. With PAV+ the magnitude of load-induced VT reduction and breathing frequency increase was significantly smaller than that during PS.


CONCLUSIONS
In critically ill patients the short-term respiratory load compensation is more efficient during proportional assist ventilation with adjustable gain factors than during pressure support.
Kondili
Eumorfia
E
Intensive Care Medicine Department, University Hospital of Heraklion, Heraklion, 711 10, Crete, Greece.
Prinianakis
George
G
Alexopoulou
Christina
C
Vakouti
Eleftheria
E
Klimathianaki
Maria
M
Georgopoulos
Dimitris
D
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006115:Greece; D006801:Humans; D007362:Intensive Care Units; D008297:Male; D008875:Middle Aged; D012121:Respiration, Artificial / Q000379:methods*; D014939:Work of Breathing / Q000502:physiology*