Volume-guaranteed pressure-support ventilation facing acute changes in ventilatory demand.
OBJECTIVE
To compare volume support ventilation (VSV) in which the pressure support level is continuously adjusted to deliver a preset tidal volume, with pressure support ventilation (PSV), in terms of patient behavior and ventilator response when ventilatory demand was increased by addition of dead space to the circuit.


METHODS
Randomized cross-over study in an intensive care unit university hospital.


METHODS
We assessed in ten patients being weaned off mechanical ventilation the effect of increasing the ventilatory demand by adding a heat-and-moisture exchanger to augment the dead space with a fixed level of PSV and VSV.


RESULTS
Arterial blood gases, breathing pattern, and respiratory effort parameters at the end of each of the four steps. Adding dead space significantly increased minute ventilation and PaCO2 values with both PSV and VSV. Indexes of respiratory effort (pressure-time index of respiratory muscles and work of breathing) increased with both ventilatory modes after dead-space augmentation. This increase was 2.5-4 times with VSV than with PSV and induced overt respiratory distress in two patients. The assistance delivered during VSV decreased significantly after dead-space augmentation, from 15.0+/-6.5 to 9.1+/-4.8 cmH2O, whereas no change occurred with PSV.


CONCLUSIONS
With a fixed level of VSV, but not of PSV, an increase in ventilatory demand results in a decrease in the pressure support provided by the ventilator, opposite to the desired response. VSV may conceivably result in respiratory distress in clinical settings.
Jaber
Samir
S
Intensive Care Unit, Anesthesia and Critical Care Department B, Saint Eloi Teaching Hospital, 34000 Montpellier, France. s-jaber@chu-montpellier.fr
Delay
Jean-Marc
JM
Matecki
Stefan
S
Sebbane
Mustapha
M
Eledjam
Jean-Jacques
JJ
Brochard
Laurent
L
D018806:APACHE; D000328:Adult; D000368:Aged; D001784:Blood Gas Analysis; D018592:Cross-Over Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration / Q000379:methods*; D011446:Prospective Studies; D029424:Pulmonary Disease, Chronic Obstructive / Q000145:classification / Q000401:mortality / Q000628:therapy*; D012128:Respiratory Distress Syndrome / Q000145:classification / Q000401:mortality / Q000628:therapy*; D015300:Ventilator Weaning / Q000379:methods*; D014939:Work of Breathing