Physiologic effects of early administered mask proportional assist ventilation in patients with chronic obstructive pulmonary disease and acute respiratory failure
M. Vitacca et al., Physiologic effects of early administered mask proportional assist ventilation in patients with chronic obstructive pulmonary disease and acute respiratory failure, CRIT CARE M, 28(6), 2000, pp. 1791-1797
Objective: To evaluate the physiologic short-term effects of noninvasive pr
oportional assist ventilation (PAV) in patients with acute exacerbation of
chronic obstructive pulmonary disease (COPD).
Design:Prospective, physiologic study.
Setting: Respiratory intermediate intensive care unit.
Patients: Seven patients with acute respiratory failure requiring noninvasi
ve mechanical ventilation because of exacerbation of COPD.
Interventions: PAV was administered by nasal mask as first ventilatory inte
rvention. The setting of PAV involved a procedure to adjust volume assist a
nd flow assist to levels corresponding to patient comfort. Volume assist wa
s also set by means of the "run-away" procedure. Continuous positive airway
pressure (CPAP) amounting to 2 cm H2O was always set by the ventilator. Th
is setting of assistance (PAV) was applied for 45 mins. Thereafter, CPAP wa
s increased to 5 cm H2O (PAV + CPAP-5) without any change in the PAV settin
g and was administered for 20 mins. Oxygen was delivered through a port of
the mask in the attempt to maintain a target Sao(2) >90%.
Measurements and Main Results: Arterial blood gases, breathing pattern, and
inspiratory effort were measured during unsupported breathing and at the e
nd of PAV, and breathing pattern and inspiratory effort were measured after
20 mins of PAV + CPAP-5. PAV determined a significant increase in tidal vo
lume and minute Ventilation (+64% and +25% on average, respectively) with u
nchanged breathing frequency and a significant improvement in arterial bloo
d gases (Pao, with the same oxygen supply, from 65 +/- 15 torr to 97 +/- 36
torr; Paco(2), from 80 +/- It torr to 76 +/- 13 torr; pH, from 7.30 +/- 0.
02 to 7.32 +/- 0.03). The pressure-time product calculated over a period of
1 min (from 318 +/- 87 to 205 +/- 145 cm H2O sec min(-1)) was significantl
y reduced. PAV + CPAP-5 resulted in a further although not significant decr
ease in the pressure-time product calculated over a period of 1 min (to 183
+/- 110 cm H2O sec min(-1)), without additional changes in the breathing p
attern.
Conclusions: Noninvasive PAV is able to improve arterial blood gases while
unloading inspiratory muscles in patients with acute exacerbation of COPD.