Extreme hypoventilation reduces ventilator-induced lung injury during ventilation with low positive end-expiratory pressure in saline-lavaged rabbits.
OBJECTIVE
To compare the degrees of ventilator-induced lung injury caused by two ventilation protocols.


METHODS
Randomized trial.


METHODS
University animal laboratory.


METHODS
Sixteen New Zealand white rabbits.


METHODS
After five sequential saline lung lavages, eight pairs of anesthetized rabbits were allocated randomly to receive either of two ventilation protocols for 4 hrs during neuromuscular blockade. Both groups received 3 cm H2O of positive end-expiratory pressure and 100% oxygen. Control group animals received an estimated tidal volume of 12 mL/kg, an inspiratory time of 0.7 sec, and a ventilatory rate adjusted for a PaCO2 of 35 to 45 torr (4.7 to 6 kPa). Study group animals were ventilated through an intratracheal catheter, with inspiratory time of 1.5 secs, ventilatory rate of 20 breaths/min, and peak inspiratory pressure of 4 to 8 cm H2O, adjusted to maintain PaCO2 at 150 to 250 torr (20 to 33 kPa).


RESULTS
Arterial blood gases were measured every 30 mins. After 4 hrs, a final lung lavage was performed. Physiologic parameters, cell counts and protein concentration in the final lavage, and lung histology were compared between groups. The alveolar-arterial oxygen tension gradient was higher in the study group over the first 1.5 hrs, but the time profile showed significantly (p = .001) greater improvement in the study group. After 4 hrs, the mean alveolar-arterial oxygen tension gradient was lower in the study group (94 torr [12.5 kPa] vs. 201 torr [26.8 kPa]). The increase in neutrophil count from the initial to the final lung lavage was lower in the study group (0.27 x 10(7) cells/L vs. 2.01 x 10(7) cells/L, p = .037), as was the absolute value of the neutrophil count in the final lavage (1.33 x 10(7) cells/L vs. 3.02 x 10(7) cells/L, p = .04). The median hyaline membrane score was lower in the study group (0.5 vs. 3.0) but the difference was not statistically significant.


CONCLUSIONS
These findings suggest that a very low tidal volume reduces ventilator-induced lung injury in saline-lavaged rabbits during ventilation at low lung volume.
Department of Intensive Care, Christchurch Hospital, New Zealand.
K G
KG
Hickling
T
T
Wright
K
K
Laubscher
I G
IG
Town
A
A
Tie
P
P
Graham
J
J
Monteath
G
G
A'Court
D000818:Animals; D001784:Blood Gas Analysis; D018893:Bronchoalveolar Lavage; D002245:Carbon Dioxide / Q000097:blood; D004195:Disease Models, Animal; D007958:Leukocyte Count; D009504:Neutrophils; D010102:Oxygen Inhalation Therapy; D011175:Positive-Pressure Respiration / Q000009:adverse effects* / Q000379:methods*; D011817:Rabbits; D011897:Random Allocation; D012128:Respiratory Distress Syndrome / Q000209:etiology* / Q000276:immunology / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D012965:Sodium Chloride; D013990:Tidal Volume; D013997:Time Factors
D002245:Carbon Dioxide; D012965:Sodium Chloride