Targeted minute ventilation and tidal volume in an animal model of acute changes in lung mechanics and episodes of hypoxemia.
BACKGROUND
Acute episodes of hypoxemia in ventilated preterm infants are triggered by changes in ventilation, lung volume (LV) and respiratory system compliance (C(RS)) that are not prevented by conventional synchronized intermittent mandatory ventilation (SIMV).


OBJECTIVE
To assess in a rabbit model of episodic hypoxemia the individual and combined efficacy of targeted tidal volume (V(T)) and minute ventilation (V'(E)) by automatic adjustment of peak inspiratory pressure (PIP) and ventilator rate, respectively.


METHODS
Six young New Zealand white rabbits were ventilated with SIMV, targeted V(T), targeted V'(E), and combined targeted V'(E) + V(T) in random sequence. Hypoxemia episodes were induced by apnea alone or by apnea combined with a reduction in LV and C(RS). Apnea was induced by a bolus of propofol. The reduction in LV and C(RS) was induced by chest compression with a cuff. PaO(2) and PaCO(2) were measured continuously by an indwelling arterial electrode.


RESULTS
During SIMV, apnea caused a decrease in ventilation and PaO(2). This was attenuated during targeted V'(E) and targeted V'(E) + V(T). Apnea plus a reduction in LV and C(RS) caused a greater decrease in ventilation and PaO(2) during SIMV. These changes were attenuated during targeted V(T) and targeted V'(E). The attenuation was more pronounced during targeted V'(E) + V(T).


CONCLUSIONS
In this animal model, targeted V'(E) was effective in reducing hypoxemia caused by apnea. When apnea was accompanied by a reduction in LV and C(RS), the combined adjustment of PIP and ventilator rate was more effective than each individually. This combined strategy may be effective in ameliorating acute episodes of hypoxemia in preterm infants but this remains to be proven.
Claure
Nelson
N
Division of Neonatology, Department of Pediatrics, University of Miami Miller School of Medicine, Miami, Fla. 33101, USA. nclaure@miami.edu
Suguihara
Cleide
C
Peng
Jinghong
J
Hehre
Dorothy
D
D'Ugard
Carmen
C
Bancalari
Eduardo
E
D000818:Animals; D001049:Apnea / Q000139:chemically induced / Q000150:complications / Q000503:physiopathology; D002138:Calibration; D004195:Disease Models, Animal; D000860:Hypoxia / Q000209:etiology / Q000503:physiopathology* / Q000628:therapy*; D007385:Intermittent Positive-Pressure Ventilation / Q000379:methods*; D008168:Lung / Q000503:physiopathology; D008170:Lung Compliance / Q000502:physiology; D011312:Pressure / Q000009:adverse effects; D015742:Propofol / Q000494:pharmacology; D012123:Pulmonary Ventilation / Q000502:physiology*; D011817:Rabbits; D015656:Respiratory Mechanics / Q000502:physiology*; D013990:Tidal Volume / Q000502:physiology
D015742:Propofol