ANIMAL & CLINICAL STUDIES
The principle of a ventilator machine is simple and the most sturdy of them all, which I call a “workhorse”, is the pressure limited, time cycled ventilator since it has minimal moving parts that can be a constant source of problems. With the help of the engineers from the Department of Engineering, the University of the Philippines, we were able to devise a pressure limited, time cycled ventilator with the solenoid valve as the heart of the machine (see Figure A). The first ventilator that was made is shown in Figure B.
A. Animal study: The OstreaVent was first tested in newborn animals at the Department of Physiology, College of Medicine, University of the Philippines and its safety and efficacy were simultaneously compared to the Sechrist, a standard commercial pressure limited, time cycled ventilator. Term, newborn piglets (N=8) were studied. After birth, the piglet was anesthetized, intubated and then alternately cycled either to a Sechrist ventilator or to the OstreaVent at varying peak inspiratory pressures or PIP (10, 13 and 15 cm H20) and ventilator rate or IMV (15, 20, 25 bpm) and at constant oxygen concentration of 40% and positive end expiratory pressure or PEEP of +4. Duplicate blood gas determinations were drawn from the umbilical artery 30 minutes after each ventilator change. Adverse effects were monitored including pneumothorax, sudden deterioration, hypotension and death. Results: There were no significant differences in the pH, PO2, PCO2 and HCO3 with either the OstreaVent or Sechrist at the rates (IMV) and pressures (PIP) used (see Figure A).
B. Clinical study: Prospective, controlled trial of 90 infants with respiratory distress randomized either to OstreaVent (N=45) or Sechrist (N=45). Power analysis for sample size based on pneumothorax as adverse outcome (one tailed) : alpha= 0.05; beta=0.82. Eligibility: Preterm infants with birth weight >1000 g, with respiratory distress and in need of ventilator support. Exclusion criteria: Infants with severe asphyxia or major congenital malformations. Informed consent was obtained. Initial ventilator settings: Fi02 = 0.6, IMV (rate) = 40, PIP = 20 cm H2O, PEEP = +4, inspiratory time of 0.4-0.6 sec. Ventilator settings were adjusted to achieve the following range of blood gases: pH = 7.25-7.35, PC02 = 45-55 mm Hg and P02 =55-60 (or 90% saturation) mm Hg. Monitored were infant’s blood gases, BP, 02 saturation by pulse oximeter and any adverse events, e.g., pneumothorax, pulmonary hemorrhage, intraventricular hemorrhage. Duration of the study for each subject was for 3 days after which the infant on the OstreaVent was switched to a conventional Sechrist ventilator. The study was approved by the Human Investigations Committee of the UP College of Medicine. Results: The patients on OstreaVent and Sechrist were not significantly different in birth weight and diagnosis (Table 1). The difference in their ventilator settings to achieve the desired blood gases were not of clinical significance (Table 2). The incidence of mortality and complications did not significantly differ between the 2 groups (Table 3). Conclusion: In both animal and clinical studies, the efficacy and safety of a prototype, pressure limited, time-cycled Philippine ventilator (OstreaVent) were comparable to a standard, commercial ventilator (Sechrist). The OstreaVent is an effective, alternative ventilator for the treatment of respiratory insufficiency in newborn infants in the Philippines. (Publication: Ostrea EM, Villanueva-Uy E., Animal and clinical trials on a prototype, pressure limited, time cycled Philippine ventilator (OstreaVent). Acta Medica Phil 2010;44:4-9).