Episodes of hypoxemia during synchronized intermittent mandatory ventilation in ventilator-dependent very low birth weight infants

Distinct patterns of asynchrony, and episodes of hypoxemia, may occur in a spontaneously breathing preterm infant during conventional intermittent mandatory ventilation (IMV) on traditional time-cycled, pressure-limited ventilators. Synchronized IMV (SIMV) and assist/control ventilation are frequent modes of patient-triggered ventilation used with infant ventilators. The objective of this study was to use computerized pulse oximetry to quantify the occurrence of episodes of hypoxemia (oxygen desaturation) during SIMV vs. IMV, in preterm infants ≤1,250 g who required mechanical ventilation at ≥14 days of age. We performed a randomized, crossover study with each infant being randomized to IMV or SIMV (Infant Star ventilator) for initial testing for a 1-hr period. Patients were subsequently tested on the alternate modality after a stabilization period of 10 min at the same ventilator and fractional inspired oxygen concentration (FiO₂) settings. Pulse oximetry data were obtained with a Nellcor N-200 monitor, a microcomputer, and a software program (SatMaster). An investigator blinded to the randomized assignment evaluated all measurements. Eighteen very low birth weight (VLBW) infants with a birth weight of 777 ± 39 g (mean ± SEM) and gestational age 25.1 ± 0.3 weeks were studied. The average pulse oximeter oxygen saturation (SaO ₂) was higher on SIMV than IMV (P < 0.01). During SIMV, these infants had significantly fewer episodes of hypoxemia (duration of episodes of oxygen desaturation as a percentage of scorable recording time) to 86-90% SaO₂ (P < 0.01), 81-85% SaO₂ (P < 0.01), and 76-80% SaO₂ (P < 0.05) when compared to IMV. There was also a significant decrease in percentage of time of desaturation to SaO₂ < 90% (P = 0.002), < 85% SaO₂ (P = 0.003), and <80% SaO₂ (P = 0.02) during SIMV vs. IMV. Our preliminary findings indicate that the use of SIMV in a population of VLBW ventilator-dependent infants (≥ 14 days of age) results in better oxygenation and decreased episodes of hypoxemia as compared to IMV.