Question

A term neonate (4 kg) was born with thick meconium following a prolonged and arduous labor. Apgar scores were 1 at 1 minute and 4 at 5 minutes of life. The neonate required full resuscitation measures at birth, was intubated and mechanically ventilated by t-piece re- suscitator in the delivery suite, and transferred to the neonatal intensive care unit. He was ventilated in the SIMV mode on the following settings: PIP 26 cm H2O, PEEP 5 cm H2O, I-time 0.4 seconds, and a respiratory rate of 45 breaths per minute FIO2 0.80. The ABG revealed the following: pH 7.09, CO2 74 mm Hg, PaO2 35 mm Hg, bicarbonate 16 mEq/L, and base excess 8. The PIP was increased to 30 cm H2O, and 5 minutes after the increase to the PIP, the following was observed: SpO2 90% to 95% and the measured tidal volume 3 ml/kg. The measured MAP on the ventilator was 16 cm H2O, and tidal volume was 12 mL (3 mL/kg). The mode of ventilation was switched to HFOV. The initial oscillator settings were MAP 18 cm H2O, amplitude 38, frequency 10 Hz, and FiO2 75%. This continued for 8 hours, during which time the clinical condition and blood gases started to improve. The chest X-ray showed good lung expansion. The amplitude was reduced as chest wiggle was pronounced and CO2 started to decrease. Oxygenation also started to improve, so FiO2 was reduced to 40% on day 2. Over the next 48 hours, the MAP was slowly reduced by increments of 1 to 2 cm H2O until a MAP of 14 cm H2O. The oxygen requirement was only 35%. On day 6 of life, the neonate was to be extubated to nasal CPAP at 4 cm H2O and an FIO2 of 0.28.

1. How do you approach setting the mean airway pressure when transitioning from conventional ventilation to HFOV?

Answer 1

Transition from conventional ventilation to High-frequency Oscillatory Ventilation (HFOV).

Prior to commencing HFOV, it is important to consider the nature of the underlying disease and to have a clear plan for ventilation strategy as different diseases benefit from a slightly different approach to the delivery of HFOV.

Preparing the patient and the monitoring environment:

Ensure that appropriate monitoring is available and ready to facilitate informed adjustment and optimization of HFOV ventilator settings after initiation of HFOV. It is useful to note the current PIP-PEEP and mean airway pressure applied during conventional ventilation, as these variables guide the initial selection of the HFOV ventilator setting. Airway secretions present a major impediment to achieving adequate tidal volume during HFOV (much more so than during conventional ventilation and pose a risk of increased oscillatory pressure transmission to proximal alveoli. Consequently, it is advisable to also perform tracheal suction prior to the commencement of HFOV to avoid clinical deterioration on the commencement of HFOV.

Setting the mean airway pressure: Mean airway pressure is the primary determinant of distending lung volume, and also influences pulmonary vascular resistance, and hence the flow of blood through the pulmonary capillaries. Consequently, the mean airway is the primary determinant of oxygen transfer from the alveolus to the pulmonary capillary. A strategy for identification of optimal mean distending pressure for first intention HFOV treatment in the setting of neonatal respiratory distress syndrome as follows.