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. What is an important aspect of setting the amplitude when transitioning to HFOV?

Answer 1

High frequency oscillatory ventilation (HFOV) is a type of mechanical ventilation that uses a constant distending pressure (mean airway pressure) with pressure variations oscillating around the mean airway pressure at very high rates.

the advantage of HFOV as compared to either conventional positive pressure is its ability to promote gas exchange and ability to maintain oxygenation and ventillation while using minimal tidal volume resulting in minimal barotrauma.

Amplitude is the degree of deflection of the piston of the oscillator. this deflection is clinically noted by the wiggles seen in the patient. it determines the tidal volume.

set amplitude to 30-35cm of H₂O, observe for good wiggle that extend up to pubic symphysis and adjust amplitude accordingly. ajust the piston control to centralize the piston.

so when HFOV applied appropriately , the continous distending pressure assists recruitment and maintainance of an optimal lung volume.