Haemodynamic monitoring during high-frequency oscillatory ventilation in adults

High-frequency oscillatory ventilation (HFOV) has been described as an effective therapy of RDS in prematurities and neonates. However, there are only few reports about using this technique in adults. The main goals of our study were establishing, during adult ventilation, the optimal parameters for monitoring HFOV, relative risk of hemodynamic disturbances connected with HFOV, and contraindications for HFOV. Until the present time six patients were enrolled to the study. The indications were: unsuccessful classical ventilation (CMV + PEEP + Plateau for at least 6 hours), or unsuccessful weaning (routine procedure for at least 7 days). After qualification all patients were ventilated using the SensorMedics 3100B oscillator. The following parameters were continuously measured: cardiac output using the Doppler technique (Abbott monitor), heart rate, blood pressures (systolic, diastolic, mean), EKG, SaO₂, and ETCO₂. Every hour CVP, arterial gases and diuresis were measured. In all patients a rapid increase in PaO₂ was observed, which enabled progressive decrease in FiO₂(20–40%). After several hours of HFOV the condition of two patients deteriorated and it was necessary to immediately resume classical ventilation. One of these patients was morbidly obese (BMI = 43.2), whereas the other had critically low ejection fraction (14.3%) and low cardiac output (2.7–3.4 l/min). The first symptom of disturbances was a decrease of signal and amplitude of the plethysmographic curve. At that moment PaCO₂ was 34.2 and 47.0 mmHg, respectively, and cardiac output was a little higher than initially. Another symptom was the disappearance of pleth signal. The next symptom was bradycardia and a sudden decrease of cardiac output (30–50%), while the stroke volume value remained unchanged. After resuming classical ventilation (CMV mode) and hemodynamic stabilization, a temporary increase of PaCO₂ was observed (60.1 and 65.3 mmHg). We concluded that: 1) The documented scenario of the deterioration was different from that typically observed during classical ventilation; 2) The SaO₂ and pleth curve monitoring during HFOV is essential for safety reasons; 3) The first symptom of deterioration during HFOV may be the decrease of amplitude and signal of the pleth curve; 4) The disappearance of the pleth signal is a sign of an imminent deterioration during HFOV; 5) The arterial gas analysis may not give sufficient information about the patient's condition; 6) Significant obesity and left ventricular insufficiency may be contraindications for HFOV in adults.