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The ∆P is generally initiated at either a value where the patient’s chest vibrates down to their mid-thigh or in our experience, a value of 20 – 30 cmH2O above what the patient’s PaCO2 was on CV (e.g. PaCO2 of 60 mmHg would mean starting the ∆P at 80 cmH20). Alternatively, initial ∆P may be set to observe adequate “chest wall vibration”. Initial frequency is usually set at 5 Hz. Patients who demonstrate rapidly rising PaCO2 on HFOV should have aggressive increases in ∆P (10 to 20 cmH2O) and reduced Hz to the lowest value achievable (3 Hz on the SensorMedics 3100B). An adjunct to improving PaCO2 elimination is to briefly disconnect the patient from HFOV and vigorously manually ventilate the patient with a PEEP-valve equipped bag. Aggressive action is required for a rapidly rising PaCO2 during initiation of HFOV because improvements in PaCO2 do not occur as quickly as is noted when changes are made to conventional ventilators. We obtain an ABG 15 to 20 minutes after starting HFOV to determine the trend of the PaCO2. Subsequent ABG’s are generally obtained at 30 to 60 minute intervals until stabilization occurs. An interesting observation in some patients with hypercapnea is that a deliberately induced cuff leak may improve the PaCO2. The presence of a cuff leak may allow the elevated end-tidal PCO2 in the airway to be “washed-out” by the bias flow gas – much like occurs with tracheal insufflation of gas at the carina with small caliber airway catheters (8). In practice, if a patient remains with severe hypercapnea (causing a pH < 7.2) despite maximum ∆P and lowest frequency settings, we will induce a small endotracheal tube cuff leak by withdrawing air from the cuff pilot balloon sufficient to lower the mPaw about 5 cmH2O. The mPaw is then readjusted to its previous value while maintaining the cuff leak. Using this technique we have seen occasional marked reductions in PaCO2 over a short time (20 – 30 minutes). Patient Positioning Hemodynamically stable patients are generally positioned with the head of the bed elevated approximately 30 degrees. Care must be taken with the patient’s head and neck positioning to ensure a smooth interface (free of kinks) between the endotracheal tube and oscillator circuit. This often requires propping the oscillator circuit on folded towels near the endotracheal tube interface. Prone positioning has been utilized successfully in adult patients on HFOV with demonstrated improvement in oxygenation (9). As with all patients who are mechanically ventilated in the prone position, a team of physicians, nurses, and respiratory therapists should be present to ensure that repositioning occurs safely without dislodging tubes and lines. If prone positioning is anticipated, it should ideally be accomplished prior to initiating HFOV. Because of the relatively inflexible oscillator circuit, the patient may have to be manually ventilated with an resuscitation bag while turning during HFOV. High vigilance for mucus plugs and excessive airway secretions should be maintained shortly after turning from prone to supine positions. 4. Complications During HFOV Hypotension Occasionally, patients will develop hypotension shortly following transfer to HFOV or as mPaw is raised.