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pH: an overlooked criterion for success in high-frequency oscillatory ventilation in acute respiratory distress syndrome?


High-frequency oscillatory ventilation (HFOV) is used for patients with refractory hypoxia and or severe oxygenation failure in our ICU. There is a unit policy regarding the timing of initiation of HFOV, and all patients were initiated with a single static recruitment manoeuvre and then managed according to local guidelines. The aim of this study was to understand which ventilatory parameters best predicted successful outcome following HFOV.


After institutional approval, we retrospectively reviewed the case notes all the adult patients who were ventilated with HFOV during the 18-month period between January 2005 and July 2006. The data were analysed using SPSS® version 13 software.


There were 33 episodes of HFOV in 31 patients; 19 females and 12 males; mean age of 56 years. First-day median APACHE II scores and predicted mortality were 23 and 41%, respectively. All the patients had acute respiratory distress syndrome (ARDS) at the time of initiation of HFOV. The main causes of ARDS were pneumonia leading to sepsis (50%), sepsis from other sources (18%), postoperative emergency laparotomy and abdominal aortic aneurysm repair (18%). Patients were ventilated with conventional ventilation for a median period of 35 hours (0–519 hours) before being ventilated with HFOV for a median period of 58 hours (7–1,080 hours). Fourteen patients (45%) were successfully weaned to conventional ventilation while two (7%) died because of cardiac arrest and in the remaining 15 patients (48%) treatment was withdrawn. Eight patients (25.8%) survived to discharge to the ward. An admission pH of less than 7.20 was found to be significantly associated (P = 0.09) with failure of treatment.


Although we believed that the unit's approach to HFOV was one of 'treatment' rather than 'rescue', our results suggest we are still using HFOV in a 'rescue' mode. While our results support the findings of other studies that earlier initiation of HFOV shows a trend towards improved outcome in adult patients with ARDS, further studies are still required to identify appropriate parameters for selecting patients in a timely manner who may benefit from HFOV. However, progressive acidosis in ARDS appears to be a relatively more important predictive criterion than parameters of failing oxygenation and ventilation.

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Madhusudana, K., Black, K. & Melville, C. pH: an overlooked criterion for success in high-frequency oscillatory ventilation in acute respiratory distress syndrome?. Crit Care 11 (Suppl 2), P201 (2007).

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