Monday, December 27, 2010

Respiratory failure and mechanical ventilation---anything new and important in 2010?

St. Louis City Hospital

Although there were no landmark trials reported in 2010 several important trends emerged in the literature.

Severity assessment in ARDS
Like several other conditions in hospital medicine (e.g. C diff disease and pancreatitis) severity assessment has treatment implications in ARDS and was a recurring theme in 2010. The major tool for severity assessment is the lung injury score (calculator here) although other methods exist. This year there were three papers dealing with special therapeutic modalities to be considered in patients with ARDS who meet severity criteria. One looked at an old modality considered, in recent years, to be outmoded: the use of paralytic agents added to sedation for severe ARDS. This could represent a swinging back of the pendulum and is likely to remain controversial for some time, at least until further systematic study is done. I discussed the NEJM paper here.

Another paper this year, discussed here, mentioned a meta-analysis suggesting that high levels of PEEP (above those recommended in the ARDSnet PEEP scale) may be beneficial in patients classified as having severe disease.

High PEEP can be considered a rescue therapy. Rescue therapies have not been validated across the board for most patients with ARDS. A recent paper (discussed here) looked at several rescue therapies including high PEEP, prone positioning, high frequency oscillation and extracorporeal life support. These are therapies to be considered in severe disease. Although considered last resort measures which may offer the patient's only chance at survival they may warrant consideration and preparation early in the course of some patients whose presentations meet severity criteria.

Low tidal volume ventilation---not just for ARDS anymore?
There is accumulating evidence that, other things being equal, concerning delivered tidal volumes in mechanical ventilation, the lower the better. Early this year I reviewed the literature on this subject and noted the first RTC to suggest that low tidal volume ventilation was beneficial in patients who did not have ARDS/ALI at presentation, because it reduced the incidence of ARDS/ALI developing during MV.

Special problems in mechanical ventilation of patients with heart disease
Known or occult heart disease presents unique problems during mechanical ventilation and can be a cause of “failure to wean” (FTW). Although this has been known for some time it is underappreciated in day to day critical care practice and seemed to get special attention this year. Awareness of the problem is being raised. Briefly, the pathophysiology of cardiac disease as a cause of FTW relates to the multiple hemodynamic benefits of mechanical ventilation which, when withdrawn, may result in acute myocardial ischemia and cardiac decompensation. Due to the special circumstances of mechanical ventilation cardiac ischemia and decompensation may not be easily recognized. Judicious use of cardiac markers and even serial echocardiograms during spontaneous breathing trials may aid the clinical assessment. I discussed papers dealing with this problem here, here and here.

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