Does PEEP matter in the OR?

SummaryAnesthetic agents lower muscle tone and cause a fall in FRC, This promotes closure of airways. The lung capillary blood will adsorb gas behind closed airways, promoting alveolar collapse (i.e. atelectasis). More than 90% of anesthetized subjects develop atelectasis. It will impede oxygenation of blood but different precautions or actions can counter hypoxemia, eg. PEEP, increased inspired oxygen concentration and circulatory support. However, high oxygen levels increase atelectasis formation and PEEP may not be enough to eliminate it. Moreover, atelectasis will reappear on discontinuation of PEEP and remain into the post-operative period, even for several days. It is a locus for infection and may be an important cause of post-operative pneumonia that carries a high mortality. PEEP or CPAP, by elevating lung volume, may thus be helpful in improving oxygenation (traditional indication for PEEP) but may be more important in countering lung infection (potential new indication for PEEP). In the latter case, maintenance of increased lung volume seems mandatory, in particular during the breathing of high oxygen concentrations.