Does a sigh breath improve oxygenation in the intubated patient receiving CPAP?

BACKGROUND: In the spontaneously breathing patient, tracheal intubation with ambient end-expiratory pressure decreases functional residual capacity, resulting in diminished arterial oxygenation and lung compliance. The sigh breath, a positive-pressure breath with a volume of 10 to 15 mL/kg applied intermittently, has been used to decrease atelectasis and prevent arterial hypoxemia. An appropriate level of CPAP or PEEP provided to the intubated patient is known to prevent or overcome loss of FRC. We sought to determine whether intermittent sigh breaths would further increase oxygenation and, thus, provide any advantage to intubated patients maintained on CPAP. METHODS: Thirty adults in the surgical intensive care unit who required tracheal intubation but who did not require ventilatory support received two modes of support in random sequence-CPAP alone or CPAP with a single sigh breath/minute (CPAP + S). Hemodynamics and arterial oxygenation were assessed at the end of 3 hours of CPAP and 3 hours of CPAP + S or 12 hours of CPAP and 12 hours of CPAP + S (in random order) depending on the anticipated duration of intubation. Data from the two groups were analyzed independently. RESULTS: Levels of CPAP and F(IO₂) were similar during both modes of therapy. Hemodynamics and gas exchange did not differ significantly when the patients received one mode of therapy or the other. CONCLUSIONS: Neither CPAP nor CPAP + S provided an advantage with respect to gas exchange or hemodynamic function. A sigh breath carries some inherent risk of barotrauma and may increase the cost and sophistication of care. A sigh breath is unneeded for spontaneously breathing patients receiving CPAP for the purpose of augmenting arterial oxygenation.