Discussion
lung derecruitment, critically ill, stroke, ARDS, RAP
CRITICALLY ILL, STROKE, HYPOXIC, ADVERSE EFFECTS, CAVITY, ARDS
In patients receiving invasive mechanical ventilation with a PEEP ≥ 10 cmHFluids should be considered as drugs with inconsistent efficacy and several adverse effects [Changing PEEP may be another way to test volume responsiveness. PEEP is transmitted to the intrathoracic pressure, which surrounds the cardiac chambers, and to the right atrium. By decreasing PEEP, the PEEP-test reduces the intramural right atrial pressure (RAP), which is the downstream pressure of venous return [Besides changing cardiac preload, PEEP also affects right ventricular afterload by increasing transpulmonary pressure [Our results may help understanding the hemodynamic effects of PEEP. It has been suggested that the effect of PEEP on cardiac preload is minimal because of two phenomena. First, PEEP is transmitted to the abdominal cavity, increasing the upstream pressure of venous return, attenuating the effect on its pressure gradient [Another phenomenon may have induced some false negatives to the PEEP-test. In theory, reducing PEEP may not decrease, but conversely increase right ventricular afterload, because of lung derecruitment and/or hypoxic pulmonary vasoconstriction. This may counterbalance the increase in CI due to volume responsiveness in volume responders. However, this theoretical phenomenon was unlikely. First, hypoxic pulmonary vasoconstriction takes a couple of minutes to occur, so that it was unlikely during the 1-min PEEP-test [Of note, the effects of PEEP, and thus of the PEEP-test, may depend on the volume status [A study in critically ill patients showed that the response of stroke volume to a transient increase in PEEP by 5 cmHWe observed that the reliability of the PEEP-test when assessed through changes in PP was low, confirming a previous study [Considering all patients, the PEEP-test significantly decreased SpOBeyond those mentioned above, our study has several limitations. First, not all patients received fluid administration, because we thought it was unethical to administer a fluid bolus even in the absence of volume responsiveness in critically ill patients, including some with ARDS, in whom an increased fluid balance is an independent risk factor of mortality [