Sigh35 and end-expiratory occlusion test assess fluid responsiveness in critically ill patients undergoing pressure support ventilation: a validation study.

Sigh35 is a hemodynamic test allowing the prediction of fluid responsiveness in critically ill patients showing spontaneous breathing activity. Sigh35 consists in the application of 35cmH20 for 4 seconds by a mechanical ventilator. The rise of the intrathoracic pressure causes a drop in pulse pressure (PP) and stroke volume index (SVI) which are proportional to preload dependency of the right ventricle (i.e. a patient who needs fluid will have a more consistent drop than a patient who does not need fluid). Sigh35 has been tested in a pilot study (ACTRN12615001232527). 2)End expiratory occlusion test (EEO) is another hemodynamic test allowing the prediction of fluid responsiveness in critically ill patients showing spontaneous breathing activity. By abolishing the inspiratory increase in intrathoracic pressure, EEO increases venous return and CO that could act as a volume challenge for detecting preload responsiveness. The EEO consists in the interruption of the inspiratory pressure delivered by the ventilator by means of a manual end-expiratory occlusion of the airways for 15 seconds. Usually, on the main screen of the ventilator is displayed an "end-expiratory" maneuver button, since the stop on inspiratory pressure is also used to calculated totale end expiratory positive pressure. 3)Fluid challenge consisting in 4 ml/kg of intravenous crystalloids (both saline 0,9% or Ringer Acetate or Lactate were allowed), administered in 10 minutes. The Fluid challenge is administered by the attending physician to correct hemodynamic instability during the surgical procedure or in intensive care unit (see also eligibility). All the patients received hemodynamic monitoring with the MostCare system which provides all the hemodynamic variables evaluated in the study before and after fluid challenge administration (PP, SVI, arterial elastance, cardiac cycle efficiency). The protocol defines: 1) The two tests will be used before fluid challenge in the same patient, and well be delivered following an order obtained by using opaque sealed envelopes to define which test (SIGH35, EEO) will be firstly delivered. This is NOT a randomized trial since there is NOT a random allocation to intervention /control group. In fact, when if patient presents the predetermined criteria for inclusion, without exclusion criteria, then he/she will be tested with Sigh35 and EEO before FC administration. Because of a potential statistical bias in the delivering the three tests always in the same order, the opaque sealed envelope will contain different orders. Each test will be delivered according to definition (SIGH 35 in 4 seconds, EEO in 15 seconds) and a pause of 3 minutes will separate each test from the others, The variations of stroke volume, cardiac output, pulse pressure and systolic pressure will be recorded after each test and will be compared to the baseline values (pre-test values). Each test will be administered only one time unless the occurrence of cough or sporadic extrasystoles after SIGH35. For these reasons SIGH35 will be repeated for a maximum of another time. The occurrence of triggering of ventilator will determine the failure of EEO. 2) Each test will be delivered by an expert ICU physician with minimum 5 years’ experience 3) Predetermined cut-offs have been described in the literature for SIGH35 (35% of pulse pressure reduction with respect to the baseline), EEO (5% of cardiac index increase with respect to the baseline). However, since a ROC curve approach will be used in the study, the cut offs of each test will be defined by the ROC curve constructed after fluid challenge administration and response.