Apnea test during brain death assessment in mechanically ventilated and ECMO patients.

PURPOSE: To evaluate the feasibility and efficacy of an apnea test (AT) technique that combines the application of positive end expiratory pressure (PEEP) with subsequent pulmonary recruitment in a large cohort of brain-dead patients. METHODS: This study was a retrospective analysis of prospectively collected data on brain-dead patients admitted to our institution (Hospital San Gerardo, Monza, Italy) between January 2010 and December 2014. The rate of aborted apnea tests (ATs), occurrence of complications (i.e., pneumothorax, cardiac arrhythmias, cardiac arrest, and severe hypoxia, defined as PaO2 < 40 mmHg), ventilator settings, hemodynamics, and blood gas analyses were evaluated. Subgroup analysis was performed, with patients classified into veno-arterial extracorporeal membrane oxygenation (ECMO) or non-ECMO groups, and into hypoxic (i.e., baseline PaO2/FiO2 < 200 mmHg) and non-hypoxic (i.e., baseline PaO2/FiO2 > 200 mmHg) groups. RESULTS: In total, 169 consecutive patients including 25 on ECMO were included in the study. No AT abortion nor severe complications were detected. The AT was completed in all patients. Fluid boluses and increases or initiation of vasoactive drugs were required in less than 10 and 3% of the AT procedures, respectively. No clinically meaningful alteration in hemodynamics was recorded. Severe hypoxia occurred during 7 (2.4%) and 4 (8%) of the ATs performed in non-ECMO and ECMO patients, respectively (p = 0.063), and it occurred more frequently in hypoxic patients than in non-hypoxic patients (11.1 vs. 4.8%, respectively; p = 0.002). CONCLUSIONS: In a large cohort of consecutive patients, including the largest patient population on ECMO reported to date, our AT technique that combines the application of PEEP with subsequent pulmonary recruitment proved to be feasible and safe.

Topographic distribution of tidal ventilation in acute respiratory distress syndrome: effects of positive end-expiratory pressure and pressure support.

OBJECTIVE: Acute respiratory distress syndrome is characterized by collapse of gravitationally dependent lung regions that usually diverts tidal ventilation toward nondependent regions. We hypothesized that higher positive end-expiratory pressure and enhanced spontaneous breathing may increase the proportion of tidal ventilation reaching dependent lung regions in patients with acute respiratory distress syndrome undergoing pressure support ventilation. DESIGN: Prospective, randomized, cross-over study. SETTING: General and neurosurgical ICUs of a single university-affiliated hospital. PATIENTS: We enrolled ten intubated patients recovering from acute respiratory distress syndrome, after clinical switch from controlled ventilation to pressure support ventilation. INTERVENTIONS: We compared, at the same pressure support ventilation level, a lower positive end-expiratory pressure (i.e., clinical positive end-expiratory pressure = 7 ± 2 cm H2O) with a higher one, obtained by adding 5 cm H2O (12 ± 2 cm H2O). Furthermore, a pressure support ventilation level associated with increased respiratory drive (3 ± 2 cm H2O) was tested against resting pressure support ventilation (12 ± 3 cm H2O), at clinical positive end-expiratory pressure. MEASUREMENTS AND MAIN RESULTS: During all study phases, we measured, by electrical impedance tomography, the proportion of tidal ventilation reaching dependent and nondependent lung regions (Vt%dep and Vt%(nondep)), regional tidal volumes (Vt(dep) and Vt(nondep)), and antero-posterior ventilation homogeneity (Vt%nondep/Vt%dep). We also collected ventilation variables and arterial blood gases. Application of higher positive end-expiratory pressure levels increased Vt%dep and Vtdep values and decreased Vt%nondep/Vt%dep ratio, as compared with lower positive end-expiratory pressure (p < 0.01). Similarly, during lower pressure support ventilation, Vt%dep increased, Vtnondep decreased, and Vtdep did not change, likely indicating a higher efficiency of posterior diaphragm that led to decreased Vt%nondep/Vt%dep (p < 0.01). Finally, PaO2/FIO2 ratios correlated with Vt%dep during all study phases (p < 0.05). CONCLUSIONS: In patients with acute respiratory distress syndrome undergoing pressure support ventilation, higher positive end-expiratory pressure and lower support levels increase the fraction of tidal ventilation reaching dependent lung regions, yielding more homogeneous ventilation and, possibly, better ventilation/perfusion coupling.

Patient-ventilator interaction in ARDS patients with extremely low compliance undergoing ECMO: a novel approach based on diaphragm electrical activity.

PURPOSE: Patients with acute respiratory distress syndrome (ARDS) requiring extracorporeal membrane oxygenation (ECMO) usually present very low respiratory system compliance (Cst(rs)) values (i.e., severe restrictive respiratory syndrome patients). As a consequence, they are at high risk of experiencing poor patient-ventilator interaction during assisted breathing. We hypothesized that monitoring of diaphragm electrical activity (EAdi) may enhance asynchrony assessment and that neurally adjusted ventilatory assist (NAVA) may reduce asynchrony, especially in more severely restricted patients. METHODS: We enrolled ten consecutive ARDS patients with very low Cst(rs) values undergoing ECMO after switching from controlled to pressure support ventilation (PSV). We randomly tested (30 min) while recording EAdi: (1) PSV30 (PSV with an expiratory trigger at 30 % of flow peak value); (2) PSV1 (PSV with expiratory trigger at 1 %); (3) NAVA. During each step, we measured the EAdi-based asynchrony index (AI(EAdi)) = flow-, pressure- and EAdi-based asynchrony events/EAdi-based respiratory rate × 100. RESULTS: AI(EAdi) was high during all ventilation modes, and the most represented asynchrony pattern was specific for this population (i.e., premature cycling). NAVA was associated with significantly decreased, although suboptimal, AI(EAdi) values in comparison to PSV30 and PSV1 (p < 0.01 for both). The PSV30-NAVA and PSV1-NAVA differences in AI(EAdi) values were inversely correlated with patients' Cst(rs) (R (2) = 0.545, p = 0.01 and R (2) = 0.425, p < 0.05; respectively). CONCLUSIONS: EAdi allows accurate analysis of asynchrony patterns and magnitude in ARDS patients with very low Cst(rs) undergoing ECMO. In these patients, NAVA is associated with reduced asynchrony.