Lung volumes and lung volume recruitment in ARDS: a comparison between supine and prone position.

BACKGROUND: The use of positive end-expiratory pressure (PEEP) and prone position (PP) is common in the management of severe acute respiratory distress syndrome patients (ARDS). We conducted this study to analyze the variation in lung volumes and PEEP-induced lung volume recruitment with the change from supine position (SP) to PP in ARDS patients. METHODS: The investigation was conducted in a multidisciplinary intensive care unit. Patients who met the clinical criteria of the Berlin definition for ARDS were included. The responsible physician set basal PEEP. To avoid hypoxemia, FiO2 was increased to 0.8 1 h before starting the protocol. End-expiratory lung volume (EELV) and functional residual capacity (FRC) were measured using the nitrogen washout/washin technique. After the procedures in SP, the patients were turned to PP and 1 h later the same procedures were made in PP. RESULTS: Twenty-three patients were included in the study, and twenty were analyzed. The change from SP to PP significantly increased FRC (from 965 ± 397 to 1140 ± 490 ml, p = 0.008) and EELV (from 1566 ± 476 to 1832 ± 719 ml, p = 0.008), but PEEP-induced lung volume recruitment did not significantly change (269 ± 186 ml in SP to 324 ± 188 ml in PP, p = 0.263). Dynamic strain at PEEP decreased with the change from SP to PP (0.38 ± 0.14 to 0.33 ± 0.13, p = 0.040). CONCLUSIONS: As compared to supine, prone position increases resting lung volumes and decreases dynamic lung strain.

Clinical assessment of auto-positive end-expiratory pressure by diaphragmatic electrical activity during pressure support and neurally adjusted ventilatory assist.

BACKGROUND: Auto-positive end-expiratory pressure (auto-PEEP) may substantially increase the inspiratory effort during assisted mechanical ventilation. Purpose of this study was to assess whether the electrical activity of the diaphragm (EAdi) signal can be reliably used to estimate auto-PEEP in patients undergoing pressure support ventilation and neurally adjusted ventilatory assist (NAVA) and whether NAVA was beneficial in comparison with pressure support ventilation in patients affected by auto-PEEP. METHODS: In 10 patients with a clinical suspicion of auto-PEEP, the authors simultaneously recorded EAdi, airway, esophageal pressure, and flow during pressure support and NAVA, whereas external PEEP was increased from 2 to 14 cm H2O. Tracings were analyzed to measure apparent "dynamic" auto-PEEP (decrease in esophageal pressure to generate inspiratory flow), auto-EAdi (EAdi value at the onset of inspiratory flow), and IDEAdi (inspiratory delay between the onset of EAdi and the inspiratory flow). RESULTS: The pressure necessary to overcome auto-PEEP, auto-EAdi, and IDEAdi was significantly lower in NAVA as compared with pressure support ventilation, decreased with increase in external PEEP, although the effect of external PEEP was less pronounced in NAVA. Both auto-EAdi and IDEAdi were tightly correlated with auto-PEEP (r = 0.94 and r = 0.75, respectively). In the presence of auto-PEEP at lower external PEEP levels, NAVA was characterized by a characteristic shape of the airway pressure. CONCLUSIONS: In patients with auto-PEEP, NAVA, compared with pressure support ventilation, led to a decrease in the pressure necessary to overcome auto-PEEP, which could be reliably monitored by the electrical activity of the diaphragm before inspiratory flow onset (auto-EAdi).

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.

Xenon anaesthesia produces better early postoperative cognitive recovery than sevoflurane anaesthesia.

BACKGROUND AND OBJECTIVE: Xenon anaesthesia may have the potential to reduce postoperative cognitive impairment after general anaesthesia. This randomized double-blind controlled trial was designed to compare the early postoperative cognitive recovery after xenon and sevoflurane anaesthesia. METHODS: After institutional ethics approval, we obtained informed written consent from 60 adults, with American Society of Anesthesiologists I or II status, scheduled for elective surgery with an estimated surgery time between 60 and 360 min. Patients were randomized to receive xenon or sevoflurane anaesthesia. Both groups received a remifentanil infusion adjusted to clinical needs based on patients' haemodynamic and state entropy of less than 60. In cases of state entropy of at least 60 during the first 15 min after induction, patients in the xenon group received a propofol infusion targeted to state entropy of less than 60. The primary end-point of the study was the early postoperative cognitive recovery evaluated by the Short Orientation Memory Concentration Test. RESULTS: There was no significant difference in the mean preoperative Short Orientation Memory Concentration Test values between groups (sevoflurane 2.7 +/- 3.2 and xenon 3.2 +/- 2.6; P, 0.53). Awakening was significantly faster in the xenon group (sevoflurane 8 +/- 4 min and xenon 3 +/- 1 min; P < 0.001). Patients receiving xenon presented significantly lower Short Orientation Memory Concentration Test scores at 30 min (sevoflurane 6.7 +/- 5.9 and xenon 3.3 +/- 3.1; P 0.003) and 60 min (xenon 2.1 +/- 3 and sevoflurane 5 +/- 4.1; P 0.003) after extubation. CONCLUSION: Xenon anaesthesia was associated with faster emergence and with better early postoperative cognitive recovery than sevoflurane anaesthesia.