German clinical trials register DRKS00004199, www.who.int/ictrp/network/drks2/en/ .

Background: Robot-assisted laparoscopic radical prostatectomy requires general anaesthesia, extreme Trendelenburg positioning and capnoperitoneum. Together these promote impaired pulmonary gas exchange caused by atelectasis and may contribute to postoperative pulmonary complications. In morbidly obese patients, a recruitment manoeuvre (RM) followed by individualised PEEP improves intraoperative oxygenation and end-expiratory lung volume (EELV). We hypothesised that individualised PEEP with initial RM similarly improves intraoperative oxygenation and EELV in nonobese individuals undergoing robot-assisted prostatectomy. Methods: Forty males (age, 49e76 yr; BMI <30 kg m À2 ) undergoing prostatectomy received volume-controlled ventilation (tidal volume 8 ml kg À1 predicted body weight). Participants were randomised to either (1) RM followed by individualised PEEP (RM/PEEP IND ) optimised using electrical impedance tomography or (2) no RM with 5 cm H 2 O PEEP. The primary outcome was the ratio of arterial oxygen partial pressure to fractional inspired oxygen (PaO 2 /F i O 2 ) before the last RM before extubation. Secondary outcomes included regional ventilation distribution and EELV which were measured before, during, and after anaesthesia. The cardiovascular effects of RM/PEEP IND were also assessed. Results: In 20 males randomised to RM/PEEP IND , the median PEEP IND was 14 cm H 2 O [inter-quartile range, 8e20]. The PaO 2 / F i O 2 was 10.0 kPa higher with RM/PEEP IND before extubation (95% confidence interval [CI], 2.6e17.3 kPa; P¼0.001). RM/ PEEP IND increased end-expiratory lung volume by 1.49 L (95% CI, 1.09e1.89 L; P<0.001). RM/PEEP IND also improved the regional ventilation of dependent lung regions. Vasopressor and fluid therapy was similar between groups, although 13 patients randomised to RM/PEEP IND required pharmacological therapy for bradycardia. Conclusion: In non-obese males, an individualised ventilation strategy improved intraoperative oxygenation, which was associated with higher end-expiratory lung volumes during robot-assisted laparoscopic prostatectomy. Clinical trial registration: DRKS00004199 (German clinical trials registry)

IntroductionProtective ventilatory strategies have been applied to prevent ventilator-induced lung injury in patients with acute lung injury (ALI). However, adjustment of positive end-expiratory pressure (PEEP) to avoid alveolar de-recruitment and hyperinflation remains difficult. An alternative is to set the PEEP based on minimizing respiratory system elastance (Ers) by titrating PEEP. In the present study we evaluate the distribution of lung aeration (assessed using computed tomography scanning) and the behaviour of Ers in a porcine model of ALI, during a descending PEEP titration manoeuvre with a protective low tidal volume.MethodsPEEP titration (from 26 to 0 cmH2O, with a tidal volume of 6 to 7 ml/kg) was performed, following a recruitment manoeuvre. At each PEEP, helical computed tomography scans of juxta-diaphragmatic parts of the lower lobes were obtained during end-expiratory and end-inspiratory pauses in six piglets with ALI induced by oleic acid. The distribution of the lung compartments (hyperinflated, normally aerated, poorly aerated and non-aerated areas) was determined and the Ers was estimated on a breath-by-breath basis from the equation of motion of the respiratory system using the least-squares method.ResultsProgressive reduction in PEEP from 26 cmH2O to the PEEP at which the minimum Ers was observed improved poorly aerated areas, with a proportional reduction in hyperinflated areas. Also, the distribution of normally aerated areas remained steady over this interval, with no changes in non-aerated areas. The PEEP at which minimal Ers occurred corresponded to the greatest amount of normally aerated areas, with lesser hyperinflated, and poorly and non-aerated areas. Levels of PEEP below that at which minimal Ers was observed increased poorly and non-aerated areas, with concomitant reductions in normally inflated and hyperinflated areas.ConclusionThe PEEP at which minimal Ers occurred, obtained by descending PEEP titration with a protective low tidal volume, corresponded to the greatest amount of normally aerated areas, with lesser collapsed and hyperinflated areas. The institution of high levels of PEEP reduced poorly aerated areas but enlarged hyperinflated ones. Reduction in PEEP consistently enhanced poorly or non-aerated areas as well as tidal re-aeration. Hence, monitoring respiratory mechanics during a PEEP titration procedure may be a useful adjunct to optimize lung aeration.

Objective To evaluate the ability of three indices derived from the airway pressure curve for titrating positive end-expiratory pressure (PEEP) to minimize mechanical stress while improving lung aeration assessed by computed tomography (CT). Design Prospective, experimental study. Setting University research facilities. Subjects Twelve pigs. Interventions Animals were anesthetized and mechanically ventilated with tidal volume of 7 ml kg−1. In non-injured lungs (n = 6), PEEP was set at 16 cmH2O and stepwise decreased until zero. Acute lung injury was then induced either with oleic acid (n = 6) or surfactant depletion (n = 6). A recruitment maneuver was performed, the PEEP set at 26 cmH2O and decreased stepwise until zero. CT scans were obtained at end-expiratory and end-inspiratory pauses. The elastance of the respiratory system (Ers), the stress index and the percentage of volume-dependent elastance (%E2) were estimated. Measurements and main results In non-injured and injured lungs, the PEEP at which Ers was lowest (8–4 and 16–12 cmH2O, respectively) corresponded to the best compromise between recruitment/hyperinflation. In non-injured lungs, stress index and %E2 correlated with tidal recruitment and hyperinflation. In injured lungs, stress index and %E2 suggested overdistension at all PEEP levels, whereas the CT scans evidenced tidal recruitment and hyperinflation simultaneously. Conclusion During ventilation with low tidal volumes, Ers seems to be useful for guiding PEEP titration in non-injured and injured lungs, while stress index and %E2 are useful in non-injured lungs only. Our results suggest that Ers can be superior to the stress index and %E2 to guide PEEP titration in focal loss of lung aeration.

Changes in heart-rate and systolic arterial pressure variability (HRV and SAPV) indexes have been used in psychophysiology to assess autonomic activation, including during tasks involving speech. The current article clearly demonstrates in a sample of 25 adult subjects that the erratic and broadband respiratory patterns during such tasks violate the usual assumption that respiration is limited to the high-frequency band (0.15-0.4 Hz). For these tasks, interindividual differences and rest-task changes in HRV and SAPV in the low-frequency band (0.04-0.15 Hz) can be explained, to a large extent, by variations in the respiratory volume signal. This makes the use of HRV and SAPV as markers of autonomic function during these tasks highly questionable. Furthermore, a number of subjects with long respiratory period at rest were identified, whose presence in the sample can bias the estimation of baseline rest values.