Recruitment of small size lungs - experimental studies

Abstract

Background: Patients - both children and adults - undergoing anesthesia and mechanical ventilation rapidly develop atelectasis. Even more severe problems occur in patients with acute lung injury/acute respiratory distress syndrome. To prevent the lung from further injury use of lung protective ventilation including a recruitment maneuver (RM) and a positive end-expiratory pressure (PEEP) titration are parts of the treatment. Children differ from adults not only in size but also in physiology. Studies in pediatric size animals should precede clinical studies. Methods: 52 pediatric size piglets, weighing about 10 kg were surfactant depleted using a lung injury model with saline lavage. In the first two of four studies tidal elimination of CO2 (VTCO2) was evaluated as a marker of optimal recruitment and dynamic compliance (Cdyn) was evaluated as a marker of incipient collapse during a RM and downward PEEP titration respectively. In all four studies the titrated PEEP was used during different follow-up-ventilation periods. Aeration, airway pressures including driving pressure (DP), Cdyn and oxygenation were recorded. Iterated CT scans were taken at every change of ventilation for measurement of aeration during the first two studies and during the follow-up-ventilation in three studies. The effect of a RM and PEEP titration for a prolonged (3 h) follow-up-ventilation was compared with a group with elevated PEEP (PEEP10-group) but without a foregoing RM. Ventilation after a RM was also compared with a control group ventilated with standard ventilation without a prior RM. In a final study continuous cardiac output (CO) was measured during the RM and PEEP titration for detailed information of central hemodynamics in eight piglets. Results: During the different follow-up-ventilation periods; 5, 15, 60 and 180 min, ventilation performed with the titrated PEEP resulted in improved aeration as assessed by repetitive CT scans, higher Cdyn, lower DP and better oxygenation compared with ventilation before the RM. VTCO2 peaked or levelled off during the recruitment and corresponding CT scans showed a recruited lung. In addition minimally improved aeration was found when airway pressure was increased above the VTCO2 peak/plateau. The first decline of Cdyn during PEEP titration corresponded to an increasing amount of lung collapse according to CT scans. CO and blood pressure decreased at the highest airway pressure during the RM. CO remained at a lower level but blood pressure recovered entirely. PEEP elevation in the PEEP10-group resulted in improved aeration, higher Cdyn and oxygenation and lower DP but not as much as in the RM-group. The control group did not improve in aeration, Cdyn or oxygenation but was stable. Conclusion: Ventilation after a RM and PEEP titration results in improved aeration, improved lung mechanics and lower airway pressures compared with baseline and compared with control groups ventilated without a foregoing lung recruitment. VTCO2 peak/plateau indicates a recruited lung and Cdyn is a good indicator of increasing derecruitment during the PEEP titration. CO was persistingly and blood pressure temporarily decreased during the RM.