SLL-PEEP Ventilation to Improve Exposure in Minimally Invasive Right Anterolateral Minithoracotomy Aortic Valve Replacement

Objective An accepted landmark to assess feasibility of surgical aortic valve replacement (SAVR) via right anterolateral minithoracotomy (RALT) is the aortic-midpoint to right-sternal-edge distance. We aimed to evaluate single left lung positive-end-expiratory-pressure (SLL-PEEP) ventilation inducing an intraoperative rightward shift of the ascending aorta to improve exposure. Methods Nineteen patients with aortic stenosis undergoing SAVR via RALT were prospectively analyzed. SLL-PEEP ventilation (20,395 cmH2O) via a double-lumen endotracheal tube was applied immediately before transthoracic aortic cross-clamping, thereby inducing rightward shift of the ascending aorta to enhance exposure. We analyzed preoperative computed tomography (CT) reconstructions and intraoperative video recordings. Primary endpoint was extent of rightward shift induced by SLL-PEEP ventilation; secondary endpoints were procedure times and safety events. Results Mean age was 61 ± 14.8 years and 6 of 19 (31.6%) were female. Mean EuroSCORE II was 0.81% ± 0.04%, STS-PROM was 1.13% ± 0.74%, and mean aortic rightward shift induced by SLL-PEEP ventilation was 10.32 ± 4.14 mm (4 to 17 mm; P = 0.003). Median shift in the group considered suitable for the RALT approach by preoperative CT-scan evaluation was 14.2 mm (IQR 11) and in the less suitable group 11.5 mm (IQR 5). Mean procedure time was 167 ± 28.9 min, CPB time was 105.7 ± 18.4 min, and cross-clamp time was 64.5 ± 13 min. Fifteen patients (79%) received SAVR via RALT with implantation of a bioprosthesis, whereas a rapid-deployment-prosthesis was used in 4 patients (21%). Ten of 19 (53%) patients who were classified as less suitable preoperatively received SAVR via RALT after SLL-PEEP ventilation. No strokes were observed. Conclusions The SLL-PEEP ventilation maneuver during SAVR via RALT significantly enhances aortic exposure. There were no safety events associated with this maneuver and we were able to demonstrate significant rightward aortic shift in every single patient.

Heart-Protective Mechanical Ventilation in Postoperative Cardiosurgical Patients

Background. This study compared the hemodynamic effects and gas exchange under several different ventilator settings—with regard to tidal volume, respiratory rate, and end-expiratory pressure—in patients after coronary artery bypass grafting (CABG). Methods. Prospective interventional cohort study with a controlled group in a single cardiosurgical ICU involving 119 patients following on-pump CABG surgery. During the 1st postoperative hour, the intervention group patients were ventilated with Vt 10 ml × kg−1, RR 14/min, PEEP 5 cmH2O (“conventional ventilation”). During the 2nd hour, RR was reduced to 8/min (“reduced RR ventilation”). At 3 hrs, Vt was decreased to 6 ml × kg−1, RR returned to 14/min, and PEEP increased to 10 cmH2O (“low Vt-high PEEP ventilation”). Results. Patients in the “low Vt-high PEEP” ventilation period showed significantly lower alveolar ventilation and thoraco-pulmonary compliance than during “reduced RR” ventilation. Mean airway pressure and Vds/Vt peaked during low Vt-high PEEP ventilation; however, driving pressure was lower. Vt decrease and PEEP increase did not lead to oxygenation improvement and worsened CO2 elimination. Hemodynamically, the study revealed significant cardiac output decrease during low Vt-high PEEP ventilation. In 23.2% of patients, catecholamine therapy was initiated. Conclusions. In postoperative cardiosurgical patients, MV with Vt 6 ml × kg−1 and PEEP 10 cm H2O is characterized by worsened oxygenation and elimination of CO2 and a less favorable hemodynamic profile than ventilation with Vt 10 ml × kg−1 and PEEP 5 cmH2O. New and Noteworthy. (i) Patients after CABG may be especially sensitive to low tidal volume and increased PEEP as it negatively affects hemodynamic profile by means of the right heart preload decrease and afterload increase. (ii) Mechanical ventilation settings aiming to minimize mean airway pressure reduce the negative effects of positive inspiratory pressure and are favorable for hemodynamics.

Effect of betamethasone, surfactant, and positive end-expiratory pressures on lung aeration at birth in preterm rabbits

Antenatal glucocorticoids, exogenous surfactant, and positive end-expiratory pressure (PEEP) ventilation are commonly provided to preterm infants to enhance respiratory function after birth. It is unclear how these treatments interact to improve the transition to air-breathing at birth. We investigated the relative contribution of antenatal betamethasone, prophylactic surfactant, and PEEP (3 cmH2O) on functional residual capacity (FRC) and dynamic lung compliance (CDL) in preterm (28 day GA) rabbit kittens at birth. Kittens were delivered by cesarean section and mechanically ventilated. FRC was calculated from X-ray images, and CDL was measured using plethysmography. Without betamethasone, PEEP increased FRC recruitment and CDL. Surfactant did not further increase FRC, but significantly increased CDL. Betamethasone abolished the benefit of PEEP on FRC, but surfactant counteracted this effect of betamethasone. These findings indicate that low PEEP levels are insufficient to establish FRC at birth following betamethasone treatment. However, surfactant reversed the effect of betamethasone and when combined, these two treatments enhanced FRC recruitment irrespective of PEEP level.

Effects of reduced tidal volume ventilation on pulmonary function in mice before and after acute lung injury

We investigated the influence of load impedance on ventilator performance and the resulting effects of reduced tidal volume (Vt) on lung physiology during a 30-min ventilation of normal mice and 10 min of additional ventilation following lavage-induced injury at two positive end-expiratory pressure (PEEP) levels. Respiratory mechanics were regularly monitored, and the lavage fluid was tested for the soluble E-cadherin, an epithelial cell adhesion molecule, and surfactant protein (SP) B. The results showed that, due to the load dependence of the delivered Vt from the small-animal ventilator: 1) uncontrolled ventilation in normal mice resulted in a lower delivered Vt (6 ml/kg at 3-cmH2O PEEP and 7 ml/kg at 6-cmH2O PEEP) than the prescribed Vt (8 ml/kg); 2) at 3-cmH2O PEEP, uncontrolled ventilation in normal mice led to an increase in lung parenchymal functional heterogeneity, a reduction of SP-B, and an increase in E-cadherin; 3) at 6-cmH2O PEEP, ventilation mode had less influence on these parameters; and 4) in a lavage model of acute respiratory distress syndrome, delivered Vt decreased to 4 ml/kg from the prescribed 8 ml/kg, which resulted in severely compromised lung function characterized by increases in lung elastance, airway resistance, and alveolar tissue heterogeneity. Furthermore, the low Vt ventilation also resulted in poor survival rate independent of PEEP. These results highlight the importance of delivering appropriate Vt to both the normal and injured lungs. By leaving the Vt uncompensated, it can significantly alter physiological and biological responses in mice.