in a Porcine Model of Mechanical Ventilation Remote Ischemic Preconditioning increases Oxygenation but also Alveolar Damage in a Porcine Model of Mechanical Ventilation Alf Kozian, M.D., Ph.D.,*^; Thomas Schilling, M.D., Ph.D., D.E.A.A.*^; Christian Breitling, M.D.*; Dörthe Jechorek, M.D.§; Astrid Bergmann, M.D.*; Th. Hachenberg, M.D., Ph.D.*; G. Hedenstierna, M.D., Ph.D.^; A. Larsson, M.D., Ph.D., D.E.A.A. # * Department of Anesthesiology and Intensive Care, Otto-von-Guericke-University Magdeburg, Germany; # Department of Surgical Sciences, Anesthesia and Intensive Care; ^ Department of Medical Sciences, Hedenstierna Laboratory, Uppsala University, Uppsala, Sweden and § Institute of Pathology, Otto-von-Guericke-University Magdeburg, Germany. UPPSALA UNIVERSITY BACKGROUND One-lung ventilation (OLV) results in alveolar injury due to increased mechanical stress, atelectasis formation, and tidal recruitment [1]. As a result, an inflammatory response in the ventilated lung characterized by leukocyte recruitment and neutrophil dependent tissue destruction is induced. Remote ischemic preconditioning (RIP), in which short episodes of ischemia are repeatedly applied to one limb, is expected to protect remote organs, i.e. the lungs. The aim of this randomized, controlled, animal experiment was to evaluate the effects of RIP on pulmonary function, i.e. arterial oxygenation, and alveolar injuries indicated by leukocyte recruitment and diffuse alveolar damage (DAD) after mechanical ventilation (MV) including OLV. Animal use has been approved by the Animal Care and Use Committee of Uppsala University. RESULTS RIP-pigs revealed increased paO2 values after OLV (table, figure) Fewer leukocytes were observed in BAL fluid of the ventilated lung after RIP (figure) MV and OLV (120min) increased DAD-scores (indicated by alveolar and interstitial edema, neutrophil infiltration, alveolar overdistension, microhemorrhage and microatelectasis) DAD was homogeneously distributed from subpleural to parahilar lung regions without differences between ventilated right, or non-ventilated left lung (figure) Alveolar edema and microhemorrhage were increased in the ventilated lungs of RIP-pigs (figure) Ventilation variables, cardiac output and shunt were not different between both groups over time (table) The data indicate that MV and OLV result in significant injury of the ventilated lungs RIP before OLV increases oxygenation and reduces alveolar leukocyte recruitment but has no global effects on alveolar damage RIP even increases alveolar edema and microhemorrhage in the ventilated lung Group / variable Baseline after RiP 120min OLV End Controls RIP Hemodynamics MAP [mmHg] 79±9 88±12 62±5 76±11* 71±3 80±10* 73±6 82±12* MPAP 15±2 17±1 15±1 21±2 20±1 19±3 19±2 SVR [dyn×sec×cm−5] 2374 ±862 2711 ±802 1843 ±292 2582 ±412* 2043 ±415 2476 ±587* 2051 ±231 2744 ±699* PVR 257±85 319±82 254±63 325±27 430±75 459±55 341±83 379±45 CO [l/min] 2.8±0.5 2.7±0.6 2.5±0.5 2.2±0.1 2.6±0.5 2.4±0.4 2.3±0.3 SvO2 [%] 53.9±6.4 59.0±3.1 49.2±5.5 57.4±7.0 43.3±4.5 50.5±4.0 44.6±9.0 52.5±4.2 Qs/Qt 3.4±0.7 2.9±0.7 3.2±0.7 3.0±0.4 4.5±0.9 4.3±1.3 7.1±2.3 8.5±1.9 Gas exchange paO2 [kpa] 24.9±1.3 25.9±0.8 23.1±1.7 24.8±0.9 18.7±2.2 20.7±2.8 20.7±1.4 24.1±1.4* paCO2 5.1±0.2 5.0±0.3 5.1±0.1 5.1±0.4 5.3±0.2 5.2±0.2 5.0±0.4 Ventilation PAW Peak 18.2±1.7 17.0±0.0 18.9±1.1 18.7±1.9 24.2±1.7 24.3±2.2 20.5±1.3 19.4±1.6 AZV [ml] 262±12 254±12 260±8 258±13 256±8 257±14 258±9 258±14 AZV/kg [ml/kg] 10.7±0.4 10.5±0.2 10.7±0.1 10.6±0.2 10.6±0.3 10.7±0.2 Compliance [ml/mmHg] 19.9±2.2 21.1±1.0 19.0±1.1 19.0±2.0 13.5±1.0 13.5±1.1 17.5±1.1 18.0±1.3 DAD FEATURES Alveolar Edema BAL RIP 4×5min BAL BAL Anesthesia Tracheotomy Preparation Recovery PIP-TLV (n=7) VT=10ml/kg PEEP 5mbar RIP / no RIP TLV (n=14) VT=10ml/kg PEEP 5mbar RIP-OLV (n=7) VT=10ml/kg PEEP 5mbar RIP / no RIP TLV (n=14) VT=10ml/kg PEEP 5mbar Tissue samples End Protocol Microhemorrhage no RIP-TLV (n=7) VT=10ml/kg PEEP 5mbar no RIP-OLV (n=7) VT=10ml/kg PEEP 5mbar paO2 at time points / RIP-pigs vs. controls Cells in BAL / RIP-pigs vs. controls 60min 45min 60min 120min 60min Time Neutrophil Infiltation STUDY TIMELINE Randomization: RIP / no RIP MATERIAL AND METHODS Piglets: n=14, 2-3 month old, weight 26±2kg, Yorkshire/Norwegian country breeds General anesthesia and tracheotomy Mechanical ventilation: VT=10ml/kg, respiratory rate adjusted to normal paCO2, FIO2=0.40 in air, PEEP=5cmH2O OLV: 2h period, lung separation by bronchial blocker, VT=10ml∙kg-1 Randomization: control group (n=7), RIP group (n=7) RIP pigs: blood pressure cuff at left hind limb, inflated up to 200mmHg for 5min followed by 5min of reperfusion after deflating the cuff, repeated for 4 times Measurements: hemodynamic data recorded continuously; blood samples; bronchoalveolar lavage (BAL) of both lungs (left non-ventilated, right ventilated) Timepoints: baseline, after RIP, and prior to and after OLV Cells: counted from BAL fluid by light microscopy Lung tissue samples: (after killing the pigs) subpleural, intermediate and parahilar locations of the lungs largest diameters, fixated and stained for histological examination Lung injury: quantified by DAD score, calculated by summarizing the products of severity and extent of alveolar edema, interstitial edema, microhemorrhage, neutrophil infiltration, microatelectasis, and alveolar overdistension Statistics: Data were analyzed by ANOVA and non-parametric tests as indicated Interstitial Edema CONCLUSIONS Mechanical ventilation results in pulmonary tissue damage indicated by increased diffuse alveolar damage scores. Remote ischemic preconditioning decreases leukocyte recruitment into the ventilated lung and increases arterial oxygenation despite higher alveolar edema and microhemorrhage. Whether RIP only benefits oxygenation but has contrary effects on alveolar injury remains to be studied. At least pulmonary tissue damage is not affected by or is even increased after RIP. [1] Kozian et al., J Cardiothorac Vasc Anesth. 2010 Aug;24(4):617-23 DAD scores/ RIP-pigs vs. controls AE and MH / RIP-pigs vs. controls Microatelectasis Alv. Overdistensionn