Prolonged heparin-free extracorporeal membrane oxygenation in multiple injured acute respiratory distress syndrome patients with traumatic brain injury.

BACKGROUND: Extracorporeal membrane oxygenation (ECMO) can be used as an "ultima ratio" strategy in multiple injured patients with severe thoracic trauma. However, systemic anticoagulation during ECMO is recommended and thus traumatic brain injury (TBI) and intracranial bleeding are well-accepted contraindications for ECMO therapy. METHODS: This report describes three cases of prolonged heparin-free venovenous ECMO in multiple injured acute respiratory distress syndrome patients with severe TBI failing conventional mechanical ventilation. RESULTS: : Using this strategy, neither ECMO-associated bleeding nor clotting of the extracorporeal circuit occurred. All patients survived. CONCLUSIONS: Based on our experience, we recommend the use of heparin-free ECMO in multiple injured patients with pulmonary failure that is not successfully controlled by lung-protective ventilation even if severe TBI is present. LEVEL OF EVIDENCE: IV, therapeutic study.

Combining "open-lung" ventilation and arteriovenous extracorporeal lung assist: influence of different tidal volumes on gas exchange in experimental lung failure.

BACKGROUND: Although low-tidal ventilation may reduce mortality in acute respiratory distress syndrome (ARDS), it can also result in severe respiratory acidosis and lung derecruitment. This study tested the hypothesis that combining "open-lung" ventilation and arteriovenous extracorporeal lung assist (av-ECLA) allows for maximal tidal volume (VT) reduction without the development of decompensated respiratory acidosis and impairment of oxygenation. MATERIAL/METHODS: After induction of ARDS in eight female pigs (56.1+/-3.2 kg), lung recruitment was performed and positive end-expiratory pressure was set 3 cmH2O above the lower inflection point of the pressure-volume curve. All animals were ventilated in the pressure-controlled ventilation mode (PCV) with VTs ranging from 0-8 ml/kg. At each VT, gas exchange and hemodynamic measurements were obtained with the av-ECLA circuit clamped and declamped. With each declamping, the gas flow through the membrane lung was set to 10 l of oxygen/min. The respiratory rate was adjusted to maintain normocapnia, but limited to 40/min. RESULTS: After lung recruitment, oxygenation remained significantly improved although VTs were minimized to 0 ml/kg (p<0.05). PaO2 was significantly improved during PCV and av-ECLA compared with PCV alone at VTs <4 ml/kg (p<0.05). With VT <6 ml/kg, severe acidosis could only be avoided if PCV was combined with av-ECLA. CONCLUSIONS: Due to sufficient CO2 elimination during av-ECLA, the VTs could be reduced to 0-2 ml/kg without the risk of decompensated respiratory acidosis. It was also shown that the "open-lung" strategy chosen was associated with sustained improvements in oxygenation, even though VTs were minimized.

[Which perioperative tidal volume for patients with healthy lungs undergoing elective surgery? A qualitative systematic review of current evidence]. / Intraoperative Beatmung--Welches Tidalvolumen sollte bei lungengesunden Patienten angewandt werden? Eine qualitativ-systematische Ubersichtsarbeit.

BACKGROUND: Lung-protective ventilation strategies for patients suffering from acute lung injury (ALI/ARDS) are well- accepted measures to improve outcome including mortality. But what tidal volume is the best for the patient with non-injured lungs undergoing elective surgery? METHODS: We searched the literature for studies that analysed perioperative tidal volume in patients not suffering from ALI/ARDS. RESULTS: 10 studies were detected that matched our query. Mostly on patients undergoing major or cardiac surgery. CONCLUSION: Only a few studies exist which examine the effect of protective ventilation settings on healthy lungs of patients not being critical-ill. The reported results are very heterogeneous and do not strongly support a lung- protective ventilation strategy. However, apart from reasoning based on pre-clinical experimental data, there is some clinical evidence, that suggests using lower tidal volumes in patients undergoing major or cardiac surgery, even if the patient does not present with an ALI/ARDS and is not critically ill at the time when the surgical procedure is performed.

Acute respiratory distress induced by repeated saline lavage provides stable experimental conditions for 24 hours in pigs.

Surfactant depletion is most often used to study acute respiratory failure in animal models. Because model stability is often criticized, the authors tested the following hypotheses: Repeated pulmonary lavage with normal saline provides stable experimental conditions for 24 hours with a PaO2/FiO2 ratio < 300 mm Hg. Lung injury was induced by bilateral pulmonary lavages in 8 female pigs (51.5 +/- 4.8 kg). The animals were ventilated for 24 hours (PEEP: 5 cm H2O; tidal volume: 6 mL/kg; respiratory rate: 30/min). After 24 hours the animals were euthanized. For histopathology slides from all pulmonary lobes were obtained. Supernatant of the bronchoalveolar fluid collected before induction of acute respiratory distress syndrome (ARDS) and after 24 hours was analyzed. A total of 19 +/- 6 lavages were needed to induce ARDS. PaO2/FiO2 ratio and pulmonary shunt fraction remained significantly deteriorated compared to baseline values after 24 hours (P < .01). Slight to moderate histopathologic changes were detected. Significant increases of tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and IL-6 were observed after 24 hours (P < .01). The presented surfactant depletion-based lung injury model was associated with increased pulmonary inflammation and fulfilled the criteria of acute ling injury (ALI) for 24 hours.

Arteriovenous Extracorporeal Lung Assist Allows For Maximization Of Oscillatory Frequencies: A Large-animal Model Of Respiratory Distress.

BACKGROUND: Although the minimization of the applied tidal volume (VT) during high-frequency oscillatory ventilation (HFOV) reduces the risk of alveolar shear stress, it can also result in insufficient CO2-elimination with severe respiratory acidosis. We hypothesized that in a model of acute respiratory distress (ARDS) the application of high oscillatory frequencies requires the combination of HFOV with arteriovenous extracorporeal lung assist (av-ECLA) in order to maintain or reestablish normocapnia. METHODS: After induction of ARDS in eight female pigs (56.5 ± 4.4 kg), a recruitment manoeuvre was performed and intratracheal mean airway pressure (mPaw) was adjusted 3 cmH2O above the lower inflection point (Plow) of the pressure-volume curve. All animals were ventilated with oscillatory frequencies ranging from 3-15 Hz. The pressure amplitude was fixed at 60 cmH2O. At each frequency gas exchange and hemodynamic measurements were obtained with a clamped and de-clamped av-ECLA. Whenever the av-ECLA was de-clamped, the oxygen sweep gas flow through the membrane lung was adjusted aiming at normocapnia. RESULTS: Lung recruitment and adjustment of the mPaw above Plow resulted in a significant improvement of oxygenation (p < 0.05). Compared to lung injury, oxygenation remained significantly improved with rising frequencies (p < 0.05). Normocapnia during HFOV was only maintained with the addition of av-ECLA during frequencies of 9 Hz and above. CONCLUSION: In this animal model of ARDS, maximization of oscillatory frequencies with subsequent minimization of VT leads to hypercapnia that can only be reversed by adding av-ECLA. When combined with a recruitment strategy, these high frequencies do not impair oxygenation.

Combination of arteriovenous extracorporeal lung assist and high-frequency oscillatory ventilation in a porcine model of lavage-induced acute lung injury: a randomized controlled trial.

BACKGROUND: To compare the combined effects of arteriovenous extracorporeal lung assist (AV-ECLA) and high-frequency oscillatory ventilation (HFOV) on pulmonary gas exchange, hemodynamics, and respiratory parameters in a lavage-induced porcine lung injury model. METHODS: A prospective, randomized animal study. Saline lung lavage was performed in 33 healthy female pigs, weighing 52 +/- 4.1 kg (mean +/- SD), until the Pao2 decreased to 53 +/- 8 mm Hg. After a stabilization period of 60 minutes, the animals were randomly assigned to four groups: group 1, pressure-controlled ventilation (PCV) with a tidal volume of 6 mL/kg; group 2, PCV with a tidal volume of 6 mL/kg and AV-ECLA; group 3, HFOV; group 4, HFOV and AV-ECLA. In groups 2 and 4, the femoral artery and vein were cannulated and a low-resistance membrane lung was interposed. After isolated evaluation of AV-ECLA, the mean airway pressure was increased by 3 cm H2O from 16 to 34 cm H2O every 20 minutes, accompanied by blood gas analyses and measurements of respiratory and hemodynamic variables. RESULTS: Only in AV-ECLA-treated animals was normocapnia achieved. No significant increase of Pao2 attributable to AV-ECLA alone was detected. Mean airway pressure augmentation resulted in a significant increase in Pao2 in all groups. Peak inspiratory pressure was significantly lower in HFOV-treated animals. CONCLUSIONS: The combination of AV-ECLA and HFOV resulted in normocapnia and comparable Pao2, although a smaller ventilator pressure amplitude was applied. Long-term animal studies are needed to assess whether this approach results in further lung protection.