Targeted fibre-optical intrabronchial lipopolysaccharide administration in pigs - a methodical refinement for improved accuracy in respiratory research.

OBJECTIVE: To establish and evaluate a standardized method of targeted, intrabronchial drug delivery in pigs. STUDY DESIGN: Randomized controlled trial. ANIMALS: A total of 16 German Landrace pigs (Sus scrofa), age range 12‒16 weeks, and weighing 28‒35 kg. METHODS: The animals were anaesthetized, intubated, and instrumented with extended cardiovascular monitoring. Lung injury was induced by administering via a flexible fibre-optic endoscope using 100 mL saline solution containing either 20 mg of Escherichia coli lipopolysaccharide (E. coli LPS) (n = 8) or no additive (sham, n = 8) into the two distal mainstem bronchi. The animals were monitored for 8 hours and arterial oxygenation, inspiratory pressure and arterial blood pressure were measured repeatedly. Post-mortem, lung tissue was prepared for histologic damage scoring and determination of proinflammatory cytokines Interleukin-6 (IL-6) and tumour necrosis factor alpha (TNFα). Statistical analyses were performed using inter-group analysis of variance and Student's t tests. Data are presented as mean ± standard deviation. A p value <0.05 was considered significant. RESULTS: The targeted application of LPS led to significant deterioration of oxygenation consistent with mild-to-moderate acute respiratory distress syndrome (ARDS) and hypotension (Horowitz ratio: sham 2 hour, 300 ± 39; LPS 2 hour, 193.7 ± 52; p < 0.001). Histologic analyses identified increased inflammation and oedema in the tissues of the animals in the LPS group IL-6 sham: 6.4 ± 4.4 × 10-5 pg mL-1; IL-6 LPS: 2.8 ± 2.4 × 10-4 pg mL-1, p = 0.015. CONCLUSIONS: The targeted application of agents via flexible fibre-optic endoscopy is a valid, reliable method of causing controlled lung damage in a porcine model. The data presented suggest the feasibility and possible advantages of controlled application and could expand the array of techniques used to help understand the critical condition of ARDS. In addition, a targeted approach could help reduce animal numbers used for this purpose.

Bi-Level ventilation decreases pulmonary shunt and modulates neuroinflammation in a cardiopulmonary resuscitation model.

BACKGROUND: Optimal ventilation strategies during cardiopulmonary resuscitation are still heavily debated and poorly understood. So far, no convincing evidence could be presented in favour of outcome relevance and necessity of specific ventilation patterns. In recent years, alternative models to the guideline-based intermittent positive pressure ventilation (IPPV) have been proposed. In this randomized controlled trial, we evaluated a bi-level ventilation approach in a porcine model to assess possible physiological advantages for the pulmonary system as well as resulting changes in neuroinflammation compared to standard measures. METHODS: Sixteen male German landrace pigs were anesthetized and instrumented with arterial and venous catheters. Ventricular fibrillation was induced and the animals were left untreated and without ventilation for 4 minutes. After randomization, the animals were assigned to either the guideline-based group (IPPV, tidal volume 8-10 ml/kg, respiratory rate 10/min, FiO21.0) or the bi-level group (inspiratory pressure levels 15-17 cmH2O/5cmH2O, respiratory rate 10/min, FiO21.0). Mechanical chest compressions and interventional ventilation were initiated and after 5 minutes, blood samples, including ventilation/perfusion measurements via multiple inert gas elimination technique, were taken. After 8 minutes, advanced life support including adrenaline administration and defibrillations were started for up to 4 cycles. Animals achieving ROSC were monitored for 6 hours and lungs and brain tissue were harvested for further analyses. RESULTS: Five of the IPPV and four of the bi-level animals achieved ROSC. While there were no significant differences in gas exchange or hemodynamic values, bi-level treated animals showed less pulmonary shunt directly after ROSC and a tendency to lower inspiratory pressures during CPR. Additionally, cytokine expression of tumour necrosis factor alpha was significantly reduced in hippocampal tissue compared to IPPV animals. CONCLUSION: Bi-level ventilation with a constant positive end expiratory pressure and pressure-controlled ventilation is not inferior in terms of oxygenation and decarboxylation when compared to guideline-based IPPV ventilation. Additionally, bi-level ventilation showed signs for a potentially ameliorated neurological outcome as well as less pulmonary shunt following experimental resuscitation. Given the restrictions of the animal model, these advantages should be further examined.

Short-Time Ocular Ischemia Induces Vascular Endothelial Dysfunction and Ganglion Cell Loss in the Pig Retina.

Visual impairment and blindness are often caused by retinal ischemia-reperfusion (I/R) injury. We aimed to characterize a new model of I/R in pigs, in which the intraocular pathways were not manipulated by invasive methods on the ocular system. After 12 min of ischemia followed by 20 h of reperfusion, reactivity of retinal arterioles was measured in vitro by video microscopy. Dihydroethidium (DHE) staining, qPCR, immunohistochemistry, quantification of neurons in the retinal ganglion cell layer, and histological examination was performed. Retinal arterioles of I/R-treated pigs displayed marked attenuation in response to the endothelium-dependent vasodilator, bradykinin, compared to sham-treated pigs. DHE staining intensity and messenger RNA levels for HIF-1α, VEGF-A, NOX2, and iNOS were elevated in retinal arterioles following I/R. Immunoreactivity to HIF-1α, VEGF-A, NOX2, and iNOS was enhanced in retinal arteriole endothelium after I/R. Moreover, I/R evoked a substantial decrease in Brn3a-positive retinal ganglion cells and noticeable retinal thickening. In conclusion, the results of the present study demonstrate that short-time ocular ischemia impairs endothelial function and integrity of retinal blood vessels and induces structural changes in the retina. HIF-1α, VEGF-A, iNOS, and NOX2-derived reactive oxygen species appear to be involved in the pathophysiology.

Ultra-low tidal volume ventilation-A novel and effective ventilation strategy during experimental cardiopulmonary resuscitation.

BACKGROUND: The effects of different ventilation strategies during CPR on patient outcomes and lung physiology are still poorly understood. This study compares positive pressure ventilation (IPPV) to passive oxygenation (CPAP) and a novel ultra-low tidal volume ventilation (ULTVV) regimen in an experimental ventricular fibrillation animal model. STUDY DESIGN: Prospective randomized controlled trial. ANIMALS: 30 male German landrace pigs (16-20 weeks). METHODS: Ventricular fibrillation was induced in anesthetized and instrumented pigs and the animals were randomized into three groups. Mechanical CPR was initiated and ventilation was either provided by means of standard IPPV (RR: 10/min, Vt: 8-9 ml/kg, FiO2: 1,0, PEEP: 5 mbar), CPAP (O2-Flow: 10 l/min, PEEP: 5 mbar) or ULTVV (RR: 50/min, Vt: 2-3 ml/kg, FiO2: 1,0, PEEP: 5 mbar). Guideline-based advanced life support was applied for a maximum of 4 cycles and animals achieving ROSC were monitored for 6 h before terminating the experiment. Ventilation/perfusion ratios were performed via multiple inert gas elimination, blood gas analyses were taken hourly and extended cardiovascular measurements were collected constantly. Brain and lung tissue samples were taken and analysed for proinflammatory cytokine expression. RESULTS: ULTVV provided sufficient oxygenation and ventilation during CPR while demanding significantly lower respiratory and intrathoracic pressures. V/Q mismatch was significantly decreased and lung injury was mitigated in surviving animals compared to IPPV and CPAP. Additionally, cerebral cytokine expression was dramatically reduced. CONCLUSION: Ultra-low-volume ventilation during CPR in a porcine model is feasible and may provide lung-protective benefits as well as neurological outcome improvement due to lower inflammation. Our results warrant further studies and might eventually lead to new therapeutic options in the resuscitation setting.

Lung injury does not aggravate mechanical ventilation-induced early cerebral inflammation or apoptosis in an animal model.

INTRODUCTION: The acute respiratory distress syndrome is not only associated with a high mortality, but also goes along with cognitive impairment in survivors. The cause for this cognitive impairment is still not clear. One possible mechanism could be cerebral inflammation as result of a "lung-brain-crosstalk". Even mechanical ventilation itself can induce cerebral inflammation. We hypothesized, that an acute lung injury aggravates the cerebral inflammation induced by mechanical ventilation itself and leads to neuronal damage. METHODS: After approval of the institutional and state animal care committee 20 pigs were randomized to one of three groups: lung injury by central venous injection of oleic acid (n = 8), lung injury by bronchoalveolar lavage in combination with one hour of injurious ventilation (n = 8) or control (n = 6). Brain tissue of four native animals from a different study served as native group. For six hours all animals were ventilated with a tidal volume of 7 ml kg-1 and a scheme for positive end-expiratory pressure and inspired oxygen fraction, which was adapted from the ARDS network tables. Afterwards the animals were killed and the brains were harvested for histological (number of neurons and microglia) and molecular biologic (TNFalpha, IL-1beta, and IL-6) examinations. RESULTS: There was no difference in the number of neurons or microglia cells between the groups. TNFalpha was significantly higher in all groups compared to native (p < 0.05), IL-6 was only increased in the lavage group compared to native (p < 0.05), IL-1beta showed no difference between the groups. DISCUSSION: With our data we can confirm earlier results, that mechanical ventilation itself seems to trigger cerebral inflammation. This is not aggravated by acute lung injury, at least not within the first 6 hours after onset. Nevertheless, it seems too early to dismiss the idea of lung-injury induced cerebral inflammation, as 6 hours might be just not enough time to see any profound effect.

Endexpiratory lung volume measurement correlates with the ventilation/perfusion mismatch in lung injured pigs.

BACKGROUND: In acute respiratory respiratory distress syndrome (ARDS) a sustained mismatch of alveolar ventilation and perfusion (VA/Q) impairs the pulmonary gas exchange. Measurement of endexpiratory lung volume (EELV) by multiple breath-nitrogen washout/washin is a non-invasive, bedside technology to assess pulmonary function in mechanically ventilated patients. The present study examines the association between EELV changes and VA/Q distribution and the possibility to predict VA/Q normalization by means of EELV in a porcine model. METHODS: After approval of the state and institutional animal care committee 12 anesthetized pigs were randomized to ARDS either by bronchoalveolar lavage (n = 6) or oleic acid injection (n = 6). EELV, VA/Q ratios by multiple inert gas elimination and ventilation distribution by electrical impedance tomography were assessed at healthy state and at five different positive endexpiratory pressure (PEEP) steps in ARDS (0, 20, 15, 10, 5 cmH2O; each maintained for 30 min). RESULTS: VA/Q, EELV and tidal volume distribution all displayed the PEEP-induced recruitment in ARDS. We found a close correlation between VA/Q < 0.1 (representing shunt and low VA/Q units) and changes in EELV (spearman correlation coefficient -0.79). Logistic regression reveals the potential to predict VA/Q normalization (VA/Q < 0.1 less than 5%) from changes in EELV with an area under the curve of 0.89 with a 95%-CI of 0.81-0.96 in the receiver operating characteristic. Different lung injury models and recruitment characteristics did not influence these findings. CONCLUSION: In a porcine ARDS model EELV measurement depicts PEEP-induced lung recruitment and is strongly associated with normalization of the VA/Q distribution in a model-independent fashion. Determination of EELV could be an intriguing addition in the context of lung protection strategies.