Capillary refill time response to a fluid challenge or a vasopressor test: an observational, proof-of-concept study.

BACKGROUND: Several studies have validated capillary refill time (CRT) as a marker of tissue hypoperfusion, and recent guidelines recommend CRT monitoring during septic shock resuscitation. Therefore, it is relevant to further explore its kinetics of response to short-term hemodynamic interventions with fluids or vasopressors. A couple of previous studies explored the impact of a fluid bolus on CRT, but little is known about the impact of norepinephrine on CRT when aiming at a higher mean arterial pressure (MAP) target in septic shock. We designed this observational study to further evaluate the effect of a fluid challenge (FC) and a vasopressor test (VPT) on CRT in septic shock patients with abnormal CRT after initial resuscitation. Our purpose was to determine the effects of a FC in fluid-responsive patients, and of a VPT aimed at a higher MAP target in chronically hypertensive fluid-unresponsive patients on the direction and magnitude of CRT response. METHODS: Thirty-four septic shock patients were included. Fluid responsiveness was assessed at baseline, and a FC (500 ml/30 mins) was administered in 9 fluid-responsive patients. A VPT was performed in 25 patients by increasing norepinephrine dose to reach a MAP to 80-85 mmHg for 30 min. Patients shared a multimodal perfusion and hemodynamic monitoring protocol with assessments at at least two time-points (baseline, and at the end of interventions). RESULTS: CRT decreased significantly with both tests (from 5 [3.5-7.6] to 4 [2.4-5.1] sec, p = 0.008 after the FC; and from 4.0 [3.3-5.6] to 3 [2.6 -5] sec, p = 0.03 after the VPT. A CRT-response was observed in 7/9 patients after the FC, and in 14/25 pts after the VPT, but CRT deteriorated in 4 patients on this latter group, all of them receiving a concomitant low-dose vasopressin. CONCLUSIONS: Our findings support that fluid boluses may improve CRT or produce neutral effects in fluid-responsive septic shock patients with persistent hypoperfusion. Conversely, raising NE doses to target a higher MAP in previously hypertensive patients elicits a more heterogeneous response, improving CRT in the majority, but deteriorating skin perfusion in some patients, a fact that deserves further research.

Beta-Lactam Antibiotics Can Be Measured in the Exhaled Breath Condensate in Mechanically Ventilated Patients: A Pilot Study.

Different techniques have been proposed to measure antibiotic levels within the lung parenchyma; however, their use is limited because they are invasive and associated with adverse effects. We explore whether beta-lactam antibiotics could be measured in exhaled breath condensate collected from heat and moisture exchange filters (HMEFs) and correlated with the concentration of antibiotics measured from bronchoalveolar lavage (BAL). We designed an observational study in patients undergoing mechanical ventilation, which required a BAL to confirm or discard the diagnosis of pneumonia. We measured and correlated the concentration of beta-lactam antibiotics in plasma, epithelial lining fluid (ELF), and exhaled breath condensate collected from HMEFs. We studied 12 patients, and we detected the presence of antibiotics in plasma, ELF, and HMEFs from every patient studied. The concentrations of antibiotics were very heterogeneous over the population studied. The mean antibiotic concentration was 293.5 (715) ng/mL in plasma, 12.3 (31) ng/mL in ELF, and 0.5 (0.9) ng/mL in HMEF. We found no significant correlation between the concentration of antibiotics in plasma and ELF (R2 = 0.02, p = 0.64), between plasma and HMEF (R2 = 0.02, p = 0.63), or between ELF and HMEF (R2 = 0.02, p = 0.66). We conclude that beta-lactam antibiotics can be detected and measured from the exhaled breath condensate accumulated in the HMEF from mechanically ventilated patients. However, no correlations were observed between the antibiotic concentrations in HMEF with either plasma or ELF.

Exploring the relationship between capillary refill time, skin blood flow and microcirculatory reactivity during early resuscitation of patients with septic shock: a pilot study.

Capillary refill time (CRT), a costless and widely available tool, has emerged as a promising target to guide septic shock resuscitation. However, it has yet to gain universal acceptance due to its potential inter-observer variability. Standardization of CRT assessment may minimize this problem, but few studies have compared this approach with techniques that directly assess skin blood flow (SBF). Our objective was to determine if an abnormal CRT is associated with impaired SBF and microvascular reactivity in early septic shock patients. Twelve septic shock patients were subjected to multimodal perfusion and hemodynamic monitoring for 24 h. Three time-points (0, 1, and 24 h) were registered for each patient. SBF was measured by laser doppler. We performed a baseline SBF measurement and two microvascular reactivity tests: one with a thermal challenge at 44 °C and other with a vascular occlusion test. Ten healthy volunteers were evaluated to obtain reference values. The patients (median age 70 years) exhibited a 28-day mortality of 50%. Baseline CRT was 3.3 [2.7-7.3] seconds. In pooled data analysis, abnormal CRT presented a significantly lower SBF when compared to normal CRT [44 (13.3-80.3) vs 193.2 (99.4-285) APU, p = 0.0001]. CRT was strongly associated with SBF (R2 0.76, p < 0.0001). An abnormal CRT also was associated with impaired thermal challenge and vascular occlusion tests. Abnormal CRT values observed during early septic shock resuscitation are associated with impaired skin blood flow, and abnormal skin microvascular reactivity. Future studies should confirm these results.

Customized normothermic machine perfusion decreases ischemia-reperfusion injury compared with static cold storage in a porcine model of liver transplantation.

BACKGROUND: Liver transplantation has been demonstrated to be the best treatment for several liver diseases, while grafts are limited. This has caused an increase in waiting lists, making it necessary to find ways to expand the number of organs available for transplantation. Normothermic perfusion (NMP) of liver grafts has been established as an alternative to static cold storage (SCS), but only a small number of perfusion machines are commercially available. METHODS: Using a customized ex situ machine perfusion, we compared the results between ex situ NMP and SCS preservation in a porcine liver transplant model. RESULTS: During NMP, lactate concentrations were 80% lower after the 3-h perfusion period, compared with SCS. Bile production had a 2.5-fold increase during the NMP period. After transplantation, aspartate transaminase (AST) and alanine transaminase (ALT) levels were 35% less in the NMP group, compared to the SCS group. In pathologic analyses of grafts after transplant, tissue oxidation did not change between groups, but the ischemia-reperfusion injury score was lower in the NMP group. CONCLUSION: NMP reduced hepatocellular damage and ischemia-reperfusion injury when compared to SCS using a customized perfusion machine. This could be an alternative for low-income countries to include machine perfusion in their therapeutic options.

Inflammatory biomarkers and pendelluft magnitude in ards patients transitioning from controlled to partial support ventilation.

The transition from controlled to partial support ventilation is a challenge in acute respiratory distress syndrome (ARDS) patients due to the risks of patient-self-inflicted lung injury. The magnitude of tidal volume (VT) and intrapulmonary dyssynchrony (pendelluft) are suggested mechanisms of lung injury. We conducted a prospective, observational, physiological study in a tertiary academic intensive care unit. ARDS patients transitioning from controlled to partial support ventilation were included. On these, we evaluated the association between changes in inflammatory biomarkers and esophageal pressure swing (ΔPes), transpulmonary driving pressure (ΔPL), VT, and pendelluft. Pendelluft was defined as the percentage of the tidal volume that moves from the non-dependent to the dependent lung region during inspiration, and its frequency at different thresholds (- 15, - 20 and - 25%) was also registered. Blood concentrations of inflammatory biomarkers (IL-6, IL-8, TNF-α, ANGPT2, RAGE, IL-18, Caspase-1) were measured before (T0) and after 4-h (T4) of partial support ventilation. Pendelluft, ΔPes, ΔPL and VT were recorded. Nine out of twenty-four patients (37.5%) showed a pendelluft mean ≥ 10%. The mean values of ΔPes, ΔPL, and VT were - 8.4 [- 6.7; - 10.2] cmH2O, 15.2 [12.3-16.5] cmH2O and 8.1 [7.3-8.9] m/kg PBW, respectively. Significant associations were observed between the frequency of high-magnitude pendelluft and IL-8, IL-18, and Caspase-1 changes (T0/T4 ratio). These results suggest that the frequency of high magnitude pendelluft may be a potential determinant of inflammatory response related to inspiratory efforts in ARDS patients transitioning to partial support ventilation. Future studies are needed to confirm these results.

Implementation and design of customized ex vivo machine perfusion. Analysis of its first results.

The lack of organs available for transplantation is a global problem. The high mortality rates on the waiting list and the high number of discarded livers are reasons to develop new tools in the preservation and transplantation process. New tools should also be available for low-income countries. This article reports the development of customized normothermic machine perfusion (NMP). An ex vivo dual perfusion machine was designed, composed of a common reservoir organ box (CRO), a centrifugal pump (portal system, low pressure), and a roller pump (arterial system, high pressure). Porcine livers (n = 5) were perfused with an oxygenated normothermic (37℃) strategy for 3 hours. Hemodynamic variables, metabolic parameters, and bile production during preservation were analyzed. Arterial and portal flow remain stable during perfusion. Total bilirubin production was 11.25 mL (4-14.5) at 180 minutes. The median pH value reached 7.32 (7.25-7.4) at 180 minutes. Lactate values decreased progressively to normalization at 120 minutes. This perfusion setup was stable and able to maintain the metabolic activity of a liver graft in a porcine animal model. Design and initial results from this customized NMP are promising for a future clinical application in low-income countries.

Acute lung injury secondary to hydrochloric acid instillation induces small airway hyperresponsiveness.

BACKGROUND: Acute respiratory distress syndrome (ARDS) is a severe form of respiratory failure characterized by altered lung mechanics and poor oxygenation. Bronchial hyperresponsiveness has been reported in ARDS survivors and animal models of acute lung injury. Whether this hyperreactivity occurs at the small airways or not is unknown. OBJECTIVE: To determine ex-vivo small airway reactivity in a rat model of acute lung injury (ALI) by hydrochloric acid (HCl) instillation. METHODS: Twelve anesthetized rats were connected to mechanical ventilation for 4-hour, and randomly allocated to either ALI group (HCl intratracheal instillation; n=6) or Sham (intratracheal instillation of 0.9% NaCl; n=6). Oxygenation was assessed by arterial blood gases. After euthanasia, tissue samples from the right lung were harvested for histologic analysis and wet-dry weight ratio assessment. Precision cut lung slice technique (100-200 µm diameter) was applied in the left lung to evaluate ex vivo small airway constriction in response to histamine and carbachol stimulation, using phase-contrast video microscopy. RESULTS: Rats from the ALI group exhibited hypoxemia, worse histologic lung injury, and increased lung wet-dry weight ratio as compared with the sham group. The bronchoconstrictor responsiveness was significantly higher in the ALI group, both for carbachol (maximal contraction of 84.5±2.5% versus 61.4±4.2% in the Sham group, P<0.05), and for histamine (maximal contraction of 78.6±5.3% versus 49.6±5.3% in the Sham group, P<0.05). CONCLUSION: In an animal model of acute lung injury secondary to HCL instillation, small airway hyperresponsiveness to carbachol and histamine is present. These results may provide further insight into the pathophysiology of ARDS.

Effect of positive end-expiratory pressure on lung injury and haemodynamics during experimental acute respiratory distress syndrome treated with extracorporeal membrane oxygenation and near-apnoeic ventilation.

BACKGROUND: Lung rest has been recommended during extracorporeal membrane oxygenation (ECMO) for severe acute respiratory distress syndrome (ARDS). Whether positive end-expiratory pressure (PEEP) confers lung protection during ECMO for severe ARDS is unclear. We compared the effects of three different PEEP levels whilst applying near-apnoeic ventilation in a model of severe ARDS treated with ECMO. METHODS: Acute respiratory distress syndrome was induced in anaesthetised adult male pigs by repeated saline lavage and injurious ventilation for 1.5 h. After ECMO was commenced, the pigs received standardised near-apnoeic ventilation for 24 h to maintain similar driving pressures and were randomly assigned to PEEP of 0, 10, or 20 cm H2O (n=7 per group). Respiratory and haemodynamic data were collected throughout the study. Histological injury was assessed by a pathologist masked to PEEP allocation. Lung oedema was estimated by wet-to-dry-weight ratio. RESULTS: All pigs developed severe ARDS. Oxygenation on ECMO improved with PEEP of 10 or 20 cm H2O, but did not in pigs allocated to PEEP of 0 cm H2O. Haemodynamic collapse refractory to norepinephrine (n=4) and early death (n=3) occurred after PEEP 20 cm H2O. The severity of lung injury was lowest after PEEP of 10 cm H2O in both dependent and non-dependent lung regions, compared with PEEP of 0 or 20 cm H2O. A higher wet-to-dry-weight ratio, indicating worse lung injury, was observed with PEEP of 0 cm H2O. Histological assessment suggested that lung injury was minimised with PEEP of 10 cm H2O. CONCLUSIONS: During near-apnoeic ventilation and ECMO in experimental severe ARDS, 10 cm H2O PEEP minimised lung injury and improved gas exchange without compromising haemodynamic stability.

Characterization of the Modulatory Effect of Hydroxychloroquine on ACE2 Activity: New Insights in relation to COVID-19.

Chloroquine (CQ) and hydroxychloroquine (HCQ) have shown the ability to inhibit in vitro viral replications of coronaviridae viruses such as SARS-CoV and SARS-CoV-2. However, clinical trial outcomes have been disparate, suggesting that CQ and HCQ antiviral mechanisms are not fully understood. Based on three-dimensional structural similarities between HCQ and the known ACE2 specific inhibitor MLN-4760, we compared their modulation on ACE2 activity. Here we describe, for the first time, in a cell-free in vitro system that HCQ directly and dose-dependently inhibits the activity of recombinant human ACE2, with a potency similar to the MLN-4760. Further analysis suggests that HCQ binds to a noncompetitive site other than the one occupied by MLN-4760. We also determined that the viral spike glycoprotein segment that comprises the RBD segment has no effect on ACE2 activity but unexpectedly was able to partially reverse the inhibition induced by HCQ but not that by MLN-4760. In summary, here we demonstrate the direct inhibitory action of HCQ over the activity of the enzyme ACE2. Then, by determining the activity of ACE2, we reveal that the interaction with the spike protein of SARS-CoV-2 leads to structural changes that at least partially displace the interaction of the said enzyme with HCQ. These results may help to explain why the effectiveness of HCQ in clinical trials has been so variable. Additionally, this knowledge could be used for to develop techniques for the detection of SARS-CoV-2.

Effects of capillary refill time-vs. lactate-targeted fluid resuscitation on regional, microcirculatory and hypoxia-related perfusion parameters in septic shock: a randomized controlled trial.

BACKGROUND: Persistent hyperlactatemia has been considered as a signal of tissue hypoperfusion in septic shock patients, but multiple non-hypoperfusion-related pathogenic mechanisms could be involved. Therefore, pursuing lactate normalization may lead to the risk of fluid overload. Peripheral perfusion, assessed by the capillary refill time (CRT), could be an effective alternative resuscitation target as recently demonstrated by the ANDROMEDA-SHOCK trial. We designed the present randomized controlled trial to address the impact of a CRT-targeted (CRT-T) vs. a lactate-targeted (LAC-T) fluid resuscitation strategy on fluid balances within 24 h of septic shock diagnosis. In addition, we compared the effects of both strategies on organ dysfunction, regional and microcirculatory flow, and tissue hypoxia surrogates. RESULTS: Forty-two fluid-responsive septic shock patients were randomized into CRT-T or LAC-T groups. Fluids were administered until target achievement during the 6 h intervention period, or until safety criteria were met. CRT-T was aimed at CRT normalization (≤ 3 s), whereas in LAC-T the goal was lactate normalization (≤ 2 mmol/L) or a 20% decrease every 2 h. Multimodal perfusion monitoring included sublingual microcirculatory assessment; plasma-disappearance rate of indocyanine green; muscle oxygen saturation; central venous-arterial pCO2 gradient/ arterial-venous O2 content difference ratio; and lactate/pyruvate ratio. There was no difference between CRT-T vs. LAC-T in 6 h-fluid boluses (875 [375-2625] vs. 1500 [1000-2000], p = 0.3), or balances (982[249-2833] vs. 15,800 [740-6587, p = 0.2]). CRT-T was associated with a higher achievement of the predefined perfusion target (62 vs. 24, p = 0.03). No significant differences in perfusion-related variables or hypoxia surrogates were observed. CONCLUSIONS: CRT-targeted fluid resuscitation was not superior to a lactate-targeted one on fluid administration or balances. However, it was associated with comparable effects on regional and microcirculatory flow parameters and hypoxia surrogates, and a faster achievement of the predefined resuscitation target. Our data suggest that stopping fluids in patients with CRT ≤ 3 s appears as safe in terms of tissue perfusion. Clinical Trials: ClinicalTrials.gov Identifier: NCT03762005 (Retrospectively registered on December 3rd 2018).

Low Spontaneous Breathing Effort during Extracorporeal Membrane Oxygenation in a Porcine Model of Severe Acute Respiratory Distress Syndrome.

BACKGROUND: A lung rest strategy is recommended during extracorporeal membrane oxygenation in severe acute respiratory distress syndrome (ARDS). However, spontaneous breathing modes are frequently used in this context. The impact of this approach may depend on the intensity of breathing efforts. The authors aimed to determine whether a low spontaneous breathing effort strategy increases lung injury, compared to a controlled near-apneic ventilation, in a porcine severe ARDS model assisted by extracorporeal membrane oxygenation. METHODS: Twelve female pigs were subjected to lung injury by repeated lavages, followed by 2-h injurious ventilation. Thereafter, animals were connected to venovenous extracorporeal membrane oxygenation and during the first 3 h, ventilated with near-apneic ventilation (positive end-expiratory pressure, 10 cm H2O; driving pressure, 10 cm H2O; respiratory rate, 5/min). Then, animals were allocated into (1) near-apneic ventilation, which continued with the previous ventilatory settings; and (2) spontaneous breathing: neuromuscular blockers were stopped, sweep gas flow was decreased until regaining spontaneous efforts, and ventilation was switched to pressure support mode (pressure support, 10 cm H2O; positive end-expiratory pressure, 10 cm H2O). In both groups, sweep gas flow was adjusted to keep Paco2 between 30 and 50 mmHg. Respiratory and hemodynamic as well as electric impedance tomography data were collected. After 24 h, animals were euthanized and lungs extracted for histologic tissue analysis. RESULTS: Compared to near-apneic group, the spontaneous breathing group exhibited a higher respiratory rate (52 ± 17 vs. 5 ± 0 breaths/min; mean difference, 47; 95% CI, 34 to 59; P < 0.001), but similar tidal volume (2.3 ± 0.8 vs. 2.8 ± 0.4 ml/kg; mean difference, 0.6; 95% CI, -0.4 to 1.4; P = 0.983). Extracorporeal membrane oxygenation settings and gas exchange were similar between groups. Dorsal ventilation was higher in the spontaneous breathing group. No differences were observed regarding histologic lung injury. CONCLUSIONS: In an animal model of severe ARDS supported with extracorporeal membrane oxygenation, spontaneous breathing characterized by low-intensity efforts, high respiratory rates, and very low tidal volumes did not result in increased lung injury compared to controlled near-apneic ventilation.

Hypoxia-related parameters during septic shock resuscitation: Pathophysiological determinants and potential clinical implications.

BACKGROUND: Assessment of tissue hypoxia at the bedside has yet to be translated into daily clinical practice in septic shock patients. Perfusion markers are surrogates of deeper physiological phenomena. Lactate-to-pyruvate ratio (LPR) and the ratio between veno-arterial PCO2 difference and Ca-vO2 (ΔPCO2/Ca-vO2) have been proposed as markers of tissue hypoxia, but they have not been compared in the clinical scenario. We studied acute septic shock patients under resuscitation. We wanted to evaluate the relationship of these hypoxia markers with clinical and biochemical markers of hypoperfusion during septic shock resuscitation. METHODS: Secondary analysis of a randomized controlled trial. Septic shock patients were randomized to fluid resuscitation directed to normalization of capillary refill time (CRT) versus normalization or significant lowering of lactate. Multimodal assessment of perfusion was performed at 0, 2, 6 and 24 hours, and included macrohemodynamic and metabolic perfusion variables, CRT, regional flow and hypoxia markers. Patients who attained their pre-specified endpoint at 2-hours were compared to those who did not. RESULTS: Forty-two patients were recruited, median APACHE-II score was 23 [15-31] and 28-day mortality 23%. LPR and ΔPCO2/Ca-vO2 ratio did not correlate during early resuscitation (0-2 h) and the whole study period (24-hours). ΔPCO2/Ca-vO2 ratio derangements were more prevalent than LPR ones, either in the whole cohort (52% vs. 23%), and in association with other perfusion abnormalities. In patients who reached their resuscitation endpoints, the proportion of patients with altered ΔPCO2/Ca-vO2 ratio decreased significantly (66% to 33%, P=0.045), while LPR did not (14% vs. 25%, P=0.34). CONCLUSIONS: Hypoxia markers did not exhibit correlation during resuscitation in septic shock patients. They probably interrogate different pathophysiological processes and mechanisms of dysoxia during early septic shock. Future studies should better elucidate the interaction and clinical role of hypoxia markers during septic shock resuscitation.

Plasma and Renal Cortex Meropenem Concentrations in Patients Undergoing Percutaneous Renal Biopsy.

BACKGROUND: Urinary tract infection (UTI) is the most common bacterial infection in the world. Some cases can have serious complication as death by septic shock. With the increasing spread of multidrug-resistant bacteria, the therapeutic possibilities against the complicated UTI are exhausted, forcing the use of broad-spectrum antibiotics such as meropenem. OBJECTIVES: To evaluate the penetrating ability of meropenem to renal tissue using an enzymatic biosensor in samples of renal cortex and its correlation with plasma levels. METHOD: We conducted a descriptive study in humans with indication of kidney biopsy. Meropenem was administered 1 hour before performing the biopsy, and the concentrations of meropenem in a series of samples of plasma and renal biopsy were determined. RESULTS: Renal biopsy and plasma samples of 14 patients, 64% women with body mass index of 26.3 kg/m2 (SD ± 2.9) and estimated glomerular filtration rate of 57.5 mL/min/1.73 m2 (SD ± 44.1), were examined. Renal biopsy was done at 68.9 minutes (SD ± 20.3), and the second plasma sample was obtained at 82.1 minutes (SD ± 21.2) and the third at 149.6 minutes (SD ± 31.5). The mean kidney meropenem concentration was 3.1 µg/mL (SD ± 1.9). For each patient, a decay curve of plasma meropenem concentration was constructed. The proportion of meropenem concentrations in renal tissue and plasma at biopsy moment was 14% (SD ± 10) with an interquartile range of 5.5-20.3%. With normal renal function, meropenem can achieve a bactericidal effect towards bacteria with MIC-90 < 0.76 µg/mL in the renal parenchyma. CONCLUSIONS: Meropenem is effective to treat the most frequent uropathogens with the bactericidal effect. Nevertheless, for resistant bacteria, it is necessary to adjust the dose to achieve adequate parenchymal concentration.

Effect of Lactamase Inhibitors on the Biosensor Penp during the Measurement of Lactam Antibiotics Concentration.

PenP is a fluorescent biosensor of lactam antibiotics (LA). It is structurally derived from the mutant lactamase TEM-1 comprising the substitution E166C, where fluorescein is covalently linked to cysteine. The presence of LA in the medium produces a change in the intrinsic fluorescence level of the biosensor, and the integral of the fluorescence level over time correlates directly with the LA concentration. Previously, we have successfully used PenP to determine the concentration of lactam antibiotics in clinical samples. The use of lactamase inhibitors (LI) is a common strategy to enhance the effect of LA due to the inhibition of an important resistance mechanism of pathogenic microorganisms. Structurally, LI and LA share the common element of recognition of lactamases (the lactam ring), but they differ in the reversibility of the mechanism of interaction with said enzyme. Because the biological recognition domain of PenP is derived from a lactamase, LI is expected to interfere with the PenP detection capabilities. Surprisingly, this work provides evidence that the effect of LI is marginal in the determination of LA concentration mediated by PenP.

Near-Apneic Ventilation Decreases Lung Injury and Fibroproliferation in an Acute Respiratory Distress Syndrome Model with Extracorporeal Membrane Oxygenation.

RATIONALE: There is wide variability in mechanical ventilation settings during extracorporeal membrane oxygenation (ECMO) in patients with acute respiratory distress syndrome. Although lung rest is recommended to prevent further injury, there is no evidence to support it. OBJECTIVES: To determine whether near-apneic ventilation decreases lung injury in a pig model of acute respiratory distress syndrome supported with ECMO. METHODS: Pigs (26-36 kg; n = 24) were anesthetized and connected to mechanical ventilation. In 18 animals lung injury was induced by a double-hit consisting of repeated saline lavages followed by 2 hours of injurious ventilation. Then, animals were connected to high-flow venovenous ECMO, and randomized into three groups: 1) nonprotective (positive end-expiratory pressure [PEEP], 5 cm H2O; Vt, 10 ml/kg; respiratory rate, 20 bpm), 2) conventional-protective (PEEP, 10 cm H2O; Vt, 6 ml/kg; respiratory rate, 20 bpm), and 3) near-apneic (PEEP, 10 cm H2O; driving pressure, 10 cm H2O; respiratory rate, 5 bpm). Six other pigs were used as sham. All groups were maintained during the 24-hour study period. MEASUREMENTS AND MAIN RESULTS: Minute ventilation and mechanical power were lower in the near-apneic group, but no differences were observed in oxygenation or compliance. Lung histology revealed less injury in the near-apneic group. Extensive immunohistochemical staining for myofibroblasts and procollagen III was observed in the nonprotective group, with the near-apneic group exhibiting the least alterations. Near-apneic group showed significantly less matrix metalloproteinase-2 and -9 activity. Histologic lung injury and fibroproliferation scores were positively correlated with driving pressure and mechanical power. CONCLUSIONS: In an acute respiratory distress syndrome model supported with ECMO, near-apneic ventilation decreased histologic lung injury and matrix metalloproteinase activity, and prevented the expression of myofibroblast markers.

Evaluation of Meropenem Pharmacokinetics in an Experimental Acute Respiratory Distress Syndrome (ARDS) Model during Extracorporeal Membrane Oxygenation (ECMO) by Using a PenP ß-Lactamase Biosensor.

INTRODUCTION: The use of antibiotics is mandatory in patients during extracorporeal membrane oxygenation (ECMO) support. Clinical studies have shown high variability in the antibiotic concentrations, as well as sequestration of them by the ECMO circuit, suggesting that the doses and/or interval administration used during ECMO may not be adequate. Thus, a fast response sensor to estimate antibiotic concentrations in this setting would contribute to improve dose adjustments. The biosensor PenP has been shown to have a dynamic range, sensitivity and specificity useful for pharmacokinetic (PK) tests in healthy subjects. However, the use of this biosensor in the context of a complex critical condition, such as ECMO during acute respiratory distress syndrome (ARDS), has not been tested. OBJECTIVES: To describe, by using PenP Biosensor, the pharmacokinetic of meropenem in a 24-h animal ARDS/ECMO model. METHODS: The PK of meropenem was evaluated in a swine model before and during ECMO. RESULTS: The PK parameters such as maximum concentration (Cmax), elimination rate constant (Ke), and cleareance (Cl), were not significantly altered during ECMO support. CONCLUSIONS: (a) ECMO does not affect the PK of meropenem, at least during the first 24 h; and (b) PenP has the potential to become an effective tool for making medical decisions associated with the dose model of antibiotics in a critical patient context.

Liquid extracorporeal carbon dioxide removal: use of THAM (tris-hydroxymethyl aminomethane) coupled to hemofiltration to control hypercapnic acidosis in a porcine model of protective mechanical ventilation.

A promising approach to facilitate protective mechanical ventilation is the use of extracorporeal CO2 removal techniques. Several strategies based on membrane gas exchangers have been developed. However, these techniques are still poorly available. The goal of this study was to assess the efficacy and safety of THAM infusion coupled to hemofiltration for the management of hypercapnic acidosis. A severe respiratory acidosis was induced in seven anesthetized pigs. Five of them were treated with THAM 8-mmol·kg(-1)·h(-1) coupled to hemofiltration (THAM+HF group) at 100 mL·kg(-1)·h(-1). After 18-hours of treatment the THAM infusion was stopped but hemofiltration was kept on until 24-hours. The 2 other animals were treated with THAM but without hemofiltration. After 1-hour of treatment in THAM+HF, PaCO2 rapidly decreased from a median of 89.0 (IQR) (80.0, 98.0) to 71.3 (65.8, 82.0) mmHg (P<0.05), while pH increased from 7.12 (7.01, 7.15) to 7.29 (7.27, 7.30) (P<0.05). Thereafter PaCO2 remained stable between 60-70 mmHg, while pH increased above 7.4. After stopping THAM at 18 hours of treatment a profound rebound effect was observed with severe hypercapnic acidosis. The most important side effect we observed was hyperosmolality, which reached a maximum of 330 (328, 332) mOsm·kg H2O(-1) at T18. The animals treated only with THAM developed severe hypercapnia, despite the fact that pH returned to normal values, and died after 12 hours. Control-group had an uneven evolution until the end of the experiment. A combined treatment with THAM coupled to hemofiltration may be an effective treatment to control severe hypercapnic acidosis.

Effects of dexmedetomidine and esmolol on systemic hemodynamics and exogenous lactate clearance in early experimental septic shock.

BACKGROUND: Persistent hyperlactatemia during septic shock is multifactorial. Hypoperfusion-related anaerobic production and adrenergic-driven aerobic generation together with impaired lactate clearance have been implicated. An excessive adrenergic response could contribute to persistent hyperlactatemia and adrenergic modulation might be beneficial. We assessed the effects of dexmedetomidine and esmolol on hemodynamics, lactate generation, and exogenous lactate clearance during endotoxin-induced septic shock. METHODS: Eighteen anesthetized and mechanically ventilated sheep were subjected to a multimodal hemodynamic/perfusion assessment including hepatic and portal vein catheterizations, total hepatic blood flow, and muscle microdialysis. After monitoring, all received a bolus and continuous infusion of endotoxin. After 1 h they were volume resuscitated, and then randomized to endotoxin-control, endotoxin-dexmedetomidine (sequential doses of 0.5 and 1.0 µg/k/h) or endotoxin-esmolol (titrated to decrease basal heart rate by 20 %) groups. Samples were taken at four time points, and exogenous lactate clearance using an intravenous administration of sodium L-lactate (1 mmol/kg) was performed at the end of the experiments. RESULTS: Dexmedetomidine and esmolol were hemodynamically well tolerated. The dexmedetomidine group exhibited lower epinephrine levels, but no difference in muscle lactate. Despite progressive hypotension in all groups, both dexmedetomidine and esmolol were associated with lower arterial and portal vein lactate levels. Exogenous lactate clearance was significantly higher in the dexmedetomidine and esmolol groups. CONCLUSIONS: Dexmedetomidine and esmolol were associated with lower arterial and portal lactate levels, and less impairment of exogenous lactate clearance in a model of septic shock. The use of dexmedetomidine and esmolol appears to be associated with beneficial effects on gut lactate generation and lactate clearance and exhibits no negative impact on systemic hemodynamics.

Extracorporeal membrane oxygenation improves survival in a novel 24-hour pig model of severe acute respiratory distress syndrome.

Extracorporeal membrane oxygenation (ECMO) is increasingly being used to treat severe acute respiratory distress syndrome (ARDS). However, there is limited clinical evidence about how to optimize the technique. Experimental research can provide an alternative to fill the actual knowledge gap. The purpose of the present study was to develop and validate an animal model of acute lung injury (ALI) which resembled severe ARDS, and which could be successfully supported with ECMO. Eighteen pigs were randomly allocated into three groups: sham, ALI, and ALI + ECMO. ALI was induced by a double-hit consisting in repeated saline lavage followed by a 2-hour period of injurious ventilation. All animals were followed up to 24 hours while being ventilated with conventional ventilation (tidal volume 10 ml/kg). The lung injury model resulted in severe hypoxemia, increased airway pressures, pulmonary hypertension, and altered alveolar membrane barrier function, as indicated by an increased protein concentration in bronchoalveolar fluid, and increased wet/dry lung weight ratio. Histologic examination revealed severe diffuse alveolar damage, characteristic of ARDS. Veno-venous ECMO was started at the end of lung injury induction with a flow > 60 ml/kg/min resulting in rapid reversal of hypoxemia and pulmonary hypertension. Mortality was 0, 66.6 and 16.6% in the SHAM, ALI and ALI + ECMO groups, respectively (p < 0.05). This is a novel clinically relevant animal model that can be used to optimize the approach to ECMO and foster translational research in extracorporeal lung support.