The effects of body temperature control on cytokine production in a rat model of ventilator-induced lung injury

Protocol for fever control using external cooling in mechanically ventilated patients with septic shock: SEPSISCOOL II randomised controlled trial

INTRODUCTION

Fever treatment is commonly applied in patients with sepsis but its impact on survival remains undetermined. Patients with respiratory and haemodynamic failure are at the highest risk for not tolerating the metabolic cost of fever. However, fever can help to control infection. Treating fever with paracetamol has been shown to be less effective than cooling. In the SEPSISCOOL pilot study, active fever control by external cooling improved organ failure recovery and early survival. The main objective of this confirmatory trial is to assess whether fever control at normothermia can improve the evolution of organ failure and mortality at day 60 of febrile patients with septic shock. This study will compare two strategies within the first 48 hours of septic shock: treatment of fever with cooling or no treatment of fever.

METHODS AND ANALYSIS

SEPSISCOOL II is a pragmatic, investigator-initiated, adaptive, multicentre, open-label, randomised controlled, superiority trial in patients admitted to the intensive care unit with febrile septic shock. After stratification based on the acute respiratory distress syndrome status, patients will be randomised between two arms: (1) cooling and (2) no cooling. The primary endpoint is mortality at day 60 after randomisation. The secondary endpoints include the evolution of organ failure, early mortality and tolerance. The target sample size is 820 patients.

ETHICS AND DISSEMINATION

The study is funded by the French health ministry and was approved by the ethics committee CPP Nord Ouest II (Amiens, France). The results will be submitted for publication in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

NCT04494074.

Mild Hypothermia via External Cooling Improves Lung Function and Alleviates Pulmonary Inflammatory Response and Damage in Two-Hit Rabbit Model of Acute Lung Injury

OBJECTIVES

Targeted temperature management (TTM) with therapeutic hypothermia (TH) has an organ-protective effect by mainly reducing inflammatory response. Here, our objective was to determine, for the first time, whether mild TH with external cooling, a simple and inexpensive method, could be safe or even beneficial in two-hit rabbit model of acute lung injury/acute respiratory distress syndrome (ALI/ARDS).

METHODS

Twenty-two New Zealand rabbits (6-month-old) were randomly divided into healthy control (HC) with conventional ventilation, but without injury, model group (ALI), and hypothermia group with external cooling (ALI-HT). After induction of ALI/ARDS through mild lung-lavages followed by non-protective ventilation, mild hypothermia was started in ALI-HT group (body temperature of 33-34 °C). All rabbits were conventionally ventilated for an additional 6-h by recording respiratory parameters. Finally, lung histopathology and inflammatory response were evaluated.

RESULTS

Hypothermia was associated with higher oxygen saturation, resulting in partial improvement in the P/F ratio (PaO2/FiO2), oxygenation index, mean airway pressure, and PaCO2, but did not affect lactate levels. The ALI-HT group had lower histopathological injury scores (hyperemia, edema, emphysema, atelectasis, and PMN infiltration). Further, tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6 and -8 levels in lung tissue and serum samples markedly reduced due to hypothermia.

CONCLUSION

Mild TH with external cooling reduced lung inflammation and damage, whereas it resulted in partial improvement in gas exchanges. Our findings highlight that body temperature control may be a potentially supportive therapeutic option for regulating cytokine production and respiratory parameters in ALI/ARDS.

Successful use of mild therapeutic hypothermia as compassionate treatment for severe refractory hypoxemia in COVID-19

BACKGROUND

COVID-19 is a disease associated with an intense systemic inflammation that could induce severe acute respiratory distress syndrome (ARDS), with life-threatening hypoxia and hypercapnia. We present a case where mild therapeutic hypothermia was associated with improved gas exchange, facing other therapies' unavailability due to the pandemic.

CASE REPORT

A healthy 38-year-old male admitted for COVID-19 pneumonia developed extreme hypoxia (PaO₂/FiO₂ ratio 42 mmHg), respiratory acidosis, and hyperthermia, refractory to usual treatment (mechanical ventilation, neuromuscular blockade, and prone position), and advanced therapies were not available. Mild therapeutic hypothermia management (target 33-34 °C) was maintained for five days, with progressive gas exchange improvement, which allowed his recovery over the following weeks. He was discharged home after 68 days without significant ICU associated morbidity.

CONCLUSIONS

Mild hypothermia is a widely available therapy, that given some specific characteristics of COVID-19, may be explored as adjunctive therapy for life-threatening ARDS, especially during a shortage of other rescue therapies.

Effects of hypothermia on lung inflammation in a rat model of meconium aspiration syndrome

PURPOSE

To evaluate the effects of hypothermia treatment on meconium-induced inflammation.

METHODS

Fifteen rats were instilled with human meconium (MEC, 1.5 mL/kg, 65 mg/mL) intratracheally and ventilated for 3 hours. Eight rats that were ventilated and not instilled with meconium served as a sham group. In MEC-hypothermia group, the body temperature was lowered to 33±0.5°C. Analysis of the blood gases, interleukin (IL)-1β, IL-6, IL-8, and tumor necrosis factor (TNF)-α in bronchoalveolar lavage (BAL) fluid samples, and histological analyses of the lungs were performed.

RESULTS

The BAL fluid TNF-α, IL-1β, IL-6 and IL-8 concentrations were significantly higher in the MEC-hypothermia group than in the MEC-normothermia (p < 0.001, p < 0.001, p = 0.001, p < 0.001, respectively) and sham-controlled groups (p < 0.001, p < 0.001, p < 0.001, p < 0.001, respectively).

CONCLUSION

Meconium-induced inflammatory cytokine production is affected by the body temperature control.

Hypothermia Promotes Interleukin-22 Expression and Fine-Tunes Its Biological Activity

Disturbed homeostasis as a result of tissue stress can provoke leukocyte responses enabling recovery. Since mild hypothermia displays specific clinically relevant tissue-protective properties and interleukin (IL)-22 promotes healing at host/environment interfaces, effects of lowered ambient temperature on IL-22 were studied. We demonstrate that a 5-h exposure of endotoxemic mice to 4°C reduces body temperature by 5.0° and enhances splenic and colonic il22 gene expression. In contrast, tumor necrosis factor-α and IL-17A were not increased. In vivo data on IL-22 were corroborated using murine splenocytes and human peripheral blood mononuclear cells (PBMC) cultured upon 33°C and polyclonal T cell activation. Upregulation by mild hypothermia of largely T-cell-derived IL-22 in PBMC required monocytes and associated with enhanced nuclear T-cell nuclear factor of activated T cells (NFAT)-c2. Notably, NFAT antagonism by cyclosporin A or FK506 impaired IL-22 upregulation at normothermia and entirely prevented its enhanced expression upon hypothermic culture conditions. Data suggest that intact NFAT signaling is required for efficient IL-22 induction upon normothermic and hypothermic conditions. Hypothermia furthermore boosted early signal transducer and activator of transcription 3 activation by IL-22 and shaped downstream gene expression in epithelial-like cells. Altogether, data indicate that hypothermia supports and fine-tunes IL-22 production/action, which may contribute to regulatory properties of low ambient temperature.

Mild hypothermia attenuate kidney injury in canines with oleic acid-induced acute respiratory distress syndrome

BACKGROUND

Hypothermia may attenuate ventilator induced-lung injury in acute respiratory distress syndrome (ARDS). However, the impact of hypothermia on extra-pulmonary organ injury in ARDS remains unclear. The purpose of this study was to investigate whether hypothermia affects extra-pulmonary organ injury in a canine ARDS model induced by oleic acid.

OBJECTIVES

Twelve anesthetized canines with oleic acid-induced ARDS were randomly divided (n=6 per group) into a hypothermia group (core temperature of 33±1°C, HT group) and a normothermia group (core temperature of 38±1°C, NT group) and treated for four hours. The liver, small intestine and kidney were assessed by evaluating biochemical parameters, plasma and tissue cytokine levels, and tissue histopathological injury scores.

RESULTS

The HT group showed a lower plateau pressure, lung elastance and pulmonary vascular resistance. Hypothermia was associated with lower oxygen consumption (138.4±55.0mlmin(-1)vs. 72.0±11.2mlmin(-1), P<0.05) and higher oxygen saturation of mixed venous blood (62.8%±8.0% vs. 77.5%±10.1%, P<0.05). Both groups had similar levels of tumour necrosis factor-α in the plasma and extra-pulmonary organ, however, plasma interleukin-10 (97.1±25.0pgml(-1)vs. 131.4±27.0pgml(-1), P<0.05) was higher in the HT group. Further, the animals in the HT group had a lower levels of plasma creatinine (54.6±19.1UL(-1)vs. 29.1±8.0UL(-1), P<0.05), and lower renal histopathological injury scores [4.0(3.5;7.0) vs. 1.5(0.8;3.0), P<0.05]. Hypothermia did not affect the histopathological injury of the liver and small intestine.

CONCLUSIONS

Short-term mild hypothermia can reduce lung elastance and pulmonary vascular resistance, increase the systemic anti-inflammatory response and attenuate kidney histopathological injury in a canine ARDS model induced by oleic acid.

Reduction in circulating level of HMGB-1 following continuous renal replacement therapy in sepsis

Early recovery from shock improves prognosis in patients with severe sepsis and septic shock. During this period, cytokine imbalances mediate the development of organ damage and mortality. In Japan, we have access to hemoperfusion using an immobilized polymyxin B fiber column for endotoxin removal (PMX-DHP) and continuous hemodiafiltration (CHDF) as artificial support for patients with septic shock, with the aim of improving hemodynamics and organ dysfunction caused by elevated inflammatory cytokines and mediators. In this Short communication, we discuss recent findings showing anti-inflammatory treatment following these continuous renal replacement therapies in sepsis.

Long-Term Effects of Induced Hypothermia on Local and Systemic Inflammation - Results from a Porcine Long-Term Trauma Model

Background

Hypothermia has been discussed as playing a role in improving the early phase of systemic inflammation. However, information on the impact of hypothermia on the local inflammatory response is sparse. We therefore investigated the kinetics of local and systemic inflammation in the late posttraumatic phase after induction of hypothermia in an established porcine long-term model of combined trauma.

Materials & Methods

Male pigs (35 ± 5kg) were mechanically ventilated and monitored over the study period of 48 h. Combined trauma included tibia fracture, lung contusion, liver laceration and pressure-controlled hemorrhagic shock (MAP < 30 ± 5 mmHg for 90 min). After resuscitation, hypothermia (33°C) was induced for a period of 12 h (HT-T group) with subsequent re-warming over a period of 10 h. The NT-T group was kept normothermic. Systemic and local (fracture hematoma) cytokine levels (IL-6, -8, -10) and alarmins (HMGB1, HSP70) were measured via ELISA.

Results

Severe signs of shock as well as systemic and local increases of pro-inflammatory mediators were observed in both trauma groups. In general the local increase of pro- and anti-inflammatory mediator levels was significantly higher and prolonged compared to systemic concentrations. Induction of hypothermia resulted in a significantly prolonged elevation of both systemic and local HMGB1 levels at 48 h compared to the NT-T group. Correspondingly, local IL-6 levels demonstrated a significantly prolonged increase in the HT-T group at 48 h.

Conclusion

A prolonged inflammatory response might reduce the well-described protective effects on organ and immune function observed in the early phase after hypothermia induction. Furthermore, local immune response also seems to be affected. Future studies should aim to investigate the use of therapeutic hypothermia at different degrees and duration of application.

Transcutaneous electromagnetic induction heating of an intramedullary nickel-titanium shape memory implant

PURPOSE

Inadequate mechanical stimuli are a major cause for nonunions following surgery for femoral and tibial shaft fractures. Adapting fixation rigidity during the course of fracture healing requires additional surgery. Nickel-titanium (NiTi) implants can change shape and rigidity by employing a temperature-dependent shape-memory effect. As a first step in the development of advanced intramedullary (IM) NiTi devices for fracture healing, this study aimed to test the feasibility and safety of transcutaneous electromagnetic induction heating of an IM NiTi implant in a rat model.

METHODS

In 51 rats, NiTi implants were introduced into the left distal femur. Forty-four animals were transferred to an induction coil, and the implant was electromagnetically heated to temperatures between 40° and 60 °C Blood samples were drawn before and four hours after the procedure. Interleukin (IL)-1, IL-4, IL-10, tumour necrosis factor alpha (TNF-α) and interferon gamma (IFN-γ) were measured. Animals were sacrificed at three weeks. Histological specimens from the hind leg and liver were retrieved and examined for inflammatory changes, necrosis or corrosion pits.

RESULTS

All animals successfully underwent the surgical procedure. Following transcutaneous induction heating, target temperature was confirmed in 37/44 rats. Postoperative controls showed no signs of undue limitations. Neither cytokine measurements nor histological specimens showed any significant differences between groups. There were no corrosion pits or necrosis.

CONCLUSION

We conclude that electromagnetic induction heating of IM NiTi implants is feasible and safe in a rat femur model. These findings reflect a further step in the development of novel concepts for IM fracture fixation that might lead to better fracture healing, less patient discomfort and less need for surgical interventions.

Effect of therapeutic hypothermia on gas exchange and respiratory mechanics: a retrospective cohort study

Targeted temperature management (TTM) may improve respiratory mechanics and lung inflammation in acute respiratory distress syndrome (ARDS) based on animal and limited human studies. We aimed to assess the pulmonary effects of TTM in patients with respiratory failure following cardiac arrest. Retrospective review of consecutive cardiac arrest cases occurring out of hospital or within 24 hours of hospital admission (2002-2012). Those receiving TTM (n=44) were compared with those who did not (n=42), but required mechanical ventilation (MV) for at least 4 days following the arrest. There were no between-group differences in age, gender, body mass index, APACHE II, or fluid balance during the study period. The TTM group had lower ejection fraction, Glasgow Coma Score, and more frequent use of paralytics. Matched data analyses (change at day 4 compared with baseline of the individual subject) showed favorable, but not statistically significant trends in respiratory mechanics endpoints (airway pressure, compliance, tidal volume, and PaO2/FiO2) in the TTM group. The PaCO2 decreased significantly more in the TTM group, as compared with controls (-12 vs. -5 mmHg, p=0.02). For clinical outcomes, the TTM group consistently, although not significantly, did better in survival (59% vs. 43%) and hospital length of stay (12 vs. 15 days). The MV duration and Cerebral Performance Category score on discharge were significantly lower in the TTM group (7.3 vs. 10.7 days, p=0.04 and 3.2 vs. 4, p=0.01). This small retrospective cohort suggests that the effect of TTM ranges from equivalent to favorable, compared with controls, for the specific respiratory and clinical outcomes in patients with respiratory failure following cardiac arrest.

Cryotherapy in inflammatory rheumatic diseases: a systematic review

The aim of this article was to review current evidence about cryotherapy in inflammatory rheumatic diseases (therapeutic and biological effects). For therapeutic effects, we performed a systematic review (PubMed, EMBASE, Cochrane Library, LILACS databases, unpublished data) and selected studies including non-operated and non-infected arthritic patients treated with local cryotherapy or whole-body cryotherapy. By pooling 6 studies including 257 rheumatoid arthritis (RA) patients, we showed a significant decrease in pain visual analogic scale (mm) and 28-joint disease activity score after chronic cryotherapy in RA patients. For molecular pathways, local cryotherapy induces an intrajoint temperature decrease, which might downregulate several mediators involved in joint inflammation and destruction (cytokines, cartilage-degrading enzymes, proangiogenic factors), but studies in RA are rare. Cryotherapy should be included in RA therapeutic strategies as an adjunct therapy, with potential corticosteroid and nonsteroidal anti-inflammatory drug dose-sparing effects. However, techniques and protocols should be more precisely defined in randomized controlled trials with stronger methodology.

Mild hypothermia increases pulmonary anti-inflammatory response during protective mechanical ventilation in a piglet model of acute lung injury

BACKGROUND

The effects of mild hypothermia (HT) on acute lung injury (ALI) are unknown in species with metabolic rate similar to that of humans, receiving protective mechanical ventilation (MV). We hypothesized that mild hypothermia would attenuate pulmonary and systemic inflammatory responses in piglets with ALI managed with a protective MV.

METHODS

Acute lung injury (ALI) was induced with surfactant deactivation in 38 piglets. The animals were then ventilated with low tidal volume, moderate positive end-expiratory pressure (PEEP), and permissive hypercapnia throughout the experiment. Subjects were randomized to HT (33.5°C) or normothermia (37°C) groups over 4 h. Plasma and tissue cytokines, tissue apoptosis, lung mechanics, pulmonary vascular permeability, hemodynamic, and coagulation were evaluated.

RESULTS

Lung interleukin-10 concentrations were higher in subjects that underwent HT after ALI induction than in those that maintained normothermia. No difference was found in other systemic and tissue cytokines. HT did not induce lung or kidney tissue apoptosis or influence lung mechanics or markers of pulmonary vascular permeability. Heart rate, cardiac output, oxygen uptake, and delivery were significantly lower in subjects that underwent HT, but no difference in arterial lactate, central venous oxygen saturation, and coagulation test was observed.

CONCLUSIONS

Mild hypothermia induced a local anti-inflammatory response in the lungs, without affecting lung function or coagulation, in this piglet model of ALI. The HT group had lower cardiac output without signs of global dysoxia, suggesting an adaptation to the decrease in oxygen uptake and delivery. Studies are needed to determine the therapeutic role of HT in ALI.

Clinical outcome, proteome kinetics and angiogenic factors in serum after thermoablation of colorectal liver metastases

Background

Thermoablation is used to treat patients with unresectable colorectal liver metastases (CRLM). We analyze clinical outcome, proteome kinetics and angiogenic markers in patients treated by cryosurgical ablation (CSA) or radiofrequency ablation (RFA).

Methods

205 patients underwent CSA (n = 20), RFA (n = 22), partial hepatectomy (PH, n = 134) or were found truly unresectable (n = 29). Clinical outcome, proteome transitions and angiogenic response in serum were analyzed at various time points after ablation.

Result

Median overall survival in CSA patients (17.6 months) was worse (p < 0.0001) when compared to RFA treated patients (51.7 months) and patients after PH (43.4 months). The complication rate was higher in the CSA group (50%) as compared to the RFA group (22%). Proteomics analyses showed consistently more changes in serum protein abundance with CSA compared to RFA. In the first four days after ablation a pro-angiogenic serum response occurred.

Conclusions

RFA of CRLM is superior to CSA with a median survival which equals survival in patients after PH. Proteomics analyses suggests a more aggravated serum response to CSA compared to RFA. Thermoablation is associated with changes in serum levels of angiogenic factors favouring a pro-angiogenic environment, but without differences between RFA and CSA.

Susceptibility to ventilator induced lung injury is increased in senescent rats

Introduction

The principal mechanisms of ventilator induced lung injury (VILI) have been investigated in numerous animal studies. However, prospective data on the effect of old age on VILI are limited. Under the hypothesis that susceptibility to VILI is increased in old age, we investigated the pulmonary and extrapulmonary effects of mechanical ventilation with high tidal volume (VT) in old compared to young adult animals.

Interventions

Old (19.1 ± 3.0 months) and young adult (4.4 ± 1.3 months) male Wistar rats were anesthetized and mechanically ventilated (positive end-expiratory pressure 5 cmH2O, fraction of inspired oxygen 0.4, respiratory rate 40/minute) with a tidal volume (VT) of either 8, 16 or 24 ml/kg for four hours.

Respiratory and hemodynamic variables, including cardiac output, and markers of systemic inflammation were recorded throughout the ventilation period. Lung histology and wet-to-dry weight ratio, injury markers in lung lavage and respiratory system pressure-volume curves were assessed post mortem. Basic pulmonary characteristics were assessed in non-ventilated animals.

Results

Compared to young adult animals, high VT (24 ml/kg body weight) caused more lung injury in old animals as indicated by decreased oxygenation (arterial oxygen tension (PaO2): 208 ± 3 vs. 131 ± 20 mmHg; P <0.05), increased lung wet-to-dry-weight ratio (5.61 ± 0.29 vs. 7.52 ± 0.27; P <0.05), lung lavage protein (206 ± 52 mg/l vs. 1,432 ± 101; P <0.05) and cytokine (IL-6: 856 ± 448 vs. 3,283 ± 943 pg/ml; P <0.05) concentration. In addition, old animals ventilated with high VT had more systemic inflammation than young animals (IL-1β: 149 ± 44 vs. 272 ± 36 pg/ml; P <0.05 - young vs. old, respectively).

Conclusions

Ventilation with unphysiologically large tidal volumes is associated with more lung injury in old compared to young rats. Aggravated pulmonary and systemic inflammation is a key finding in old animals developing VILI.

In a porcine model of mixed acidemia HES 130/0.4 may support more stable hemodynamics during CVVH when compared to gelatine

PURPOSE

Continuous veno-venous hemofiltration (CVVH) and mixed acidemia often occur simultaneously in critically ill patients. In a previous study in non-acidemic pigs we found that colloids and CVVH interact specifically with respect to hemodynamic stability, with favorable effects for 6% HES 130/0.4 versus 4% gelatine (GEL) infusion. In a porcine model, we investigated whether these colloid-type associated differences are still dominant under acidemic conditions.

METHODS

We utilized 5 groups, a non-acidemic reference group receiving HES130 and CVVH; two acidemic groups receiving HES130 infusion (one with and one without CVVH); and two acidemic groups receiving GEL infusion (one with and one without CVVH). Mixed acidemia (pH ~7.20) was established by low tidal volume ventilation and acid infusion. Stable acidemia/CVVH application was maintained for 3 hours. Hemodynamics and blood gases were recorded.

RESULTS

Mixed acidemia led to a significant decrease in MAP and increase in MPAP in all groups. CVVH led to a further decrease in MAP but improved MPAP. During CVVH, HES130 ensured significantly higher MAP, Hb, and DO2 values than GEL infusion. In the groups without CVVH these differences between HES 130/0.4 and GEL were not observed.

CONCLUSIONS

As in a previous study in non-acidemic pigs, we found a colloid-specific influence of HES130 versus GEL on hemodynamics during CVVH under acidemia. Again, HES130 infusion may lead to favorable effects. In contrast, acidemia without CVVH application was dominant over the impact of a respective colloid. The application of a CVVH seems to be an important trigger for the overall circulatory response to a particular colloid.

Facts and fiction: the impact of hypothermia on molecular mechanisms following major challenge

Numerous multiple trauma and surgical patients suffer from accidental hypothermia. While induced hypothermia is commonly used in elective cardiac surgery due to its protective effects, accidental hypothermia is associated with increased posttraumatic complications and even mortality in severely injured patients. This paper focuses on protective molecular mechanisms of hypothermia on apoptosis and the posttraumatic immune response. Although information regarding severe trauma is limited, there is evidence that induced hypothermia may have beneficial effects on the posttraumatic immune response as well as apoptosis in animal studies and certain clinical situations. However, more profound knowledge of mechanisms is necessary before randomized clinical trials in trauma patients can be initiated.

Fever control using external cooling in septic shock: a randomized controlled trial

RATIONALE

Fever control may improve vascular tone and decrease oxygen consumption, but fever may contribute to combat infection.

OBJECTIVES

To determine whether fever control by external cooling diminishes vasopressor requirements in septic shock.

METHODS

In a multicenter randomized controlled trial, febrile patients with septic shock requiring vasopressors, mechanical ventilation, and sedation were allocated to external cooling (n = 101) to achieve normothermia (36.5-37°C) for 48 hours or no external cooling (n = 99). Vasopressors were tapered to maintain the same blood pressure target in the two groups. The primary endpoint was the number of patients with a 50% decrease in baseline vasopressor dose after 48 hours.

MEASUREMENTS AND MAIN RESULTS

Body temperature was significantly lower in the cooling group after 2 hours of treatment (36.8 ± 0.7 vs. 38.4 ± 1.1°C; P < 0.01). A 50% vasopressor dose decrease was significantly more common with external cooling from 12 hours of treatment (54 vs. 20%; absolute difference, 34%; 95% confidence interval [95% CI], -46 to -21; P < 0.001) but not at 48 hours (72 vs. 61%; absolute difference, 11%; 95% CI, -23 to 2). Shock reversal during the intensive care unit stay was significantly more common with cooling (86 vs. 73%; absolute difference, 13%; 95% CI, 2 to 25; P = 0.021). Day-14 mortality was significantly lower in the cooling group (19 vs. 34%; absolute difference, -16%; 95% CI, -28 to -4; P = 0.013).

CONCLUSIONS

In this study, fever control using external cooling was safe and decreased vasopressor requirements and early mortality in septic shock.

Mild hypothermia reduces ventilator-induced lung injury, irrespective of reducing respiratory rate

In the era of lung-protective mechanical ventilation using limited tidal volumes, higher respiratory rates are applied to maintain adequate minute volume ventilation. However, higher respiratory rates may contribute to ventilator-induced lung injury (VILI). Induced hypothermia reduces carbon dioxide production and might allow for lower respiratory rates during mechanical ventilation. We hypothesized that hypothermia protects from VILI and investigated whether reducing respiratory rates enhance lung protection in an in vivo model of VILI. During 4 h of mechanical ventilation, VILI was induced by tidal volumes of 18 mL/kg in rats, with respiratory rates set at 15 or 10 breaths/min in combination with hypothermia (32°C) or normothermia (37°C). Hypothermia was induced by external cooling. A physiologic model was established. VILI was characterized by increased pulmonary neutrophil influx, protein leak, wet weights, histopathology score, and cytokine levels compared with lung protective mechanical ventilation. Hypothermia decreased neutrophil influx, pulmonary levels, systemic interleukin-6 levels, and histopathology score, and it tended to decrease the pulmonary protein leak. Reducing the respiratory rate in combination with hypothermia did not reduce the parameters of the lung injury. In conclusion, hypothermia protected from lung injury in a physiologic VILI model by reducing inflammation. Decreasing the respiratory rate mildly did not enhance protection.

Differential expression of pro-inflammatory cytokines, endothelin-1 and nitric oxide synthases in the rat carotid body exposed to intermittent hypoxia

The enhanced carotid body (CB) chemosensory response to hypoxia induced by chronic intermittent hypoxia (CIH) has been attributed to oxidative stress, which is expected to increase the expression of chemosensory modulators including chemoexcitatory pro-inflammatory cytokines in the CB. Accordingly, we studied the time-course of the changes in the immunohistological expression of TNF-α, IL-1β, IL-6, ET-1, iNOS, eNOS and 3-nitrotyrosine in the CB, along with the progression of enhanced CB chemosensory responses to acute hypoxia in male Sprague-Dawley rats exposed to CIH (5%O₂, 12 times/h per 8h) for 7, 14 and 21 days. Exposure to CIH for 7 days resulted in a sustained potentiation of CB chemosensory responses to acute hypoxia, which persisted until 21 days of CIH. The chemosensory potentiation was paralleled by an increased 3-nitrotyrosine expression in the CB. On the contrary, CIH produced a transient 2-fold increase of ET-1 immunoreactivity at 7 days, a decrease in eNOS immunoreactivity, and a delayed but progressive increase of TNF-α, IL-1β and iNOS immunoreactivity, which was not associated with changes in systemic plasma levels or immune cell invasion within the CB. Thus, present results suggest that the local expression of chemosensory modulators and pro-inflammatory cytokines in the CB may have different temporal contribution to the CB chemosensory potentiation induced by CIH.

Long-term subcutaneous microdialysis sampling and qRT-PCR of MCP-1, IL-6 and IL-10 in freely-moving rats

Cytokines are important mediators of the wound healing response. However, sampling of cytokines from the interstitial fluid at a healing wound site in experimental animals is a challenge. Microdialysis sampling is an in vivo collection option for this purpose as it permits continuous sampling, while remaining contiguous with the wound microenvironment. The polymeric membrane of the microdialysis probe is a foreign material thus allowing a unique approach to sample cytokines generated during a foreign body response (FBR). The focus of these studies was to use microdialysis sampling to collect cytokines from a microdialysis probe implant site in a rat model of a FBR up to 6 days post implantation. Fluorescent bead-based immunoassays (Luminex™) were used to quantify monocyte chemoattractant protein-1 (MCP-1/CCL2), interleukin-6 (IL-6) and interleukin-10 (IL-10) in the dialysates. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was used to cross validate the protein measurements obtained via micorodialysis sampling. A histological examination of tissue was also performed to assess the progression in leukocyte extravasation and collagen deposition surrounding implanted probes. Our findings demonstrate that in vivo microdialysis sampling can be used to collect temporal concentrations of cytokines which are consistent with wound healing and the development of a FBR.

Body temperature effects on lung injury in ventilated preterm lambs

AIMS

Mechanical ventilation causes lung injury in premature infants. Hypothermia may protect against and hyperthermia may augment lung injury. We tested the effects of hypo- and hyperthermia on ventilation induced acute lung injury in preterm lambs.

METHODS

Twin sheep fetuses at 128 d GA (term 150 d) were surgically delivered and randomized to unventilated control (UVC), normothermia (38-39 degrees C) without lung injury (NTNI), or to 1 of 3 injurious ventilation groups: hypothermic (33-34 degrees C, LT), normothermic (38-39 degrees C, NT) or hyperthermic (40-41 degrees C, HT). NT, LT and HT groups had 15 min of injurious ventilation (PEEP 0 cmH(2)O, V(T) escalation to 15 mL/kg) following delivery and prior to surfactant. The animals were then gently ventilated (PEEP 5cmH(2)O, V(T) 7.5 mL/kg) for 2h 45 min. NTNI lambs received surfactant at birth prior to gentle ventilation. The lambs were then euthanized, and bronchoalveolar lavage (BAL) fluid and lung tissue were used to evaluate lung injury, inflammatory cell counts, inflammatory markers and cytokine mRNA.

RESULTS

Target temperatures were achieved by 15 min of age and maintained for 3h. All ventilated groups had increased BAL protein, lung inflammation and increased cytokine mRNA. HT animals developed acidosis, premature death, pneumothoraces, impaired lung function and increased inflammatory mRNA expression. LT animals remained clinically stable without pneumothoraces or death, had improved ventilatory efficiency and trended toward lower inflammatory mRNA expression than NT animals.

CONCLUSION

Hyperthermia exacerbated ventilator induced lung injury, while hypothermia may protect against lung injury in the preterm lamb.