Effect of core body temperature on ventilator-induced lung injury

Acute lung injury and post-cardiac arrest syndrome: a narrative review

BACKGROUND

Post-cardiac arrest syndrome (PCAS) presents a multifaceted challenge in clinical practice, characterized by severe neurological injury and high mortality rates despite advancements in management strategies. One of the important critical aspects of PCAS is post-arrest lung injury (PALI), which significantly contributes to poor outcomes. PALI arises from a complex interplay of pathophysiological mechanisms, including trauma from chest compressions, pulmonary ischemia-reperfusion (IR) injury, aspiration, and systemic inflammation. Despite its clinical significance, the pathophysiology of PALI remains incompletely understood, necessitating further investigation to optimize therapeutic approaches.

METHODS

This review comprehensively examines the existing literature to elucidate the epidemiology, pathophysiology, and therapeutic strategies for PALI. A comprehensive literature search was conducted to identify preclinical and clinical studies investigating PALI. Data from these studies were synthesized to provide a comprehensive overview of PALI and its management.

RESULTS

Epidemiological studies have highlighted the substantial prevalence of PALI in post-cardiac arrest patients, with up to 50% of survivors experiencing acute lung injury. Diagnostic imaging modalities, including chest X-rays, computed tomography, and lung ultrasound, play a crucial role in identifying PALI and assessing its severity. Pathophysiologically, PALI encompasses a spectrum of factors, including chest compression-related trauma, pulmonary IR injury, aspiration, and systemic inflammation, which collectively contribute to lung dysfunction and poor outcomes. Therapeutically, lung-protective ventilation strategies, such as low tidal volume ventilation and optimization of positive end-expiratory pressure, have emerged as cornerstone approaches in the management of PALI. Additionally, therapeutic hypothermia and emerging therapies targeting mitochondrial dysfunction hold promise in mitigating PALI-related morbidity and mortality.

CONCLUSION

PALI represents a significant clinical challenge in post-cardiac arrest care, necessitating prompt diagnosis and targeted interventions to improve outcomes. Mitochondrial-related therapies are among the novel therapeutic strategies for PALI. Further clinical research is warranted to optimize PALI management and enhance post-cardiac arrest care paradigms.

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.

Acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is an acute respiratory illness characterised by bilateral chest radiographical opacities with severe hypoxaemia due to non-cardiogenic pulmonary oedema. The COVID-19 pandemic has caused an increase in ARDS and highlighted challenges associated with this syndrome, including its unacceptably high mortality and the lack of effective pharmacotherapy. In this Seminar, we summarise current knowledge regarding ARDS epidemiology and risk factors, differential diagnosis, and evidence-based clinical management of both mechanical ventilation and supportive care, and discuss areas of controversy and ongoing research. Although the Seminar focuses on ARDS due to any cause, we also consider commonalities and distinctions of COVID-19-associated ARDS compared with ARDS from other causes.

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.

[Perioperative management for CRS and HIPEC : Anesthesiological aspects]

Cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) are therapeutic options for the treatment of intra-abdominal neoplasms. Following the resection of all visible tumor areas by CRS, microscopic tumor areas are treated with HIPEC. This procedure increases the quality of life and survival. The CRS with HIPEC is a complex surgical procedure in which the mainly younger and often otherwise healthy patients undergo several pathophysiological changes during the operation. The main concern of the anesthesiologist is the massive volume loss, volume shift and metabolic alterations. Patients with a high comorbidity should undergo preoperative optimization to reduce the perioperative morbidity and mortality especially by protracted interventions.

The Association of Fever and Antipyretic Medication With Outcomes in Mechanically Ventilated Patients: A Cohort Study

BACKGROUND

Fever is common in mechanically ventilated patients and may be uniquely detrimental in those with lung injury because of its injurious effects on pulmonary vascular permeability and alveolar epithelium. We evaluated the association of fever and antipyretic medication with mortality in mechanically ventilated emergency department (ED) patients.

METHODS

This is a retrospective cohort study of 1,264 patients requiring mechanical ventilation initiated in the ED with subsequent admission to an intensive care unit. Maximum body temperature was recorded for the first 24 h after ED admission and categorized into four categories: <37°C, 37°C to 38.2°C, 38.3°C to 39.4°C, and ≥39.5°C. The primary outcome was 28-day mortality. We conducted a planned subgroup analysis of patients with sepsis at the time of intubation. Multivariable Cox proportional hazard ratios (HRs) were used to assess the relationship between temperature, antipyretics, and mortality.

RESULTS

Multivariable Cox proportional HRs demonstrated that a maximum temperature ≥39.5°C was associated with increased mortality (adjusted hazard ratio [aHR] 1.59 [95% confidence interval, CI, 1.05-2.39]). In the subgroup of patients with sepsis, a maximum temperature of 38.3°C to 39.4°C was associated with survival (aHR 0.61 [95% CI, 0.39-0.99]). There was no difference in 28-day mortality between patients who did and did not receive antipyretic medication in either the overall cohort or the septic subgroup.

CONCLUSION

High fever (≥39.5°C) was associated with increased risk for mortality in mechanically ventilated patients. However, in patients with sepsis, moderate fever (38.3°C-39.4°C) was protective. Antipyretic medication was not associated with changes in outcome. This suggests that fever may have different implications in septic versus nonseptic mechanically ventilated patients.

[Perioperative management for CRS and HIPEC : Anesthesiological aspects]

Cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) are therapeutic options for the treatment of intra-abdominal neoplasms. Following the resection of all visible tumor areas by CRS, microscopic tumor areas are treated with HIPEC. This procedure increases the quality of life and survival. The CRS with HIPEC is a complex surgical procedure in which the mainly younger and often otherwise healthy patients undergo several pathophysiological changes during the operation. The main concern of the anesthesiologist is the massive volume loss, volume shift and metabolic alterations. Patients with a high comorbidity should undergo preoperative optimization to reduce the perioperative morbidity and mortality especially by protracted interventions.

Hypothesis: Fever control, a niche for alpha-2 agonists in the setting of septic shock and severe acute respiratory distress syndrome?

During severe septic shock and/or severe acute respiratory distress syndrome (ARDS) patients present with a limited cardio-ventilatory reserve (low cardiac output and blood pressure, low mixed venous saturation, increased lactate, low PaO2/FiO2 ratio, etc.), especially when elderly patients or co-morbidities are considered. Rescue therapies (low dose steroids, adding vasopressin to noradrenaline, proning, almitrine, NO, extracorporeal membrane oxygenation, etc.) are complex. Fever, above 38.5-39.5°C, increases both the ventilatory (high respiratory drive: large tidal volume, high respiratory rate) and the metabolic (increased O2 consumption) demands, further limiting the cardio-ventilatory reserve. Some data (case reports, uncontrolled trial, small randomized prospective trials) suggest that control of elevated body temperature ("fever control") leading to normothermia (35.5-37°C) will lower both the ventilatory and metabolic demands: fever control should simplify critical care management when limited cardio-ventilatory reserve is at stake. Usually fever control is generated by a combination of general anesthesia ("analgo-sedation", light total intravenous anesthesia), antipyretics and cooling. However general anesthesia suppresses spontaneous ventilation, making the management more complex. At variance, alpha-2 agonists (clonidine, dexmedetomidine) administered immediately following tracheal intubation and controlled mandatory ventilation, with prior optimization of volemia and atrio-ventricular conduction, will reduce metabolic demand and facilitate normothermia. Furthermore, after a rigorous control of systemic acidosis, alpha-2 agonists will allow for accelerated emergence without delirium, early spontaneous ventilation, improved cardiac output and micro-circulation, lowered vasopressor requirements and inflammation. Rigorous prospective randomized trials are needed in subsets of patients with a high fever and spiraling toward refractory septic shock and/or presenting with severe ARDS.

Time-sensitive therapeutics

Much of what we now do in Critical Care carries an air of urgency, a pressing need to discover and act, with priorities biased toward a reactive response. However, efficacy often depends not simply upon what we do, but rather on whether, when, and how persistently we intervene. The practice of medicine is based upon diagnosis, integration of multiple sources of information, keen judgment, and appropriate intervention. Timing may not be everything, as the well-known adage suggests, but in the intensive care unit (ICU) timing issues clearly deserve more attention than they are currently given. Successfully or not, the patient is continually attempting to adapt and re-adjust to acute illness, and this adaptive  process takes time. Knowing that much of what we do carries potential for unintended harm as well as benefit, the trick is to decide whether the patient is winning or losing the adaptive struggle and whether we can help. Costs of modern ICU care is enormous and the trend line shows no encouraging sign of moderation. To sharpen our effectiveness, reduce hazard, and pare cost we must learn to time our interventions, help the patient adapt, and at times withhold treatment rather than jump in on the impulse to rescue and/or to alter the natural course of disease. Indeed, much of the progress made in our discipline has resulted both from timely intervention when called for and avoidance or moderation of hazardous treatments when not. Time-sensitive ICU therapeutics requires awareness of trends in key parameters, respect for adaptive chronobiology, level-headed evaluation of the need to intervene, and awareness of the costs of disrupting a potentially constructive natural response to illness.

The Association of Fever with Total Mechanical Ventilation Time in Critically Ill Patients

This research aims to investigate the impact of fever on total mechanical ventilation time (TVT) in critically ill patients. Subgroup analysis was conducted using a previous prospective, multicenter observational study. We included mechanically ventilated patients for more than 24 hours from 10 Korean and 15 Japanese intensive care units (ICU), and recorded maximal body temperature under the support of mechanical ventilation (MAX(MV)). To assess the independent association of MAX(MV) with TVT, we used propensity-matched analysis in a total of 769 survived patients with medical or surgical admission, separately. Together with multiple linear regression analysis to evaluate the association between the severity of fever and TVT, the effect of MAX(MV) on ventilator-free days was also observed by quantile regression analysis in all subjects including non-survivors. After propensity score matching, a MAX(MV) ≥ 37.5°C was significantly associated with longer mean TVT by 5.4 days in medical admission, and by 1.2 days in surgical admission, compared to those with MAX(MV) of 36.5°C to 37.4°C. In multivariate linear regression analysis, patients with three categories of fever (MAX(MV) of 37.5°C to 38.4°C, 38.5°C to 39.4°C, and ≥ 39.5°C) sustained a significantly longer duration of TVT than those with normal range of MAX(MV) in both categories of ICU admission. A significant association between MAX(MV) and mechanical ventilator-free days was also observed in all enrolled subjects. Fever may be a detrimental factor to prolong TVT in mechanically ventilated patients. These findings suggest that fever in mechanically ventilated patients might be associated with worse mechanical ventilation outcome.

Best practice for perioperative management of patients with cytoreductive surgery and HIPEC

Due to the significantly improved outcome and quality of life of patients with different tumor entities after cytoreductive surgery (CRS) and HIPEC, there is an increasing number of centers performing CRS and HIPEC procedures. As this procedure is technically challenging with potential high morbidity and mortality, respectively, institutional experience also in the anesthetic and intensive care departments is essential for optimal treatment and prevention of adverse events. Clinical pathways have to be developed to achieve also good results in more comorbid patients with border line indications and extensive surgical procedures. The anesthesiologist has deal with relevant fluid, blood and protein losses, increased intraabdominal pressure, systemic hypo-/hyperthermia, and increased metabolic rate in patients undergoing cytoreductive surgery with HIPEC. It is of utmost importance to maintain or restore an adequate volume by aggressive substitution of intravenous fluids, which counteracts the increased fluid loss and venous capacitance during this procedure. Supplementary thoracic epidural analgesia, non-invasive ventilation, and physiotherapy are recommended to guarantee adequate pain therapy and postoperative extubation as well as fast-track concepts. Advanced hemodynamic monitoring is essential to help the anesthesiologist picking up information about the real-time fluid status of the patient. Preoperative preconditioning is mandatory in patients scheduled for HIPEC surgery and will result in improved outcome. Postoperatively, volume status optimization, early nutritional support, sufficient anticoagulation, and point of care coagulation management are essential. This is an extensive update on all relevant topics for anesthetists and intensivists dealing with CRS and HIPEC.

Mechanical Power and Development of Ventilator-induced Lung Injury

Background

The ventilator works mechanically on the lung parenchyma. The authors set out to obtain the proof of concept that ventilator-induced lung injury (VILI) depends on the mechanical power applied to the lung.

Methods

Mechanical power was defined as the function of transpulmonary pressure, tidal volume (TV), and respiratory rate. Three piglets were ventilated with a mechanical power known to be lethal (TV, 38 ml/kg; plateau pressure, 27 cm H2O; and respiratory rate, 15 breaths/min). Other groups (three piglets each) were ventilated with the same TV per kilogram and transpulmonary pressure but at the respiratory rates of 12, 9, 6, and 3 breaths/min. The authors identified a mechanical power threshold for VILI and did nine additional experiments at the respiratory rate of 35 breaths/min and mechanical power below (TV 11 ml/kg) and above (TV 22 ml/kg) the threshold.

Results

In the 15 experiments to detect the threshold for VILI, up to a mechanical power of approximately 12 J/min (respiratory rate, 9 breaths/min), the computed tomography scans showed mostly isolated densities, whereas at the mechanical power above approximately 12 J/min, all piglets developed whole-lung edema. In the nine confirmatory experiments, the five piglets ventilated above the power threshold developed VILI, but the four piglets ventilated below did not. By grouping all 24 piglets, the authors found a significant relationship between the mechanical power applied to the lung and the increase in lung weight (r2 = 0.41, P = 0.001) and lung elastance (r2 = 0.33, P &lt; 0.01) and decrease in Pao2/Fio2 (r2 = 0.40, P &lt; 0.001) at the end of the study.

Conclusion

In piglets, VILI develops if a mechanical power threshold is exceeded.

[Is control fever mandatory in severe infections?]

Temperature control during severe sepsis is currently used in intensive care and involves 66% and 70% of severe sepsis and septic shock, respectively. Nevertheless, the conclusive evidence of the benefit of such a strategy is still lacking.We might wonder, with regards to experimental works and recent noninterventional studies, about the risk of a control strategy on an ongoing infectious process, the patient's outcome, and the safety of the means implemented to obtain temperature control. On the other hand, it is also demonstrated that fever increases oxygen consumption, which may lead in some clinical situations to tissular ischemia and that fever may be associated with a deleterious focal inflammatory process. Methods to control the temperature include external and/or internal cooling and/or antipyretic medications such as paracetamol and nonsteroidal antiinflammatory drugs. In septic patients, external cooling and paracetamol are the mains means used to control temperature. Despite the uncertainties about the benefit to control or not the temperature, it could be stated that extreme temperature (hypo- or hyperthermia) should be avoided and that the benefit/risk of temperature control must be individually weighted.

Advances in the support of respiratory failure: putting all the evidence together

Considerable progress has been made recently in the understanding of how best to accomplish safe and effective ventilation of patients with acute lung injury. Mechanical and nonmechanical factors contribute to causation of ventilator-associated lung injury. Intervention timing helps determine the therapeutic efficacy and outcome, and the stage and severity of the disease process may determine the patient's vulnerability as well as an intervention's value. Reducing oxygen consumption and ventilatory demands are key to a successful strategy for respiratory support of acute respiratory distress syndrome. Results from major clinical trials can be understood against the background of the complex physiology of ventilator-induced lung injury.

Lung inhomogeneities and time course of ventilator-induced mechanical injuries

BACKGROUND

During mechanical ventilation, stress and strain may be locally multiplied in an inhomogeneous lung. The authors investigated whether, in healthy lungs, during high pressure/volume ventilation, injury begins at the interface of naturally inhomogeneous structures as visceral pleura, bronchi, vessels, and alveoli. The authors wished also to characterize the nature of the lesions (collapse vs. consolidation).

METHODS

Twelve piglets were ventilated with strain greater than 2.5 (tidal volume/end-expiratory lung volume) until whole lung edema developed. At least every 3 h, the authors acquired end-expiratory/end-inspiratory computed tomography scans to identify the site and the number of new lesions. Lung inhomogeneities and recruitability were quantified.

RESULTS

The first new densities developed after 8.4 ± 6.3 h (mean ± SD), and their number increased exponentially up to 15 ± 12 h. Afterward, they merged into full lung edema. A median of 61% (interquartile range, 57 to 76) of the lesions appeared in subpleural regions, 19% (interquartile range, 11 to 23) were peribronchial, and 19% (interquartile range, 6 to 25) were parenchymal (P < 0.0001). All the new densities were fully recruitable. Lung elastance and gas exchange deteriorated significantly after 18 ± 11 h, whereas lung edema developed after 20 ± 11 h.

CONCLUSIONS

Most of the computed tomography scan new densities developed in nonhomogeneous lung regions. The damage in this model was primarily located in the interstitial space, causing alveolar collapse and consequent high recruitability.

Body temperature and mortality in patients with acute respiratory distress syndrome

BACKGROUND

Little is known about the relationship between body temperature and outcomes in patients with acute respiratory distress syndrome (ARDS). A better understanding of this relationship may provide evidence for fever suppression or warming interventions, which are commonly applied in practice.

OBJECTIVE

To examine the relationship between body temperature and mortality in patients with ARDS.

METHODS

Secondary analysis of body temperature and mortality using data from the ARDS Network Fluid and Catheter Treatment Trial (n = 969). Body temperature at baseline and on study day 2, primary cause of ARDS, severity of illness, and 90-day mortality were analyzed by using multiple logistic regression.

RESULTS

Mean baseline temperature was 37.5°C (SD, 1.1°C; range, 27.2°C-40.7°C). At baseline, fever (≥ 38.3°C) was present in 23% and hypothermia (< 36°C) in 5% of the patients. Body temperature was a significant predictor of 90-day mortality after primary cause of ARDS and score on the Acute Physiology and Chronic Health Evaluation III were adjusted for. Higher temperature was associated with decreased mortality: for every 1°C increase in baseline temperature, the odds of death decreased by 15% (odds ratio, 0.85; 95% CI, 0.73-0.98, P = .03). When patients were divided into 5 temperature groups, mortality was lower with higher temperature (P for trend = .02).

CONCLUSIONS

Early in ARDS, fever is associated with improved survival rates. Fever in the acute phase response to lung injury and its relationship to recovery may be an important factor in determining patients' outcome and warrants further study.

Anaesthetic management of cytoreductive surgery followed by hyperthermic intrathoracic chemotherapy perfusion

BACKGROUND

Macroscopic cytoreductive surgery and hyperthermic intrathoracic chemotherapy perfusion (HITHOC) is a new multimodal approach for selected patients with primary and secondary pleural tumors, which may provide the patient with better local tumor control and increased overall survival rate.

METHODS

We present a single-center study including 20 patients undergoing cytoreductive surgery and HITHOC between September 2008 and April 2013 at the University Medical Center Regensburg, Germany. Objective of the study was to describe the perioperative, anaesthetic management with special respect to pain and complication management.

RESULTS

Anaesthesia during this procedure is characterized by increased intrathoracic airway and central venous pressure, hemodynamic alterations and the risk of systemic hypo- and hyperthermia. Securing an adequate intravascular volume is one of the primary goals to prevent decreased cardiac output as well as pulmonary edema. Transfusion of packed red blood cells (PRBC) was necessary in seven of 20 (35%) patients. Only two patients (10%) showed an impairment of coagulation in postoperative laboratory analysis. Perioperative forced diuresis is recommended to prevent postoperative renal insufficiency. Supplementary thoracic epidural analgesia in 13 patients (65%) showed a significant reduction of post-operative pain compared with peroral administration of opioid and non-opioid analgesics.

CONCLUSION

This article summarizes important experiences of the anaesthesiological and intensive care management in patients undergoing HITHOC.

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.

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.

Our favorite unproven ideas for future critical care

The future of critical care medicine will be shaped not only by the evidence-validated foundations of science, but also by innovations based on unproven and, in many cases, untested concepts and thoughtful visions of scientists and clinicians familiar with the complex problems actually faced in clinical practice. Clinical investigations and trials often lag behind collective experience and impressions, in a well-intentioned and necessary quest to determine the fallacy or validity of ongoing practice. Progress made in this way can be painfully slow, and imperfect theory may prove difficult to challenge. On occasion, an innovative paradigm shift fostered by a novel approach can reorient the forces of academic investigation toward generating an evidence base upon which such concepts and interpretations can find scientific justification. This discussion presents a selected set of ideas to improve the future practice of critical care - each having a defensible rationale, but unconfirmed validity.

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.

Death receptors mediate the adverse effects of febrile-range hyperthermia on the outcome of lipopolysaccharide-induced lung injury

We have shown that febrile-range hyperthermia enhances lung injury and mortality in mice exposed to inhaled LPS and is associated with increased TNF-α receptor activity, suppression of NF-κB activity in vitro, and increased apoptosis of alveolar epithelial cells in vivo. We hypothesized that hyperthermia enhances lung injury and mortality in vivo by a mechanism dependent on TNF receptor signaling. To test this, we exposed mice lacking the TNF-receptor family members TNFR1/R2 or Fas (TNFR1/R2(-/-) and lpr) to inhaled LPS with or without febrile-range hyperthermia. For comparison, we studied mice lacking IL-1 receptor activity (IL-1R(-/-)) to determine the role of inflammation on the effect of hyperthermia in vivo. TNFR1/R2(-/-) and lpr mice were protected from augmented alveolar permeability and mortality associated with hyperthermia, whereas IL-1R(-/-) mice were susceptible to augmented alveolar permeability but protected from mortality associated with hyperthermia. Hyperthermia decreased pulmonary concentrations of TNF-α and keratinocyte-derived chemokine after LPS in C57BL/6 mice and did not affect pulmonary inflammation but enhanced circulating markers of oxidative injury and nitric oxide metabolites. The data suggest that hyperthermia enhances lung injury by a mechanism that requires death receptor activity and is not directly associated with changes in inflammation mediated by hyperthermia. In addition, hyperthermia appears to enhance mortality by generating a systemic inflammatory response and not by a mechanism directly associated with respiratory failure. Finally, we observed that exposure to febrile-range hyperthermia converts a modest, survivable model of lung injury into a fatal syndrome associated with oxidative and nitrosative stress, similar to the systemic inflammatory response syndrome.

The effect of induced hypothermia on respiratory parameters in mechanically ventilated patients

AIM

Mild hypothermia is increasingly applied in the intensive care unit. Knowledge on the effects of hypothermia on respiratory parameters during mechanical ventilation is limited. In this retrospective study, we describe the effect of hypothermia on gas exchange in patients cooled for 24 h after a cardiac arrest.

METHODS

Respiratory parameters were derived from electronic patient files from 65 patients at the start and end of the hypothermic phase and at every centigrade increase in body temperature until normo-temperature, including tidal volume, positive end expiratory pressure (PEEP), plateau pressure, respiratory rate, exhaled CO(2) concentrations (etCO(2)) and FIO(2). Static compliance was calculated as V(T)/P(plateau)-PEEP. Dead space ventilation was calculated as (PaCO(2)-etCO(2))/PaCO(2).

RESULTS

During hypothermia, PaCO(2) decreased, at unchanged PaCO(2)-etCO(2) gap and minute ventilation. During rewarming, PaCO(2) did not change, while etCO(2) increased at unchanged minute ventilation. Dead space ventilation did not change during hypothermia, but lowered during rewarming. During hypothermia, PaO(2)/FIO(2) ratio increased at unchanged PEEP levels. Respiratory static compliance did not change during hypothermia, nor during rewarming.

CONCLUSION

Hypothermia possibly improves oxygenation and ventilation in mechanically ventilated patients. Results may accord with the hypothesis that reducing metabolism with applied hypothermia may be beneficial in patients with acute lung injury, in whom low minute ventilation results in severe hypercapnia.

Suspended animation inducer hydrogen sulfide is protective in an in vivo model of ventilator-induced lung injury

Purpose

Acute lung injury is characterized by an exaggerated inflammatory response and a high metabolic demand. Mechanical ventilation can contribute to lung injury, resulting in ventilator-induced lung injury (VILI). A suspended-animation-like state induced by hydrogen sulfide (H₂S) protects against hypoxia-induced organ injury. We hypothesized that suspended animation is protective in VILI by reducing metabolism and thereby CO₂ production, allowing for a lower respiratory rate while maintaining adequate gas exchange. Alternatively, H₂S may reduce inflammation in VILI.

Methods

In mechanically ventilated rats, VILI was created by application of 25 cmH₂O positive inspiratory pressure (PIP) and zero positive end-expiratory pressure (PEEP). Controls were lung-protective mechanically ventilated (13 cmH₂O PIP, 5 cmH₂O PEEP). H₂S donor NaHS was infused continuously; controls received saline. In separate control groups, hypothermia was induced to reproduce the H₂S-induced fall in temperature. In VILI groups, respiratory rate was adjusted to maintain normo-pH.

Results

NaHS dose-dependently and reversibly reduced body temperature, heart rate, and exhaled amount of CO₂. In VILI, NaHS reduced markers of pulmonary inflammation and improved oxygenation, an effect which was not observed after induction of deep hypothermia that paralleled the NaHS-induced fall in temperature. Both NaHS and hypothermia allowed for lower respiratory rates while maintaining gas exchange.

Conclusions

NaHS reversibly induced a hypometabolic state in anesthetized rats and protected from VILI by reducing pulmonary inflammation, an effect that was in part independent of body temperature.

Electronic supplementary material

The online version of this article (doi:10.1007/s00134-010-2022-2) contains supplementary material, which is available to authorized users.

Pretreatment with atorvastatin attenuates lung injury caused by high-stretch mechanical ventilation in an isolated rabbit lung model

OBJECTIVE

We hypothesized that pretreatment with atorvastatin improves alveolar capillary permeability and hemodynamics and, thus, confers protection against lung injury caused by high-stretch mechanical ventilation.

METHODS

Twenty-four isolated sets of normal rabbit lungs were utilized. Treated animals received atorvastatin (20 mg/kg body weight/day by mouth) for 3 days before surgery. Lungs were perfused constantly (300 mL/min) and ventilated for 1 hr with pressure-control ventilation at either 23 (high pressure; resulting in tidal volume approximately 22 mL/kg) or 11 (low pressure; tidal volume approximately 10 mL/kg) cm H2O peak inspiratory pressure and positive end-expiratory pressure of 3 cm H2O. Four groups were examined: high pressure-no statin, high pressure-statin pretreatment, low pressure-no statin, and low pressure-statin pretreatment.

RESULTS

The high-pressure-no statin group sustained more damage than the low-pressure groups. In high-pressure groups, lungs of statin-pretreated vs. no statin-pretreated animals sustained a significantly lower increase in ultrafiltration coefficient (an accurate marker of alveolar capillary permeability; high-pressure-statin pretreatment vs. high-pressure-no statin, -0.013 +/- 0.017 g/min/mm Hg/100g vs. 1.723 +/- 0.495 g/min/mm Hg/100g; p < .001), lower weight gain (i.e., less edema formation; 4.62 +/- 1.50 grams vs. 17.75 +/- 4.71 grams; p = .005), improved hemodynamics (i.e., lower increase in mean pulmonary artery pressure; 0.56 +/- 0.51 mm Hg vs. 5.62 +/- 1.52 mm Hg; p = .04), lower protein concentration in bronchoalveolar lavage fluid (p < .001), and fewer histologic lesions (p = .013). Apoptosis of lung parenchyma cells was not different (p = .97). There was no difference between low-pressure-statin pretreatment and low-pressure-no statin groups regarding these outcomes.

CONCLUSION

In this model, atorvastatin improves alveolar capillary permeability and hemodynamics and, thus, attenuates lung injury caused by high-stretch mechanical ventilation.

The role of mild hypothermia in air embolism-induced acute lung injury

BACKGROUND

Mild hypothermia has become an important treatment for ischemic brain injury. However, the role of mild hypothermia in air embolism-induced lung injury has not been explored. In this study, we investigated whether treatment with mild hypothermia before and synchronous with air infusion can attenuate acute lung injury induced by air embolism.

METHODS

In this rat model study (Sprague-Dawley rats), pulmonary air embolism was induced by venous infusion of air at a rate of 25 microL/min for 40 minutes. Control animals received no air infusion. The rats were randomly assigned to 2 control groups of normothermia (37 degrees C) and mild hypothermia (34 degrees C) and 3 air embolism groups of mild hypothermia induced before air infusion, normothermia with air infusion, and mild hypothermia induced synchronous with air infusion. At the end of the experiment, the variables of lung injury were assessed.

RESULTS

Air infusion elicited a significant increase in lung wet/dry weight ratio and protein, lactate dehydrogenase, and tumor necrosis factor-alpha concentration of the bronchoalveolar lavage fluid. Myeloperoxidase activity, neutrophil infiltration, and interstitial edema in lung tissue were also significantly increased. In addition, nuclear factor-kappaB activity was significantly increased in the lungs. Treatment with mild hypothermia before air infusion reduced increases in these variables, whereas mild hypothermia synchronous with air infusion had no significant effect on them.

CONCLUSIONS

Our study suggests that mild hypothermia before air infusion decreases air embolism-induced acute lung injury. The protective mechanism seems to be the inhibition of inflammation.

Induced hypothermia attenuates the acute lung injury in hemorrhagic shock

BACKGROUND

In previous animal studies, induction of therapeutic hypothermia (HT) in hemorrhagic shock (HS) had beneficial effects on the hemodynamic and metabolic parameters and on the survival. However, the effect of induced HT on acute lung injury (ALI) in HS has not been investigated. We sought to determine the effects of HT on ALI in HS.

METHODS

Male Sprague-Dawley rats (350-390 g; n = 8 per group) were randomized to the normothermia (NT; 36-37 degrees C) group or the moderate HT (27-30 degrees C) group and were subjected to volume-controlled (2 mL/100 g weight) HS (90 minutes) followed by 90 minutes of resuscitation. ALI score, lung malondialdehyde content, and myeloperoxidase activity were measured. The expression of glycogen synthase kinase 3beta (GSK-3beta), phosphorylated GSK-3beta, inducible nitric oxide synthase (iNOS), heat shock protein (HSP) 72, and nuclear factor-kappaB (NF-kappaB) in the lung were compared.

RESULTS

ALI score, lung malondialdehyde content, and myeloperoxidase were lower in the HT group. GSK-3beta and iNOS gene expressions in lung tissue were significantly decreased in the HT group (p < 0.05). On the contrary, the expression of phosphorylated GSK-3beta was increased in the HT group (p < 0.001). HSP 72 was expressed in the HT group but not in the NT group. The activated p65 NF-kappaB levels in lung nuclear extract were significantly lower in the NT group (p = 0.03).

CONCLUSIONS

HT attenuates HS-induced ALI in rats by the modulation of GSK, HSP 72, iNOS, and NF-kappaB.

Febrile-range hyperthermia augments lipopolysaccharide-induced lung injury by a mechanism of enhanced alveolar epithelial apoptosis

Fever is common in critically ill patients and is associated with worse clinical outcomes, including increased intensive care unit mortality. In animal models, febrile-range hyperthermia (FRH) worsens acute lung injury, but the mechanisms by which this occurs remain uncertain. We hypothesized that FRH augments the response of the alveolar epithelium to TNF-alpha receptor family signaling. We found that FRH augmented LPS-induced lung injury and increased LPS-induced mortality in mice. At 24 h, animals exposed to hyperthermia and LPS had significant increases in alveolar permeability without changes in inflammatory cells in bronchoalveolar lavage fluid or lung tissue as compared with animals exposed to LPS alone. The increase in alveolar permeability was associated with an increase in alveolar epithelial apoptosis and was attenuated by caspase inhibition with zVAD.fmk. At 48 h, the animals exposed to hyperthermia and LPS had an enhanced lung inflammatory response. In murine lung epithelial cell lines (MLE-15, LA-4) and in primary type II alveolar epithelial cells, FRH enhanced apoptosis in response to TNF-alpha but not Fas ligand. The increase in apoptosis was caspase-8 dependent and associated with suppression of NF-kappaB activity. The FRH-associated NF-kappaB suppression was not associated with persistence of IkappaB-alpha, suggesting that FRH-mediated suppression of NF-kappaB occurs by means other than alteration of IkappaB-alpha kinetics. These data show for the first time that FRH promotes lung injury in part by increasing lung epithelial apoptosis. The enhanced apoptotic response might relate to FRH-mediated suppression of NF-kappaB activity in the alveolar epithelium with a resultant increase in susceptibility to TNF-alpha-mediated cell death.

Short-term administration of a high oxygen concentration is not injurious in an ex-vivo rabbit model of ventilator-induced lung injury

BACKGROUND

Mechanical ventilation and administration of a high oxygen concentration are simultaneously used in the management of respiratory failure. We conducted this study to evaluate the effect of a high inspired oxygen concentration on ventilator-induced lung injury.

METHODS

Forty sets of isolated/perfused rabbit lungs were randomized for 60 min of pressure-control ventilation at a plateau inspiratory pressure of 25 or 15 cm H(2)O and positive end-expiratory pressure of 3 cm H(2)O while receiving 100% or 21% O(2). The temperature, pH, and partial pressure of CO(2) in the perfusate were maintained the same in all groups (n = 10 for each group). The outcome measures used to assess lung injury included: the change in weight gain and ultrafiltration coefficient, the frequency of vascular failure, the histological lesions and the concentration of tumor necrosis factor-alpha and malondialdehyde in the bronchoalveolar lavage fluid.

RESULTS

The two groups ventilated at the higher inspiratory pressure/tidal volume experienced greater weight gain and increases in the ultrafiltration coefficient, more frequently suffered vascular failure, and presented higher composite scores of histological damage than the two groups ventilated at the lower inspiratory pressure/tidal volume. Hyperoxia was not found to further increase any of the monitored markers of lung injury. No difference was noticed among the four experimental groups in the alveolar lavage fluid levels of tumor necrosis factor-alpha or malondialdehyde.

CONCLUSIONS

These findings suggest that short-term administration of a high oxygen concentration is not a major determinant of ventilator-induced lung injury in this experimental model.

High and low body temperature during the initiation of ventilation for near-term lambs

AIMS

Recent literature suggests hypothermia may protect against lung injury. We evaluated body temperature as a variable in lung inflammation due to oxygenation and mechanical ventilation following delivery of near-term lambs.

METHODS

Twin fetuses were randomized prior to delivery at 140 d GA (term 150 d): unventilated controls, normothermic ventilated with room air, normothermic ventilated with 100% oxygen, low temperature ventilated (target 35 degrees C) with 100% oxygen, and high temperature (target 40 degrees C) with 100% oxygen. Lambs were intubated for gentle mechanical ventilation (tidal volume 7-8ml/kg). Temperature targeting was with radiant warmers and plastic wrap for normothermia, with heat lamps for hyperthermia, and with ice packs for hypothermia. Lambs were euthanized after 2h mechanical ventilation. Post-mortem, bronchoalveolar lavage fluid and lung tissue samples were evaluated for inflammatory responses by measuring inflammatory cell counts, protein, myeloperoxidase, protein carbonyl, and pro-inflammatory cytokine mRNA.

RESULTS

Target temperatures were achieved by 30min of age and tightly maintained for the 2h study. There were no differences in physiologic variables among groups except those directly resulting from study protocol-PaO2 from air vs. 100% oxygen and body temperature. Indicators of inflammation increased similarly in all ventilated groups compared to unventilated controls.

CONCLUSION

Moderate hyperthermia or hypothermia did not affect lung injury responses to the initiation of ventilation at birth in near-term lambs.

Manipulations of core temperatures in ischemia-reperfusion lung injury in rabbits

The present study was designed to determine the effect of various core temperatures on acute lung injury induced by ischemia-reperfusion (I/R) in our isolated rabbit lung model. Typical acute lung injury was successfully induced by 30 min of ischemia followed by 90 min of reperfusion observation. The I/R elicited a significant increase in pulmonary arterial pressure, microvascular permeability (measured by using the capillary filtration coefficient, Kfc), Delta Kfc ratio, lung weight gain and the protein concentration of the bronchoalveolar lavage fluid. Mild hypothermia significantly attenuated acute lung injury induced by I/R, all parameters having decreased significantly (p<0.05); conversely, mild hyperthermia did not further exacerbate acute lung injury. These experimental data suggest that mild hypothermia significantly ameliorated acute lung injury induced by ischemia-reperfusion in rabbits.

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.

Modulating cofactors of acute lung injury 2005–2006: any closer to ‘prime time’?

PURPOSE OF REVIEW

Considerable progress has recently been made in understanding the modulation of acute lung injury by cofactors that are not traditionally considered 'pulmonary' in nature. We will review findings regarding some of these extrapulmonary cofactors, focusing on those most readily manipulated in the current clinical setting.

RECENT FINDINGS

Recent studies have demonstrated that limiting fluid administration in the setting of acute lung injury might improve surrogate outcomes; that hypercapnea and induced hypothermia might protect against or attenuate acute lung injury; that corticosteroids can improve mechanics but not mortality in acute respiratory distress syndrome; a potential role for concomitant administration of colloid and diuretic in acute lung injury; and the potential benefits of inhaled beta agonists in acute lung injury.

SUMMARY

There are a number of simple, low-cost, and rapidly deployable approaches to reducing the severity of acute lung injury that are not directly pulmonary in origin. These interventions could be rapidly implemented in any intensive care unit, once evidence for their efficacy and safety is adequate.

Serum procalcitonin level and leukocyte antisedimentation rate as early predictors of respiratory dysfunction after oesophageal tumour resection

Introduction

Postoperative care after oesophageal tumour resection holds a high risk of respiratory complications. We therefore aimed to determine the value of systemic inflammatory markers in predicting arterial hypoxaemia as the earliest sign of developing lung injury after oesophageal tumour resection.

Methods

In a prospective observational study, 33 consecutive patients were observed for three days (T1–T3) after admission (T0) to an intensive care unit following oesophageal tumour resection. The daily highest values of the heart rate, axillary temperature, leukocyte count and PaCO₂ were recorded. Serum C-reactive protein and procalcitonin concentrations and the leukocyte antisedimentation rate (LAR) were determined at T1 and T2. Respiratory function was monitored 6-hourly measurement of the PaO₂/FIO₂ ratio, and the lowest value was recorded at T3. Patients were categorised as normoxaemic or hypoxaemic using the cutoff value of 300 mmHg for PaO₂/FIO₂.

Results

Seventeen out of 33 patients were classified as hypoxaemic and 16 patients as normoxaemic at T3. Increases of temperature at T0 and of the procalcitonin and LAR values at T2 were predictive of hypoxaemia at T3 (P < 0.05, P < 0.01 and P < 0.001, respectively). The area under the receiver-operating characteristic curve was 0.65 for the temperature at T0, which was significantly lower than that for the procalcitonin level at T2 (0.83; 95% confidence interval, 0.69–0.97; P < 0.01) and that for LAR at T2 (0.89; 95% confidence interval, 0.77–1.00; P < 0.001).

Conclusion

These results suggest that an elevated LAR (>15%) and an elevated procalcitonin concentration (>2.5 ng/ml) measured on the second postoperative day can predict next-day arterial hypoxaemia (PaO₂/FIO₂ < 300 mmHg) after oesophageal tumour resection.

Limitations of clinical trials in acute lung injury and acute respiratory distress syndrome

PURPOSE OF REVIEW

To review the challenges and limitations of randomized clinical trials in acute respiratory distress syndrome, with special emphasis on those pertaining to ventilatory management.

RECENT FINDINGS

Superbly executed randomized trials of ventilatory strategy have garnered deserved attention from the critical care community and yet have illustrated the limitations of our current approach to clinical research in this area. Inexact definitions, incomplete mechanistic understanding of complex pathophysiology, inappropriate outcome variables, diverse therapeutic environments, lengthy data acquisition time and ethical constraints on trial design limit the applicability of randomized control trial methodology to acute respiratory distress syndrome and acute lung injury. As yet, clinical practice does not seem to have been greatly impacted by the implications of completed randomized controlled trials per se. Recent issues, both ethical and interpretive, regarding control group participants have raised troubling and theoretically important issues that are yet to be fully resolved.

SUMMARY

Without tighter definitions of the condition under treatment, more specific targets for interventions to act upon, stratification that recognizes key interactive elements, and cointerventions based on better mechanistic understanding, randomized controlled trials of new drugs, ventilatory strategy, and other management approaches in acute respiratory distress syndrome are likely to remain a blunt instrument for investigation. As valuable as they are for calling important therapeutic principles to attention and for helping to suggest general guidelines for care, the limitations of randomized controlled trials for treating the individual with acute respiratory distress syndrome must be acknowledged.

Effects of drotrecogin alfa activated on microcirculatory alterations in patients with severe sepsis

OBJECTIVE

Microvascular alterations may play an important role in the development of sepsis-induced organ dysfunction. Drotrecogin alfa activated (DAA) improves outcome in patients with severe sepsis, but its precise mechanism of action is not entirely defined. We investigated whether DAA can influence microcirculatory alterations in patients with severe sepsis.

DESIGN

Prospective, nonrandomized study.

SETTING

A 31-bed, medico-surgical intensive care unit of a university hospital.

PATIENTS

Forty adult patients with severe sepsis who met the EU criteria for DAA administration.

INTERVENTIONS

Twenty patients received the drug (DAA) and 20 had a contraindication to DAA administration (control).

MEASUREMENTS AND MAIN RESULTS

An orthogonal polarization spectral imaging technique was used to visualize the sublingual microcirculation. In all patients, measurements were obtained at baseline, 4 hrs later, and then every 24 hrs for up to 7 days. In patients receiving DAA, measurements were also obtained just before and 4 hrs after the end of DAA infusion. The two groups were well matched for severity of disease, number of failing organs, and the degree of microvascular alterations at baseline. The proportion of perfused capillaries increased in the DAA treated patients already at 4 hrs (from 64% [51-80%] to 84% [71-88%], p < .01) but not in the control group (from 67% [59-76%] to 68% [61-71%], p = not significant). Microvascular perfusion decreased transiently at the end of DAA infusion. The improvement in microvascular blood flow was associated with a more rapid resolution of hyperlactatemia.

CONCLUSIONS

DAA administration rapidly improves sepsis-induced microvascular alterations, whereas its cessation is associated with a transient deterioration.

Whole-body moderate hypothermia confers protection from wood smoke-induced acute lung injury in rats: The therapeutic window*

OBJECTIVE

Toxic smoke inhalation causes acute lung injury. We studied the efficacy and therapeutic window of whole-body hypothermia in rats with wood smoke-induced acute lung injury.

DESIGN

Randomized, controlled study.

SETTING

Research laboratory.

SUBJECTS

Anesthetized, paralyzed, and artificially ventilated rats (n = 100) were used.

INTERVENTIONS

Air or wood smoke (30 breaths) was delivered into the lung using a respirator. Immediately after challenge, the rat's colonic temperature was kept a) 37 degrees C (normothermia, NT) for 1 (NT-1-Air and NT-1-Smoke), 2.5 (NT-2.5-Air and NT-2.5-Smoke), or 5 hrs (NT-5-Air and NT-5-Smoke) in six groups; b) 30 degrees C (hypothermia, HT) for 2.5 (HT-2.5-Smoke) or 5 hrs (HT-5-Air and HT-5-Smoke) in three groups; c) 30 degrees C for the first 2.5 hrs followed by 37 degrees C for another 2.5 hrs (HT-NT-5-Smoke) in one group; or d) 37 degrees C for the first 2.5 hrs followed by 30 degrees C for another 2.5 hrs (NT-HT-5-Smoke) in on group.

MEASUREMENTS AND MAIN RESULTS

Various acute lung injury indexes were assessed at 1, 2.5, or 5 hrs after challenge. In the air group, whole-body hypothermia did not affect the level of lung lipid peroxidation and the amount of proteins, total and differential cell counts, and concentrations of tumor necrosis factor-alpha and interleukin-1beta in bronchoalveolar lavage fluid. In the smoke groups, these acute lung injury indexes were increased showing that NT-5-Smoke > NT-2.5-Smoke > NT-1-Smoke. Whole-body hypothermia prevented increases in these acute lung injury indexes in the HT-2.5-Smoke and HT-5-Smoke groups. The efficacy of whole-body hypothermia in the HT-NT-5-Smoke group was superior to that in the NT-HT-5-Smoke group and similar to that in the HT-5-Smoke group. Whole-body hypothermia also alleviated smoke-induced poor gas exchange, pulmonary edema, and pathohistologic injurious signs.

CONCLUSIONS

Whole-body hypothermia confers protection from wood smoke-induced acute lung injury in rats by suppressing oxidant bronchoalveolar damage and pulmonary inflammation. Early and short-period (2 hrs) application of whole-body hypothermia provides favorable therapeutic effects.

The Last 100 Years of Sepsis

Over the last 100 years, huge advances have been made in the field of sepsis in terms of pathophysiology, epidemiology, diagnosis, monitoring, and therapeutics. Here, we offer our perspective of the key changes and current situation in each of these areas. Despite these changes, mortality rates remain unacceptably high and continued progress, particularly in early diagnosis and therapy, is urgently needed.

Induced hypothermia as a new approach to lung rest for the acutely injured lung*

OBJECTIVE

To investigate whether low-frequency ventilation during hypothermia could attenuate lung injury associated with endotoxin and mechanical ventilation.

DESIGN

: Experimental animal study.

SETTING

University-affiliated animal laboratory.

SUBJECTS

Forty-eight Sprague-Dawley rats.

INTERVENTIONS

: Lipopolysaccharide was administered to rats intratracheally to induce acute lung injury. After 1 hr of this treatment, animals were assigned to normothermia-only (NO, rectal temperature 37 degrees C, ventilatory frequency 90/min), normothermia-lung rest (NR, 37 degrees C, 45/min), hypothermia-only (HO, 27 degrees C, 90/min), or hypothermia-lung rest (HR, 27 degrees C, 45/min). After 1 hr of injurious ventilation, the lungs of the rats were removed for bronchoalveolar lavage and histologic examination.

MEASUREMENTS AND MAIN RESULTS

Compared with the normothermia groups (NO, NR), the neutrophil counts (per milliliter) (NO, 7708 +/- 5704; NR, 10,479 +/- 11,152; HO, 1638 +/- 955; HR, 805 +/- 591) and interleukin-1beta levels (pg/mL) (1180 +/- 439, 1081 +/- 652, 620 +/- 426, 420 +/- 182, respectively) in the bronchoalveolar lavage fluid, the wet-to-dry lung weight ratios (6.0 +/- 0.4, 5.7 +/- 0.4, 5.6 +/- 0.2, 5.2 +/- 0.2, respectively), and histologic acute lung injury scores (8.3 +/- 2.7, 10.4 +/- 3.1, 3.5 +/- 2.1, 3.1 +/- 2.2, respectively) of the hypothermia groups (HO, HR) were lower (all p < .001). Compared with the HO group, the neutrophil counts and protein content (HO, 1367 +/- 490 mug/mL vs. HR, 831 +/- 369 mug/mL) in the bronchoalveolar lavage fluid, the serum lactate dehydrogenase levels (units/mL) (9.1 +/- 3.6 vs. 5.3 +/- 1.5), and the wet-to-dry lung weight ratios of the HR group were lower (all p < .05).

CONCLUSIONS

Reduction of ventilatory frequency in conjunction with hypothermia attenuated many variables of acute lung injury in rats. Use of hypothermia could be exploited as a new approach to lung rest for the ventilatory management of the acutely injured lung.

Febrile-range hyperthermia augments neutrophil accumulation and enhances lung injury in experimental gram-negative bacterial pneumonia

We previously demonstrated that exposure to febrile-range hyperthermia (FRH) accelerates pathogen clearance and increases survival in murine experimental Klebsiella pneumoniae peritonitis. However, FRH accelerates lethal lung injury in a mouse model of pulmonary oxygen toxicity, suggesting that the lung may be particularly susceptible to injurious effects of FRH. In the present study, we tested the hypothesis that, in contrast with the salutary effect of FRH in Gram-negative peritonitis, FRH would be detrimental in multilobar Gram-negative pneumonia. Using a conscious, temperature-clamped mouse model and intratracheal inoculation with K. pneumoniae Caroli strain, we showed that FRH tended to reduce survival despite reducing the 3 day-postinoculation pulmonary pathogen burden by 400-fold. We showed that antibiotic treatment rescued the euthermic mice, but did not reduce lethality in the FRH mice. Using an intratracheal bacterial endotoxin LPS challenge model, we found that the reduced survival in FRH-treated mice was accompanied by increased pulmonary vascular endothelial injury, enhanced pulmonary accumulation of neutrophils, increased levels of IL-1beta, MIP-2/CXCL213, GM-CSF, and KC/CXCL1 in the bronchoalveolar lavage fluid, and bronchiolar epithelial necrosis. These results suggest that FRH enhances innate host defense against infection, in part, by augmenting polymorphonuclear cell delivery to the site of infection. The ultimate effect of FRH is determined by the balance between accelerated pathogen clearance and collateral tissue injury, which is determined, in part, by the site of infection.

Effect of excessive environmental heat on core temperature in critically ill patients. An observational study during the 2003 European heat wave

BACKGROUND

The primary goal of this study was to investigate the relation between the core temperature of critically ill patients and hot ambient temperatures during a heat wave. The second goal was to evaluate the impact of such a heat wave on the number of microbiological tests ordered.

METHODS

During a heat wave, from August 3 to 22, 2003, we conducted an observational study in the surgical intensive care unit (ICU) of a French hospital that had no air-conditioning at the time. The core temperature of 18 critically ill patients and 36 health-care workers was measured with a non-contact, infrared tympanic membrane thermometer. The association between the core body temperature in infected and non-infected critically ill patients and the staff members, and the ambient temperature in the ICU was analysed using linear regression. The number of microbiological tests ordered was also recorded and compared with the same period in the previous year.

RESULTS

The equation of the regression line for infected critically ill patients was: core temperature=33.5+0.16 x ambient temperature (R(2)=0.53; P<0.0001). The regression line was steeper than that for the non-infected patients (0.077; P<0.0001). The slopes of the regression lines for non-infected and control patients were similar (P=0.20). More blood cultures were carried out during the heat wave than at the same period during the year 2002 (4.80 blood cultures per 1000 patient-days vs 2.47 per 1000 patient-days; P=0.0006).

CONCLUSION

During a sustained high ambient temperature, hyperthermia can occur in critically ill infected patients and to a lesser extent in non-infected patients and health-care workers. The number of blood cultures requested rises substantially, leading to increased costs. Installation of air-conditioning is therefore recommended.