Effect of speed of rewarming and administration of anti-inflammatory or anti-oxidant agents on acute lung injury in an intestinal ischemia model treated with therapeutic hypothermia

Microcirculatory effects of rewarming in experimental hemorrhagic shock

BACKGROUND

Rewarming is a recommended therapy during the resuscitation of hypothermic patients with hemorrhagic shock. In experimental models, however, it increases inflammatory response and mortality. Although microcirculation is potential target of inflammation, the microvascular effects of rewarming during the resuscitation of hemorrhagic shock have not been studied. Our goal was to assess the systemic and microcirculatory effects of an increase in core temperature (T°) during the retransfusion of hemorrhagic shock in sheep. Our hypothesis was that rewarming could hamper microcirculation.

METHODS

In anesthetized and mechanically ventilated sheep, we measured systemic, intestinal, and renal hemodynamics and oxygen transport. O₂ consumption (VO₂) and respiratory quotient were measured by indirect calorimetry. Cortical renal, intestinal villi and sublingual microcirculation were assessed by IDF-videomicroscopy. After basal measurements, hemorrhagic shock was induced and T° was reduced to ~33 °C. After 1 h of shock and hypothermia, blood was retransfused and Ringer lactate solution was administered to prevent arterial hypotension. In the control group (n = 12), T° was not modified, while in the intervention (rewarming) group, it was elevated ~3 °C. Measurements were repeated after 1 h.

RESULTS

During shock, both groups showed similar systemic and microvascular derangements. After retransfusion, VO₂ remained decreased compared to baseline in both groups, but was lower in the control compared to the rewarming group. Perfused vascular density has a similar behavior in both groups. Compared to baseline, it remained reduced in peritubular (control vs. rewarming group, 13.8 [8.7-17.5] vs. 15.7 [10.1-17.9] mm/mm², PNS) and villi capillaries (14.7 [13.6-16.8] vs. 16.3 [14.2-16.9] mm/mm², PNS), and normalized in sublingual mucosa (19.1 [16.0-20.3] vs. 16.6 [14.7-17.2] mm/mm², PNS).

CONCLUSIONS

This is the first experimental study assessing the effect of rewarming on systemic, regional, and microcirculatory perfusion in hypothermic hemorrhagic shock. We found that a 3 °C increase in T° neither improved nor impaired the microvascular alterations that persisted after retransfusion. In addition, sublingual mucosa was less susceptible to reperfusion injury than villi and renal microcirculation.

Hypothermia-rewarming: A Double-edged sword?

Hypothermia is a condition in which the body's core temperature drops below 35.0 °C. Hypothermia is the opposite of hyperthermia, which the metabolism and body functions are abnormal. Severe hypothermia is a life-threatening problem that may cause atrial and ventricular dysrhythmias, coagulopathy, cardiac, and central nervous system depression. What is worse, it is fatal when untreated or treated improperly. Accidental deaths due to hypothermia resulting from immersion in cold water, especially involving naval fighters and maritime victims have occurred continually in the past years. Currently, the treatment of hypothermia has become a research focus. Rewarming is the only approach that should be considered for hypothermia treatment. However, the treatment is of low efficiency, and few active rewarming cases have been reported. It is well known that timely reperfusion is the best way to save the lives of patients with ischemia. Similarly, reoxygenation is effective for hypoxia. However, several studies have identified that improper reperfusion of ischemic tissues and reoxygenation of hypoxic tissues give rise to further injury. Analogically, this study attempts to propose the hypothesis that hypothermia-rewarming injury may also exist. When suffered from hypothermia, both the blood circulation and the oxygen supply in the body will be affected in a deficient state, an injury may also appear in the improper rewarming process. In a word, hypothermia-rewarming may be a double-edged sword.

Association between rewarming duration and neurological outcome in out-of-hospital cardiac arrest patients receiving therapeutic hypothermia

AIM

The European Resuscitation Council guidelines recommend a slow rate of rewarming of 0.25 °C/h-0.5 °C/h for out-of-hospital cardiac arrest (OHCA) patients receiving therapeutic hypothermia (TH). Conversely, a very slow rewarming of 1 °C/day is generally applied in Japan. The rewarming duration ranged from less than 24 h up to more than 50 h. No randomized control trials have examined the optimal rewarming speed for TH in OHCA patients. Therefore, we examined the association between the rewarming duration and neurological outcomes in OHCA patients who received TH.

METHODS

This study was a secondary analysis of the Japanese Population-based Utstein-style study with defibrillation and basic/advanced Life Support Education and implementation-Hypothermia (J-PULSE-HYPO) study registry, a multicenter prospective cohort study. Patients suffering from OHCA who received TH (target temperature, 34 °C) after the return of spontaneous circulation from 2005 to 2011 in 14 hospitals throughout Japan were enrolled. The rewarming duration was defined as the time from the beginning of rewarming at a target temperature of 34 °C until reaching 36 °C. The primary outcome was an unfavorable neurological outcome at hospital discharge, i.e., a cerebral performance category of 3-5.

RESULTS

The J-PULSE-HYPO study enrolled 452 OHCA patients. Of these, 328 were analyzed; 79.9% survived to hospital discharge, of which 56.4% had a favorable neurological outcome. Multivariable logistic regression analysis revealed that the rewarming duration was independently associated with unfavorable neurological outcomes [odds ratio (per 5 h), 0.89; 95% confidence interval, 0.79-0.99; p =  0.032].

CONCLUSION

A longer rewarming duration was significantly associated with and was an independent predictor of favorable neurological outcomes in OHCA patients who received TH.

Is Therapeutic Hypothermia for Acute Respiratory Distress Syndrome the Future?

INTRODUCTION

Severe acute respiratory distress syndrome (ARDS) has a high mortality, and there is limited knowledge about management of severe ARDS refractory to standard therapy. Early evidence suggests that therapeutic hypothermia (TH) could be a viable treatment for acute respiratory failure. We present 2 cases where TH was successfully used to manage refractory ARDS on extracorporeal membrane oxygenation (ECMO) and a review of the literature around TH and acute respiratory failure.

RESULTS

We present 2 cases of ARDS secondary to H1N1 influenza and human metapneumovirus. Both patients were treated with the current evidence-based therapy for ARDS. Venovenous ECMO was used in both patients for refractory hypoxemia. Therapeutic hypothermia was applied for 24 hours with improved oxygenation. We did a review of the literature summarizing 38 patients in 10 publications where TH was successfully utilized in the treatment of acute respiratory failure.

CONCLUSION

Therapeutic hypothermia may be a viable salvage therapy for ARDS refractory to the current evidence-based therapy but needs further evaluation.

Rapid rewarming after therapeutic hypothermia worsens outcome in sepsis

OBJECTIVE

This study was performed to investigate the effect of the rewarming rate on survival and acute lung injury in sepsis.

METHODS

Male Sprague-Dawley rats underwent cecal ligation and incision. After 1 hour of sepsis induction, normothermia (37°C±0.5°C, NT group) or hypothermia (32°C±0.5°C) was induced. Hypothermia was maintained for 4 hours and rats were divided into two groups according to the rewarming rate: RW1 group, 1 hour of rewarming; and RW2 group, 2 hours of rewarming. In the survival study, rats were observed for 12 hours after sepsis induction (n=6 per group). In the second experiment, rats were sacrificed 7 hours after sepsis induction, and lung tissues and plasma were harvested (n=10 per group).

RESULTS

In the survival study, the RW2 group survived longer than the RW1 group (P<0.05), but the RW1 and NT groups showed no significant difference in survival duration (P>0.05). The histological lung injury score and malondialdehyde concentrations in the lung tissues were significantly higher in the RW1 group than in the RW2 group (P<0.05). Plasma interleukin (IL)-6 concentration and the ratio of IL-6 to IL-10 were higher in the RW1 group than in the RW2 group (P<0.05).

CONCLUSION

Rapid rewarming after therapeutic hypothermia results in a shorter survival period and acute lung injury in sepsis, which could be associated with the inflammatory responses.

Effect of therapeutic hypothermia according to severity of sepsis in a septic rat model

AIM OF STUDY

The effects of therapeutic hypothermia (HT) during experimental sepsis may be influenced by disease severity. We experimentally investigated the effect of therapeutic HT on varying disease severity in a septic rat model.

MATERIALS AND METHODS

An adult male Sprague-Dawley rat model of intra-abdominal sepsis was used. To modify the disease severity, we used two different models; a moderate severe sepsis model (MSSM) and a severe septic shock model (SSSM). All rats were randomized to a hypothermia group (HT, 30-32°C) or a normothermia group (NT, 36-38°C) 1h after sepsis induction in each model. HT was maintained for 4h and rewarming was conducted for 2h. Survival time was recorded for up to 12h in the SSSM group and 24h in the MSSM group. Acute lung and liver injury, cytokine, and malondialdehyde (MDA) levels were investigated 7h after sepsis induction. Hemodynamic profiles were also evaluated.

RESULTS

In the SSSM, there were survival benefits and reduced acute lung and liver injury with therapeutic HT. Therapeutic HT was also associated with significantly reduced levels of plasma interleukin-6 and tissue malondialdehyde (MDA) levels in the liver and lung compared with the NT group in the SSSM. There was a tendency for the mean arterial pressure to be higher in the HT group compared to the NT group in the SSSM. In MSSM, however, there was no such beneficial effect.

CONCLUSION

In this rat model of severe septic shock, therapeutic HT showed beneficial effects. In contrast, therapeutic HT did not show protective effect in the moderate sepsis model.

Pulmonary impact of N-acetylcysteine in a controlled hemorrhagic shock model in rats

BACKGROUND

Experimental hemorrhagic shock (HS) is based on controlling bleeding and the treatment of fluid resuscitation to restore tissue oxygenation and perfusion. The HS could promote ischemia/reperfusion injury, which induces a general exacerbation of the inflammatory process, initially compromising the lungs. N-acetylcysteine (NAC), an antioxidant, may attenuate ischemia/reperfusion injury. This study evaluated the effect of NAC in association with fluid resuscitation on pulmonary injury in a controlled HS model in rats.

METHODS

Male Wistar rats were submitted to controlled HS (mean arterial pressure of 35 mm Hg for 60 min). Two groups were constituted according to resuscitation solution administered: RLG (Ringer's lactate solution) and RLG+NAC (Ringer's lactate in association with 150 mg/kg NAC. A control group was submitted to catheterization only. After 120 min of resuscitation, bronchoalveolar lavage was performed to assess intra-alveolar cell infiltration and pulmonary tissue was collected for assessment of malondialdehyde, interleukin 6, and interleukin 10 and histopathology.

RESULTS

Compared with the RLG group, the RLG+NAC group showed lower bronchoalveolar lavage inflammatory cell numbers, lower interstitial inflammatory infiltration in pulmonary parenchyma, and lower malondialdehyde concentration. However, tissue cytokine (interleukin 6 and interleukin 10) expression levels were similar.

CONCLUSION

N-acetylcysteine was associated with fluid resuscitation-attenuated oxidative stress and inflammatory cell infiltration in pulmonary parenchyma. N-acetylcysteine did not modify cytokine expression.

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.

Controlled mild hypothermia prolongs survival in a rat model of large scald burns

OBJECTIVES

Early surface cooling of burns reduces pain and depth of injury and improves healing. However, there are concerns that cooling of large burns may result in hypothermia and worsen outcomes. In contrast, controlled mild hypothermia improves outcomes after cardiac arrest and traumatic brain injury. The authors hypothesized that controlled mild hypothermia would prolong survival in a rat model of large scald burns.

METHODS

Thirty-six Sprague-Dawley rats (250-300 g) were anesthetized with 40 mg/kg intramuscular ketamine and 5 mg/kg xylazine, with supplemental inhalational isoflurane as needed. A single full-thickness scald burn covering 40% of total body surface area was created on each of the rats using a Mason-Walker template placed in boiling water (100 °C) for a period of 10 seconds. The rats were then randomized to hypothermia (n = 18) or no hypothermia (n = 18). Core body temperature was continuously monitored with a rectal temperature probe. In the experimental group, mild hypothermia was induced by applying ice packs over the prone rats until their rectal temperature was reduced by 2 °C for a period of 2 hours. After 2 hours of hypothermia, the rats were rewarmed back to their baseline temperature with a heating pad. The control rats were not cooled. The rats were monitored until death or for a period of 7 days, whichever was greater. The primary outcome was time to death. The difference in survival between the groups was determined using Kaplan-Meier analysis and the log-rank test.

RESULTS

  Hypothermia was induced in all experimental rats within a mean of 22 minutes (95% confidence interval [CI] = 17 to 27). The numbers of nonhypothermic and hypothermic rats that were dead at each time point were as follows: 2 hours, five versus none; 18 hours, 16 versus five; 24 hours, 18 versus eight; and 48 hours, 18 versus 13 (p = 0.05). There were no additional deaths after 48 hours. The mean time to survival of the hypothermic rats was significantly greater than that of the nonhypothermic rats (p < 0.001).

CONCLUSIONS

Induction of brief, mild hypothermia prolongs survival and increases the survival rate in nonresuscitated rats with large scald burns.

Therapeutic hypothermia attenuates acute lung injury in paraquat intoxication in rats

AIM OF THE STUDY

Paraquat intoxication induces acute lung injury and numerous fatalities have been reported. The mechanism of toxic effect of paraquat is oxidative injury and inflammation. Therapeutic hypothermia has been known to have antioxidant and anti-inflammatory effects. This study was designed to evaluate the effect of therapeutic hypothermia on paraquat intoxication.

METHODS

Male Sprague-Dawley rats were given 50 mg/kg of paraquat intraperitoneally and divided into the normothermia (36-38°C) group and the hypothermia (30-32°C) group after 1h of paraquat administration. The hypothermia group underwent 2 h of hypothermia followed by 2 h of rewarming. In the survival study, mortality was observed for 24 h after paraquat administration. An in the second experiment, lung tissues and plasma were harvested at 6 h after paraquat administration.

RESULTS

The 12 h survival rate was significantly higher in the hypothermia group than in the normothermia group (100% vs. 50%, p<0.05), but survival rates for 24 h were not different. Acute lung injury score was lower in the hypothermia group than in the normothermia group (p<0.05). Thmalondialdehyde contents of lung tissues, plasma interleukin-6 and nitrite/nitrate concentrations were significantly decreased in the HT group compared to the NT group (p<0.05).

CONCLUSION

Therapeutic hypothermia delayed early mortality and attenuated acute lung injury in paraquat intoxication.