Local Hypothermia during Early Reperfusion Protects Skeletal Muscle from Ischemia-Reperfusion Injury:

Effects of upper limb ischemia-reperfusion on regional oxidative stress during aortic surgery with moderate hypothermia

INTRODUCTION

This study aims to evaluate the effect of acute, iatrogenic right arm ischemia and reperfusion (I/R) due to right axillary cannulation on regional oxidative stress using tissue perfusion markers such as central venous oxygen saturation, lactate, the difference between central venous and arterial CO₂ pressure, near-infrared spectroscopy (NIRS) measurements, and biomarkers like sialic acid, malondialdehyde, advanced oxidative protein products in aortic surgery with moderate hypothermia.

METHODS

Adult patients undergoing ascending aorta repair with antegrade cerebral perfusion via the axillary artery participated. Blood samples were collected from the internal jugular vein, right arm cubital vein, and left arm cubital vein, and analysis was performed at intraoperative time points.

RESULTS

Right-arm venous oxygen saturation levels are significantly lower than left arm and central venous, as expected in iatrogenic ischemia. Right arm lactate levels are significantly higher. Somatic right arm NIRS values are significantly lower than somatic left arm. There are no significant differences for biomarkers throughout the time points.

CONCLUSIONS

We have concluded that well-known markers reflect the results of ischemia-reperfusion more rapidly, and are more valuable than novel biomarkers. NIRS is a promising monitor in terms of providing information about tissue oxygenation. Oxidative stress biomarkers do not change quickly enough to give useful information in a short enough period of time; moreover, their costs are high and laboratory studies take time. Although axillary cannulation is controlled limb ischemia, the local effects of I/R did not completely normalize at the end of the surgery, and this regional I/R did not affect the global body organism.

Surgical embolectomy in a cat with cardiogenic aortic thromboembolism

A seven-year-old, spayed female, domestic longhair cat was referred for management of a sudden aortic thromboembolism (ATE). Echocardiography showed hypertrophic cardiomyopathy with severe left atrial enlargement. Ultrasonography of the abdominal aorta confirmed a large thrombus at the level of the aortic trifurcation, involving both iliac arteries. Considering the recent onset and bilateral involvement of the iliac arteries, the cat underwent emergent surgical embolectomy (SE) of the aortoiliac embolus. A standard caudal celiotomy was performed and the abdominal aorta was identified. Vessel loops with tourniquets were placed around the abdominal aorta proximal to the thrombus and on both iliac arteries distal to the thrombus. A full-thickness incision was made in the ventral surface of the aorta. The aortic thromboembolus was removed. The trifurcation was subsequently flushed with sterile saline. The SE resulted in a good outcome, with both clinical and ultrasound signs of complete reperfusion of the rear limbs within a few hours. Long-term treatment included antiplatelet drugs, furosemide and benazepril. Eighteen months after surgery, the cat was free of clinical signs, without recurrence of ATE or congestive heart failure. Based on the present case, SE could be considered as a feasible alternative to traditional conservative treatment in cats with a very recent onset of bilateral ATE.

A modified axillo-femoral perfusion for acute type a aortic dissection accompanied with lower limb malperfusion

Background

Lower limb malperfusion accompanied with acute type A dissection (AAD) is reported to be an independent predictor for mortality. Timely treatment is required. However, staged approach to restore the perfusion of the ischemic leg before aortic repair has a continuously increase risk of aortic rupture. Aortic repair under isolated axillary artery perfusion also has the risk of prolonging leg ischemia. Here we introduce our experience in performing axillo-femoral perfusion, which is supposed to bring benefits for treating lower limb malperfuison.

Methods

Thirty patients who suffered AAD accompanied by lower limb ischemia enrolled in our study. All patients received aortic repair as soon as possible using the modified axillo-femoral perfusion approach. The cardiopulmonary bypass and cooling started with the right axillary artery perfusion. Then the femoral artery of the ischemic side was exposed and sewn to a graft connected with another inflow cannula. The rectal temperature was about 31 °C when the femoral perfusion started. The perfusion of the ischemic legs preoperative was estimated after the surgery by the clinical signs, the saturation of the distal-limb, and computed tomography scan.

Results

Twenty-eight patients got good perfusion of the lower body after the surgery. Two patients received femoral-femoral artery bypass immediately after surgery because of the thrombosis in the right common iliac artery, without further injury. No peripheral vessels damage occurred, and no compartment fasciotomy or amputation needed. One patient died for the sepsis and the subsequent multi organ failure 28 days postoperative.

Conclusions

The modified axllio-femoral perfusion could restore the lower limbs’ perfusion simultaneously during the aortic surgery without neither delaying dissection repair nor prolonging the ischemic time. It is a simple, but safe and effective technique.

A Study on the Effects of the Use of Propofol in Experimental Model Inferior Epigastric Island Flap on Ischemia-Reperfusion Injury

Problems concerning vascular blood flow are the most frequently encountered ones after flap applications. The flap tissue starts to develop ischemia in patients with a vascular blood flow insufficiency. And reperfusion starts in those patients in whom the ischemia is temporary, triggering an ischemia-reperfusion injury depending on the duration of the ischemia. The aim of this study was to evaluate the effect of propofol, which is an anesthetic agent known to have an antioxidant effect and a free radical scavenging feature on the ischemia-reperfusion injury created on an experimental epigastric island flap.Thirty Sprague-Dawley rats were used in the study. The rats were divided into 3 groups of 10 rats each. Inferior epigastric artery-based abdominal flaps were prepared in all the groups. In group 1 (sham), the flap was elevated but no ischemia was applied. In groups 2 (control) and 3 (propofol), the flap was exposed to ischemia for 2 hours after it was elevated. All the rats were sacrificed and biochemical and histopathological assessments were made on the tissue samples taken on the 14th day. As a result of a comparison between the groups, the flap viability rates and the superoxide dismutase, total antioxidant capacity, and catalase values were found to be significantly higher (P < 0.001) in the propofol group while the malondialdehyde and total oxidative stress values were lower (P < 0.001). Based on the data obtained from the present study, the use of propofol was observed to have a protective effect against ischemia-reperfusion injuries in flap surgeries.

The effect of hypothermia on adnexal torsion/detorsion injury in a rat ovary model

PURPOSE

Much attention has been given to hypothermia as it is effective in inhibiting inflammatory responses and also ischemia/reperfusion injury. Therefore, the aim of this study was to evaluate the effect of hypothermia on torsion/detorsion injury in rats.

METHODS

Twenty-eight rats were randomly divided into four groups of sham-operated (SG), adnexal torsion/detorsion group (TG), adnexal torsion/detorsion+hypothermia group (THG) and hypothermia group (HG). In the SG group, right ovaries were excised after 3-h fixation to abdominal wall. In the TG, right adnexal underwent 720° torsion in a counterclockwise direction for 3h and then excised after 3-h detorsion period. In the THG, after 3-h torsion period, ovaries were immediately subjected to hypothermia (4°C) for 30-min and they were excised after 3-h detorsioned period. In the HG, the right ovaries were subjected to hypothermia for 30-min and excised after 3-h fixation period. One half of each ovary was immediately stored for antioxidant enzyme activity and tissue lipid peroxidation. The remainder was fixed for histopathological examination.

RESULTS

Adnexal torsion and detorsion significantly increased the tissue level of Malondialdehyde, Superoxide dismutase and Reduced glutathione. On the other hand, hypothermia significantly reduced these oxidative stress parameters. The histopathological changes were less in the THG group; these changes were not statistically different from the other groups.

CONCLUSION

The results of this study suggested that hypothermia inhibited the production of oxidative stress in the ovaries subjected to torsion/detorsion injury.

Concomitant femoro-femoral bypass graft during surgery for acute type A dissection to treat lower limb malperfusion

We report the case of a 69-year-old male patient who was admitted to our department with an acute type A dissection complicated by ischemia of the left lower limb. During surgery for acute type A dissection, the patient underwent concomitant femoro-femoral crossover bypass graft placement to ensure blood supply of the left lower limb during surgery and minimize ischemia-reperfusion injury. The patient underwent supracoronary replacement of the ascending aorta while in deep circulatory arrest with a deepest core temperature of 25°C. Postoperative computed tomography showed antegrade perfusion and patency of the crossover bypass. Postoperative course was eventless without sequelae, especially of the left lower limb. We conclude that concomitant crossover bypass graft reduces the risk of ischemia-reperfusion injury in lower limb ischemia in patients undergoing surgery for acute type A dissection.

Hypothermia protects human neurons

BACKGROUND AND AIMS

Hypothermia provides neuroprotection after cardiac arrest, hypoxic-ischemic encephalopathy, and in animal models of ischemic stroke. However, as drug development for stroke has been beset by translational failure, we sought additional evidence that hypothermia protects human neurons against ischemic injury.

METHODS

Human embryonic stem cells were cultured and differentiated to provide a source of neurons expressing β III tubulin, microtubule-associated protein 2, and the Neuronal Nuclei antigen. Oxygen deprivation, oxygen-glucose deprivation, and H2 O2 -induced oxidative stress were used to induce relevant injury.

RESULTS

Hypothermia to 33°C protected these human neurons against H2 O2 -induced oxidative stress reducing lactate dehydrogenase release and Terminal deoxynucleotidyl transferase dUTP nick end labeling-staining by 53% (P ≤ 0·0001; 95% confidence interval 34·8-71·04) and 42% (P ≤ 0·0001; 95% confidence interval 27·5-56·6), respectively, after 24 h in culture. Hypothermia provided similar protection against oxygen-glucose deprivation (42%, P ≤ 0·001, 95% confidence interval 18·3-71·3 and 26%, P ≤ 0·001; 95% confidence interval 12·4-52·2, respectively) but provided no protection against oxygen deprivation alone. Protection (21%) persisted against H2 O2 -induced oxidative stress even when hypothermia was initiated six-hours after onset of injury (P ≤ 0·05; 95% confidence interval 0·57-43·1).

CONCLUSION

We conclude that hypothermia protects stem cell-derived human neurons against insults relevant to stroke over a clinically relevant time frame. Protection against H2 O2 -induced injury and combined oxygen and glucose deprivation but not against oxygen deprivation alone suggests an interaction in which protection benefits from reduction in available glucose under some but not all circumstances.

The effect of ischemia reperfusion injury on skeletal muscle

Ischemia reperfusion (IR) injury occurs when tissue is reperfused following a period of ischemia, and results from acute inflammation involving various mechanisms. IR injury can occur following a range of circumstances, ranging from a seemingly minor condition to major trauma. The intense inflammatory response has local as well as systemic effects because of the physiological, biochemical and immunological changes that occur during the ischemic and reperfusion periods. The sequellae of the cellular injury of IR may lead to the loss of organ or limb function, or even death. There are many factors which influence the outcome of these injuries, and it is important for clinicians to understand IR injury in order to minimize patient morbidity and mortality. In this paper, we review the pathophysiology, the effects of IR injury in skeletal muscle, and the associated clinical conditions; compartment syndrome, crush syndrome, and vascular injuries.

Temperature-sensitive release of prostaglandin E₂ and diminished energy requirements in synovial tissue with postoperative cryotherapy: a prospective randomized study after knee arthroscopy

BACKGROUND

Local external cooling of the surgical field after joint surgery is intended to enhance recovery and to facilitate the use of outpatient surgery by reducing pain and improving mobility. We hypothesized that the effects of postoperative cooling and compression after knee arthroscopy would be reflected in changes in the concentrations of metabolic and inflammatory markers in the synovial membrane.

METHODS

Forty otherwise healthy patients who were to undergo knee arthroscopy were included in the study, and half were randomized to receive postoperative cooling and compression. Microdialysis of the synovial membrane was performed postoperatively, and the concentrations of prostaglandin E₂ (PGE₂), glucose, lactate, glycerol, and glutamate as well as the ethanol exchange ratio (which indicates blood flow) were measured. The temperature of the knee was monitored, and postoperative pain was assessed by the patient with use of a visual analog scale, a numeric rating scale, and the need for rescue medication.

RESULTS

Application of the cooling and compression device after knee arthroscopy significantly lowered the temperature in the operatively treated knee (as measured on the skin, within the joint capsule, and intra-articularly). The cooling and compression appeared to decrease inflammation, as indicated by a temperature-sensitive decrease in the PGE₂ concentration. The hypothermia also decreased the metabolic rate of the synovial tissue and thus decreased energy requirements, as shown by the stability of the lactate concentration over time despite the decreased blood flow that was indicated by the increasing ethanol exchange ratio. No effect of the compression and cooling on postoperative pain was detected.

CONCLUSIONS

Local cryotherapy and compression after knee arthroscopy significantly lowered the temperature in the knee postoperatively, and the synovial PGE₂ concentration was correlated with the temperature. Since PGE₂ is a marker of pain and inflammation, the postoperative local cooling and compression appeared to have a positive anti-inflammatory effect.

Noninvasive measurement of edema in partial thickness burn wounds

A lack of noninvasive tools to quantify edema has limited our understanding of burn wound edema pathophysiology in a clinical setting. Near-infrared spectroscopy (NIR) is a new noninvasive tool able to measure water concentration/edema in tissue. The purpose of this study was to determine whether NIR could detect water concentration changes or edema formation in acute partial-thickness burn injuries. Adult burn patients within 72 hours postinjury, thermal etiology, partial-thickness burn depth, and <20% TBSA were included. Burn wounds were stratified into partial-thickness superficial or deep wounds based on histology and wound healing time. NIR devices were used to quantify edema in a burn and respective control sites. The sample population consisted of superficial (n = 12) and deep (n = 5) partial-thickness burn injuries. The patients did not differ with respect to age (40 +/- 15 years), TBSA (5 +/- 4%), and mean time for edema assessment (2 days). Water content increased 15% in burned tissue compared with the respective control regions. There were no differences in water content at the control sites. At 48 hours, deep partial-thickness injuries showed a 23% increase in water content compared with 18% superficial partial-thickness burns. NIR could detect differences in water content or edema formation in partial-thickness burns and unburned healthy regions. NIR holds promise as a noninvasive, portable clinical tool to quantify water content or edema in burn wounds.

Thrombospondin-1/CD47 blockade following ischemia-reperfusion injury is tissue protective

BACKGROUND

Nitric oxide has prosurvival effects that can limit ischemia-reperfusion injuries. However, the matrix glycoprotein thrombospondin-1 is induced following ischemia-reperfusion injury and limits nitric oxide signaling by engaging its cell surface receptor CD47. In this article, the authors examine whether postinjury blocking of this inhibitory signal can protect from ischemia-reperfusion injury in a rat flap model.

METHODS

A total of 40 tissue flaps were created in rats based solely on the deep inferior epigastric vessels. Microvascular clamps were used to create 45 minutes of ischemia time to the flaps. The flaps were then treated using a monoclonal antibody to CD47 or an isotype-matched control immunoglobulin G1 5 or 30 minutes after clamp removal. Twenty-four or 72 hours postoperatively, the necrotic area of the flap was determined, and serum, deep inferior epigastric vessels, and flaps were harvested for analysis from five rats in each respective group.

RESULTS

Treatment with a CD47 antibody 5 minutes after reperfusion significantly reduces flap necrosis compared with immunoglobulin G1 control (9 percent versus 43 percent; p < 0.01). The protective effect is even more dramatic when treatment is delayed until 30 minutes after reperfusion (10 percent versus 88 percent for control; p < 0.01). Markers of neutrophil and endothelial cell activation along with total leukocytes are reduced in CD47 antibody-treated flaps, as are tissue malondialdehyde levels. Levels of cyclic guanosine monophosphate are elevated 72 hours postoperatively in the CD47 antibody-treated deep inferior epigastric vessels versus the control flaps.

CONCLUSIONS

Therapies targeting the thrombospondin-1 receptor CD47 offer potential for increasing tissue survival in ischemia-reperfusion injuries. The ability to protect when given after ischemia-reperfusion injury enables a broader clinical applicability.

The role of nitric oxide synthase and heme oxygenase in the protective effect of hypothermia in ischemia-reperfusion injury

BACKGROUND

Ischemia-reperfusion injury plays an important role in limb salvage following limb ischemia. The purpose of the present study was to evaluate the effect of local hypothermia and chemical modulators on microvascular permeability following ischemia-reperfusion injury in skeletal muscle.

METHODS

Sprague-Dawley rats were randomized into nine groups. Postcapillary venules of the extensor digitorum longus muscle were visualized with use of intravital microscopy. Following an intravenous bolus of fluorescein isothiocyanate-labeled albumin, the intravascular and extravascular space was examined for leak. Rats in the sham group underwent a one-hour mock ischemic period without the application of a femoral artery tourniquet, followed by one hour of mock reperfusion. The treatment groups (n = 5 in each group) had the tourniquet applied for one hour, followed by one hour of reperfusion at 10 degrees C (cold) alone, at 10 degrees C with nitric oxide synthase inhibitor, at 10 degrees C with heme oxygenase inhibitor, at 10 degrees C with a combination of inhibitors, at 34 degrees C (warm) alone, at 34 degrees C with a heme oxygenase inducer, at 34 degrees C with a nitric oxide synthase inducer, or at 34 degrees C with a combination of inducers.

RESULTS

Rats in the sham group did not show a significant increase in microvascular permeability. Rats in the warm ischemia/reperfusion group displayed significant increases in microvascular permeability, as did the rats that received inhibitors of heme oxygenase and nitric oxide synthase at 10 degrees C. No significant increase in microvascular permeability was observed in the animals in the cold ischemia/reperfusion group or in animals that received inducers of heme oxygenase and nitric oxide synthase at 34 degrees C.

CONCLUSIONS

Local hypothermia protects skeletal muscle from increased microvascular permeability following ischemia-reperfusion injury. This protective effect is also seen with the induction of the nitric oxide synthase and heme oxygenase systems at physiologic temperature. We also have shown that the protective effects of hypothermia are blocked by giving heme oxygenase and nitric oxide synthase inhibitors while keeping the muscle hypothermic. These findings demonstrate that heme oxygenase and nitric oxide synthase play a combined role in ischemia-reperfusion injury, suggesting possible pathways for clinical intervention to modulate injury seen following trauma, tourniquet use, vascular surgery, and microvascular surgery.

The effect of adipose-derived stem cells on ischemia-reperfusion injury: immunohistochemical and ultrastructural evaluation

BACKGROUND

Advances in the treatment of reperfusion injury have created an opportunity for plastic surgeons to apply these treatments to flaps and implanted tissues. The authors examined the direct and indirect effects of adipose-derived stem cells on ischemia-reperfusion injury on a skin flap model to determine the in vivo differentiation of adipose-derived stem cells to endothelial cells; the levels of vascular endothelial growth factor (VEGF), transforming growth factor-beta, and fibroblast growth factor; and the ultrastructural changes apparent with scanning electron microscopy to clarify the initial events and the following cascades.

METHODS

Two identical cranial based random flaps with a dimension of 1 x 5 cm were elevated on the dorsums of 20 ICR mice. The left flap was designated as the control and the right flap was injected with adipose-derived stem cells. The flaps were then subjected to 6 hours of ischemia by clamping the pedicle, and then reperfusion.

RESULTS

The mean viable flap length in the control and experimental groups was 15.2 +/- 3.4 mm and 24.4 +/- 2.9 mm, respectively. The mean viable flap area in the control and experimental groups was 12.9 +/- 4.1 mm and 21.8 +/- 3.7 mm, respectively. The in vivo differentiation of adipose-derived stem cells to endothelial cells was observed. The immunohistochemical stainings, VEGF, transforming growth factor-beta, and fibroblast growth factor revealed increased levels in the experimental groups. Scanning electron microscopy indicated mild injury in the experimental group.

CONCLUSIONS

The adipose-derived stem cells could prevent ischemia-reperfusion injury, mainly by regulating the growth factors. Although VEGF was the foremost inhibitor of injury, the overall cascade was enhanced by adipose-derived stem cells, with the help of the other growth factors.

Local cooling provides muscle flaps protection from ischemia-reperfusion injury in the event of venous occlusion during the early reperfusion period

Clinicians often place patients in heated rooms following muscle flap transfers. We hypothesize that exposure of flaps to heated room temperatures could result in an unnecessary hyperthermic ischemic insult if the flaps were to be compromised by venous outflow obstruction, while exposure of elective flaps to local cooling during early perfusion may provide protection in the event of venous occlusion. The rat rectus femoris muscle flap was elevated and clamped for 1 h. The muscle was then exposed to various temperatures for 1 h of perfusion followed by complete venous occlusion for 3 h. Occlusion clamps were removed and flaps were allowed to reperfuse for 24 h. Flaps were assessed for muscle necrosis and edema. Venous occluded muscles demonstrated decreased muscle necrosis and edema in the locally cooled group (8.5 +/- 6.7%, 3.06 +/- 0.14; P < 0.001) compared to the room temperature group (76.2 +/- 23.0%, 3.73 +/- 0.13), and the local warming group (97.3 +/- 1.4%, 3.84 +/- 0.29) respectively. No difference was noted in muscle necrosis nor edema amongst non-ischemic muscles irrespective of temperature exposure. These results suggest a beneficial role for exposure of elective flaps to local cooling during the early perfusion period in order to provide protection from ischemia reperfusion injury in the event of a venous occlusion insult. The prophylactic exposure of flaps to local cooling is further supported by the lack of a harmful effect when flaps were not compromised by venous occlusion.

Protective effects of preconditioned local somatothermal stimulation on neuromuscular plasticity against ischemia--reperfusion injury in rats

The aim of this study was to investigate whether preconditioned local somatotheral stimulation (LSTS) protects the muscle and nerve against ischemia-reperfusion (I/R) injuries. Male rats were randomly assigned to normal, preconditioned LSTS only, and I/R-injured groups with or without LSTS preconditioning. I/R injuries of the lower limb were induced by rubber band wrapping, followed by measurements of gait function and nerve conduction, muscle pathology, serum enzymatic activity, and the expression of heat-shock protein 70 (HSP-70) in the gastrocnemius muscles. No significant change of neuromuscular function was found between LSTS (-) and LSTS (+) groups on the first day after I/R injury. In contrast, gait stride length, compound motor action potential, and serum creatine phosphokinase MM isoenzyme were significantly improved on the eighth day after one or two doses of preconditioned LSTS and subsequent I/R injury. Western blot analysis disclosed no significant change of HSP-70 expression in the muscle of I/R injured limbs between LSTS (-) and LSTS (+) groups. We conclude that preconditioned LSTS is a safe modality that improves the neuromuscular plasticity against I/R injured limbs, which provides a new strategy for I/R injury in clinical applications, such as intraoperative use of tourniquets.

Reperfusion Injury

The restoration of blood flow to ischemic tissues causes additional damage, which is termed reperfusion injury. All tissues are susceptible to reperfusion injury, but this susceptibility varies between tissues. Reperfusion has wide clinical relevance. It influences the outcome of patients after myocardial infarction, stroke, organ transplantation, and cardiovascular surgery. Advances in the treatment of reperfusion injury have created an opportunity for plastic surgeons to apply these treatments to flaps and reimplanted tissues. The main putative mechanisms identified in animal models involve leukocyte-endothelium interactions, reactive oxygen species, and the complement system. However, it has become evident that these fundamental biological systems are controlled by many interrelated pathways. Attempts to bypass this complexity have led to a search for the early "upstream" initiating events, rather than the "downstream" cascading events. This contrasts with current clinical efforts that are directed toward hypothermia, intraarterial flushing, and preconditioning. This article outlines the molecular and cellular events that occur during reperfusion injury and then reviews the efforts that have been made to exploit this knowledge for clinical advantage.

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.