Hemodynamic changes in rat leg muscles during tourniquet-induced ischemia-reperfusion injury observed by near-infrared spectroscopy

Intratracheal cobinamide (vitamin B12 analog) administration increases survivability in rabbits exposed to a lethal dose of inhaled hydrogen sulfide

BACKGROUND

Hydrogen sulfide is a highly toxic, flammable, and colorless gas. Hydrogen sulfide has been identified as a potential terrorist chemical threat agent in mass-casualty events. Our previous studies showed that cobinamide, a vitamin B12 analog, effectively reverses the toxicity from hydrogen sulfide poisoning. In this study, we investigate the effectiveness of intratracheally administered cobinamide in treating a lethal dose hydrogen sulfide gas inhalation and compare its performance to saline control administration.

METHODS

A total of 53 pathogen-free New Zealand White rabbits were used for this study. Four groups were compared: (i) received no saline solution or drug intratracheally (n = 15), (ii) slow drip saline intratracheally (n = 15), (iii) fast drip saline intratracheally (n = 15), and (iv) slow drip cobinamide intratracheally (n = 8). Blood pressure was continuously monitored, and deoxy- and oxyhemoglobin concentration changes were monitored in real-time in vivo using continuous wave near-infrared spectroscopy.

RESULTS

The mean (± standard deviation) weight for all animals (n = 53) was 3.87 ± 0.10 kg. The survival rates of the slow cobinamide and the fast saline groups were 75 percent and 60 percent, respectively, while the survival rates in the slow saline and control groups were 26.7 percent and 20 percent, respectively. A log-rank (Mantel-Cox) test showed that survival in fast saline and slow cobinamide groups were significantly greater than those of no saline control and slow saline groups (P < 0.05). The slow and no saline control groups were not significantly different (P = 0.59). The slow cobinamide group did significantly better than the slow saline group (P = 0.021).

DISCUSSION

The ability to use intratracheal cobinamide as an antidote to hydrogen sulfide poisoning is a novel approach to mass-casualty care. The major limitations of this study are that it was conducted in a single species at a single inhaled hydrogen sulfide concentration. Repeated investigations in other species and at varying levels of hydrogen sulfide exposure will be needed before any definitive recommendations can be made.

CONCLUSIONS

We demonstrated that intratracheal cobinamide and fast saline drip improved survival for hydrogen sulfide gas inhalation in rabbit models. Although further study is required, our results suggest that intratracheal administration of cobinamide and fast saline may be useful in hydrogen sulfide mass-casualty events.

Tourniquet use following blast-associated complex lower limb injury and traumatic amputation promotes end organ dysfunction and amplified heterotopic ossification formation

Background

Traumatic heterotopic ossification (tHO) is characterized by ectopic bone formation in extra-skeletal sites leading to impaired wound healing, entrapment of neurovascular structures, pain, and reduced range of motion. HO has become a signature pathology affecting wounded military personnel who have sustained blast-associated traumatic amputations during the recent conflicts in Iraq and Afghanistan and can compound recovery by causing difficulty with prosthesis limb wearing. Tourniquet use to control catastrophic limb hemorrhage prior to surgery has become almost ubiquitous during this time, with the recognition the prolonged use may risk an ischemia reperfusion injury and associated complications. While many factors influence the formation of tHO, the extended use of tourniquets to limit catastrophic hemorrhage during prolonged field care has not been explored.

Methods

Utilizing an established pre-clinical model of blast-associated complex lower limb injury and traumatic amputation, we evaluated the effects of tourniquet use on tHO formation. Adult male rats were subjected to blast overpressure exposure, femur fracture, and soft tissue crush injury. Pneumatic tourniquet (250–300 mmHg) applied proximal to the injured limb for 150-min was compared to a control group without tourniquet, before a trans-femoral amputation was performed. Outcome measures were volume to tHO formation at 12 weeks and changes in proteomic and genomic markers of early tHO formation between groups.

Results

At 12 weeks, volumetric analysis with microCT imaging revealed a 70% increase in total bone formation (p = 0.007) near the site of injury compared to rats with no tourniquet time in the setting of blast-injuries. Rats subjected to tourniquet usage had increased expression of danger-associated molecular patterns (DAMPs) and end organ damage as early as 6 h and as late as 7 days post injury. The expressions of pro-inflammatory cytokines and chemokines and osteochondrogenic genes using quantitative RT-PCR similarly revealed increased expression as early as 6 h post injury, and these genes along with hypoxia associated genes remained elevated for 7 days compared to no tourniquet use.

Conclusion

These findings suggest that tourniquet induced ischemia leads to significant increases in key transcription factors associated with early endochondral bone formation, systemic inflammatory and hypoxia, resulting in increased HO formation.

Evaluation of the Influence of Short Tourniquet Ischemia on Tissue Oxygen Saturation and Skin Temperature Using Two Portable Imaging Modalities

BACKGROUND

The exact influence of tourniquet ischemia on a treated extremity remains unclear.

METHODS

Twenty patients received an operation on one hand under tourniquet ischemia. Twenty healthy volunteers received 10 min of tourniquet ischemia on one of their arms. Measurements of tissue oxygen saturation using near-infrared reflectance-based imaging and skin temperature of the dorsum of the hand were performed at five different timepoints (t0 was performed just before the application of the tourniquet ischemia, t1 directly after the application of the tourniquet ischemia, t2 before the release of the ischemia, t3 directly after the release of the ischemia, and t4 on the following day).

RESULTS

In both groups, tissue oxygen saturation dropped after the application of the tourniquet ischemia compared to t0 and increased after the release of the tourniquet ischemia. In the patient group, tissue oxygen saturation at t4 was higher compared to t0; in contrast, the level of tissue oxygen saturation in the participant group dropped slightly at t4 compared to t0. The measured skin temperature in the patient group showed an increase during the observation period, while it continuously decreased in the group of healthy participants.

CONCLUSIONS

Short-term ischemia did not appear to permanently restrict perfusion in this study design. The non-invasive imaging modalities used were easy to handle and allowed repetitive measurement.

Administration of particulate oxygen generators improves skeletal muscle contractile function after ischemia-reperfusion injury in the rat hindlimb

Extended tourniquet application, often associated with battlefield extremity trauma, can lead to severe ischemia-reperfusion (I/R) injury in skeletal muscle. Particulate oxygen generators (POGs) can be directly injected into tissue to supply oxygen to attenuate the effects of I/R injury in muscle. The goal of this study was to investigate the efficacy of a sodium percarbonate (SPO)-based POG formulation in reducing ischemic damage in a rat hindlimb during tourniquet application. Male Lewis rats were anesthetized and underwent tourniquet application for 3 h at a pressure of 300 mmHg. Shortly after tourniquet inflation, animals received intramuscular injections of either 0.2 mg/mL SPO with catalase (n = 6) or 2.0 mg/mL SPO with catalase (n = 6) directly into the tibialis anterior (TA) muscle. An additional Tourniquet-Only group (n = 12) received no intervention. Functional recovery was monitored by in vivo contractile testing of the hindlimb at 1, 2, and 4 wk after injury. By the 4 wk time point, the Low-Dose POG group continued to show improved functional recovery (85% of baseline) compared with the Tourniquet-Only (48%) and High-Dose POG (56%) groups. In short, the low-dose POG formulation appeared, at least in part, to mitigate the impact of ischemic tissue injury, thus improving contractile function after tourniquet application. Functional improvement correlated with maintenance of larger muscle fiber cross-sectional area and the presence of fewer fibers containing centrally located nuclei. As such, POGs represent a potentially attractive therapeutic solution for addressing I/R injuries associated with extremity trauma.NEW & NOTEWORTHY Skeletal muscle contraction was evaluated in the same animals at multiple time points up to 4 wk after injury, following administration of particulate oxygen generators (POGs) in a clinically relevant rat hindlimb model of tourniquet-induced ischemia. The observed POG-mediated improvement of muscle function over time confirms and extends previous studies to further document the potential clinical applications of POGs. Of particular significance in austere environments, this technology can be applied in the absence of an intact circulation.

Development of a Rat Model of Fasciotomy Treatment for Compartment Syndrome

Skeletal muscle injuries are a major cause of disability for military and civilian populations. Compartment syndrome (CS) in skeletal muscle results from an edema-induced increase in intracompartmental pressure (ICP) after primary injury. Untreated ICP will occlude the tissue vasculature, tissue necrosis, and potential loss of limb. The current standard of care for CS is surgical fasciotomy, an incision through the muscle fascia to relieve ICP. Early fasciotomy will preserve the limb, but often leaves patients with long-term scarring and reduced muscle function. Our group previously developed and characterized a rat model of CS to explore the pathophysiology of CS and test new therapies. We present an expansion of this CS model, including the fasciotomy, to better simulate clinical treatment. CS was induced on the hind limb of adult male Lewis rats and fasciotomy was performed 24 h later. Less than 20% of the rats that underwent fasciotomy showed detectable force 4 days after injury, compared with the 75% of rats that underwent CS induction without fasciotomy. Muscles undergoing fasciotomy showed a significant increase in fibrosis and an increased number of macrophages, Pax7⁺ satellite cells, and α-smooth muscle actin⁺ myofibroblasts at 7 days postinjury. These data indicate that the use of fasciotomy in a rat model of CS resulted in injury sequelae that reflect the severity of human clinical disease presentation along with current standard of care. Impact Statement Current animal models of skeletal muscle injury struggle to accurately reflect the injury sequelae seen in humans, particularly in rats and mice. These animals also recover faster than humans do. More accurate recapitulation of the injury is needed to better study the injury progression, as well as screen for novel therapies. This research combines an existing model of compartment syndrome with its clinical standard of care (fasciotomy), creating a more accurate rat model of injury, and providing for a better treatment screening tool. These results show how our model leads to a sustained skeletal muscle deficit with increased inflammation.

Talus Fracture Dislocation Management With Crossed Kirschner Wires in Children

Skeletal trauma accounts for 10% to 15% of all childhood injuries, with approximately 15% to 30% of these representing physeal injuries. Talus fractures are rare injuries in children with an estimated prevalence of 0.008% of all childhood fractures. Cast immobilization is sufficient treatment for non-displaced fractures, however displaced fractures of the talus require surgical intervention to minimize the risk of trauma-related avascular necrosis (AVN) due to disruption of the vascular supply originating from the talar neck. A 13-year-old boy was brought to the accident and emergency (A/E) department following a road traffic accident while he was pillion riding a bike. Following the accident, he was unable to bear weight on his right foot and his anterior ankle region was swollen, with no neurological deficit or open wound. He had no other injury and no medical or surgical history. On review of the ankle and foot radiographs, he was noted to have a right talar neck fracture with subtalar and ankle dislocation. His computer tomographic (CT) images demonstrated a Hawkins Type IV talus fracture. Initial treatment involved a plaster of Paris (POP) back slab with the ankle in a neutral position. His right leg was elevated on pillows and treated with elevation and ice to alleviate the swelling. As the fracture was comminuted and displaced with ankle and subtalar dislocation, operative intervention (open reduction and fixation of talus with crossed K wires) was planned. The patient was discharged in below knee slab which was changed to a non-walking cast at two weeks. The patient was kept non-weight bearing until fracture united. These types of fractures are rare in children and proper clinical and radiological evaluation is essential. Such fractures should be reduced as early as possible to reduce the ischemia time thus prevent the chances of osteonecrosis. Lastly avoid tourniquets and stable anatomical reduction of fracture is must.

The role of neutrophil extracellular traps and TLR signaling in skeletal muscle ischemia reperfusion injury

Ischemia reperfusion (IR) injury results in devastating skeletal muscle fibrosis. Here, we recapitulate this injury with a mouse model of hindlimb IR injury which leads to skeletal muscle fibrosis. Injury resulted in extensive immune infiltration with robust neutrophil extracellular trap (NET) formation in the skeletal muscle, however, direct targeting of NETs via the peptidylarginine deiminase 4 (PAD4) mechanism was insufficient to reduce muscle fibrosis. Circulating levels of IL-10 and TNFα were significantly elevated post injury, indicating toll-like receptor (TLR) signaling may be involved in muscle injury. Administration of hydroxychloroquine (HCQ), a small molecule inhibitor of TLR7/8/9, following injury reduced NET formation, IL-10, and TNFα levels and ultimately mitigated muscle fibrosis and improved myofiber regeneration following IR injury. HCQ treatment decreased fibroadipogenic progenitor cell proliferation and partially inhibited ERK1/2 phosphorylation in the injured tissue, suggesting it may act through a combination of TLR7/8/9 and ERK signaling mechanisms. We demonstrate that treatment with FDA-approved HCQ leads to decreased muscle fibrosis and increased myofiber regeneration following IR injury, suggesting short-term HCQ treatment may be a viable treatment to prevent muscle fibrosis in ischemia reperfusion and traumatic extremity injury.

Duration of extremity tourniquet application profoundly impacts soft-tissue antibiotic exposure in a rat model of ischemia-reperfusion injury

INTRODUCTION

Extremity tourniquet (TNK) application is an effective means of achieving compressible hemorrhage control in the emergency prehospital and clinical trauma setting. Modern United States military medical doctrine recommends TNK use to prevent lethal hemorrhage from extremity injury, followed by systemic prophylactic antibiotics to prevent wound infection. Because tissue pharmacokinetics of prophylactic antimicrobials during and after TNK-induced limb ischemia are largely unknown, this study was conducted to empirically determine the relationship between TNK application time and soft tissue antibiotic exposure in order to guide medical personnel in the management of extremity trauma.

MATERIALS AND METHODS

Hind limbs of anesthetized male Sprague Dawley rats were exsanguinated, and ischemia maintained by a pneumatic cuff placed at the level of the mid femur on one limb; the non-ischemic contralateral limb served as comparison tissue. Systemic prophylactic antibiotics (cefazolin, moxifloxacin, or ertapenem) were administered intravenously before or after TNK release following 2 or 4 h of ischemia with subsequent re-dosing every 12 h for 3 days. Free antibiotic in the interstitial fluid (ISF) of the tibialis anterior muscle of both hind limbs was recovered via microdialysis during ischemia and over three periods during reperfusion: immediately following TNK release, at 24 h post TNK release, and at 72 h post TNK release. Plasma and ISF free drug concentrations were determined by high-performance liquid chromatography.

RESULTS

Tourniquet application prevented delivery of prophylactic antibiotics into distal soft tissue for the duration of ischemia, and caused a profound reduction in skeletal muscle drug exposure for up to 72 h following TNK release. A progressive decline in tissue antibiotic exposure during reperfusion was observed as TNK times increased from 2 h to 4 h. The timing and severity of reduced drug distribution in post-ischemic skeletal muscle varied substantially among the three antibiotic classes evaluated.

CONCLUSIONS

Prolonged tourniquet application can significantly reduce distribution of prophylactic antibiotics into soft tissue during and after ischemia, potentially impairing prophylaxis of extremity wound infection. Our findings support the examination of alternative approaches to wound infection prophylaxis under conditions of delayed casualty evacuation when occlusive hemorrhage control measures are utilized.

Tourniquet-induced tissue hypoxia characterized by near-infrared spectroscopy during ankle surgery: an observational study

BACKGROUND

Pneumatic tourniquet inflation during extremity surgery leads to profound and prolonged tissue ischemia. Its effect on tissue oxygenation is inadequately studied.

METHODS

Patients undergoing elective ankle surgery with tourniquet application participated in this observational cohort study. Somatic and cerebral tissue oxygen saturation (SstO₂ and SctO₂) were monitored using tissue near-infrared spectroscopy. Oxygenation was monitored distally (SstO₂-distal) and proximally to the tourniquet, on the contralateral leg, and the forehead (a total of 4 tissue beds). Tissue oxygenation at different time points was compared. The magnitude, duration, and load (product of magnitude and duration) of tissue desaturation during tourniquet inflation were correlated with tissue resaturation and hypersaturation after tourniquet deflation.

RESULTS

Data of 26 patients were analyzed. The tourniquet inflation time was 120 ± 31 mins. Following a rapid desaturation from 77 ± 8% pre-inflation to 38 ± 20% 10 mins post-inflation, SstO₂-distal slowly and continuously desaturated and reach the nadir (16 ± 11%) toward the end of inflation. After deflation, SstO₂-distal rapidly resaturated from 16 ± 11% to 91 ± 5% (i.e., hypersaturation); SstO₂ monitored proximally to the tourniquet and on contralateral leg had significant but small desaturation (~ 2-3%, p <  0.001); in contrast, SctO₂ remained stable. The desaturation load had a significant correlation with resaturation magnitude (p <  0.001); while the desaturation duration had a significant correlation with hypersaturation magnitude (p = 0.04).

CONCLUSIONS

Tissue dys-oxygenation following tourniquet application can be reliably monitored using tissue oximetry. Its outcome significance remains to be determined.

Phonomyography as a non-invasive continuous monitoring technique for muscle ischemia in an experimental model of acute compartment syndrome

BACKGROUND

In acute compartment syndrome (ACS), clinicians have difficulty diagnosing muscle ischemia provoked by increased intra-compartmental pressure in a timely and non-invasive manner. Phonomyography records the acoustic signal produced by muscle contraction. We hypothesize that alterations in muscle contraction caused by muscle ischemia can be detected with phonomyography, serving as a potential non-invasive technique in the detection of ACS.

METHODS

The left hind limb of 15 Sprague-Dawley rats was submitted to a reversible ischemic model of limb injury for 30min and 1, 2, 4, 6h (3 rats in each group). The right limb served as control. Phonomyography microphones were placed over the posterior calf of both limbs and the sciatic nerve was stimulated percutaneously at 10-min intervals to evaluate muscle contraction. Histopathological analysis of muscles and nerves biopsies was performed and correlation was made between duration of injury, phonomyography output and degree of muscle and nerve necrosis.

RESULTS

There was a statistically significant decrease in the phonomyography signal output in the ischemic limb that correlated with the duration of ischemia and histological findings of muscle and nerve necrosis. The phonomyography signal decrease and histological findings were respectively: 55.5% (n=15;p=0.005) with rare muscle and nerve necrosis at 30min, 65.6% (n=12;p=0.005) with 5-10% muscle necrosis at 1h, 68.4% (n=9;p=0.015) with 100% muscle necrosis and little nerve damage at 2h, 72.4% (n=6;p=0.028) with 100% muscle necrosis and severe nerve damage at 4h, and 92.8% (n=3;p=0.109) with 100% muscle necrosis and severe nerve degeneration at 6h.

CONCLUSION

Changes in phonomyography signal are observed in early ischemic injury prior to the onset of nerve or muscle necrosis. Therefore, phonomyography could serve as a non-invasive technique to detect early ischemic muscle changes in acute compartment syndrome.

CLINICAL RELEVANCE

The detection of abnormal muscle contraction in a timely fashion and non-invasive manner is of interest in clinical settings where the presence of ischemia is not easy to diagnose.

Quantitative photoacoustic imaging for early detection of muscle ischemia injury

Acute lower extremity ischemia is a limb-and life-threatening problem. The timing of clinical intervention is critical to achieving optimal outcomes. However, there has been a lack of effective techniques capable of evaluating muscle and limb damage. Microcirculatory injury is the initial pathological change during ischemic muscle injury. Here, we performed photoacoustic imaging (PAI) in real time to quantitatively detect the degree of microcirculatory injury of ischemic muscles in a rat model in which Evans blue (EB), which strongly binds to albumin in blood, was used as a nontoxic molecular PA probe. The right lower hind limbs of Sprague-Dawley (SD) rats were subjected to 2 or 3 hours of tourniquet-induced ischemia. Then, PA imaging of the tibialis anterior (TA) muscles in the anterior compartment was performed for 0-24 h after the release of compression. Twenty-four hours after reperfusion, rats were euthanized and examined for pathology, edema and muscle viability. Imaging at 680 nm on rats revealed that there was significant signal enhancement in the TA muscles of the two injury groups compared to the control group, and the 3-h injury group had significantly higher PA signal intensity than the 2-h injury group at each time point. Histopathology results obtained from both the normal and the damaged muscles correlated well with the PAI findings. In conclusion, PA imaging is a promising modality for quantitatively detecting limb and muscle ischemic injury and may pave the road for further clinical application.

Monitoring cerebral oxygenation and local field potential with a variation of isoflurane concentration in a rat model

We aimed to investigate experimentally how anesthetic levels affect cerebral metabolism measured by near-infrared spectroscopy (NIRS) and to identify a robust marker among NIRS parameters to discriminate various stages of anesthetic depth in rats under isoflurane anesthesia. In order to record the hemodynamic changes and local field potential (LFP) in the brain, fiber-optic cannulae and custom-made microelectrodes were implanted in the frontal cortex of the skull. The NIRS and LFP signals were continuously monitored before, during and after isoflurane anesthesia. As isoflurane concentration is reduced, the level of oxyhemoglobin and total hemoglobin concentrations of the frontal cortex decreased gradually, while deoxyhemoglobin increased. The reflectance ratio between 730nm and 850nm and burst suppression ratio (BSR) correspond similarly with the change of oxyhemoglobin during the variation of isoflurane concentration. These results suggest that NIRS signals in addition to EEG may provide a possibility of developing a new anesthetic depth index.

Postischemic conditioning does not reduce muscle injury after tourniquet-induced ischemia-reperfusion injury in rats

BACKGROUND

The widespread application of tourniquets has reduced battlefield mortality related to extremity exsanguinations. Tourniquet-induced ischemia-reperfusion injury (I/R) can contribute to muscle loss. Postischemic conditioning (PostC) confers protection against I/R in cardiac muscle and skeletal muscle flaps. The objective of this study was to determine the effect of PostC on extremity muscle viability in an established rat hindlimb tourniquet model.

METHODS

Rats were randomly assigned to PostC-1, PostC-2, or no conditioning ischemic groups (n = 10 per group). Postischemic conditioning, performed immediately after tourniquet release, consisted of four 15-second cycles (PostC-1) or eight 15-second cycles (PostC-2) of alternating occlusion and perfusion of hindlimbs. Twenty-four hours later, muscles were excised. The primary end points were muscle edema and viability; secondary end points were histologic and markers of oxidative stress.

RESULTS

Ischemia-reperfusion injury decreased viability in all tourniquet limbs, but viability was not improved in either PostC group. Likewise, I/R resulted in substantial muscle edema that was not reduced by PostC. The predominant histologic feature was necrosis, but no significant differences were found among groups. Markers of oxidative stress were increased similarly among groups after I/R, although myeloperoxidase activity was significantly increased only in the no conditioning ischemic group. A protective effect from PostC was not observed in our model suggesting that PostC was not effective in reducing I/R skeletal muscle injury or any benefits of PostC were not sustained for 24 hours when tissues were assessed.

CONCLUSION

These negative findings are pertinent as the military investigates different strategies to extend the safe time for tourniquet application.

Characterization of a compartment syndrome-like injury model

INTRODUCTION

Acute compartment syndrome (CS) is caused by an elevation of pressure within a muscular compartment that can be caused by numerous factors, including blunt trauma. In this study, we characterized a rodent model of CS-like injury.

METHODS

Forty male athymic rats received a standardized injury of ischemia and compression to their hindlimbs, while the intracompartmental pressure (ICP) was measured using an implantable transmitter. Tetanic muscle function was evaluated, and histology was performed on the tibialis anterior (TA) muscle.

RESULTS

ICPs were held at 260.70 ± 2.70 mm Hg during injury. Injured muscles recovered 59% of their total function 4 weeks after injury, and histology showed high levels of edema, inflammation (CD68(+) ), angiogenesis (CD31(+) ), and fibrosis within 72 hours after injury.

CONCLUSIONS

We describe a novel CS-like injury model and a novel method to measure ICP, which could potentially be used to develop innovative therapies to manage CS injury in patients.

Effect of recombinant human MG53 protein on tourniquet-induced ischemia-reperfusion injury in rat muscle

INTRODUCTION

Skeletal muscle ischemia-reperfusion injury (I-R) is a complex injury process that includes damage to the sarcolemmal membrane, contributing to necrosis and apoptosis. MG53, a muscle-specific TRIM family protein, has been shown to be essential for regulating membrane repair and has been shown to be protective against cardiac I-R and various forms of skeletal muscle injury. The purpose of this study was to determine if recombinant human MG53 (rhMG53) administration offered protection against I-R.

METHODS

rhMG53 was administered to rats immediately before tourniquet-induced ischemia and again immediately before reperfusion. Two days later muscle damage was assessed histologically.

RESULTS

rhMG53 offered no protective effect, as evidenced primarily by similar Evans blue dye inclusion in the muscles of rats administered rhMG53 or saline.

CONCLUSIONS

Administration of rhMG53 does not offer protection against I-R in rat skeletal muscle. Additional studies are required to determine if the lack of a response is species-specific.

The vitamin B12 analog cobinamide is an effective hydrogen sulfide antidote in a lethal rabbit model

BACKGROUND AND PURPOSE

Hydrogen sulfide (H2S) is a highly toxic gas for which no effective antidotes exist. It acts, at least in part, by binding to cytochrome c oxidase, causing cellular asphyxiation and anoxia. We investigated the effects of three different ligand forms of cobinamide, a vitamin B12 analog, to reverse sulfide (NaHS) toxicity.

METHODS

New Zealand white rabbits received a continuous intravenous (IV) infusion of NaHS (3 mg/min) until expiration or a maximum 270 mg dose. Animals received six different treatments, administered at the time when they developed signs of severe toxicity: Group 1-saline (placebo group, N = 9); Group 2--IV hydroxocobalamin (N = 7); Group 3--IV aquohydroxocobinamide (N = 6); Group 4--IV sulfitocobinamide (N = 6); Group 5--intramuscular (IM) sulfitocobinamide (N = 6); and Group 6-IM dinitrocobinamide (N = 8). Blood was sampled intermittently, and systemic blood pressure and deoxygenated and oxygenated hemoglobin were measured continuously in peripheral muscle and over the brain region; the latter were measured by diffuse optical spectroscopy (DOS) and continuous wave near infrared spectroscopy (CWNIRS).

RESULTS

Compared with the saline controls, all cobinamide derivatives significantly increased survival time and the amount of NaHS that was tolerated. Aquohydroxocobinamide was most effective (261.5 ± 2.4 mg NaHS tolerated vs. 93.8 ± 6.2 mg in controls, p < 0.0001). Dinitrocobinamide was more effective than sulfitocobinamide. Hydroxocobalamin was not significantly more effective than the saline control.

CONCLUSIONS

Cobinamide is an effective agent for inhibiting lethal sulfide exposure in this rabbit model. Further studies are needed to determine the optimal dose and form of cobinamide and route of administration.

A pediatric comminuted talar fracture treated by minimal K-wire fixation without using a tourniquet

BACKGROUND

Pediatric comminuted talar fractures are reported to be rare, and treatment options such as minimal internal K-wire fixation without using a tourniquet to prevent avascular necrosis have not previously been investigated.

CASE DESCRIPTION

We report a case of a comminuted talar body and a non-displaced neck fracture with dislocation of the tibiotalar, talonavicular and subtalar joints with bimalleolar epiphyseal fractures in an 11-year-old boy due to a fall from height. We present radiological findings, the surgical procedure and clinical outcomes of minimal internal K-wire fixation without using a tourniquet.

LITERATURE REVIEW

Avascular necrosis rates are reported to be between 0 % and 66 % after fractures of the neck of the talus and the talar body in children. The likelihood of developing avascular necrosis increases with the severity of the fracture.

CLINICAL RELEVANCE

To avoid avascular necrosis in a comminuted talar fracture accompanied by tibiotalar, talonavicular, subtalar dislocations and bimalleolar epiphyseal fractures, a minimal internal K-wire fixation without the use of a tourniquet was performed. The outcome was evaluated by the American Orthopedic Foot and Ankle Society score (AOFAS). A score of 90 (excellent) was found at the end of the second year of follow up. Radiology revealed preservation of the joint with no evidence of avascular necrosis, and clinical findings revealed a favorable functional outcome after two years.

LEVEL OF EVIDENCE

4.

Noninvasive monitoring of treatment response in a rabbit cyanide toxicity model reveals differences in brain and muscle metabolism

Noninvasive near infrared spectroscopy measurements were performed to monitor cyanide (CN) poisoning and recovery in the brain region and in foreleg muscle simultaneously, and the effects of a novel CN antidote, sulfanegen sodium, on tissue hemoglobin oxygenation changes were compared using a sub-lethal rabbit model. The results demonstrated that the brain region is more susceptible to CN poisoning and slower in endogenous CN detoxification following exposure than peripheral muscles. However, sulfanegen sodium rapidly reversed CN toxicity, with brain region effects reversing more quickly than muscle. In vivo monitoring of multiple organs may provide important clinical information regarding the extent of CN toxicity and subsequent recovery, and facilitate antidote drug development.

Hemodynamic and oxidative mechanisms of tourniquet-induced muscle injury: near-infrared spectroscopy for the orthopedics setting

During orthopedic procedures, the tourniquets used to maintain bloodless surgical fields cause ischemia and then reperfusion (I/R), leading to oxidative muscle injury. Established methods exist neither for monitoring orthopedic I/R nor for predicting the extent of tourniquet-associated oxidative injury. To develop a predictive model for tourniquet-associated oxidative muscle injury, this study combined real-time near-infrared spectroscopy (NIRS) monitoring of I/R with Western blotting (WB) for oxidized proteins. We hypothesized strong correlations between NIRS-derived I/R indices and muscle protein oxidation. In 17 patients undergoing ankle fracture repair, a thigh tourniquet was inflated on the injured limb (300 mmHg). Using a continuous-wave (CW) NIRS setup, oxygenated (O2Hb), deoxygenated (HHb), and total (tHb) hemoglobin were monitored bilaterally (tourniquet versus control) in leg muscles. Leg muscle biopsies were collected unilaterally (tourniquet side) immediately after tourniquet inflation (pre) and before deflation (post). Average ischemia duration was 43.2 ± 14.6 min. In post-compared to pre-biopsies, muscle protein oxidation (quantified using WB) increased 172.3%± 145.7% (P<0.0005). Changes in O2Hb and tHb were negatively correlated with protein oxidation (respectively: P=0.040, R2=0.25 and P=0.003, R2=0.58). Reoxygenation rate was positively correlated with protein oxidation (P=0.041, R2=0.25). These data indicate that using CW NIRS, it is possible to predict orthopedic tourniquet-associated muscle oxidative injury noninvasively.

Noninvasive tissue oxygen saturation determined by near-infrared spectroscopy following peripheral nerve block

BACKGROUND

Noninvasive physiologic measurement of cutaneous tissue oxygenation using near-infrared spectroscopy (NIRS) has become increasingly common in cardiovascular and plastic surgery. The aim of this study was to determine whether clinically available NIRS-based monitors could detect changes in tissue oxygen saturation (rSO(2)) following a variety of peripheral nerve blocks. We hypothesize that peripheral nerve blocks will produce detectable changes in cutaneous tissue oxygenation levels that can be measured by noninvasive NIRS-based oximetry.

METHODS

Forty adult patients scheduled for pre-operative peripheral nerve block placement were enrolled. Prior to block placement, NIRS sensors were placed on the operative and nonoperative (control) limb. Baseline tissue oxygen saturation values were obtained prior to dosing of the nerve block, and measurements were recorded every 5 min thereafter.

RESULTS

Initial rSO(2) values were higher in the operative vs. control limbs prior to nerve block placement. Tissue oxygen saturation increased in the blocked, but not control, limbs with time. Subgroup analysis suggested statistically significant differences in rSO(2) values in blocked vs. control limbs for cervical paravertebral, infraclavicular, and femoral nerve blocks.

CONCLUSIONS

Our results demonstrated sustained increases in tissue rSO(2) values following peripheral nerve block placement, in addition to higher initial rSO(2) values in operative limbs prior to block placement. Further investigations are necessary to define the expected baseline rSO(2) values in operative and control limbs. Future efforts utilizing NIRS-based detection of tissue ischemia should consider the small but significant changes in rSO(2) resulting from a successful nerve block.

Protective effects of the preconditioning with different doses of sodium aescinate on tourniquet-induced ischemic reperfusion

OBJECTIVE

To evaluate the protective effects of sodium aescinate (SA) preconditioning on the tourniquet-induced ischemia-reperfusion (I/R) injury after limbs operation.

METHODS

Seventy-five patients with grade I-II issued by American Society of Anesthesiology undergoing lower limb operation were randomly assigned to 3 groups: the control group, low-dose SA-treated group and high-dose SA-treated group; each group enrolled 25 patients. The patients were treated with 5 mg and 10 mg SA 30 min before tourniquet inflation in the two treatment groups separately, while the patients in the control group received normal saline. Venous blood samples were obtained before tourniquet was inflated (T0 baseline). And 5 (T1), 10 (T2), 20 (T3) min after tourniquet was released. The nitric oxide (NO), malondialdehyde (MDA) and superoxide dismutase (SOD) levels were determined by commercial kits. Meanwhile, arterial pressure (MAP) and heart rate (HR) were monitored from an automatic invigilator.

RESULTS

In the control group, MDA and NO levels were increased, and SOD and MAP were decreased significantly after tourniquet deflation compared to T0 baseline (P<0.05). After tourniquet deflation, MDA and NO levels in the two treated groups were significantly decreased; meanwhile, SOD levels and MAP were increased, and the variations of HR were more stable compared with the control group (all P<0.05). There was no significant difference in all of the above between the two treated groups (P>0.05).

CONCLUSION

The protective effects of SA preconditioning on tourniquet-induced limb I/R injury might possibly contribute to the increasing of SOD levels, and MAP and the decreasing of MDA and NO levels.

Acute traumatic compartment syndrome of the leg in children: diagnosis and outcome

BACKGROUND

Currently, the most common clinical scenario for compartment syndrome in children is acute traumatic compartment syndrome of the leg. We studied the cause, diagnosis, treatment, and outcome of acute traumatic compartment syndrome of the leg in children.

METHODS

Forty-three cases of acute traumatic compartment syndrome of the leg in forty-two skeletally immature patients were collected from two large pediatric trauma centers over a seventeen-year period. All children with acute traumatic compartment syndrome underwent fasciotomy. The mechanism of injury, date and time of injury, time to diagnosis, compartment pressures, time to fasciotomy, and outcome at the time of the latest follow-up were recorded.

RESULTS

Thirty-five (83%) of the forty-two patients were injured in a motor-vehicle accident and sustained tibial and fibular fractures. The average time from injury to fasciotomy was 20.5 hours (range, 3.9 to 118 hours). In general, the functional outcome was excellent at the time of the latest follow-up. No cases of infection were noted when fasciotomy was performed long after the injury. At the time of the latest follow-up, forty-one (95%) of forty-three cases were associated with no sequelae (such as pain, loss of function, or decreased sensation). The two patients who lost function had fasciotomy 82.5 and eighty-six hours after the injury.

CONCLUSIONS

Despite a long period from injury to fasciotomy, most children who are managed for acute traumatic compartment syndrome of the leg have an excellent outcome. This delay may occur because acute traumatic compartment syndrome manifests itself more slowly in children or because the diagnosis is harder to establish in this age group. The results of the present study should raise awareness of late presentation and the importance of vigilance for developing compartment syndrome in the early days after injury. Fasciotomy during the acute swelling phase, even long after injury, produced excellent results with no cases of infection.

Cytogenetic damage after ischemia and reperfusion

Tourniquets are often used to provide a bloodless operating field. However, they carry the risk of adverse effects caused by DNA damage from the free radicals generated during postischemic reperfusion of the blood. The aim of this study was to evaluate the cytogenetic damage caused by postischemic reperfusion on peripheral lymphocytes of five women and six men undergoing total knee arthroplasty "bloodless" operation using samples received before, during, immediately, and 1 h after the operations. The sister chromatid exchange assay was applied to peripheral blood lymphocyte cultures and the levels of sister chromatid exchanges were analyzed as a quantitative index of genotoxicity, along with the values of mitotic index and proliferation rate index as qualitative indices of cytotoxicity and cytostaticity, respectively. We observed that postischemic reperfusion induced cytogenetic damages specifically through reperfusion. DNA effects were most pronounced after tourniquet release and declined afterward without returning to preischemic baseline values. Our findings suggest the presence of a functional association between postischemic reperfusion and cytogenetic damage that may have important clinical implications.

Sulfanegen sodium treatment in a rabbit model of sub-lethal cyanide toxicity. Toxicol Appl Pharmacol. 2010;248:269-276. [PMID: 20705081 DOI: 10.1016/j.taap.2010.08.002]

The aim of this study is to investigate the ability of intramuscular and intravenous sulfanegen sodium treatment to reverse cyanide effects in a rabbit model as a potential treatment for mass casualty resulting from cyanide exposure. Cyanide poisoning is a serious chemical threat from accidental or intentional exposures. Current cyanide exposure treatments, including direct binding agents, methemoglobin donors, and sulfur donors, have several limitations. Non-rhodanese mediated sulfur transferase pathways, including 3-mercaptopyruvate sulfurtransferase (3-MPST) catalyze the transfer of sulfur from 3-MP to cyanide, forming pyruvate and less toxic thiocyanate. We developed a water-soluble 3-MP prodrug, 3-mercaptopyruvatedithiane (sulfanegen sodium), with the potential to provide a continuous supply of substrate for CN detoxification. In addition to developing a mass casualty cyanide reversal agent, methods are needed to rapidly and reliably diagnose and monitor cyanide poisoning and reversal. We use non-invasive technology, diffuse optical spectroscopy (DOS) and continuous wave near infrared spectroscopy (CWNIRS) to monitor physiologic changes associated with cyanide exposure and reversal. A total of 35 animals were studied. Sulfanegen sodium was shown to reverse the effects of cyanide exposure on oxyhemoglobin and deoxyhemoglobin rapidly, significantly faster than control animals when administered by intravenous or intramuscular routes. RBC cyanide levels also returned to normal faster following both intramuscular and intravenous sulfanegen sodium treatment than controls. These studies demonstrate the clinical potential for the novel approach of supplying substrate for non-rhodanese mediated sulfur transferase pathways for cyanide detoxification. DOS and CWNIRS demonstrated their usefulness in optimizing the dose of sulfanegen sodium treatment.

Intramuscular cobinamide sulfite in a rabbit model of sublethal cyanide toxicity. Ann Emerg Med. 2010;55:352-363. [PMID: 20045579 DOI: 10.1016/j.annemergmed.2009.12.002]

STUDY OBJECTIVE

Exposure to cyanide in fires and industrial exposures and intentional cyanide poisoning by terrorists leading to mass casualties is an ongoing threat. Current treatments for cyanide poisoning must be administered intravenously, and no rapid treatment methods are available for mass casualty cyanide exposures. Cobinamide is a cobalamin (vitamin B(12)) analog with an extraordinarily high affinity for cyanide that is more water-soluble than cobalamin. We investigate the use of intramuscular cobinamide sulfite to reverse cyanide toxicity-induced physiologic changes in a sublethal cyanide exposure animal model and determine the ability of an intramuscular cobinamide sulfite injection to rapidly reverse the physiologic effects of cyanide toxicity.

METHODS

New Zealand white rabbits were given 10 mg sodium cyanide intravenously over 60 minutes. Quantitative diffuse optical spectroscopy and continuous-wave near-infrared spectroscopy monitoring of tissue oxyhemoglobin and deoxyhemoglobin concentrations were performed concurrently with blood cyanide level measurements and cobinamide levels. Immediately after completion of the cyanide infusion, the rabbits were injected intramuscularly with cobinamide sulfite (n=6) or inactive vehicle (controls, n=5).

RESULTS

Intramuscular administration led to rapid mobilization of cobinamide and was extremely effective at reversing the physiologic effects of cyanide on oxyhemoglobin and within deoxyhemoglobin extraction. Recovery time to 63% of their baseline values in the central nervous system occurred within a mean of 1,032 minutes in the control group and 9 minutes in the cobinamide group, with a difference of 1,023 minutes (95% confidence interval 116 to 1,874 minutes). In muscle tissue, recovery times were 76 and 24 minutes, with a difference of 52 minutes (95% confidence interval 7 to 98 minutes). RBC cyanide levels returned toward normal significantly faster in cobinamide sulfite-treated animals than in control animals.

CONCLUSION

Intramuscular cobinamide sulfite rapidly and effectively reverses the physiologic effects of cyanide poisoning, suggesting that a compact cyanide antidote kit can be developed for mass casualty cyanide exposures.