Hydroxocobalamin Versus Sodium Thiosulfate for the Treatment of Acute Cyanide Toxicity in a Swine (Sus scrofa) Model

The effect of sodium thiosulfate on immune cell metabolism during porcine hemorrhage and resuscitation

Introduction

Sodium thiosulfate (Na₂S₂O₃), an H₂S releasing agent, was shown to be organ-protective in experimental hemorrhage. Systemic inflammation activates immune cells, which in turn show cell type-specific metabolic plasticity with modifications of mitochondrial respiratory activity. Since H₂S can dose-dependently stimulate or inhibit mitochondrial respiration, we investigated the effect of Na₂S₂O₃ on immune cell metabolism in a blinded, randomized, controlled, long-term, porcine model of hemorrhage and resuscitation. For this purpose, we developed a Bayesian sampling-based model for ¹³C isotope metabolic flux analysis (MFA) utilizing 1,2-¹³C₂-labeled glucose, ¹³C₆-labeled glucose, and ¹³C₅-labeled glutamine tracers.

Methods

After 3 h of hemorrhage, anesthetized and surgically instrumented swine underwent resuscitation up to a maximum of 68 h. At 2 h of shock, animals randomly received vehicle or Na₂S₂O₃ (25 mg/kg/h for 2 h, thereafter 100 mg/kg/h until 24 h after shock). At three time points (prior to shock, 24 h post shock and 64 h post shock) peripheral blood mononuclear cells (PBMCs) and granulocytes were isolated from whole blood, and cells were investigated regarding mitochondrial oxygen consumption (high resolution respirometry), reactive oxygen species production (electron spin resonance) and fluxes within the metabolic network (stable isotope-based MFA).

Results

PBMCs showed significantly higher mitochondrial O₂ uptake and lower O 2 • - production in comparison to granulocytes. We found that in response to Na₂S₂O₃ administration, PBMCs but not granulocytes had an increased mitochondrial oxygen consumption combined with a transient reduction of the citrate synthase flux and an increase of acetyl-CoA channeled into other compartments, e.g., for lipid biogenesis.

Conclusion

In a porcine model of hemorrhage and resuscitation, Na₂S₂O₃ administration led to increased mitochondrial oxygen consumption combined with stimulation of lipid biogenesis in PBMCs. In contrast, granulocytes remained unaffected. Granulocytes, on the other hand, remained unaffected. O 2 • - concentration in whole blood remained constant during shock and resuscitation, indicating a sufficient anti-oxidative capacity. Overall, our MFA model seems to be is a promising approach for investigating immunometabolism; especially when combined with complementary methods.

Main group cyanides: from hydrogen cyanide to cyanido-complexes

Homoleptic cyanide compounds exist of almost all main group elements. While the alkali metals and alkaline earth metals form cyanide salts, the cyanides of the lighter main group elements occur mainly as covalent compounds. This review gives an overview of the status quo of main group element cyanides and cyanido complexes. Information about syntheses are included as well as applications, special substance properties, bond lengths, spectroscopic characteristics and computations. Cyanide chemistry is presented mainly from the field of inorganic chemistry, but aspects of chemical biology and astrophysics are also discussed in relation to cyano compounds.

Biological Connection of Psychological Stress and Polytrauma under Intensive Care: The Role of Oxytocin and Hydrogen Sulfide

This paper explored the potential mediating role of hydrogen sulfide (H2S) and the oxytocin (OT) systems in hemorrhagic shock (HS) and/or traumatic brain injury (TBI). Morbidity and mortality after trauma mainly depend on the presence of HS and/or TBI. Rapid "repayment of the O2 debt" and prevention of brain tissue hypoxia are cornerstones of the management of both HS and TBI. Restoring tissue perfusion, however, generates an ischemia/reperfusion (I/R) injury due to the formation of reactive oxygen (ROS) and nitrogen (RNS) species. Moreover, pre-existing-medical-conditions (PEMC's) can aggravate the occurrence and severity of complications after trauma. In addition to the "classic" chronic diseases (of cardiovascular or metabolic origin), there is growing awareness of psychological PEMC's, e.g., early life stress (ELS) increases the predisposition to develop post-traumatic-stress-disorder (PTSD) and trauma patients with TBI show a significantly higher incidence of PTSD than patients without TBI. In fact, ELS is known to contribute to the developmental origins of cardiovascular disease. The neurotransmitter H2S is not only essential for the neuroendocrine stress response, but is also a promising therapeutic target in the prevention of chronic diseases induced by ELS. The neuroendocrine hormone OT has fundamental importance for brain development and social behavior, and, thus, is implicated in resilience or vulnerability to traumatic events. OT and H2S have been shown to interact in physical and psychological trauma and could, thus, be therapeutic targets to mitigate the acute post-traumatic effects of chronic PEMC's. OT and H2S both share anti-inflammatory, anti-oxidant, and vasoactive properties; through the reperfusion injury salvage kinase (RISK) pathway, where their signaling mechanisms converge, they act via the regulation of nitric oxide (NO).

Evaluation of aqueous dimethyl trisulfide as an antidote to a highly lethal cyanide poisoning in a large swine model

BACKGROUND

Cyanide is a rapid acting, lethal, metabolic poison and remains a significant threat. Current FDA-approved antidotes are not amenable or efficient enough for a mass casualty incident.

OBJECTIVE

The objective of this study is to evaluate short and long-term efficacy of intramuscular aqueous dimethyl trisulfide (DMTS) on survival and clinical outcomes in a swine model of cyanide exposure.

METHODS

Anesthetized swine were instrumented and acclimated until breathing spontaneously. Potassium cyanide infusion was initiated and continued until 5 min after the onset of apnea. Subsequently, animals were treated with intramuscular DMTS (n = 11) or saline control (n = 10). Laboratory values and DMTS blood concentrations were assessed at various time points and physiological parameters were monitored continuously until the end of the experiment unless death occurred. A subset of animals treated with DMTS (n = 5) were survived for 7 days to evaluate muscle integrity by repeat biopsy and neurobehavioral outcomes.

RESULTS

Physiological parameters and time to apnea were similar in both groups at baseline and at time of treatment. Survival in the DMTS-treated group was 90% and 30% in saline controls (p = 0.0034). DMTS-treated animals returned to breathing at 12.0 ± 10.4 min (mean ± SD) compared to 22.9 ± 7.0 min (mean ± SD) in the 3 surviving controls. Blood collected prior to euthanasia showed improved blood lactate concentrations in the DMTS treatment group; 5.47 ± 2.65 mmol/L vs. 9.39 ± 4.51 mmol/L (mean ± SD) in controls (p = 0.0310). Low concentrations of DMTS were detected in the blood, gradually increasing over time with no elimination phase observed. There was no mortality, histological evidence of muscle trauma, or observed adverse neurobehavioral outcomes, in DMTS-treated animals survived to 7 days.

CONCLUSION

Intramuscular administration of aqueous DMTS improves survival following cyanide poisoning with no observed long-term effects on muscle integrity at the injection site or adverse neurobehavioral outcomes.

Antidotal effects of methylene blue against cyanide neurological toxicity: in vivo and in vitro studies

The aim of the present study was to determine whether methylene blue (MB) could directly oppose the neurological toxicity of a lethal cyanide (CN) intoxication. KCN, infused at the rate of 0.375 mg/kg/min intravenously, produced 100% lethality within 15 min in unanaesthetized rats (n = 12). MB at 10 (n = 5) or 20 mg/kg (n = 5), administered 3 min into CN infusion, allowed all animals to survive with no sequelae. No apnea and gasping were observed at 20 mg/kg MB (P < 0.001). The onset of coma was also significantly delayed and recovery from coma was shortened in a dose-dependent manner (median of 359 and 737 seconds, respectively, at 20 and 10 mg/kg). At 4 mg/kg MB (n = 5), all animals presented faster onset of coma and apnea and a longer period of recovery than at the highest doses (median 1344 seconds, P < 0.001). MB reversed NaCN-induced resting membrane potential depolarization and action potential depression in primary cultures of human fetal neurons intoxicated with CN. MB restored calcium homeostasis in the CN-intoxicated human SH-SY5Y neuroblastoma cell line. We conclude that MB mitigates the neuronal toxicity of CN in a dose-dependent manner, preventing the lethal depression of respiratory medullary neurons and fatal outcome.

Toxic inhalational injury

A middle-aged patient presented with toxic inhalational injury, and was resuscitated prehospitally and treated in the emergency department for smoke inhalation, carbon monoxide (CO) exposure and cyanide poisoning with the use of antidotes. Due to the CO effects on spectrophotometry, an anaemia initially identified on blood gas analysis was thought to be artefactual, but was later confirmed by laboratory testing to be accurate. In addition, cyanide can confound haemoglobin testing due to its use in the analytical process and non-cyanide analysis is required when there is suspected exposure. Although no consensus exists on a first-line cyanide antidote choice, hydroxocobalamin is the only antidote without a serious side effect profile and/or deleterious cardiovascular effects. We propose prehospital enhanced care teams consider carrying hydroxocobalamin for early administration in toxic inhalational injury.

Modest and variable efficacy of pre-exposure hydroxocobalamin and dicobalt edetate in a porcine model of acute cyanide salt poisoning

Background: Dicobalt edetate and hydroxocobalamin are widely used to treat hydrogen cyanide poisoning. However, comparative and quantitative efficacy data are lacking. Although post-exposure treatment is typical, it may be possible to administer these antidotes before exposure to first attenders entering a known site of cyanide release, as supplementary protection to their personal protective equipment.Methods: We established an anaesthetised Gottingen minipig model of lethal bolus potassium cyanide (KCN) injection to simulate high dose hydrogen cyanide inhalation. Doses were similar to human lethal doses of KCN. Dicobalt edetate and hydroxocobalamin were administered shortly before KCN and their effect on metabolic and cardiovascular variables and survival time were measured.Results: Increases in arterial lactate were similar after 0.08 and 0.12 mmol/kg KCN. KCN 0.08 mmol/kg was survived by 4/4 animals with moderate cardiovascular effects, while the 0.12 mmol/kg dose was lethal in 4/4 animals, with a mean time to euthanasia of 28.3 (SEM: 13.9) min. Administration of dicobalt edetate (0.021 mmol/kg, 8.6 mg/kg) or hydroxocobalamin (0.054 mmol/kg, 75 mg/kg) at clinically licenced doses had modest effect on lactate concentrations but increased survival after administration of KCN 0.12 mmol/kg (survival: dicobalt edetate 4/4, hydroxocobalamin 2/4) but not 0.15 mmol/kg (0/4 and 0/4, respectively). In a subsequent larger study, doubling the dose of hydroxocobalamin (0.108 mmol/kg, 150 mg/kg) was associated with a modest but inconsistent increased survival after 0.15 mmol/kg KCN (survival: control 0/8, 75 mg/kg 1/10, 150 mg/kg 3/10) likely due to variable pharmacokinetics.Conclusions: In this porcine study of cyanide exposure, with pre-exposure antidote administration, licenced doses of dicobalt edetate and hydroxocobalamin were effective at just lethal doses but ineffective at less than twice the estimated LD₅₀. The efficacy of a rapidly-administered double-dose of hydroxocobalamin was limited by variable pharmacokinetics. In clinical poisoning scenarios, with delayed administration, the antidotes are likely to be even less effective. New antidotes are required for treatment of cyanide exposures appreciably above the minimum lethal dose.

The central role of protein kinase C epsilon in cyanide cardiotoxicity and its treatment

In adult mouse myocytes, brief exposure to sodium cyanide (CN) in the presence of glucose does not decrease ATP levels, yet produces profound reduction in contractility, intracellular Ca2+ concentration ([Ca2+]i) transient and L-type Ca2+ current (ICa) amplitudes. We analyzed proteomes from myocytes exposed to CN, focusing on ionic currents associated with excitation-contraction coupling. CN induced phosphorylation of α1c subunit of L-type Ca2+ channel and α2 subunit of Na+-K+-ATPase. Methylene blue (MB), a CN antidote that we previously reported to ameliorate CN-induced reduction in contraction, [Ca2+]i transient and ICa amplitudes, was able to reverse this phosphorylation. CN decreased Na+-K+-ATPase current contributed by α2 but not α1 subunit, an effect that was also counteracted by MB. Peptide consensus sequences suggested CN-induced phosphorylation was mediated by protein kinase C epsilon (PKCε). Indeed, CN stimulated PKC kinase activity and induced PKCε membrane translocation, effects that were prevented by MB. Pre-treatment with myristoylated PKCε translocation activator or inhibitor peptides mimicked and inhibited the effects of CN on ICa and myocyte contraction, respectively. We conclude that CN activates PKCε, which phosphorylates L-type Ca2+ channel and Na+-K+-ATPase, resulting in depressed cardiac contractility. We hypothesize that this inhibition of ion fluxes represents a novel mechanism by which the cardiomyocyte reduces its ATP demand (decreased ion fluxes and contractility), diminishes ATP turnover and preserves cell viability. However, this cellular protective effect translates into life-threatening cardiogenic shock in vivo, thereby creating a profound disconnect between survival mechanisms at the cardiomyocyte level from those at the level of the whole organism.

Burn Casualty Care in the Deployed Setting

Management of wartime burn casualties can be very challenging. Burns frequently occur in the setting of other blunt and penetrating injuries. This clinical practice guideline provides a manual for burn injury assessment, resuscitation, wound care, and specific scenarios including chemical and electrical injuries in the deployed or austere setting. The clinical practice guideline also reviews considerations for the definitive care of local national patients, including pediatric patients, who are unable to be evacuated from theater. Medical providers are encouraged to contact the US Army Institute of Surgical Research (USAISR) Burn Center when caring for a burn casualty in the deployed setting.

Inhalation Injury and Toxic Industrial Chemical Exposure

Toxic industrial chemicals include chlorine, phosgene, hydrogen sulfide, and ammonia have variable effects on the respiratory tract, and maybe seen alone or in combination, secondary to inhalation injury. Other considerations include the effects of cyanide, carbon monoxide, and fire suppressants. This Clinical Practice Guideline (CPG) will provide the reader with a brief overview of these important topics and general management strategies for each as well as for inhalation injury. Chlorine, phosgene, hydrogen sulfide, and ammonia are either of intermediate or high water solubility leading to immediate reactions with mucous membranes of the face, throat, and lungs and rapid symptoms onset after exposure. The exception to rapid symptom onset is phosgene which may take up to a day to develop severe acute respiratory distress syndrome. Management of these patients includes early airway management, lung-protective ventilator strategies, aggressive pulmonary toilet, and avoidance of volume overload.

Intramuscular sodium tetrathionate as an antidote in a clinically relevant swine model of acute cyanide toxicity

Background: Cyanide is a metabolic poison used in multiple industries and is a high threat chemical agent. Current antidotes require intravenous administration, limiting their usefulness in a mass casualty scenario. Sodium tetrathionate reacts directly with cyanide yielding thiosulfate and the non-toxic compound thiocyanate. Thiosulfate, in turn, neutralizes a second molecule of cyanide, thus, per mole, sodium tetrathionate neutralizes two moles of cyanide. Historical studies examined its efficacy as a cyanide antidote, but it has not been evaluated in a clinically relevant, large animal model, nor has it previously been administered by intramuscular injection.Objective: The objective of this study is to evaluate the efficacy of intramuscular sodium tetrathionate on survival and clinical outcomes in a large, swine model of severe cyanide toxicity.Methods: Anesthetized swine were instrumented for continuous monitoring of hemodynamics, then acclimated and breathing spontaneously prior to potassium cyanide infusion (0.17 mg/kg/min). At 6-min post-apnea (no breaths for 20 s), the cyanide infusion was terminated, and animals were treated with sodium tetrathionate (∼18 mg/kg) or normal saline control. Clinical parameters and laboratory values were evaluated at various time points until death or termination of the experiment (90 min post-treatment).Results: Laboratory values, vital signs, and time to apnea were similar in both groups at baseline and treatment. Survival in the sodium tetrathionate treated group was 100% and 17% in controls (p = 0.0043). All animals treated with sodium tetrathionate returned to breathing at a mean time of 10.85 min after antidote, and all but one control remained apneic through end of the experiment. Animals treated with tetrathionate showed improvement in blood lactate (p ≤ 0.002) starting at 30 min post-treatment. The average time to death in the control group is 63.3 ± 23.2 min. No systemic or localized adverse effects of intramuscular administration of sodium tetrathionate were observed.Conclusion: Sodium tetrathionate significantly improves survival and clinical outcomes in a large, swine model of acute cyanide poisoning.

Intramuscular dimethyl trisulfide: efficacy in a large swine model of acute severe cyanide toxicity

BACKGROUND

Cyanide is a deadly compound used as a terrorist agent. Current FDA approved antidotes require intravenous administration, limiting their utility in a mass casualty scenario. Dimethyl trisulfide (DMTS), a sulfur-based molecule, binds cyanide converting it to the less toxic by-product thiocyanate. Studies evaluating efficacy in rodents have been performed, but a large, clinically relevant animal model has not been reported.

OBJECTIVE

This study evaluates the efficacy of intramuscular DMTS on survival and clinical outcomes in a swine model of acute, severe cyanide toxicity.

METHODS

Anesthetized swine were instrumented for continuous monitoring of hemodynamics. Prior to potassium cyanide infusion animals were acclimated and breathing spontaneously. At 5-minutes post-apnea animals were treated with DMTS or saline. Vital signs, hemodynamics, and laboratory values were evaluated at various time points.

RESULTS

Baseline values and time to apnea were similar in both groups. Survival in the DMTS treated group was 83.3% and 0% in saline controls (p = .005). The DMTS group returned to breathing at a mean time of 19.3 ± 10 min after antidote, control animals did not return to breathing (CI difference 8.8, 29.8). At the end of the experiment or time of death, mean lactate was 9.41 mmol/L vs. 4.35 mmol/L (CI difference -10.94,0.82) in the saline and DMTS groups, respectively and pH was 7.20 vs. 7.37 (CI difference -0.04, 0.38). No adverse effects were observed at the injection site.

CONCLUSION

Intramuscular administration of DMTS improves survival and clinical outcomes in our large animal swine model of acute cyanide toxicity.

Intravenous Hydroxocobalamin Versus Hextend Versus Control for Class III Hemorrhage Resuscitation in a Prehospital Swine Model

Background

Hydroxyethyl starch (Hextend) has been used for hemorrhagic shock resuscitation, however, hydroxyethyl starch may be associated with adverse outcomes.

Objective

To compare systolic blood pressure (sBP) in animals that had 30% of their blood volume removed and treated with intravenous hydroxocobalamin, hydroxyethyl starch, or no fluid.

Methods

Twenty-eight swine (45-55 kg) were anesthetized and instrumented with continuous femoral and pulmonary artery pressure monitoring. Animals were hemorrhaged 20 mL/kg over 20 minutes and then administered 150 mg/kg IV hydroxocobalamin in 180 mL saline, 500 mL hydroxyethyl starch, or no fluid and monitored for 60 minutes. Data were modeled using repeated measures multivariate analysis of variance.

Results

There were no significant differences before treatment. At 20 minutes after hemorrhage, there was no significant difference in mean sBP between treated groups, however, control animals displayed significantly lower mean sBP (p < 0.001). Mean arterial pressure and heart rate improved in the treated groups but not in the control group (p < 0.02). Prothrombin time was longer and platelet counts were lower in the Hextend group (p < 0.05). Moreover, thromboelastography analysis showed longer clotting (K) times (p < 0.05) for the hydroxyethyl starch-treated group.

Conclusion

Hydroxocobalamin restored blood pressure more effectively than no treatment and as effectively as hydroxyethyl starch but did not adversely affect coagulation.

Rationally designed molecules for resurgence of cyanide mitigated cytochrome c oxidase activity

Cytochrome c oxidase (CcOX) containing binuclear heme a₃-Cu B centre (BNC) mechanises the process of electron transfer in the last phase of cellular respiration. The molecular modelling based structural analysis of CcOX - heme a₃-Cu B complex was performed and the disturbance to this complex under cyanide poisoning conditions was investigated. Taking into consideration the results of molecular docking studies, new chemical entities were developed for clipping cyanide from the enzyme and restoring its normal function. It was found that the molecules obtained by combining syringaldehyde, oxindole and chrysin moieties bearing propyl/butyl spacing groups occupy the BNC region and effectively remove cyanide bound to the enzyme. The binding constant of compound 2 with CN^- was 2.3 × 10⁵ M^-1 and its ED₅₀ for restoring the cyanide bound CcOX activity in 10 min was 16 µM. The compound interacted with CN^- over the pH range 5-10. The comparison of the loss of enzymatic activity in the presence of CN^- and resumption of enzymatic activity by compound 2 mediated removal of CN^- indicated the efficacy of the compound as antidote of cyanide.

Characterization of a Swine (Sus scrofa) Model of Oral Potassium Cyanide Intoxication

Cyanide is a readily available and potentially lethal substance. Oral exposure can result in larger doses, compared with other routes. Currently, there are no antidotes specific for use in the treatment of oral cyanide poisoning, and studies cannot be done in humans. We report on a new large animal model of oral cyanide toxicity to evaluate potential antidotes. Six female swine (Sus scrofa; weight, 45 to 55 kg) were anesthetized, intubated, and instrumented. Animals received a KCN bolus of either 5 or 8 mg/kg delivered via orogastric tube. Time to apnea was recorded; parameters monitored included heart rate, respiratory rate, blood pressure, pulse oximetry, end-tidal CO2, arterial blood gasses, and lactate concentrations. The Welch t test was used to calculate confidence intervals, mean, and standard deviation, and a Kaplan-Meier survival curve was used to compare survival between the 2 groups. At baseline, all animals in both groups were similar. Animals in the 5-mg/kg group had a more rapid time to apnea (5.1 ± 2.1 min), longer time to death (48.5 ± 38.1 min), and a greater rate of survival than the 8-mg/kg group (apnea, 10.6 ± 10.7 min; death, 26.1 ± 5.8 min). All animals displayed signs of toxicity (acidemia, hyperlactatemia, hypotension, apnea). We here report a large animal (swine) model of oral cyanide poisoning with dose-dependent effects in regard to time to death and survival rate. This model likely will be valuable for the development of medical countermeasures for oral cyanide poisoning.

Rationally Designed Circularly Arranged Sextuple Molecule with Dimethoxyphenolic Tentacles for Ample Hunting of Cyanide

Herein, we report the design, synthesis, and cyanide-scavenging behavior of circularly arranged sextuple molecule 4. The six syringaldehyde units carrying equal number of dimethoxyphenolic moieties projecting at the periphery make the molecule highly efficient for cleaning up cyanide from the aqueous solution. The stoichiometric data 1:6 showed that six units of cyanide interact with one unit of compound 4. The association constant of the compound for cyanide was 2.5 × 10⁴ M^-1, and its detection limit for cyanide was 10 nM. The compound was also found to remove cyanide bound to cytochrome c oxidase.

Methylene blue counteracts cyanide cardiotoxicity: cellular mechanisms

In adult left ventricular mouse myocytes, exposure to sodium cyanide (NaCN) in the presence of glucose dose-dependently reduced contraction amplitude, with ~80% of maximal inhibitory effect attained at 100 µM. NaCN (100 µM) exposure for 10 min significantly decreased contraction and intracellular Ca2+ concentration ([Ca2+]i) transient amplitudes, systolic but not diastolic [Ca2+]i, and maximal L-type Ca2+ current ( ICa) amplitude, indicating acute alteration of [Ca2+]i homeostasis largely accounted for the observed excitation-contraction abnormalities. In addition, NaCN depolarized resting membrane potential ( Em), reduced action potential (AP) amplitude, prolonged AP duration at 50% (APD50) and 90% repolarization (APD90), and suppressed depolarization-activated K+ currents but had no effect on Na+-Ca2+ exchange current ( INaCa). NaCN did not affect cellular adenosine triphosphate levels but depolarized mitochondrial membrane potential (ΔΨm) and increased superoxide (O2·-) levels. Methylene blue (MB; 20 µg/ml) added 3 min after NaCN restored contraction and [Ca2+]i transient amplitudes, systolic [Ca2+]i, Em, AP amplitude, APD50, APD90, ICa, depolarization-activated K+ currents, ΔΨm, and O2·- levels toward normal. We conclude that MB reversed NaCN-induced cardiotoxicity by preserving intracellular Ca2+ homeostasis and excitation-contraction coupling ( ICa), minimizing risks of arrhythmias ( Em, AP configuration, and depolarization-activated K+ currents), and reducing O2·- levels. NEW & NOTEWORTHY Cyanide poisoning due to industrial exposure, smoke inhalation, and bioterrorism manifests as cardiogenic shock and requires rapidly effective antidote. In the early stage of cyanide exposure, adenosine triphosphate levels are normal but myocyte contractility is reduced, largely due to alterations in Ca2+ homeostasis because of changes in oxidation-reduction environment of ion channels. Methylene blue, a drug approved by the U.S. Food and Drug Administration, ameliorates cyanide toxicity by normalizing oxidation-reduction state and Ca2+ channel function.

Smoke Inhalation Injury: Etiopathogenesis, Diagnosis, and Management

Smoke inhalation injury is a major determinant of morbidity and mortality in fire victims. It is a complex multifaceted injury affecting initially the airway; however, in short time, it can become a complex life-threatening systemic disease affecting every organ in the body. In this review, we provide a summary of the underlying pathophysiology of organ dysfunction and provide an up-to-date survey of the various critical care modalities that have been found beneficial in caring for these patients. Major pathophysiological change is development of edema in the respiratory tract. The tracheobronchial tree is injured by steam and toxic chemicals, leading to bronchoconstriction. Lung parenchyma is damaged by the release of proteolytic elastases, leading to release of inflammatory mediators, increase in transvascular flux of fluids, and development of pulmonary edema and atelectasis. Decreased levels of surfactant and immunomodulators such as interleukins and tumor-necrosis-factor-α accentuate the injury. A primary survey is conducted at the site of fire, to ensure adequate airway, breathing, and circulation. A good intravenous access is obtained for the administration of resuscitation fluids. Early intubation, preferably with fiberoptic bronchoscope, is prudent before development of airway edema. Bronchial hygiene is maintained, which involves therapeutic coughing, chest physiotherapy, deep breathing exercises, and early ambulation. Pharmacological agents such as beta-2 agonists, racemic epinephrine, N-acetyl cysteine, and aerosolized heparin are used for improving oxygenation of lungs. Newer agents being tested are perfluorohexane, porcine pulmonary surfactant, and ClearMate. Early diagnosis and treatment of smoke inhalation injury are the keys for better outcome.

Sodium Nitrite and Sodium Thiosulfate Are Effective Against Acute Cyanide Poisoning When Administered by Intramuscular Injection

STUDY OBJECTIVE

The 2 antidotes for acute cyanide poisoning in the United States must be administered by intravenous injection. In the out-of-hospital setting, intravenous injection is not practical, particularly for mass casualties, and intramuscular injection would be preferred. The purpose of this study is to determine whether sodium nitrite and sodium thiosulfate are effective cyanide antidotes when administered by intramuscular injection.

METHODS

We used a randomized, nonblinded, parallel-group study design in 3 mammalian models: cyanide gas inhalation in mice, with treatment postexposure; intravenous sodium cyanide infusion in rabbits, with severe hypotension as the trigger for treatment; and intravenous potassium cyanide infusion in pigs, with apnea as the trigger for treatment. The drugs were administered by intramuscular injection, and all 3 models were lethal in the absence of therapy.

RESULTS

We found that sodium nitrite and sodium thiosulfate individually rescued 100% of the mice, and that the combination of the 2 drugs rescued 73% of the rabbits and 80% of the pigs. In all 3 species, survival in treated animals was significantly better than in control animals (log rank test, P<.05). In the pigs, the drugs attenuated an increase in the plasma lactate concentration within 5 minutes postantidote injection (difference: plasma lactate, saline solution-treated versus nitrite- or thiosulfate-treated 1.76 [95% confidence interval 1.25 to 2.27]).

CONCLUSION

We conclude that sodium nitrite and sodium thiosulfate administered by intramuscular injection are effective against severe cyanide poisoning in 3 clinically relevant animal models of out-of-hospital emergency care.

Diagnosis and management of inhalation injury: an updated review

In this article we review recent advances made in the pathophysiology, diagnosis, and treatment of inhalation injury. Historically, the diagnosis of inhalation injury has relied on nonspecific clinical exam findings and bronchoscopic evidence. The development of a grading system and the use of modalities such as chest computed tomography may allow for a more nuanced evaluation of inhalation injury and enhanced ability to prognosticate. Supportive respiratory care remains essential in managing inhalation injury. Adjuncts still lacking definitive evidence of efficacy include bronchodilators, mucolytic agents, inhaled anticoagulants, nonconventional ventilator modes, prone positioning, and extracorporeal membrane oxygenation. Recent research focusing on molecular mechanisms involved in inhalation injury has increased the number of potential therapies.

Acute Cyanide Poisoning: Hydroxocobalamin and Sodium Thiosulfate Treatments with Two Outcomes following One Exposure Event

Cyanide is rapidly reacting and causes arrest of aerobic metabolism. The symptoms are diffuse and lethal and require high clinical suspicion. Remediation of symptoms and mortality is highly dependent on quick treatment with a cyanide antidote. Presently, there are two widely accepted antidotes: sodium thiosulfate and hydroxocobalamin. These treatments act on different components of cyanide's metabolism. Here, we present two cases resulting from the same source of cyanide poisoning and the use of both antidotes separately used with differing outcomes.

A prospective, randomized trial of intravenous hydroxocobalamin versus whole blood transfusion compared to no treatment for Class III hemorrhagic shock resuscitation in a prehospital swine model

OBJECTIVES

The objective was to compare systolic blood pressure (sBP) over time in swine that have had 30% of their blood volume removed (Class III shock) and treated with intravenous (IV) whole blood or IV hydroxocobalamin, compared to nontreated control animals.

METHODS

Thirty swine (45 to 55 kg) were anesthetized, intubated, and instrumented with continuous femoral and pulmonary artery pressure monitoring. Animals were hemorrhaged a total of 20 mL/kg over a 20-minute period. Five minutes after hemorrhage, animals were randomly assigned to receive 150 mg/kg IV hydroxocobalamin solubilized in 180 mL of saline, 500 mL of whole blood, or no treatment. Animals were monitored for 60 minutes thereafter. A sample size of 10 animals per group was determined based on a power of 80% and an alpha of 0.05 to detect an effect size of at least a 0.25 difference (>1 standard deviation) in mean sBP between groups. sBP values were analyzed using repeated-measures analysis of variance (RANOVA). Secondary outcome data were analyzed using repeated-measures multivariate analysis of variance (RMANOVA).

RESULTS

There were no significant differences between hemodynamic parameters of IV hydroxocobalamin versus whole blood versus control group at baseline (MANOVA; Wilks' lambda; p = 0.868) or immediately posthemorrhage (mean sBP = 47 mm Hg vs. 41 mm Hg vs. 37 mm Hg; mean arterial pressure = 39 mm Hg vs. 28 mm Hg vs. 34 mm Hg; mean serum lactate = 1.2 mmol/L vs. 1.4 mmol/L vs. 1.4 mmol/L; MANOVA; Wilks' lambda; p = 0.348). The outcome RANOVA model detected a significant difference by time between groups (p < 0.001). Specifically, 10 minutes after treatment, treated animals showed a significant increase in mean sBP compared to nontreated animals (mean sBP = 76.3 mm Hg vs. 85.7 mm Hg vs. 51.1 mm Hg; p < 0.001). RMANOVA modeling of the secondary data detected a significant difference in mean arterial pressure, heart rate, and serum lactate (p < 0.001). Similar to sBP, 10 minutes after treatment, treated animals showed a significant increase in mean arterial pressure compared to nontreated animals (mean arterial pressure = 67.7 mm Hg vs. 61.4 mm Hg vs. 40.5 mm Hg). By 10 minutes, mean heart rate was significantly slower in treated animals compared to nontreated animals (mean heart rate = 97.3 beats/min vs. 95.2 beats/min vs. 129.5 beats/min; p < 0.05). Serum lactate, an early predictor of shock, continued to rise in the control group, whereas it did not in treated animals. Thirty minutes after treatment, serum lactate values of treated animals were significantly lower compared to nontreated animals (p < 0.05). This trend continued throughout the 60-minute observation period such that 60-minute values for lactate were 1.4 mmol/L versus 1.1 mmol/L versus 3.8 mmol/L. IV hydroxocobalamin produced a statistically significant increase in systemic vascular resistance compared to control, but not whole blood, with a concomitant decrease in cardiac output.

CONCLUSIONS

Intravenous hydroxocobalamin was more effective than no treatment and as effective as whole blood transfusion, in reversing hypotension and inhibiting rises in serum lactate in this prehospital, controlled, Class III swine hemorrhage model.

Intraosseous versus intravenous infusion of hydroxocobalamin for the treatment of acute severe cyanide toxicity in a Swine model

OBJECTIVES

Easily administrated cyanide antidotes are needed for first responders, military troops, and emergency department staff after cyanide exposure in mass casualty incidents or due to smoke inhalation during fires involving many victims. Hydroxocobalamin has proven to be an effective antidote, but cannot be given intramuscularly because the volume of diluent needed is too large. Thus, intraosseous (IO) infusion may be an alternative, as it is simple and has been recommended for the administration of other resuscitation drugs. The primary objective of this study was to compare the efficacy of IO delivery of hydroxocobalamin to intravenous (IV) injection for the management of acute cyanide toxicity in a well-described porcine model.

METHODS

Twenty-four swine (45 to 55 kg) were anesthetized, intubated, and instrumented with continuous mean arterial pressure (MAP) and cardiac output monitoring. Cyanide was continuously infused until severe hypotension (50% of baseline MAP), followed by IO or IV hydroxocobalamin treatment. Animals were randomly assigned to receive IV (150 mg/kg) or IO (150 mg/kg) hydroxocobalamin and monitored for 60 minutes after start of antidotal infusion. The primary outcome measure was the change in MAP after antidotal treatment from onset of hypotension (time zero) to 60 minutes. A sample size of 12 animals per group was determined by group size analysis based on power of 80% to detect a one standard deviation of the mean MAP between the groups with an alpha of 0.05. Whole blood cyanide, lactate, pH, nitrotyrosine (nitric oxide marker) levels, cerebral and renal near infrared spectrometry (NIRS) oxygenation, and inflammatory markers were also measured. Repeated-measures analysis of variance was used to determine statistically significant changes between groups over time.

RESULTS

At baseline and at the point of hypotension, physiologic parameters were similar between groups. At the conclusion of the study, 10 out of 12 animals in the IV group and 10 out of 12 in IO group survived (p = 1.0). Both groups demonstrated a similar return to baseline MAP (p = 0.997). Cardiac output, oxygen saturation, and systemic vascular resistance were also found to be similar between groups (p > 0.4), and no difference was detected between bicarbonate, pH, and lactate levels (p > 0.8). Cyanide levels were undetectable after the hydroxocobalamin infusion throughout the study in both groups (p = 1.0). Cerebral and renal NIRS oxygenation decreased in parallel to MAP during cyanide infusion and increased after antidote infusion in both groups. Serum nitrotyrosine increased during cyanide infusion in all animals and then decreased in both study arms after hydroxocobalamin infusion (p > 0.5). Serum cytokines increased starting at cyanide infusion and no difference was detected between groups (tumor necrosis factor-α, interleukin [IL]-1β, IL-6, and IL-10).

CONCLUSIONS

The authors found no difference in the efficacy of IV versus IO hydroxocobalamin in the treatment of severe cyanide toxicity in a validated porcine model.

Intravenous cobinamide versus hydroxocobalamin for acute treatment of severe cyanide poisoning in a swine (Sus scrofa) model

STUDY OBJECTIVE

Hydroxocobalamin is a Food and Drug Administration-approved antidote for cyanide poisoning. Cobinamide is a potential antidote that contains 2 cyanide-binding sites. To our knowledge, no study has directly compared hydroxocobalamin with cobinamide in a severe, cyanide-toxic large-animal model. Our objective is to compare the time to return of spontaneous breathing in swine with acute cyanide-induced apnea treated with intravenous hydroxocobalamin, intravenous cobinamide, or saline solution (control).

METHODS

Thirty-three swine (45 to 55 kg) were intubated, anesthetized, and instrumented (continuous mean arterial pressure and cardiac output monitoring). Anesthesia was adjusted to allow spontaneous breathing with FiO2 of 21% during the experiment. Cyanide was continuously infused intravenously until apnea occurred and lasted for 1 minute (time zero). Animals were then randomly assigned to receive intravenous hydroxocobalamin (65 mg/kg), cobinamide (12.5 mg/kg), or saline solution and monitored for 60 minutes. A sample size of 11 animals per group was selected according to obtaining a power of 80%, an α of .05, and an SD of 0.17 in mean time to detect a 20% difference in time to spontaneous breathing. We assessed differences in time to death among groups, using Kaplan-Meier estimation methods, and compared serum lactate, blood pH, cardiac output, mean arterial pressure, respiratory rate, and minute ventilation time curves with repeated-measures ANOVA.

RESULTS

Baseline weights and vital signs were similar among groups. The time to apnea and cyanide dose required to achieve apnea were similar. At time zero, mean cyanide blood and lactate concentrations and reduction in mean arterial pressure from baseline were similar. In the saline solution group, 2 of 11 animals survived compared with 10 of 11 in the hydroxocobalamin and cobinamide groups (P<.001 between the 2 treated groups and the saline solution group). Time to return of spontaneous breathing after antidote was similar between hydroxocobalamin and cobinamide (1 minute 48 seconds versus 1 minute 49 seconds, respectively). Blood cyanide concentrations became undetectable at the end of the study in both antidote-treated groups, and no statistically significant differences were detected between the 2 groups for mean arterial pressure, cardiac output, respiratory rate, lactate, or pH.

CONCLUSION

Both hydroxocobalamin and cobinamide rescued severely cyanide-poisoned swine from apnea in the absence of assisted ventilation. The dose of cobinamide was one fifth that of hydroxocobalamin.

Combined administration of hyperbaric oxygen and hydroxocobalamin improves cerebral metabolism after acute cyanide poisoning in rats

Hyperbaric oxygen therapy (HBOT) or intravenous hydroxocobalamin (OHCob) both abolish cyanide (CN)-induced surges in interstitial brain lactate and glucose concentrations. HBOT has been shown to induce a delayed increase in whole blood CN concentrations, whereas OHCob may act as an intravascular CN scavenger. Additionally, HBOT may prevent respiratory distress and restore blood pressure during CN intoxication, an effect not seen with OHCob administration. In this report, we evaluated the combined effects of HBOT and OHCob on interstitial lactate, glucose, and glycerol concentrations as well as lactate-to-pyruvate ratio in rat brain by means of microdialysis during acute CN poisoning. Anesthetized rats were allocated to three groups: 1) vehicle (1.2 ml isotonic NaCl intra-arterially); 2) potassium CN (5.4 mg/kg intra-arterially); 3) potassium CN, OHCob (100 mg/kg intra-arterially) and subsequent HBOT (284 kPa in 90 min). OHCob and HBOT significantly attenuated the acute surges in interstitial cerebral lactate, glucose, and glycerol concentrations compared with the intoxicated rats given no treatment. Furthermore, the combined treatment resulted in consistent low lactate, glucose, and glycerol concentrations, as well as in low lactate-to-pyruvate ratios compared with CN intoxicated controls. In rats receiving OHCob and HBOT, respiration improved and cyanosis disappeared, with subsequent stabilization of mean arterial blood pressure. The present findings indicate that a combined administration of OHCob and HBOT has a beneficial and persistent effect on the cerebral metabolism during CN intoxication.

Hydroxocobalamin in cyanide poisoning

INTRODUCTION

On theoretical grounds, hydroxocobalamin is an attractive antidote for cyanide poisoning as cobalt compounds have the ability to bind and detoxify cyanide. This paper reviews the pharmacokinetic and pharmacodynamic aspects of hydroxocobalamin, its efficacy in human cyanide poisoning and its adverse effects.

METHODS

PubMed was searched for the period 1952 to April 2012. A total of 71 papers were identified in this way; and none was excluded. PHARMACOKINETICS AND PHARMACODYNAMICS: Pharmacokinetic studies in dogs and humans suggest a two-compartment model, with first order elimination kinetics. Pharmacodynamic studies in animals suggest that hydroxocobalamin would be a satisfactory antidote for human cyanide poisoning. EFFICACY IN HUMAN POISONING: There is limited evidence that hydroxocobalamin alone is effective in severe poisoning by cyanide salts. The evidence for the efficacy of hydroxocobalamin in smoke inhalation is complicated by lack of evidence for the importance of cyanide exposure in fires and the effects of other chemicals as well as confounding effects of other therapeutic measures, including hyperbaric oxygen. Evidence that hydroxocobalamin is effective in poisoning due to hydrogen cyanide alone is lacking; extrapolation of efficacy from poisoning by ingested cyanide salts may not be valid. The rate of absorption may be greater with inhaled hydrogen cyanide and the recommended slow intravenous administration of hydroxocobalamin may severely limit its clinical effectiveness in these circumstances.

ADVERSE EFFECTS

Both animal and human data suggest that hydroxocobalamin is lacking in clinically significant adverse effects. However, in one human volunteer study, delayed but prolonged rashes were observed in one-sixth of subjects, appearing 7 to 25 days after administration of 5 g or more of hydroxocobalamin. Rare adverse effects have included dyspnoea, facial oedema, and urticaria.

CONCLUSIONS

Limited data on human poisonings with cyanide salts suggest that hydroxocobalamin is an effective antidote; data from smoke inhalation are less clear-cut. Although clinically important reactions to hydroxocobalamin have not been seen, some, non-life threatening, adverse reactions can occur.