Potential Interference by Hydroxocobalamin on Cooximetry Hemoglobin Measurements During Cyanide and Smoke Inhalation Treatments

Elevated methemoglobin levels in patients treated with high-dose hydroxocobalamin

OBJECTIVE

The aim of this study was to assess the impact of hydroxocobalamin (OHCbl) infusion on arterial blood gas and oximetry values in patients with vasoplegic syndrome.

METHODS

Blood samples collected from 95 patients receiving OHCbl infusion were assayed using the ABL90 FLEX Plus blood gas analyzer for the concentration of methemoglobin (MetHb), total hemoglobin (tHb), carboxyhemoglobin (COHb), arterial oxygen saturation (SaO2), arterial oxygen partial pressure (PaO2), and arterial carbon dioxide partial pressure (PaCO2). Interference of OHCbl on these variables was evaluated using the measured difference between the preinfusion and postinfusion samples.

RESULTS

Blood MetHb (%) measured after the infusion of OHCbl (5g) were significantly higher than the baseline levels, with a median of 4.8 (IQR, 3.0-6.5) versus 1.0 (IQR, 1.0-1.2) (P < .001). Blood COHb (%) increased from a median of 1.3 (IQR, 1.0-1.8) to 1.7 (IQR, 1.3-2.2) (P < .001) following the OHCbl infusion. No differences were seen in median levels of tHb, PaO2, PaCO2, and SaO2 between pre- and post-OHCbl treatment.

CONCLUSION

The presence of OHCbl in blood clearly interfered with the oximetry measurements of the hemoglobin component fractions by falsely increasing the levels of MetHb and COHb. Blood levels of MetHb and COHb cannot be reliably determined by the co-oximetry when OHCbl is known or suspected.

Hydroxocobalamin infusion in a patient monitored for plasma free hemoglobin levels

Hemolysis is one of the most common preanalytical concerns in the clinical laboratory. Hydroxocobalamin administration causes red pigmentation of plasma that may mimic hemolysis and may interfere with chemistry assays. A male patient in his sixties was placed on extracorporeal membrane oxygenation (ECMO) as a bridge to transplantation. Daily plasma free hemoglobin measurements were ordered to monitor for adverse ECMO events. An intensely red plasma specimen was inconsistent with modestly elevated hemoglobin levels and became pink on dilution. Follow-up with providers indicated that the red plasma could be attributed to hydroxocobalamin administration. Performance of scanning spectrophotometry and assessment of a sample spiked with hydroxocobalamin indicated that the red colored hydroxocobalamin did not interfere with our 3,3',5,5'-tetramethylbenzidine based methodology for free plasma hemoglobin measurement. It is important for the laboratory professionals to be aware of the possibility of interference in hemoglobin assays due to hydroxocobalamin.

Elevated methemoglobin levels in patients treated with hydroxocobalamin: a case series and in-vitro analysis

BACKGROUND

Historically, the first step in treating cyanide (CN^-) toxicity utilized antidotes to induce methemoglobinemia. This is concerning in patients who are already hypoxemic or have elevated carboxyhemoglobin. Hydroxocobalamin (OHCbl) is now the first-line antidote for CN^- toxicity and is not known to induce methemoglobinemia. We observed elevated methemoglobin (MetHb) levels in several patients treated with OHCbl and sought to investigate the incidence of MetHb formation following administration of OHCbl.

METHODS

Chart review: A single-center, retrospective case series of patients who received 5 or 10 g of hydroxocobalamin from 01/01/2011 through 04/30/2019. Data was analyzed using descriptive statistics. In-vitro study: Discarded blood was separated into whole blood and plasma samples. OHCbl and normal saline was added to reach 0×, 1×, 2×, and 4× peak therapeutic concentrations and analyzed at times 0, 2, and 4 h after administration.

RESULTS

Chart review: Twenty-seven cases of OHCbl administration were identified. The median age was 53 years (IQR 38 - 64) and 20 (74.1%) were male. Exposure to a house fire or smoke inhalation was the reason for OHCbl administration in 21 (77.8%) patients. Five (18.5%) patients received 10 g of OHCbl while the rest received 5 g. Six (22.2%) patients developed methemoglobinemia, all after 5 g OHCbl administration; four had been exposed to fire and smoke, two received the medication for severe acidosis of unknown etiology not related to fire or smoke. The median peak level was 7.1% (IQR 2.2 - 16.4%) at a median time of 11.4 h post-administration. Two patients received methylene blue (MB), neither responded. Death occurred in 17 (63%) cases. In-vitro study: We observed a dose dependent elevation in total hemoglobin but did not detect any increase in MetHb.

CONCLUSION

We observed a noteworthy temporal association between the formation of methemoglobinemia and the administration of hydroxocobalamin. This does not appear to be an artifact of the CO-oximeters. This could have profound implications for patients who are already hypoxemic or have impaired oxygen carrying capacity from carboxyhemoglobin.

Intraosseous administration of hydroxocobalamin after enclosed structure fire cardiac arrest

Smoke inhalation is the most common cause of acute cyanide poisoning in the developed world. Hydroxocobalamin is an antidote for cyanide poisoning. There is little published about human intraosseous antidote administration. We present a case of intraosseous hydroxocobalamin administration in an adult smoke inhalation victim, found in cardiac arrest inside her burning manufactured home. Return of spontaneous circulation was achieved after 20 min of cardiopulmonary resuscitation. Five grams of hydroxocobalamin were subsequently given intraosseously. On hospital arrival, patient was found to have a respiratory-metabolic acidosis. She had red-coloured urine without haematuria, a known sequela of hydroxocobalamin administration. Patient's neurological status deteriorated, and she died 4 days after admission. This case highlights that intraosseously administered hydroxocobalamin seems to adequately flow into the marrow cavity and enter the circulatory system despite the non-compressible glass antidote vial. This appears to be only the second reported human case of intraosseous hydroxocobalamin administration.

Hydroxocobalamin interference in routine laboratory tests: Development of a protocol for identifying samples and reporting results from patients treated with CyanokitTM

OBJECTIVES

Hydroxocobalamin (OHCob) is an antidote for cyanide poisoning in patients rescued from house fires and is known to cause interference with certain laboratory tests. Consensus is lacking on the extent of this interference and on how to handle these samples. The objectives of this study were to characterize OHCob interference across a wide range of laboratory tests and to develop protocols for identifying and reporting these samples.

DESIGNS & METHODS

Patient plasma samples (n = 5) were spiked with OHCob (1.5 mg/mL) and compared to controls without this drug. A series of analytes were measured using chemistry, urinalysis, coagulation, hematology, and blood gas instruments. Dose-response testing was performed on a subset of assays that showed interferences ≥10%.

RESULTS

Of the 77 analytes evaluated, 27 (35%) showed interference from OHCob, with chemistry and coagulation analytes showing the greatest effects. Of those affected, 22 analytes had a positive interference, whereas 5 analytes had negative interference. Dose-response studies showed dose-dependent increases and/or decreases consistent with initial spiking studies. Although red in colour, plasma samples with OHCob did not trigger hemolysis index flags, necessitating a special sample identification and reporting protocol.

CONCLUSION

OHCob had significant effects on several analytes across different instruments. These findings led to the development of special sample handling and reporting protocols to identify OHCob samples and ensure only accurate results are released. It is vital for emergency departments to document and notify their laboratories whenever blood samples from these patients are drawn.

The Diagnosis and Treatment of Carbon Monoxide Poisoning

BACKGROUND

The symptoms of carbon monoxide (CO) poisoning are nonspecific, ranging from dizziness and headache to unconsciousness and death. A German national guideline on the diagnosis and treatment of this condition is lacking at present.

METHODS

This review is based on a selective literature search in the PubMed and Cochrane databases, as well as on existing guidelines from abroad and expert recommendations on diagnosis and treatment.

RESULTS

The initiation of 100% oxygen breathing as early as possible is the most important treatment for carbon monoxide poisoning. In case of CO poisoning, the reduced oxygen-carrying capacity of the blood, impairment of the cellular respiratory chain, and immune-modulating processes can lead to tissue injury in the myocardium and brain even after lowering of the carboxyhemoglobin (COHb) concentration. In patients with severe carbon monoxide poisoning, an ECG should be obtained and biomarkers for cardiac ischemia should be measured. Hyperbaric oxygen therapy (HBOT) should be critically considered and initiated within six hours in patients with neurologic deficits, unconsciousness, cardiac ischemia, pregnancy, and/or a very high COHb concentration. At present, there is no general recommendation for HBOT, in view of the heterogeneous state of the evidence from multiple trials. Therapeutic decision-making is directed toward the avoidance of sequelae such as cognitive dysfunction and cardiac complications, and the reduction of mortality. Smoke intoxication must be considered in the differential diagnosis. The state of the evidence on the diagnosis and treatment of this condition is not entirely clear. Alternative or supplementary pharmacological treatments now exist only on an experimental basis.

CONCLUSION

High-quality, prospective, randomized trials that would enable a definitive judgment of the efficacy of HBOT are currently lacking.

Burns Centre and fire services: What information can be exchanged to manage the burn patient?

AIM

To describe the experience of using a "Burns Extrication Form" at a regional Burns Centre. Communication between the fire services and burns team previously has been regarded as poor. Significant information is collected by the fire services at the scene and this can aid the management of the patient.

METHODS

The Burns Extrication Form was devised to provide a clear framework of communication between the two services. Information regarding time frames, exposure to heat & smoke, fire loading (potential severity of a fire in a given space by measuring amount of combustible material in confined space), building construction, chemicals involved is passed to the medical team through this form through a National Health Service mailbox. Also, treatment provided by the fire service was documented. All data collected by this form was collated for the purpose of this study. Data ranging from 2014 to 2017 was included in this descriptive study.

RESULTS

The patient journey following contact by fire services shows that out of the 598 persons who were involved in a fire only 92 (15%) attended the Accident and Emergency (A&E) department at the Queen Elizabeth Hospital. Signs of smoke inhalation, singed nose hair and coughing were found in 190 (32%) patients; the fire service administered oxygen to 106 (18%) of these patients although this may have been initiated by Ambulance crews who were on scene prior to the Fire Crew. The remaining 506 (85%) may have not attended A&E at UHB or may have attended another A&E in the West Midlands base on the location of the incident and clinical needs. Of the 92 patients who attended the A&E at UHB 48 (52%) were admitted to the Burns Centre in the hospital. Nine (19%) of these patients had smoke inhalation and three of these patients were managed by intubation. Birmingham North and Black Country North had the highest incidence of burns incidents, 120 and 103 respectively. Whilst, the lowest numbers were found in Birmingham South and Coventry and Solihull with 65 and 61 respectively. Additional results are described in the study.

CONCLUSION

Data provided by the Fire Extrication forms helps us to assess the magnitude of fire-related injury across the West Midlands. The fire services have been shown to provide important first aid as one of the first responders at the scene. Their value in assessing the environment in and patient status helps clinicians further down the patient's journey.

Acquired methemoglobinemia after hydroxocobalamin administration in a patient with burns and inhalation injury

CONTEXT

Hydroxocobalamin is an effective cyanide antidote. While erythema, hypertension, and chromaturia are recognized side effects, methemoglobinemia has not been reported. Methemoglobin levels are most accurately measured by co-oximetry. We describe an extensively burned patient who developed methemoglobinemia within an hour of hydroxocobalamin administration.

CASE DETAILS

A 47-year old man without genetic deficiencies or abnormal hemoglobin variants presented with 61% body surface area thermal burns and grade 1 inhalation injury sustained during a tugboat engine explosion. On admission, lactate was 9.24 mmol/L, methemoglobin 1%, and carboxyhemoglobin 0.2% by blood gas analysis with co-oximetry. Despite large-volume resuscitation, lactate remained elevated (7-8 mmol/L). Intravenous hydroxocobalamin (5 g) was administered at postburn hour 19 for possible cyanide toxicity. Immediately thereafter, he became hypertensive with reflex bradycardia. Lactate decreased to 5.51 mmol/L, methemoglobin rose to 4.10%, and oxygen saturation by pulse oximetry decreased to 74-80% (despite arterial oxygen saturation of 95% by cooximetry). Methemoglobin concentration peaked at 13.40% at postburn hour 33. Methylene blue was not administered.

CONCLUSIONS

Methemoglobinemia in our patient was temporally associated with hydroxocobalamin administration.

Hemolysis index to detect degree of hydroxocobalamin interference with common laboratory tests

BACKGROUND

Cyanokit^® (hydroxocobalamin OHCo) is the recommended treatment for cyanide poisoning. OHCo is a red chromophore and may cause interference with some biochemical measurements. In this study, we assessed the possible interference of Cyanokit on several cooximetric and plasma biochemistry tests and then determined the possible mathematical correction for some analytes. We studied the possibility of detecting and evaluating the degree of interference with the hemolysis index (HI) provided by our autoanalyzer because it is not possible to measure the OHCo concentration in conventional laboratories.

METHODS

Several pools of plasma samples spiked with increasing concentrations of OHCo were prepared. Each one was compared to the pool without interferent. Interference was considered when the bias was more than 10%. An interferograph was developed for those analytes with significant interference. The correlation between interference agent concentration and HI was calculated by Spearman correlation coefficient. We used multiple regression analysis to determine the mathematical correction for amylase, creatinine, and lactate.

RESULTS

We detected significant interference in the amylase, carboxyhemoglobin, creatinine, creatine kinase, bilirubin, lactate, and total protein measurement. The HI was positively correlated with OHCo concentration. Corresponding equations for estimating lactate and creatinine concentrations were obtained.

CONCLUSIONS

OHCo interferes with many laboratory assays in an unpredictable way making some results invalid and confounding clinical decision making. We can detect and evaluate the degree of interference with the HI. We can still estimate real creatinine and lactate levels using the regression equation obtained in this study.

Effects of hydroxocobalamin on carboxyhemoglobin measured under physiologic and pathologic conditions

CONTEXT

Pre-hospital administration of hydroxocobalamin (B12a) is used for empiric treatment of cyanide poisoning because cyanide poisoning is difficult to identify and requires immediate treatment. B12a interferes with the accuracy of several blood laboratory tests. This study aimed to explore how B12a affects carboxyhemoglobin (COHb) measurements in human blood at both physiologic and pathologic COHb levels.

METHODS

Several clinically relevant concentrations of B12a were added to human blood samples containing physiologic (∼ 3%) and pathologic (30% and 50%) COHb levels. We then measured the COHb levels of the samples using two different co-oximeters, the Radiometer ABL 700 and the Rapidpoint 500, and compared to their actual baseline COHb levels.

RESULTS

B12a had minimal effects on the COHb measured at both physiologic and pathologic levels when measured on the Radiometer. In contrast, the Rapidpoint B12a caused a dose-dependent decrease in the COHb measured, especially of pathologic COHb levels (∼ 30 and 50%).

CONCLUSION

The magnitude of B12a interference on measured COHb is dependent upon the specific co-oximeter used, the actual COHb level and the serum B12a concentration. These errors may potentially influence clinical decision making and thus affect patient outcomes. Our findings emphasize the importance of measuring COHb levels on blood samples collected prior to B12a administration.

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.

Supramolecular ferric porphyrins and a cyclodextrin dimer as antidotes for cyanide poisoning

OBJECTIVES

This study aimed to evaluate the antidotal effect of a newly developed supramolecular complex, ferric porphyrins and a cyclodextrin dimer (Fe(III)PIm3CD), that possess a higher binding constant and quicker binding rate to cyanide ions than those of hydroxocobalamin (OHCbl) in the presence of serum protein.

METHODS

First, in vitro cytochrome activity and cell viability were evaluated in murine fibroblast cells cultured with various doses of Fe(III)PIm3CD and potassium cyanide (KCN). Next, BALB/c mice were pretreated with intravenous OHCbl (0.23 mmol/kg), Fe(III)PIm3CD (0.23 mmol/kg), or saline and then received KCN (lethal dose 100% (LD100): 0.23 mmol/kg) through a stomach tube. Finally, as a resuscitation model, KCN-induced apnea was treated with a bolus injection of an equimolar dose of antidotes followed by a slow infusion of the same reagent.

RESULTS

Fe(III)PIm3CD showed dose-dependent antidotal effects in vitro. Pretreatment with Fe(III) PIm3CD prevented KCN-induced apnea significantly better than OHCbl. Resuscitation with Fe(III)PIm3CD resulted in an earlier resumption of respiration than that seen with OHCbl. However, 24-h survival was similar among the treatments (Fe(III)PIm3CD, nine of nine mice; OHCbl, eight of nine mice).

CONCLUSION

Fe(III)PIm3CD exerted significant antidotal effects on cyanide toxicity in vitro and in vivo, with a potency equal in the mortality of cyanide-poisoned mice or superior in the respiratory status during an acute phase to those of OHCbl.

Effect of hydroxocobalamin on surface oximetry in nonexposed humans

INTRODUCTION

The newer cyanide antidote, hydroxocobalamin, due to its pigmentation, has been found to cause interferences in some laboratory assays. Co-oximetry may also be affected by hydroxocobalamin, leading to false elevations in hemoglobin concentration, methemoglobin, carboxyhemoglobin, and false decreases in oxyhemoglobin. The Masimo Radical-7 is a medical device that performs noninvasive oximetry and estimates hemoglobin (Hb) concentration and percent carboxyhemoglobin (COHb), methemoglobin (MetHb), and oxyhemoglobin saturation (O2Hb).

STUDY OBJECTIVES

The study sought to determine the effect of hydroxocobalamin on noninvasive measurement of hemoglobin indices using the Masimo Radical-7 monitor.

METHODS

Seven asymptomatic volunteers who were unexposed to cyanide had baseline heart rate (HR), blood pressure (BP), and oximeter measurements recorded followed by an infusion of five grams of hydroxocobalamin over 15 minutes. The above parameters were subsequently recorded at: 5, 10, 15, 30 and 60 minutes post infusion. Data were analyzed by calculating the area under the curve (AUC) for each variable and comparing the results to expected values by paired t tests. Expected AUC values were calculated by extrapolating baseline values across the entire time period.

RESULTS

The mean differences from baseline values with 95% confidence intervals and t tests of mean difference were: SBP: 11 mm Hg (95% CI, 0-22; P = .051); HR: -9 (95% CI, -15 to -3; P = .01); Hb: -0.1 (95% CI, -0.7 to 0.4; P = .57); O2Hb: 0 g/dL (95% CI, -1 to 1; P = .41); COHb: -1 (95% CI, -3 to 1; P = .25); MetHb: -0.2 (95% CI, -0.3 to 0; P = .03).

DISCUSSION

After infusion of hydroxocobalamin there was a significant elevation of systolic blood pressure and decrease in heart rate. There were no significant differences in Hb, O2Hb, and COHb. Although percent methemoglobin concentrations were statistically lower, the authors feel this difference is of trivial clinical significance.

CONCLUSION

The administration of hydroxocobalamin does not significantly impact noninvasive oximetry.

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.

Review article: management of cyanide poisoning

Cyanide poisoning is uncommon, but generates interest because of the presumed utility of an antidote immediately available in those areas with a high risk of cyanide exposure. As part of its regular review of guidelines, the Australian Resuscitation Council conducted a systematic review of the human evidence for the use of various proposed cyanide antidotes, and a narrative review of the relevant pharmacological and animal studies. There have been no relevant comparative or placebo-controlled human trials. Nine case series were identified. Treatment with hydroxocobalamin was reported in a total of 361 cases. No serious adverse effects of hydroxocobalamin were reported, and many patients with otherwise presumably fatal poisoning survived. Sodium thiosulphate use was reported in two case series, similarly with no adverse effects. Treatment with a combination of sodium nitrite, amyl nitrite and sodium thiosulphate was reported in 74 patients, with results indistinguishable from those of hydroxocobalamin and sodium thiosulphate. No case series using dicobalt edetate or 4-dimethylaminophenol were identified, but successful use in single cases has been reported. Hydroxocobalamin and sodium thiosulphate differ from alternatives in having negligible adverse effects, and on the basis of current evidence are the antidotes of choice. The indications for the use of an antidote, the requirements for supportive care and a recommended approach for workplaces where there is a risk of cyanide poisoning are presented.

A review of acute cyanide poisoning with a treatment update

Cyanide causes intracellular hypoxia by reversibly binding to mitochondrial cytochrome oxidase a(3). Signs and symptoms of cyanide poisoning usually occur less than 1 minute after inhalation and within a few minutes after ingestion. Early manifestations include anxiety, headache, giddiness, inability to focus the eyes, and mydriasis. As hypoxia progresses, progressively lower levels of consciousness, seizures, and coma can occur. Skin may look normal or slightly ashen, and arterial oxygen saturation may be normal. Early respiratory signs include transient rapid and deep respirations. As poisoning progresses, hemodynamic status may become unstable. The key treatment is early administration of 1 of the 2 antidotes currently available in the United States: the well-known cyanide antidote kit and hydroxocobalamin. Hydroxocobalamin detoxifies cyanide by binding with it to form the renally excreted, non-toxic cyanocobalamin. Because it binds with cyanide without forming methemoglobin, hydroxocobalamin can be used to treat patients without compromising the oxygen-carrying capacity of hemoglobin.

Cyanide intoxication as part of smoke inhalation--a review on diagnosis and treatment from the emergency perspective

This paper reviews the current literature on smoke inhalation injuries with special attention to the effects of hydrogen cyanide. It is assumed that cyanide poisoning is still an overlooked diagnosis in fire victims. Treatment against cyanide poisoning in the emergency setting should be given based on the clinical diagnosis only. Oxygen in combination with a recommended antidote should be given immediately, the first to reduce cellular hypoxia and the second to eliminate cyanide. A specific antidote is hydroxycobalamin, which can be given iv. and has few side effects.

Hemodialysis complications of hydroxocobalamin: a case report

Hydroxocobalamin is a new antidote approved by the FDA for the treatment of cyanide poisoning. Our report describes a patient with cyanide poisoning who survived after treatment with hydroxocobalamin and complications we encountered with hemodialysis. A 34-year-old female presented to the emergency department after a syncopal event and seizures. Her systolic blood pressure was 75 mmHg, her QRS complex progressively widened, and pulses were lost. She was intubated and resuscitated with fluids, sodium bicarbonate for her QRS widening and vasopressors. Venous blood gas demonstrated a pH of 6.36 with an O₂ saturation of 99%. Due to the acidemia with a normal pulse oximetry, simultaneous venous and arterial blood gases were obtained. Venous gas demonstrated a pH of 6.80 with a PO₂ of 222 mmHg, an O₂ saturation of 99%. The arterial blood gas showed a pH of 6.82, a PO₂ 518 mmHg, an O₂ saturation of 100%. Cyanide was suspected and hydroxocobalamin and sodium thiosulfate were given. Within 40 min of hydroxocobalamin administration, vasopressors were discontinued. Initially, nephrology attempted dialysis for metabolic acidosis; however, the dialysis machine repeatedly shut down due to a “blood leak”. This was an unforeseen effect attributed to hydroxocobalamin. Cyanide level, drawn 20 min after the antidote was completed, was elevated at 22 mcg/dL. Her urinary thiocyanate level could not be analyzed due to an “interfering substance”. Hydroxocobalamin is an effective antidote. However, clinicians must be aware of its effects on hemodialysis machines which could delay the initiation of this important treatment modality in the severely acidemic patient.

Comparison of cobinamide to hydroxocobalamin in reversing cyanide physiologic effects in rabbits using diffuse optical spectroscopy monitoring

Our purpose is to compare cobinamide to hydroxocobalamin in reversing cyanide (CN)-induced physiologic effects in an animal model using diffuse optical spectroscopy (DOS). Cyanide poisoning is a major threat worldwide. Cobinamide is a novel molecule that can bind two molecules of cyanide, has a much higher binding affinity than hydroxocobalamin, and is more water soluble. We investigated the ability of equimolar doses of cobinamide and hydroxocobalamin to reverse the effects of cyanide exposure in an animal model monitored continuously by DOS. Cyanide toxicity was induced in 16 New Zealand white rabbits by intravenous infusion. Animals were divided into three groups: controls (n=5) received saline following cyanide, hydroxocobalamin (N=6) following cyanide, and cobinamide (N=5) following cyanide. Cobinamide caused significantly faster and more complete recovery of oxy- and deoxyhemoglobin concentrations in cyanide-exposed animals than hydroxocobalamin- or saline-treated animals, with a recovery time constant of 13.8+/-7.1 min compared to 75.4+/-25.1 and 76.4+/-42.7 min, for hydroxocobalamin- and saline-treated animals, respectively (p<0.0001). This study indicates that cobinamide more rapidly and completely reverses the physiologic effects of cyanide than equimolar doses of cobalamin at the dose used in this study, and CN effects and response can be followed noninvasively using DOS.

Role of hydroxocobalamin in acute cyanide poisoning

OBJECTIVE

To review the recently approved cyanide antidote, hydroxocobalamin, and describe its role in therapy.

DATA SOURCES

Relevant publications were identified through a systematic search of PubMed using the MeSH terms and key words hydroxocobalamin and cyanide. This search was then limited to human studies published since 2000. Systematic searches were conducted through January 2008. References from identified articles were reviewed for additional pertinent human studies.

STUDY SELECTION AND DATA EXTRACTION

The literature search retrieved 7 studies on the safety and/or efficacy of hydroxocobalamin in humans. Four new studies were identified by the search and 3 studies were identified from the references.

DATA SYNTHESIS

Studies of antidote efficacy in humans are ethically and logistically difficult. A preclinical study demonstrated that intravenous doses of hydroxocobalamin 5 g are well tolerated by volunteer subjects. Hydroxocobalamin has been shown to reduce cyanide concentrations in controlled studies of nitroprusside therapy and in heavy smokers. A retrospective study of 14 acute cyanide poisonings also demonstrated hydroxocobalamin's safety and efficacy. Two studies examining hydroxocobalamin for smoke inhalation-associated cyanide poisoning indicated a possible benefit, but they are insufficient to establish definitive criteria for use in this setting. Randomized controlled trials of hydroxocobalamin and traditional cyanide antidotes (nitrites/thiosulfate) are lacking.

CONCLUSIONS

Cyanide poisoning can rapidly cause death. Having an effective antidote readily available is essential for facilities that provide emergency care. In cases of cyanide ingestion, both the nitrite/thiosulfate combination and hydroxocobalamin are effective antidotes. Hydroxocobalamin offers an improved safety profile for children and pregnant women. Hydroxocobalamin also appears to have a better safety profile in the setting of cyanide poisoning in conjunction with smoke inhalation. However, current data are insufficient to recommend the empiric administration of hydroxocobalamin to all victims of smoke inhalation.

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