Experimental tricyclic antidepressant toxicity: a randomized, controlled comparison of hypertonic saline solution, sodium bicarbonate, and hyperventilation

Re-evaluating intra-cardiac arrest adjunctive medications and routes of drug administration

PURPOSE OF REVIEW

This narrative review summarizes the evidence for the most commonly used intra-cardiac arrest adjunctive medications and routes of administration and discusses promising new therapies from preclinical animal models.

RECENT FINDINGS

Large trials on the administration of calcium as well as the combination of vasopressin and glucocorticoids during cardiac arrest have been published. Calcium administration during cardiopulmonary resuscitation does not improve outcomes and might cause harm. Vasopressin and glucocorticoid administration during cardiopulmonary resuscitation improve the chance of return of spontaneous circulation but has uncertain effects on survival. We identified a total of seven ongoing clinical trials investigating the potential role of bicarbonate, of vasopressin and glucocorticoids, and of intravenous versus intraosseous vascular access. Several medications such as levosimendan and inhaled nitric oxide show promise in preclinical studies, and clinical trials are either planned or actively recruiting.

SUMMARY

Large trials on intra-cardiac arrest administration of calcium and vasopressin with glucocorticoids have been performed. Several trials are ongoing that will provide valuable insights into the potential benefit of other intra-cardiac arrest medications such as bicarbonate as well as the potential benefit of intravenous or intraosseous vascular access.

Esmolol for intractable ventricular arrhythmias in major amitriptyline toxicity

A massive tricyclic overdose of 10 g of amitriptyline resulted in cardiovascular collapse with multiple episodes of ventricular tachycardia and ventricular fibrillation despite aggressive attention to current recommended therapy of sodium bicarbonate and hypertonic saline, and correction of electrolytes. Second-line antiarrhythmic therapies failed to reduce the recurrent deterioration to malignant ventricular rhythms. Progression to extracorporeal support was avoided by the use of a titrated esmolol infusion. We discuss the physiological rationale by which esmolol may prevent tachyarrhythmia and fibrillation in severe amitriptyline toxicity.

Optimising alkalinisation and its effect on QRS narrowing in tricyclic antidepressant poisoning

AIMS

The objectives were to determine the effect of NaHCO₃ and/or mechanical ventilation on the biochemical profile and serum alkalinisation in tricyclic antidepressant (TCA) poisoning and investigate the impact of effective alkalinisation therapy on the QRS interval in TCA poisoning.

METHODS

This was a retrospective review of TCA poisonings from three Australian toxicology units and a poisons information centre (Jan 2013 to Jan 2019). We included patients with TCA toxicity who ingested>10 mg/kg or had clinically significant toxicities consistent with TCA poisoning, and analysed patients' clinical, electrocardiogram and biochemical data.

RESULTS

Of 210 patients, 84 received NaHCO₃ and ventilation (dual therapy), 12 NaHCO₃ , 46 ventilation and 68 supportive care treatment. When compared with single/supportive groups, patients who received dual therapy had taken a significantly higher median dose of TCA (1.5 g vs1.3 g, P < .001), a longer median maximum QRS interval (124 ms, interquartile ranges [IQR] 108-138 vs106 ms, IQR 98-115, P < .001) and were more likely to have seizures (14% vs3%, P = .006) and arrhythmias (17% vs1%, P < .001). The dual therapy group demonstrated greater increases in serum pH (median 0.11, IQR 0.04-0.17) compared to the single/supportive therapy group (median 0.03, IQR -0.01-0.09, p < .001). A greater proportion of patients reached the target pH 7.45-7.55 in the dual therapy group (59%) compared to the single/supportive therapy group (10%) (P < .001). For each 100 mmol bolus of NaHCO₃ given, the median increase in serum sodium was 2.5 mmol/L (IQR 1.5-4.0). QRS narrowing occurred twice as quickly in the dual therapy vs single/supportive therapy group.

CONCLUSIONS

A combination of NaHCO₃ and mechanical ventilation was most effective in achieving serum alkalinisation and was associated with a more rapid narrowing of the QRS interval. We advise that the maximal dose of NaHCO₃ should be <400 mmol (6 mmol/kg).

[Cardiac arrest under special circumstances]

These guidelines of the European Resuscitation Council (ERC) Cardiac Arrest under Special Circumstances are based on the 2020 International Consensus on Cardiopulmonary Resuscitation Science with Treatment Recommendations. This section provides guidelines on the modifications required for basic and advanced life support for the prevention and treatment of cardiac arrest under special circumstances; in particular, specific causes (hypoxia, trauma, anaphylaxis, sepsis, hypo-/hyperkalaemia and other electrolyte disorders, hypothermia, avalanche, hyperthermia and malignant hyperthermia, pulmonary embolism, coronary thrombosis, cardiac tamponade, tension pneumothorax, toxic agents), specific settings (operating room, cardiac surgery, cardiac catheterization laboratory, dialysis unit, dental clinics, transportation [in-flight, cruise ships], sport, drowning, mass casualty incidents), and specific patient groups (asthma and chronic obstructive pulmonary disease, neurological disease, morbid obesity, pregnancy).

European Resuscitation Council Guidelines 2021: Cardiac arrest in special circumstances

These European Resuscitation Council (ERC) Cardiac Arrest in Special Circumstances guidelines are based on the 2020 International Consensus on Cardiopulmonary Resuscitation Science with Treatment Recommendations. This section provides guidelines on the modifications required to basic and advanced life support for the prevention and treatment of cardiac arrest in special circumstances; specifically special causes (hypoxia, trauma, anaphylaxis, sepsis, hypo/hyperkalaemia and other electrolyte disorders, hypothermia, avalanche, hyperthermia and malignant hyperthermia, pulmonary embolism, coronary thrombosis, cardiac tamponade, tension pneumothorax, toxic agents), special settings (operating room, cardiac surgery, catheter laboratory, dialysis unit, dental clinics, transportation (in-flight, cruise ships), sport, drowning, mass casualty incidents), and special patient groups (asthma and COPD, neurological disease, obesity, pregnancy).

Management of pharmaceutical and recreational drug poisoning

BACKGROUND

Poisoning is one of the leading causes of admission to the emergency department and intensive care unit. A large number of epidemiological changes have occurred over the last years such as the exponential growth of new synthetic psychoactive substances. Major progress has also been made in analytical screening and assays, enabling the clinicians to rapidly obtain a definite diagnosis.

METHODS

A committee composed of 30 experts from five scientific societies, the Société de Réanimation de Langue Française (SRLF), the Société Française de Médecine d'Urgence (SFMU), the Société de Toxicologie Clinique (STC), the Société Française de Toxicologie Analytique (SFTA) and the Groupe Francophone de Réanimation et d'Urgences Pédiatriques (GFRUP) evaluated eight fields: (1) severity assessment and initial triage; (2) diagnostic approach and role of toxicological analyses; (3) supportive care; (4) decontamination; (5) elimination enhancement; (6) place of antidotes; (7) specificities related to recreational drug poisoning; and (8) characteristics of cardiotoxicant poisoning. Population, Intervention, Comparison, and Outcome (PICO) questions were reviewed and updated as needed, and evidence profiles were generated. Analysis of the literature and formulation of recommendations were then conducted according to the GRADE® methodology.

RESULTS

The SRLF-SFMU guideline panel provided 41 statements concerning the management of pharmaceutical and recreational drug poisoning. Ethanol and chemical poisoning were excluded from the scope of these recommendations. After two rounds of discussion and various amendments, a strong consensus was reached for all recommendations. Six of these recommendations had a high level of evidence (GRADE 1±) and six had a low level of evidence (GRADE 2±). Twenty-nine recommendations were in the form of expert opinion recommendations due to the low evidences in the literature.

CONCLUSIONS

The experts reached a substantial consensus for several strong recommendations for optimal management of pharmaceutical and recreational drug poisoning, mainly regarding the conditions and effectiveness of naloxone and N-acetylcystein as antidotes to treat opioid and acetaminophen poisoning, respectively.

Utility of Hypertonic Saline and Diazepam in COVID-19-Related Hydroxychloroquine Toxicity

Background

Hydroxychloroquine (HCQ) poisoning is a life-threatening but treatable toxic ingestion. The scale of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection (COVID-19) and the controversial suggestion that HCQ is a treatment option have led to a significant increase in HCQ use. HCQ poisoning should be at the top-of-mind for emergency providers in cases of toxic ingestion. Treatment for HCQ poisoning includes sodium bicarbonate, epinephrine, and aggressive electrolyte repletion. We highlight the use of hypertonic saline and diazepam.

Case Report

We describe the case of a 37-year-old man who presented to the emergency department after the ingestion of approximately 16 g of HCQ tablets (initial serum concentration 4270 ng/mL). He was treated with an epinephrine infusion, hypertonic sodium chloride, high-dose diazepam, sodium bicarbonate, and aggressive potassium repletion. Persistent altered mental status necessitated intubation, and he was managed in the medical intensive care unit until his QRS widening and QTc prolongation resolved. After his mental status improved and it was confirmed that his ingestion was not with the intent to self-harm, he was discharged home with outpatient follow-up.

Why Should an Emergency Physician Be Aware of This?

For patients presenting with HCQ overdose and an unknown initial serum potassium level, high-dose diazepam and hypertonic sodium chloride should be started immediately for the patient with widened QRS. The choice of hypertonic sodium chloride instead of sodium bicarbonate is to avoid exacerbating underlying hypokalemia which may in turn potentiate unstable dysrhythmia. In addition, early intubation should be a priority in vomiting patients because both HCQ toxicity and high-dose diazepam cause profound sedation.

Lethal Tricyclic Antidepressant Overdose

Tricyclic antidepressant remains widely prescribed despite its dangerous cardiovascular and neurological effects in overdosed patients. We present a case of lethal dothiepin overdose and discuss the major complications and its management strategies.

A Literature Review of the Use of Sodium Bicarbonate for the Treatment of QRS Widening

Sodium bicarbonate is a well-known antidote for tricyclic antidepressant (TCA) poisoning. It has been used for over half a century to treat toxin-induced sodium channel blockade as evidenced by QRS widening on the electrocardiogram (ECG). The purpose of this review is to describe the literature regarding electrophysiological mechanisms and clinical use of this antidote after poisoning by tricyclic antidepressants and other agents. This article will also address the literature supporting an increased serum sodium concentration, alkalemia, or the combination of both as the responsible mechanism(s) for sodium bicarbonate's antidotal properties. While sodium bicarbonate has been used as a treatment for cardiac sodium channel blockade for multiple other agents including citalopram, cocaine, flecainide, diphenhydramine, propoxyphene, and lamotrigine, it has uncertain efficacy with bupropion, propranolol, and taxine-containing plants.

Antidote Use in the Critically Ill Poisoned Patient

The proper use of antidotes in the intensive care setting when combined with appropriate general supportive care may reduce the morbidity and mortality associated with severe poisonings. The more commonly used antidotes that may be encountered in the intensive care unit ( N-acetylcysteine, ethanol, fomepizole, physostigmine, naloxone, flumazenil, sodium bicarbonate, octreotide, pyridoxine, cyanide antidote kit, pralidoxime, atropine, digoxin immune Fab, glucagon, calcium gluconate and chloride, deferoxamine, phytonadione, botulism antitoxin, methylene blue, and Crotaline snake antivenom) are reviewed. Proper indications for their use and knowledge of the possible adverse effects accompanying antidotal therapy will allow the physician to appropriately manage the severely poisoned patient.

Can empirical hypertonic saline or sodium bicarbonate treatment prevent the development of cardiotoxicity during serious amitriptyline poisoning? Experimental research

OBJECTIVE

The aim of this experimental study was to investigate whether hypertonic saline or sodium bicarbonate administration prevented the development of cardiotoxicity in rats that received toxic doses of amitriptyline.

METHOD

Thirty-six Sprague Dawley rats were used in the study. The animals were divided into six groups. Group 1 received toxic doses of i.p. amitriptyline. Groups 2 and 3 toxic doses of i.p. amitriptyline, plus i.v. sodium bicarbonate and i.v. hypertonic saline, respectively. Group 4 received only i.v. sodium bicarbonate, group 5 received only i.v. hypertonic saline, and group 6 was the control. Electrocardiography was recorded in all rats for a maximum of 60 minutes. Blood samples were obtained to measure the serum levels of sodium and ionised calcium.

RESULTS

The survival time was shorter in group 1. In this group, the animals' heart rates also decreased over time, and their QRS and QTc intervals were significantly prolonged. Groups 2 and 3 showed less severe changes in their ECGs and the rats survived for a longer period. The effects of sodium bicarbonate or hypertonic saline treatments on reducing the development of cardiotoxicity were similar. The serum sodium levels decreased in all the amitriptyline-applied groups. Reduction of serum sodium level was most pronounced in group 1.

CONCLUSION

Empirical treatment with sodium bicarbonate or hypertonic saline can reduce the development of cardiotoxicity during amitriptyline intoxication. As hypertonic saline has no adverse effects on drug elimination, it should be considered as an alternative to sodium bicarbonate therapy.

Comparison of intravenous lipid emulsion, bicarbonate, and tailored liposomes in rabbit clomipramine toxicity

OBJECTIVES

Liposome (LIP)-like lipid dispersions have emerged as useful detoxification vehicles in vitro. The authors compare resuscitation with tailored LIPs, 20% intravenous lipid emulsion (ILE), and sodium bicarbonate (BIC), in a rabbit model of clomipramine toxicity.

METHODS

Sedated, instrumented New Zealand white rabbits underwent clomipramine infusion at 3.2 mg/kg/min to 50% baseline mean arterial pressure (MAP) and then at 1.6 mg/kg/min for 30 minutes. BIC (3 mL/kg 8.4%), ILE (3 mL/kg 20%), or LIP (24 mg/kg) were infused as rescue treatments at toxicity and were repeated at 10 minutes (n = 5 in each group).

RESULTS

Thirty-minute MAP was greatest in ILE-treated animals: 61 mm Hg ILE (interquartile range [IQR] = 49 to 64 mm Hg), 43 mm Hg LIP (IQR = 36.5 to 49 mm Hg), and 10 mm Hg BIC (IQR = 10 to 44 mm Hg; all p = 0.02). Two of the five BIC-treated animals survived to 30 minutes, compared with all five of the ILE-treated animals and all five of the LIP-treated animals (p = 0.044).

CONCLUSIONS

Both ILE and LIPs improved hemodynamic recovery compared with bicarbonate in clomipramine-induced cardiotoxicity in rabbits. Greater 30-minute MAP was observed in the ILE group.

Utility of the electrocardiogram in drug overdose and poisoning: theoretical considerations and clinical implications

The ECG is a rapidly available clinical tool that can help clinicians manage poisoned patients. Specific myocardial effects of cardiotoxic drugs have well-described electrocardiographic manifestations. In the practice of clinical toxicology, classic ECG changes may hint at blockade of ion channels, alterations of adrenergic tone, or dysfunctional metabolic activity of the myocardium. This review will offer a structured approach to ECG interpretation in poisoned patients with a focus on clinical implications and ECG-based management recommendations in the initial evaluation of patients with acute cardiotoxicity.

Brugada-like ECG pattern induced by tricyclic antidepressants

We present the case report of a 57-year-old woman with severe monointoxication with dosulepine (Prothiaden) who developed a Brugada-like electrocardiographic pattern. In tricyclic antidepressants (TCAs) poisoning the Brugada-like pattern on electrocardiogram is a characteristic albeit rare manifestation of the frequently occurring conduction abnormalities in the myocardium and its recognition is imperative as it is associated with a higher degree of morbidity and mortality. An overview of the literature is given and recommendations concerning treatment of TCA-induced arrhythmias are provided. After successful treatment, the electrocardiogram in the patient normalized. However, 4 days after intoxication, the ajmaline test was positive (pharmacological induction of a type I Brugada-like pattern), but a subsequent one, repeated after 11 days, was reportedly normal, probably because of the slow clearance of dosulepine. This raises questions about the specificity of ajmaline testing for Brugada syndrome in patients taking dosulepine and perhaps other TCAs and neuroleptic agents.

Drugs and pharmaceuticals: management of intoxication and antidotes

The treatment of patients poisoned with drugs and pharmaceuticals can be quite challenging. Diverse exposure circumstances, varied clinical presentations, unique patient-specific factors, and inconsistent diagnostic and therapeutic infrastructure support, coupled with relatively few definitive antidotes, may complicate evaluation and management. The historical approach to poisoned patients (patient arousal, toxin elimination, and toxin identification) has given way to rigorous attention to the fundamental aspects of basic life support--airway management, oxygenation and ventilation, circulatory competence, thermoregulation, and substrate availability. Selected patients may benefit from methods to alter toxin pharmacokinetics to minimize systemic, target organ, or tissue compartment exposure (either by decreasing absorption or increasing elimination). These may include syrup of ipecac, orogastric lavage, activated single- or multi-dose charcoal, whole bowel irrigation, endoscopy and surgery, urinary alkalinization, saline diuresis, or extracorporeal methods (hemodialysis, charcoal hemoperfusion, continuous venovenous hemofiltration, and exchange transfusion). Pharmaceutical adjuncts and antidotes may be useful in toxicant-induced hyperthermias. In the context of analgesic, anti-inflammatory, anticholinergic, anticonvulsant, antihyperglycemic, antimicrobial, antineoplastic, cardiovascular, opioid, or sedative-hypnotic agents overdose, N-acetylcysteine, physostigmine, L-carnitine, dextrose, octreotide, pyridoxine, dexrazoxane, leucovorin, glucarpidase, atropine, calcium, digoxin-specific antibody fragments, glucagon, high-dose insulin euglycemia therapy, lipid emulsion, magnesium, sodium bicarbonate, naloxone, and flumazenil are specifically reviewed. In summary, patients generally benefit from aggressive support of vital functions, careful history and physical examination, specific laboratory analyses, a thoughtful consideration of the risks and benefits of decontamination and enhanced elimination, and the use of specific antidotes where warranted. Data supporting antidotes effectiveness vary considerably. Clinicians are encouraged to utilize consultation with regional poison centers or those with toxicology training to assist with diagnosis, management, and administration of antidotes, particularly in unfamiliar cases.

Toxicology in the critical care unit

Toxicologic conditions are encountered in critically ill patients due to intentional or unintentional misuse of or exposure to therapeutic or illicit drugs. Additionally, toxicities related to medical interventions may develop in hospitalized patients. This review focuses on recent developments in the field of critical care toxicology. Early interventions to decrease absorption or enhance elimination of toxins have limited value. Specific interventions to manage toxicities due to analgesics, sedative-hypnotics, antidepressants, antipsychotics, cardiovascular agents, alcohols, carbon monoxide, and cholinergic agents are reviewed. Hospital-acquired toxicities due to methemoglobinemia, propylene glycol, and propofol should be recognized and treated. The clinician is continually required to incorporate clinical judgment along with available scientific data and clinical evidence to determine the best therapy for toxicologic conditions.

Review article: hypertonic saline use in the emergency department

Hypertonic saline (HS) is being increasingly used for the management of a variety of conditions, most notably raised intracranial pressure. This article reviews the available evidence on HS solutions as they relate to emergency medicine, and develops a set of recommendations for its use. To conclude, HS is recommended as an alternative to mannitol for treating raised intracranial pressure in traumatic brain injury. HS is also recommended for treating severe and symptomatic hyponatremia, and is worth considering for both recalcitrant tricyclic antidepressant toxicity and for cerebral oedema complicating paediatric diabetic ketoacidosis. HS is not recommended for hypovolaemic resuscitation.

Dolasetron overdose resulting in prolonged QTc interval and severe hypotension: a case report and literature review

Dolasetron (Anzemet) overdose is uncommon, and, to our knowledge, this is the only case report of an intentional overdose. Dolasetron (dolasetron mesylate) is a selective 5-hydroxytryptamine 3 antagonist derived from pseudopelletierine, and is used in the prevention and treatment of nausea and vomiting. Transient and asymptomatic ECG changes, including QRS widening and PR and QTc prolongation, have been reported in therapeutic doses. The case of a 21-year-old woman who presented after an intentional overdose of 10x200 mg dolasetron tablets resulting in prolongation of the QTc interval and severe hypotension is reported here. Management of hypotension included intravenous fluid resuscitation and norepinephrine infusion with invasive monitoring in a high dependency unit. Sodium cardiac channel block contributes to cardiotoxicity observed in dolasetron overdose. Sodium bicarbonate was used in an attempt to reduce cardiac sodium channel block, although we observed no apparent benefit. As dolasetron becomes more commonly used in the outpatient setting, both doctors and patients need to be aware of the dangers of dolasetron in toxic doses. The pharmacology and toxicology of dolasetron are discussed.

Toxicologic issues during cardiopulmonary resuscitation

PURPOSE OF REVIEW

The following review intends to outline the unique aspects of providing cardiopulmonary resuscitation for the poisoned patient and highlights both current practice and new therapies that apply to toxicologic cases.

RECENT FINDINGS

Although there are few prospective randomized studies to further evidence-based care of the poisoned patient, there have been several reports of novel uses of both established medications and new medications in toxicologic patients. These case reports highlight treatment possibilities and potential avenues for further research.

SUMMARY

It is important for providers to recognize the limitations of standard advanced cardiac life support algorithms when caring for poisoned patients. Toxicologic causes of cardiopulmonary compromise should be considered along with administration of appropriate antidotes and adjunctive therapies.

Intralipid outperforms sodium bicarbonate in a rabbit model of clomipramine toxicity

STUDY OBJECTIVE

Previous investigators have demonstrated amelioration of lipid-soluble drug toxidromes with infusion of lipid emulsions. Clomipramine is a lipid-soluble tricyclic antidepressant with significant cardiovascular depressant activity in human overdose. We compare resuscitation with Intralipid versus sodium bicarbonate in a rabbit model of clomipramine toxicity.

METHODS

Thirty sedated and mechanically ventilated New Zealand White rabbits were infused with clomipramine at 320 mg/kg per hour. At target mean arterial pressure of 50% initial mean arterial pressure, animals were rescued with 0.9% NaCl 12 mL/kg, 8.4% sodium bicarbonate 3 mL/kg, or 20% Intralipid 12 mL/kg. Pulse rate, mean arterial pressure, and QRS duration were sampled at 2.5-minute intervals to 15 minutes. In the second phase of the experiment, 8 sedated and mechanically ventilated rabbits were infused with clomipramine at 240 mg/kg per hour to a mean arterial pressure of 25 mm Hg. Animals received either 2 mL/kg 8.4% sodium bicarbonate or 8 mL/kg 20% Intralipid as rescue therapy. External cardiac compression and intravenous adrenaline were administered in the event of cardiovascular collapse.

RESULTS

Mean difference in mean arterial pressure between Intralipid- and saline solution-treated groups was 21.1 mm Hg (95% confidence interval [CI] 13.5 to 28.7 mm Hg) and 19.5 mm Hg (95% CI 10.5 to 28.9 mm Hg) at 5 and 15 minutes, respectively. Mean difference in mean arterial pressure between Intralipid- and bicarbonate-treated groups was 19.4 mm Hg (95% CI 18.8 to 27.0 mm Hg) and 11.5 mm Hg (95% CI 2.5 to 20.5 mm Hg) at 5 and 15 minutes. The rate of change in mean arterial pressure was greatest in the Intralipid-treated group at 3 minutes (6.2 mm Hg/min [95% CI 3.8 to 8.6 mm Hg/min] Intralipid versus -0.25 mm Hg/min [95% CI -1.9 to 1.4 mm Hg/min] saline solution) and 5 minutes (4.4 mm Hg/min [95% CI 3.0 to 5.9 mm Hg/min] Intralipid versus 0.06 mm Hg/min [95% CI -0.9 to 1.1 mm Hg/min] saline solution). In the second phase of the experiment spontaneous circulation was maintained in all Intralipid-treated rabbits (n=4). All animals in the bicarbonate-treated group developed pulseless electrical activity and proved refractory to resuscitation at 10 minutes (n=4, P=.023).

CONCLUSION

In this rabbit model, Intralipid infusion resulted in more rapid and complete reversal of clomipramine-induced hypotension compared with sodium bicarbonate. Additionally, Intralipid infusion prevented cardiovascular collapse in a model of severe clomipramine toxicity.

Chemically Induced Seizures

Drug- and toxin-associated seizures (DTS) may result from exposure to a wide variety of agents. Most DTS can be managed with supportive care. First-line anticonvulsant therapy should include benzodiazepines, unless agents require a specific antidote. Phenytoin is generally not expected to be useful for DTS and in some instances may be harmful. In this article the authors discuss the pathophysiology of DTS, the potential differential diagnosis, and the clinical presentation. They also review selected agents that cause DTS and provide an overview of how the clinician should approach the management of patients who have DTS.

Prolonged clinical effects in modified-release amitriptyline poisoning

BACKGROUND

Tricyclic antidepressant poisoning is often associated with significant cardiovascular and central nervous system toxicity. Effective treatment includes the use of appropriate gastric decontamination techniques, the administration of sodium bicarbonate, and meticulous supportive care. Tricylcic antidepressant toxicity typically lasts 24-48 hours following a significant overdose.

CASE REPORT

We describe a case of tricyclic antidepressant poisoning where significant clinical toxicity (QRS prolongation, metabolic acidosis) was observed for up to 4 days following ingestion of a modified-release preparation of amitriptyline. Successful patient recovery was associated with the use of multidose activated charcoal and repeated administration of intravenous sodium bicarbonate.

CONCLUSIONS

Clinicians should be aware of the potential for prolonged tricyclic toxicity in patients who have ingested modified-release amitriptyline in overdose. Gastric decontamination techniques such as multidose activated charcoal and whole bowel irrigation should be considered where there is evidence of ongoing tricyclic antidepressant absorption or clinical toxicity following ingestion of a modified-release preparation. These interventions may be indicated for prolonged periods (greater than 36 hours) post ingestion.

ECG Manifestations: The Poisoned Patient

Despite that drugs have widely varying indications for therapeutic use, many unrelated drugs share a common cardiac pharmacologic effect if taken in overdose. The purpose of this article is to group together agents that cause similar electrocardiographic effects,review their pharmacologic actions, and discuss the electrocardiographic findings reported in the medical literature.

A Critical Reconsideration of the Clinical Effects and Treatment Recommendations for Sodium Channel Blocking Drug Cardiotoxicity

The cardiac sodium channel is comprised of proteins that span the cardiac cell membrane and form the channel pore. Depolarisation causes the proteins to move and open the sodium channel. Once the channel is open (active conformation), sodium ions move into the cell. The channel then changes from the active conformation to an inactive conformation - the channel remains open, but influx of sodium ions ceases. Recovery occurs as the channel moves from the inactive conformation back to the closed conformation and is then ready to open following the next depolarisation. Sodium channel blocking drugs (NCBDs) occupy receptors in the channel during the active and inactive conformations. The drug dissociates from most of the channel receptors during recovery, but the time it takes the drug to dissociate slows recovery. The slowed recovery prolongs conduction time, the main toxicity of NCBD overdose. Conduction time is further prolonged if heart rate increases as there are more available active and inactive conformations/unit time, which increases channel receptor binding sites for the NCBD. In addition to prolonging conduction time, NCBDs also decrease inotropy. Treatment of NCBD cardiotoxicity has been based on in vitro and animal experiments, and case reports. Assumptions based on this evidence must now be reassessed. For example, canines consistently develop ventricular tachycardia (VT) when tricyclic antidepressants (TCAs) are administered. Much of the literature discussing NCBD cardiotoxicity assumes that TCA poisoning induces VT in humans with the same regularity that occurs in canines. Seemingly, in support of this assumption was the finding that patients with remote myocardial infarction developed VT when therapeutically ingesting a NCBD. However, conduction is prolonged in myocardium that is or has been ischaemic. NCBD prolong conduction more in previously ischaemic myocardium than in normal myocardium, which causes nonuniform conduction and allows the development of re-entrant arrhythmias such as VT. Although some nonuniform conduction may occur in the healthy heart following a NCBD overdose, there is no evidence that nonuniform conduction occurs to the extent that it will cause re-entrant arrhythmias in this setting. Using various animal models and a variety of NCBDs, sodium ions, bicarbonate ions and alkalosis have been compared for the treatment of ventricular arrhythmias, hypotension and mortality. The results of these experiments have been extrapolated to NCBD overdose in humans. Animal models and single treatment approaches may have narrowed our scope. More recent evidence indicates that properties of each individual NCBD may require unique treatment. There is limited evidence that glucagon, which increases initial sodium ion influx into the cardiac cell, should be considered early in the treatment of cardiotoxicity. Another consideration may be treatment of NCBD with faster kinetics. Conduction time is decreased if a NCBD occupying the receptor is replaced by a NCBD that moves off and on the receptor more quickly. There is less evidence for this treatment, as risk may be greater. With greater understanding of the sodium channel and NCBDs, we must reassess our approach to the treatment of patients with healthy hearts who overdose on NCBD.

Drug- and toxin-associated seizures

Drug- and toxin-associated seizures may result from exposure to a wide variety of agents. Obtaining a comprehensive history behind the exposure is generally more helpful than diagnostic testing. Most DTS may be managed with supportive care, including benzodiazepines, except in the case of agents that require a specific intervention or antidote.

Acute poisoning: understanding 90% of cases in a nutshell

The acutely poisoned patient remains a common problem facing doctors working in acute medicine in the United Kingdom and worldwide. This review examines the initial management of the acutely poisoned patient. Aspects of general management are reviewed including immediate interventions, investigations, gastrointestinal decontamination techniques, use of antidotes, methods to increase poison elimination, and psychological assessment. More common and serious poisonings caused by paracetamol, salicylates, opioids, tricyclic antidepressants, selective serotonin reuptake inhibitors, benzodiazepines, non-steroidal anti-inflammatory drugs, and cocaine are discussed in detail. Specific aspects of common paediatric poisonings are reviewed.

Management of the Cardiovascular Complications of Tricyclic Antidepressant Poisoning

Experimental studies suggest that both alkalinisation and sodium loading are effective in reducing cardiotoxicity independently. Species and experimental differences may explain why sodium bicarbonate appears to work by sodium loading in some studies and by a pH change in others. In the only case series, the administration of intravenous sodium bicarbonate to achieve a systemic pH of 7.5-7.55 reduced QRS prolongation, reversed hypotension (although colloid was also given) and improved mental status in patients with moderate to severe tricyclic antidepressant poisoning. This clinical study supports the use of sodium bicarbonate in the management of the cardiovascular complications of tricyclic antidepressant poisoning. However, the clinical indications and dosing recommendations remain to be clarified. Hypotension should be managed initially by administration of colloid or crystalloid solutions, guided by central venous pressure monitoring. Based on experimental and clinical studies, sodium bicarbonate should then be administered. If hypotension persists despite adequate filling pressure and sodium bicarbonate administration, inotropic support should be initiated. In a non-randomised controlled trial in rats, epinephrine resulted in a higher survival rate and was superior to norepinephrine both when the drugs were used alone or when epinephrine was used in combination with sodium bicarbonate. Sodium bicarbonate alone resulted in a modest increase in survival rate but this increased markedly when sodium bicarbonate was used with epinephrine or norepinephrine. Clinical studies suggest benefit from norepinephrine and dopamine; in an uncontrolled study the former appeared more effective. Glucagon has also been of benefit. Experimental studies suggest extracorporeal circulation membrane oxygenation is also of potential value. The immediate treatment of arrhythmias involves correcting hypoxia, electrolyte abnormalities, hypotension and acidosis. Administration of sodium bicarbonate may resolve arrhythmias even in the absence of acidosis and, only if this therapy fails, should conventional antiarrhythmic drugs be used. The class 1b agent phenytoin may reverse conduction defects and may be used for resistant ventricular tachycardia. There is also limited evidence for benefit from magnesium infusion. However, class 1a and 1c antiarrhythmic drugs should be avoided since they worsen sodium channel blockade, further slow conduction velocity and depress contractility. Class II agents (beta-blockers) may also precipitate hypotension and cardiac arrest.

Poisonings and overdoses in the intensive care unit: General and specific management issues

OBJECTIVE

To provide current information on general and specific interventions for overdoses likely to require intensive care.

DESIGN

Review of literature relevant to selected interventions for general management of overdoses and specific poisons.

RESULTS

The benefit of interventions to decrease absorption or enhance elimination of toxins is limited to a relatively small number of specific agents. Antidotes and certain interventions may be helpful in preventing or treating toxicity in specific poisonings when used appropriately. Intensive supportive care is also necessary to achieve good outcomes.

CONCLUSION

Knowledge of the indications and limitations of current interventions for poisonings and overdoses is important for care of the critically ill poisoned patient.

Reversal of severe tricyclic antidepressant-induced cardiotoxicity with intravenous hypertonic saline solution

A 29-year-old woman ingested 8 g of nortriptyline and presented to the emergency department with coma, hypotension, and widened QRS interval. After intubation, gastric lavage, hyperventilation, and therapy with intravenous normal saline solution, sodium bicarbonate boluses (rapid intravenous push), and high doses of norepinephrine and dopamine, she transiently improved, only to deteriorate on arrival to the ICU. Because her arterial pH was alkalemic at 7.5 at this point, she was given additional sodium in the form of 200 mL of 7.5% NaCl by means of rapid intravenous infusion (intravenous push) to treat hypotension and widening QRS interval with ventricular ectopy. A continuous 12-lead ECG documented narrowing of her QRS interval with concomitant improvement of hypotension within 3 minutes of hypertonic saline solution infusion. Hypertonic saline solution should be considered for wide complex QRS and hypotension caused by tricyclic antidepressant-induced cardiotoxicity that is unresponsive to standard therapies.