Overview
Definition:
Tricyclic antidepressant (TCA) overdose is a life-threatening condition characterized by excessive ingestion of TCAs, leading to a spectrum of neurological and cardiovascular toxicity
Sodium bicarbonate is a cornerstone therapy in managing the cardiotoxicity associated with TCA overdose.
Epidemiology:
While TCA overdose incidence has decreased with newer antidepressants, they remain a significant cause of poisoning-related deaths
Pediatric ingestions are often accidental, though intentional overdoses can occur in adolescents
The severity is dose-dependent and influenced by individual metabolism.
Clinical Significance:
TCA overdose is a medical emergency due to its potential for rapid deterioration, particularly cardiac conduction abnormalities and seizures
Prompt and accurate management, including the judicious use of sodium bicarbonate, is critical to preventing morbidity and mortality in pediatric patients, and is a high-yield topic for DNB and NEET SS examinations.
Clinical Presentation
Symptoms:
Dry mucous membranes
Blurred vision
Urinary retention
Sedation or coma
Seizures
Agitation or delirium
Tachycardia
Hypotension
Flushing.
Signs:
Vital signs: Tachycardia (often sinus tachycardia), hypotension, hyperthermia
Neurologic: Altered mental status ranging from lethargy to deep coma, myoclonus, hyperreflexia, seizures
Cardiovascular: QRS widening (>100 ms), prolonged QT interval, arrhythmias (ventricular tachycardia, torsades de pointes, asystole), decreased myocardial contractility
Anticholinergic toxidrome: dry skin/mucous membranes, flushed skin, mydriasis, urinary retention, decreased bowel sounds.
Diagnostic Criteria:
Diagnosis is primarily clinical, based on suspected ingestion and characteristic signs and symptoms
A history of TCA ingestion, coupled with anticholinergic and cardiotoxic manifestations, strongly suggests TCA overdose
ECG findings of QRS widening are highly suggestive and a key indicator for management decisions.
Diagnostic Approach
History Taking:
Inquire about the specific TCA ingested (e.g., amitriptyline, nortriptyline, imipramine, clomipramine), the amount ingested, the time of ingestion, and any co-ingestions
Note any pre-existing cardiac or neurological conditions in the child
Confirm any recent psychiatric history or stressors in adolescents.
Physical Examination:
Perform a rapid assessment of airway, breathing, and circulation (ABC)
Assess mental status (Glasgow Coma Scale)
Examine for anticholinergic signs
Auscultate heart and lungs
Palpate abdomen for distension
Assess for neurological deficits and signs of seizures.
Investigations:
Serum TCA levels are often not readily available or helpful for acute management decisions
The ECG is paramount: assess QRS duration (≥100 ms indicates increased risk of seizures and arrhythmias), QT interval, and rhythm
Serum electrolytes (including bicarbonate), glucose, renal function, and liver function tests are important
Arterial blood gas (ABG) analysis to assess for acidosis
Consider toxicology screen for co-ingestions.
Differential Diagnosis:
Other anticholinergic poisonings (e.g., atropine, scopolamine, antihistamines)
Sympathomimetic overdose (e.g., amphetamines, cocaine)
Opioid overdose
Sedative-hypnotic overdose
Metabolic encephalopathy
Sepsis.
Management
Initial Management:
Ensure ABCs are secured
Administer activated charcoal if ingestion is recent (<1-2 hours) and the patient is conscious and able to protect their airway
Gastric lavage is rarely indicated and may be harmful
Monitor vital signs, cardiac rhythm, and neurological status closely
IV access is crucial.
Medical Management:
Sodium bicarbonate: Administer a bolus of 1-2 mEq/kg IV push, aiming for a serum pH of 7.45-7.55 and a QRS duration <100 ms
Repeat boluses as needed, titrating to ECG changes and pH
Continuous infusion of sodium bicarbonate may be used to maintain alkalosis and prolong QRS narrowing
Treatment of seizures: Benzodiazepines (e.g., diazepam, lorazepam) are first-line
If seizures persist or are refractory, consider phenobarbital or phenytoin
Management of arrhythmias: Treat hypotension with IV fluids and vasopressors (e.g., norepinephrine)
Avoid antiarrhythmics that prolong QRS duration (e.g., flecainide, propafenone)
Lidocaine may be used cautiously for ventricular arrhythmias if sodium bicarbonate is ineffective
Hyperthermia management: Cooling measures such as cooling blankets, fans, and antipyretics (avoiding salicylates).
Surgical Management:
Not applicable for TCA overdose management
Focus is on supportive and medical interventions.
Supportive Care:
Continuous cardiac monitoring with telemetry
Frequent neurological assessments
Maintain oxygenation and ventilation
Provide adequate hydration
Monitor urine output
Consider nasogastric tube for gastric decompression if ileus develops
Monitor fluid balance to avoid hyponatremia with bicarbonate therapy.
Complications
Early Complications:
Refractory seizures (status epilepticus)
Fatal cardiac arrhythmias (ventricular tachycardia, torsades de pointes, asystole)
Respiratory arrest
Pulmonary edema
Rhabdomyolysis
Acute kidney injury
Hyperthermia
Cerebral edema.
Late Complications:
Neurological sequelae from prolonged seizures or hypoxic brain injury
Cognitive deficits
Peripheral neuropathy
Chronic pain syndromes
Psychiatric sequelae related to underlying conditions.
Prevention Strategies:
Secure storage of medications away from children
Prescription of smaller quantities of TCAs for outpatients
Patient and caregiver education regarding the dangers of overdose
Close psychiatric monitoring for adolescents at risk.
Prognosis
Factors Affecting Prognosis:
The amount and type of TCA ingested, time to initiation of treatment, presence and severity of cardiovascular toxicity (QRS widening, arrhythmias), and occurrence of seizures are critical prognostic factors
Rapid response to sodium bicarbonate is a positive indicator.
Outcomes:
With prompt and aggressive management, including sodium bicarbonate for cardiotoxicity, many pediatric patients can recover
However, severe overdoses can lead to significant morbidity or mortality
A QRS duration >100 ms on ECG in TCA overdose is associated with a higher risk of seizures and cardiac arrhythmias.
Follow Up:
Long-term follow-up should address any underlying psychiatric issues that may have contributed to the overdose
Neurological assessments may be required if seizures or significant CNS depression occurred
Renal and liver function should be re-evaluated as needed.
Key Points
Exam Focus:
The hallmark ECG finding of TCA overdose is QRS widening (>100 ms)
Sodium bicarbonate is the primary treatment for cardiotoxicity
Aim for serum pH 7.45-7.55 and QRS <100 ms
Seizures are treated with benzodiazepines.
Clinical Pearls:
Never assume a non-toxic ingestion in a pediatric TCA overdose
always treat aggressively
Serial ECGs are crucial to monitor response to therapy
Be prepared to manage seizures and arrhythmias aggressively
Monitor for hyponatremia with aggressive bicarbonate use and fluid management.
Common Mistakes:
Delaying sodium bicarbonate therapy in the presence of QRS widening
Using antiarrhythmic drugs that prolong the QRS interval
Underestimating the severity of TCA overdose
Inadequate monitoring of ECG and vital signs.