What are the clinical presentations of a sodium nitrite overdose?

Clinical Presentation of Sodium Nitrite Overdose

Sodium nitrite overdose presents with a characteristic triad of cyanosis, severe hypotension, and altered mental status due to methemoglobinemia, with symptoms appearing rapidly after ingestion and potentially progressing to cardiovascular collapse and death within minutes to hours. 1

Cardiovascular Manifestations

• Severe hypotension is a hallmark feature, mediated primarily by increased venous capacitance and vasodilation 1
• Cardiac dysrhythmias develop as methemoglobin levels increase, ranging from tachycardia at lower levels to bradycardia and complete cardiovascular collapse at higher levels 1, 2
• Patients may present in bradycardic cardiac arrest despite aggressive resuscitation efforts, particularly with large ingestions 2, 3
• Hypotension can be profound and refractory to standard vasopressor therapy 2

Dermatologic and Oxygen-Related Signs

• Cyanosis becomes clinically apparent at methemoglobin levels of 10-20%, presenting as a distinctive blue-gray discoloration of skin and mucous membranes 1, 2
• Pulse oximetry characteristically remains around 85% despite supplemental oxygen administration, which is a critical diagnostic clue 2
• Blood drawn from venipuncture appears dark brown or chocolate-colored, distinguishing it from normal red blood 2, 3
• The blood flowing through extracorporeal circuits maintains the same brown color, indicating persistent methemoglobinemia 3

Neurological Symptoms

• Altered consciousness ranging from anxiety and confusion to coma develops as methemoglobin levels rise 1, 3
• Central nervous system depression becomes prominent at higher methemoglobin levels 1
• Patients may present initially conscious but rapidly deteriorate to unresponsiveness 4, 2
• Loss of consciousness at the scene is associated with particularly poor prognosis 4

Respiratory Manifestations

• Dyspnea is an early symptom, appearing at methemoglobin levels as low as 15% 1
• Hypoxia develops despite adequate ventilation due to impaired oxygen-carrying capacity 2
• Desaturation persists despite high-flow oxygen or mechanical ventilation 3

Gastrointestinal Symptoms

• Nausea can occur early in the clinical course at methemoglobin levels around 15% 1
• Gastrointestinal symptoms are less prominent than cardiovascular and neurological manifestations 1

Dose-Related Severity

• Oral doses as low as 1 gram have been reported to cause or significantly contribute to mortality in adults 1
• Intravenous doses as low as 600 mg can be fatal 1
• Documented fatal ingestions have ranged from approximately 12.5 grams to over 100 grams 4, 5
• A 17-month-old child died after receiving an adult dose of 300 mg IV followed by 150 mg 1

Methemoglobin Level Correlations

• 15% methemoglobin: Anxiety, dyspnea, nausea, and tachycardia become apparent 1
• 10-20% methemoglobin: Cyanosis becomes clinically visible 1
• Above 70% methemoglobin: Usually fatal without immediate intervention 1
• Documented levels in survivors: Range from 54.6% with immediate treatment 4
• Documented levels in fatalities: Up to 90.3% in cases where resuscitation failed 4

Temporal Progression

• Symptoms develop rapidly after ingestion, often within minutes 2, 5
• Rapid decompensation can occur during transport, progressing from hypotension to cardiac arrest 2
• Patients may collapse at the scene with massive ingestions 4
• In survivors who receive early methylene blue, all symptoms typically resolve within 24 hours 5

Critical Pitfalls in Recognition

• Point-of-care testing may fail to provide methemoglobin levels during resuscitation, leading to missed diagnosis 3
• The characteristic brown blood color may be the only visual clue during extracorporeal support 3
• Sodium nitrite is readily accessible through online vendors and increasingly used in suicide attempts, making it more likely to be encountered 5
• Return of spontaneous circulation may never be achieved despite prolonged ECPR if methemoglobinemia goes untreated 3