Rosen & Barkin's 5-Minute Emergency Medicine Consult (453 page)

TREATMENT

• Bring to hospital all substances patient may have ingested.
  
• Question witnesses and observe scene for household products and other potential coingestants:
  
  • Document and relay findings to emergency medical staff.
    
• Commercial or industrial sites:
  
  • Obtain relevant material safety data sheets (MSDSs) if available to identify commercial or chemical products.
    
  • Avoid dermal exposures.
    

• ABCs:
  
  • Cardiac monitor
    
  • Isotonic crystalloids as needed for hypotension
    
• Naloxone, thiamine, and dextrose (D
  ₅₀
  W) as indicated for altered mental status
  
• Supplemental oxygen
  

• Decontamination:
  
  • If owing to acute ingestion/overdose within previous 1–2 hr, and protective airway reflexes are intact, administer 50–100 g of activated charcoal PO.
    
• Remove source of oxidant stress.
  
• Methylene blue:
  
  • Indications:
    
    • Asymptomatic with levels >30%
      
    • Symptomatic patients with levels >10–20%, especially if comorbid diseases are present
      
  • Expect transient worsening of saturations on pulse oximetry after methylene blue is administered:
    
    • Interferes with pulse oximetry measurement and no specific intervention required
      
  • Use with caution in patients with glucose-6 pyruvate decarboxylase deficiency:
    
    • May cause hemolysis
      
• If no improvement with methylene blue, consider that source of oxidant stress is not eliminated, or that sulfhemoglobinemia is present:
  
  • Sulfhemoglobin is sulfur molecule bound to hemoglobin. Presents similar to methemoglobin, but is self-limited and not responsive to methylene blue.
    
• RBC transfusion:
  
  • May be necessary to increase blood oxygen-carrying capacity
    
  • Consider in the presence of HA.
    
• Exchange transfusion:
  
  • Especially with neonates/infants
    
• Hyperbaric oxygen therapy:
  
  • Increases oxygen delivery to tissues by allowing more oxygen to be dissolved in the blood, independent of hemoglobin.
    
  • Use in life-threatening methemoglobinemia if immediately available.
    

• Children may develop significant methemoglobinemia from apparently minor ingestions.
  
• Symptoms delayed several hours after ingestion, so prolonged observation necessary
  
• Neonates are also at higher risk of methemoglobinemia (owing to decreased stores of NADH methemoglobin reductase).
  

• Dextrose 50%: 25 g (50 mL) (peds: 0.5–1 g/kg of dextrose) IV for hypoglycemia
  
• Methylene blue: 0.1–0.2 mL/kg 1% solution IV over 5 min (adults and peds)
  
  • May repeat if no improvement in 1 hr
    
  • Doses of 0.3 to 1 mg/kg IV have been effective in neonates. Has been used IO over 3–5 min.
    
• Naloxone: 0.4–2 mg (peds: 0.1 mg/kg) IV, may repeat up to 10 mg for suspected opioid intoxication
  
• Thiamine: 100 mg (peds: 1 mg/kg) IM or IV
  

FOLLOW-UP

• Severely symptomatic patients
  
• Patients requiring multiple doses of methylene blue
  
• Dapsone may cause prolonged recurrent methemoglobinemia
  

Methemoglobin levels <20% and falling with no symptoms or comorbid disease

Toxicology consult for significant exposures

Occupational medicine referral for work-related exposures

• Pulse oximetry is
  inaccurate
  in methemoglobinemia.
  
• Obtain an ABG.
  
• Administer methylene blue for significant levels/symptoms.
  

A special thanks to Dr. Gerald Maloney who contributed to the previous edition.

• Barclay JA, Ziemba SE, Ibrahim RB. Dapsone-induced methemoglobinemia: A primer for clinicians.
  Ann Pharmacother.
  2011;45:1103–1115.
  
• Bradberry SM, Aw TC, Williams NR, et al. Occupational methaemoglobinaemia.
  Occup Environ Med
  . 2001;58:611–615.
  
• Guay J. Methemoglobinemia related to local anesthetics: A summary of 242 episodes.
  Anesth Analg.
  2009;108:837–845.
  
• Price D. Methemoglobin inducers. In: Flomenbaum NE, Goldfrank LR, Hoffman RS, et al., eds.
  Goldfrank’s Toxicologic Emergencies.
  9th ed. New York, NY: McGraw-Hill; 2011.
  
• Wright RO, Lewander WJ, Woolf AD. Methemoglobinemia: Etiology, pharmacology, and clinical management.
  Ann Emerg Med
  . 1999;34:646–656.
  

CODES

289.7 Methemoglobinemia

BASICS

• Bulging of 1 or both of the mitral valve leaflets into the left atrium during systole
  
• Occurs when the leaflet edges of the mitral valve do not coapt
  
• Commonly due to abnormal stretching of 1 of the mitral valve leaflets during systole:
  
  • Myxomatous proliferation of the spongiosa layer within the valve causing focal interruption of the fibrosa layer
    
  • Excessive stretching of the chordae tendineae, leading to traction on papillary muscles
    
• Theoretical explanations for associated chest pain:
  
  • Focal ischemia from coronary microembolism due to platelet aggregates and fibrin deposits in the angles between the leaflets
    
  • Coronary artery spasm
    
• Mitral regurgitation (MR) may occur in some patients.
  
• Age of onset is 10–16 yr
  
• Female > male (3:1)
  
• Typically benign in young women, whereas men >50 yr tend to have serious sequelae and more often develop severe regurgitation requiring surgical intervention
  
• Can be identified by ECG in 2–4% of the general population and in 7% of autopsies
  
• A variety of neuroendocrine and autonomic disturbances occur in some patients
  
• Genetics:
  
  • Strong hereditary component
    
  • Sometimes transmitted as an autosomal dominant trait with varying penetrance
    

• Marfan syndrome
  
• Relapsing polychondritis
  
• Ehlers–Danlos syndrome (i.e., types I, II, IV)
  
• Osteogenesis imperfecta
  
• Pseudoxanthoma elasticum
  
• Stickler syndrome
  
• Systemic lupus erythematosus
  
• Polyarteritis nodosa
  
• Polycystic kidney disease
  
• von Willebrand syndrome
  
• Duchenne muscular dystrophy
  

DIAGNOSIS

Separated into 3 categories:

• Symptoms related to autonomic dysfunction
  
• Symptoms related to the progression of MR
  
• Symptoms that occur as a result of an associated complication (i.e., stroke, endocarditis, or arrhythmia)
  

• Palpitations in up to 40% of cases:
  
  • Usually ventricular premature beats or paroxysmal supraventricular tachycardia
    
  • Up to 40% have symptoms of dysautonomia
    
• Chest pain occurs in 10%:
  
  • Sharp, localized, of variable duration, and nonexertional
    
  • Rarely may respond to nitroglycerin
    
• Panic attacks
  
• Anxiety
  
• Fatigue
  
• Depression in up to 70%
  
• Nervousness
  
• Migraine headaches
  
• Irritable bowel
  
• Syncope/presyncope:
  
  • Occurs in 0.9% of patients
    
• Orthostasis
  
• Dyspnea and fatigue relatively uncommon