Rosen & Barkin's 5-Minute Emergency Medicine Consult (99 page)

Barbiturate Poisoning

The author would like to provide special thanks to the author of the prior edition, Matthew Valento.

CODES

969.4 Poisoning by benzodiazepine-based tranquilizers

BASICS

• Cardiovascular: β
  ₁
  -receptors:
  
  • ATP converted to cAMP by adenyl cyclase with stimulation of β-receptors.
    
  • cAMP activates protein kinase, which phosphorylates proteins of the sarcoplasmic reticulum.
    
  • Sarcoplasmic reticulum releases calcium.
    
  • Excitation–contraction coupling occurs.
    
• Effects of β-blockers:
  
  • Cardiovascular:
    
    • Decreased excitation/contraction
      
    • Membrane stabilizing activity
      
    • Sodium channel blockade causes a prolongation of the QRS complex (with some agents).
      
    • Prolongation of QTc interval leading to ventricular dysrhythmias (with some agents)
      
    • Intrinsic sympathomimetic activity
      
    • Partial agonist properties (with some agents)
      
  • Neurologic:
    
    • CNS effects with the lipophilic agents (propranolol, metoprolol, labetalol)
      

DIAGNOSIS

• Cardiovascular:
  
  • Hypotension
    
  • Bradycardia
    
  • Cardiac conduction delays
    
  • Heart block
    
  • Heart failure
    
  • Electrical mechanical dissociation
    
  • Loss of β-selectivity in overdose settings
    
• Neurologic:
  
  • Coma
    
  • Seizures
    
• Pulmonary:
  
  • Bronchospasm
    
  • Pulmonary edema
    
• Metabolic:
  
  • Hypoglycemia
    

• Inquire about risk of medication error.
  
• Inquire about risk of suicidal ideation with intent.
  
• Inquire about possible exposure to medications with a pediatric patient.
  

• Hypotension
  
• Bradycardia
  
• Dysrhythmias
  

• With unknown ingestion: Suspect β-blocker poisoning with bradycardia/hypotension.
  
• ECG:
  
  • Conduction delays
    
  • 1st-, 2nd-, or 3rd-degree heart block
    
  • Bradycardia
    

• CBC
  
• Electrolytes, BUN, creatinine, glucose
  
• Toxicology screen if coingestants suspected
  

• Calcium-channel blocker toxicity
  
• Clonidine toxicity
  
• Digitalis toxicity
  
• Acute myocardial infarction with heart block
  

TREATMENT

• Transport pills and pill bottles when overdose suspected.
  

• ABCs:
  
  • Airway protection as indicated by mental status
    
  • Supplemental oxygen as needed
    
  • 0.9% NS IV access
    
  • Close hemodynamic monitoring
    
• Naloxone and thiamine if altered mental status
  
• Bedside glucose determination, treat hypoglycemia with D
  ₅₀
  W
  
• Treat prolonged seizures with benzodiazepines
  

• Heart rate >60 beats per minute
  
• Systolic BP >90 mm Hg
  
• Adequate urine output
  
• Improving level of consciousness
  

• Syrup of ipecac: Contraindicated in the prehospital and ED setting.
  
• Consider lavage with Ewald tube if ingestion within 1 hr:
  
  • Propranolol may cause esophageal spasm producing difficulty with passage and removal of gastric lavage tube.
    
• Activated charcoal helpful especially in the presence of coingestants.
  

• Atropine:
  
  • Initial agent
    
  • Low success rate
    
• Glucagon:
  
  • Initial drug of choice for β-blocker–induced hemodynamic instability
    
  • Administer if atropine does not increase heart rate.
    
  • Promotes cAMP production through a receptor site other than the β-receptor
    
  • May cause nausea and vomiting
    
  • Mix with NS or D
    ₅
    W
    
• IV fluids:
  
  • Administer cautiously in the hypotensive patient
    
  • Swan-Ganz catheter or central venous pressure (CVP) monitoring to help follow volume status
    
• Amrinone:
  
  • Selective phosphodiesterase inhibitor
    
  • Indirectly increases cAMP leading to increased inotropy
    
  • Use in conjunction with glucagon to treat symptomatic sustained bradycardia.
    
• Vasopressor agents:
  
  • Initiate when symptomatic hypotension/bradycardia persists after atropine/glucagon.
    
  • Use invasive monitoring to help guide therapy.
    
  • Utility may be limited owing to β-blockade:
    
    • Higher doses may be required.
      
  • Isoproterenol (nonselective β-agonist):
    
    • Titrate for BP and heart rate.
      
  • Epinephrine (potent α- and β-receptor agonist):
    
    • BP increases as a result of direct myocardial stimulation, increase in heart rate, and vasoconstriction.
      
    • Use if no BP response with isoproterenol
      
  • High-dose dopamine
    
• Sodium bicarbonate:
  
  • In theory, this is used if there is evidence of prolongation of QRS >100 ms owing to some of the β-blockers also causing sodium channel blockade leading to a prolonged QRS.
    
  • Not routinely administered for all β-blocker toxicities
    
• Electrical pacing: When other treatment options have failed
  

• Consult with local poison center
  
• High-dose insulin:
  
  • Promotes more efficient myocardial metabolism
    
  • Hypoglycemia commonly seen in β-blocker overdose, will require frequent monitoring of glucose concentration
    
  • Perform in consultation with local poison center
    
• IV fat emulsion therapy (20% intralipid)
  

• Hemodialysis helpful with water-soluble β-blocking agents:
  
  • Nadolol
    
  • Atenolol
    
  • Sotalol
    
• IV fat emulsion (20% Intralipid):
  
  • Potential treatment in the future
    

• Activated charcoal: 1 g/kg PO
  
• Amrinone: Loading dose 0.75 mg/kg; maintenance drip 2–20 μg/kg/min; titrate for effect
  
• Atropine: 0.5 mg (peds: 0.02 mg/kg) IV; repeat 0.5–1 mg IV (peds: 0.04 mg/kg)
  
• Dopamine: 2–20 μg/kg/min IV
  
• Dextrose: D
  ₅₀
  W 1 ampule (50 mL or 25 g; peds: D
  ₂₅
  W 2–4 mL/kg) IV
  
• Epinephrine: 2 μg/min (peds: 0.01 mg/kg [0.1 mL/kg 1:10,000]); titrate to effect
  
• Glucagon: 3–5 mg IV over 1–2 min (peds: 0.03–0.1 mg/kg) bolus followed by 70 μg/kg/h infusion
  
• Insulin (regular insulin): 1 IU/kg bolus IV followed by 0.5–1 IU/kg/h titrated to clinical response (be sure to supplement with dextrose)
  
• Isoproterenol: 5 μg/min IV and titrate for heart rate effect
  
• Norepinephrine: Start 2–4 μg/min IV, titrate up to 1–2 μg/kg/min IV
  
• Sodium bicarbonate: 1 mEq/kg IVP
  

• IV fluids
  
• Glucagon
  
• Vasopressor agents
  

• Sodium bicarbonate
  
• Hemodialysis
  

FOLLOW-UP