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Digitalis Intoxication

Digitalis Intoxication. The foxglove plant, from which digitalis is derived. DIGITALIS Perspective. Principles of Disease Pathophysiology. In therapeutic doses, digitalis has two effects:

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Digitalis Intoxication

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  1. Digitalis Intoxication Zohair Al Aseri MD,FRCPC EM & CCM

  2. The foxglove plant, from which digitalis is derived. DIGITALIS Perspective Zohair Al Aseri MD,FRCPC EM & CCM

  3. Principles of Disease Pathophysiology In therapeutic doses, digitalis has two effects: (1) increasing the force of myocardial contraction to increase cardiac output in patients with heart failure. (2) decreasing atrioventricular (AV) conduction to slow the ventricular rate in atrial fibrillation. Zohair Al Aseri MD,FRCPC EM & CCM

  4. Principles of Disease Pathophysiology • It inhibits membrane sodium-potassium adenosine triphosphatase (ATPase), which increases intracellular sodium and calcium and increases extracellular potassium. • At therapeutic doses, the effects on serum electrolyte levels are minimal. Zohair Al Aseri MD,FRCPC EM & CCM

  5. Principles of Disease Pathophysiology • With toxic levels, digitalis paralyzes the Na-K pump, potassium cannot be transported into cells, and serum potassium can rise as high as 13.5 mEq/L. Zohair Al Aseri MD,FRCPC EM & CCM

  6. Principles of Disease Pathophysiology • At therapeutic levels, digitalis indirectly increases vagal activity and decreases sympathetic activity. • At toxic levels, digitalis can directly halt the generation of impulses in the SA node, depress conduction through the AV node, and increase the sensitivity of the SA and AV nodes to catecholamines. Zohair Al Aseri MD,FRCPC EM & CCM

  7. Principles of Disease Pathophysiology • Because bradydysrhythmias and tachydysrhythmias can appear and alternate in the same patient, administering one class of drugs to treat tachycardias may later contribute to more refractory bradycardias and AV block. Zohair Al Aseri MD,FRCPC EM & CCM

  8. Principles of Disease Pathophysiology • It enhances automaticity resulting from increased rate of phase 4 repolarization and delayed after depolarizations result premature ventricular contractions, the most common manifestation of digitalis toxicity. Zohair Al Aseri MD,FRCPC EM & CCM

  9. Principles of Disease Pathophysiology • Digitalis can produce virtually any dysrhythmia or conduction block, and bradycardias are as common as tachycardias. Zohair Al Aseri MD,FRCPC EM & CCM

  10. DYSRHYTHMIAS ASSOCIATED WITH DIGITALIS TOXICITY Zohair Al Aseri MD,FRCPC EM & CCM

  11. Principles of Disease Pathophysiology • The volume of distribution (Vd) of digoxin is 5 L/kg for adults but varies from 3.5 L/kg in premature infants to 16.3 L/kg in older infants. • This indicates that only a small fraction of digitalis remains in the intravascular space, and the drug is highly concentrated in cardiac tissue. • The myocardial-to-serum ratio at equilibrium ranges from 15 : 1 to 30 : 1.  • The Vd for digitoxin is 0.5 L/kg. Zohair Al Aseri MD,FRCPC EM & CCM

  12. Principles of Disease Pathophysiology • The elimination half-life of digoxin, which is primarily excreted in the urine, is 30 hours, and the half-life of digitoxin, which is metabolized in the liver, is 7 days.  • Whereas digoxin undergoes only a small enterohepatic circulation, that for digitoxin is large. Zohair Al Aseri MD,FRCPC EM & CCM

  13. Principles of Disease Pathophysiology • The significant protein binding and large volume of distribution suggest that hemodialysis, hemoperfusion, and exchange transfusion are ineffective. Zohair Al Aseri MD,FRCPC EM & CCM

  14. FACTORS ASSOCIATED WITH INCREASED RISK OF DIGITALIS TOXICITY Zohair Al Aseri MD,FRCPC EM & CCM

  15. Clinical Features • The symptoms and signs of chronic digitalis intoxication are nonspecific. The most common symptoms are • Nausea • Anorexia • Fatigue • Visual disturbance. Zohair Al Aseri MD,FRCPC EM & CCM

  16. NONCARDIAC SYMPTOMS OF DIGITALIS INTOXICATION IN ADULTS AND CHILDREN Zohair Al Aseri MD,FRCPC EM & CCM

  17. Clinical Features • Significant differences exist between acute and chronic intoxication. • Chronic poisoning has an insidious onset and is accompanied by a higher mortality rate. • In cases of chronic intoxication, the LL50 (the level with a 50% mortality) is only 6 ng/ml.  • Chronically intoxicated patients almost always have underlying heart disease, which contributes to morbidity and mortality. Zohair Al Aseri MD,FRCPC EM & CCM

  18. Chronic versus Acute Digitalis Intoxication Zohair Al Aseri MD,FRCPC EM & CCM

  19. Diagnostic Strategies • Serum digoxin levels. • It is the steady state, rather than peak level, that correlates with tissue toxicity and is used to calculate antidote dosages. Zohair Al Aseri MD,FRCPC EM & CCM

  20. Diagnostic Strategies • Peak levels after an oral dose of digoxin occur in 1.5 to 2 hours, with a range of 0.5 to 6 hours.  • Steady-state serum concentrations are not achieved until after distribution, or 6 to 8 hours after a dose or overdose, and may be only one fourth to one fifth of the peak level. Zohair Al Aseri MD,FRCPC EM & CCM

  21. Diagnostic Strategies • The ideal serum digoxin concentration for patients with heart failure is considered to be 0.7 to 1.1 ng/mL.  Zohair Al Aseri MD,FRCPC EM & CCM

  22. Diagnostic Strategies • A level drawn too soon after the last maintenance dose falsely suggests toxicity, especially in cases of chronic intoxication, in which significant morbidity and mortality can occur at levels of 2 to 6 ng/ml.  Zohair Al Aseri MD,FRCPC EM & CCM

  23. Diagnostic Strategies • After an acute massive overdose in a patient who is rapidly becoming symptomatic, however, it may be impractical to wait 6 to 8 hours for the first reading.  • It is unlikely that early levels exceeding 10 to 20 ng/mL will fade to clinical insignificance at 6 to 8 hours after ingestion. Zohair Al Aseri MD,FRCPC EM & CCM

  24. Diagnostic Strategies • Patients taking digitalis therapeutically often take diuretics as well, and they often have low serum and total body potassium levels. • The acutely poisoned patient, in contrast, may have life-threatening hyperkalemia. Zohair Al Aseri MD,FRCPC EM & CCM

  25. Management • With the availability of digoxin-specific fragment antigen-binding (Fab) antibodies (Digibind and DigiFab), all other therapies are considered temporizing. Zohair Al Aseri MD,FRCPC EM & CCM

  26. Management • There is no evidence to support gastric emptying for the treatment of digoxin overdose. • Activated charcoal, no improvement in outcome has been established. • Multidose charcoal has no proven benefit Zohair Al Aseri MD,FRCPC EM & CCM

  27. Electrolyte Correction K • In cases of chronic intoxication, often exacerbated by hypokalemia, raising the serum potassium level to 3.5 to 4 mEq/L is an important early treatment. • Potassium can be administered orally (which is safer) or intravenously (IV) although a rate more rapid than 10 to 40 mEq/hour is dangerous. Zohair Al Aseri MD,FRCPC EM & CCM

  28. Electrolyte Correction K • In acute poisoning, serum potassium may begin to rise rapidly within 1 to 2 hours of ingestion, potassium should be withheld, even if mild hypokalemia is measured initially. Zohair Al Aseri MD,FRCPC EM & CCM

  29. Electrolyte Correction K • A serum potassium level greater than 5 mEq/L warrants consideration of digitalis antibody (ovine Fab fragment) treatment. • If digitalis antibodies are not immediately available, severe hyperkalemia should be treated with IV glucose, insulin, and sodium bicarbonate. Zohair Al Aseri MD,FRCPC EM & CCM

  30. Electrolyte Correction Ca • Although hypercalcemia can exacerbate digitalis intoxication, recent studies indicate that IV calcium can be safely given for hyperkalemia in the setting of digitalis intoxication.  • Calcium salts should be administered over several minutes through a secure peripheral IV site or through a central venous catheter. Zohair Al Aseri MD,FRCPC EM & CCM

  31. Electrolyte Correction Mg • Many patients on diuretic therapy are also magnesium-depleted, even when the measured serum magnesium level is normal. • If significant magnesium depletion is suggested, 1 to 2 g of magnesium sulfate can be given over 10 to 20 minutes (child: 25 mg/kg), followed by a constant infusion of 1 to 2 g/hour. • Patients must be closely monitored for respiratory depression, which is usually preceded by progressive loss of deep tendon reflexes. Zohair Al Aseri MD,FRCPC EM & CCM

  32. Electrolyte Correction Mg • Hypermagnesemia can exacerbate digitalis toxicity, but magnesium has been reported to reverse digoxin-induced tachydysrhythmias. • It is prudent to infuse magnesium slowly and stop the infusion if heart block or bradycardia develops. Avoid magnesium in patients with renal failure. • The role of magnesium in bradydysrhythmias and conduction blocks is less clear but probably dangerous because hypermagnesemia can impair impulse formation and AV conduction. Zohair Al Aseri MD,FRCPC EM & CCM

  33. Atropine • Atropine is generally used for severe bradycardia and advanced AV block, with mixed results. • Generally, an external or transvenous pacemaker should be prepared when bradycardia or AV block appears. Zohair Al Aseri MD,FRCPC EM & CCM

  34. Pacing • It may be safer to temporize with an external rather than a transvenous pacemaker while waiting for Fab fragments to take effect. • Cardioversion and defibrillation can cause asystole after attempts to treat tachydysrhythmias. • Lower energy settings, such as 25 to 50 J, may be less hazardous. Zohair Al Aseri MD,FRCPC EM & CCM

  35. Carotid Sinus Massage • Carotid sinus massage may result in bradyasystole and cardiac arrest in the setting of digitalis toxicity. Zohair Al Aseri MD,FRCPC EM & CCM

  36. Phenytoin and Lidocaine • Phenytoin and lidocaine are believed to be the safest of the antidysrhythmic drugs for controlling tachydysrhythmias in the setting of digitalis intoxication. • Phenytoin may enhance AV conduction. • Phenytoin has been infused at 25 to 50 mg/min to a loading dose of 10 to 15 mg/kg. Zohair Al Aseri MD,FRCPC EM & CCM

  37. Phenytoin and Lidocaine • Lidocaine can be given initially at a dosage of 1 to 3 mg/kg over several minutes, followed by an infusion of 1 to 4 mg/min. • Most other cardiac drugs (isoproterenol, procainamide, amiodarone, beta-blockers, calcium antagonists) may worsen dysrhythmias or depress AV conduction. • Digoxin immune Fab fragments are the preferred therapy for dysrhythmias. Zohair Al Aseri MD,FRCPC EM & CCM

  38. Fab Fragments (Digibind or Digifab) • The mortality rate before Fab fragment therapy was 23%. • Fab fragment treatment is well established in both chronic and acute poisonings, with a 90% response rate.  Zohair Al Aseri MD,FRCPC EM & CCM

  39. Fab Fragments (Digibind or Digifab) • Digitalis antibodies are derived from sheep immunized with digoxin. Side Effect • Reactions have included erythema, urticaria, and facial edema, all of which are responsive to the usual treatment. • Hypokalemia • Exacerbation of congestive heart failure • Increase in ventricular rate with atrial fibrillation. Zohair Al Aseri MD,FRCPC EM & CCM

  40. Fab Fragments (Digibind or Digifab) • Indicated for serious cardiovascular toxicity • Not for prophylactic administration of higher than expected serum levels. • The primary indication for antibody treatment in cases of acute poisoning is hyperkalemia with a serum potassium level greater than 5.5 mEq/L or ECG changes. Zohair Al Aseri MD,FRCPC EM & CCM

  41. Fab Fragments (Digibind or Digifab) • The median time to initial response is 19 minutes after completion of the Fab infusion, but complete resolution of digitalis-toxic rhythms may require hours.  Zohair Al Aseri MD,FRCPC EM & CCM

  42. Fab Fragments (Digibind or Digifab) • Fab fragment therapy should be used before transvenous pacing, which carries significant risk. Zohair Al Aseri MD,FRCPC EM & CCM

  43. RECOMMENDATIONS FOR ADMINISTRATION OF DIGITALIS ANTIBODY FRAGMENTS Zohair Al Aseri MD,FRCPC EM & CCM

  44. Fab Fragments (Digibind or Digifab) Three approaches: • The first is empirical. A patient has a history of digitalis ingestion, consistent symptoms, and life-threatening dysrhythmias. • There is no time to assess serum digoxin levels, either at 1 hour or in steady state. • 10 vials over 30 minutes through a 0.22-?m filter for the average acute ingestion • 4 to 6 vials for the average chronic ingestion. • In cardiac arrest, 20 vials can be administered undiluted by IV bolus Zohair Al Aseri MD,FRCPC EM & CCM

  45. Fab Fragments (Digibind or Digifab) Second approach • One vial of Digibind or Digifab contains 38 mg of Fab fragments, which bind 0.5 mg of digoxin or digitoxin. Third approach • is to base the dosage on the steady-state serum digoxin or digitoxin level after 6 to 8 hours. Zohair Al Aseri MD,FRCPC EM & CCM

  46. Fab Fragments (Digibind or Digifab) • Because most assays measure both bound and unbound drug, digitalis levels will be elevated for up to 1 week, with values often greater than 100 ng/mL. Zohair Al Aseri MD,FRCPC EM & CCM

  47. SAMPLE CALCULATION OF DIGIBIND OR DIGIFAB BASED ON INGESTED DOSE OF DIGOXIN OR DIGITOXIN Zohair Al Aseri MD,FRCPC EM & CCM

  48. SAMPLE CALCULATION OF DIGIBIND OR DIGIFAB BASED ON STEADY-STATE DIGOXIN CONCENTRATION Zohair Al Aseri MD,FRCPC EM & CCM

  49. CALCULATION BASED ON STEADY-STATE DIGITOXIN CONCENTRATION Zohair Al Aseri MD,FRCPC EM & CCM

  50. Pediatric Considerations • Children at greatest risk are those on chronic digitalis therapy for heart disease. • Children with healthy hearts have been known to tolerate massive acute oral ingestions without digitalis antibody treatment.  Zohair Al Aseri MD,FRCPC EM & CCM

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