Recovery from severe cyclic antidepressant overdose with hypertonic saline/dextran in a swine model

Cardiovascular Drug Toxicity

Managing unstable poisoned patients is often associated with clinician cognitive overload. This article summarizes the mechanisms of toxicity; clinical presentations; and the current evidence available for the treatment of cardiovascular drug toxicity due to calcium channel blockers, beta-blockers, cardiac glycosides, and sodium channel blockers. In addition, management approaches are proposed.

Antidote Use in the Critically Ill Poisoned Patient

The proper use of antidotes in the intensive care setting when combined with appropriate general supportive care may reduce the morbidity and mortality associated with severe poisonings. The more commonly used antidotes that may be encountered in the intensive care unit ( N-acetylcysteine, ethanol, fomepizole, physostigmine, naloxone, flumazenil, sodium bicarbonate, octreotide, pyridoxine, cyanide antidote kit, pralidoxime, atropine, digoxin immune Fab, glucagon, calcium gluconate and chloride, deferoxamine, phytonadione, botulism antitoxin, methylene blue, and Crotaline snake antivenom) are reviewed. Proper indications for their use and knowledge of the possible adverse effects accompanying antidotal therapy will allow the physician to appropriately manage the severely poisoned patient.

Miscellaneous central nervous system intoxicants

The topic of central nervous system intoxicants encompasses a multitude of agents. This article focuses on three classes of therapeutic drugs, with specific examples in which overdoses require admission to the intensive care unit. Included are some of the newer antidepressants, the atypical neuroleptic agents, and selected anticonvulsant drugs. The importance of understanding pertinent physiology and applicable supportive care is emphasized.

Review article: hypertonic saline use in the emergency department

Hypertonic saline (HS) is being increasingly used for the management of a variety of conditions, most notably raised intracranial pressure. This article reviews the available evidence on HS solutions as they relate to emergency medicine, and develops a set of recommendations for its use. To conclude, HS is recommended as an alternative to mannitol for treating raised intracranial pressure in traumatic brain injury. HS is also recommended for treating severe and symptomatic hyponatremia, and is worth considering for both recalcitrant tricyclic antidepressant toxicity and for cerebral oedema complicating paediatric diabetic ketoacidosis. HS is not recommended for hypovolaemic resuscitation.

A Critical Reconsideration of the Clinical Effects and Treatment Recommendations for Sodium Channel Blocking Drug Cardiotoxicity

The cardiac sodium channel is comprised of proteins that span the cardiac cell membrane and form the channel pore. Depolarisation causes the proteins to move and open the sodium channel. Once the channel is open (active conformation), sodium ions move into the cell. The channel then changes from the active conformation to an inactive conformation - the channel remains open, but influx of sodium ions ceases. Recovery occurs as the channel moves from the inactive conformation back to the closed conformation and is then ready to open following the next depolarisation. Sodium channel blocking drugs (NCBDs) occupy receptors in the channel during the active and inactive conformations. The drug dissociates from most of the channel receptors during recovery, but the time it takes the drug to dissociate slows recovery. The slowed recovery prolongs conduction time, the main toxicity of NCBD overdose. Conduction time is further prolonged if heart rate increases as there are more available active and inactive conformations/unit time, which increases channel receptor binding sites for the NCBD. In addition to prolonging conduction time, NCBDs also decrease inotropy. Treatment of NCBD cardiotoxicity has been based on in vitro and animal experiments, and case reports. Assumptions based on this evidence must now be reassessed. For example, canines consistently develop ventricular tachycardia (VT) when tricyclic antidepressants (TCAs) are administered. Much of the literature discussing NCBD cardiotoxicity assumes that TCA poisoning induces VT in humans with the same regularity that occurs in canines. Seemingly, in support of this assumption was the finding that patients with remote myocardial infarction developed VT when therapeutically ingesting a NCBD. However, conduction is prolonged in myocardium that is or has been ischaemic. NCBD prolong conduction more in previously ischaemic myocardium than in normal myocardium, which causes nonuniform conduction and allows the development of re-entrant arrhythmias such as VT. Although some nonuniform conduction may occur in the healthy heart following a NCBD overdose, there is no evidence that nonuniform conduction occurs to the extent that it will cause re-entrant arrhythmias in this setting. Using various animal models and a variety of NCBDs, sodium ions, bicarbonate ions and alkalosis have been compared for the treatment of ventricular arrhythmias, hypotension and mortality. The results of these experiments have been extrapolated to NCBD overdose in humans. Animal models and single treatment approaches may have narrowed our scope. More recent evidence indicates that properties of each individual NCBD may require unique treatment. There is limited evidence that glucagon, which increases initial sodium ion influx into the cardiac cell, should be considered early in the treatment of cardiotoxicity. Another consideration may be treatment of NCBD with faster kinetics. Conduction time is decreased if a NCBD occupying the receptor is replaced by a NCBD that moves off and on the receptor more quickly. There is less evidence for this treatment, as risk may be greater. With greater understanding of the sodium channel and NCBDs, we must reassess our approach to the treatment of patients with healthy hearts who overdose on NCBD.

Management of the Cardiovascular Complications of Tricyclic Antidepressant Poisoning

Experimental studies suggest that both alkalinisation and sodium loading are effective in reducing cardiotoxicity independently. Species and experimental differences may explain why sodium bicarbonate appears to work by sodium loading in some studies and by a pH change in others. In the only case series, the administration of intravenous sodium bicarbonate to achieve a systemic pH of 7.5-7.55 reduced QRS prolongation, reversed hypotension (although colloid was also given) and improved mental status in patients with moderate to severe tricyclic antidepressant poisoning. This clinical study supports the use of sodium bicarbonate in the management of the cardiovascular complications of tricyclic antidepressant poisoning. However, the clinical indications and dosing recommendations remain to be clarified. Hypotension should be managed initially by administration of colloid or crystalloid solutions, guided by central venous pressure monitoring. Based on experimental and clinical studies, sodium bicarbonate should then be administered. If hypotension persists despite adequate filling pressure and sodium bicarbonate administration, inotropic support should be initiated. In a non-randomised controlled trial in rats, epinephrine resulted in a higher survival rate and was superior to norepinephrine both when the drugs were used alone or when epinephrine was used in combination with sodium bicarbonate. Sodium bicarbonate alone resulted in a modest increase in survival rate but this increased markedly when sodium bicarbonate was used with epinephrine or norepinephrine. Clinical studies suggest benefit from norepinephrine and dopamine; in an uncontrolled study the former appeared more effective. Glucagon has also been of benefit. Experimental studies suggest extracorporeal circulation membrane oxygenation is also of potential value. The immediate treatment of arrhythmias involves correcting hypoxia, electrolyte abnormalities, hypotension and acidosis. Administration of sodium bicarbonate may resolve arrhythmias even in the absence of acidosis and, only if this therapy fails, should conventional antiarrhythmic drugs be used. The class 1b agent phenytoin may reverse conduction defects and may be used for resistant ventricular tachycardia. There is also limited evidence for benefit from magnesium infusion. However, class 1a and 1c antiarrhythmic drugs should be avoided since they worsen sodium channel blockade, further slow conduction velocity and depress contractility. Class II agents (beta-blockers) may also precipitate hypotension and cardiac arrest.

Reversal of severe tricyclic antidepressant-induced cardiotoxicity with intravenous hypertonic saline solution

A 29-year-old woman ingested 8 g of nortriptyline and presented to the emergency department with coma, hypotension, and widened QRS interval. After intubation, gastric lavage, hyperventilation, and therapy with intravenous normal saline solution, sodium bicarbonate boluses (rapid intravenous push), and high doses of norepinephrine and dopamine, she transiently improved, only to deteriorate on arrival to the ICU. Because her arterial pH was alkalemic at 7.5 at this point, she was given additional sodium in the form of 200 mL of 7.5% NaCl by means of rapid intravenous infusion (intravenous push) to treat hypotension and widening QRS interval with ventricular ectopy. A continuous 12-lead ECG documented narrowing of her QRS interval with concomitant improvement of hypotension within 3 minutes of hypertonic saline solution infusion. Hypertonic saline solution should be considered for wide complex QRS and hypotension caused by tricyclic antidepressant-induced cardiotoxicity that is unresponsive to standard therapies.

Plasma alkalinization for tricyclic antidepressant toxicity: a systematic review

OBJECTIVE

To review the evidence that plasma alkalinization improves the outcome in tricyclic antidepressant toxicity.

METHODS

Medline search from 1966 to October 2000 (articles in all languages were included) and examination of bibliographies. Published papers including animal studies, in vitro studies, human case reports, case series and retrospective studies were reviewed.

RESULTS

Our search identified 115 publications, all of which were retrieved. Human studies included eight case reports, four case series, one controlled study and two retrospective chart reviews. No randomized controlled human trials were found. Twelve animal studies were identified that investigated pH manipulation or saline load and their effects on physiological parameters in tricyclic antidepressant toxicity.

CONCLUSIONS

The practice of alkalinization for tricyclic antidepressant toxicity is based on animal studies, case reports and opinion. The mechanism of action appears to be multifaceted and may vary between different tricyclic antidepressants. Significant interspecies variation makes extrapolation from animal studies to humans difficult. Alkalinization therapy appears reasonable in patients with compromising dysrhythmias and shock when supportive interventions have been ineffective; however, the available evidence does not support prophylactic alkalinization in the absence of life-threatening cardiovascular toxicity.

Hypertonic saline treatment of severe hyperkalemia in nonnephrectomized dogs

OBJECTIVES

To determine whether a hypertonic saline bolus improves cardiac conduction or plasma potassium levels more than normal saline infusion within 15 minutes of treatment for severe hyperkalemia. Previously with this model, 8.4% sodium chloride (NaCl) and 8.4% sodium bicarbonate (NaHCO(3)) lowered plasma potassium equally effectively.

METHODS

This was a crossover study using ten conditioned dogs (14-20 kg) that received, in random order, each of three intravenous (IV) treatments in separate experiments at least one week apart: 1) 2 mmol/kg of 8.4% NaCl over 5 minutes (bolus); 2) 2 mmol/kg of 0.9% NaCl over one hour (infusion); or 3) no treatment (control). Using isoflurane anesthesia and ventilation (pCO(2) = 35-40 torr), 2 mmol/kg/hr of IV potassium chloride (KCl) was infused until conduction delays (both absent p-waves and >/=20% decrease in ventricular rate in </=5 minutes) were sustained for 15 minutes. The KCl was then decreased to 1 mmol/kg/hr (maintenance) for 2 hours and 45 minutes. Treatment (0 minutes) began after 45 minutes of maintenance KCl.

RESULTS

From 0 to 15 minutes, mean heart rate increased 29.6 (95% CI = 12.2 to 46; p < 0.005) beats/min more with bolus than infusion and 23.4 (95% CI = 2.6 to 43.5; p < 0.03) beats/min more with bolus than control. No clinically or statistically significant difference was seen in heart rate changes from 0 to 30 minutes. Decreases in potassium from 0 to 15 minutes were similar with bolus, infusion, and control.

CONCLUSIONS

In this model, 8.4% NaCl bolus reversed cardiac conduction abnormalities within the first 15 minutes after treatment, more rapidly than did the 0.9% NaCl infusion or control. This reversal occurred despite similar reductions in potassium levels.

Experimental tricyclic antidepressant toxicity: a randomized, controlled comparison of hypertonic saline solution, sodium bicarbonate, and hyperventilation

STUDY OBJECTIVE

We sought to compare the effects of hypertonic sodium chloride solution (HTS), sodium bicarbonate solution, and hyperventilation (HV) on severe tricyclic antidepressant (TCA) toxicity in a swine model.

METHODS

Twenty-four mixed-breed, domestic swine of either sex were given an intravenous infusion of nortriptyline (NT) until development of both a QRS duration longer than 120 ms and a systolic blood pressure (SBP) less than or equal to 50 mm Hg. Animals were randomly assigned to 1 of 4 groups. On reaching toxicity, the control group received 10 mL/kg of 5% dextrose in water (D5W); the HTS group received 10 mL/kg of 7.5% NaCl solution (15 mEq Na+/kg); the NaHCO3 group received 3 mEq/kg of 8.4% sodium bicarbonate solution followed by enough D5W solution to equal 10 mL/kg of total volume; and the HV group was mechanically hyperventilated to maintain arterial pH between 7.50 and 7.60 and given 10 mL/kg of D5W.

RESULTS

The mean SBP 10 minutes after treatment was 54+/-18 mm Hg in the control group, 134+/-21 mm Hg in the HTS group, 85+/-19 mm Hg in the NaHCO3 group, and 60+/-12 mm Hg in the HV group (P<.05). Mean QRS duration 10 minutes after treatment was 144+/-38 ms in the control group, 80+/-14 ms in the HTS group, 105+/-38 ms in the NaHCO3 group, and 125+/-46 ms in the HV group (P<.05).

CONCLUSION

In this model of TCA, toxicity HTS was more effective than sodium bicarbonate. Hyperventilation had little effect. Sodium loading may be the most important factor in reversing TCA toxicity.

Serial electrocardiogram changes in acute tricyclic antidepressant overdoses

OBJECTIVES

To describe the changes over time of the QRS interval and terminal 40-msec QRS frontal axis (T40-ms) in patients with acute tricyclic antidepressant poisoning, to identify clinical factors and treatment associated with these changes, and to determine if patients with tricyclic antidepressant-related complications (seizures and/or arrhythmias) had differences in such serial electrocardiogram (ECG) changes when compared with patients without complications.

DESIGN

Prospective, observational, cohort study.

SETTING

Emergency departments of community and university-based hospitals in Massachusetts that consulted a large regional poison center.

PATIENTS

Thirty-six patients who presented with an acute ingestion (< 24 hrs) of a tricyclic antidepressant, who had at least three electrocardiograms in the first 8 hrs and serial ECGs until discharge, and who had a peak tricyclic antidepressant concentration of > 300 ng/mL.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The maximal limb-lead QRS interval and T40-ms axis were measured manually in all ECGs. The maximum recorded QRS interval occurred at the time of presentation for 24(80%) of 30 patients whose QRS was > or = 100 msecs and a median time of 3 hrs (range 1 to 9) for the other six patients. The maximum recorded T40-ms axis occurred at the time of presentation for 31(86%) of 36 patients and at a median time of 3 hrs (range 1 to 5) for the remaining five patients. The minimum QRS interval observed remained > or = 100 msecs in 15 patients (range 100 to 140 msecs) and decreased to < 100 msecs in 15 patients. The median time from presentation to the first ECG with a QRS < 100 msecs was 20 hrs (range 1 to 153) in those 15 patients. There were no significant differences in clinical characteristics and treatment (including sodium bicarbonate therapy) between the two groups. The minimum recorded T40-ms remained > or = 120 degrees in 30 patients and decreased to < 120 degrees in six patients. The median time from presentation until the first ECG with a T40-ms axis < 120 degrees was 13 hrs (range 2 to 30) for the six patients. All ECG measurements were greater and remained abnormal for a significantly longer duration in those patients who developed seizures and/or ventricular arrhythmias. These two ECG parameters demonstrated ongoing changes and persistent abnormalities despite clinical improvement in all patients except one.

CONCLUSIONS

The conduction abnormalities seen in severe tricyclic antidepressant toxicity vary widely in the time observed for resolution of these abnormalities and sometimes remain persistently abnormal. All ECG parameters were significantly more abnormal in those patients who developed seizures and/or arrhythmias. Clinical improvement occurred both before and during these ECG changes.

Does a sodium-free buffer affect QRS width in experimental amitriptyline overdose?

STUDY OBJECTIVES

We carried out this study to determine the effects of pH alteration on QRS width with administration of tromethamine, a non-sodium-containing buffering agent, in experimental amitriptyline overdose.

DESIGN

Prospective, nonblinded trial.

PARTICIPANTS

Adult mongrel dogs.

INTERVENTIONS

Pentobarbital-anesthetized dogs were overdosed with amitriptyline 5 mg/kg followed by infusion at 1.0 mg/kg/minute until the QRS width doubled, then decreased to .5 mg/kg/minute until the end of the experiment. At two defined points of toxicity, the dose of tromethamine required to raise the pH to 7.50 +/- 4 was given. pH and QRS width at a speed of 100 mm/second were measured over a 30-minute period after each tromethamine dose. Data were analyzed with non-linear-regression analysis.

RESULTS

At toxicity 1 the mean pH was 7.32, with a QRS width of 11.6 mm. Two minutes after the tromethamine dose the pH rose to 7.51, with narrowing of the QRS width to 8.4 mm. At toxicity 2 the pH was 7.40, with QRS width of 10.6 mm. Two minutes after tromethamine, the pH rose to 7.49 and the QRS width decreased to 9.7 mm. Regression analysis showed a correlation between pH and QRS width; as pH increased, QRS width decreased (P = .0001).

CONCLUSION

Cardiac toxicity of amitriptyline overdose, as manifested by QRS widening, is reversible by pH changes alone.