Michael L. Callaham

Tricyclic antidepressant overdose.

First introduced in the early 1960s, tricyclic antidepressants (TCAs) have been seen increasingly in overdoses, accounting for 10% to 20% of all cases. 1-5 This is not surprising, for amitriptyline was the 29th most frequently prescribed drug in the United States in 1974. 8 Since suicide-prone depressed patients and young children being treated for nocturnal enuresis1,2, ~ are the most common recipients of these drugs, overdoses probably will continue. These overdoses have a multiplicity of toxic effects, the most alarming of which are cardiac, 1 and a high mortality. The purpose of this article is to review current knowledge on TCA overdose and toxicity, with particular emphasis on pharmacology as the foundation of rational therapy.

Prediction of outcome of cardiopulmonary resuscitation from end-tidal carbon dioxide concentration.

Capnography is a valuable tool in the management of cardiac arrest, since end-tidal CO2 (Petco2) correlates well with cardiac output and there are no other suitable noninvasive ways to measure this important variable during resuscitation. Animal studies also suggest that Petco2 correlates well with the likelihood of resuscitation, but this has never been confirmed in humans. We prospectively studied 55 adult, nontraumatic prehospital cardiac arrest patients, Petco2 was monitored with an in-line sensor on arrival in the ED and throughout the arrest, which was managed by the usual advanced cardiac life-support treatment guidelines. Chest compression was carried out mechanically. Patients were assessed for return of spontaneous pulse as evidence of initial resuscitation; hospital discharge and long-term survival were not examined.Fourteen patients developed spontaneous pulses and were resuscitated, and 41 were not. The length and aggressiveness of treatment and CPR were not different between the two groups, nor were there differences in down time, resuscitation time, or other factors known to affect outcome. Patients who developed a pulse had a mean Petco2 of 19 ± 14 (SD) torr at the start of resuscitation, and those who did not had a mean Petco2 of 5 ± 4 torr (p < .0001). This difference was significant both in nonperfusing rhythms (asystole and ventricular fibrillation) and in potentially perfusing rhythms (electromechanical dissociation). An initial Petco2 of 15 torr correctly predicted eventual return of pulse with a sensitivity of 71%, a specificity of 98%, a positive predictive value of 91%, and a negative predictive value of 91%, A receiver operating curve was generated for sensitivity and specificity of the test at varying Petco2 thresholds. (Crit Care Med 1990; 18:358)

Epidemiology of fatal tricyclic antidepressant ingestion: implications for management

Although there is a large body of literature documenting the lethal cardiotoxic complications of tricyclic antidepressant (TCA) overdose, the absence of reliable predictive signs has led to a policy of admitting even trivial-appearing overdoses for inpatient observation. A study of 18 fatal cases revealed that with the exception of two that received clearly inadequate medical care, all fatal ingestions developed major signs of toxicity mandating admission within two hours of arrival at the hospital, and the mean time from arrival to death was only 5.43 hours. All patients who died of direct TCA toxicity did so within 24 hours of arrival. In addition, half the fatal cases presented with only trivial signs of poisoning, but deteriorated catastrophically within one hour. These data lead to an algorithm to guide admission of serious cases.

Quantifying the Scanty Science of Prehospital Emergency Care

Research can produce false-positive results just as can diagnostic tests. Uncontrolled studies have a specificity of only 11%, versus 88% for randomized controlled trials (RCTs), which have been designed to minimize the bias of investigators toward a positive outcome. A search of all the scientific studies in Medicine since 1985 revealed 5,842 publications on prehospital EMS, but only 54 were RCTs (and therefore unlikely to produce false-positive results). By way of comparison, during the same time hundreds of RCTs have been conducted on major medical emergency conditions, and RCTs on even minor topics such as urticaria and constipation exceed the scientific database on all of EMS. Of the 54 EMS RCTs, 4 (7%) reported harm from the new therapy, and 74% reported no effect of the new therapy at all. Only 7 (13%) RCTs showing a positive outcome of the intervention were uncontradicted; of these only 1 examined a major outcome such as survival, and only 1 compared the intervention with a placebo and could therefore evaluate the efficacy of EMS itself. Because there is such a paucity of scientific support for EMS interventions and because monitoring of outcomes and adverse effects is so poor, a serious reexamination of EMS practice is indicated.

Active compression-decompression resuscitation: A novel method of cardiopulmonary resuscitation

Chest compression is an important part of cardiopulmonary resuscitation (CPR), but it only aids circulation during a portion of the compression cycle and has been shown to only minimally increase blood flow to vital organs. The purpose of this study was to quantitate the short-term hemodynamic effects of CPR with a hand-held suction device that incorporates both active compression and decompression of the chest. The suction device was applied to the middle of the sternum and compared with standard manual CPR in eight nonventilated anesthetized dogs. Coronary perfusion pressure, systolic and diastolic aortic pressures, right atrial diastolic pressure, and the velocity time integral (an analog of cardiac output), which were obtained by means of transesophageal pulsed wave Doppler echocardiography from the main pulmonary artery, were measured every 30 seconds during CPR. Minute ventilation was measured over the last minute of each CPR technique. Both active compression-decompression CPR and standard CPR were sequentially performed for 2 minutes in random order 30 seconds after induced ventricular fibrillation. The CPR techniques consisted of 100 compressions per minute, with a compression depth of 1.5 to 2 inches and a 50% duty cycle. Coronary perfusion pressure, velocity time integral (cardiac output analog), minute ventilation, and systolic arterial pressure were all significantly improved by active compression-decompression CPR when compared with standard CPR. We conclude that active compression-decompression CPR is a simple technique that appears to improve coronary perfusion pressure, systolic arterial pressure, cardiac output, and minute ventilation in nonventilated animals when compared with standard CPR.(ABSTRACT TRUNCATED AT 250 WORDS)

Prophylactic antibiotics in common dog bite wounds: a controlled study.

A double-blind prospective study of 98 patients was carried out, but 57 (58%) returned for follow-up and form the basis of this report. Wound irrigation and debridement were found to be important in reducing infection. Hand wounds were most likely to become infected; face and scalp wounds were at low risk. Puncture wounds became infected more often than did lacerations. Suturing wounds did not increase the likelihood of infection except on the hand, where the data were equivocal. Prophylactic penicillin decreased the incidence of infection in high-risk wounds; there was no difference in low-risk wounds. Cultures of wounds showed many different organisms but were of no predictive value. Pasteurella multocida was found very rarely. Staphylococcus aureus accounted for 10% of all infections, a finding which makes use of a penicillinase-resistant penicillin logical.

Treatment of common dog bites: infection risk factors.

In a retrospective study of 106 patients with complete follow-up of dog bites treated in the emergency department the following factors greatly increased the risk of infection: age greater than 50 years, delay in seeking treatment, location on an upper extremity, and puncture wounds. Debridement and irrigation decreased the incidence of infection, and sutured wounds were not more likely to become infected than those left open. Prophylactic antibiotics provided no benefit in this series. In the literature, overall infection rates varied widely according to the various patient populations. Up to 50% of infections from dog bites are caused by pasturella multocida, and the remainder by a wide range of organisms, including streptococcus. Ninety-five percent of these organisms will be sensitive to penicillin.

Relationship of Timeliness of Paramedic Advanced Life Support Interventions to Outcome in Out-of-Hospital Cardiac Arrest Treated by First Responders With Defibrillators

STUDY OBJECTIVE We sought to determine whether the interval between the arrival of first responder/defibrillators and paramedic advanced life support (ALS) interventions is associated with outcome. METHODS We carried out a prospective observational study of adults in out-of-hospital cardiac arrest treated by both first responders and paramedics in an urban emergency medical services system between July 15, 1992, and May 27, 1993 (N = 544). RESULTS The gap between first-responder and medic arrival was short (3.2 minutes); medics arrived before first-responder shock in 22% of ventricular fibrillation (VF) cases. Just 10% of patients has a pulse when medics arrived, but the presence of pulse on medic arrival was a powerful predictor of hospital discharge (odds ratio [OR], 20.5; sensitivity, 39%; specificity, 98%; positive predictive value, 55%; negative predictive value, 97%) or a Cerebral Performance Category score on discharge of 1 or 2 (OR, 2.9). No response or individual ALS treatment interval was related to outcome, including the interval from first-responder to medic arrival. ALS interventions by medics were associated with poorer outcomes; even the need for nothing more than additional defibrillation by medics decreased the survival rate of VF patients threefold. By contrast, bystander CPR improved survival more than fourfold and early defibrillation of VF by first responders more than ninefold. Ninety-one percent of all patients discharged from the hospital who received only minimal ALS other than intubation had good neurologic outcome and longer survival after discharge. Half the total survivors of VF arrest (and 59% of all arrest survivors) were resuscitated by medics with aggressive ALS measures, but 80% had very poor neurologic outcomes and 50% died within a year of hospital discharge. Even the need for only additional defibrillation by medics worsened neurologic outcome by a factor of 2.8. CONCLUSION Faster response by medics, or any individual ALS intervention other than first-responder defibrillation, demonstrated no benefit in this urban population with short intervals between responder arrivals. Aggressive ALS increased the number of survivors but also decreased their neurologic quality. The benefit of rapid ALS backup to first responder/defibrillators needs further study in other systems. System performance cannot be judged without knowledge of neurologic outcome.

Quality-of-Life and Formal Functional Testing of Survivors of Out-of-Hospital Cardiac Arrest Correlates Poorly With Traditional Neurologic Outcome Scales☆☆☆★

STUDY HYPOTHESIS The traditional (and unvalidated) five-point Cerebral Performance Category (CPC) score at hospital discharge does not correlate with the results yielded by a validated functional status instrument and subjective quality-of-life assessment. METHODS We compared CPC scores with the results of prospective standardized testing after discharge in survivors of out-of-hospital cardiac arrest. Consenting survivors were tested with the validated Functional Status Questionnaire (FSQ), a subjective quality-of-life assessment, and traditional CPC scoring. RESULTS Of the 3,130 arrests during the 52 months of the study, 93 patients survived. Thirty-five patients were tested (71% of those eligible at the time of follow-up). Of these patients, 34% said their quality of life was worse, 38% said it was the same, and 28% said it was better than before the cardiac arrest. Fifty-four percent of patients scored normally on all FSQ subscales, but the remainder had an average 2.1 areas (of 6) with significant impairment. CPC score correlated very poorly with quality-of-life rating and with all scores and subscores on the FSQ. A CPC of 1 on discharge (supposedly normal function) had a sensitivity of 78%, a specificity of 43%, a positive predictive value of 64%, and a negative predictive value of 60% for quality of life the same as or better than that before arrest. With regard to ability to predict the presence of any major areas of impairment on the FSQ, the respective figures were 32%, 43%, 43%, and 32%. CONCLUSION The CPC score, relied on as a measure of functional outcome in cardiac arrest, correlates poorly with subsequent subjective quality of life and with validated objective functional testing instruments, and conclusions based on it are suspect. Future researchers should employ standardized testing instruments.

Prehospital cardiac arrest treated by urban first-responders: Profile of patient response and prediction of outcome by ventricular fibrillation waveform

STUDY OBJECTIVES To determine the speed and characteristics of patient response to urban first-responder defibrillation and to determine whether amplitude of ventricular fibrillation (VF) can predict outcome in these patients. TYPE OF PARTICIPANTS All adult patients in prehospital VF treated by fire department first-responders (265). DESIGN AND INTERVENTIONS A prospective observational study occurring between February 1, 1989, and January 1, 1991. Patients were defibrillated according to advanced cardiac life support and first-responder protocols. ECG and time data were recorded digitally. MAIN RESULTS Sixty-five percent of patients converted from VF to a more stable rhythm at least once during first-responder monitoring. Fifty-four percent of converted patients refibrillated at least once, and 42% of all stable conversions occurred after at least one episode of refibrillation. Seventy percent of all refibrillations occurred less than six minutes after the defibrillator was turned on, and 23% occurred after more than ten minutes. The proportion of stable conversions decreased from 30% on first conversion to 2% on fourth conversion. With each successive conversion the interval to refibrillation grew shorter, and development of a pulse or blood pressure became less likely. Presence of blood pressure or pulse after conversion had a sensitivity for hospital discharge of 54% and a specificity of 98%. Maximum VF amplitude before countershock was highly predictive of postshock rhythm, stable conversion in the field, time interval before refibrillation, inpatient admission, and hospital discharge. VF amplitude was unrelated to response interval or interval to defibrillation but was positively related to bystander CPR. Logistic regression identified VF amplitude as the most important predictor of hospital discharge; traditional variables such as response interval and bystander CPR were not predictive once amplitude had been accounted for. Changes in VF amplitude during the course of resuscitation efforts were frequent and also predictive of outcome. CONCLUSION Patients in VF who were treated by early countershock refibrillated much more frequently than previously reported. Refibrillations occur both early and late. Initial VF maximum amplitude is strongly predictive of outcome. Future reports of VF cardiac arrest should control for this previously neglected variable. Increased amplitude of VF during repeated refibrillation episodes is associated with increased hospital discharge, so future studies of advanced cardiac life support interventions should explore changes in VF amplitude as an outcome variable.