Biomedical subjects
M Callaham
Publications and source records attributed to M Callaham.
Prophylactic antibiotics in dog bite wounds: nipping at the heels of progress.
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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.
A randomized clinical trial of high-dose epinephrine and norepinephrine vs standard-dose epinephrine in prehospital cardiac arrest.
OBJECTIVE: To determine the relative efficacy of high- vs standard-dose catecholamines in initial treatment of prehospital cardiac arrest. DESIGN: Randomized, prospective, double-blind clinical trial. SETTING: Prehospital emergency medical system of a major US city. PATIENTS: All adults in nontraumatic cardiac arrest, treated by paramedics, who would receive epinephrine according to American Heart Association advanced cardiac life support guidelines. INTERVENTIONS: High-dose epinephrine (HDE, 15 mg), high-dose norepinephrine bitartrate (NE, 11 mg), or standard-dose epinephrine (SDE, 1 mg) was blindly substituted for advanced cardiac life support doses of epinephrine. MAIN OUTCOME MEASURES: Restoration of spontaneous circulation in the field, admission to hospital, hospital discharge, and Cerebral Performance Category score. RESULTS: Of 2694 patients with cardiac arrests during the study period, resuscitation was attempted on 1062 patients. Of this total, 816 patients met study criteria and were enrolled. In the entire cardiac arrest population, 63% of the survivors were among the 11% of patients who were defibrillated by first responders. The three drug treatment groups were similar for all independent variables. Thirteen percent of patients receiving HDE regained a pulse in the field vs 8% of those receiving SDE (P = .01), and 18% of HDE patients were admitted to the hospital vs 10% of SDE patients who were admitted to the hospital (P = .02). Similar trends for NE were not significant. There were 18 survivors; 1.7% of HDE patients and 2.6% of NE patients were discharged from the hospital compared with 1.2% of SDE patients, but this was not significant (P = .37; beta = .38). There was a nonsignificant trend for Cerebral Performance Category scores to be worse for HDE (3.2) and NE patients (3.7) than for SDE patients (2.3) (P = .10; beta = .31). No significant complications were identified. High-dose epinephrine did not produce longer hospital or critical care unit stays. CONCLUSIONS: High-dose epinephrine significantly improves the rate of return of spontaneous circulation and hospital admission in patients who are in prehospital cardiac arrest without increasing complications. However, the increase in hospital discharge rate is not statistically significant, and no significant trend could be determined for neurological outcome. No benefit of NE compared with HDE was identified. Further study is needed to determine the optimal role of epinephrine in prehospital cardiac arrest.
Effect of epinephrine on the ability of end-tidal carbon dioxide readings to predict initial resuscitation from cardiac arrest.
OBJECTIVE: To determine if the administration of epinephrine changes the partial pressure of end-tidal CO2 during cardiac arrest, as previously reported. Such a change could diminish the demonstrated ability of end-tidal CO2 measurements to predict resuscitation from cardiac arrest. DESIGN: The partial pressures of end-tidal CO2 of adult cardiac arrest patients who received i.v. epinephrine in doses from 1 to 15 mg were monitored throughout arrest. SETTING: Emergency department of a university hospital. PATIENTS: Adults (n = 64) in cardiac arrest with a mean age of 70 +/- 12 yrs, of whom 35 were males and 15 had a mean time of return of spontaneous circulation of 6.5 +/- 11 hrs. INTERVENTIONS: End-tidal CO2 (in torr) was analyzed on arrival, before the first dose of epinephrine, and 4 mins after epinephrine was administered in varying doses chosen by the supervising physician. MEASUREMENTS AND RESULTS: The end-tidal CO2 decreased an average of 0.3 torr (0.04 kPa) after epinephrine was administered. Patients with a return of pulse had a decrease of -2 torr (-0.3 kPa) vs. an increase of 0.3 torr (0.04 kPa) for those patients with no return of pulse (p = .07). In 33% of patients, there was no change; in 28%, the partial pressure of end-tidal CO2 increased, and in 39%, it decreased. There was no correlation between the change in end-tidal CO2 after epinephrine and whether or not patients regained a pulse (r2 = .08, p = .07), although a decrease in end-tidal CO2 was most often associated with return of pulse. At a threshold of 10 torr (1.3 kPa), the first end-tidal CO2 had a positive predictive value for return of pulse of 50% and a negative predictive value of 82%. Just before epinephrine administration, the positive predictive value was 71% and the negative predictive value was 83%; 4 mins after epinephrine administration, the positive predictive value was 64% and the negative predictive value was 86%. A decrease in end-tidal CO2 after epinephrine had a positive predictive value of 53% and a negative predictive value of 92%. End-tidal CO2 readings predicted resuscitation most accurately when taken after initial stabilization and before administration of epinephrine. CONCLUSIONS: Although epinephrine administration may decrease end-tidal CO2 tensions in cardiac arrest, it does so unpredictably in individual patients, and it does not eliminate the predictive value of this measurement.
Potential complications of high-dose epinephrine therapy in patients resuscitated from cardiac arrest.
Adults resuscitated from nontraumatic cardiac arrest who received intravenous epinephrine in doses chosen by the treating physician and who survived at least 6 hours were studied to determine if high-dose epinephrine produced more complications than standard-dose. A total of 68 patients were enrolled and evaluated for postresuscitation complications attributable to epinephrine, using a two-tailed t test, and contingency analysis. The 33 patients receiving high-dose epinephrine and 35 patients receiving standard-dose epinephrine were similar in demographics and variables known to affect outcome. There was no difference in potential complications between groups except serum calcium, which was 1.97 mmol/L (SD, 0.20) in the high-dose epinephrine group and 2.10 (SD, 0.20) in the standard-dose group. Hospital discharge rates (18% in the high-dose vs 30% in the standard-dose group) and neurological status on discharge were not significantly different. High-dose epinephrine did not produce increased direct complications in this cardiac arrest population compared with standard-dose epinephrine.
High-dose epinephrine improves the return of spontaneous circulation rates in human victims of cardiac arrest.
STUDY OBJECTIVES: To evaluate the return of spontaneous circulation (RSC) rates in human victims of cardiac arrest treated with standard doses of epinephrine (SDE) or high-dose epinephrine (HDE). DESIGN: Prospective case series. SETTING: A university hospital emergency department during 1987 through 1989. PARTICIPANTS: Forty-nine adult victims of nontraumatic cardiac arrest. INTERVENTIONS: At the discretion of the treating physician, patients received epinephrine in bolus doses ranging from 1 to 15 mg. HDE was defined as a dose of at least 0.2 mg/kg; smaller doses were defined as SDE. Patients were grouped as +RSC if they developed a sustained spontaneous palpable pulse or blood pressure and as -RSC if they did not develop a pulse or blood pressure. MEASUREMENTS: Patients were grouped as +RSC if they developed a sustained spontaneous palpable pulse or blood pressure and as -RSC if they did not develop a pulse or blood pressure. Patients were also grouped by their presenting rhythm. Potentially perfusing rhythm was electromechanical dissociation or ventricular tachycardia. Nonperfusing rhythm was asystole or ventricular fibrillation. Rates were analyzed using the Fisher exact test and the two-tailed unpaired t test. HDE improved the rate of initial resuscitation (P = .008). The effect was greatest in patients with nonperfusing rhythms (P = .014) and disappeared when evaluating patients with potentially perfusing rhythms. No patient survived to hospital discharge. CONCLUSION: High-dose epinephrine improves initial resuscitation rates in human victims of cardiac arrest. Its greatest effect is in patients with a nonperfusing rhythm.
Lack of correlation between end-tidal carbon dioxide concentrations and Paco2 in cardiac arrest.
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High-dose epinephrine in cardiac arrest.
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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 less than .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.
Fulminant bacterial meningitis without meningeal signs.
Common clinical practice relies on the absence of neck stiffness or other meningeal signs to rule out meningitis in the alert, healthy adult. The literature does not address this specifically but implies that meningeal signs are reliable and usually present in awake patients, except infants, the elderly, and the immunosuppressed. In the following three cases two adults and a 4-year-old child, none of them immunosuppressed, presented with bacterial meningitis with no meningeal signs. In the first case, mental status was completely normal; in the second, there was only minor lethargy attributed to pain medication. In the third, lethargy was attributed to head trauma. In all three the diagnosis of meningitis was delayed up to 19 hours; lumbar puncture was performed while meningeal signs were still absent and cerebrospinal fluid analysis was grossly abnormal. All three patients had Streptococcus pneumoniae meningitis, and all three suffered massive brain damage within 24 hours of presentation and eventually died. Although the true incidence of absent meningeal signs in meningitis is unknown, the condition is rare. Clinicians cannot rely on the absence of neck stiffness to rule out meningitis, even in healthy and awake adults, and lumbar puncture should be performed whenever there is serious consideration of that diagnosis.
Epinephrine doses in cardiac arrest: is it time to outgrow the orthodoxy of ACLS?
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Hypoxic hazards of traditional paper bag rebreathing in hyperventilating patients.
It is traditional practice to treat acute hyperventilation (thought to be due to anxiety) by having patients rebreathe into a brown paper bag. The author reports three cases in which this treatment, erroneously applied to patients who were hypoxemic or had myocardial ischemia, resulted in death. This clinical experience motivated a study of the effects of paper bag rebreathing in normal volunteers. Subjects deliberately hyperventilated to an average end-tidal CO2 concentration of 21.6 (SD, 3.2) mm Hg and then continued to hyperventilate into a no. 4 Kraft brown paper bag containing the calibrated sensors for a Hewlett-Packard 47210A capnograph and a Teledyne TED 60J digital oxygen monitor. Fourteen men and six women with an average age of 36 years (SD, 6.1) were tested. Results are reported as mm Hg. After 30 seconds of rebreathing, mean change in O2 from room air was -15.9 (SD, 4.6) and mean CO2 was 38.7 (SD, 6.2); at 60 seconds, -20.5 (6.0) and 40.2 (6.4); at 90 seconds -22 (6.8) and 40.5 (6.4); at 120 seconds -23.6 (6.8) and 40.7 (6.5); at 150 seconds -25.1 (1.2) and 41 (7.3); and at 180 seconds -26.6 (8.4) and 41.3 (7.5). A few subjects achieved CO2 levels as high as 50, but many never reached 40. The mean maximal drop in O2 was 26 (8.8); seven subjects had drops in oxygen of 26 mm Hg at three minutes, four had drops of 34 mm Hg, and one had a drop of 42 mm Hg.(ABSTRACT TRUNCATED AT 250 WORDS)
Controversies in antibiotic choices for bite wounds.
In the last decade much progress has been made in our understanding of animal bites. Two major areas of remaining controversy are discussed. Recent study of human bites has shown that the early literature depicting all human bites as having an extraordinarily high infection and complication rate was biased by its emphasis on human bites of the hand that presented late with infection already present. These bites, the so-called closed-fist injuries (CFI), do indeed have a poor prognosis, but it may be as much due to their location and initial neglect as to the source of the injury. Human bites elsewhere do not seem to have any higher risk than animal bites, which have an infection rate of about 10%. Human bites of the face, lips, and ears are at very low risk for infection (less than 3%) if properly treated. The CFI should be identified early and aggressively irrigated and debrided (if possible). CFI wounds can be treated on an outpatient basis if uninfected and less than 24 hours old. The economical outpatient antibiotics of choice for CFI are penicillin plus dicloxacillin; the former is needed to cover Eikenella corrodens and the latter to cover Staphylococcus aureus, both common in these wounds. Diabetics with hand infection frequently have Gram-negative infection and may warrant parenteral aminoglycosides. Second- and third-generation cephalosporins are very effective but should be reserved for special situations due to their expense. Prophylactic antibiotics are not indicated for typical bite wounds, which are low risk. The choice of antibiotic (when needed) in other bite wounds is a matter of confusion, because the only scientific data available are in vitro sensitivities, which are a very poor and crude reflection of the clinical reality. Antibiotic effectiveness in vivo is dependent on a complex summation of absorption, tissue levels (not just serum levels), host immune defenses, and the interrelationships between bacterial species present. For dog bite wounds, dicloxacillin and cephalexin are both good choices because they cover most of the broad spectrum of infecting pathogens; dicloxacillin is significantly cheaper.(ABSTRACT TRUNCATED AT 400 WORDS)
Phenytoin prophylaxis of cardiotoxicity in experimental amitriptyline poisoning.
Tricyclic antidepressants (TCA) are drugs with Type IA antiarrhythmic properties that cause severe cardiac conduction blocks, hypotension, and ventricular dysrhythmias at toxic levels. Phenytoin has been proposed as a prophylaxis and treatment of these dysrhythmias, since it is thought to improve conduction in this setting. Anesthetized dogs were given a loading dose of phenytoin, followed by constant amitriptyline infusion until death. Variables known to affect TCA toxicity, such as arterial pH, were carefully controlled. There were no significant differences between the phenytoin and control group in any physiologic parameter, including toxicity, drug levels, or dose to death. However, duration and frequency of episodes of ventricular tachycardia were dramatically increased in the phenytoin group. It is concluded that prophylactic phenytoin in this animal model provides no benefits and may in fact increase the severity of ventricular tachycardia and hypotension. In addition, it is speculated that similar adverse effects of phenytoin might be seen in other Type IA antiarrhythmics if the extremely toxic levels seen in this study with TCA were reached.
Inaccuracy and expense of the leukocyte count in making urgent clinical decisions.
The care of 172 patients with abnormal white blood count (WBC) results was examined by chart review and physician interview. Neither the total leukocyte count, the neutrophil count, nor the band count reliably distinguished between bacterial, nonbacterial, and noninfectious disease. The positive predictive value for bacterial disease of a WBC greater than or equal to 12,500/mm3 was only 26%, with either a neutrophil count greater than or equal to 10,000/mm3 or a band count greater than or equal to 500/mm3, the positive predictive value was only 33%. Of WBCs, 21% were ordered by mistake when another (or no) test was desired. Only 18 abnormal WBCs of 172 (10.4%) (of the total 860 obtained) had any impact on the patient's clinical management, and only ten caused impact judged to be neutral or beneficial. Based on a WBC and differential costs of +23.50, obtaining an abnormal result that had a clearly beneficial impact on patient care would cost +10,105 in unneeded tests. The WBC does not in itself reliably predict severity or cause of disease in acutely ill adults, and its widespread use as a screening test in this setting probably should be abandoned.
A controlled study of dihydroergotamine in the treatment of acute migraine headache.
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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.