Scott A Syverud

Bicarbonate therapy for the cardiovascular toxicity of amitriptyline in an animal model

The beneficial hemodynamic effects of sodium bicarbonate as treatment for tricyclic antidepressant poisoning were investigated in an animal model. Seven adult dogs (17.5 to 20 kg) were poisoned by an intravenous infusion of amitriptyline. Toxicity was defined as a doubling of the initial QRS width. A continuous infusion was used to maintain toxicity for 30 minutes after which 44.5 mEq of sodium bicarbonate was administered intravenously. Five of the animals survived to completion of the experiment. Three of the surviving animals developed dysrhythmias. All dysrhythmias ceased within one minute of administration of sodium bicarbonate. An increase in mean blood pressure (P less than .05) and serum pH (P less than .05) and a decrease in mean QRS width (P less than .05) occurred following administration of sodium bicarbonate. The maintenance of toxicity for 30 minutes suggests that this model can be used for future studies of tricyclic antidepressant poisoning.

Closed thoracic cavity lavage in the treatment of severe hypothermia in human beings

Life-threatening hypothermia can be treated by active and passive rewarming techniques, the treatment of choice being partial cardiopulmonary bypass. The use of closed thoracic cavity lavage has been evaluated in animals, but no formal presentations in human beings have been reported. We report two cases in which rapid rewarming in severe hypothermia was accomplished when cardiopulmonary bypass was not available.

Early versus late fluid resuscitation: Lack of effect in porcine hemorrhagic shock

The benefit of IV fluid therapy in the prehospital management of hemorrhagic shock is unproven. We used a reproducible, lightly anesthetized model of porcine continuous hemorrhage to evaluate the usefulness of pre-hospital IV fluid therapy. Incorporated into the model were time delays associated with ambulance request and dispatch, patient evaluation and treatment, and transport to the hospital in the average urban prehospital care system. Treatment occurred concurrently with hemorrhage. Twenty-eight immature swine (15 to 20 kg) were bled at a rate of 1.25 mL/kg/min. Animals in the prehospital IV group (n = 14) received fluid resuscitation at 1 mL/kg/min beginning 20 minutes after initiation of hemorrhage; those in the in-hospital IV group (n = 14) received fluid at a rate of 3 mL/kg/min beginning 35 minutes after hemorrhage. Both groups received blood and saline at 3 mL/kg/min 45 minutes after hemorrhage began, and both groups had hemorrhage controlled 25 minutes after simulated hospital arrival. Survival was 57% in both groups, and there were no statistically significant differences seen in measured hemodynamic or biochemical parameters. We conclude that early administration of IV normal saline has no effect on hemodynamics or survival in this porcine hemorrhagic shock model simulating an urban prehospital care system.

Transcutaneous and transvenous cardiac pacing for early bradyasystolic cardiac arrest

Emergency transcutaneous cardiac pacing was studied prospectively in 19 patients presenting to the emergency department with a bradyasystolic cardiopulmonary arrest of 20 minutes duration or less. Pacing was initiated when conventional advanced cardiac life support (including atropine administration) and a fluid challenge failed to restore a pulse. Seventeen patients also had placement of transvenous pacemaker electrodes for cardiac pacing. Transcutaneous cardiac pacing rapidly established a blood pressure in the two patients who for clinical reasons did not receive a transvenous pacemaker. Five patients were transcutaneously paced within five minutes of cardiac arrest (Group 1) and the remaining 14 were paced between five and 20 minutes following cardiac arrest (Group 2). Two of the Group 1 patients were admitted and subsequently recovered full neurological and prearrest cardiac function. Fewer Group 2 patients developed a blood pressure (P = .04), and there were no patients with full neurologic recovery in this group (P = .06). Similar results were found for transvenous cardiac pacing; there was a greater incidence of a palpable pulse and measurable blood pressure (P = .05 for both) in the Group 1 patients than in the Group 2 patients. No difference in clinical outcome was noted between the two pacing techniques. These results support the concept that cardiac pacing must be initiated early if the outcome of bradyasystolic cardiac arrest is to be altered.

Transcutaneous cardiac pacing: Determination of myocardial injury in a canine model

Transcutaneous cardiac pacing holds promise as the initial cardiac pacing technique for emergency patients. Determination of the extent of myocardial injury associated with the use of commercial transcutaneous pacemaker devices has been limited. This study was undertaken to document electrocardiographic, enzymatic, and histologic changes following transcutaneous pacing. Ten mongrel dogs were paced with a transcutaneous cardiac pacemaker for 30 minutes. Electrical pulses of 100 mA lasting 20 ms each were delivered at a rate of 80/min via cutaneous electrodes on the anterior and posterior thorax. Myocardial damage was assessed by serial electrocardiograms (ECGs), serial creatine kinase (CK) determinations with myocardial band (MB) fractionation, and gross and microscopic pathologic examination. Double blind reading of the ECGs showed no significant changes after pacing. CK levels peaked an average of 78 units over baseline levels at 4 hours; however, there was no rise in the CK MB fraction. Pathologic examination revealed micro-infarcts adjacent to intramural vessels in 5 animals, but no clinically significant myocardial injury in the 10 dogs. The absence of enzymatic, cardiographic, and clinically significant pathologic findings was statistically significant (P less than .05). Transcutaneous pacing at low currents and for short periods appears to be a safe technique. This pacing technique deserves further evaluation, and may hold promise as a clinical tool during resuscitation.

Developments in transcutaneous and transthoracic pacing during bradyasystolic arrest

Transthoracic cardiac pacing historically has been relegated to the role of the technique of last resort in treating cardiac arrest. Recent studies have shown that this technique has a high rate of successful electrical capture, but often without mechanical activity. Survival rates have been shown to be dismal when the technique is used late in cardiac arrest. Results of several recent studies of patients paced by the transcutaneous technique have suggested that electrical capture can often be rapidly obtained in asystolic or pulseless bradycardic patients. Even though electrical capture can occur late in a cardiac arrest, the development of mechanical activity with survival is rare. Survivors generally have been treated early in their arrest and have had hemodynamically ineffective bradycardias. These findings suggest that rapid initiation of transcutaneous pacing in patients with Stokes-Adams attacks, increasing heart block associated with myocardial ischemia, postdefibrillation asystole, or pulseless bradycardia may improve survival. However, victims of a prolonged cardiac arrest whose myocardium has irreversibly ceased to function mechanically are unlikely to benefit from any pacing technique.

Iced gastric lavage for treatment of heatstroke: efficacy in a canine model

This study was undertaken to evaluate a central cooling technique for heatstroke, gastric lavage with iced tap water, for speed of cooling and efficacy of treatment in an anesthetized canine heatstroke model. Eleven mongrel dogs were anesthetized, shaved, and externally heated until core temperature reached 43.0 C (109.4 F). Control animals (n = 6) were cooled passively in room air. Treatment animals (n = 5) were cooled with the addition of gastric lavage with iced tap water through a large-bore orogastric tube. Temperatures were monitored using thermocouples in the brain, pulmonary artery, rectum, and subcutaneous tissue of the chest wall. Serial enzymatic and hematologic laboratory studies and hemodynamic parameters were measured prior to heating, at the end of heating, and at 0, 0.5, 1, 2, and 12 hours after heating. Animals were sacrificed 12 hours after heatstroke induction and gross and microscopic pathologic examination was performed. Central cooling rates achieved in the lavage group were five to six times faster than in the control group, (P less than .01) and are comparable with those reported in the literature for external cooling techniques. No significant complications were induced by tap water lavage. Rapid cooling in the lavage group resulted in a statistically significant improvement in serum creatinine and LDH after heatstroke induction (P less than .05). Gastric lavage with iced tap water appears to be an effective alternative or adjunctive cooling technique for heatstroke in the dog.

Dantrolene sodium for treatment of heatstroke victims: lack of efficacy in a canine model.

Dantrolene sodium, a skeletal-muscle relaxant known to be effective for treatment of malignant hyperthermia, was evaluated for efficacy in treatment of heatstroke. Non-exertional heatstroke was induced in 11 dogs by external heating following barbiturate anesthesia. When core temperature reached 43 degrees C (109.4 degrees F) heating was discontinued and control animals (n = 6) were allowed to cool passively in room air. Treatment animals (n = 5) received 5 mg/kg dantrolene sodium intravenously at the start of room-air cooling. Serial temperatures (pulmonary arterial, rectal, cerebral, and subcutaneous), blood chemistry tests (including electrolytes, liver enzymes, and complete blood count), and hemodynamic parameters (including cardiac output, arterial pressure, and urinary output) were followed for 12 hours after induction of heatstroke. Autopsies, including gross and microscopic examination, were performed on all animals. Dantrolene administration did not significantly affect cooling rates, hemodynamic parameters, pathological changes, or clinical outcome. Statistically significant changes in urinary output and serum creatinine observed in the first hours after dantrolene administration can be attributed to the mannitol vehicle in which the drug was delivered. There were no statistically significant differences in these values at 12 hours. Dantrolene sodium does not appear to enhance passive cooling in treatment of non-exertional canine heatstroke.

The effect of ethanol on survival time in hemorrhagic shock in an unanesthetized swine model

Controversy exists as to whether ethanol intoxication causes exaggerated hypotension or increased mortality during hemorrhagic shock. Previous studies have used anesthetized animals. This limits data interpretation as anesthetic agents, particularly pentobarbital, have well-documented effects on hemodynamics and the response to hemorrhage. We studied the effects of moderate ethanol intoxication on blood pressure and survival time during fatal hemorrhagic shock in unanesthetized swine. Immature female swine weighing 15 to 20 kg were splenectomized and instrumented with chronic indwelling aortic catheters, right atrial catheters, and gastrostomy tubes. Four to seven days later the unanesthetized animals underwent hemorrhagic shock. Thirty minutes prior to the start of hemorrhage, the experimental group (n = 8) received 3 mL/kg of 100% ethanol mixed as a 1:3 solution with water through a gastrostomy tube. The control group (n = 8) received an equal amount of water. The distal aortic catheter was connected to a roller pump and blood was removed at a rate of 1 mL/kg/min until the animal died. Arterial pressure, heart rate, lactate ethanol and glucose levels, hematocrit, and arterial blood gases were measured in both groups at baseline and every 15 minutes thereafter. A mean ethanol level of 1,500 to 1,700 micrograms/mL was produced in the experimental group from baseline through 60 minutes. Data were analyzed using Students two-tailed t test, and analysis of variance for repeated measures. There was no significant difference in survival time between the control (63.1 +/- 2.8 min) and ethanol (59.9 +/- 5.9 min) groups. Systolic blood pressure was significantly lower in the ethanol group after 15 minutes of hemorrhage (81 +/- 22 to 59 +/- 14 mm Hg, P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamics of transcutaneous cardiac pacing

Transcutaneous cardiac pacing has recently been rediscovered as a rapid means of initiating emergency cardiac pacing. Potential myocardial injury from extended transcutaneous pacing could adversely affect cardiac hemodynamics during pacing. This canine study compares the hemodynamics of transcutaneous and transvenous cardiac pacing in animals with induced chronic heart block. One to two weeks following chemical ablation of the His bundle, hemodynamic measurements were made during 60 minutes of transcutaneous and 5-minute periods of conventional right ventricular endocardial pacing. Cardiac index and output were found to increase significantly (P less than 0.005), and systemic vascular resistance was found to decrease significantly (P less than 0.005) from baseline values with both pacing techniques. A hemodynamic difference between pacing techniques was evident only for mean arterial blood pressure; pressure measurements during transvenous pacing were slightly greater than those during transcutaneous cardiac pacing. The hemodynamic measurements were found to be stable during a 60-minute period of transcutaneous cardiac pacing. This study demonstrates that transcutaneous cardiac pacing is as effective hemodynamically as conventional transvenous pacing in animals with induced chronic heart block.