Use of a cardiocerebral-protective drug cocktail prior to countershock in a porcine model of prolonged ventricular fibrillation.

OBJECTIVES: This was the third study in a series exploring whether the use of combination pharmacotherapy with delayed countershock would produce higher rates of return of spontaneous circulation (ROSC) and one-hour survival when compared with standard advanced cardiac life support (ACLS) therapy in prolonged ventricular fibrillation (VF). METHODS: Twenty-four female, mixed-breed, domestic swine (ranging in mass from 22 to 25 kg) were used in this prospective, blinded, randomized, experimental trial. Animals were sedated (ketamine/xylazine), anesthetized (alpha-chloralose), paralyzed (pancuronium), mechanically ventilated with room air, and monitored with electrocardiography, arterial pressure, and Swan-Ganz catheters. VF was induced with a 3 s, 60 Hz, 100 mA transthoracic shock, and remained untreated for 8 min. One minute of basic life support followed (standardized by use of a mechanical device). At 9 min, animals were treated with one of three regimes: Group 1, cardiocerebral-protective cocktail (antioxidant U-74389G (3.0 mg/kg), epinephrine (0.2 mg/kg), lidocaine (1.0 mg/kg), bretylium (5.0 mg/kg), magnesium (2.0 g), and propranolol (1.0 mg)); Group 2, magnesium (2.0 g); and Group 3, standard ACLS. Groups 1 and 2 received drugs at minute nine (first countershock at minute 11), while Group 3 received first countershock at minute nine. Data were analyzed with two-tailed Fisher's exact tests. RESULTS: ROSC was achieved in Group 1, 7/7 (100%); Group 2, 3/9 (33%, P versus Group 1=0.01); and Group 3, 3/8 (38%; P versus Group 1=0.02). One-hour survival was attained in Group 1, 7/7 (100%); Group 2, 3/9 (33%; P versus Group 1=0.01), and Group 3, 1/8 (13%; P versus Group 1=0.001). CONCLUSIONS: Combination pharmacotherapy with a cardiocerebral-protective drug cocktail prior to countershock produced superior rates of ROSC and one-hour survival when compared with singular drug therapy (Group 2) and standard ACLS (Group 3) in this porcine model of prolonged VF.

A randomized, crossover comparison of various ventilation devices in a swine pneumothorax model.

OBJECTIVE: Bag-valve-mask devices (BVMs), manually triggered ventilators (MTVs), and automatic transport ventilators (ATVs) are three available options for out-of-hospital artificial ventilation. Use of the MTV and the ATVs has been limited by concern for causing or worsening a pneumothorax (PTX). The purpose of this study was to compare the effects of ventilation with a BVM, ATV, and MTV in a swine PTX model. METHODS: This was a randomized, crossover study. Six fasted swine (21.2-24.5 kg, mean = 23.5 kg) were sedated and paralyzed. The swine were intubated with a cuffed endotracheal tube. A lung injury was created with a hemostat under direct visualization after the pleural cavity was entered by sharp dissection. A 16-Fr Foley catheter was inserted and sealed in the pleural space at the injury site. Prior to each trial, a PTX was created by instilling 300 mL of air through the Foley catheter. Each swine underwent 10-minute ventilation trials, at a rate of 12-14 breaths/min, with BVM, MTV, and ATV by the same investigator following each trial; PTX size was determined by withdrawing air through the Foley catheter. Analysis of variance for repeated measures (alpha = 0.05) was used for statistical analysis. RESULTS: There was no difference in the extent of PTX expansion produced by ventilation with BVM (339.8 +/- 35.9 mL), MTV 327.8 +/- 28.9 mL), or ATV (321.8 +/- 22.2 ml). CONCLUSION: BVMs, MTVs, and ATVs do not differ in their effects on PTX volumes. Concern for excessive expansion of PTX by MTVs and ATVs is not supported. Prospective evaluation is warranted to determine the efficacy of these ventilation techniques.

Spontaneous agonal respiration in a swine model of out-of-hospital cardiac arrest.

OBJECTIVE: To describe ventilatory dynamics following the onset of ventricular fibrillation (VF) in an experimental swine model. METHODS: Twelve female mixed-breed domestic swine (mean mass 21.3 +/- 1.7 kg) were sedated with IM ketamine (10 mg/kg) and xylazine (1 mg/kg), anesthetized with alpha-chloralose (40 mg/kg loading dose, 10 mg/kg/hr maintenance infusion), intubated, and mechanically ventilated on room air. ECG, and aortic and pulmonary artery pressures were monitored continuously. VF was induced with a 3-sec, 60-Hz, 100-mA transthoracic shock, and left untreated for 8 minutes. Respiratory rate, tidal volume, and minute ventilation were recorded until respiratory activity ceased. RESULTS: All 12 animals (100%) had agonal respirations through the first 2 minutes of arrest. This decreased to 11 (92%) at minute 3, five (42%) at minute 4, and two (17%) at minute 7. Mean respiratory rates ranged from 6 to 11 breaths/min. Mean tidal volumes ranged from 502 to 852 mL. Mean minute ventilations ranged from 3.3 to 5.8 L. CONCLUSION: In this swine model, 11 of 12 (92%) continued to have spontaneous agonal respirations for the first 3 minutes of VF cardiac arrest. Many animals had supranormal tidal volumes, and near-normal minute ventilations. These findings have potential implications for lay-rescuer and first-responder contributions to resuscitation of victims of out-of-hospital cardiac arrest.

Lower esophageal sphincter pressure during prolonged cardiac arrest and resuscitation.

STUDY OBJECTIVE: Unprotected airway ventilation models have been based on a lower esophageal sphincter (LES) pressure found in human beings under general anesthesia. Whether this assumption is applicable during cardiac arrest in human beings is unknown. We attempted to determine the effects of prolonged ventricular fibrillation (VF) on the tension of the LES in a swine model of cardiac arrest. DESIGN: Prospective experimental trial using 18 female mixed-breed domestic swine (mean weight, 21.9 +/- 2.0 kg). RESULTS: Animals were anesthetized, intubated, and fitted with instruments for the monitoring of LES pressure. LES tone was measured with a LECTRON 302 esophageal monitor (American Antec, Incorporated). VF was induced with a 3-second, 100 mA transthoracic shock and left untreated for 8 minutes; then resuscitation was attempted. LES tension was measured during the first 7 minutes of the arrest. If return of spontaneous circulation (ROSC) occurred, LES pressure was measured for 7 more minutes. The mean baseline LES pressure was 20.6 +/- 2.8 cm H2O. During minutes 1 through 7 of the arrest the LES tone (mean +/- SD) decreased from 18.0 +/- 3.0 to 3.3 +/- 4.2. ROSC occurred in 10 of the 18 trials. In the 7 minutes after ROSC, LES pressure increased from 4.7 +/- 3.8 to 9.8 +/- 3.0. CONCLUSION: This study demonstrated a rapid and severe decrease in LES tone during prolonged cardiac arrest. When ROSC occurred, LES tension increased quickly but did not return to baseline.