Effects of an Impedance Threshold Device on Hemodynamics andRestoration of Spontaneous Circulation in Prolonged Porcine Ventricular Fibrillation

Abstract

Background. An impedance threshold device (ITD) has been designed to enhance circulation during CPR by creating a negative intrathoracic pressure during the relaxation phase of chest compression. Hypothesis. We sought to determine the effects of the ITD on coronary perfusion pressure (CPP), return of spontaneous circulation (ROSC), andshort-term survival (20 minutes after ROSC). We hypothesized that the ITD would improve all 3 variables when compared to standard CPR. Methods. Using a case-control design nested within a randomized primary study, we compared CPR with the ITD (ITD-CPR) to standard CPR without the device (S-CPR). We systematically assigned 36 domestic swine, weighing 23–29 kg, (18 per group) to resuscitation with either ITD-CPR or S-CPR after 8 minutes of untreated ventricular fibrillation (VF). At minute 8, mechanical chest compression andventilation began, anddrugs (0.1 mg/kg epinephrine, 40U vasopressin, 1.0 mg propranolol, 1 mEq/kg sodium bicarbonate) were given. The first rescue shock (150J biphasic) was delivered at minute 11 of VF. We recorded CPP, ROSC (systolic pressure > 80 mmHg sustained for 60 s continuously), andsurvival. Data were analyzed with Fisher's exact test andgeneralized estimating equations (GEE), with alpha = 0.05. Results. We analyzed 3,150 compressions. CPP for the ITD-CPR group (28.1 mmHg [95% CI 27–29.3 mmHg]), did not differ from the S-CPR group (32.3 mmHg [95% CI 31.2–33.4 mmHg]). ROSC occurred in 6/18 (33%) animals in the ITD-CPR, and14/18 (78%) in the S-CPR group (p = 0.02). Survival occurred in 3/18 (17%) ITD-CPR and13/18 (72%) S-CPR group (p = 0.003). Conclusions. ITD-CPR did not improve CPP compared to S-CPR. ROSC andsurvival were significantly lower with ITD-CPR.

Key words::

• ventricular fibrillation
• heart arrest
• defibrillation
• cardiopulmonary resuscitation