MECHANICAL VENTILATION MAY NOT BE ESSENTIAL FOR INITIAL CARDIOPULMONARY-RESUSCITATION

Background: In a rodent model of cardiac arrest and resuscitation in w hich the inspired gas mixture was enriched with oxygen, resuscitabilit y and survival were unaffected by positive pressure ventilation. In th e present study, in a larger animal model, tidal volumes generated dur ing precordial compression and with spontaneous gasping were quantitat ed. Methods: Domestic pigs with an average weight of 34 kg were anesth etized with pentobarbital. Ventricular fibrillation (VF) was induced e lectrically. Precordial compression was begun after 4 min of untreated VF. Each of 22 animals received one of two interventions in conjuncti on with precordial compression: positive pressure ventilation with oxy gen or oxygen supplied at the port of a tracheal tube at ambient press ure. After 8 min of precordial compression, defibrillation was attempt ed. Results: Only very moderate increases in arterial Pco(2) were docu mented during cardiopulmonary resuscitation in the absence of mechanic al ventilation but arterial oxygen tension was consistently in excess of 100 mm Hg. Cardiac resuscitability and 48-h survival were approxima tely the same in animals maintained on inspired oxygen whether or not they were mechanically ventilated (7/11 or 8/11). In the absence of me chanical ventilation, precordial compression and spontaneous gasping y ielded minute volumes that exceeded 5 L. Conclusion: Positive pressure mechanical ventilation did not improve resuscitability or postresusci tation outcome in this porcine model of cardiac arrest.