Air trapping in the lungs during cardiopulmonary resuscitation in dogs. A mechanism for generating changes in intrathoracic pressure.

Abstract

To test the hypothesis that during cardiopulmonary resuscitation, chest compression with an unobstructed trachea raises and maintains intrathoracic pressure by collapsing airways and trapping air in the lung, we studied 11 dogs (20-32 kg). An inflatable vest compressed the thorax after induction of ventricular fibrillation. First, tracheal airflow was measured by a pneumotachometer during vest inflation and deflation in nine of the dogs. As expected, during the initial phase of vest inflation of cycles after ventilation, air moved out of the lungs, but then airflow stopped. After vest deflation, however, more air moved out of the lungs in eight of the nine dogs; this occurrence indicated that a portion of the inspired tidal volume was trapped during vest inflation. During cycles without prior ventilation, the amount of air expired by chest compression decreased, paradoxically, at higher peak vest pressure (p less than 0.002); this occurrence indicated that air was trapped at the higher vest pressures. The change in right atrial pressure was higher on cycles after ventilation than on cycles without prior ventilation (79 +/- 12 vs. 67 +/- 12 mm Hg [mean +/- SEM], p less than 0.005), and lung volume was higher on cycles after ventilation (p less than 0.001). Next, a 5-Fr micromanometer was advanced down the airway in eight of the dogs. With the tip of the micromanometer 5-8 cm distal to the carina, a zone of high pressure was noted in seven dogs; this high pressure suggested a zone of airway collapse distal to the carina.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiopulmonary resuscitation with a novel chest compression device in a porcine model of cardiac arrest

“…It has been well-described that blood moves during CPR chest compression because of some combination of direct cardiac compression and intrathoracic pressure manipulation (8,10,18 -20). This intrathoracic pressure model was instrumental in developing vest CPR (5,13), which could generate normal levels of flow during CPR, likely mediated by collapse of medium-sized airways, trapping air in the lungs (10). Both A-CPR and C-CPR caused a 20% reduction in the anterior-posterior dimension of the chest.…”

“…Blood flow itself is related to the amount of sternal displacement and compression time during CPR (8,9). Airway mechanisms may also be important in generating flow (10). Because manual CPR is often done incorrectly (11,12), especially during transportation, automated devices may eliminate the variability and fatigue inherent in manual CPR, decrease interruptions, augment airway mechanisms, and improve blood flow and survival.…”

Cardiac Arrest: the Changing Incidence of Ventricular Fibrillation

“…Animal studies demonstrate that chest compressions produce airway collapse which may impair ventilation [70] while efforts to quantify the amount of ventilation produced solely from chest compressions suggest that it is not sufficient to provide for adequate ventilation [71, 72]. Animal studies have also demonstrated that cerebral oxygen delivery falls to negligible amounts in compression-only CPR within a few minutes after the onset of VF arrest [73].…”

Effect of decreased inspiratory times on tidal volume

“…During the chest compression phase, intrathoracic pressure can exceed 100 cm-H 2 O [6]. Thus, in synchronous ventilation-compression experiments in the 1980s, special ventilators providing airway pressures over 100 cmH 2 O had to be employed to allow ventilation during the entire chest compression phase in intubated animals [3].…”