The Mechanism of Blood Flow in Cardiopulmonary Resuscitation—introducing the Lung Pump
Highlights
- The role of the heart as the pump was questioned by observations that intrathoracic venous pressure was similar to arterial pressure during external cardiac massage 2, 3. The cardiac compression hypothesis was further challenged by the inability to perform effective CPR in patients with flail chest until the chest was bound [4|4]; suggesting that an increase in intrathoracic pressure was required to obtain an effective output (View Highlight)
- Criley et al. described `cough CPR' after observing patients in ventricular fibrillation generating a cardiac output by continuous coughing [5|5], a situation where there is no external cardiac compression. (View Highlight)
- Accumulating evidence necessitated the concept of a `thoracic pump model' of blood flow in CPR. Intrinsic to this theory is a generalised increase in thoracic pressure and the presence of thoracic inlet venous valves (View Highlight)
- In proposing the lung pump model, the inlet valve is represented by the pulmonary valve; the compression chamber by the lung vasculature, left atrium and ventricle; and the outlet valve by the aortic valve. Thus the heart is neither the entire pump nor a passive conduit as described by the cardiac or thoracic pump hypotheses but is an essential part of the lung pump (View Highlight)
- With the lung pump hypothesis atrioventricular valves are not essential for pump action as they simply divide different compartments of the compression chamber. The lungs, left atrium and left ventricle are the compression chamber. The contribution of each part of the compression chamber may vary depending on the blood volume of each component and local distortions related to the technique of compression. (View Highlight)
- The lung pump hypothesis would predict that Fontan patients would not generate a satisfactory output during external massage because of the lack of an inlet valve to prevent retrograde blood flow out of the lungs during compression (View Highlight)
- cardiac output from both the thoracic pump (reliant on thoracic inlet venous valves) and the cardiac pump (with an intact systemic ventricle) should be unaffected by the Fontan procedure (View Highlight)
- Lung pump performance will be compromised by loss of energy across the diaphragm, a flail chest or an open airway (View Highlight)
- Simultaneous ventilation and compression would also be expected to increase the intrathoracic pressure (View Highlight)
- The three postulates required for a cyclical pump are; an inlet valve, an outlet valve and a compression chamber (View Highlight)