 Airway control and ventilation is vital during cardiopulmonary resuscitation CPR in cardiac arrest. Endotracheal intubation is the gold standard for airway control, but several studies have shown high rates of unrecognized placements of the tube in the esophagus instead of in the airway out-of-hospital. This is lethal. There are no failproof technique for recognising such mistakes clinically in the cardiac arrest situation. Changes on the air volume in the lungs with ventilation changes the impedance resistance to alternating current through the thorax. This impedance is already measured routinely by the defibrillators used during CPR. We propose that we can measure ventilation volumes and also discover failed intubations by monitoring this impedance during CPR with the possibility of giving feedback on both to the rescuers. 