The term Inspiratory Impedance Threshold Device has somewhat confused the EMS community. It sure confused me, particularly after I looked up each word individually and assembled them together. What this product really is – is a one-way pressure actuated valve.
The ResQPod works sort of like a PEEP valve only backwards – after you ventilate through the ResQPod and compress the chest forcing all the air out, air is prevented from re-entering the lungs passively between breaths. No more gas can enter the lungs again until the next delivered ventilation. PEEP holds pressure in while the ResQPod holds pressure out.
The ventilatory device used with most studies of the ResQPod, are those using it with BVM’s. BVM’s have some well documented problems generating positive pressure where you need it. While notorious for delivering high airway pressures, BVM’s typically deliver very low pressures in the lung. In one recent study of ventilation using a BVM, “The average percentage of time a positive pressure was recorded in the lung was 47.3%.” The BVM type device when used for CPR typically produces very little if any pressure changes in the thorax.
What really moves blood around during CPR is not just a negative pressure as often claimed by some Sales Reps, it is PRESSURE CHANGES. Since the BVM does not produce much positive pressure the ResQPod really helps by creating a negative pressure, thereby producing pressure changes that did not exist before. The ResQPod has demonstrated that it improves blood flow by creating negative intrathorasic pressures. It has been shown to produce -7.3 +/- 4.5 mm Hg which relates to cmH20 as shown below.
-7.3 mmHg = 9.9cm H2O
Remember that during the active phase of chest compression, the ventilation gas you deliver is forced back out under your hands, returning the lung to a low or zero pressure state (atmospheric). Most ventilators typically use between at least 25-30cm H2O of pressure when ventilating an adult patient. When you do CPR with a good EMS type Ventilator, you will go from a high pressure of at least 25-30cm down to a low of 0cm. With the ResQPod on a BVM you go from about 0cm down to –9.9cm.
What if you could improve minute volumes, control inspiratory pressures, and go from 25-35cm down to -9.9? In other words, what would happen if you combined the superior control of a volume constant ventilator WITH the hemodynamic enhancement of the ResQPod?