This invention relates to an improved apparatus and method for guiding a rescuer in the application of cardiopulmonary resuscitation chest compressions.

It has been demonstrated that responders who perform CPR and compress too fast often do not achieve the appropriate depth required for efficacious CPR compressions. One reason for this deficiency may be because it is physically challenging to compress deep and fast at the same time.

Some defibrillators incorporate user guidance prompting for cardiac rescues that includes prompted periods for applying CPR compressions, e.g. CPR “pause” periods, interleaved with prompted periods for “hands-off” ECG analysis for determining whether a defibrillating shock is needed, e.g. analysis periods. One such defibrillator which provides for an uninterruptible CPR pause period is described in U.S. patent application Ser. No. 11/917,511 filed Nov. 16, 2005 and entitled “AED HAVING MANDATORY PAUSE FOR ADMINISTERING CPR”, the disclosure of which is herein incorporated by reference.

The prior art has addressed this problem in several ways. US20080145827A1 entitled “Signal Processing Device for Providing Feedback on Chest Compression in CPR” describes a depth measuring device and a force measuring device, the outputs of which provide CPR guidance to the user. US20140323928A1 entitled “Compression Depth Monitor with Variable Release Velocity Feedback” describes the use of an accelerometer in a chest-applied device to monitor for CPR-related chest displacements. And EP1491175A1 entitled “Cardio-pulmonary resuscitation device with feedback from measurement of pulse and/or blood oxygenation” describes a pulse sensor measuring a pulse rate of a victim and a SpO2 sensor measuring blood oxygenation. Electronics process the outputs of the sensors and determine actions of a rescuer who performs cardio-pulmonary resuscitation (CPR). A prompting device conveys the actions to the rescuer.

The inventors have identified several problems with the prior art teachings such as those described above. Devices which directly sense depth and force of CPR compressions are relatively expensive. Such devices also typically are configured as ancillary inputs to other rescue gear such as defibrillators and monitors, and so require cables or wireless data connections. Such equipment has not been widely adopted by cardiac rescue agencies.

Prior art devices which monitor CPR compressions all require additional equipment for use during CPR. The delay entailed in the application of these devices detrimentally effects therapy. The devices also increase the complexity of the rescue. For example, guidance prompts to the rescuer tend to be lengthy (e.g. a continuous synchronization clock) and distracting from other efforts. For example, several prior art devices incorporate metronomes to try to keep the rate correct. Metronomes are effective to some degree, but some users will tire and change rates even with the sound. Overall, studies have shown that such prompting is difficult for the user in adjusting to a proper compressions rate and depth, especially over the entire duration of a rescue.

Thus what is needed is an improved apparatus and method of guiding CPR therapy which avoids the problems presented by the prior art.

The inventors have discovered that an incorrect rate of CPR compressions, and in particular a large change in the rate of CPR compressions, often corresponds to an incorrect depth of compressions as well. The inventors further realize that a prompt for responders to adjust their depth of compressions in response to the sensed rate of compressions or change in rate of compressions can be effective to guide the responder s to the correct depth. This improvement is enabled without the need for additional acceleration, force, or displacement sensors to be deployed at the patient's body. This discovery is also counter-intuitive to the prior art, which simply teaches prompts of adjusting depth based on sensed depth of compressions, of adjusting rate based on sensed rate of compressions, and other such prompts which correlate directly to the characteristic which needs adjustment.

The inventors have in particular discovered that by monitoring changes in the rate of compressions during CPR, they can ascertain when an appropriate prompt for depth of compressions should be provided. Thus a simple prompt to “pay attention to depth” in the presence of a large change in rate may actually guide the errant CPR provider to correct both of her depth of compressions and her rate of compressions. This feature may be incorporated into devices such as defibrillators which can more easily detect rate of compressions via trans-thoracic impedance changes but cannot easily detect depth of compressions. A particular advantage of this discovery is that more accurate CPR guidance can be obtained without the need to purchase and apply additional sensors such as accelerometers, force sensors, SpO2 sensors and the like.

In accordance with the principles of the present invention, and in one preferred embodiment of the invention, an automated external defibrillator (AED) for guiding the application of cardiopulmonary resuscitation (CPR) compressions is described. The AED comprises a pair of electrodes configured to obtain electrical signals related to changes in a transthoracic impedance related to a plurality of CPR compressions, a front end circuit in electrical communication with the pair of electrodes and configured to convert the electrical signals into a plurality of CPR compressions signals, a processor in communication with the front end circuit and configured to determine a CPR rate and a change in the CPR rate based upon the plurality of CPR compressions signals, and a user output configured to issue at least an aural CPR guidance prompt. The CPR guidance prompt is related to adjusting the depth of compression based upon a determined change in the CPR rate. Examples of the guidance prompt are “push hard”, “push two inches”, “check depth”, and similar instructions related to depth. Another related guidance prompt may be “push harder.”

In an alternative embodiment, the AED further issues at least an aural CPR guidance prompt related to adjusting the depth of compression based upon an inadequate CPR rate, such as a determined zero CPR rate, which persists for a predetermined duration of time.

In another preferred embodiment of the invention, a method for improving CPR guidance comprises a step of providing a device for guiding the application of cardiopulmonary resuscitation (CPR) compressions, the device including a housing, a sensor operable to detect a parameter related to a CPR compression and to output the parameter, a processor disposed in the housing, the processor configured to receive the parameter from the sensor, determine a CPR rate based on the parameter and determine a change in CPR rate from the CPR rate, and a user output configured to issue a CPR guidance prompt related to adjusting the depth of compression based upon the determined change in CPR rate. The method further comprises the steps of automatically detecting a change in the CPR rate by the device, and of issuing a guidance instruction related to a depth of compression based on the automatically detecting step. Examples of the guidance instruction are provided previously.

The method described above includes a number of alternative embodiments. The issuing step may issue at least an aural CPR guidance prompt related to adjusting the depth of compression based upon a determined zero CPR rate for a predetermined duration of time. The issuing step may occur only during a CPR pause period.

The inventive solution of identifying insufficient depth of compressions from CPR rate information enables more effective guidance of CPR while avoiding the cost, complexity, and confusion of deploying CPR displacement sensors at the rescue scene.

