MEDEST

The objective of chest compressions in CPR is to compress the heart and in particular the Left Ventricle (LV) to generate a stroke volume (SV) trough the Left Ventricular Outflow Tract (LVOT) to perfuse the heart the brain and the rest of the organs.

Performing CPR we blindly compress the center of the chest on the sternum approximately at the level of intermammillar line (as recommended by the 2015 CPR Guidelines) but we risk to apply the Area of Maximum Compression (AMC) not only on the LV but also on the Aortic Valve (AV) and the Ascending Aorta (AA) closing them and generating less (or none) LV stroke volume but just an ineffective retrograde flow.

Image Attribution: Nestaas et al. Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine (2016) 24:54. Radiological assessment of chest compression point and achievable compression depth in cardiac patients.

Depending on how much the AMC is positioned on the left ventricle or on the aortic part of the heart chest compressions are respectively more or less efficacious to perfuse the brain the heart and the organs.

This is not just theory but was demonstrated in animal and human studies (See References links at the bottom).

In particular Sung Oh Hwang and coll. in the article “Compression of the Left Ventricular Outflow Tract During Cardiopulmonary Resuscitation” observe that”the magnitude of compression of the left ventricle is more significant when a maximal compression occurs at the LVOT than when a maximal compression occurs at the ascending aorta during external chest compression“. They also determined “that external chest compression at the hand position currently recommended by the AHA guidelines compresses the LVOT or the ascending aorta.” and conclude that “(….) the compression location currently recommended by the AHA guidelines may not be effective in generating forward blood flow during CPR.”(….) it is possible that compressing the caudal part of the sternum will improve the quality of CPR and reduce rescuer fatigue.“

The investigators stated also that the Optimal Compression Point (OCP) cannot be definitively addressed because it depends on many variables and varies from patient to patient depending “on the configuration of the heart in the thorax.”

All those findings were assessed using Trans Esophageal Echocardiography (TEE) inserted during CPR in real cases scenarios to visualise the heart to measure the LV stroke volume in order to find the best OCP.

TEE in fact is a good method to study proposition but in a short future will be a good clinical instrument to individually and visually assess the OCP, to deliver biphasic shock and to pace the heart. It is of rapid insertion in the intubated patients, is remotely and in real time monitorizza from team leader doesn’t implicate chest compressions interruption and is safe.

In another study based on a real case series “Clinical pilot study of different hand positions during manual chest compressions monitored with capnography” published in 2013, Eric Qvigstad and coll. found “that the chest compression point generating the highest EtCO2 value was evenly distributed between the patients, indicate that there is no common optimal chest com-pression point within the area tested.” 

Image attribution: Qvigstad E, et al. Clinical pilot study of different hand positions during manual chest compressions monitored with capnography. Resuscitation (2013), http://dx.doi.org/10.1016/j.resuscitation.2013.03.010

They individually chosen the best hand position during chest compressions on the basis of EtCO2 values.

So which are the clinical implications for our current clinical practice?

I would like to divide the clinical take home points in two different categories:

1. Actual applications 
2. Future development 

Actual applications for clinical practice

• The recommended chest compression point can be ineffective to generate enough outflow because the Area of Maximum Compression is not on the Left Ventricle but either on the Aortic Valve or the Ascending tract of the Aorta

• Emergency providers can adjust the compression point based on EtCO2 values.

• If, despite technically correct chest compressions, the EtCO2 remains below 10, try to adjust the compression point.

• In those cases, the Optimal Compression Point is usually positioned caudally to the recommended one on the lower third of the sternum

Future development for clinical practice

• TEE is a clinical useful instrument to

  • individually and visually assess the OCP

  • deliver biphasic shock

  • pace the heart

• TEE is of rapid insertion in the intubated patients, can be remotely and in real time controlled from team leader, doesn’t implicate chest compressions interruption and is safe.

To lear  more…..

Link to reference folder

• Mechanism of closed chest cardiopulmonary resuscitation investigated by transoesophageal echocardiography
• Left Ventricular Compressions Improve Hemodynamics in a Swine Model of Out-of- Hospital Cardiac Arrest 
• Ventricular Compressions Improve Hemodynamics in a Swine Model of Out-of- Hospital Cardiac Arrest 
• Clinical pilot study of different hand positions during manual chest compressions monitored with capnography
• Trans-Esophageal Echo in Resuscitation
• Radiological assessment of chest compression point and achievable compression depth in cardiac patients
• Compression of the Left Ventricular Outflow Tract During Cardiopulmonary Resuscitation
• The Role of TEE in Cardiac Arrest
• Potential benefit of transesophageal defibrillation: an experimental evaluation

Tag:beyondguidelines, cardiac arrest, emergency medicine, emergency ultrasound, Out of Hospital Cardiac Arrest, point of care ultrasound