Sternum CPR Position: Ensuring Correct Compression

Performing CPR correctly can mean the difference between life and death, and proper hand placement is crucial. Compressions that are too high or too low on the sternum can reduce blood flow or cause injury, making precise positioning essential.

Sternum Anatomy in CPR

The sternum, or breastbone, serves as the central structure for chest compressions, providing a rigid surface that facilitates force transmission to the heart. This flat bone, located in the middle of the chest, connects to the ribcage via costal cartilage, forming the anterior portion of the thoracic cavity. Its structure allows for controlled compression of the heart between the sternum and the spine, promoting circulation when spontaneous cardiac activity has ceased.

Composed of three regions—the manubrium, body, and xiphoid process—the sternum varies in thickness and rigidity. The manubrium, the uppermost section, articulates with the clavicles and first pair of ribs, forming the superior boundary of the chest. This region is too high for effective compressions, as force applied here may not adequately compress the heart and could impact the trachea or major blood vessels. The body of the sternum, the longest and most robust portion, provides the optimal site for compressions due to its direct alignment with the heart. Its broad, flat surface distributes force efficiently, reducing the risk of fractures while maximizing pressure transmission. The xiphoid process, a small cartilaginous extension at the lower end, is vulnerable to injury if compressions are placed too low, as excessive force can lead to fractures or damage to underlying organs such as the liver.

The sternum’s articulation with the ribs influences thoracic compliance, affecting compression depth and effectiveness. Studies have shown that optimal compression depth—typically 5 to 6 cm for adults—relies on the sternum’s ability to depress sufficiently without excessive resistance. Research published in Resuscitation indicates that inadequate sternal displacement correlates with poor perfusion, while excessive force increases the likelihood of rib fractures. This balance underscores the importance of precise compressions to maximize cardiac output while minimizing harm.

Landmark Identification for Compressions

Accurate hand placement ensures effective chest compressions, optimizing circulation while minimizing injury risk. Three primary landmarks—the sternal notch, the body of the sternum, and the xiphoid process—serve as reference points for determining the appropriate compression site.

Sternal Notch

The sternal notch, or jugular notch, is the concave depression at the superior border of the manubrium, located between the clavicles. This landmark is easily palpable and serves as an upper boundary reference for chest compressions. Since the manubrium is not an ideal compression site due to its proximity to the trachea and major blood vessels, identifying the sternal notch helps rescuers avoid placing their hands too high.

In clinical practice, the sternal notch is often used as a reference point when assessing airway positioning, but in CPR, it primarily functions as a guide to locate the correct compression zone. Studies in Resuscitation have shown that compressions applied too close to the manubrium reduce cardiac output due to insufficient force transmission. By recognizing the sternal notch and moving downward to the body of the sternum, rescuers can ensure compressions are applied in the most effective location.

Body of the Sternum

The body of the sternum, or gladiolus, is the longest and most structurally robust portion, making it the optimal site for chest compressions. It extends from the manubrium to the xiphoid process and serves as the primary surface for force application. The American Heart Association (AHA) recommends placing the heel of one hand on the lower half of the sternum, avoiding the xiphoid process, to maximize compression efficiency while minimizing injury risk.

Research published in Circulation has demonstrated that compressions applied to the lower half of the sternal body result in the highest cardiac output, as this region aligns directly with the heart’s ventricles. Proper hand placement ensures force is transmitted effectively through the sternum to compress the heart between the sternum and the spine, promoting adequate perfusion. Additionally, the broad, flat surface of the sternal body helps distribute pressure evenly, reducing the likelihood of fractures.

Xiphoid Process

The xiphoid process is the small, cartilaginous extension at the inferior end of the sternum, gradually ossifying with age. This structure is a critical landmark in CPR because compressions placed too low can result in xiphoid fracture, potentially leading to damage of underlying organs such as the liver. The AHA advises rescuers to avoid placing their hands over or below the xiphoid process to prevent complications.

A study in The American Journal of Emergency Medicine found that incorrect compression positioning near the xiphoid process significantly increases the incidence of liver lacerations and diaphragmatic injuries. To mitigate these risks, rescuers are trained to locate the xiphoid process and position their hands just above it, ensuring compressions are applied to the lower half of the sternal body rather than the vulnerable inferior sternum.

Mechanical Force Distribution

The effectiveness of chest compressions depends on proper hand placement and how mechanical force is distributed across the sternum and underlying structures. The sternum acts as the primary interface for this force, transmitting energy to the heart, which is compressed between the sternum and the vertebral column. The way this force is distributed determines the efficiency of cardiac output and the likelihood of injury.

The central portion of the sternal body provides the most stable area for compression, as its broad, flat surface evenly disperses pressure. In contrast, regions near the sternal edges or lower sternum exhibit greater flexibility, increasing the risk of fractures or damage to underlying organs. Studies using cadaver models and force sensors have demonstrated that peak force application should be concentrated in the mid-to-lower sternal body, where the greatest compression depth can be achieved without excessive rib deflection.

The depth and frequency of compressions also play a significant role. The AHA recommends a compression depth of 5 to 6 cm in adults, with a rate of 100 to 120 compressions per minute. Too shallow a compression fails to generate sufficient pressure, reducing perfusion, while excessive depth increases the risk of sternal fractures. Finite element modeling studies have shown that compressions beyond 6 cm substantially elevate the probability of rib and sternum fractures, particularly in older individuals with reduced bone density.

Variations in Thoracic Anatomy

The human thorax exhibits significant anatomical variation, influencing the mechanics of chest compressions. Factors such as age, sex, body composition, and skeletal differences affect responsiveness to compressions and injury risk.

Age-related changes in thoracic anatomy are particularly relevant, as the flexibility of the ribcage decreases over time due to progressive calcification of costal cartilage. Pediatric patients have a more compliant chest wall, which can lead to greater thoracic deformation during compressions, requiring adjustments in technique. In contrast, elderly individuals often exhibit reduced thoracic compliance, increasing the likelihood of rib fractures even with standard compression depths. A study in The Journal of Trauma and Acute Care Surgery found that rib fractures occur in over 80% of CPR cases in patients over 70, highlighting the fragility of the aging thorax.

Sex-based differences also influence compression mechanics. Studies have shown that females tend to have a shorter and narrower sternum compared to males, which can alter force distribution. This may necessitate subtle adjustments in hand positioning to ensure optimal pressure is directed toward the heart. Additionally, variations in muscle and fat distribution affect how force is transmitted through the chest wall, with higher body fat percentages potentially dampening compression effectiveness.

Hand Positioning Considerations

Proper hand placement is fundamental to effective CPR, directly influencing compression depth, force distribution, and resuscitation success. Incorrect positioning—whether too high, too low, or off-center—can reduce circulation efficiency and increase the risk of complications.

The recommended technique involves placing the heel of one hand on the lower half of the sternum, just above the xiphoid process, with the other hand positioned directly on top. Fingers should be interlocked, and pressure applied with the heels of the hands rather than the fingers to concentrate force over the sternum. This technique ensures a stable downward motion, reducing lateral displacement that could compromise compression effectiveness. The rescuer’s shoulders should be aligned directly over their hands, allowing compressions to be driven by body weight rather than arm strength.

Hand positioning must also be adapted to the patient’s physical characteristics. In individuals with larger chest cavities, ensuring compressions remain centered over the sternum prevents force from being unevenly distributed. Conversely, in smaller individuals or those with fragile bone structures, careful attention to pressure application is necessary to avoid excessive force that could result in fractures.