Mechanical Monitoring

Several mechanical factors can be monitored during CPR to improve quality. A simple method is a visual or auditory metronome to ensure an adequate rate of chest compressions. An improved method monitors not only the rate of compressions but also depth, rebound relaxation, and any interruptions with visual or auditory feedback. This provides very useful information about any areas of improvement needed in future resuscitation efforts. 

Physiological Monitoring

There are many more physiological parameters other than ECG and pulse checks available to monitor patients in cardiac arrest. Research indicates that incorporating other parameters such as CPP, end-tidal CO₂, and ScvO₂ can help evaluate the patient during and after an arrest. This information may guide treatment by changing ventilatory parameters, improving CPR, choosing cardiac arrest medications, and determining if ROSC is achieved. 

Pulse

Palpating the pulse is usually done during compressions to determine if they are effective. However, while pulse can indicate ROSC, carotid pulsations do not necessarily indicate effective heart or brain perfusion, and other physiological parameters provide better feedback. Taking too long (> 10 seconds) to find a pulse can also cause an unnecessary interruption to compressions. If the responder is unsure of feeling a pulse, the team should immediately restart compressions. 

End-tidal CO₂

End-tidal CO₂ (ETCO₂) measures the exhaled carbon dioxide concentration at the end of expiration. The CO₂ detected by capnography methods is very nearly identical to the pressure of ETCO₂ (PETCO₂) in the blood perfusing the lungs since there are only trace amounts of CO₂ in room air. 

Therefore, waveform capnography is often used in intubated patients to ensure high-quality CPR, provide immediate feedback on ventilation, and ensure early detection of ROSC. An ETCO₂ that suddenly increases to normal levels (35–40 mm Hg) or more suggests that ROSC has been achieved. However, a level of < 10 mm Hg suggests poor-quality CPR. 

Additionally, if the ETCO₂ is persistently < 10 mm Hg in an intubated patient receiving CPR, the team should check the ET tube. If the ET tube is not obstructed or misplaced, an ETCO₂ < 10 mm Hg indicates achieving ROSC is unlikely. If this level lasts for 20 minutes, it is one criterion (among others) to discontinue CPR. Of note, in patients who do not have an advanced airway, a single ETCO₂ measurement should not be used to guide treatment.

Waveform Capnography: ROSC Following CPR

Perfusion Pressures

During CPR, relaxation pressures are achieved during the period of chest recoil. The pressure during arterial relaxation is equivalent to diastolic pressure that occurs with normal cardiac activity. 

CPP is equivalent to the aortic relaxation pressure minus the right atrial relaxation pressure. An increase in these pressures signals improved blood flow and increases the likelihood of ROSC. As mentioned previously, research indicates that ROSC is correlated with a CPP of 155 mm Hg or more during CPR.

Unfortunately, CPP is difficult to measure clinically as it requires evaluation of both the aortic and central venous pressures. An alternative is the pressure during arterial relaxation, which is evaluated with an arterial line (brachial, radial, or femoral). 

This pressure is also useful for determining if ROSC has been achieved or if a detected rhythm is organized. While an optimal pressure is not known, the pressure should be > 20 mm Hg to signify adequate resuscitation efforts. 

Oxygen Saturation in the Central Veins

This measurement can be a proxy for cardiac output when hemoglobin concentration, oxygen use, and oxygen saturation are constant. SCVO₂ can be a monitor of CPR quality and guide therapies to improve CPR and determine if ROSC is achieved. It is usually measured via a central venous line in the pulmonary artery or superior vena cava. 

Basics regarding SCVO₂ include:

• The optimal range is 60–80%.
• In patients managed with CPR in cardiac arrest, the average range is 25–35%.
• When SCVO₂ is < 30%, improving chest compressions or administering epinephrine should be considered. 

Pulse Oximetry

The use of pulse oximetry is usually not beneficial in patients with cardiac arrest as there is too little perfusion of the periphery to allow an accurate signal to be read. However, sudden detection of a signal likely indicates ROSC, and pulse oximetry can be used for monitoring in post-cardiac arrest care. 

Arterial Blood Gasses (ABGs)

ABGs are not reliable in patients with cardiac arrest and may not adequately evaluate hypoxemia or hypercarbia. Routine evaluation of ABGs during this time is not indicated. However, all team members must understand how to do basic ABG interpretation.

Related Video: Understanding and Interpreting ABGs Part 1: Introduction to ABGs

Related Video: Understanding and Interpreting ABGs Part 2: Hypoxemia

Related Video: Understanding and Interpreting ABGs Part 3: Acid Base Introduction

Related Video: Understanding and Interpreting ABGs Part 4: Respiratory Alkalosis

Important Considerations

Other important considerations include how long to continue CPR, when to stop CPR, and how to be supportive of family members during this stressful time.