Is The CASA Protocol Ready For The House of Medicine?

The notification phone rings: “Cardiac arrest, intubated, ETA 3 minutes.” Take a breath. You look around and notice you have a loaded team! EMS rolls in and moves that patient to the stretcher. Your awesome nurses get IV access on the first try while you promptly assemble the LUCAS device and press on. Respiratory is there and you astutely apply ETCO2 and see a good waveform to confirm ET tube placement. Your superstar PGY5 EM/IM is smoothly running the code. Now, what do you do?

Let’s review the pearls and pitfalls of point-of-care ultrasound (POCUS) in cardiac arrest.

Goals of POCUS in cardiac arrest:

1. Don’t interfere with chest compressions: keep pulse checks less than 10 secs
2. Assess for reversible causes of arrest
3. Confirm endotracheal intubation
4. Assist in pulse checks
5. Assist in the quality of chest compressions
6. Identify medically futility

Keep pulse checks less than 10 seconds

POCUS has been associated with prolonged pulse checks.^1,2 Reasons for prolonged pulse checks associated with ultrasound may include difficulty obtaining adequate views secondary to gastric insufflation and defibrillator pads.³ Prolonged interruptions result in reduced perfusion to vital organs and decrease the chance of survival with good neurologic outcomes.^4,5

How to avoid prolonged pulse checks?

1. Assign someone to count 10 seconds out loud. Chest compressions should resume within 10 seconds. No exceptions.
2. Obtain one US view (subxiphoid, apical 4 chamber, parasternal long) per pulse check.
3. Put the probe on the chest prior to pulse check to identify common structures. You can then fine-tune the view during the pulse check.
4. Obtain clips during pulse check and then analyze them after CPR resumes, not during the pulse check.
5. Have the most experienced ultrasonographer perform the studies.

Assess for reversible causes of arrest

Consider the Cardiac Arrest Sonographic Assessment (CASA) protocol⁶: a protocol for use in non-traumatic cardiac arrest.

The CASA protocol⁶

Subxiphoid: Pericardial effusion?

Probe: Cardiac Phased Array

Start here as it’s typically the easiest view to obtain during CPR. Assess for pericardial effusion suggestive of tamponade. Tamponade may be the cause of cardiac arrest in 4-15% of non-traumatic cardiac arrest.^7,8,9 If identified, pericardiocentesis is associated with 15.4% survival to hospital discharge.⁹ Of note, it may be difficult to differentiate a meaningful pericardial effusion (tamponade) from incidental effusions. Mechanical trauma from CPR may cause pericardial effusion.

Cardiac Tamponade in PEA arrest, from thepocusatlas.com

Apical 4-chamber: RV dilation?

Probe: Cardiac Phased Array

Assess for right heart strain which may suggest PE (4.8-7.6% percent of cases.)^10,11 Right heart strain during cardiac arrest may be detected by RV dilatation. Normal RV to LV ratio is less than 0.6; an abnormal ratio is, therefore, greater than 0.6.

RV dilation with clot, from thepocusatlas.com

However, not all RV strain may be due to PE. Other acute causes of right heart strain may include RV MI. Chronic conditions, such as cor pulmonale from chronic lung disease such as COPD, may also cause RV dilation and may be difficult to differentiate from acute right heart strain. RV wall thickness greater than 5 mm (parasternal long or subxiphoid view) indicates RV hypertrophy which can be a clue for chronic increased pulmonary pressures.^12,13

Chronic RV dilation, from thepocusatlas.com

Additionally, prolonged cardiac arrest from other causes (hypoxia, LV MI, dysrhythmia) may also result in RV dilation as a result of LV failure.¹³ A recent, retrospective cross-sectional study demonstrated electrocardiographic (ECG) evidence of RV strain preceding 47% of PEA/asystole arrests.¹⁴ In these patients, pulmonary embolism was found in only 20% of cases by CTA and 31% by autopsy.¹⁴ Only 41% demonstrated ultrasonographic evidence of right ventricular dysfunction when performed within 24 hours of arrest.¹⁴ Additional studies have also demonstrated ultrasonographic evidence of RV enlargement secondary to other cause (hypoxia, hypovolemia, dysrhythmia) but are largely limited to porcine studies.^15,16,17

If you identify RV enlargement, consider the risks and benefits of tPA in the context of the clinical picture. A young, otherwise healthy patient with recent surgery and signs of symptoms of DVT may prompt you to administer thrombolytics. If unsure of acute PE, you can also perform a DVT study, A positive DVT study (with a moderate to high pretest probability of PE) has a positive likelihood ratio of 16.2 (95% CI: 5.6-46.7).¹⁸

Assess for medical futility:

Parasternal long: Cardiac activity?

Probe: Cardiac Phased Array

In certain instances, the detection of hyperdynamic or hypodynamic cardiac activity, may indicate the cause and guide therapeutic interventions. For example, hyperdynamic cardiac activity may suggest hypovolemia and a provider may aggressively fluid resuscitate. Likewise, hypodynamic cardiac activity may suggest alternate causes (hypothermia, hyperkalemia).¹⁹

More often, the absence of cardiac activity may predict prognosis. A multicenter, prospective, observational ED study (n=793) in US and Canada of non-traumatic cardiac activity found that an absence of cardiac activity had a positive predictive value for non-survival of 0.99 (95% CI: 0.99-1.0) for asystole and 1.00 (95% CI: 0.98-1.0) for PEA.⁹

Additional views:

Pneumothorax

Probe: Linear

Can be performed during chest compressions

Check for lung sliding. In an intubated patient, beware that right-main stem intubation can also cause the absence of lung sliding in the left lung. Before performing a thoracostomy, consider checking the depth of your ET tube or retracting and re-examining beforehand.

Lung point, indicating a pneumothorax. From thepocusatlas.com

FAST

Probe: Curvilinear or Phased Array

Can be performed during chest compressions

Consider looking for signs of free fluid which could represent hemoperitoneum in the right clinical context (e.g. ruptured ectopic, ruptured AAA).

Positive FAST exam. From thepocusatlas.com

Confirm endotracheal intubation

Probe: Linear

Can be performed during chest compressions

A recent systematic review and meta-analysis found ultrasound to have higher sensitivity (98.7% vs 93%) and similar specificity (97.1% vs 97%) to quantitative capnography for detection of endotracheal intubation.²⁰ Ultrasound may be even more valuable for this purpose in cardiac arrest where capnography has been found to be less sensitive (65-68%), perhaps secondary to reduced pulmonary blood flow.^19,20 The study can be performed quickly, with a mean of 13 seconds.²⁰

See here, for how to perform the study.²¹

Pulse checks? “Is that a pulse or is that my own heartbeat?”

Why not just look at the artery to check for pulsations?

Prior studies have demonstrated that providers are slow and inaccurate in manual detection of a pulse.^22,23,24 A recent, prospective randomized control trial on live volunteers showed POCUS to be non-inferior to manual pulse detection of the carotid artery.²⁵ Furthermore, this study demonstrated that a 15-minute training was sufficient and suggested that POCUS could improve first-attempt pulse detection (99% vs 85%) and that speed can be improved with prior US experience (average of 3.13 sec). Additional studies are needed to determine if POCUS-assisted pulse detection can improve patient-centered outcomes.

Probe: Linear

Can be performed during chest compressions

Check proximal vessels such as carotid or femoral for pulsations using B-mode (standard mode). Obtain your cross-sectional view while chest compressions are in process to identify the artery. There should be visible pulsations if providing adequate chest compressions. You should also be able quickly to determine the presence or absence of pulsations during the pulse check.

Note: if you do not have two ultrasound machines available, you may elect to perform the above CASA protocol first and later use ultrasound to assist in pulse checks.

The Future: Can ultrasound assist in the quality of chest compression?

Transesophageal echocardiogram (TEE) is emerging as a tool for use in the ED management of cardiac arrest. A major theoretical advantage of TEE over transthoracic echocardiogram (TTE) in cardiac arrest is that TEE can be performed simultaneously during chest compressions and may avoid prolonged pulse checks associated with TTE.^1,2 A 2019 retrospective study from a single US center demonstrated decreased pulse check times associated with use of TEE (9 seconds) compared with TTE (19 seconds) or without ultrasound (11 seconds).²⁶ Furthermore, TEE may provide additional information that cannot be obtained from TTE.

Ultrasonography of the left ventricular outflow tract using TEE may act as a surrogate for the quality of chest compressions and may predict survival.²⁷ Further studies are needed to determine if TEE can improve patient-centered outcomes such as survival to hospital discharge and survival with good neurologic function.

The disadvantages of TEE include cost, cleaning, and the need for advanced training. A 2020 study demonstrated that a single 2.5-hour hands-on course with TEE may increase knowledge and comfort in its use in cardiac arrest.²⁸ TEE, while generally safe, is rarely associated with complications such as iatrogenic esophageal perforation and gastrointestinal bleeding.²⁹

However, in the absence of few, if any, proven treatments of non-traumatic cardiac arrest, it may be worthwhile to investigate if TEE may offer any patient-centered benefits.

The argument for POCUS in cardiac arrest:

EBM skeptics (myself included) will and should point out that there is no evidence that POCUS in cardiac arrest improves patient-centered outcomes such as survival to hospital discharge or survival with good neurological outcomes.³⁰ In patients with shockable rhythms secondary to ventricular arrhythmias from acute myocardial ischemia, POCUS will be of minimal benefit.³ Again, if a provider chooses to use ultrasound, the utmost effort should be made not to prolong pulse checks nor to interfere with good-quality chest compressions.

However, the lack of evidence does not equate to definitive evidence that POCUS is not beneficial in select patient populations, in particular patients with PEA arrest. The majority of critical care studies on cardiac arrest are biased towards null as they include a very sick population (they’re basically dead.) For example, nothing in modern-day medicine will revive a 90-year-old nursing home patient found cold in bed to any meaningful degree. Whereas, a healthy 30-year-old female on OCPs who collapsed on the way back from the airport from international flight may have a reversible cause (i.e. massive PE) that if quickly identified (perhaps using POCUS) and treated (i.e. thrombolysis) can improve the outcome of this particular patient. I believe that critical care research should focus on this latter population in which interventions are more likely to be beneficial.

Thus, by narrowing our aims to populations that have the highest potential for intervenable conditions, POCUS may have benefits. As advanced resuscitationists, we can and should move beyond ACLS to identify reversible causes and act upon them. POCUS in cardiac arrest has the potential to assist us in identifying reversible and provide focused and meaningful resuscitation.

Recap:

1. In non-traumatic cardiac arrest, consider the use of ultrasound only if it does not interfere with high-quality CPR
2. Avoid prolonged pulse checks by assigning a team member to count to 10 out loud
3. Identify and treat reversible causes of cardiac arrest
4. RV dilatation may not always indicate massive pulmonary embolism
5. Consider the use of ultrasound for confirmation of endotracheal intubation and detection of proximal arterial pulsation