Ultrasonographic Assessment During Cardiopulmonary Resuscitation

Summary

Here, we present a US-CAB (Ultrasound, Circulation/Airway/Breathing) protocol for use during cardiopulmonary resuscitation (CPR). US-C evaluates the subxiphoid view of the heart and inferior vena cava. After intubation, tracheal US (US-A) and lung US (US-B) help confirm endotracheal intubation and proper ventilation.

Abstract

The US-CAB (Ultrasound, Circulation/Airway/Breathing) protocol integrates several sonographic techniques into a structured assessment of the circulation, airway, and breathing status of a patient during cardiopulmonary resuscitation (CPR) in an advanced life support-compliant manner. US-C provides a subxiphoid view of the heart, to look for potentially reversible causes of disease, such as pericardial effusion, pulmonary embolism, hypovolemia, and acute coronary thrombosis. Sonographic cardiac activity during CPR not only helps differentiate pseudo-pulseless electrical activity (PEA) from true PEA but also represents a higher chance of the return of spontaneous circulation (ROSC) and survival. Evaluation of the inferior vena cava (IVC) shows the fluid status of the patient and indicates the best methods to use for fluid resuscitation. If aortic dissection is suspected, a subxiphoid view of the aorta is suggested for identifying an intimal flap. Once intubation is done, tracheal ultrasound (US-A) at the suprasternal notch helps differentiate endotracheal intubation (one air-mucosal interface with one comet-tail) from esophageal intubation (double tract sign). Immediately following US-A, bilateral lung US (US-B) should be done to confirm proper bilateral ventilation using the lung sliding sign. In addition, US-C can be serially followed to see the dynamic changes in the cardiac chambers and IVC, or any cardiac contraction suggestive of ROSC. US-B can also detect coexisting lung or pleural pathologies without interfering with the performance of CPR. The main concern when implementing this method is maintaining high-quality CPR without delays in chest compressions when performing US-CAB. Rigorous training and continued practice are key to minimize any interruptions during resuscitation.

Introduction

Effective cardiopulmonary resuscitation (CPR) for cardiac arrest is key to successful revival of a patient. Circulation (C), airway (A), and breathing (B) are the three crucial components in either basic (BLS) or advanced life support (ALS). The evaluation of the C-A-B status during CPR basically relies on pulse checks, auscultation, and capnography¹. In true clinical conditions, however, CPR is often complex and chaotic, and these methods may have limitations^2,3. For example, the accuracy of pulse checks is often suboptimal even when performed by healthcare providers⁴. More than half of one lung intubations might be misdirected if guided by auscultation alone⁵. Even wave capnography can be affected by factors such as low cardiac output, low pulmonary flow, and use of epinephrine during CPR². Therefore, more effective, accurate evaluation of the C-A-B status is mandatory.

When trying to search for the etiology of cardiac arrest or any potentially reversible factors during CPR, medical history and physical examination are often insufficient. The detection of reversible causes, such as the 5Hs (i.e., hypoxia, hypovolemia, hyperkalemia/hypokalemia, acidosis, and hypothermia) and the 5Ts (i.e., cardiac tamponade, tension pneumothorax, pulmonary thromboembolism, coronary thrombosis, and toxins or tablets), often requires advanced examinations.

Ultrasound (US) is a useful imaging modality in emergency and critical care settings. The European Resuscitation Council (ERC) Guidelines suggest that US can be an integral part of resuscitation⁶. US can readily identify critical but potentially reversible factors that negatively affect CPR, such as cardiac tamponade, pulmonary thromboembolism, and hypovolemia^7,8,9. US also helps rule out pneumothorax and acute coronary syndrome. Moreover, US confers prognostic implications even when CPR is being performed. The presence of sonographic cardiac activity during CPR has been reported to confer higher chances of ROSC, survival, and hospital discharge^10,11. In addition to sonographic evaluation of the heart and circulation status, tracheal US is employed for confirmation of proper endotracheal intubation¹², while lung US is applied to confirm proper bilateral pulmonary ventilation¹³.

While high-quality CPR with minimal interruptions to the compressions is the most important factor for resuscitation, it is important to understand how to seamlessly integrate US into the process of resuscitation without interfering with CPR. We therefore developed a novel, ALS-compliant US-CAB protocol for use during CPR¹⁴. This paper presents a detailed description of the settings, personnel, and instruments necessary for better integration of the US protocol into the regular CPR process that first-line physicians can easily incorporate and implement into their practice.

Protocol

This procedure was approved by the Institutional Review Board of the National Taiwan University Hospital and registered at ClinicalTrials.gov (NCT02952768).

1. Instrumentation

1. Use a US machine equipped with a curvilinear 2–5 MHz probe. A portable US is more suitable for CPR.

2. Personnel and their roles in the resuscitation team

1. Ideally, a resuscitation team should be comprised of six members: 1) a leader; 2) a member for airway management (A) and ventilation (B); 3) one for chest compressions (C); 4) one for defibrillation (D); 5) one for intravenous (IV) catheterization and medication; and 6) a recorder.
2. If the personnel is limited, have the roles overlap. When US is integrated into the CPR process, the sonographer should be an independent member of the team who is well trained and experienced in resuscitation US and can intervene and interpret the US images in a timely manner without interrupting or delaying resuscitation efforts. However, the leader can also be the sonographer. He or she can use US to search for any potentially reversible causes of resuscitation failure as early as possible while leading the whole CPR process.

3. Cardiopulmonary resuscitation process

1. Perform all resuscitation procedures according to the ALS guidelines⁶.
2. When US is integrated into the CPR process, strict control to minimize interruption of the chest compressions is the highest priority. Restrict the hands-off interval for pulse checks/rhythm analysis and simultaneous US evaluation to no longer than 10 s.
   1. Use a timer with preset alarms to remind the sonographer of the time intervals. Set the alarm for every 2 min of CPR and 10 s for pulse checks.

4. US-CAB protocol

1. US-C: Use cardiac US (US-C) at the start of CPR and at the end of the first five cycles of chest compressions.
   1. Use the subxiphoid four-chamber view (Figure 1A) to check pericardial effusion, the size of the right and left ventricles, and sonographic cardiac activity.
   2. Turn the probe 90° (parallel to the long axis of the patient) to measure the diameter of the IVC (Figure 1B).
2. US-A: Use US-A to check the endotracheal tube location after intubation.
   1. Place the probe transversely at the suprasternal notch (Figure 1C).
   2. Note the one air-mucosal interface with one comet-tail artifact (single tract sign) for tracheal intubation.
   3. Move the probe to the lateral side of the neck to reconfirm the single tract sign.
   4. Perform reintubation if there are two air-mucosal interfaces with two comet-tail artifacts (double tract sign)¹².
3. US-B: Use US-B to check proper ventilation.
   1. Put the probe on either side of the chest at the 4^th–5^th intercostal spaces over the midaxillary line (Figure 1D).
   2. Detect lung sliding to evaluate pulmonary ventilation^11,13.
   3. If lung sliding is absent on one side, adjust the depth of the endotracheal tube until bilateral lung sliding is noticed.
4. US-C: Repeat US-C every 2 min when chest compression is stopped for pulse checks.
5. Repeat US-AB after transportation and bed transfer of the patient.

5. Settings and approach during CPR

1. Keep the US machine ready in the resuscitation room of the emergency department. In cases of in-hospital cardiac arrest, a portable US device can be brought to the scene immediately, and turned on instantly.
2. Because a lot of resuscitation procedures are performed around the head, neck, and chest of the patient (e.g., chest compressions, defibrillation, intubation, ventilation, etc.), place the US machine in the caudal area of the patient (Figure 2). For example, it should be located over the patient’s right side for a right-handed sonographer and vice versa. This way the sonographer can get the probe ready and immediately assess the patient’s condition.

6. Image acquisition and recording

1. Have the US images interpreted by the sonographer and print or store important images for medical records and further discussion with the resuscitation team.
2. Ideally, store the US images in the hard disk of the US machine for regular (e.g., monthly) review, either for quality assurance or teaching purposes. Video recording is even better, as it not only provides important information that is less well characterized by still photos but also offers materials for training or subsequent analysis.

7. Data interpretation and analysis

1. Have the sonographer interpret the US images during CPR on-site to help with clinical judgement and decision making. A sonographer, after structured training and continued practice, can perform sonographic evaluation and interpret the data in real CPR scenarios. The interpretation and discussion of the data can also be done by all resuscitation team members during debriefing immediately after the post-CPR phase. The discussion focuses not only on US diagnosis, but on the therapeutic interventions and impact on CPR outcomes following the US examination.
2. For research purposes, also have interpretation done afterwards by blinded researchers.

Representative Results

US-C with subxiphoid evaluation of the heart displays a cardiac four-chamber view as shown in Figure 3A. At this point, detection of any of the three typical patterns suggestive of specific etiologies or reversible factors is possible.

Identify the presence and characters of pericardial effusion: If pericardial effusion is present, notice if the right heart chambers (i.e., the right atrium or even the right ventricle) are compressed. If compression of the right atrium and ventricle is noted (Figure 3A), pericardiocentesis is indicated and should be done immediately. If there is no compression of the right heart chambers, whatever the effusion amount is, CPR should be continued and pericardiocentesis should not be performed to not waste time. Pericardial effusion is also of diagnostic value. If the echogenicity is high or blood clots are present in the pericardial sac, the etiology could be cancer, aortic dissection with rupture into pericardium, etc. The nature of the pericardial effusion and the possible underlying etiologies can guide the decision whether to perform pericardiocentesis.

If pericardial effusion is absent, evaluate the size of the ventricles. If the right ventricle is dilated, with the interventricular septum compressing the left ventricle, increased right ventricular pressure is likely. Pulmonary embolism should be taken into consideration in this case, especially if there is jugular vein engorgement or unilateral leg swelling.

If the right heart chambers are small in size or even collapsed, marked hypovolemia is suspected in patients with substantial gastrointestinal bleeding or dehydration.

While verifying the three typical patterns (i.e., cardiac tamponade, pulmonary embolism, and hypovolemia), sonographic cardiac activity should be clarified. This can help differentiate pseudo-PEA from true PEA, detect fine ventricular fibrillation, and identify regional wall motion abnormalities in specific coronary artery territories.

US-C with subxiphoid evaluation of the IVC can be demonstrated by a vertical approach (Figure 1B). Visual identification of the IVC diameter helps assess the fluid status of the patient (Figure 3B). The IVC can also be evaluated with the subxiphoid transverse view (Figure 3C).

US-C with subxiphoid verification of the descending abdominal aorta can be approached via a vertical (Figure 3D) or transverse view (Figure 3C). Though optional, this evaluation is recommended if aortic dissection is suspected from clinical presentation or when hemopericardium is observed on US-C cardiac evaluation (Figure 3A).

US-A for confirmation of the location of the endotracheal tube can be done after intubation or any time during CPR when dislodgement is suspected. Endotracheal intubation is confirmed if a single tract sign is observed (Figure 4A). If there is a double tract sign, esophageal intubation is highly likely.

US-B is usually done immediately after US-A when auscultation or capnography is being performed by other team members. However, it can also be done any time during CPR when displacement of the endotracheal tube with one lung intubation is suspected, or when specific etiologies such as pneumothorax (Figure 4B) or hemothorax need to be ruled out.

Figure 1: Ultrasonographic (US) approach in US-CAB protocol. (A) Subxiphoid assessment of the heart. (B) Subxiphoid vertical approach for assessment of the inferior vena cava and aorta. (C) Tracheal US with the probe placed transversely on the anterior neck superior to the suprasternal notch. (D) Lung US with probe placed on mid axillary line at the 4^th to 5^th intercostal space, left side first and then right side. Please click here to view a larger version of this figure.

Figure 2: Settings of ultrasound (US) and sonographers during cardiopulmonary resuscitation. Please click here to view a larger version of this figure.

Figure 3: Representative images of US-C, A and B. (A) Subxiphoid four-chamber view of the heart showing pericardial effusion with compression of the right ventricle (arrow). (B) Subxiphoid vertical view of the IVC. (C) Subxiphoid transverse view of the IVC and aorta. (D) Subxiphoid vertical view of the aorta. Please click here to view a larger version of this figure.

Figure 4: Ultrasonographic (US) assessment of endotracheal tube location and bilateral ventilation. (A) Tracheal US demonstration of single air-mucosa interface (asteroid = single comet tail sign). (B) Lung US assessment for lung sliding sign (left, 2D image; right, M-mode image). Please click here to view a larger version of this figure.

Discussion

US is a noninvasive, real-time, and readily available imaging modality in emergency and critical care settings. Application of US during CPR plays an important role in diagnosis, guidance of therapeutic intervention, or monitoring¹⁵. While many US protocols have been introduced for use with CPR, the US-CAB protocol complies with the sequence of advanced life support (ALS). It integrates important US techniques to detect possibly reversible causes of any issues, and to evaluate the C-A-B status during the whole process of resuscitation^11,14.

The scanning sequence of the US-CAB protocol is: 1) C, at the start of resuscitation; 2) AB, after intubation; 3) C, every 2 min during pulse checks and rhythm analysis; 4) AB, after transportation. US-C helps detect possible reversible causes of cardiac arrest and the existence of cardiac contractility. US-AB is used for confirmation of endotracheal tube location and proper ventilation. This can guide the first-line physician's management resuscitation appropriately. For example, when pericardial effusion is detected, pericardiocentesis can be performed immediately. When a double tract sign is noted after intubation, removal of the endotracheal tube and reintubation can be quickly accomplished.

According to our experience, the hands-off interval for pulse checks and rhythm analysis (which takes less than 10 s) is enough for sonographic examination after proper training^11,14. However, if the sonographer cannot complete US-C within 10 s, the team needs to resume chest compressions. US-C can be performed again during the next pulse check.

Tracheal ultrasound (US-A) exhibits a high sensitivity and a high specificity for confirmation of tracheal intubation¹². However, evidence is still lacking for detection of the supraglottic airway. In addition, pitfalls occur in patients with proximal esophageal dilatation, which mimics a double tract sign¹⁶.

Although the scanning sequence is performed in an arbitrary order, the order can be changed according to a sonographer's experience. For example, US-B can be performed at the start of resuscitation while using a bag-ventilation mask (BVM) to rule in proper ventilation or rule out pulmonary pathologies. In addition, US-B can be first performed on the right side of the patient, and then on the left side. Because the right side is checked first, if sliding is detected, it is evident that the endotracheal tube is in the trachea even when checking the right bronchus (which can be identified in the next step and also gives a baseline for comparison on the left side). If sliding is not seen, the airway can be checked again, then pneumothorax can be considered.

Concerns regarding interruption of chest compressions to use US have been raised^17,18. Perfect integration of the US-CAB protocol into the CPR process necessitates familiarity with the US-C, US-A, and US-B techniques, qualified personnel, optimal instruments, and well-organized teamwork. Structured training and continued practice are needed, and show remarkable improvement in US performance^18,19. Therefore, the potential delay of chest compressions can be minimized. Moreover, experienced individuals can try subxiphoid US-C when chest compression is ongoing²⁰. Though the quality of imaging can be limited by a number of factors, such as obesity, it is possible to get a glance at the heart and IVC to rule out important reversible causes for CPR failure as quickly as possible. Similarly, though the initial assessment of US-A and US-B are usually performed immediately after intubation, when chest compressions stop for auscultation, the follow-up US-AB can also be done during chest compressions whenever dislodgement or displacement of the endotracheal tube is suspected.

In conclusion, US-CAB is feasible and provides diagnostic and prognostic abilities during CPR. Through rigorous training and continued practice, as well as adequate integration of the protocol with an organized resuscitation team, the impact of US-CAB protocol can be maximized.

Materials

Name	Company	Catalog Number	Comments
Ultrasound	Cannon, Japan	SSA-550A	nil