Point-of-Care Ultrasound Assessment of the Carotid Artery during Cardiopulmonary Resuscitation

Do you feel the pulse? Humans have notorious difficulty detecting pulses manually in cardiac arrest patients¹, so much so that the American Heart Association removed pulse checks from guidelines for lay responders.² But there’s hope! Point-of-care ultrasound (POCUS) might be a valuable adjunct for detecting pulses in patients undergoing CPR.

The fundamental goal of cardiopulmonary resuscitation (CPR) is to provide adequate blood flow through the pulmonary vasculature to achieve oxygenation and then provide enough cardiac output (CO) to circulate oxygenated blood to perfuse critical tissues. The essential factors of CPR include chest compression depth, rate of compression, avoiding left ventricular outflow tract (LVOT) obstruction, and achieving an adequate chest compression fraction (CCF). 

Recent research has led to important insights into best practices for CPR. For example, while existing guidelines recommend a compression rate of 100 – 120 beats per minute, a study of in-hospital cardiac arrest patients illustrated that a compression rate of 121 – 140 was associated with an increased likelihood of achieving a return of spontaneous circulation (ROSC), even when controlling for CCF and other variables.³ Additionally, the traditional hand position for chest compressions in patients with underlying cardiovascular disease may result in obstruction of the LVOT, preventing anterograde flow and significantly decreasing cardiac output.^4,5 Despite our evolving understanding of intra-arrest physiology and resuscitation, maximizing “time on the chest” and CCF remains necessary for adequate CPR. Higher CCF has been clearly associated with a higher likelihood of ROSC.^3,6 However, because blood flow is not typically measured, it remains unclear in individual patients whether these interventions lead to sufficient brain perfusion.

Point-of-care ultrasonography (POCUS) is a vital adjunct during CPR. It can play several roles, such as identifying reversible causes of arrest, helping to understand intra-arrest physiology, and improving the efficiency of pulse checks to increase CCF. Notably, health care workers can be inaccurate when performing manual palpation (MP), especially during CPR, which can prolong pulse checks, interrupt chest compressions, and decrease CCF.^7,8

POCUS of the carotid arteries during CPR is an accurate and efficient method of performing pulse checks. There have been several proof-of-concept studies. One study of cardiac bypass patients tested the accuracy of this technique by having physicians perform POCUS of the carotid artery during various flow states (systolic blood pressure 90, 70 – 90, < 70, and pulseless), they reported that POCUS of the carotid artery had a sensitivity of 91% and specificity of 90% for accurate pulse detection.⁹ A separate study of 20 cardiopulmonary bypass patients demonstrated that 2-D POCUS of the carotid artery had similar accuracy to using color flow when assessing for pulsatility; while the color flow was able to detect a slightly lower mean arterial pressure (56 mm Hg versus 62 mm Hg for 2-D), it was not as reliable.¹⁰ Furthermore, POCUS of the carotid artery is an easy technique to learn with high rates of success in under one hour or less of training.^11,12 Until recently, data on performing POCUS of the carotid artery and comparing this technique to MP during CPR has been lacking. 

In July 2022, Kang et. al. published a landmark study comparing POCUS carotid artery compression (POCUS-CAC) to MP during CPR.¹² POCUS-CAC was performed by using a linear transducer in the transverse orientation to find the carotid artery and then compress until the internal jugular vein collapsed. An absent pulse was defined as a lack of pulsation or complete compression of the carotid artery; a present pulse was defined as any visualized pulsation or incomplete compression of the carotid artery. Their protocol was designed on the assumption that during CPR even optimal compressions only produce 20 – 40% of pre-arrest CO. Therefore, the carotid artery would be collapsible during CPR. The study cohort included 25 patients undergoing CPR at Samsung Medical Center in Seoul, Korea. The physician performing MP and interpreting the electrical rhythm was blinded by the physician performing POCUS-CAC. They reported an average pulse check of 1.62 seconds using POCUS-CAC compared to 3.50 seconds for MP. POCUS-CAC was 0.44 times shorter than the average MP time across 155 total pulse checks. Importantly, POCUS-CAC never took longer than 10 seconds, and the proportion of pulse checks that took over 5 seconds was statistically significantly lower than compared to MP. The main limitation of this study was that only 8 patients had arterial lines, making it difficult to verify the accuracy of POCUS-CAC in determining pulsatility. 

Beyond improving pulse check efficiency, POCUS-CAC has the potential to provide useful information. In the Kang study, ROSC was achieved in 10 patients, and, in 6 of the 10 patients, the carotid artery was no longer collapsible on POCUS-CAC during compressions prior to the pulse check, suggesting that this could be a predictor of ROSC.¹² A separate cohort of 16 patients undergoing CPR used doppler flow of the carotid artery to measure a variety of variables.¹³ In 2 patients, they observed forward flow during compression and reverse flow during decompression or “recoil.” They hypothesized that this could correlate with early cerebral edema. However, a cerebral circulatory arrest is normally assessed on ultrasound of the internal carotid artery. A variety of factors, volume status, flow in the external carotid artery, and aortic valve pathology, could all affect flow in the common carotid artery.

In the same study, the investigators also measured end-diastolic velocity (EDV) in the common carotid artery during extracorporeal-CPR and conventional CPR.¹³ EDV is an important parameter because it is a marker for diastolic blood flow, which is necessary for coronary artery perfusion. The EDV in the common carotid artery is approximately 20 – 30 cm/s during a normal physiologic state. In this small, single-center study, mean EDV in the conventional CPR group was lower compared to the extracorporeal-CPR group, though the difference was not statistically significant in this underpowered study. Interestingly, there was a trend toward higher EDV in those patients where ROSC was achieved, mean EDV of 28.6 cm/s. While this trend warrants further investigation and suggests that EDV may be a target for resuscitation in the future, the data remains limited and not validated. Furthermore, performing accurate doppler ultrasonography during compressions is challenging, even for providers experienced with POCUS.

POCUS-CAC should be implemented during CPR. We recommend the following:

1. When resources allow, there should be one dedicated ultrasonographer.
2. POCUS trans-thoracic echo should be used only for a specific clinical question as a diagnostic modality to search for reversible causes. It should not be used for pulse checks as it has been associated with worse CCF.¹⁴ If used, positioning of the ultrasound transducer can occur during CPR. Images should be obtained during rhythm or pulse checks or other clinically necessary interruptions in CPR for no more than 10 seconds. A clip 3-5 second clip should be saved, which can be reviewed once CPR is resumed.
3. POCUS-CAC should be performed (semi)-continuously during compressions and used for pulse checks.
4. Using POCUS-CAC removes the responsibility of MP from the code leader, allowing them to focus on rhythm interpretation.
5. Place an arterial line when feasible.
6. Be mindful of low-flow states where the carotid artery is partially collapsible though still pulsatile, as this would change clinical management.

References

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2. Merchant RM, Topjian AA, Panchal AR, et al. Part 1: Executive Summary: 2020 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2020;142(2):S337-S357. doi:10.1161/CIR.0000000000000918
3. Kilgannon JH, Kirchhoff M, Pierce L, Aunchman N, Trzeciak S, Roberts BW. Association between chest compression rates and clinical outcomes following in-hospital cardiac arrest at an academic tertiary hospital. Resuscitation. 2017;110:154-161. doi:10.1016/j.resuscitation.2016.09.015
4. Catena E, Ottolina D, Fossali T, et al. Association between left ventricular outflow tract opening and successful resuscitation after cardiac arrest. Resuscitation. 2019;138:8-14. doi:10.1016/J.RESUSCITATION.2019.02.027
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7. Ochoa FJ, Ramalle-Gómara E, Carpintero JM, Garcı́a A, Saralegui I. Competence of health professionals to check the carotid pulse. Resuscitation. 1998;37(3):173-175. doi:10.1016/S0300-9572(98)00055-0
8. Lapostolle F, le Toumelin P, Agostinucci JM, Catineau J, Adnet F. Basic cardiac life support providers checking the carotid pulse: performance, degree of conviction, and influencing factors. Acad Emerg Med. 2004;11(8):878-880. doi:10.1111/j.1553-2712.2004.tb00772.x
9. Sanchez S, Miller M, Asha S. Assessing the validity of two-dimensional carotid ultrasound to detect the presence and absence of a pulse. Resuscitation. 2020;157:67-73. doi:10.1016/j.resuscitation.2020.10.002
10. Germanoska B, Coady M, Ng S, Fermanis G, Miller M. The reliability of carotid ultrasound in determining the return of pulsatile flow: A pilot study. Ultrasound. 2018;26(2):118-126.
11. Badra K, Coutin A, Simard R, Pinto R, Lee JS, Chenkin J. The POCUS pulse check: A randomized controlled crossover study comparing pulse detection by palpation versus by point-of-care ultrasound. Resuscitation. 2019;139:17-23. doi:10.1016/J.RESUSCITATION.2019.03.009
12. Kang SY, Jo IJ, Lee G, et al. Point-of-care ultrasound compression of the carotid artery for pulse determination in cardiopulmonary resuscitation. Resuscitation. Published online July 2022. doi:10.1016/j.resuscitation.2022.06.025
13. Koch M, Mueller M, Warenits AM, Holzer M, Spiel A, Schnaubelt S. Carotid Artery Ultrasound in the (peri-) Arrest Setting—A Prospective Pilot Study. J Clin Med. 2022;11(2):469. doi:10.3390/jcm11020469
14. Huis in ’t Veld MA, Allison MG, Bostick DS, et al. Ultrasound use during cardiopulmonary resuscitation is associated with delays in chest compressions. Resuscitation. 2017;119:95-98. doi:10.1016/j.resuscitation.2017.07.021

Samuel G. Rouleau, MD, Department of Emergency Medicine, UC Davis Health, Sacramento, CA
Roderick Fontenette, MD, MHCM, CPE, FACEP, FCCM, Department of Emergency Medicine, UC Davis Health, Sacramento, CA
Nicholas J. Johnson, MD, FACEP, FCCM, Department of Emergency Medicine & Division of Pulmonary, Critical Care, and Sleep Medicine, University of Washington, Seattle, WA