T.H.Gijtenbeek , J. E. Lopez Matta [1,3], P.R. Tuinman [2,3], M.E. Haaksma [2,3], M.L.A. Heldeweg [2,3], J.M. Smit [2,3], D.J. van Westerloo [1,3], J.A. Janson [1,3], C.V. Elzo Kraemer  1 Department of Intensive Care, Leiden University Medical Center, Leiden, the Netherlands 2 Department of Intensive Care, Amsterdam UMC, Vrije Universiteit Amsterdam, Amsterdam 3 Amsterdam Leiden Intensive care Focused Echography (ALIFE, www.alifeofpocus.com)
C.V. Elzo Kraemer - email@example.com
POCUS series: ultrasound during cardiopulmonary resuscitation
This article is part of the point-of-care ultrasound (POCUS) series. During cardiopulmonary resuscitation, bedside ultrasound has important clinical value for confirming a diagnosis, establishing a prognosis and in therapeutic decision-making. In this article we provide a practical review on how to implement and apply POCUS during cardiopulmonary resuscitation and discuss its merits and pitfalls.
Point-of-care ultrasound (POCUS) has shown promise in a variety of clinical scenarios. In most emergency wards and intensive care departments, ultrasound devices are standard equipment and ultrasound skills are becoming more commonplace. An increasing amount of evidence has been acquired from large clinical studies indicating the added diagnostic and prognostic value of dedicated ultrasound application during cardiac arrest. During advanced cardiac life support (ACLS) in a patient in cardiac arrest, the establishment of a diagnosis and the early start of specific therapies can improve outcome. The traditional approach for the identification of treatable causes during a cardiac arrest can nowadays be bolstered by the implementation of ultrasound. The merits of POCUS during ACLS are threefold. Firstly, the use of POCUS improves standard ACLS, by confirming the return of spontaneous circulation (ROSC), based on the presence of cardiac motion and carotid flow. Secondly, POCUS has proven to be a reliable tool for providing an ‘on the spot’ diagnosis for common causes of cardiac arrest and to shorten time to treatment.[1-3] And lastly, POCUS may be used during ACLS for prognostication of survival. Several clinical algorithms have been developed for the use of POCUS during cardiac arrest. In this article, we provide a practical review on the use of POCUS in ACLS, with our main focus on the subxiphoid view (figure 1).[2,3]
Protocols and training
Many POCUS protocols have been developed, each with their own acronym, set of diagnostic algorithms, and required training (examples in table 1).[4-6] What they all have in common is the focus on the cardiac view from the subxiphoid window. Any other cardiac window can be chosen in ACLS protocols, provided interference with thoracic compressions is avoided.[4-6] The differences in these protocols are mainly found in whether they include pulmonary, abdominal and vascular examinations. Also the order of sequence in which these organ systems are evaluated differs. Applying such a protocol provides a standard of care for quality and training purposes and most of these protocols are being evaluated in studies on clinical outcome. Regardless of the protocol chosen, team training is essential to appropriately integrate POCUS into the workflow of ACLS. Delays in the rhythm check can easily be caused, but should be avoided at all costs. The operator should therefore be skilled enough to make and save the required images during the rhythm checks, with timeframes of no more than 10 sec. Next, the operator must systematically review the results with the team members during the next CPR cycle. Given the demands these requirements take on the person performing the POCUS examination (figure 2), delegating the task of team leader to another ACLS member should be considered early, because maintaining an adequate level of situational awareness may not be possible during sonography. A therapeutic strategy can be chosen from team-based decision-making and this may improve the effectiveness of ACLS.[4-6] Bringing POCUS to this performance level in cardiopulmonary resuscitation requires practice during advanced life support training. This improves time efficiency and the overall performance of the team (figure 3). Specific criteria for an adequate performance level could not be found in the literature.
In general, being certified for an already existing ultrasound protocol, having received a period of supervision or reviews from peers and maintaining the obtained skills with a minimum amount of images per unit of time should suffice. Incorporating ultrasound in regular ACLS training should condition the team for the presence of POCUS during a real event. As previous studies have pointed out, adhering to and practising established ultrasound protocols is necessary to benefit from POCUS, without interfering with the standards of care of ACLS.
As mentioned in the previous section, the only moment for acquiring images is during the rhythm check. Usage of this limited timeframe should be optimised by placing the phased array probe (cardiac probe) in the subxiphoidal space in anticipation of the rhythm check.[4,6] Other cardiac views, such as the apical, parasternal short-axis and long-axis views are usually less appropriate and inaccessible since these views generally require more time to acquire and interfere with the resuscitation procedure. Views directed at excluding tension pneumothorax or at signs of pulmonary embolism (e.g. venous duplex exam of popliteal and femoral veins) can be incorporated as a next step, as is done in the SESAME protocol of Lichtenstein.
Quality of CPR, presence of cardiac activity and confirmation of ROSC Recently, two studies were performed that compared ultrasound detection of flow through the carotid artery with manual carotid pulse palpation.[8,9] Badra et al. found that ultrasound pulse confirmation was more successful than manual palpation in healthy volunteers, with ultrasound being correct in 99.1% of cases, whereas manual palpation was correct in only 85.6% (p<0.0001).
An observer confirmed the pulse detection whilst simultaneously palpating the radial pulse. Independent reviewers measured the time to successful pulse detection from audio recordings. In this study, ultrasound had no negative effects on the duration of the pulse check. Mastering ultrasound pulse confirmation required little training and improved post-training confidence in pulse detection as compared with traditional manual confirmation alone. Whether manual carotid pulse finding during ACLS can be replaced by ultrasound techniques needs to be evaluated in further studies. The mode (standard 2D grey-scale, Doppler, M-mode) which is most accurate for confirming a carotid flow that provides an adequate cerebral flow has not been validated either. To investigate the influence of POCUS on patient management, Breitkreutz et al. performed a prospective study of 230 cardiac arrest patients without a palpable pulse, of which 51 were diagnosed with pulseless electrical activity and 37 had asystole. In the group with pulseless electrical activity, 38 patients had viable cardiac activity on ultrasound. These patients had a better prognosis than those who did not. In the asystole group, based on pulse palpation, 13 patients had detectable wall motion on ultrasound. This deviation can possibly be explained by a misinterpretation of the ECG. Whether these study patients had, in hindsight, reversible fine ventricular fibrillation, was not known.
Diagnosing specific causes and guidance of treatment
The findings obtained during POCUS-guided ACLS may lead to accelerated decision-making and faster application of life-saving therapies. For diagnosing pulmonary embolism, cardiac tamponade, hypovolaemia and pneumothorax, POCUS assisted diagnosis has been shown to improve outcome.[11,12] Integration of POCUS into the existing ACLS approach increases the diagnostic and therapeutic abilities of the CPR team.
Ultrasonographic signs indicative of pulmonary embolism are right ventricular dilation, interventricular septal displacement to the left side or both; thrombus in transit and/or finding non-compressible popliteal or femoral veins. POCUS can expedite the confirmation of this diagnosis, with reduction of the time to administering thrombolysis, catheter thrombectomy, surgery or even the start of extracorporeal life resuscitation. This acceleration in decisionmaking can be lifesaving, as demonstrated in a case report by Piggot et al. Accurately confirming or rejecting the diagnosis of pulmonary embolism based on ultrasound is challenging. Due to the asymmetric geometry of the right ventricle, correctly assessing its dimensions in a short time frame can be difficult. Another key point to keep in mind is the differential diagnosis of right ventricular dilatation, such as increased intrathoracic pressure (dynamic hyperinflation, tension pneumothorax), pulmonary hypertension, ischaemic cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy.
Cardiac tamponade can be easily diagnosed by POCUS. Pericardial effusions can be visualised as an increased space (usually >10 mm) separating the two pericardial layers. The earliest signs of tamponade are a widened inferior vena cava and atrial late systolic collapse. Later in the process, early diastolic right ventricular collapse may be observed. POCUS examination for the clinical question of cardiac tamponade has excellent diagnostic accuracy with a sensitivity of 96% and a specificity of 98%. Amongst the common pitfalls is mistaking epicardial fat for pericardial effusion or intrapericardial thrombus. During the assessment, one should keep in mind that pericardial fat is usually hyperechoic as compared with pericardial effusions and does not cause compression of the atria and ventricles. Pericardial collections consisting of pus, fibrin-rich material or haematoma will usually have a more inhomogeneous appearance with varying echogenicity. These can be regionally localised and are therefore more easy to miss on a single subxiphoid view. When pericardial fluid is found to be the cause of cardiac arrest, immediate needle pericardiocentesis should be performed.[11,14] Circulation can be immediately restored in a significant proportion of cases.
Ultrasound can be used to diagnose hypovolaemia, indicating the need for aggressive fluid resuscitation. However, the collapsability of the inferior vena cava (IVC) is unreliable as a parameter for fluid responsiveness. Many factors, including chest compressions and positive pressure ventilation, can alter the diagnostic accuracy of IVC diameter and collapsability Therefore, relying on ultrasound alone to determine hypovolaemia as the cause for cardiac arrest is likely to be inaccurate. However, collapsing hyperdynamic atria and/ or ventricles can be seen in extreme cases. ROSC can be achieved when adequate preload is restored.
Tension pneumothorax can be reliably diagnosed in patients with spontaneous circulation, without mechanical ventilation. Absence of ultrasound ‘lung sliding’ between the visceral and parietal pleura has a sensitivity of over 92% and specificity of 99% for pneumothorax. The visualisation of a ‘lung point’ carries a specificity for pneumothorax close to 100%. It is likely that these percentages can still be approximated in intubated patients during CPR, as long as the tube has been placed at the correct depth such that both lungs are equally ventilated by either a bag-mask-valve apparatus or mechanical ventilator. Abdominal ultrasound is usually not part of POCUS during cardiopulmonary resuscitation, but significant free fluid can be reliably excluded and signs for a ruptured aortic aneurysm can be found. The ultrasound sensitivity and specificity of experienced sonographers for diagnosing abdominal aortic aneurysms can reach 99% and 98%, respectively. The Focussed Assessment with Sonography in Trauma (FAST) protocol can be followed to screen for intrapericardial and intraperitoneal free fluid. The FAST exam consists of a subxiphoid, left flank, right flank view and pelvic view.
Life support assisted by POCUS can also be used for predicting the prognosis of resuscitation efforts. In a non-randomised prospective study of 223 patients, those with absent cardiac activity on ultrasound were less likely to have a return of spontaneous circulation (ROSC) than those with activity: 19.5% ROSC (95% CI 13-25%) vs 76% ROSC (95% CI 57-94%). Beckett et al. performed a study in cardiac arrest patients presenting to the emergency ward. When asystole was seen on ultrasound, survival to discharge was only 0.8%. In a systematic review of 1486 patients, visible cardiac activity on ultrasound was associated with an odds ratio for survival to hospital discharge of 8.03 (95% CI 3.01-21.39) compared with absence of cardiac activity. The ACLS teams in the included studies were not blinded, making the review vulnerable to bias. A second systematic review, however, found similar results. Based on the trend in these studies, it may be argued that presence of cardiac activity on POCUS warrants continuation of resuscitation.[20,21] Integrating POCUS into resuscitation care may therefore lead to more patients achieving ROSC and prevent premature cessation of resuscitation efforts, by continuing CPR in those with cardiac contractions on ultrasound, irrespective of the tracings on the ECG. The presumed rationale behind it is that POCUS distinguishes those patients with unrecoverable cardiac standstill from those that still have recoverable heart function (e.g. pseudopulseless electrical activity, low grade ventricular fibrillation, and incorrect diagnosis of asystole).
One of the important points to consider is that up to this point in time, randomised trials have not been performed to definitely prove that POCUS improves outcome. Yet, in individual cases performing POCUS can be decisive in finding a treatable cause of cardiac arrest. In this regard, a crucial limitation of POCUS assisted ACLS is that POCUS may prolong the rhythm check. This potentially reduces the effectiveness of the cardiopulmonary resuscitation and thereby an immediate reduction in cerebral blood flow. One study found a medium increase of 6 sec in the duration of the pulse check pause by applying ultrasound. Two factors were identified to influence the increase. The first factor was the level of ultrasound skill and the second was related to the POCUS provider being the resuscitation leader at the same time. In another study of 23 patients, an increase in mean pulse check duration of 8.4 sec was found. The prerequisites of the POCUS provider are therefore an adequate training level and delegating the team leadership task. Resuscitation efforts can be unnecessarily obstructed if too much emphasis is placed on taking better images. Placing the probe in advance during ongoing CPR may prevent this from happening. Other modalities for obtaining a diagnosis should be sought if acquiring adequate images is simply not possible. At all times, priority should be given to recommencing high-quality chest compressions after completing the rhythm check. Preventing delays in administering defibrillation during ventricular fibrillation equally applies. The time for producing adequate images is therefore highly limited. Saving images provides the opportunity to analyse these during the next cycle of compressions. Taken together, POCUS may only be of use during ACLS if it is performed swiftly by experienced sonographers and only minimally increases down time during ACLS compressions.
Transoesophageal echocardiography (TEE) has the potential to overcome the limitations mentioned in the previous section. For a detail explanation of POCUS-TEE, see our recent POCUS-article about this topic. This technique allows cardiac images to be taken without disrupting the CPR cycles. One retrospective study of 139 pulse checks by Fair et al. showed that TEE had a shorter mean compression pause of 9 sec (95% CI 5-12 sec) as compared with TTE: 19 sec (95% CI 16-22 sec). Measuring colour Doppler flow from transoesophageal images allows for continuous monitoring of the adequacy of thoracic compression. Furthermore, TEE can be used to detect left ventricular outflow tract obstruction caused by malpositioned thoracic compressions. These and other studies conducted on the application of TEE during CPR have shown promising results.[29,30]
The application of POCUS has opened up new vistas for improving ACLS, by aiding in establishing a diagnosis, implementing specific treatments and prognostication. The subxiphoidal view can be quickly obtained at the bedside, with modest ultrasound skills. Obtaining other cardiac views can be included as long as the cycles of thoracic compressions are not interrupted. A holistic diagnostic approach, in which pulmonary and abdominal pathology are sought after, as well as deep vein thrombosis, only adds to the value that ultrasound skills have to offer. POCUS should therefore be an integral part of the practice of ACLS.
All authors declare no conflict of interest. No funding or financial support was received.
We would like to thank Bostjan van Hemel for his assistance with the illustrations in figure 2.
- Hussein L, Rehman MA, Sajid R, Annajjar F, Al-Janabi T. Bedside ultrasound in cardiac standstill: a clinical review. Ultrasound J. 2019;11:1-8.
- Blanco P, Martínez Buendía C, Point-of-care ultrasound in cardiopulmonary resuscitation: a concise review. J Ultrasound. 2017;20:193-8.
- Atkinson P, Taylor L, Milne J, Diegelmann L. Does Point of Care Ultrasound Improve Resuscitation Markers in Undifferentiated Hypotension? An International Randomized Controlled Trial From The Sonography in Hypotension and Cardiac Arrest in the Emergency Department (SHoC-ED) Series. Cureus. 2020;12:1-8.
- Niewiara S, Strychar J, Liniarski M, Kilian T, et al. Ultrasonography protocols used in the diagnosis of reversible causes of cardiac arrest. J Publ Health Nurs Med Rescue. 2017;6:13-23.
- Finn TE, Ward JL, Wu CT, Giles A. COACHRED: A protocol for the safe and timely incorporation of focused echocardiography into the rhythm check during cardiopulmonary resuscitation. Emerg Med Australas. 2019;31:1115-8.
- Clattenburg EJ, Wroe PC, Gardner K, et al. Implementation of the Cardiac Arrest Sonographic Assessment (CASA) protocol for patients with cardiac arrest is associated with shorter CPR pulse checks. Resuscitation. 2018;131:69-73.
- Atkinson P, Bowra J, Milne J, et al. International Federation for Emergency Medicine Consensus Statement: Sonography in hypotension and cardiac arrest (SHoC): An international consensus on the use of point of care ultrasound for undifferentiated hypotension and during cardiac arrest. CJEM. 2017;19:459-70.
- Sanchez S, Miller, Asha S. Assessing the validity of two-dimensional carotid ultrasound to detect the presence and absence of a pulse. Resuscitation. 2020;157:67-73.
- Badra K, Coutin A, Simard R, et al. 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.
- Breitkreutz R, Price S, Steiger HV, et al. Focused echocardiographic evaluation in life support and peri-resuscitation of emergency patients: A prospective trial. Resuscitation. 2010;81:1527-33.
- Long B, Alerhand S, Maliel K, Koyfman A. Echocardiography in cardiac arrest: An emergency medicine review. Am J Emerg Med. 2018;36:488-93.
- Milne J, Atkinson P, Lewis D, Fraser J. Sonography in Hypotension and Cardiac Arrest (SHoC): Rates of Abnormal Findings in Undifferentiated Hypotension and During Cardiac Arrest as a Basis for Consensus on a Hierarchical Point of Care Ultrasound Protocol. Cureus. 2016;8:1-6.
- Piggott Z, Jelic T, Pulmonary embolism with cardiac arrest: a STEMI patient’s unexpected course. CJEM. 2018;20:31-6.
- Schellenberg M, Inaba K, Critical Decisions in the Management of Thoracic Trauma. Emerg Med Clin N Am. 2018;36:135-47.
- Whitson MR, Mayo PH. Ultrasonography in the emergency department. Mayo Crit Care. 2016;20:227:1-8.
- Atkinson P, Beckett N, French J, Banerjee A, Fraser J, Lewis D. Does Point-of-care Ultrasound Use Impact Resuscitation Length, Rates of Intervention, and Clinical Outcomes During Cardiac Arrest? A Study from the Sonography in Hypotension and Cardiac Arrest in the Emergency Department (SHoC-ED) Investigators. Cureus. 2019;11:1-9.
- Beckett N, Atkinson P, Fraser J, et al. Do combined ultrasound and electrocardiogram- rhythm findings predict survival in emergency department cardiac arrest patients? The Second Sonography in Hypotension and Cardiac Arrest in the Emergency Department (SHoC-ED2) study. CJEM. 2019;21:739-43.
- Lalande E, Burwash-Brennan T, Burns K, et al. Is point-of-care ultrasound a reliable predictor of outcome during atraumatic, non-shockable cardiac arrest? A systematic review and meta-analysis from the SHoC investigators. Resuscitation. 2019; 139:159-66.
- Kedan I, Ciozda W, Palatinus JA, Palatinus HN, Kimchi A. Prognostic value of pointof-care ultrasound during cardiac arrest: a systematic review. Cardiovasc Ultrasound. 2020;18:1-10.
- Lalande E, Woo MY. POCUS predicts prognosis in cardiac arrest. CJEM. 2019;21:689- 90.
- Reynolds JC, Del Rios M. Point-of-care cardiac ultrasound during cardiac arrest: a reliable tool for termination of resuscitation? Curr Opin Crit Care. 2020;26:603-11.
- De Wilde RBP, Helmerhorst HJF, Westerloo DJ. Cerebral blood flow velocity during chest compressions in cardiac arrest. Neth J Crit Care. 2017;25:137-9.
- Clattenburg EJ, Wroe P, Brown S, et al. Point-of-care ultrasound use in patients with cardiac arrest is associated prolonged cardiopulmonary resuscitation pauses: A prospective cohort study. Resuscitation. 2018;122:65-8.
- 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: 95-8.
- Smallwood N, Dachsel M. Point-of-care ultrasound (POCUS): unnecessary gadgetry or evidence-based medicine? Clin Med. 2018;18:219-24.
- Elzo Kraemer CV, López Matta JE, Friedericy HJ, Elzo Kraemer AX. POCUS series: Focused transoesophageal echocardiography, a view from the inside. Neth J Crit Care May 2021;29:130-9.
- Fair III J, Mallin MP, Adler A, et al. Transesophageal Echocardiography During Cardiopulmonary Resuscitation Is Associated With Shorter Compression Pauses Compared With Transthoracic Echocardiography. Ann Emerg Med. 2019;73:610-6.
- Hwang SO, Zhao PG, Choi HJ, et al. Compression of the Left Ventricular Outflow Tract During Cardiopulmonary Resuscitation. Acad Emerg Med. 2019;16:928-33.
- Teran F, Prats MI, Nelson BP, et al. Focused Transesophageal Echocardiography During Cardiac Arrest Resuscitation: JACC Review Topic of the Week. J Am Coll Cardiol. 2020;76:745-54.
- Orihashi K. Transesophageal Echocardiography During Cardiopulmonary Resuscitation (CPR-TEE). Circulation. 2020;84:820-4.