A novel US-CAB protocol for ultrasonographic evaluation during cardiopulmonary resuscitation

Abstract

Ultrasonography (US) is increasingly used in the emergency settings, and has been suggested as an integral part of resuscitation [[1]Monsieurs K. Nolan J. Bossaert L. Greif R. Maconochie I. Nikolaou N. et al.European Resuscitation Council Guidelines for Resuscitation 2015: Section 1. Executive summary.Resuscitation. 2015; 95: 1-80Abstract Full Text Full Text PDF PubMed Scopus (645) Google Scholar]. To compensate the limitations of traditional circulation-airway-breathing (C-A-B) check during cardiopulmonary resuscitation (CPR), and further enhance the roles of US in early detection of potentially reversible causes and confounding factors, we proposed a novel US-CAB protocol, named after C-A-B sequences in an advanced life support (ALS)-compliant manner (Fig. 1). It involved a 3-part assessment:C: sub-xiphoid view of the heart and inferior vena cava (IVC);A: tracheal US;B: bilateral lung sliding sign (2-D and/or M-mode). Only one curvilinear 2–5 MHz probe was needed. A sub-xiphoid, four-chamber view of the heart was first used to identify any contraction of the heart (C). Meanwhile, any signs of cardiac tamponade (pericardial effusion with right heart compression), massive pulmonary embolism (enlarged right ventricle with a flattened left ventricle), or hypovolemia (flattened right heart chambers) could be detected [[2]Hernandez C. Shuler K. Hannan H. Sonyika C. Likourezos A. Marshall J. C.A.U.S.E.: cardiac arrest ultra-sound exam – a better approach to managing patients in primary non-arrhythmogenic cardiac arrest.Resuscitation. 2008; 76: 198-206Abstract Full Text Full Text PDF PubMed Scopus (177) Google Scholar]. The probe was then rotated 90° parallel to IVC to evaluate the fluid status and any sings of hypovolemia (small IVC diameter or kissing signs). Next, the probe was placed transversely on the anterior neck superior to the suprasternal notch for tracheal US (A). Tracheal intubation was confirmed if only one air–mucosa interface with a comet-tail artifact was observed. Esophageal intubation was identified if two interfaces were present [3Chou H.C. Tseng W.P. Wang C.H. Ma M.H. Wang H.P. Huang P.C. et al.Tracheal rapid ultrasound exam (T.R.U.E.) for confirming endotracheal tube placement during emergency intubation.Resuscitation. 2011; 82: 1279-1284Abstract Full Text Full Text PDF PubMed Scopus (135) Google Scholar, 4Chou H.C. Chong K.M. Sim S.S. Ma M.H. Liu S.H. Chen N.C. et al.Real-time tracheal ultrasonography for confirmation of endotracheal tube placement during cardiopulmonary resuscitation.Resuscitation. 2013; 84: 1708-1712Abstract Full Text Full Text PDF PubMed Scopus (78) Google Scholar]. Third, the probe was moved to bilateral chest at 4th–5th intercostal spaces in the mid-axillary line to detect one-lung intubation or pneumothorax using the lung sliding sign (B) [[5]Sim S.S. Lien W.C. Chou H.C. Chong K.M. Liu S.H. Wang C.H. et al.Ultrasonographic lung sliding sign in confirming proper endotracheal intubation during emergency intubation.Resuscitation. 2012; 83: 307-312Abstract Full Text Full Text PDF PubMed Scopus (74) Google Scholar]. After establishment of the US-CAB protocol, a prospective, multi-center study was conducted from August 2014 to March 2016 to verify its feasibility. Seventy emergency physicians from the National Taiwan University Hospital, Far-Eastern Memorial Hospital, and Chang-Kung Memorial Hospital (Supplementary Table 1) participated in the study. These novice sonographers first attended a half-day training course, including a 1-h didactics and a 3-h small-group, rotatory, hand-on session (Supplementary Curriculum). The study was approved by the hospitals’ Institutional Review Boards. Inform consents were obtained prior to the training. A written test was done before and after the course. Skill performance was evaluated after the training using healthy volunteers. After completing the course, there was a significant improvement in written test scores (8.8 ± 1.3 pre-test vs. 9.4 ± 0.9 post-test, P < 0.0001). For US performance, the image acquisition time for C/A/B categories were 16.4 ± 7.2, 10.5 ± 5.0, and 25.4 ± 11.4 s, respectively (Supplementary Table 2). Generally the process could be completed within 1 min. There was no significant difference between senior and junior physicians. The results implied that the US-CAB protocol could be easily learned and effectively performed even by novice sonographers. Nevertheless, limitations do exist since US evaluation could be more challenging in real CPR scenarios. In conclusion, the novel US-CAB protocol integrates several US techniques into a systematic evaluation of C-A-B status during CPR. This study demonstrates its feasibility among novice sonographers after a brief training. Further deployment in clinical practice and validation of its impact on CPR efficacy and outcomes are mandated.