Intraoperative Point of Care Ultrasound: Taking the Guess Work Out of Diagnosis

Read an expert commentary on this article HERE.

By Denise Joffe, MD
Seattle Children’s Hospital

 

A 12 year old girl with a history of idiopathic recurrent portal vein thrombosis was scheduled for revision of a thrombosed porto-renal shunt.  She was otherwise healthy.  She had an uncomplicated induction.  Prior to starting the surgical procedure, the surgeons placed a subclavian line. As the last suture was being tied to secure the line, her tidal volumes decreased significantly, her saturation fell to 85%, and her blood pressure decreased to a systolic of 55 mmHg. She had severely decreased air entry bilaterally and no other clinical abnormalities.

The obvious differential diagnosis included complications related to central line placement such as a tension pneumothorax, hemothorax, and tamponade.  In addition, given her history of multiple thromboses, a pulmonary embolus and acute right heart failure were also possible.  A lung ultrasound was negative for a pneumothorax or pleural effusion.  A focused cardiac ultrasound (FCU) exam demonstrated a hyperdynamic and under filled left ventricle. The results of the point of care (POC) ultrasound exams, which were completed in less than 5 minutes, directed us to the treatment and management of what turned out to be an anaphylactic reaction to vancomycin.

Another case involved a healthy 10 month old girl having an inguinal hernia repair.  After a mask induction with sevoflurane she developed significant and profound hypotension that was unresponsive to more than 20 ml/kg of intravenous fluid.  A FCU exam demonstrated marked left ventricular (LV) enlargement with severely decreased LV function. Cardiology was called stat, and she was diagnosed with an anomalous left coronary artery from the pulmonary artery.  Her management was significantly altered based on the findings of the FCU exam.

POC ultrasound refers to using portable bedside ultrasound for diagnosis and management purposes.  Although POC ultrasound is being used on almost any body part these days, this discussion will focus on the intraoperative use of cardiac and lung ultrasound exams by pediatric anesthesiologists. POC ultrasound is an extension of the physical exam, and it can serve as a valuable adjunct to our intraoperative monitors.  The main utility of POC ultrasound in the intraoperative setting is in the rapid diagnosis of treatable abnormalities in patients with severe cardiorespiratory perturbations1,2.

Cardiopulmonary arrest in the OR, where multiple physiologic changes occur simultaneously, is often a matter of treating every possible diagnosis rather than a goal directed approach. Clinical conjectures based on indirect parameters such as vital signs (including saturation and end tidal C02), breath sounds, and heart tones can be minimized.  It is crucial to understand that neither exam is meant to replace a comprehensive echocardiogram or CXR or to help identify minor abnormalities that require advanced training.

The FCU exam includes as many as five views obtained with two dimensional (2D) transthoracic imaging3 that can help diagnose or rule out moderate to severe global left ventricular dysfunction, pericardial effusions, marked hypovolemia or “relative hypovolemia,” i.e. hyperdynamic function as a result of vasodilation, or severe right ventricular dilation or dysfunction1,2. These POC techniques do not include color or spectral Doppler assessment. With practice, a 3-5 view FCU takes minutes to perform.

Lung ultrasound can be used to rule out a pneumothorax and diagnose pleural effusions, and it can verify bilateral lung ventilation4. Lung ultrasound is quick and sensitive for diagnosing an effusion and specific for ruling out a pneumothorax. For example, when a pneumothorax is part of the differential diagnosis after line placement, lung ultrasound can be completed in as little as 20 seconds, faster than calling for a CXR.  The presence of ultrasound findings such as lung sliding or lung pulses, essentially rules out a pneumothorax.4

Ultrasound use by non-specialists is more common in the adult population than in pediatrics.  Specialties that have embraced POC ultrasound include emergency medicine (EM) and critical care2.  EM in particular has been using POC ultrasound for over 10 years, and although they have training guidelines (which include other POC ultrasound techniques), there are no national credentialing standards. In anesthesiology, there are established training guidelines and credentialing for perioperative transesophageal echocardiography, but none exist for perioperative POC ultrasound.

In order to set up a successful program, there are many factors to consider such as training, the type of equipment available, image storage, assessment of competence, and continuing medical education.  Training includes an advanced understanding of the physics of ultrasound beyond that used in regional anesthesia and vascular access, machine “knobology,” and acquisition and interpretation skills. It is ideal to develop a collaborative relationship with cardiology and radiology colleagues.  Although our cardiologists at Seattle Children's Hospital were initially concerned about the potential harm of misdiagnosis in the hands of anesthesiologists, they have generally supported our mission.  It is absolutely imperative to have a clear understanding of the indications and limitations of POC ultrasound and FCU in particular.1,2

Until guidelines and credentialing are established, my recommendation is to attend courses available at most major anesthesiology meetings.  The course should offer a theoretical and practical component. There are many excellent instructional on line resources as well.5 Lung ultrasound is an easier technique to learn than cardiac imaging. 

At work, lung ultrasound can be practiced after intubations and can be especially helpful when intubating neonates in order to confirm bilateral ventilation. After cardiac and thoracic procedures, a lung ultrasound exam should be compared against the postoperative CXR in order to become proficient at recognizing pathology such as a pneumothorax or effusion. 

Learning cardiac ultrasound requires more effort.  At our institution, the pediatric cardiac anesthesiologists are the first to receive training in FCU because of our understanding of cardiac disease and because the cardiologists know our small group. We received introductory lectures on ultrasound physics, knobology, and image acquisition.  We participate in reading echocardiograms with the cardiologists, and importantly we spend time with the echo technicians in order to learn acquisition skills. Until the cardiologists are satisfied with our proficiency, we perform the FCU exam at the same time as the cardiologist is called to confirm our diagnosis. 

The higher incidence of congenital heart disease (CHD) in our population makes it even more complicated to learn than in adults and most patients with known CHD remain outside the domain of our expertise.  However, even in that group, the FCU exam performed for unexpected cardiorespiratory decompensation can often demonstrate readily interpretable findings, including global ventricular function, volume status, or pericardial effusions.  That information can be used to assist management prior to the arrival of a cardiologist for a more comprehensive echocardiogram.

It is not uncommon to hear about cases during our monthly morbidity and mortality rounds that would have benefitted from POC ultrasound but where the attending didn’t appreciate the potential advantages.  Clearly, it will take some time before the benefit of the prompt and improved diagnostic capabilities of ultrasound are appreciated.

POC ultrasound education is now incorporated into our residency teaching lectures, and trainees have the opportunity to learn the technique during ICU and cardiac anesthesiology rotations.  In some medical schools, ultrasound techniques are being taught as part of the physical exam curriculum starting the first year of medical education so that in the future we can expect trainees to have much more knowledge of the basic ultrasound exams.6,7

POC ultrasound is an extremely valuable tool available to all anesthesiologists. We need to develop training and credentialing guidelines for the intraoperative setting in order to catch up to our clinical need. In the mean time, we recommend that pediatric anesthesiology departments consider developing formal training at their own institutions, and we pediatric cardiac anesthesiologists are uniquely positioned to champion this effort in collaboration with our cardiology and radiology colleagues.

Read an expert commentary on this article HERE.

References:

1. Holm JH, Frederiksen CA, Juhl-Olsen P et al.  Perioperative use of focus assessed transthoracic echocardiography.  Anesth Analg 2012;155(5):1029-32.
2. Labovitz AJ, Noble VE, Bierig M, Goldstein SA, et al.  Focused cardiac ultrasound in the emergent setting.  A consensus statement of the American Society of Echocardiography and the American College of Emergency Physicians. J Am Soc Echocardiogr 2010:23:1225-30.
3. Shillcutt SK, Bick JS. A comparison of basic transthoracic and transesophageal echocardiography views in the perioperative setting. Anesth Analg 2013;116(6), 1231-36.
4. Piette E, Daoust R, Denault A. Basic concepts in the use of thoracic and lung ultrasound.  Curr Opin Anesthesiol 2013, 26:20-30.
5. http://www.usa.philips.com/healthcare/education-resources/education-training/ultrasound-education-critical-care-emergency-medicine see tutorials
6. Baltarowich OH, Di Salvo DN, Scoutt LM et al.  National ultrasound curriculum for medical students.  Ultrasound Quarterly 2014:30(1): 13-19.
7. Solomon SD, Saldana F.  Point-Of-Care Ultrasound in Medical Education- Stop Listening and Look.  NEJM 2014:370(12):1083-85.