Given the well-established benefits of PoCUS as well as the momentum behind learning and teaching these skills, now is the time for anesthesiologists to embrace PoCUS to improve bedside patient care and management.
In this article, we will discuss the many relevant clinical applications of PoCUS for the anesthesiologist. We will provide a brief review of Airway, Lung, Cardiac, Gastric and Abdominal ultrasound.
Our goal is to encourage anesthesiologists to seek further education and training in these PoCUS skills.
Citation: Stephen C. Haskins, Ansara M. Vaz, Sean Garvin. Perioperative Point-of-Care Ultrasound (PoCUS) for the Anesthesiologist. J Anesth Perioper Med 2018; 5: X-XX. online first, doi:10.24015/JAPM.2017.0090
The terms ubiquitous or pervasive describe the role ultrasound (US) plays in the modern anesthesiologist’s daily practice. Ultrasound is essential for the rapid and safe placement of central venous catheters, for performing ultrasound-guided peripheral nerve blocks and to assessing cardiac and valvular disease in the cardiothoracic operating room. Ultrasound is now expanding upon its role in the perioperative setting via Point-of-Care Ultrasound (PoCUS). PoCUS involves clinicians using ultrasound at the bedside to simultaneously obtain and interpret US images for rapid assessment of patients for clinically relevant endpoints, such as endotracheal intubation, risk stratification for aspiration, and to diagnose obviously, yet often life-threatening, pathology.
PoCUS has been described as the “21st-century stethoscope” as it is a non-invasive technique that uses imaging to add meaningful clinical data to the traditional bedside exam. There has recently been a push by many anesthesiology subspecialties, such as regional anesthesia (1), critical care (2) obstetrics and pediatrics to embrace PoCUS skills relevant to their practice. Building on this momentum, there has been a “call to action” for the perioperative US use to be embraced by all anesthesiologists in the form of a structured educational training program for current and future anesthesia trainees (3). A framework for such a training program exists in the form of the Focused periOperative Risk Evaluation Sonography Involving Gastroabdominal Hemodynamic and Transthoracic ultrasound (FORESIGHT) exam, which has been shown to be an effective means to teach a comprehensive PoCUS exam to anesthesia residents (4). Given the well-established benefits of PoCUS as well as the momentum behind learning and teaching these skills, now is the time for anesthesiologists to embrace PoCUS to improve bedside patient care and management. In this article, we will discuss the many relevant clinical applications of PoCUS for the anesthesiologist. We will provide a brief review of Airway, Lung, Cardiac, Gastric and Abdominal ultrasound (Figure). Our goal is to encourage anesthesiologists to seek further education and training in these PoCUS skills.
One of the newer PoCUS applications is airway ultrasound to confirm endotracheal intubation either by directly scanning the anterior neck during or immediately post-intubation or by indirectly examining the pleura or diaphragm for signs of ventilation. Using ultrasonography for the detection of esophageal intubation is both highly sensitive and specific (0.93 and 0.97, respectively) (5). Furthermore, tracheal ultrasonography allows for real-time visualization of the ETT passing into the trachea or esophagus (5). Moreover, correct identification of tracheal versus bronchial intubation occurs more frequently in patients examined by the Pulmonary tree and Lung expansion Ultrasound Study (PLUS) as opposed to auscultation (62% via auscultation [sensitivity 0.66, specificity 0.59] vs. 95% via ultrasound [sensitivity 0.93, specificity 0.96]) (6). The PLUS exam includes evaluation of bilateral anterior chest walls for pleural sliding, followed by an examination of the anterior neck for tracheal dilation, all of which can be done in under 3 minutes (162 +/- 38s) (6). In the setting of a difficult airway, airway ultrasound can also be used to locate the cricothyroid membrane or tracheal rings before or during emergency airway management.
Lung UltraSonography (LUS) is a simple yet arguably essential skill for all anesthesiologists. US is routinely used for procedures that are performed near the pleura and vascular structures, such as peripheral nerve blocks and central venous cannulation. These procedures risk complications such as pneumothorax, hemothorax, and phrenic nerve paralysis. LUS is a quick and reliable way to differentiate between these complications. LUS has been shown to be superior to chest radiography in evaluating for pneumothorax (sensitivity 0.88 vs. 0.52, specificity 0.99 vs. 1.00) (7). The LUS findings of lung sliding, lung pulse, B-lines, and the M-mode sea-shore sign rule out a pneumothorax, while lung point is diagnostic (8). Evaluation for B-lines assists in the assessment of interstitial syndromes such as congestive heart failure, acute respiratory distress syndrome, and pneumonia; while the diaphragmatic function may be assessed using either hepatic or splenic acoustic windows or intercostal windows (8).
Lung US can be used not only to evaluate for potential procedural complications, but it can also differentiate among different causes of respiratory distress in the perioperative setting. For example, the Bedside Lung Ultrasound in Emergency (BLUE) protocol can be used to rapidly diagnosis various causes of acute respiratory failure in 90.5% of cases. By evaluating artifacts (A-lines and B-lines), lung sliding, pleural effusions and alveolar consolidation, one can easily distinguish between pulmonary edema, COPD/asthma, pneumothorax, and pneumonia (9).
Focused Cardiac Ultrasound (FoCUS) has garnered a significant amount of attention in anesthesiology literature recently (10,11) with calls for the incorporation of FoCUS into daily clinical practice (10). Many protocols designed to diagnose obvious cardiac pathology have been published; however, the original and oldest of the protocols is Transthoracic Echocardiography (FATE) protocol (11). A FoCUS exam is a simple, rapid, goal-oriented and repeatable exam used to answer basic “yes or no” clinical questions to assist in perioperative management. The most common obvious pathologies that are either diagnosed or ruled out with a FoCUS exam are pericardial effusions, severe left and right ventricular failure, regional wall motion abnormalities suggestive of coronary artery disease, gross valvular pathology and a dynamic assessment of the inferior vena cava (2,10). Given this pathology, a FoCUS exam most benefits management of the following patients in the perioperative setting: the critically ill, patients in shock, the trauma patient, or a patient in cardiac arrest (2,10).
Basic FoCUS skills can be learned via multiple pathways, including short courses for anesthesiology trainees (4,12). For example, Frederiksen and colleagues demonstrated that novice anesthesiology trainees given a one-day course followed by 50 supervised examinations were able to identify pericardial effusions, ventricular dilatation, left ventricular (LV) failure, LV hypertrophy and aortic stenosis with excellent agreement with cardiologists (95.6% of cases) (12).
The American Society of Echocardiography (ASE) has published recommendations for FoCUS (13) delineating the scope of practice for non-cardiologists. The Society of Critical Care Anesthesiologists (SCCA) has also published goals for fellowship trained anesthesiology critical care specialists (2). But, this is just the first step. A formal consensus between the different societies, including the ASE, SCCA, Society of Critical Care Medicine, American College of Cardiology, and American Society of Regional Anesthesia and Pain Medicine, will allow for a standardized educational program to demonstrate proficiency specific to their practice.
While a detailed description of a FoCUS exam, image acquisition, and interpretation is beyond the scope of this opinion piece, both Haskins et al. and Zimmerman et al. have recently published thorough overviews of FOCUS (14,15) as an excellent starting point to familiarize oneself with the basic views and relevant pathology.
Aspiration of gastric contents under anesthesia care is of grave concern to anesthesiologists worldwide as pulmonary aspiration remains a leading cause of perioperative morbidity and mortality. Gastric ultrasound can estimate gastric volume before elective and unplanned or emergency surgery and even in patients who are pregnant or obese, thereby allowing for real-time risk stratification and decision making (16). US assessment of cross-sectional area (CSA) of the antrum correlates with gastric volume and patients undergoing emergency surgery with a larger CSA are at greater risk for aspiration (16). The Gastric US can be qualitatively stratified into “low risk” (antrum empty, clear fluids) and “high risk” (solids), which can potentially change anesthetic timing or technique. Additionally, tracing the antral area including the serosa in the right lateral decubitus position can be used to derive a relative gastric volume with the following equation: gastric volume = 27+14.6x CSA-1.28 x age with a r=0.86 (17).
The Focused Assessment with Sonography for Trauma (FAST) is a well-established PoCUS exam for determining the presence of free fluid in the peritoneum as well as assessing for pericardial effusions. Although, its value in emergency medicine and trauma has been validated, only recently has the FAST exam been shown to be of benefit to the anesthesiologist in the perioperative setting. Intra-Abdominal Fluid Extravasation (IAFE) following hip arthroscopy is a complication that in severe settings has been associated with abdominal compartment syndrome and death (18). Haskins et al. evaluated patients following hip arthroscopy with the FAST exam and demonstrated that the incidence of IAFE was quite common (14%) and that patients with IAFE were at an increased risk for postoperative pain (19). Assessing for IAFE is just one clinical example of the role abdominal ultrasound plays in the perioperative setting. The FAST exam can also be utilized to assess for postoperative urinary retention by only utilizing the pelvic views. As more anesthesiologists learn this PoCUS skill, then even more clinical applications will present themselves.
Point-of-Care Ultrasound has emerged as a powerful tool for that we believe will revolutionize how anesthesiologists evaluate patients at the bedside. PoCUS has many benefits in the perioperative setting (Table). Preoperatively, PoCUS can improve airway assessment, evaluate for significant cardiac pathology such as severe aortic stenosis or ventricular failure, as well as help risk-stratify patients with concern for aspiration based on gastric contents. Intraoperatively, PoCUS can be used to assess for correct endotracheal tube placement, evaluate for volume status as well as aid in determining the causes of intraoperative hypoxia, acute respiratory distress, and new onset hemodynamic instability. Postoperatively, PoCUS can be used to guide management of the patient exhibiting signs of shock or respiratory distress as well as diagnose new intraperitoneal fluid following hip arthroscopy.
As each generation of trainees continues to learn these skills earlier in their training (20), it is inevitable that PoCUS will become more commonplace. Therefore, it is essential for current anesthesia practitioners to learn and embrace PoCUS clinical skills to stay ahead of the curve; otherwise, they will certainly be left behind.