COVID-19: The New Ultrasound Alphabet in SARS-CoV-2 Era

 

COVID-19: The New Ultrasound Alphabet in SARS-CoV-2 Era

 To the Editor

We applaud the proposal of Piliego et al1 to use lung ultrasound (US) as a bedside test for triage of coronavirus disease 2019 (COVID-19) patients and for subsequent management of clinical workload and level of care in the scenario of a hospital overloaded with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic patients.2 We describe an expanded role for US. Preliminary reports from the Italian outbreak2 prompted us to adopt some variations on our standard clinical protocols and to implement or upgrade techniques we already use in our critical care practice before SARS-CoV-2 pandemic. We propose the following COVID-US alphabet (Figure).

 C: cardiac evaluation 1. Cardiac chambers diameters and kinesis 2. Pericardium (effusion, tamponade) 3. pulmonary artery pressure 4. ejection fraction% 5. inferior vena cava diameter variations differential 

O: outputs 1. renal resistive index 2. velocity-time integral 

V: ventilation 1. B-lines patterns 2. B-lines spatial distribution 3. Hyperinflation and recruitment response 4. Lung score 5. Search for pneumothorax/effusion

 I: intubation 1. Prediction of difficult laryngoscopy/intubation 2. Endotracheal intubation confirmation 

D: Doppler and deep venous thromboembolism/ pulmonary embolism 

The study of cardiac function, diameters and kinesis, including pericardium, is performed bedside at admission and at times when there are significant hemodynamic changes during the intensive care unit (ICU) stay. Cardiac evaluation includes determination of EF%, PAPs, aortic VTI at apical fifth chamber time/velocity integral at apical fifth chamber at aortic efflux as a more comprehensive parameter than sole stroke volume variation (SVV%),3 ΔIVCD%4 with respiratory cycle and RRI.3 Comparative observation of preload parameters (inferior vena cava diameter variations differential %) with contractile (EF%) and ejective function (VTI) and perfusion indexes such as RRI, allow us to tailor hemodynamic and ventilator therapy based on the specific physiopathological picture of the single patient and to exclude pulmonary embolism. Hemodynamic management of COVID-19 patients is particularly challenging because of cardiopulmonary interactions in mechanically ventilated patients. COVID-19 patients show specific lung abnormality patterns, including lesser effect on pulmonary compliance, increase in pulmonary vascular resistance with consequences to the right ventricle, inferior vena cava and renal function, and on left ventricle and systemic perfusion. In this setting, US is useful in decisions regarding pharmacological choices, fluid administration, ventilator adjustments together with metabolic indexes (ie, blood lactate), and the whole clinical picture. In this perspective, RRI, though not as well established as EF or VTI, is added to US hemodynamic evaluation with emphasis on evaluation of “effective” organ perfusion,4 and as added decisional support for administration of vasoactive drugs, diuretics, or renal vasodilators,5 for renal replacement therapy, including Cyto-Sorb (CytoSorbents Corp, Monmouth Junction, NJ) for cytokine storm control. 

Similarly, the choice of best positive end-expiratory pressure (PEEP) is based not only on arterial oxygen partial pressure/fraction of inspired oxygen ratio and driving pressure evaluation but also on its hemodynamic effects and kidney repercussions. In a 22-patient sample, we observed 9% (2 cases) of exnovo kidney failure, compared with 22.2% in New York6 experience. Ventilation was regularly assessed by US between 3 and 4 times in 24 hours to follow evolutional trends of COVID-19–specific US lung findings,7 to score the amount of B-lines and titrate ventilation accordingly. Response to recruitment maneuver with PEEP escalation was evaluated with US, addressing the need for high (recruiters) or low (nonrecruiters) PEEP settings and the decision for early/late/no prone positioning.2 A potential US application that we have not yet adopted is the assessment of respiratory fatigue through respiratory muscle evaluation, with implications for decision to intubate after the noninvasive ventilation trial2 and extubation readiness assessment. 

In our practice, we also use US for preintubation airway evaluation, given the aerosolization risk associated with the performance of conventional tests (measuring interincisor distance, determining Mallampati score),8 intubation confirmation when end-tidal CO2 is not immediately available,2 diagnosis of intubation-related complications (pneumothorax, pneumomediastinum, airway trauma), and for lung and ventilation assessment.7 Finally, evaluation of right cardiac chamber diameters and lung windows, and eventual integration with lower limbs US, is used to monitor thromboembolic phenomena as part of the routine coagulative evaluation (thromboelastography/thromboelastometry), given the high thrombotic risk associated with COVID-19.7 

We believe that our approach has 2 important novelties.

 First of all, it is not only lung US but integrated US, involving cardiac and pulmonary evaluation, fluid repletion status and perfusion, airway evaluation, and thrombosis screening. 

The second point is that COVID-US approach is not only a diagnostic tool but also an integrated monitoring approach following patient’s evolution and step-by-step clinical and therapeutic decisional support. 

US applications in COVID-19 patients are promising, though they deserve larger studies and robust data to be validated and adopted in clinical practice. We propose a simple, patient-tailored, bedside approach to COVID-19 patients that reflects the multiorgan involvement of SARS-CoV-2.

Antonio Anile, MD Giacomo Castiglione, MD Anesthesia and Intensive Care Policlinico San Marco University Hospital Catania, Italy 

Chiara Zangara, MD Chiara Calabrò, MD Postgraduate School Anesthesia and Intensive Care University of Catania Catania, Italy

 Mauro Vaccaro, MD Postgraduate School Emergency Medicine University of Catania Catania, Italy 

Massimiliano Sorbello, MD Anesthesia and Intensive Care Policlinico San Marco University Hospital Catania, Italy maxsorbello@gmail.com