Multi-organ point-of-care ultrasound for COVID-19 (PoCUS4COVID): international expert consensus

LUS is more accurate than CXR for diagnosing respiratory conditions [21], including interstitial diseases [22], pneumonia [23] and COVID-19 pneumonia [24]. The diagnostic accuracy of addition of LUS outperforms standard emergency department tests for dyspnea [25, 26]. LUS can diagnose COVID-19 pneumonia in patients with normal vital signs [27] and distinguish viral and bacterial pneumonias [28].

LUS findings associated with COVID-19 pneumonia are reported to be similar to previously described viral pneumonias [12, 22]. Frequently observed are [Additional files 2‐5]: heterogeneous B-lines clusters, separated or confluent (corresponding to ground glass opacities on CT), large band-like longitudinal artifacts arising from normal pleural line (characterized as “light beam” [12]), pleural line irregularities, subpleural consolidations and areas with decreased lung sliding due to poor ventilation. Large consolidations with air bronchograms may be present, more commonly in patients requiring mechanical ventilation, possibly representing progression to ARDS or superimposed bacterial infection. At presentation, the distribution, although bilateral, is usually asymmetrical and patchy [29‐31]. Lung involvement may be limited to dorsal/basal areas in milder COVID-19 pneumonia [32]. LUS shows good agreement with CT in recognizing lung pathology and its severity [33, 34] thus, identifying patients at higher risk of clinical deterioration, ICU admission, mechanical ventilation and mortality [34‐36]. B-line count, consolidations and thickened pleural lines are associated with positive RT-PCR tests and clinical severity [37, 38]. Coupled with pretest probability, bilateral B-lines [single and/or confluent], irregular pleural line and subpleural consolidations increase the likelihood of diagnosing COVID-19 [39, 40], while non-specific, bilateral heterogeneous patterns [Additional file 6], combined with a typical clinical presentation, strongly suggest viral pneumonia. Conversely, if pre-test probability is low [41], a bilateral A-pattern on LUS may exclude COVID-19 pneumonia owing to its high negative predictive value for pneumonia [12, 30].

Multi-organ PoCUS yields a better diagnostic performance for causes of respiratory failure than LUS alone [42]. As a rapid, accurate diagnostic approach to acute dyspnea [43‐45], it outperforms standard tests [26]. Similar results have been reported in undifferentiated shock [46]. PoCUS is recommended as a first-line diagnostic test for investigating respiratory failure and/or hypotension [22, 47]. PoCUS may raise suspicions of falsely negative RT-PCR and/or alternate diagnoses [48]. Recognition of comorbidities (chronic RV or LV dysfunction) and COVID-19-associated complications (DVT and RV failure) may influence patient disposition, and PoCUS can change their management [40].

We present a conceptual framework for triage of respiratory failure [Additional file 7]. Without more data, triage protocols cannot be developed that are universally applicable.

More data are required to establish the accuracy of LUS findings for the diagnosis of COVID-19 pneumonia versus other viral pneumonias. PoCUS use for risk stratification, outcome prediction, and its impact on management of COVID-19 needs study.

Echocardiography and FoCUS are established tools for diagnosing cardiovascular disease [47, 63, 64]. FoCUS can detect pre-existing cardiac disease [Additional file 8] and acute RV and/or LV dysfunction [47]. Echocardiography [65] and FoCUS are recommended by American and European Echocardiography societies as diagnostic/monitoring tools in COVID-19 [66, 67]. FoCUS can guide decisions on coronary angiography [68] and inotropic/mechanical circulatory support [59, 69, 70]. Overt symptoms of myocardial ischemia, raised cardiac biomarkers, ECG changes and new LV regional wall motion abnormalities should be carefully evaluated so that myocardial infarction [Additional file 9] diagnostic/therapeutic pathways are followed expediently [54, 67, 68]. Low voltage QRS complexes, myocardial hyper-echogenicity, diffuse hypokinesia or regional wall motion abnormalities suggest myocarditis [71] [Additional file 11]. Acute cor-pulmonale can occur in COVID-19 [58, 72], and FoCUS can detect RV dilatation, paradoxical septal motion and RV longitudinal dysfunction [47] [Additional file 10]. Thus, FoCUS/echocardiography together with clinical and biochemical indices can enhance management of cardiovascular compromise.

Whether subtypes of COVID-19 exist with more severe cardiovascular involvement and worse prognosis, requires investigation. Study of diastolic function may be of interest in COVID-19.

Ultrasound is the mainstay of DVT diagnosis [83]. Screening is advised, when feasible, in the general management of COVID-19 patients [84]. Many factors limit access to formal duplex venous sonography [85]. Although routine screening is not widely recommended [86], twice weekly ultrasound surveillance can detect DVT, avert PE and reduce mortality in ICU patients [87].

Lower extremity ultrasound is recommended in COVID-19 patients with unexplained RV dysfunction, unexplained/refractory hypoxemia, or in patients with suspected PE who are too unstable for intra-hospital transport [86].

DVT prevalence and its role in risk stratification in mild COVID-19 are not known. Correlation of DVT with different COVID-pneumonia phenotypes needs study.

Like CT, LUS accurately characterizes regional lung pathology and identifies ARDS in COVID-19 pneumonia [33, 34, 40, 95]. LUS may discriminate mild-moderate from moderate-severe aeration loss, distinguishing different ARDS phenotypes [96] (Fig. 3).

Importantly, LUS may facilitate identification of patients with greater hypoxemia than expected for their alveolar lung injury (Fig. 3), in whom the pathophysiology may involve deranged perfusion (PE, micro-thrombosis, loss of pulmonary vasoconstriction, extrapulmonary shunt).

Global LUS score is strongly associated with lung tissue density/aeration measured with CT [97]. Using LUS to guide mechanical ventilation has been recommended [98] (Fig. 4). However, recruitment demonstrated by LUS correlates with recruitment estimated by pressure–volume curves [99], but not CT [97]. Although LUS may not predict oxygenation response to prone positioning, it does predict re-aeration of dorsal zones [100] (Fig. 5). LUS findings also correlate with extravascular lung water in ARDS [101, 102] and can monitor changes in aeration [103]. This has also been suggested in COVID-19 [104‐106].

The benefit of LUS in ventilated COVID-19 patients is only theoretical. Studies to predict response to prone positioning, PEEP titration and other interventions are awaited. Role of LUS to decide invasive mechanical ventilation is unknown.

A large international survey found that PoCUS was the most frequently used approach to assess fluid responsiveness in critically ill COVID-19 patients [108]. While FoCUS can detect early signs of severe central hypovolemia [47] [Additional file 12], interpretation of inferior and superior vena cava collapsibility/distensibility indices is difficult when a variety of ventilation modalities are employed [18, 109]. Transesophageal echocardiography has inherent risks and limitations related to manpower and infection control [110].

Dynamic indices based on stroke volume variation, passive leg raising and mini-bolus administration techniques are good predictors of fluid responsiveness [111, 112] and can be assessed with transthoracic echocardiography.

In non-COVID-19 pneumonia patients, LUS has been shown to provide information on fluid tolerance and detect the consequences on the lung of overzealous fluid resuscitation [113, 114]. Resolution of B-lines during hemodialysis has been described [115] and also observed in COVID-19 patients [116, 117].

In COVID-19 pneumonia, the severity of the bilateral interstitial manifestations may either be due to variations in the inflammatory condition of the lung or changes due to pulmonary congestion. Simplified PoCUS-guided fluid management could be beneficial in resource-limited settings and needs further studies.

Evolution of LUS findings and their quantification using scoring systems are effective in monitoring progression or resolution of lung injury, especially in terms of variations in aeration and extravascular water content [22, 98, 103, 121, 122]. LUS is very sensitive, but is not specific enough to identify all causes of respiratory deterioration [22]. A comprehensive semi-quantitative LUS approach [97] can assess severity of lung injury and distribution patterns.

In patients with COVID-19 pneumonia, progression of LUS findings has been correlated with clinical and radiological deterioration. Thus, it can accurately monitor the evolution throughout its spectrum of severity, from mechanically ventilated [104, 105, 123] or veno-venous-ECMO patients [106], to milder cases [124,125, 126]. LUS has helped in identifying superimposed bacterial infections [127], and the response to antibiotic treatment [128]. LUS Monitoring has reduced use of CT and CXR in critically ill and COVID-19 populations [129, 130].

LUS has limitations and requires further research in early identification of patients who are more likely to progress to severe respiratory failure with inflammation, their pneumonia phenotype, and separate them from those with congestion.

DETECTION OF MECHANICAL VENTILATION-RELATED COMPLICATIONS: Approximately 2.5% of all COVID-19 patients [118] and up 88% of those admitted to ICU [9] require invasive mechanical ventilation, which may often last for weeks. The diagnosis of complications associated with prolonged ventilation requires imaging that may be limited due to risk of exposure to healthcare workers and environmental contamination. Thus, PoCUS, performed at the beside by the treating physician, may provide an accurate alternative.

Pneumothorax. LUS has significantly higher sensitivity than CXR for the diagnosis of pneumothorax [79% versus 40%], whereas specificity is equally excellent [131]. However, most of these data are from trauma and post-procedural studies and may overestimate diagnostic performance of LUS in COVID-19. The negative predictive value of LUS for pneumothorax is approximately 100% (if pleural sliding, lung pulse and B or C patterns are observed) [132].

Ventilator-associated pneumonia. In the appropriate context, large consolidations not responsive to recruitment maneuvers or suction [133] are highly suggestive of secondary bacterial infection [127, 134].

Diaphragmatic dysfunction, and weaning failure from mechanical ventilation. Ventilation-induced diaphragmatic injury can be reliably assessed with ultrasound [135]. Combining LUS score with the evaluation of LV and diaphragm function may improve the success of weaning trials [136‐139]. Assessment of parasternal intercostal muscles thickening fraction seems promising for predicting weaning failure [140]. Detection and treatment of unresolved pulmonary conditions can facilitate weaning [141, 142].

Acute cor-pulmonale. The effects of mechanical ventilation on RV function have been well-described. Acute cor-pulmonale becomes an important factor to be considered in the ventilation strategy [61, 143].

The safety and cost-saving impact of LUS in diagnosing complications of mechanical ventilation is yet to be demonstrated. A decision process based on PoCUS for tracheal extubation vs. tracheostomy mandates validation.

FoCUS and echocardiography are recommended for hemodynamic monitoring in critical care [47, 63, 64]. A recent survey found that ultrasound is the most frequently used monitoring tool to assess cardiac output and pulmonary artery pressures in critical COVID-19 patients [108].

Validated PoCUS-driven hemodynamic management protocols in COVID-19 are needed.

PoCUS FOR MONITORING OF OTHER ORGANS: Many critically ill COVID-19 patients develop secondary organ dysfunction, including acute kidney injury (AKI), liver injury, rhabdomyolysis and gastrointestinal complications [118, 144]. Hemodynamic factors and viral tropism for tubular cells may contribute to AKI [145]. Gastrointestinal complications may result from sepsis, deranged hemodynamics, or microvascular thrombosis [75]. Neurological complications are also not infrequent in COVID-19 [146].

PoCUS can exclude post- and pre-renal causes of AKI (by assessing volume status and hemodynamics). It can detect systemic and renal venous congestion, important factors in AKI [147, 148], acute gastrointestinal complications [149, 150] including cholestasis and bowel ischemia in COVID-19 patients [151]. The use of PoCUS for the diagnosis and management of neurological conditions is acknowledged [152] and may be applicable in COVID-19.

Expertise and data on PoCUS applications to detect organ dysfunction in COVID-19 especially AKI and acute abdomen are limited and need further study.

Laptop/tablet/pocket-sized machines provide reasonable compromise between portability and capability [153] (Fig. 6). Multi-frequency probes may be preferable to visualize both deep and superficial structures. While a single phased-array probe is suitable for FoCUS and LUS [154], a convex probe has been recommended by some experts [22]. Topographic zones and scanning techniques require standardization [12, 22, 30]. There is also a growing interest in telemedicine technology including robotic examinations [155] for remote guidance of minimally trained operators [156, 157] [Additional file 14].

To protect healthcare workers and patients, stringent infection control practices are crucial. Available guidance deals with environmental transmission and spread to personnel [158]. Recommendations on disinfectants [159] and information on SARS-CoV-2 survival on fomites [160] are also available.

Information on quality, safety, remote mentoring/monitoring and archiving in COVID-19 is limited. Evidence for safety and efficacy of different disinfectants and methods of cleaning contaminated equipment is needed to make robust infection control policies.