The lung ultrasound "Rule of 7" in the prognosis of COVID-19 patients: Results from a prospective multicentric study

Abstract

Purpose: There is growing evidence regarding the imaging findings of coronavirus disease 2019 (COVID-19) in lung ultrasound (LUS), however the use of a combined prognostic and triage tool has yet to be explored.To determine the impact of the LUS in the prediction of the mortality of patients with highly suspected or confirmed COVID-19.The secondary outcome was to calculate a score with LUS findings with other variables to predict hospital admission and emergency department (ED) discharge.

Material and methods: Prospective study performed in the ED of three academic hospitals. Patients with highly suspected or confirmed COVID-19 underwent a LUS examination and laboratory tests.

Results: A total of 228 patients were enrolled between March and September 2020. The mean age was 61.9 years (Standard Deviation - SD 21.1). The most common findings in LUS was a right posteroinferior isolated irregular pleural line (53.9%, 123 patients). A logistic regression model was calculated, including age over 70 years, C-reactive protein (CRP) over 70 mg/L and a lung score over 7 to predict mortality, hospital admission and discharge from the ED. We obtained a predictive model with a sensitivity of 56.8% and a specificity of 87.6%, with an AUC of 0.813 [p < 0.001].

Conclusions: The combination of LUS, clinical and laboratory findings in this easy to apply "rule of 7" showed excellent performance to predict hospital admission and mortality.

Keywords: C-reactive protein; COVID-19; Chest; Emergency departments; Logistic regression; Point-of-care.

Fig. 1

The 11 zones of the chest. R – RIGHT. L – LEFT. R1 and R2 are right anterior; R3 and R4, right lateral; R5 and R6 are right posterior. L1 is left anterior; L2 and L3 are left lateral and L4, L5 are left posterior.

Fig. 2

Lung ultrasound in patients with COVID-19 and lung score. (a) A lines: pattern of horizontal (thin arrow) lines parallel to pleura (p). (b) Focal B lines. Pattern of vertical lines that reach the depth of field ant start from the pleura line (dashed line). The pleural line is fragmented, like irregular pleura (ip). (c) Confluent B lines. In the form of a “white lung” (thick arrow) the B lines (dashed line) converge. The pleural line increases her irregularity, generating a subpleural consolidation (spc). (d) If the subpleural consolidation progresses, or in superinfection cases, translobar consolidations appear (arrowhead), achiving a look liver tissue-like. Pleural effusion could appear in severe cases (d). Lung score: We summed every area's points, obtaining the patient's lung score, ranging from 0 to 33. *: Irregular pleural lines and focal B lines = 1 point, **: Confluent B lines = 2 point, ***: Subpleural or lobar consolidation or pleural effusion = 3 points.

Fig. 3

Participant flow chart.

Fig. 4

Receiver operating characteristic (ROC) curve for predicting mortality. Orange line = reference line; blue line = only LUS score > 7; red line = LUS score > 7 + CRP > 70 mg/L; green line = LUS score > 7 + CRP > 70 mg/L + age > 70. (1) All patients with clinical COVID19 compatible. Receiver operating characteristic (ROC) curve for predicting mortality according to lung ultrasonography (LUS) score above 7 [area under the curve (AUC) of 59.9%, p = 0.064], with also CRP above 70 [AUC of 69.3%, p ≤ 0.001] and adding Age above 70 [AUC of 74.3%, p < 0.001]. (2) Patients with clinical COVID19 compatible and positive RT-PCR. Receiver operating characteristic (ROC) curve for predicting mortality according to lung ultrasonography (LUS) score above 7 [area under the curve (AUC) of 54%, p = 0.557], with also CRP above 70 [AUC of 68.9%, p = 0.006] and adding Age above 70 [AUC of 75%, p < 0.001]. (3) Patients with clinical COVID19 compatible and negative RT-PCR. Receiver operating characteristic (ROC) curve for predicting mortality according to lung ultrasonography (LUS) score above 7 [area under the curve (AUC) of 63.0%, p = 0.154], with also CRP above 70 [AUC of 70.8%, p = 0.022] and adding Age above 70 [AUC of 71.9%, p = 0.016]. (4) Patients with clinical COVID19 compatible, chest X-ray COVID19 compatible and negative RT-PCR. Receiver operating characteristic (ROC) curve for predicting mortality according to lung ultrasonography (LUS) score above 7 [area under the curve (AUC) of 66.7%, p = 0.230], with also CRP above 70 [AUC of 80.6%, p = 0.028] and adding Age above 70 [AUC of 52.8%, p = 0.841].