Setting and study population
This is an observational, prospective, single-center study that was conducted in the intensive care unit of Adan General Hospital from May 1st, 2020, to June 25, 2020. The study protocol was approved by the Ethical Committee of the Ministry of Health in Kuwait; informed consent was obtained from every patient or from his or her next of kin.
Patients were included if they were age > 18, suspected to have COVID-19 and had been transferred to the ICU with fever or suspected respiratory infection plus one of the following: respiratory rate > 30 breaths/min; severe respiratory distress; SpO2 < 93% on room air (5). Patients were admitted to the ICU directly from the ED after reverse transcriptase-polymerase chain reaction (RT-PCR) resting was performed at the central virology laboratory in Kuwait. Clinical data were entered on a separate standardized data collection form at the time of patient enrollment by the treating critical care physician. Clinical data included the patient’s age and sex, presenting symptoms, medical history, oxygen saturation from pulse oximetry and chest radiograph. An intensivist certified in critical care ultrasound who was blinded to the RT-PCR results, if available at the time of examination, performed the lung ultrasound within 12 hours of the patient’s admission to the ICU.
We performed lung ultrasonography for every patient admitted to the ICU with COVID-19 suspicion using a 12-zone method (6). There were six zones for each hemithorax: two anterior, two axillary, and two posterior zones on each side. The anterior chest wall was defined as extending from the parasternal line to the anterior axillary line. This zone was divided into upper and lower regions at the third intercostal space. The lateral area from the anterior to the posterior axillary line was divided into upper and lower halves. The posterior zone was identified from the posterior axillary line to the paravertebral line. The ultrasound images were saved to a hard drive and reviewed by a senior intensivist trained in critical care ultrasound. The ultrasound imaging was performed using a portable ultrasound machine (GE Vivid iq, Horten, Norway) equipped with a 3.5-MHz broadband curvilinear transducer. The probe was placed in an oblique position on the intercostal space, and the pleural line was centered in the middle of the image by adjusting the depth settings. The oblique position of the probe on the intercostal space allows visualization of a large portion of the pleural line without interruption by rib shadows.
Pleural sliding and A-lines (repetitive lines parallel to the pleural line) on ultrasound are seen in normal healthy lungs (5). Interstitial syndrome is indicated by the presence of multiple B lines (more than three lines in one region). The four signs of COVID-19 pneumonia on lung ultrasound evaluation are as follows (6) (see Fig. 1, 2):
Bilateral B-lines in both separate and coalescent forms, sometimes patchy, frequently giving the appearance of a shining white lung. The B lines maintain their brightness until the end of the screen. They arise either directly from limited sliding pleura or from a small subpleural consolidation.
Bilateral diffuse irregularities of the pleural line.
Absence of significant pleural effusion.
Presence of multiple subpleural consolidations of various sizes.
Each lung zone was assigned a score to predict overall lung aeration (6). Score 0: predominant A-lines or < 3 separated B-lines. Score 1: at least three B-lines or coalescent B-lines occupying <_50% of the screen without a clearly irregular pleural line. Score 1p: at least three B-lines or coalescent B-lines occupying <_50% of the screen with a clearly irregular pleural line. Score 2: coalescent B-lines occupying > 50% of the screen without a clearly irregular pleural line. Score 2p: coalescent B-lines occupying > 50% of the screen with a clearly irregular pleural line. Score 3: large consolidations (at least > 1 cm).
Elevated left ventricular filling pressure (LVFP) is indirectly evaluated by echocardiography, reflecting the myocardial relaxation and stiffness diseases of LV [8, 9]. Tissue Doppler imaging of early mitral annular velocity (e’) is a good indicator of LV myocardial relaxation. After measuring the transmitral peak early filling velocity, E is the ratio of E/e’ and is used as an indirect measure of LVFP. E/e’ lateral > 12, E/e’ mean > 13, or E/e’ septal > 15 indicates elevated LVFP, whereas E/e’ <8 (any location) indicates normal LVFP .
In both systole and diastole, the E and e’ velocities are measured from the apical four-chamber view by placing a 5-mm sample volume over the lateral or medial part of the mitral annulus to cover the longitudinal excursion of the mitral annulus. The velocity scale is set to approximately 20 cm/sec above and below the zero-velocity baseline; we reduced to the minimum the angulation between the plane of cardiac motion and the ultrasound beam. The recommendation for spectral recordings is a sweep speed of 50 to 100 mm/sec at end expiration .
The average from 3 consecutive cycles was measured for all reported echocardiographic measurements. The LV volume and LV ejection fraction were assessed as recommended by the ASE (7). Mitral inflow was analyzed for peak E (early diastolic) and peak A (late diastolic) velocities, E/A ratio, and deceleration time of E velocity.
Data analysis: Statistical analyses were performed using Statistical Package for the Social Sciences (IBM SPSS 19). Patients with acute hypoxic respiratory failure admitted with suspicion of COVID-19 were divided into two groups: patients with confirmed COVID-19 pneumonia and patients with non-COVID-19 disease. Student’s t-test was used to assess differences between the groups in the case of a normal distribution. Fisher’s exact test was used for categorical data. Statistical significance was assumed at P < 0.05.