Residual Respiratory Impairment After COVID-19 Pneumonia

Francesco Lombardi; Angelo Calabrese; Bruno Iovene; Chiara Pierandrei; Marialessia Lerede; Francesco Varone; Luca Richeldi; Giacomo Sgalla


BMC Pulm Med. 2021;21(241) 

In This Article


Characteristics of the Study Population

One hundred and fifty-seven patients included in the post-Covid follow-up program were screened for inclusion in the study. Twenty-six patients were excluded due to positivity at the nasopharyngeal SARS-Cov-2 swab; eighteen patients were excluded due to lack of radiological evidence of COVID-19 pneumonia at the time of hospitalization; twenty-seven patients were excluded because they had not been hospitalized (discharged from the Emergency Department). Eighty-six patients were included in the analyses.

The characteristics of the study population are reported in Table 1. Study visit occurred 35 (SD: ± 21) days after hospital discharge. At the time of hospital admission, chest imaging (i.e., chest X-ray or chest CT scan) revealed bilateral ground-glass opacities (GGO) with or without consolidations in 70 patients (81%). Sixteen patients (19%) had unilateral lung involvement. During hospitalization, 56 (65%) patients required supplemental oxygen and 15 patients (17%) were admitted to the intensive care unit.

Pulmonary function testing (Figure 1) showed overall preserved lung volumes, with mean percent predicted total lung capacity (TLC) of 89.6% (± 14.6%) and mean percent predicted forced vital capacity (FVC) of 104.6% (± 18.5%). Mean percent predicted forced expiratory volume in one second (FEV1) was 102.8% (± 16.0%). Mean percent predicted residual volume (RV) was the only respiratory volume reduced under the 5th percentile (74.8 ± 18.1%). Percent predicted DLco was also mildly reduced (77.2 ± 16.5%).

Figure 1.

Overall cohort pulmonay function tests. Total Lung Capacity (TLC), Forced Vital Capacity (FVC), Forced Expiratory Volume in the first second (FEV-1), Residual Volume (RV) Diffusion Lung capacity for carbon monoxide (DLco)

Mean partial pressure of oxygen (pO2) was 91.4 mmHg (± 8.0) and mean alveolar-arterial oxygen gradient (d(A-a)) was 13.0 mmHg (± 7.5). Approximately one month after hospital discharge, patients reported more dyspnoea than pre-admission values (VAS score estimated mean difference: 15.3 mm; p < 0.001) (Figure 2; Table 2).

Figure 2.

Overall cohort trends of the VAS scores for dyspnoea and cough before hospitalization, during hospitalization, and at follow-up

Comparison of Study Groups by p/F Ratio

Most patients (n = 76, 88%) had an ABG performed during the hospitalization and were therefore included in this analysis. Among excluded patients, 8 patients had no ABG and 2 patients had an ABG performed with unknown oxygen inhaled fraction.

Gender, smoking status and comorbidities were not different across groups. Six patients (21%) in the mild hypoxemia group had a history of asthma. Patients in the severe hypoxemia group were older (63.1 years, p = 0.014 vs other groups), had a longer hospitalization time (23.0 days, p < 0.001 vs other groups) and were treated with anti-IL-6 drugs and enoxaparin more frequently (respectively 81% and 95%, p < 0.001 vs other groups).

Lung volumes were generally lower in the severe hypoxemia group, including lower percent of predicted FVC (p = 0.005), lower percent of predicted FEV1 (p = 0.009) and lower percent of predicted TLC (p = 0.012) (Table 3). In the severe hypoxemia group mean percent predicted TLC was 80.4% (± 3.1), indicating a residual restrictive impairment after 35 days from hospital discharge. DLco was also more reduced (64.9 ± 3.2% predicted) in the severe hypoxemia group than in the other two groups (p < 0.001).

As expected, the alveolar-arterial oxygen gradient increased progressively across study groups, ranging from 10.1 mmHg (± 1.4) in the mild hypoxemia group to 16.6 mmHg (± 1.6) in the severe hypoxemia group (p = 0.011). Compared to patients in the severe hypoxemia group, patients in the mild hypoxemia group demonstrated greater exercise tolerance (+ 80.0 m in 6MWD; p = 0.004) and higher nadir in SpO2 (+ 2.5%; p = 0.005). Dyspnoea and cough levels at the time of study visit were similar across groups.