Increased intrapulmonary shunt and alveolar dead space post-COVID-19

Increased intrapulmonary shunt (Q_S/Q_t) and alveolar dead space (V_D/V_T) are present in early recovery from 2019 Novel Coronavirus (COVID-19). We hypothesized patients recovering from severe critical acute illness (NIH category 3-5) would have greater and longer lasting increased Q_S/Q_t and V_D/V_T than patients with mild-moderate acute illness (NIH 1-2). Fifty-nine unvaccinated patients (33 males, aged 52 [38-61] yr, body mass index [BMI] 28.8 [25.3-33.6] kg/m²; median [IQR], 44 previous mild-moderate COVID-19, and 15 severe-critical disease) were studied 15-403 days postacute severe acute respiratory syndrome coronavirus infection. Breathing ambient air, steady-state mean alveolar Pco₂, and Po₂ were recorded simultaneously with arterial Po₂/Pco₂ yielding aAPco₂, AaPo₂, and from these, Q_S/Q_t%, V_D/V_T%, and relative alveolar ventilation (40 mmHg/[Formula: see text], VArel) were calculated. Median [Formula: see text] was 39.4 [35.6-41.1] mmHg, [Formula: see text] 92.3 [87.1-98.2] mmHg; [Formula: see text] 32.8 [28.6-35.3] mmHg, [Formula: see text] 112.9 [109.4-117.0] mmHg, AaPo₂ 18.8 [12.6-26.8] mmHg, aAPco₂ 5.9 [4.3-8.0] mmHg, Q_S/Q_t 4.3 [2.1-5.9] %, and V_D/V_T16.6 [12.6-24.4]%. Only 14% of patients had normal Q_S/Q_t and V_D/V_T; 1% increased Q_S/Q_t but normal V_D/V_T; 49% normal Q_S/Q_t and elevated V_D/V_T; 36% both abnormal Q_S/Q_t and V_D/V_T. Previous severe critical COVID-19 predicted increased Q_S/Q_t (2.69 [0.82-4.57]% per category severity [95% CI], P < 0.01), but not V_D/V_T. Increasing age weakly predicted increased V_D/V_T (1.6 [0.1-3.2]% per decade, P < 0.04). Time since infection, BMI, and comorbidities were not predictors (all P > 0.11). VArel was increased in most patients. In our population, recovery from COVID-19 was associated with increased Q_S/Q_t in 37% of patients, increased V_D/V_T in 86%, and increased alveolar ventilation up to ∼13 mo postinfection. NIH severity predicted Q_S/Q_t but not elevated V_D/V_T. Increased V_D/V_T suggests pulmonary microvascular pathology persists post-COVID-19 in most patients.NEW & NOTEWORTHY Using novel methodology quantifying intrapulmonary shunt and alveolar dead space in COVID-19 patients up to 403 days after acute illness, 37% had increased intrapulmonary shunt and 86% had elevated alveolar dead space likely due to independent pathology. Elevated shunt was partially related to severe acute illness, and increased alveolar dead space was weakly related to increasing age. Ventilation was increased in the majority of patients regardless of previous disease severity. These results demonstrate persisting gas exchange abnormalities after recovery.