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

Abstract

Increased intrapulmonary shunt(QS/Qt) and alveolar dead space(VD/VT) are present in early recovery from COVID-19. We hypothesized patients recovering from severe-critical acute illness(NIH category 3-5) would have greater and longer-lasting increased QS/Qt and VD/VT than patients with mild-moderate acute illness(NIH 1-2). Methods: 59 unvaccinated patients (33 male, age 52[38-61] years, 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 post-acute SARS-CoV-2 infection. Breathing ambient air, steady-state mean alveolar PCO2 and PO2 were recorded simultaneously with arterial PO2/PCO2 yielding aAPCO2, AaPO2, and from these, QS/Qt%, VD/VT%, and relative alveolar ventilation (40 mmHg/PACO2, VArel) calculated. Results: Median PaCO2 was 39.4[35.6-41.1] mmHg, PaO2 92.3[87.1-98.2mmHg; PACO2 32.8[28.6-35.3] mmHg, PAO2 112.9[109.4-117.0] mmHg, AaPO2 18.8[12.6-26.8] mmHg, aAPCO2 5.9 [4.3-8.0] mmHg, QS/Qt 4.3 [2.1-5.9] % and VD/VT16.6 [12.6-24.4] %. Only 14% of patients had normal QS/Qt and VD/VT;1% increased QS/Qt but normal VD/VT; 49% normal QS/Qt and elevated VD/VT;36% both abnormal QS/Qt and VD/VT. Previous severe-critical COVID-19 predicted increased QS/Qt (2.69 [0.82-4.57]% per category severity [95% CI], p<0.01), but not VD/VT. Increasing age weakly predicted increased VD/VT (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. Conclusions: In our population, recovery from COVID-19 was associated with increased QS/Qt in 37% of patients, increased VD/VT in 86%, and increased alveolar ventilation up to ~13 months post infection. NIH severity predicted QS/Qt but not elevated VD/VT. Increased VD/VT suggests pulmonary micro-vascular pathology persists post COVID-19 in most patients.

Recent advances in cardiorespiratory monitoring in acute respiratory distress syndrome patients

“…In a seminal study, Nuckton et al demonstrated that physiological dead space is significantly higher in non-ARDS survivors than in survivors [ 18 ]. Like in ARDS patients, COVID-19 pneumonia is characterized by an increase in minute ventilation and an increase in the dead space fraction [ 19 , 20 ]. Additionally, in COVID-19 ARDS patients, there is a significant association between the amount of dead space computed in the first 7 days and mortality [ 21 ].…”