RESUMO
BACKGROUND: Ventilation/perfusion inequalities impair gas exchange in acute respiratory distress syndrome (ARDS). Although increased dead-space ventilation (VD/VT) has been described in ARDS, its mechanism is not clearly understood. We sought to evaluate the relationships between dynamic variations in VD/VT and extra-pulmonary microcirculatory blood flow detected at sublingual mucosa hypothesizing that an altered microcirculation, which is a generalized phenomenon during severe inflammatory conditions, could influence ventilation/perfusion mismatching manifested by increases in VD/VT fraction during early stages of ARDS. METHODS: Forty-two consecutive patients with early moderate and severe ARDS were included. PEEP was set targeting the best respiratory-system compliance after a PEEP-decremental recruitment maneuver. After 60 min of stabilization, hemodynamics and respiratory mechanics were recorded and blood gases collected. VD/VT was calculated from the CO2 production ([Formula: see text]) and CO2 exhaled fraction ([Formula: see text]) measurements by volumetric capnography. Sublingual microcirculatory images were simultaneously acquired using a sidestream dark-field device for an ulterior blinded semi-quantitative analysis. All measurements were repeated 24 h after. RESULTS: Percentage of small vessels perfused (PPV) and microcirculatory flow index (MFI) were inverse and significantly related to VD/VT at baseline (Spearman's rho = - 0.76 and - 0.63, p < 0.001; R2 = 0.63, and 0.48, p < 0.001, respectively) and 24 h after (Spearman's rho = - 0.71, and - 0.65; p < 0.001; R2 = 0.66 and 0.60, p < 0.001, respectively). Other respiratory, macro-hemodynamic and oxygenation parameters did not correlate with VD/VT. Variations in PPV between baseline and 24 h were inverse and significantly related to simultaneous changes in VD/VT (Spearman's rho = - 0.66, p < 0.001; R2 = 0.67, p < 0.001). CONCLUSION: Increased heterogeneity of microcirculatory blood flow evaluated at sublingual mucosa seems to be related to increases in VD/VT, while respiratory mechanics and oxygenation parameters do not. Whether there is a cause-effect relationship between microcirculatory dysfunction and dead-space ventilation in ARDS should be addressed in future research.
RESUMO
OBJETIVO: Avaliar a razão entre espaço morto e volume corrente fisiológicos (V D/V T) como preditor do fracasso na extubação em 42 crianças ventiladas (idade média: 4,75 anos). MÉTODO: Prontidão para extubação foi determinada usando os critérios propostos pela 6ª Conferência Internacional de Consenso em Medicina Intensiva adaptados a crianças. RESULTADOS: A ventilação não invasiva (VNI) foi usada em quatro pacientes que desenvolveram insuficiência respiratória após a extubação; nenhum foi reintubado. Crianças que precisaram de VNI para evitar a reintubação tiveram razão V D/V T significativamente maior do que as que foram extubadas sem VNI (p < 0,001). O valor de corte da razão V D/V T foi 0,55, e a área sob a curva ROC foi 0,86. CONCLUSÃO: Nossos achados confirmam o bom valor preditivo do sucesso/fracasso do desmame pela razão V D/V T e sugere seu papel como preditor da necessidade de VNI após extubação.
OBJECTIVE: To evaluate the physiological deadspace/tidal volume ratio (V D/V T) as a predictor of extubation failure in 42 ventilated children (median age: 4.75 years). METHOD: Extubation readiness was determined using the criteria proposed by the 6th International Consensus Conference on Intensive Care Medicine adapted to children. RESULTS: Non-invasive ventilation (NIV) was used in four patients who developed respiratory failure after extubation; none was reintubated. Children who needed NIV to avoid reintubation had a significantly higher V D/V T ratio than those who were extubated without NIV (p < 0.001). The cut-off value of V D/V T ratio was 0.55 and the area under the receiver operating characteristic curve was 0.86. CONCLUSION: Our findings confirm the good predictive value of weaning success/failure of the V D/V T ratio and suggest its role for predicting the need for NIV after extubation.