RESUMEN
We report the feasibility of a combined approach of very low low tidal volume (VT) and mild therapeutic hypothermia (MTH) to decrease the ventilatory load in a severe COVID-19-related acute respiratory distress syndrome (ARDS) cohort. Inclusion criteria was patients ≥18-years-old, severe COVID-19-related ARDS, driving pressure ∆P >15 cmH2O despite low-VT strategy, and extracorporeal therapies not available. MTH was induced with a surface cooling device aiming at 34°C. MTH was maintained for 72 h, followed by rewarming of 1°C per day. Data were shown in median (interquartile range, 25%-75%). Mixed effects analysis and Dunnett's test were used for comparisons. Seven patients were reported. Ventilatory load decreased during the first 24 h, minute ventilation (VE) decreased from 173 (170-192) to 152 (137-170) mL/kg/min (P = 0.007), and mechanical power (MP) decreased from 37 (31-40) to 29 (26-34) J/min (P = 0.03). At the end of the MTH period, the VT, P, and plateau pressure remained consistently close to 3.9 mL/kg predicted body weight, 12 and 26 cmH2O, respectively. A combined strategy of MTH and ultraprotective mechanical ventilation (MV) decreased VE and MP in severe COVID-19-related ARDS. The decreasing of ventilatory load may allow maintaining MV within safety thresholds.
Asunto(s)
Presión de las Vías Aéreas Positiva Contínua , Lesión Pulmonar , Humanos , Diafragma , Lesión Pulmonar/terapia , Pulmón , TóraxRESUMEN
OBJECTIVE: Accurate and reliable noninvasive methods to estimate gas exchange are necessary to guide clinical decisions to avoid frequent blood samples in children with pediatric acute respiratory distress syndrome (PARDS). We aimed to investigate the correlation and agreement between end-tidal P CO 2 ${P}_{{\mathrm{CO}}_{2}}$ measured immediately after a 3-s inspiratory-hold (PLAT CO2 ) by capnometry and P aCO 2 ${P}_{{\mathrm{aCO}}_{2}}$ measured by arterial blood gases (ABG) in PARDS. DESIGN: Prospective cohort study. SETTING: Seven-bed Pediatric Intensive Care Unit, Hospital El Carmen de Maipú, Chile. PATIENTS: Thirteen mechanically ventilated patients aged ≤15 years old undergoing neuromuscular blockade as part of management for PARDS. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: All patients were in volume-controlled ventilation mode. The regular end-tidal P CO 2 ( P ETCO 2 ) ${P}_{{\mathrm{CO}}_{2}}({P}_{{\mathrm{ETCO}}_{2}})$ (without the inspiratory hold) was registered immediately after the ABG sample. An inspiratory-hold of 3 s was performed for lung mechanics measurements, recording P ETCO 2 ${P}_{{\mathrm{ETCO}}_{2}}$ in the breath following the inspiratory-hold. (PLAT CO2 ). End-tidal alveolar dead space fraction (AVDSf) was calculated as [ ( P aCO 2 - P ETCO 2 ) / P aCO 2 ] $[({P}_{{\mathrm{aCO}}_{2}}\mbox{--}{P}_{{\mathrm{ETCO}}_{2}})/{P}_{{\mathrm{aCO}}_{2}}]$ and its surrogate (S)AVDSf as [ ( PLAT CO 2 - P ETCO 2 ) / PLAT CO 2 ] $[{(}_{\mathrm{PLAT}}{\mathrm{CO}}_{2}\mbox{--}{P}_{{\mathrm{ETCO}}_{2}}){/}_{\mathrm{PLAT}}{\mathrm{CO}}_{2}]$ . Measurements of P aCO 2 ${P}_{{\mathrm{aCO}}_{2}}$ were considered the gold standard. We performed concordance correlation coefficient (ρc), Spearman's correlation (rho), and Bland-Altmann's analysis (mean difference ± SD [limits of agreement, LoA]). Eleven patients were included, with a median (interquartile range) age of 5 (2-11) months. Tidal volume was 5.8 (5.7-6.3) mL/kg, PEEP 8 (6-8), driving pressure 10 (8-11), and plateau pressure 17 (17-19) cm H2 O. Forty-one paired measurements were analyzed. P aCO 2 ${P}_{{\mathrm{aCO}}_{2}}$ was higher than P ETCO 2 ${P}_{{\mathrm{ETCO}}_{2}}$ (52 mmHg [48-54] vs. 42 mmHg [38-45], p < 0.01), and there were no significant differences with PLAT CO2 (50 mmHg [46-55], p > 0.99). The concordance correlation coefficient and Spearman's correlation between P aCO 2 ${P}_{{\mathrm{aCO}}_{2}}$ and PLAT CO2 were robust (ρc = 0.80 [95% confidence interval [CI]: 0.67-0.90]; and rho = 0.80, p < 0.001.), and for P ETCO 2 ${P}_{{\mathrm{ETCO}}_{2}}$ were weak and strong (ρc = 0.27 [95% CI: 0.15-0.38]; and rho = 0.63, p < 0.01). The bias between PLAT CO2 and P aCO 2 ${P}_{{\mathrm{aCO}}_{2}}$ was -0.4 ± 3.5 mmHg (LoA -7.2 to 6.4), and between P ETCO 2 ${P}_{{\mathrm{ETCO}}_{2}}$ and P aCO 2 ${P}_{{\mathrm{aCO}}_{2}}$ was -8.5 ± 4.1 mmHg (LoA -16.6 to -0.5). The correlation between AVDSf and (S)AVDSf was moderate (rho = 0.55, p < 0.01), and the mean difference was -0.5 ± 5.6% (LoA -11.5 to 10.5). CONCLUSION: This pilot study showed the feasibility of measuring end-tidal CO2 after a 3-s end-inspiratory breath hole in pediatric patients undergoing controlled ventilation for ARDS. Encouraging preliminary results warrant further study of this technique.
RESUMEN
OBJECTIVES: To examine frictional, viscoelastic, and elastic resistive components, as well threshold pressures, during volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV) in pediatric patients with acute respiratory distress syndrome (ARDS). DESIGN: Prospective cohort study. SETTING: Seven-bed PICU, Hospital El Carmen de Maipú, Chile. PATIENTS: Eighteen mechanically ventilated patients less than or equal to 15 years old undergoing neuromuscular blockade as part of management for ARDS. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: All patients were in VCV mode during measurement of pulmonary mechanics, including: the first pressure drop (P1) upon reaching zero flow during the inspiratory hold, peak inspiratory pressure (PIP), plateau pressure (P PLAT ), and total positive end-expiratory pressure (tPEEP). We calculated the components of the working pressure, as defined by the following: frictional resistive = PIP-P1; viscoelastic resistive = P1-P PLAT ; purely elastic = driving pressure (ΔP) = P PLAT -tPEEP; and threshold = intrinsic PEEP. The procedures and calculations were repeated on PCV, keeping the same tidal volume and inspiratory time. Measurements in VCV were considered the gold standard. We performed Spearman correlation and Bland-Altman analysis. The median (interquartile range [IQR]) for patient age was 5 months (2-17 mo). Tidal volume was 5.7 mL/kg (5.3-6.1 mL/kg), PIP cm H 2 O 26 (23-27 cm H 2 O), P1 23 cm H 2 O (21-26 cm H 2 O), P PLAT 19 cm H 2 O (17-22 cm H 2 O), tPEEP 9 cm H 2 O (8-9 cm H 2 O), and ΔP 11 cm H 2 O (9-13 cm H 2 O) in VCV mode at baseline. There was a robust correlation (rho > 0.8) and agreement between frictional resistive, elastic, and threshold components of working pressure in both modes but not for the viscoelastic resistive component. The purely frictional resistive component was negligible. Median peak inspiratory flow with decelerating-flow was 21 (IQR, 15-26) and squared-shaped flow was 7 L/min (IQR, 6-10 L/min) ( p < 0.001). CONCLUSIONS: P PLAT , ΔP, and tPEEP can guide clinical decisions independent of the ventilatory mode. The modest purely frictional resistive component emphasizes the relevance of maintaining the same safety limits, regardless of the selected ventilatory mode. Therefore, peak inspiratory flow should be studied as a mechanism of ventilator-induced lung injury in pediatric ARDS.