End-Tidal Carbon Dioxide Pressure Measurement after Prolonged Inspiratory Time Gives a Good Estimation of the Arterial Carbon Dioxide Pressure in Mechanically Ventilated Patients

Impaired Capillary Recruitment Capacity in Obesity: A Subgroup Analysis of Prospective Observational Study on Anesthesia Effects

BACKGROUND This subgroup analysis of prospective observational research, involving 71 participants, compared the effects of anesthesia on microvascular reactivity in obese vs lean individuals using near-infrared spectroscopy and vascular occlusion tests. The correlation between the body mass index (BMI) and microvascular reactivity under general anesthesia was also investigated. MATERIAL AND METHODS This study enrolled adult patients classified as American Society of Anesthesiologists physical status I or II, undergoing elective surgery under general anesthesia. The microcirculatory variables measured before (Tpre) and 30 min following the induction of anesthesia (Tpost) were as follows: baseline tissue oxygen saturation (StO₂), occlusion slope (∇occl), and recovery slope (∇recov). The patients were grouped according to their BMI (lean [BMI <25 kg/m²] vs obese [BMI ≥25 kg/m²]). Data are presented as medians and interquartile ranges. RESULTS There were 43 patients in the lean group and 28 in the obese group. At Tpre, baseline StO2, ∇occl, and ∇recov were not different between the 2 groups (P=0.860, 0.659, and 0.518, respectively). At Tpost, the baseline StO₂ and ∇occl were not different between the 2 groups (P=0.343 and 0.791); however, the ∇recov was lower in the obese group than in the lean group (3.245 [2.737, 3.977] vs 4.131 [3.491, 4.843], P=0.003). At Tpost, BMI showed a moderate correlation with ∇recov (correlation coefficient: -0.319, P=0.007). CONCLUSIONS In obese patients, capillary recruitment capacity during general anesthesia is compromised compared to lean patients.

Capnometry after an inspiratory breath hold, PLAT CO2 , as a surrogate for P aCO 2 ${P}_{{\mathrm{aCO}}_{2}}$ in mild to moderate pediatric acute respiratory distress syndrome: A feasibility study

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-tidalP CO 2 ${P}_{{\mathrm{CO}}_{2}}$ measured immediately after a 3-s inspiratory-hold (PLAT CO2 ) by capnometry andP 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-tidalP 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, recordingP 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 ofP 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 thanP 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 betweenP 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 forP 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 andP aCO 2 ${P}_{{\mathrm{aCO}}_{2}}$ was -0.4 ± 3.5 mmHg (LoA -7.2 to 6.4), and betweenP ETCO 2 ${P}_{{\mathrm{ETCO}}_{2}}$ andP 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.