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Abstract Background The association between bedside ventilatory parameters—specifically arterial carbon dioxide pressure (PaCO2) and ventilatory ratio (VR)—and mortality in patients with acute respiratory distress syndrome (ARDS) remains a topic of debate. Additionally, the persistence of this association over time is unclear. This study aims to investigate the relationship between 28-day mortality in ARDS patients and their longitudinal exposure to ventilatory inefficiency, as reflected by serial measurements of PaCO2 and VR. Methods We conducted a secondary analysis of four randomized controlled trials (FACTT, ALTA, EDEN, and SAILS) from the ARDS Network. All included patients were intubated and received mechanical ventilation. Patients were excluded if they underwent extracorporeal life support or were on mechanical ventilation for less than one day. The primary outcome was 28-day mortality. Bayesian joint models were employed to estimate the strength of associations over time. Results A total of 2,851 patients were included in our analysis. The overall 28-day mortality rate was 21.3%, with a median duration of invasive mechanical ventilation of 9 days (IQR: 4–28 days). After adjustment, each daily increment in PaCO2 (HR 1.008, 95% CI 0.997–1.018) was not associated with mortality, while a daily increment in VR (HR 1.548, 95% CI 1.309–1.835) was associated with increased mortality. This association persisted during the prolonged stages (Days 0–23) of mechanical ventilation. Furthermore, a significant increase in the risk of death was related to daily exposure to VR > 2 (HR 1.088 per day, 95% CI 1.034–1.147) and its cumulative effect (HR 1.085 per area, 95% CI 1.050–1.122), whereas PaCO2 was found to be insignificant. Conclusion VR, which reflects ventilatory inefficiency, should be closely monitored during invasive mechanical ventilation. Cumulative exposure to high intensities of VR may be associated with increased mortality in patients with ARDS.

Background: The dead space fraction (VD/VT) has proven to be a powerful predictor of higher mortality in acute respiratory distress syndrome (ARDS). However, its measurement relies on expired carbon dioxide, limiting its widespread application in clinical practice. Several estimates employing routine variables have been found to be reliable substitutes for direct measurement of VD/VT. In this study, we evaluated the prognostic value of these dead space estimates obtained in the first 7 days following the initiation of ventilation. Methods: This retrospective observational study was conducted using data from the Chinese database in intensive care (CDIC). Eligible participants were adult ARDS patients receiving invasive mechanical ventilation while in the intensive care unit between 1st January 2014 and 31st March 2021. We collected data during the first 7 days of ventilation to calculate various dead space estimates, including ventilatory ratio (VR), corrected minute ventilation (V˙Ecorr), VD/VT (Harris–Benedict), VD/VT (Siddiki estimate), and VD/VT (Penn State estimate) longitudinally. A time-dependent Cox model was used to handle these time-varying estimates. Results: A total of 392 patients (median age 66 [interquartile range: 55–77] years, median SOFA score 9 [interquartile range: 7–12]) were finally included in our analysis, among whom 132 (33.7%) patients died within 28 days of admission. VR (hazard ratio [HR]=1.04 per 0.1 increase, 95% confidence interval [CI]: 1.01 to 1.06; P=0.013), V˙Ecorr (HR=1.08 per 1 increase, 95% CI: 1.04 to 1.12; P < 0.001), VD/VT (Harris–Benedict) (HR=1.25 per 0.1 increase, 95% CI: 1.06 to 1.47; P=0.006), and VD/VT (Penn State estimate) (HR=1.22 per 0.1 increase, 95% CI: 1.04 to 1.44; P=0.017) remained significant after adjustment, while VD/VT (Siddiki estimate) (HR=1.10 per 0.1 increase, 95% CI: 1.00 to 1.20; P=0.058) did not. Given a large number of negative values, VD/VT (Siddiki estimate) and VD/VT (Penn State estimate) were not recommended as reliable substitutes. Long-term exposure to VR >1.3, V˙Ecorr >7.53, and VD/VT (Harris–Benedict) >0.59 was independently associated with an increased risk of mortality in ARDS patients. These findings were validated in the fluid and catheter treatment trial (FACTT) database. Conclusions: In cases where VD/VT cannot be measured directly, early time-varying estimates of VD/VT such as VR, V˙Ecorr, and VD/VT (Harris–Benedict) can be considered for predicting mortality in ARDS patients, offering a rapid bedside application.

Underground telecommunication cables are highly susceptible to damage from excavation activities. Preventing accidental damage to underground telecommunication cables is critical and necessary. In this study, we present field trial results of monitoring excavation activities near underground fiber cables using an intensity-based phase-sensitive optical time-domain reflectometer (φ-OTDR). The reasons for choosing intensity-based φ-OTDR for excavation monitoring are presented and analyzed. The vibration signals generated by four typical individual excavation events, i.e., cutting, hammering, digging, and tamping at five different field trial sites, as well as five different mixed events in the fifth field trial site were investigated. The findings indicate that various types of events can generate vibration signals with different features. Typically, fundamental peak frequencies of cutting, hammering and tamping events ranged from 30 to 40 Hz, 11 to 15 Hz, and 30 to 40 Hz, respectively. Digging events, on the other hand, presented a broadband frequency spectrum without a distinct peak frequency. Moreover, due to differences in environmental conditions, even identical excavation events conducted with the same machine may also generate vibration signals with different characteristics. The diverse field trial results presented offer valuable insights for both research and the practical implementation of excavation monitoring techniques for underground cables.