# Mechanics Meet Perfusion: A Retrospective Cohort Study on Optimizing Ventilatory Parameters in Traumatic Flail Chest

## TL;DR

This study shows that combining lung mechanics and dead-space measurements can better predict outcomes in patients with traumatic flail chest, guiding ventilator settings more effectively than oxygenation alone.

## Contribution

The study introduces a novel approach to ventilator titration by integrating dead-space surrogates with lung mechanics in traumatic flail chest patients.

## Key findings

- High dead-space burden was associated with significantly higher ICU mortality (29.9% vs. 10.1%).
- Increased driving pressure correlated with higher mortality risk, while improved dynamic compliance was protective.
- High dead space also predicted worse ventilator-free days and longer ICU stays.

## Abstract

Background

A traumatic flail chest impairs chest wall mechanics and gas exchange. Bedside indices that integrate lung mechanics (driving pressure and dynamic compliance) with perfusion efficiency (dead-space surrogates) may guide ventilator titration more effectively than oxygenation alone.

Objective

To determine whether dead-space burden, driving pressure, and dynamic compliance are associated with intensive care unit (ICU) mortality and other clinically relevant outcomes (ventilator-free days to day 28 (VFD-28), ICU length of stay (LOS), barotrauma, and ICU-acquired pneumonia) in invasively ventilated adults with a flail chest.

Methods

We conducted a retrospective cohort study in the Anesthesia Department of Lady Reading Hospital (Peshawar, Pakistan). Consecutive adults with flail chest admitted between March 1, 2024, and February 28, 2025, were included. Exposures were time-weighted mechanics (driving pressure and dynamic compliance) and dead-space measures, including alveolar dead-space fraction (AVDSf) when available or ventilatory ratio (VR) otherwise. The primary outcome was ICU mortality. Secondary outcomes were VFD-28, ICU LOS, barotrauma, and ICU-acquired pneumonia. The pre-specified models included multivariable logistic, negative binomial, quasi-Poisson, Fine-Gray competing risk, and time-updated mixed-effects analyses.

Results

Of the 318 patients screened, 272 (85.5%) met the inclusion criteria. High dead space (AVDSf ≥ 0.25 or VR ≥ 1.5) occurred in 134/272 (49.3%) patients. ICU mortality was 54/272 (19.9%) overall and higher with high versus low dead space (40/134, 29.9% vs. 14/138, 10.1%; risk ratio = 2.97; 95% CI = 1.73-5.09; χ² (1) = 16.59; P < 0.001). In the adjusted models, high dead space remained associated with mortality (adjusted odds ratio (aOR) = 2.21; 95% CI = 1.24-3.93; z = 2.69; P = 0.007). Each 1-cmH₂O increase in driving pressure increased mortality risk (aOR = 1.05; 95% CI = 1.01-1.09; z = 2.51; P = 0.012), whereas each 10-mL/cmH₂O increase in dynamic compliance was protective (aOR = 0.82; 95% CI = 0.70-0.96; z = −2.46; P = 0.014). High dead space was associated with lower VFD-28 (adjusted rate ratio = 0.83; 95% CI = 0.71-0.98; z = −2.27; P = 0.023) and longer ICU LOS (incidence rate ratio (IRR) = 1.22; 95% CI = 1.05-1.41; z = 2.64; P = 0.008). Barotrauma occurred in 36/272 (13.2%) patients and was tracked with a higher driving pressure (subhazard ratio (SHR) per +5 cmH₂O = 1.58; 95% CI = 1.02-2.47; z = 2.23; P = 0.026).

Conclusion

In a traumatic flail chest, integrating dead-space surrogates with driving pressure and dynamic compliance identifies high-risk ventilatory phenotypes and correlates with clinically relevant outcomes. Pending prospective validation, a practical titration bundle, routinely calculating and trending VR or AVDSf alongside driving pressure, aiming for a VR <1.5 and a driving pressure in the low-teens (e.g., ≤14 cmH₂O) while maintaining adequate perfusion, may complement analgesia and surgical stabilization pathways and help standardize ventilator management in trauma ICUs.