Performing Accurate Standard 12 Lead ECGs on patients with Burns to the Chest.

The use of the electrocardiogram (ECG) in critical care settings is a long-established cardiovascular monitoring tool. The effectiveness of the routine 12-lead ECG relies on accurate lead placement that is consistent and replicable. Improper lead placement may display erroneous ECG patterns and affect patient management decisions.1,2 In the setting of an acute injury, such as a torso burn to the ventral surface, accurate lead placement may be compromised or impossible. The regional burn center, which is part of our organization, sees approximately 500 patients per year. Of those patients, burns to the chest accounted for 21% of admissions during 2020 and 2021. This significant fraction of burn injury patients requires modification of our standard approach to provide an accurate ECG. Baseline ECGs are routinely acquired on the burn unit per protocol and for monitoring of patient response to numerous pharmaceutical therapies.

Value and limitations of transpulmonary pressure calculations during intra-abdominal hypertension.

OBJECTIVE: To clarify the effect of progressively increasing intra-abdominal pressure on esophageal pressure, transpulmonary pressure, and functional residual capacity. DESIGN: Controlled application of increased intra-abdominal pressure at two positive end-expiratory pressure levels (1 and 10 cm H2O) in an anesthetized porcine model of controlled ventilation. SETTING: Large animal laboratory of a university-affiliated hospital. SUBJECTS: Eleven deeply anesthetized swine (weight 46.2 ± 6.2 kg). INTERVENTIONS: Air-regulated intra-abdominal hypertension (0-25 mm Hg). MEASUREMENTS: Esophageal pressure, tidal compliance, bladder pressure, and end-expiratory lung aeration by gas dilution. MAIN RESULTS: Functional residual capacity was significantly reduced by increasing intra-abdominal pressure at both positive end-expiratory pressure levels (p ≤ 0.0001) without corresponding changes of end-expiratory esophageal pressure. Above intra-abdominal pressure 5 mm Hg, plateau airway pressure increased linearly by ~ 50% of the applied intra-abdominal pressure value, associated with commensurate changes of esophageal pressure. With tidal volume held constant, negligible changes occurred in transpulmonary pressure due to intra-abdominal pressure. Driving pressures calculated from airway pressures alone (plateau airway pressure--positive end-expiratory pressure) did not equate to those computed from transpulmonary pressure (tidal changes in transpulmonary pressure). Increasing positive end-expiratory pressure shifted the predominantly negative end-expiratory transpulmonary pressure at positive end-expiratory pressure 1 cm H2O (mean -3.5 ± 0.4 cm H2O) into the positive range at positive end-expiratory pressure 10 cm H2O (mean 0.58 ± 1.2 cm H2O). CONCLUSIONS: Despite its insensitivity to changes in functional residual capacity, measuring transpulmonary pressure may be helpful in explaining how different levels of positive end-expiratory pressure influence recruitment and collapse during tidal ventilation in the presence of increased intra-abdominal pressure and in calculating true transpulmonary driving pressure (tidal changes of transpulmonary pressure). Traditional interpretations of respiratory mechanics based on unmodified airway pressure were misleading regarding lung behavior in this setting.

Positional effects on the distributions of ventilation and end-expiratory gas volume in the asymmetric chest-a quantitative lung computed tomographic analysis.

BACKGROUND: Body positioning affects the configuration and dynamic properties of the chest wall and therefore may influence decisions made to increase or decrease ventilating pressures and tidal volume. We hypothesized that unlike global functional residual capacity (FRC), component sector gas volumes and their corresponding regional tidal expansions would vary markedly in the setting of unilateral pleural effusion (PLEF), owing to shifting distributions of aeration and collapse as posture changed. METHODS: Six deeply anesthetized swine underwent tracheostomy, thoracostomy, and experimental PLEF with 10 mL/kg of radiopaque isotonic fluid randomly instilled into either pleural space. Animals were ventilated at VT = 10 mL/kg, frequency = 15 bpm, I/E = 1:2, PEEP = 1 cmH2O, and FiO2 = 0.5. Quantitative lung computed tomographic (CT) analysis of regional aeration and global FRC measurements by nitrogen wash-in/wash-out technique was performed in each of these randomly applied positions: semi-Fowler's (inclined 30° from horizontal in the sagittal plane); prone, supine, and lateral positions with dependent PLEF and non-dependent PLEF. RESULTS: No significant differences in total FRC were observed among the horizontal positions, either at baseline (p = 0.9037) or with PLEF (p = 0.58). However, component sector total gas volumes in each phase of the tidal cycle were different within all studied positions with and without PLEF (p = < .01). Compared to other positions, prone and lateral positions with non-dependent PLEF had more homogenous VT distributions among quadrants (p = .051). Supine position was associated with most dependent collapse and greatest tendency for tidal recruitment (48 vs ~ 22%, p = 0.0073). CONCLUSIONS: Changes in body position in the setting of effusion-caused chest asymmetry markedly affected the internal distributions of gas volume, collapse, ventilation, and tidal recruitment, even though global FRC measurements provided little indication of these potentially important positional changes.

Non-pulmonary factors strongly influence the stress index.

PURPOSE: A quantitative measure of the airway pressure-time tracing during passive inflation [stress index (SI)] has been suggested as an indicator of tidal lung recruitment and/or overinflation. If reliable, this simple index could help guide positive end-expiratory pressure (PEEP) and tidal volume selection. The compartment surrounding the lungs should impact airway pressure and could, therefore, affect SI validity. To explore the possibility, we determined SI in a swine model of pleural effusion (PLEF). METHODS: Unilateral PLEF was simulated by instilling fluid (13 ml/kg-moderate, 26 ml/kg-large) into the right pleural space of five anesthetized, paralyzed, mechanically ventilated pigs. Animals were ventilated with constant flow ventilation: tidal volume (V (T)) 9 ml/kg, f set to end-tidal CO2 (ETCO2) of 30-40 mmHg, inspiratory to expiratory ratio (I/E) 1:2, PEEP 1 or 10 cmH2O. Respiratory system mechanics and computed tomography (CT) were acquired at end-inspiration and end-expiration to determine % tidal recruitment and overinflation. RESULTS: Prior to PLEF instillation, SI values derived at PEEP = 1 and 10 cmH2O were 0.90 and 1.22, respectively. Moderate PLEF increased these SI values to 1.06 and 1.24 and large PLEF further increased SI to 1.23 and 1.27 despite extensive tidal recruitment and negligible overdistention by CT. The initial half of the tidal pressure curve produced SI values (range 0.82-1.17) that were significantly lower than those of the second half (0.98-1.37). CONCLUSIONS: In the presence of pleural fluid, SI indicated overinflation when virtually none was present and tidal lung recruitment predominated. When the extrapulmonary environment is abnormal, caregivers are advised to interpret the SI with caution.