Breath-to-breath analysis of abdominal and rib cage motion in surfactant-depleted piglets during high-frequency oscillatory ventilation

Monitoring Lung Volumes During Mechanical Ventilation

Respiratory inductive plethysmography (RIP) is a non-invasive method of measuring change in lung volume which is well-established as a monitor of tidal ventilation and thus respiratory patterns in sleep medicine. As RIP is leak independent, can measure end-expiratory lung volume as well as tidal volume and is applicable to both the ventilated and spontaneously breathing patient, there has been a recent interest in its use as a bedside tool in the intensive care unit.

Effect of sustained inflation vs. stepwise PEEP strategy at birth on gas exchange and lung mechanics in preterm lambs

BACKGROUND

Sustained inflation (SI) at birth facilitates establishment of functional residual capacity (FRC) in the preterm lung, but the ideal lung recruitment strategy is unclear. We have compared the effect of SI and a stepwise positive end-expiratory pressure (PEEP; SEP) strategy in a preterm model.

METHODS

127 d gestation lambs received either 20-s SI (n = 9) or 2 cmH2O stepwise PEEP increases to 20 cmH2O every 10 inflations, and then decreases to 6 cmH2O (n = 10). Ventilation continued for 70 min, with surfactant administered at 10 min. Alveolar-arterial oxygen gradient (AaDO2), compliance (C(dyn)), end-expiratory thoracic volume (EEVRIP; respiratory inductive plethysmography), and EEV and C(dyn) in the gravity-dependent and nondependent hemithoraces (electrical impedance tomography) were measured throughout. Early mRNA markers of lung injury were analyzed using quantitative real-time PCR.

RESULTS

From 15 min of life, AaDO2 was lower in SEP group (P < 0.005; two-way ANOVA). SEP resulted in higher and more homogeneous C(dyn) (P < 0.0001). Mean (SD) EEVRIP at 5 min was 18 (9) ml/kg and 6 (5) ml/kg following SEP and SI, respectively (P = 0.021; Bonferroni posttest); this difference was due to a greater nondependent hemithorax EEV. There was no difference in markers of lung injury.

CONCLUSION

An SEP at birth improved gas exchange, lung mechanics, and EEV, without increasing lung injury, compared to the SI strategy used.

Bench test assessment of mainstream capnography during high frequency oscillatory ventilation

To assess the feasibility, stability and predictability of pCO2 measurement (PETCO2) using a main stream capnograph in a high frequency oscillatory ventilation circuit. A commercially available capnograph was mounted into a high frequency oscillatory ventilator patient circuit, adjustable CO2 flow was introduced into an artificial lung and the output of the CO2 sensor assessed under varying ventilator settings. Influence of oxygen content, pressures, heat and moisture were recorded. A linear relationship between CO2 flow rate and PETCO2 was found. Varying ventilator settings influenced the measurements, but the results for PETCO2 remained within a range of 1.5 mmHg above or under then mean measurement value. Measurements remained stable despite humidification, heat, pressure amplitudes or mean airway pressure changes. From this bench test, we conclude it is feasible to measure PETCO2 using a main stream capnograph during high frequency oscillatory conditions, these measurements were stable during the experiment. Changes in CO2 production or output can be detected. The system may prove to be of clinical value, but further in vivo measurements are warranted.

Manual vibration increases expiratory flow rate via increased intrapleural pressure in healthy adults: an experimental study

QUESTION

What is the relationship between vibration of the chest wall and the resulting chest wall force, chest wall circumference,intrapleural pressure, and expiratory flow rate? Is the change in intrapleural pressure during vibration the sum of the intrapleural pressure due to recoil of the lung, chest wall compression, and chest wall oscillation?

DESIGN

Randomised, within-subject,experimental study.

PARTICIPANTS

Seven experienced cardiopulmonary physiotherapists and three healthy adults.

INTERVENTION

Vibration (compression + oscillation), compression alone, and oscillation alone were applied manually to the chest walls of healthy participants during passive exertion and compared with passive expiration alone.

OUTCOME MEASURES

Chest wall force, chest wall circumference, intrapleural pressure, and expiratory flow rate.

RESULTS

During vibration, coherence was high(r2 > 0.97) between external chest wall force, chest wall circumference, intrapleural pressure, and expiratory flow. The mean change in intrapleural pressure during vibration was 9.55 cmH2O (SD 1.66), during chest compression alone was 8.06 cmH2O(SD 1.65), during oscillation alone was 7.93 cmH2O (SD 1.57), and during passive expiration alone was 6.82 cmH2O (SD 1.51). During vibration, compression contributed 13% of the change in intrapleural pressure, oscillation contributed 12%, and lung recoil contributed the remaining 75%.

CONCLUSIONS

During vibration the chest behaves as a highly linear system. Changes in intrapleural pressure occurring during vibration appear to be the sum of changes in pressure due to lung recoil and the compressive and oscillatory components of the technique, which suggests that all three components are required to optimise expiratory flow.