Partitioning of respiratory system resistance in children with respiratory insufficiency

Non-interventional monitoring of expiratory flow limitation during experimental mechanical ventilation

Background

Expiratory flow limitation (EFL) is common among patients in the intensive care unit under mechanical ventilation (MV) and may have significant clinical consequences. In the present study, we examine the possibility of non-interventional detection of EFL during experimental MV.

Methods

Eight artificially ventilated New Zealand rabbits were included in the experiments. EFL was induced during MV by application of negative expiratory pressure (−5, −8 and −10 hPa) and detected by the negative expiratory pressure technique. Airway pressure (P_aw) and gas flow (V′) were digitally recorded and processed off-line for the evaluation of respiratory mechanics. The method is based on the computation and monitoring of instantaneous respiratory resistance R_rs(t). The resistive pressure (P_aw,res(t)) is calculated by subtracting from P_aw its elastic component and the end-expiratory pressure, as assessed by linear regression. Then, R_rs(t) is computed as the instant ratio P_aw,res(t)/V′(t).

Results

Two completely different patterns of expiratory R_rs(t) separate the cases with EFL from those without EFL. Small and random fluctuations are noticed when EFL is absent, whereas the onset of EFL is accompanied by an abrupt and continuous rise in R_rs(t), towards the end of expiration. Thus, EFL is not only detected but may also be quantified from the volume still to be expired at the time EFL occurs.

Conclusion

The proposed technique is a simple, accurate and non-interventional tool for EFL monitoring during MV.

Respiratory system resistance in expiratory flow limitation during mechanical ventilationhttps://bit.ly/34hU6Bv

Effect of increasing inspiratory time on respiratory mechanics in mechanically ventilated neonates

OBJECTIVE

To investigate the effect of inspiratory time and inspiratory flow on the respiratory mechanics of intubated and ventilated neonates.

DESIGN

Physiology study.

SETTING

Tertiary university neonatal intensive care unit.

PATIENTS

Neonates requiring mechanical ventilation with (group 1, n = 9) and without lung disease (group 2, n = 6).

INTERVENTIONS

All infants were ventilated with a Servo 900C Siemens ventilator in the volume-controlled constant-flow mode. Flow and pressure were measured at the Y-piece, while different inspiratory times (25%, 33%, 50%, and 67% of the respiratory cycle) were applied randomly without changing tidal volume.

MEASUREMENTS

The constant flow end-inspiratory airway occlusion technique allowed partitioning of the total respiratory system resistance (R(tot,rs)) into a standard intrinsic flow resistance (R(int,rs)) and a lung/thorax tissue viscoelastic component (DeltaR(rs)), and it allowed partitioning of the dynamic respiratory system elastance (E(dyn,rs)) into a static (E(st,rs)) and a lung/thorax tissue viscoelastic component (DeltaE(rs)). A two-compartment model of the respiratory system was applied to the experimental data.

MAIN RESULTS

All respiratory mechanics components were significantly higher in group 1 compared with group 2. Both groups showed increasing R(int,rs) with increasing flow and increasing DeltaR(rs) with increasing inspiratory time. DeltaR(rs) represented 40% to 75% of R(tot,rs) whatever the group. E(dyn,rs) and E(st,rs) changed with inspiratory time in the very low (<0.4 secs) and the very long inspiratory time range (>1.0 secs). No change was found when clinically, commonly used inspiratory times were applied (0.4-1.0 secs). DeltaE(rs) represented 17% to 19% of E(dyn,rs). The relationship between DeltaR(rs) and increasing inspiratory time fitted the exponential two-compartment model (r =.99, p <.001).

CONCLUSIONS

Total respiratory mechanics and its components in ventilated newborns with and without lung disease showed inspiratory time dependence. DeltaR(rs) increased with increasing inspiratory time as predicted by the two-compartment lung model, whereas standard R(int,rs) and E(dyn,rs) decreased.