The GC is a sensitive respiratory detection device; however, the GC/BNCPAP interface requires a minimum Ti of 0.3 sec and an adequate respiratory effort to achieve the desired pressure and to synchronously trigger the BNCPAP.
Background Nasal intermittent positive pressure ventilation (NIPPV) is a widely used mode of support in neonates, during which ventilator inflations may or may not coincide with spontaneous breathing. Objective We tested the hypothesis that inflations delivered with NIPPV via RAM ® cannula and not accompanied by patient effort produce minimal tidal volume as measured by respiratory inductance plethysmography. Design/Methods Fourteen subjects were monitored while receiving NIPPV. We compared tidal volumes during ventilatorsupported breaths, unsupported breaths, and ventilator inflations not accompanied by patient effort (defined using electrical activity of the diaphragm). Results Mean tidal volumes in arbitrary units were 0.30 ± 0.22 in NIPPV inflations associated with patient effort and 0.27 ± 0.15 in spontaneous breaths without ventilator assistance (p = 0.82). Tidal volumes during ventilator-only inflations were 0.06 ± 0.04 (p < 0.005 vs. both ventilator-assisted and unassisted efforts). Conclusions NIPPV via RAM cannula produces minimal, clinically insignificant tidal volumes during non-spontaneous inflations.
Accurate mechanics measurements during high-frequency oscillatory ventilation (HFOV) facilitate optimizing ventilator support settings. Yet, these are influenced substantially by endotracheal tube (ETT) contributions, which may dominate when leaks around uncuffed ETT are present. We hypothesized that 1) the effective removal of ETT leaks may be confirmed via direct comparison of measured vs. model-predicted mean intratracheal pressure [mPtr (meas) vs. mPtr (pred)], and 2) reproducible respiratory system resistance (Rrs) and compliance (Crs) may be derived from no-leak oscillatory Ptr and proximal flow. With the use of ETT test-lung models, proximal airway opening (Pao) and distal (Ptr) pressures and flows were measured during slow-cuff inflations until leaks are removed. These were repeated for combinations of HFOV settings [frequency, mean airway pressure (Paw), oscillation amplitudes (ΔP), and inspiratory time (%t(I))] and varying test-lung Crs. Results showed that leaks around the ETT will 1) systematically reduce the effective distending pressures and lung-delivered oscillatory volumes, and 2) derived mechanical properties are increasingly nonphysiologic as leaks worsen. Mean pressures were systematically reduced along the ventilator circuit and ETT (Paw > Pao > Ptr), even for no-leak conditions. ETT size-specific regression models were then derived for predicting mPtr based on mean Pao (mPao), ΔP, %t(I), and frequency. Next, in 10 of 11 studied preterm infants (0.77 ± 0.24 kg), no-to-minimal leak was confirmed based on excellent agreement between mPtr (meas) and mPtr (pred), and consequently, their oscillatory respiratory mechanics were evaluated. Infant resistance at the proximal ETT (R(ETT); resistance airway opening = R(ETT) + Rrs; P < 0.001) and ETT inertance (P = 0.014) increased significantly with increasing ΔP (50%, 100%, and 150% baseline), whereas Rrs showed a modest, nonsignificant increase (P = 0.14), and Crs was essentially unchanged (P = 0.39). We conclude that verifying no-leak conditions is feasible by comparison of model-derived vs. distending mPtr (meas). This facilitated the reliable and accurate assessment of physiologic respiratory mechanical properties that can objectively guide ventilatory management of HFOV-treated preterm infants.
SummaryWe compared three methods of reporting maximal expiratory flow (V′max FRC ) measured in partial expiratory flow-volume curves (PEFVCs) at the point of functional residual capacity (FRC). PEFVCs were obtained with the rapid thoracoabdominal compression technique (RTC) on a total of 446 occasions in 281 HIV-negative, asymptomatic infants (4.8-28.1 months old). Three different expressions of V′max FRC were recorded: 1) the highest measured flow (maxV′ FRC ), 2) the mean of the three highest flows (mean3V′ FRC ), and 3) the flow at FRC in a composite curve (compV′ FRC ) consisting of PEFVCs, obtained at different jacket pressures and superimposed at their distal limb. The numerical value of maxV′ FRC was 7.4% (±5.6%) higher than the mean3V
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Author Manuscript Author ManuscriptAuthor ManuscriptAuthor Manuscript ′ FRC , and 11.9% (±17.7%) higher than the compV′ FRC ; the mean3V′ FRC was 5% (±18.3%) higher than the compV′ FRC . Bland-Altman analysis was used to evaluate the agreement between the three indices. The mean difference and 95% limits of agreement were: maxV′ FRC − mean3V′ FRC , 14±18 ml/sec; maxV′ FRC − compV ′ FRC , 23±58 ml/sec; and mean3V′ FRC − compV′ FRC , 10±52 ml/sec. The differences between the slopes of the three indices (regressed against height) were statistically significant, although clinically unimportant. We conclude that despite their high correlation, the mean3V′ FRC and maxV′ FRC should not be used interchangeably, and that the composite analysis, although useful, does not improve the reproducibility of V′max FRC , and thus it cannot be recommended for routine use in its current form.
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