Tidal volume delivery during nasal intermittent positive pressure ventilation: infant cannula vs. nasal continuous positive airway pressure prongs.

OBJECTIVE: To measure tidal volume delivery during nasal intermittent positive pressure ventilation with two nasal interfaces: infant cannula and nasal prongs. STUDY DESIGN: A single-center crossover study of neonates with mild respiratory distress. Fifteen preterm neonates were randomized to initial interface of infant cannula or nasal prongs and monitored on a sequence of pressure settings first on the initial interface, then repeated on the alternate interface. We compared relative tidal volumes between the two interfaces with two-way repeated measures ANOVA during three breath types: synchronized (I), patient effort without ventilator breaths (II), and ventilator breaths without patient effort (III). Clinical trial #NCT04326270. RESULTS: Type III breaths delivered no significant tidal volume. No significant difference was measured in relative tidal volume delivery between the interfaces when breath types were matched. CONCLUSIONS: Nasal intermittent positive pressure ventilation delivers neither clinically nor statistically significant tidal volume with either infant cannula or nasal prongs.

Work of Breathing in Premature Neonates: Noninvasive Neurally-Adjusted Ventilatory Assist versus Noninvasive Ventilation.

BACKGROUND: We tested whether work of breathing in premature newborns estimated by phase angle (θ) by using respiratory inductance plethysmography is decreased during neurally-adjusted ventilatory assist (NAVA) noninvasive ventilation (NIV) versus NIV alone. METHODS: NAVA NIV and NIV were applied in random order while using respiratory inductance plethysmography to measure the phase angle. RESULTS: Patient-ventilator asynchrony was decreased during NAVA NIV; however, the phase angle was not different between the modes. A large number of repeated assists with switches to backup were found when using NAVA NIV. Results of the analysis indicated these were due to the apnea alarm limit set during NAVA NIV. CONCLUSIONS: The improvement in patient-ventilator synchrony supports the hypothesis that work of breathing may be decreased with NAVA NIV; however, we were unable to demonstrate this with our study design. Short apnea time settings with NAVA NIV led to a large number of switches to backup and repeated assists during the same neural effort. (ClinicalTrials.gov registration NCT02788110.).

Tidal volume transmission during non-synchronized nasal intermittent positive pressure ventilation via RAM® cannula.

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 ventilator-supported 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.

Maximal expiratory flow at FRC (V'maxFRC): Methods of selection and differences in reported values.

We compared three methods of reporting maximal expiratory flow (V'maxFRC) 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'maxFRC 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'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'maxFRC, and thus it cannot be recommended for routine use in its current form.

Synchronized neonatal non-invasive ventilation-a pilot study: the graseby capsule with bi-level NCPAP.

OBJECTIVES: (1) To evaluate the Graseby capsule (GC) as a respiratory detection device when compared to respiratory inductance plethysmography (RIP); (2) to evaluate the response to the Graseby signal of a commercially available bi-level nasal CPAP device (BNCPAP) designed for use with the GC; and (3) to assess the performance of the GC/BNCPAP device when fitted on preterm infants. STUDY DESIGN: The study consisted of four parts: (1) The response characteristics of the GC/BNCPAP were assessed without connection to an infant; (2) the respiratory detection of both GC and RIP were compared in six preterm infants (mean 1,242 g, range 900-1,530 g); (3) the GC/BNCPAP was connected in six preterm infants (mean 1,568 g, range 1,040-1,835 g), isolating the BNCPAP and the infant interaction by substituting an artificial "nose" for the infant and assessing performance using inspiratory times (Ti) of 0.1 through 0.5 sec with pressure levels of both 10/6 and 8/5 cmH2 O; and (4) the GC/BNCPAP was employed as a respiratory support device in six preterm infants (mean 1,189 g, range 785-1,795 g) using clinically required pressures and evaluating performance using Ti of 0.3, 0.4 and 0.5 sec. RESULTS: (1) Within 26 ms of stimulation of the GC, the BNCPAP initiated air flow; however, the time to reach peak pressure was much longer; (2) the GC, when placed in the subxiphoid position, tracked the RIP signal nearly identically and occurred sooner; (3) a Ti of at least 0.3 sec was required to reach the desired high pressure setting; and (4) synchrony of the GC/BNCPAP occurred in 72-74% of infant breaths. CONCLUSIONS: 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.

Respiratory mechanics during high-frequency oscillatory ventilation: a physical model and preterm infant study.

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.