Effectiveness of Inspiratory Termination Synchrony with Automatic Cycling During Noninvasive Pressure Support Ventilation

Effect of nasal high-flow oxygen humidification on patients after cardiac surgery

Background

Although high-flow humidified oxygen therapy (HFNC) has emerged as an important treatment for respiratory failure, few studies have reported on whether HFNC is appropriate for patients with hypoxemia after cardiac surgery, and the clinical efficacy of HFNC in patients undergoing cardiac surgery is unclear.

Objective

To investigate the clinical effect of HFNC after cardiac surgery.

Methods

Convenience sampling was used to select 76 patients who underwent invasive mechanical ventilation and oxygen therapy after valve replacement or coronary artery bypass grafting from July 2019 to June 2021. The patients were divided into the routine group and the HFNC group according to the oxygen therapy provided after the operation. The patients in the routine group (N = 38) were treated with oxygen inhalation by face mask after the operation, while those in the HFNC group (N = 38) were treated with HFNC via nasal cavity. The arterial partial pressure of oxygen (PaO2), the arterial partial pressure of carbon dioxide (PaCO2) and the oxygenation index (OI) were observed and compared between the two groups at 6 h, 12 h and 24 h after treatment. The sputum viscosity, incidence of second intubation and the intensive care unit (ICU) stay time were evaluated.

Results

The difference in PaCO2 between the two groups was statistically significant at 24 h after treatment (p < 0.05). The PaO2 in the HFNC group was significantly higher than in the routine group at 24 h after treatment, and the OI of the routine group was lower than in the HFNC group at 6 h, 12 h and 24 h after treatment (p < 0.05). The sputum viscosity in the HFNC group was better than in the routine group at 12 h and 24 h after treatment. The second intubation rate and ICU stay time in the HFNC group were lower than in the routine group (p < 0.05).

Conclusion

Compared with conventional mask oxygen inhalation, HFNC can effectively reduce sputum viscosity, improve oxygenation, reduce the incidence of repeated intubation and meet patients' comfort needs. It is an advantageous respiratory support strategy for patients after cardiac surgery compared with invasive mechanical ventilation to oxygen therapy and is beneficial to the recovery of cardiopulmonary function.

Effects of jet nebulization on ventilator performance with different invasive ventilation modes: A bench study

Background

The effects of jet nebulization on ventilator performance in the volume control mode (VC) and pressure control mode (PC) of ventilation have not been determined.

Objectives

The present study investigated the impact of jet nebulization on ventilator performance in different modes in vitro.

Methods

Two types of jet nebulizer (ventilator-integrated jet nebulizers, external jet nebulizer) and six types of ventilator were connected with a simulated lung to simulate aerosol therapy during mechanical ventilation. The ventilation modes were set to VC and PC, and the driving flows of external jet nebulizer were set at 4 L/min and 8 L/min, respectively. Jet nebulizers were placed between patient airway and Y-piece or at 15 cm from the Y-piece in the inspiratory limb. The effects of jet nebulization were compared with the baseline of triggering performance, control performance, and tidal volume under different experimental conditions.

Results

Ventilator-integrated jet nebulizers had no effect on ventilator performance in different modes (all P &gt; 0.05). However, the effects of external jet nebulizers on ventilator performance varied widely: for triggering performance, all parameters were increased in different modes and nebulization positions (all P &lt; 0.05), including the time from the beginning of the inspiratory effort to the lowest value of airway pressure needed to trigger the ventilator (TPmin), the time to trigger (Ttrig), and the magnitude of airway pressure drop needed to trigger (Ptrig); for control performance, peak inspiratory pressure (Ppeak) and peak inspiratory flow(Pflow) were increased in the VC mode (P &lt; 0.05), but not significantly changed in the PC mode (P &gt; 0.05);the actual tidal volume (VT) and expiratory tidal volume monitored (VTe) were significantly increased (P &lt; 0.05), however, the inspiratory tidal volume monitored (VTi) was not affected by jet nebulization in the VC mode. In the PC mode, there were no significant changes in VT, whereas VTi decreased and VTe increased (P &lt; 0.05). The higher the driving flow of external jet nebulizers, the stronger the impact on ventilator performance (all P &lt; 0.05).

Conclusion

Triggering performance was decreased in both the VC and PC modes when using an external jet nebulizer, while the effects of nebulization on control performance and tidal volume varied significantly.

Continuous estimation of airway resistance in non-invasive ventilation

BACKGROUND

This study aimed to evaluate the accuracy of expiratory time constant (RC_exp) to continuously calculate the airway resistance (R_aw).

MATERIAL AND METHODS

A Respironics V60 ventilator was connected to a lung simulator for modeling different profiles of respiratory mechanics.

RESULTS

During assisted ventilation, the respiratory system compliance (C_rs) calculation was always overestimated in most lung models. The R_aw estimation using the expiratory resistance (R_exp) method was close to the calculated value with the occlusion method during volume-controlled ventilation (VCV). In expiratory flow limitation (EFL) lung models, similar results were obtained in the estimation of inspiratory resistance (R_insp), but different variations were observed in the calculation of the R_exp. The results estimated with RC_exp and with dynamic signal analysis had significant variation and accuracy (p < 0.001).

CONCLUSION

The RC_exp method is a robust approach to provide real-time assessments of R_insp and R_exp in spontaneously breathing patients during noninvasive ventilation. An underestimation of R_exp was observed in EFL lung models.

Accuracy of the dynamic signal analysis approach in respiratory mechanics during noninvasive pressure support ventilation: a bench study

OBJECTIVE

To evaluate the accuracy of respiratory mechanics using dynamic signal analysis during noninvasive pressure support ventilation (PSV).

METHODS

A Respironics V60 ventilator was connected to an active lung simulator to model normal, restrictive, obstructive, and mixed obstructive and restrictive profiles. The PSV was adjusted to maintain tidal volumes (V_T) that achieved 5.0, 7.0, and 10.0 mL/kg body weight, and the positive end-expiration pressure (PEEP) was set to 5 cmH₂O. Ventilator performance was evaluated by measuring the flow, airway pressure, and volume. The system compliance (C_rs) and airway resistance (inspiratory and expiratory resistance, R_insp and R_exp, respectively) were calculated.

RESULTS

Under active breathing conditions, the C_rs was overestimated in the normal and restrictive models, and it decreased with an increasing pressure support (PS) level. The R_insp calculated error was approximately 10% at 10.0 mL/kg of V_T, and similar results were obtained for the calculated R_exp at 7.0 mL/kg of V_T.

CONCLUSION

Using dynamic signal analysis, appropriate tidal volume was beneficial for R_rs, especially for estimating R_exp during assisted ventilation. The C_rs measurement was also relatively accurate in obstructive conditions.

Effects of assist parameter on the performance of proportional assist ventilation in a lung model of chronic obstructive pulmonary disease

BACKGROUND

How the assist parameters affect synchronization and inspiratory workload in proportional assist ventilation (PAV) remains unknown.

PURPOSE

This bench study aimed to optimize the PAV parameters by evaluating their effects on patient-ventilator synchrony and work of breathing (WOB) in a chronic obstructive pulmonary disease (COPD) model during noninvasive ventilation, compared with the pressure support ventilation (PSV) mode.

METHODS

The Respironics V60 ventilator was connected to an ASL5000 lung simulator, which simulates lung mechanics in COPD (compliance, 50mL/cmH₂O; expiratory resistance, 20 cmH₂O/L/s; respiratory rate, 15 breaths/min; inspiratory time, 1.6 s). PAV was applied with different assistance levels, including flow assist (FA, 40-90% respiratory resistance) and volume assist (VA, 50-90% elastance). PSV was assessed using the same model. Measurements were obtained at a leak flow rate of 25-28 L/min. Performance characteristics, simulator-ventilator synchrony, and WOB were assessed.

RESULTS

Runaway was prone to occur, and severe premature cycling was observed with VA75+FA level>65%. Compared with PSV, lower tidal volume (≤400mL) was observed during PAV with VA75+FA40-50 and FA50+VA40-80; similar and improved cycling synchrony was observed for FA50+VA80 and FA50+VA90 (cycling delay: -117.60±6.13 and -61.50±8.03 vs. -101.20±7.32ms). The reduced triggering workload was observed for VA75+FA60-65 and FA50+VA80-90. Total and patient WOB was improved with all tested assist level combinations, except for FA50+VA90.

CONCLUSIONS

PAV reduces WOB but can induce asynchrony if improper settings are set, but the most optimal settings still need more clinical observations.

Comparison of Inspiratory Effort, Workload and Cycling Synchronization Between Non-Invasive Proportional-Assist Ventilation and Pressure-Support Ventilation Using Different Models of Respiratory Mechanics

Background

This study assessed lung models for the influence of respiratory mechanics and inspiratory effort on breathing pattern and simulator-ventilator cycling synchronization in non-invasive ventilation.

Material/Methods

A Respironics V60 ventilator was connected to an active lung simulator modeling mildly restrictive, severely restrictive, obstructive and mixed obstructive/restrictive profiles. Pressure-support ventilation (PSV) and proportional-assist ventilation (PAV) were set to obtain similar tidal volume (V_T). PAV was applied at flow assist (FA) 40–90% of resistance (Rrs) and volume assist (VA) 40–90% of elastance (Ers). Measurements were performed with system air leak of 25–28 L/minute. Ventilator performance and simulator-ventilator asynchrony were evaluated.

Results

At comparable V_T, PAV had slightly lower peak inspiratory flow and higher driving pressure compared with PSV. Premature cycling occurred in the obstructive, severely restrictive and mildly restrictive models. During PAV, time for airway pressure to achieve 90% of maximum during inspiration (T90) in the severely restrictive model was shorter than those of the obstructive and mixed obstructive/restrictive models and close to that measured in the PSV mode. Increasing FA level reduced inspiratory trigger workload (PTP₃₀₀) in obstructive and mixed obstructive/restrictive models. Increasing FA level decreased inspiratory time (T_I) and tended to aggravate premature cycling, whereas increasing VA level attenuated this effect.

Conclusions

PAV with an appropriate combination of FA and VA decreases work of breathing during the inspiratory phase and improves simulator-ventilator cycling synchrony. FA has greater impact than VA in the adaptation to inspiratory effort demand. High VA level might help improve cycling synchrony.

Effect of Jet Nebulization on Noninvasive Positive-Pressure Ventilation Administered with Noninvasive or Intensive Care Unit Ventilators: A Bench Study

BACKGROUND

Most of the patients on noninvasive positive pressure ventilation require aerosol inhalation therapy to moisturize the airways or deliver drugs in acute settings. However, the effect of jet nebulization on noninvasive positive pressure ventilation (NPPV) has not been determined.

OBJECTIVES

This study was designed to investigate the impact of jet nebulization on NPPV applied in ventilators.

METHODS

Aerosol therapy during NPPV was conducted in a simulated lung. The jet nebulizer was connected at both the distal and proximal end of the exhalation valve for the noninvasive ventilators, while it was placed both in front of the Y tube proximal to the patient and at 15 cm distance from the Y-tube inspiratory limb distal to the patient for the intensive care unit (ICU) ventilators. Driving flow was set at 4 and 8 L/min, respectively.

RESULTS

TPmin (time from the beginning of the lung simulator's inspiratory effort to the lowest value of airway pressure needed to trigger the ventilator), Ttrig (time to trigger), and Ptrig (the magnitude of airway pressure drop needed to trigger) were not significantly altered by jet nebulization in the noninvasive ventilators, while they were significantly increased in the ICU ventilators. The greater the driving flow, the stronger the impact on TPmin, Ttrig, and Ptrig. The actual tidal volume and control performance were not significantly affected by jet nebulization in either noninvasive or ICU ventilators. The tidal volume monitored was significantly increased at 8 L/min driving flow. The greater the driving flow, the stronger the impact on the tidal volume monitored.

CONCLUSION

The effect of jet nebulization on NPPV was different when compared to invasive ventilation. Jet nebulization only affected the tidal volume monitored in the noninvasive ventilator. Jet nebulization also affected the triggering performance and tidal volume monitored in the ICU ventilator.