Latest News - Part 13
Influence of Two Different Interfaces for Noninvasive Ventilation Compared to Invasive Ventilation on the Mechanical Properties and Performance of a Respiratory System: Inspiratory Effort
With a helmet, the use of PS decreased delay times significantly, whereas this effect was relatively small during NIV-FM or invasive ventilation. These results suggest that the highest PEEP and PS levels clinically indicated and tolerated by the patient should be used when NIV with a helmet is used in order to enhance the trigger sensitivity. more
The DelayPEEP seems to be important for patients with acute hypoxemic lung failure who continuously need a high alveolar distending pressure. Lungs collapse, and recruitment may occur rapidly on a breath-by-breath basis with time constants not longer than 400 ms. Depending on the PEEP and PS levels provided, DelayPEEP averaged between 81 ms and 397 ms. This time interval would allow collapse of unstable lung units with fast time constants. However, a decrease in Paw during a spontaneous inspiration is always secondary to an increase in the transpulmonary pressure, and should therefore not cause atelectasis.
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Influence of Two Different Interfaces for Noninvasive Ventilation Compared to Invasive Ventilation on the Mechanical Properties and Performance of a Respiratory System: Technical Aspects
The performance of our modern ICU ventilator was significantly affected by the use of a helmet designed for NIV because delay times were more than twice as long with a helmet compared to a face mask or invasive ventilation. The level of PS and CPAP had a major effect on delay times when a helmet was used, but not with a face mask or during invasive ventilation. In addition, PTP was smaller with NIV-H compared to NIV-FM or invasive ventilation, but not so when a complete inspiration with PS was evaluated. Wasted efforts occurred earlier during NIV-H and were aggravated with rising PS, RR, and compliance.
The data presented are based on trials in a mechanical lung model and are highly influenced by the compliance of the used interface and the degree of leakage. Repeated measurements with different helmets showed a relative wide range of measured time intervals due to varying compliance values of these helmets. Thus, delay times and PTPs reported in this study may vary if different helmets or tubing are used. The DelayTRlGGER was defined as the time interval between the initiation of an inspiration until the deflection of the Paw-time curve showed no further decrease in Paw, because the latter time point can easily and reliably be identified. other
Influence of Two Different Interfaces for Noninvasive Ventilation Compared to Invasive Ventilation on the Mechanical Properties and Performance of a Respiratory System: PTPs
During PS, the time course of Paw differed not only during the trigger phase but also later during pressurization (Fig 4). A rapid increase of Paw occurred after the trigger delay during NIV-FM and invasive ventilation, whereas this increase in Paw occurred more slowly during NIV-H. Consequently, PTP was slightly lower during the first 250 ms of inspiration with a helmet compared to NIV-FM and invasive ventilation, but not during the complete inspiration.
Interestingly, not only PTPtot but also PTPtrigger and PTPpeep were significantly influenced by the level of PS (p < 0.001) [Fig 5]. Mean PTPtrigger values averaged over all PS settings were significantly lower in NIV-H (mean, — 77 ± 41 cm H2O X s) than NIV-FM (mean, — 239 ± 54 cm H2O X s) or invasive ventilation (mean — 215 ± 15 cm H2O X s) [p < 0.001], and a similar pattern was observed for PTPpeep resulting in a significant difference for all PS settings in the post hoc analysis. However, there was no significant difference of average PTPtot values among NIV-H (mean, 8,744 ± 5,594 cm H2O X s), NIV-FM (mean, 7,161 ± 5,584 cm H2O X s) or invasive ventilation (mean, 9,902 ± 6,659 cm H2O X s), although significant differences between NIV-FM and invasive ventilation were observed at higher PS levels (Fig 5).
Influence of Two Different Interfaces for Noninvasive Ventilation Compared to Invasive Ventilation on the Mechanical Properties and Performance of a Respiratory System: Delay Times
The second chamber, representing the “lung,” was connected to the tested ventilator (Evita 4; Drager Medical). The lung is passively displaced when the driving chamber is inflated by the ventilator. The following settings were studied: (1) RRs of10, 20, 30, and 40 breaths per minute; (2) PS levels raised in 1 cm H2O steps every minute until wasted inspiratory efforts occurred or up to a maximum of 30 cm H2O; (3) flow trigger set to 0.5 L/min and 15 L/min, respectively; and (4) respiratory compliance set at 30, 60, and 90 mL/cm H2O, respectively. The occurrence of wasted efforts was detected visually (failure of the ventilator-driven chamber to activate the passively driven lung chamber) and by analyzing the pressure volume curves off-line.
Statistical analysis was performed using self-programmed and commercially available software. Data are given as mean ± SD if not stated otherwise. Using a two-way analysis of variance, delay times and PTPs were analyzed for differences between the used interfaces (helmet vs mask vs endotracheal tube) and the applied PEEP or PS levels. If a significant difference was detected, a post hoc analysis using the Scheffe test was performed. A p level < 0.05 was considered to be significant. further
Influence of Two Different Interfaces for Noninvasive Ventilation Compared to Invasive Ventilation on the Mechanical Properties and Performance of a Respiratory System: Measurements of Time Delay
To simulate spontaneous breathing, we used a modified lung model (LS1500; Drager Medical). This lung model consists of an electrically driven pneumatic lung simulator that allows the adjustment of tidal volume, RR, compliance, and resistance.
To analyze the effect of the different interfaces on trigger sensitivity, effort, and the resulting PTPs, we defined three phases during the pressure curve (Fig 2): (1) the time interval (DelayTRlGGER), and the corresponding PTP interval between the initiation of an inspiration and the time point when the deflection of the Paw-time curve showed no further decrease in Paw (PTPtrigger); (2) the time interval from the initiation of an inspiration until the preset positive end-expiratory pressure (PEEP) was reached again (DelayPEEP), and the corresponding PTP from the initiation of an inspiration until the preset PEEP was reached again (PTPpeep); and (3) complete inspiration: during PS ventilation (PSV), the complete inspiration including the unassisted (DelayTRlGGER) and the pressurization segment was added to get the total PTP (PTP calculated over complete inspiration [PTPtot]). Flow and Paw were recorded with a sampling rate of 200 Hz. For the initiation of single breaths, data acquisition, and data analysis, specially programmed software was used. www.birthcontroltab.com
Influence of Two Different Interfaces for Noninvasive Ventilation Compared to Invasive Ventilation on the Mechanical Properties and Performance of a Respiratory System: Equipment
CPAP and NPSV were performed with a helmet (Starmed Castar R; Mirandola; Modena, Italy) or a face mask (King Systems Corporation; Noblesville, IN) put on a glass head that was connected to a lung model (Fig 1). The Castar R Helmet (size medium) has an internal volume of 7.5 L with inflated cuffs. When the head is inserted into the helmet, the internal volume is reduced to approximately 2.4 L due to the volume of the glass head used in this study. Two underarm laces attached to a ring at the lower site of the helmet should prevent the helmet from lifting when it is inflated. A plastic collar fitting around the neck prevents leakage during ventilation. Inspiratory and expiratory tube connectors are fitted in the upper part of the helmet.
The standard face mask (size medium, 125-mL internal gas volume) has an inflatable cushion fitted tightly to the head by dedicated rubber head straps. The cushion was inflated with 10 to 20 mL of air to adhere tightly to the glass head. When the mask is put on the head, the internal gas volume is reduced to approximately 100 mL.
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Influence of Two Different Interfaces for Noninvasive Ventilation Compared to Invasive Ventilation on the Mechanical Properties and Performance of a Respiratory System
Noninvasive ventilation (NIV) is increasingly used ’ in the treatment of acute and chronic respiratory failure and during weaning from invasive ventilation. NIV has been applied in patients with acute hypoxemic respiratory failure, severe cardiogenic pulmonary edema, or acute exacerbation of COPD in order to decrease the need and the complications of endotracheal intubation. other
Noninvasive respiratory support can be applied either as continuous positive airway pressure (CPAP) alone or as NIV with inspiratory pressure support (NPSV) by means of a nasal or face mask. Problems with the widely used face masks result partially from air leakage,- discomfort of the patient, and pressure-related ulcerations of the nose.’ These problems may limit the duration of use and account for a large proportion of NIV failures. In an attempt to improve NIV tolerance, a helmet was developed that has been successfully used in different clinical situ-ations.”
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