A new prototype of an electronic jet-ventilator and its humidification system

Abstract

Adequate humidification in long-term jet ventilation is a critical aspect in terms of clinical safety. To assess a prototype of an electronic jet-ventilator and its humidification system. Forty patients with respiratory insufficiency were randomly allocated to one of four groups. The criterion for inclusion in this study was respiratory insufficiency exhibiting a Murray score above 2. The four groups of patients were ventilated with three different respirators and four different humidification systems. Patients in groups A and B received superimposed high-frequency jet ventilation (SHFJV) by an electronic jet-ventilator either with (group A) or without (group B) an additional humidification system. Patients in group C received high-frequency percussive ventilation (HFPV) by a pneumatic high-frequency respirator, using a hot water humidifier for warming and moistening the inspiration gas. Patients in group D received conventional mechanical ventilation using a standard intensive care unit respirator with a standard humidification system. SHFJV and HFPV were used for a period of 100 h (4days). < 0.05) but rose to an average of 98 ± 2.8% after 2 h. The average percentage across all four groups amounted to 98 ± 0.4% after 2 h. Inflammation of the tracheal mucosa was found in patients in group B and the mucosal injury score (MIS) was significantly higher than in all the other groups. Patients in groups A, C and D showed no severe evidence of airway damage, exhibiting adequate values of relative humidity and temperature of the inspired gas. The problems of humidification associated with jet ventilation can be fully prevented by using this new jet-ventilator. These data were sustained by nondeteriorating MIS values at the end of the 4-day study period in groups A, C and D.

Background:

Adequate humidification in long-term jet ventilation is a critical aspect in terms of clinical safety.

Aim:

To assess a prototype of an electronic jet-ventilator and its humidification system.

Methods:

Forty patients with respiratory insufficiency were randomly allocated to one of four groups. The criterion for inclusion in this study was respiratory insufficiency exhibiting a Murray score above 2. The four groups of patients were ventilated with three different respirators and four different humidification systems. Patients in groups A and B received superimposed high-frequency jet ventilation (SHFJV) by an electronic jet-ventilator either with (group A) or without (group B) an additional humidification system. Patients in group C received high-frequency percussive ventilation (HFPV) by a pneumatic high-frequency respirator, using a hot water humidifier for warming and moistening the inspiration gas. Patients in group D received conventional mechanical ventilation using a standard intensive care unit respirator with a standard humidification system. SHFJV and HFPV were used for a period of 100 h (4days).

Results:

< 0.05) but rose to an average of 98 ± 2.8% after 2 h. The average percentage across all four groups amounted to 98 ± 0.4% after 2 h. Inflammation of the tracheal mucosa was found in patients in group B and the mucosal injury score (MIS) was significantly higher than in all the other groups. Patients in groups A, C and D showed no severe evidence of airway damage, exhibiting adequate values of relative humidity and temperature of the inspired gas.

Conclusion:

The problems of humidification associated with jet ventilation can be fully prevented by using this new jet-ventilator. These data were sustained by nondeteriorating MIS values at the end of the 4-day study period in groups A, C and D.

Introduction

].

], for example, hot water humidifiers, cold water humidifiers and heat and moisture exchangers. The most commonly used humidification system in our institution is the hot water humidifier (Aquapor, Type 8406640, Draeger Corp, Luebeck, Germany).

The aim of this study was to show that the problems of humidification associated with SHFJV can be prevented by using the correct humidification system. Proper methods for showing possible epithelial damage were used.

Statistical analysis

< 0.05 was regarded as statistically significant.

Since homogeneity of variances were seen, statistical evaluation was performed using single factorial analysis. However, as the small number of spot samples impaired the standard distribution, a nonparametric method (variance analysis by Kruskal–Wallis) was also used. Both methods showed the same significant differences between the groups. Furthermore, a pathanalysis was calculated to check the statistical relevance of the hypothetical influence of the forms of ventilation on temperature and humidity.

, fractional inspiratory oxygen concentration; LF, lowfrequency; HF, high frequency.

Patient characteristics and demographic data at study entry

, fractional inspiratory oxygen concentration; I:E, inspiration to expiration time ratio.

] and European American Consensus Conference 1994 values)

, fractional inspiratory oxygen Concentration; PEEP, positive end-expiratory pressure; ARDS, acute respiratory distress syndrome; ALI, acute lung insufficiancy; ap, anterior-posterior; PCWP, pulmonary capillary wedge pressure.

Relative humidity

< 0.05). Patients in group A showed a mean relative humidity of 71.2%, patients in group C showed a mean relative humidity of 92.2% and patients in group D showed a mean relative humidity of 92.0%.

After 20 min of ventilation the mean relative humidity of the inspiration gas was still lower in patients in group B (92.8%) compared with patients in group A (96.8%), group C (97.4%), and group D (98.6%).

After 2 h of ventilation patients in all four groups showed almost equivalent mean values (98 ± 0.4%). All measurements taken from this point until the end of the 100-h study protocol showed no more significant changes compared to the values measured after 2 h.

Temperature

< 0.05). Patients in group A had a mean gas temperature of 31.4 ± 2.8°C, those in group C had a mean gas temperature of 32.1 ± 2.6°C, and those in group D had a mean gas temperature of 34.2 ± 2.7°C.

After 20 min of ventilation the inspiration gas temperature was still lower in patients in group B (27.1 ± 1.8°C) compared with patients in group A (32 ± 1.8°C), patients in group C (32.5 ± 2.3°C), and patients in group D (34.1 ± 2.5°C).

After 2 h of ventilation the trend was similar (patients in group B, 27.1 ± 1.8°C; patients in group A, 32.4 ± 1.1°C; patients in group C, 32.6 ± 1.6°C; and patients in group D, 34.3 ± 2.3°C).

After 2 days the values were: patients in group B, 28.0 ± 1.6°C; patients in group A, 33.2 ± 1.7°C; patients in group C, 33.2 ± 2.5°C; patients in group D, 34.5 ± 1.8°C.

After 4 days the values were: patients in group B, 28.0 ± 1.9°C; patients in group A, 33.0 ± 1.7°C; patients in group C, 33.6 ± 2.5°C; patients in group D, 34.3± 1.8°C.

Mucosal injury score

). During bronchoscopy, a tracheobronchial secretion was removed. The bronchial epithelium (area C) showed no pathologic evidence. Typical changes to the mucosa were not detected in patients in any group other than those in group B.

In group A, C and D no epithelial damage could be found in any area. Eight patients (group independent) who were in an intermittent prone position (usually turned every 12 h) showed little tracheal damage at the end of the tube.

Although one patient in group C died as a result of severe sepsis, their tracheobronchial mucosa showed no adverse tissue change when compared to the control group. As the period of ventilation (72 h) was probably sufficient to induce any injury as a result of the humidification system, data from this patient were not excluded in our comparison. The statistical relevance of the hypothetical influence of the forms of ventilation on temperature and humidity were checked by pathanalysis. Only group B appeared to show any influence.

Humidification rate of the additional humidification system

). This was changed depending on the bronchoscopic aspect of the tracheobronchial mucosa and the presence of dry secretion. Patients in group A showed an average setting of 30 ± 10 ml/h, starting at 20 ml/h and rising to 40ml/h on the second day. Patients in group B showed the highest demand for saline solution, with an average setting of 45 ± 5 ml/h and a peak of 50 ml/h on the fourth day. Patients in groups C and D were served by a hot water humidifier without an additional humidification system.

Percentage of relative humidity (RH) of the inspiration gas for each group initially, after 20 min, 2 h, after 2 days and after 4 days of ventilation (mean± standard deviation).

Temperature of the inspiration gas of each group initially, after 20 min, 2 h, after 2 days and after 4 days of ventilation (mean ± standard deviation).

Mucosal injury score of each group initially, after 20 min, 2 h, after 2 days and after 4 days of ventilation (mean± standard deviation).

Mucosal injury score and humidification rate settings during the course of superimposed high-frequency jet ventilation

Discussion

].

The continuous 0.9% saline infusion into the humidification line of the jet adapter started at 20 ml/h. Regular checks on the mucosa showed that over 75% of all patients needed higher humidification over the whole study period, in some cases an increase of 200%. This increase was dependent on the bronchoscopic aspect of the tracheobronchial mucosa and the presence of dry secretions. Detecting these changes for alteration of the humidification settings requires a lot of experience and cannot be explained merely by facts, figures and equations.

. These basic physical principles of humidification are well known, and are accepted in ventilation therapy. The saline solution was warmed by a fluid warmer to 39°C before it reached the jet adapter, allowing for a possible warm up of 42°C if necessary, to compensate for the temperature drop of the gas after decompression (Joule-Thompsen effect) and possible epithelial lesions.

In fact, increasing the temperature of the inspired gas delivered during high-frequency jet ventilation from 39°C–42°C might appear insufficient. After decompression of the gas into the trachea, there is a sudden drop in the temperature of 5–10°C. As a consequence, to reach 37°C in the tracheobronchial tree, inspired gas should be warmed to at least 45°C.

) of the additional humidification system, which differed more than 50% from patient to patient.

], and intubation and ventilation bring this ISB further back along the tracheobronchial tract. Thus, the ability of the lungs to facilitate an adequate temperature and amount of moisture in the inspiration gas is dramatically impaired, leading to the problems that are associated with inadequate humidification and warming.

At present, equipment to monitor humidity is not sufficiently sophisticated to allow accurate breath to breath measurements of humidity within the airway. The estimation of humidification requirements must therefore be based on scientific evidence and clinical impression. Humidification of inspired gases should not be considered in isolation but as part of total airway management. It should be associated with careful fluid balance, physiotherapy, bronchial aspiration and appropriate drug therapy.

]. As the mucus secretion becomes increasingly hyperosmolar and dry, it is trapped and encapsulated beneath the surface. Cellular injury occurs and neutrophil sequestration is exaggerated due to the increase in blood supply. In this situation, with aggravating tissue damage, an exsudate is formed that appears as blisters below the mucosal surface. Because of the external force from mechanical ventilation or jet ventilation, the encapsulated mucus penetrates and causes sloughing of the tracheal epithelial cells.

] showed an increase in chronic upper respiratory tract problems in children with reduced ciliary beat frequency. Damage to the tracheal mucosa occurs during endotracheal intubation and ventilation whatever the inspired humidity. Using dry inspired gas the damage is dramatically worse; therefore, clinical procedures should aim to reduce the use of dry gases in ventilator circuits.

] showed in a multicenter clinical trial that the incidence of necrotizing tracheobronchitis is similar comparing HFJV with CMV in neonates.

] proposed that regional or generalized airway ischemia was the mechanism for airway damage, based on the appearance of mucosal damage with a lack of warming.

] might also have affected tracheal blood flow, although the authors concede that the hyperemia effects appear to relate to shear stress and water removal rather than alveolar partial pressure of carbon dioxide. They found blood flow improvements in the tracheal mucosa, with the highest increase using dry gas.

] shows that longer periods of ventilation (33 h) produce no significant differences in airway damage when comparing CMV with HFJV.

]. They claim that greater shear stresses with HFJV may also alter mucosal epithelia permeability and secondarily affect the blood flow.

Our study showed that, by providing proper humidification and warming of the inspiration gases, epithelial damage to the tracheobronchial mucosa can be prevented, as can possible inflammation and necrotizing tracheobronchitis, even in long-term applications.

] showed that, by providing adequate moisture and proper temperature of the inspiration gases, deleterious effects on the tracheobronchial mucosa can be prevented. Although their mechanical expenditures and material costs were much higher than ours, the outcome of their studies were just as satisfactory as the results of this study. SHFJV has been shown to be a serious alternative to CMV. Using the Alexander 1, the problems of humidification and warming of the ventilation gas can be handled very well.

Keywords

• bronchoscopy
• conventional mechanical ventilation
• electronic jet ventilation
• jet adapter
• humidification system