Superimposed High-frequency Jet Ventilation Research Articles

Effects of unilateral superimposed high-frequency jet ventilation on porcine hemodynamics and gas exchange during one-lung flooding.

Superimposed high-frequency jet ventilation (SHFJV) is suitable for respiratory motion reduction and essential for effective lung tumor ablation. Fluid filling of the target lung wing one-lung flooding (OLF) is necessary for therapeutic ultrasound applications. However, whether unilateral SHFJV allows adequate hemodynamics and gas exchange is unclear. To compared SHFJV with pressure-controlled ventilation (PCV) during OLF by assessing hemodynamics and gas exchange in different animal positions. SHFJV or PCV was used alternatingly to ventilate the non-flooded lungs of the 12 anesthetized pigs during OLF. The animal positions were changed from left lateral position to supine position (SP) to right lateral position (RLP) every 30 min. In each position, ventilation was maintained for 15 min in both modalities. Hemodynamic variables and arterial blood gas levels were repeatedly measured. Unilateral SHFJV led to lower carbon dioxide removal than PCV without abnormally elevated carbon dioxide levels. SHFJV slightly decreased oxygenation in SP and RLP compared with PCV; the lowest values of PaO2 and PaO2/FiO2 ratio were found in SP [13.0; interquartile range (IQR): 12.6-5.6 and 32.5 (IQR: 31.5-38.9) kPa]. Conversely, during SHFJV, the shunt fraction was higher in all animal positions (highest in the RLP: 0.30). In porcine model, unilateral SHFJV may provide adequate ventilation in different animal positions during OLF. Lower oxygenation and CO2 removal rates compared to PCV did not lead to hypoxia or hypercapnia. SHFJV can be safely used for lung tumor ablation to minimize ventilation-induced lung motion.

A multi-centre prospective random control study of superimposed high-frequency jet ventilation and conventional jet ventilation for interventional bronchoscopy.

Introduction: Superimposed high-frequency jet ventilation (SHFJV) is a new type of jet ventilation that simultaneously uses high- and low-frequency types of jet ventilation. We compared SHFJV with the conventional high-frequency jet ventilation (CHFJV) in interventional bronchoscopy in terms of safety and effectiveness. Methods: A multi-centre prospective random single-blind clinical trial was conducted by three interventional bronchoscopy centres. Patients who underwent diagnostic or therapeutic bronchoscopy under general anaesthesia were admitted and divided into two groups: SHFJV group (trial group) and CHFJV group (control group). PaO2 and PaCO2 were recorded before anaesthesia and during and after the procedure. SpO2 and etCO2 were recorded every 10min throughout the procedure. Patients were observed until 24h post-bronchoscopy. Results: Sixty patients were included in the study. Twenty-nine were in the trial group, and 31 were in the control group. Both groups had no significant differences in demographic data. In the control group, the PaO2 measured in the operation was higher than that in the trial group (p = 0.023). The values of etCO2 in the control group were more dispersed than those of the trial group. When the procedure time was over 90minutes, the etCO2 in the control group significantly increased (p = 0.01), while the etCO2 in trial group remained stable (p = 0.594). There were more patients with PaCO2 ≥ 50mmHg during the procedure in the control group than in the trial group (p = 0.042). Conclusion: SHFJV is effective and safe in interventional bronchoscopy. It may provide more effective and stabilised ventilation than CHFJV in cases with long procedure times.

Superimposed High Frequency Jet Ventilation Minimises Diaphragm, Bronchus, and Mediastinum Motion during One-Lung Flooding

Background: One-Lung Flooding (OLF) represents an ideal acoustic pathway for focused ultrasound ablation of lung tumours. Despite stabilization of the adjacent hemidiaphragm by OLF, standard Pressure-Controlled Ventilation (PCV) of the contralateral lung causes an unacceptable movement of the flooded lung. We examined whether Superimposed High Frequency Jet Ventilation (SHFJV) reduces lung motion compared to PCV during OLF. Methods: The study included 15 pigs: 10 underwent OLF; 5 controls underwent two-lung ventilation without OLF. Using ultrasound, diaphragm displacement on the flooded lung side was measured during PCV and SHFJV in the left lateral (LLP), Supine (SP), and Right Lateral Positions (RLP). Bronchus and mediastinum displacements were measured in the right lateral position. Results: Diaphragm displacement on the flooded lung side was significantly reduced during SHFJV, compared with PCV, in all animal positions (LLP: 7mm [4.75-8.0] vs. 17mm [14.75-19.0], P=0.0039; SP: 4mm [3.75-4.25] vs. 17mm [16.0–18.5], P=0.0039; RLP: 8mm [5.75-9.0] vs. 20mm [14.0-23.25], P=0.0078). Displacement of both the bronchus and mediastinum were significantly reduced during SHFJV, compared with PCV, in RLP (bronchus: 2.0mm [1.75-2.25] vs. 3.0mm [2.75-3.0], P=0.027; mediastinum: 4.5mm [4.0-5.0] vs. 10mm [7.0-10.0], P=0.0078. Conclusion: Thus, SHFJV minimises diaphragm, bronchus, and mediastinum motion during OLF, which is a prerequisite for effective lung tumour ablation.

Airway management for microlaryngeal surgery

Theoretical basis: Microlaryngeal surgery can be conducted in an awake patient, frequently under conscious sedation, or with the patient anesthetized. The ventilation options under general anesthesia consist of “tube” (i.e., endotracheal intubation) and “tubeless” techniques, with the latter represented by the techniques of Spontaneous ventilation, Apneic intermittent ventilation (AIV), and Jet Ventilation (JV). Results: The use of a small (5.0-mm ID) MLT tube with positive-pressure ventilation remains the standard for airway management in most nonlaser microlaryngeal surgery, and it is associated with minimal or no intraoperative complications. Spontaneous ventilation is rarely used in adult microlaryngeal surgery, but it is commonly employed in the pediatric patient population. AIV remains a relatively popular technique for microlaryngeal surgical procedures of short duration in some surgical centers. Superimposed High-Frequency Jet Ventilation (SHFJV), which combines highfrequency and low-frequency ventilation modes, has been used effectively in surgical treatment of high-grade laryngeal and tracheal stenosis. Conclusion: General anesthesia for microlaryngeal surgery represents a unique example of close cooperation between the surgeon and the anesthesiologist.

Predictors for failure of supraglottic superimposed high-frequency jet ventilation during endoscopic upper airway surgery in pediatric patients.

Airway surgery in pediatric patients is challenging with regard to balancing surgical exposure with ventilation requirements, as during the procedure the airway must be shared between laryngologist and anesthetist. For endoscopic laryngeal surgery, different methods of ventilation are used, among others jet ventilation via a specifically adapted suspension laryngoscope using a dual jet stream(Supraglottic Superimposed High Frequency Jet ventilation, SSHFJV) (1).High BMI and a history of pulmonary pathology proved to be factors contributing to failing of SSHFJV in adult patients (2). However, factors influencing the failure of SSHFJV in pediatric patients have never been described yet.

Respiratory failure in children with oncohematological and immunological diseases: methods of treatment

Acute respiratory distress syndrome (ARDS) against the background of a lung infection is one of the chief reasons for a fatal outcome in children with oncohematological and immunological diseases. This is due to the fact that in 16–24% of these patients, it is not possible to treat critical hypoxemia successfully using the traditional methods of mechanical ventilation (MV) of the lungs. For patients with ARDS, the method of choice for treating critical hypoxemia is extracorporeal membrane oxygenation (ECMO), but pronounced cytopenia, immunosuppression and hemostatic system disorders constitute absolute contraindications for ECMO, owing to a high risk of numerous fatal complications. Therefore, there remains currently a rather relevant problem: specifically, the search for alternative methods of mechanical ventilation, which would aim to improve oxygenation and gas exchange during severe forms of ARDS in children with oncohematological and immunological diseases. One of such methods is superimposed high-frequency jet ventilation (SHFJV).

A New and Safe Mode of Ventilation for Interventional Pulmonary Medicine: The Ease of Nasal Superimposed High Frequency Jet Ventilation.

We use pulmonary interventional procedures for the diagnosis of pulmonary diseases either for benign or malignant lesions. Flexible bronchoscopy with or without radial endobronchial ultrasound, convex-probe endobronchial ultrasound and electromagnetic navigation are procedures performed in centers with experience in diagnostic pulmonary medicine. The method of sedation and ventilation is very important in order to avoid or handle with success complications. Proper respiration during pulmonary (or other interventional) procedures is a key factor. Apart from the proper sedation method we have to choose the proper ventilation method which decides respiratory movement. Superimposed high-frequency jet ventilation (SHFJV) is supposed to be safe and effective in clinical practice. Although this perception is commonly accepted, there is no study proving its safety on the basic of reliable data. We analyzed the data of 100 patients in different interventional settings (bronchoscopy with or without navigational approach, left atrial appendage closure (LAAC) or intracardiac catheterization) using nasal SHFJV. Mainly analyzed were capillary ABG-Data at the beginning and end of the intervention under sedation. The aim was to analyze if a risk scenario for the patient by using the nasal SHFJV can be derived by measuring the changes of pCO2, pO2, cBase Excess, cHCO3 and PH. Due to our data we conclude that this method of ventilation can be easily and safely used in interventional medicine for patients with all kind of comorbidities such as; chronic respiratory disease, lung cancer, interstitial lung disease, structural heart disease and heart failure.

Total intravenous anaesthesia- Target Controlled Infusion and Superimposed High-Frequency Jet Ventilation – an anaesthetic protocol for interventional bronchoscopy in cancer patients

Introduction: Diagnostic or therapeutic bronchoscopy may be performed under general anaesthesia in special circumstances aiming for patient safety and operator comfort. Tracheobronchial instrumentation requires an open system ventilatory support. We report the first case series of oncologic patients managed with Total Intravenous Anaesthesia–Target Controlled Infusion (TIVA-TCI) and Superimposed High-Frequency Jet Ventilation (SHFJV) during flexible and rigid bronchoscopy in our institution. We evaluated the safety profile of this technique in cancer patients. Methods: We analysed 24 oncological patients requiring bronchoscopy under general anaesthesia during a 9 months period. The anaesthetic protocol consisted in TIVA-TCI with propofol, Schnider model, site effect concentration, with standard intra-anaesthetic monitoring plus hypnosis and neuromuscular function monitoring and SHFJV using Twin StreamTM ventilator. Results: A number of 25 interventions were performed - 19 flexible and 6 rigid bronchoscopy. During the procedures, optimal anaesthesia depth (bispectral index=40-60) was maintained with a mean propofol site effect concentration Ce=3.1 (+/-0.6) µg/ml. Hemodynamic parameters varied +/-10-20% of preoperative values. SpO2 was stable with a mean value of 98.5% (FiO2=0.5-1) and intermittently measured etCO2 had a mean value of 32 (+/-5.4) mmHg. Airway pressures varied according to procedural particularities with a safety upper limit of 25 mmHg. We recorded no intra-anaesthetic or post-interventional complications. Conclusion: The anaesthetic protocol including TIVA-TCI and SHFJV is a safe and effective method of maintaining adequate depth of anaesthesia, cardiovascular stability and gas exchange during diagnostic or therapeutic bronchoscopy in cancer patients.

Influence of Tracheal Obstruction on the Efficacy of Superimposed High-frequency Jet Ventilation and Single-frequency Jet Ventilation.

Both superimposed high-frequency jet ventilation (SHFJV) and single-frequency (high-frequency) jet ventilation (HFJV) have been used with success for airway surgery, but SHFJV has been found to provide higher lung volumes and better gas exchange than HFJV in unobstructed airways. The authors systematically compared the ventilation efficacy of SHFJV and HFJV at different ventilation frequencies in a model of tracheal obstruction and describe the frequency and obstruction dependence of SHFJV efficacy. Ten anesthetized animals (weight 25 to 31.5 kg) were alternately ventilated with SHFJV and HFJV at a set of different fHF from 50 to 600 min. Obstruction was created by insertion of interchangeable stents with ID 2 to 8 mm into the trachea. Chest wall volume was measured using optoelectronic plethysmography, airway pressures were recorded, and blood gases were analyzed repeatedly. SHFJV provided greater than 1.6 times higher end-expiratory chest wall volume than HFJV, and tidal volume (VT) was always greater than 200 ml with SHFJV. Increase of fHF from 50 to 600 min during HFJV resulted in a more than 30-fold VT decrease from 112 ml (97 to 130 ml) to negligible values and resulted in severe hypoxia and hypercapnia. During SHFJV, stent ID reduction from 8 to 2 mm increased end-expiratory chest wall volume by up to 3 times from approximately 100 to 300 ml and decreased VT by up to 4.2 times from approximately 470 to 110 ml. Oxygenation and ventilation were acceptable for 4 mm ID or more, but hypercapnia occurred with the 2 mm stent. In this in vivo porcine model of variable severe tracheal stenosis, SHFJV effectively increased lung volumes and maintained gas exchange and may be advantageous in severe airway obstruction.

Superimposed high-frequency jet ventilation combined with continuous positive airway pressure/assisted spontaneous breathing improves oxygenation in patients with H1N1-associated ARDS

BackgroundNumerous cases of swine-origin 2009 H1N1 influenza A virus (H1N1)-associated acute respiratory distress syndrome (ARDS) bridged by extracorporeal membrane oxygenation (ECMO) therapy have been reported; however, complication rates are high. We present our experience with H1N1-associated ARDS and successful bridging of lung function using superimposed high-frequency jet ventilation (SHFJV) in combination with continuous positive airway pressure/assisted spontaneous breathing (CPAP/ASB).MethodsWe admitted five patients with H1N1 infection and ARDS to our intensive care unit. Although all patients required pure oxygen and controlled ventilation, oxygenation was insufficient. We applied SHFJV/CPAP/ASB to improve oxygenation.ResultsInitial PaO2/FiO2 ratio prior SHFJV was 58-79 mmHg. In all patients, successful oxygenation was achieved by SHFJV (PaO2/FiO2 ratio 105-306 mmHg within 24 h). Spontaneous breathing was set during first hours after admission. SHFJV could be stopped after 39, 40, 72, 100, or 240 h. Concomitant pulmonary herpes simplex virus (HSV) infection was observed in all patients. Two patients were successfully discharged. The other three patients relapsed and died within 7 weeks mainly due to combined HSV infection and in two cases reoccurring H1N1 infection.ConclusionsSHFJV represents an alternative to bridge lung function successfully and improve oxygenation in the critically ill.

Percutaneous dilational tracheostomy (PDT) and prevention of blood aspiration with superimposed high-frequency jet ventilation (SHFJV) using the tracheotomy-endoscope (TED): results of numerical and experimental simulations

We describe an innovative computer-based method for the analysis of gas flow using a modified airway management technique to perform percutaneous dilatational tracheotomy (PDT) with a rigid tracheotomy endoscope (TED). A test lung was connected via an artificial trachea with the tracheotomy endoscope and ventilated using superimposed high-frequency jet ventilation. Red packed cells were instilled during the puncture phase of a simulated percutaneous tracheotomy in a trachea model and migration of the red packed cells during breathing was continuously measured. Simultaneously, the calculation of the gas-flow within the endoscope was numerically simulated. In the experimental study, no backflow of blood occurred during the use of superimposed high-frequency jet ventilation (SHFJV) from the trachea into the endoscope nor did any transportation of blood into the lower respiratory tract occur. In parallel, the numerical simulations of the openings of TED show almost positive volume flows. Under the conditions investigated there is no risk of blood aspiration during PDT using the TED and simultaneous ventilation with SHFJV. In addition, no risk of impairment of endoscopic visibility exists through a backflow of blood into the TED. The method of numerical simulation offers excellent insight into the fluid flow even under highly transient conditions like jet ventilation.

Boost of the pulsation rate from 600/min to 1200/min during supraglottic, superimposed high frequency jet ventilation (SHFJV) optimises the operating conditions during vocal cord surgery and does not influence pulmonary pressures

Boost of the pulsation rate from 600/min to 1200/min during supraglottic, superimposed high frequency jet ventilation (SHFJV) optimises the operating conditions during vocal cord surgery and does not influence pulmonary pressures

From low-tidal-volume ventilation to lowest-tidal-volume ventilation

The therapeutic measures of lung-protective mechanical ventilation used in treatment of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) have revived the interest in high-frequency ventilation (HFV). The reduction of the tidal volume during the conventional ventilation (CV) in terms of low-tidal-volume ventilation is not unboundedly feasible. However, HFV allows a further reduction of tidal volume. Established HFV techniques are high-frequency oscillation (HFO), high-frequency percussive ventilation (HFPV) and superimposed high-frequency jet ventilation (SHFJV). The aim of this study was to evaluate the amelioration of the oxygenation index (OI).

Superimposed high-frequency jet ventilation (SHFJV) for endoscopic laryngotracheal surgery in more than 1500 patients

Superimposed high-frequency jet ventilation (SHFJV), which does not require any tracheal tubes or catheters, was developed specifically for use in laryngotracheal surgery. SHFJV uses two jet streams with different frequencies simultaneously and is applied in the supraglottic space using a jet laryngoscope and jet ventilator. Between 1990 and 2004, SHFJV was studied in 1515 consecutive patients (including 158 children requiring laryngotracheal surgery) prospectively. Ventilation was performed with an air/oxygen mixture and anaesthesia was administered i.v. Adequate oxygenation and ventilation was achieved in 1512 patients. Arterial blood gas analyses (BGA) were performed between 1990 and 1994; thereafter BGA was only performed in patients with high-grade stenosis of the larynx/trachea or high-risk patients [n=623, mean Pa(O(2)) 133.8 (39.4) mm Hg and mean Pa(CO(2)) 42.3 (10.1) mm Hg]. There were no significant changes in Pa(O(2)) or Pa(CO(2)) during the entire period of SHFJV. No complications secondary to the ventilation technique were observed; in particular, no barotrauma occurred. Three patients required tracheal intubation. SHFJV was also successfully used for laser surgery (n=312). It proved to be a safe mode of ventilation without any complications such as airway fire, major haemorrhage, or aspiration of debris. SHFJV is an advanced ventilation mode playing a pivotal role in the (open) ventilatory support/ventilation of patients with laryngotracheal stenosis. It is particularly indicated in cases of severe stenosis and offers optimal conditions for laryngotracheal surgery, including laser surgery and stent implantation techniques.

P48: General anesthesia with super-imposed high frequency jet ventilation can reduce peak airway pressure and improve oxygenation during laparoscopic bariatric surgery

Laparoscopic bariatric surgery rapidly spread worldwide because of less invasiveness. Despite of advantages, laparoscopic surgery is associated with more pronounced intra-operative respiratory changes than open surgery. Morbid obesity patients have a decrease in respiratory system compliance. These changes cause a decreased pulmonary reserve, faster desaturations and make them more difficult to ventilate with positive pressure ventilation. Pneumoperitoneum during laparoscopic surgery contributes to high peak airway pressure (PAP), decrease in the Functional Residual Capacity (FRC) and increasing PaCO2.

Superimposed high-frequency jet ventilation and oleic-acid-induced acute lung injury piglets: an experimental study

Superimposed high-frequency jet ventilation (SHFJV) is a special form of combined high-frequency jet ventilation described in other studies as an effective respiratory therapy of acute lung injury (ALI) patients. We compared this technique with conventional mechanical ventilation in oleic-acid-induced ALI piglets over a study period of 5 hours. After ALI induction, 18 pigs were randomly assigned to three groups. A SHFJV group with a high-frequency (500 bpm) and a low-frequency (15–20 bpm) jet stream and a PEEP of 10 cmH2O; a CPPV group (continuous positive pressure ventilation) presenting VT = 10 ml/kg, I:E = 1:1, PEEP = 10 cmH2O; and a IPPV group (control group; intermittent positive pressure ventilation) VT = 10 ml/kg, I:E = 1:1, zero PEEP. SHFJV animals showed an earlier and more efficient improvement in oxygenation compared with group B (90 vs 180 min; PaO2 70.5 ± 11.3 vs 41.2 ± 7.9 kPa) despite lower mean airway pressures applied (16 ± 1.4 vs 22 ± 1.8 mbar). CO2 elimination was also more effective (6.0 ± 1.4 vs 8.2 ± 1.6) although peak airway pressures were the lowest (30 ± 3.8 vs 45 ± 4.6 mmHg). SHFJV may therefore be useful in ALI management.

Superimposed high frequency jet ventilation (SHFJV) for endoscopic laryngotracheal surgery, experiences with 1515 patients

Department of Anaesthesiology and General Intensive Care, Medical University of Vienna, Vienna, Austria

Superimposed High-Frequency Jet Ventilation for Laryngeal and Tracheal Surgery

Objective To describe our experience with superimposed high-frequency jet ventilation (SHFJV), which does not require any endotracheal tubes or catheters, for performing laryngeal and tracheal surgery. Design A case series of 500 patients. Setting A university medical center. Patients Four hundred sixty adult patients and 40 children in a consecutive sample who required laryngeal or tracheal surgery under SHFJV. Interventions The SHFJV uses 2 jet streams with different frequencies simultaneously and is applied using a jet laryngoscope. Ventilation was performed with an air-oxygen mixture, and intravenous agents were used for anesthesia. Arterial blood gas values were analyzed. Main Outcome Measures Reported values of oxygenation and ventilation during the application of SHFJV and laryngotracheal surgery. Results In 497 patients, adequate oxygenation with a mean±SD PaO 2 of 91.8±22.9 mm Hg and ventilation with a PaCO 2 of 29.7±5.5 mm Hg were achieved using SHFJV. The average duration of the application of ventilation was 27 minutes, and the longest duration was 118 minutes. No complications due to the ventilation technique were observed. Laser surgery was performed in 150 patients. Conclusions The use of SHFJV in combination with the jet laryngoscope provides patients with sufficient ventilation during laryngotracheal surgery. Even in patients at high risk because of pulmonary or cardiac disease, this technique can be applied safely. In patients with stenosis, the ventilation is applied from above the stenosis, reducing the risk of barotrauma. The SHFJV can be used for tracheobronchial stent insertion, and laser can be used without any additional protective measures.

Superimposed high-frequency jet ventilation for laryngeal and tracheal surgery.

To describe our experience with superimposed high-frequency jet ventilation (SHFJV), which does not require any endotracheal tubes or catheters, for performing laryngeal and tracheal surgery. A case series of 500 patients. A university medical center. Four hundred sixty adult patients and 40 children in a consecutive sample who required laryngeal or tracheal surgery under SHFJV. The SHFJV uses 2 jet streams with different frequencies simultaneously and is applied using a jet laryngoscope. Ventilation was performed with an air-oxygen mixture, and intravenous agents were used for anesthesia. Arterial blood gas values were analyzed. Reported values of oxygenation and ventilation during the application of SHFJV and laryngotracheal surgery. In 497 patients, adequate oxygenation with a mean +/- SD PaO2 of 91.8 +/- 22.9 mm Hg and ventilation with a PaCO2 of 29.7 +/- 5.5 mm Hg were achieved using SHFJV. The average duration of the application of ventilation was 27 minutes, and the longest duration was 118 minutes. No complications due to the ventilation technique were observed. Laser surgery was performed in 150 patients. The use of SHFJV in combination with the jet laryngoscope provides patients with sufficient ventilation during laryngotracheal surgery. Even in patients at high risk because of pulmonary or cardiac disease, this technique can be applied safely. In patients with stenosis, the ventilation is applied from above the stenosis, reducing the risk of barotrauma. The SHFJV can be used for tracheobronchial stent insertion, and laser can be used without any additional protective measures.

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

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: A significantly low inspiration gas temperature was noted in patients in group B, initially (27.2 +/- 2.5 degrees C) and after 2 days (28.0 +/- 1.6 degrees C) (P < 0.05). The percentage of relative humidity of the inspiration gas in patients in group B was also initially significantly low (69.8 +/- 4.1%; P < 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.