High frequency jet ventilation

A case is described where high frequency jet ventilation was used to avoid the cardiovascular depressant effects associated with conventional ventilation. Early weaning from inotropic and ventilatory support proved possible.     

Isocapnic high frequency jet ventilation: dead space depends on frequency, inspiratory time and entrainment

Twelve healthy pigs were ventilated with high frequency jet ventilation via a Mallinckrodt HiLo jet tube. The expired gas was led to a conventional ventilator and CO2 analyzer which were used to measure CO2 elimination. There was no bias flow, so that the jet entrained only expired gas, i.e. rebreathing occurred. Frequency was varied between 2 and 11 Hz and the duration of inspiration, as a fraction of the ventilatory cycle (Ti/Ttot), from 5 to 20%. The minute ventilation, Vjet, delivered by the jet ventilator was adjusted to maintain a constant PaCO2. At 2 Hz and a Ti/Ttot of 5%, Vjet was of the same magnitude as ventilation during conventional intermittent positive pressure ventilation, and the total dead space fraction, VD/VT was 0.32. Both increasing frequency at a constant Ti/Ttot, and increasing Ti/Ttot at a constant frequency, increased VD/VT which was maximal (0.8) at 11 Hz and a Ti/Ttot of 20%. When entrainment was blocked, tidal jet volume had to be greatly increased. The continuous measurement of CO2 elimination was found to be useful for maintaining isocapnia when the jet ventilator setting was changed.     

High frequency jet ventilation for microlaryngeal laser surgery

The use of a triple lumen central venous catheter, which can be shielded from laser irradiation by metal tape, as a conduit for high frequency jet ventilation in six children, is described. The problems of anaesthesia for laryngeal laser surgery and the advantages of the technique described in this paper are discussed.     

Transtracheal high frequency jet ventilation for endoscopic airway surgery: a multicentre study

Serious complications during high frequency jet ventilation(HFJV) are rare and have been documented in animals and in casereports or short series of patients with a difficult airway.We report complications of transtracheal HFFJV in a prospectivemulticentre study of 643 patients having laryngoscopy or laryngeallaser surgery. A transtracheal catheter could not be insertedin two patients (0.3%). Subcutaneous emphysema (8.4%) was morefrequent after multiple tracheal punctures. There were sevenpneumothoraces (1%), two after laser damage to the injector,one after difficult laryngoscopy, four with no clear cause.Arterial desaturation of oxygen was more frequent during lasersurgery and in overweight patients. Transtracheal ventilationfrom a ventilator with an automatic cut-off device is a reliablemethod for experienced users. Control of airway pressure doesnot prevent a low frequency of pneumothorax. Br J Anaesth 2001; 87: 870–5     

Air entrainment during high-frequency jet ventilation in a model of upper tracheal stenosis

BACKGROUND: Previous work has demonstrated that when high-frequency jet ventilation (HFJV) is applied above an airway stenosis, higher distal airway pressures are produced compared with when the same ventilation is delivered below the stenosis (BSV). This study aimed to investigate the mechanisms underlying this finding. METHODS: HFJV was applied to a model of laryngo-tracheal stenosis with the jet located above the stenosis (ASV), with a catheter passed through the stenosis (TSV) or with HFJV delivered by a side port BSV. For each configuration and over a range of diameters of stenosis (2.5-8.5 mm), distal tracheal pressures and delivered minute volume were measured and air entrainment estimated. Experiments were repeated using the same model with the addition of a simulated 'pharynx' around the stenosis. RESULTS: Distal airway pressures, minute volumes, and air entrainment were consistently higher during ASV compared with BSV and TSV. The presence of the 'pharynx' made no significant difference to airway pressures or air entrainment. Delivered minute volumes varied between ASV, TSV, and BSV, and were also dependent on the stenosis diameter. With ASV, there appeared to be a range of stenosis diameters (4.0-5.5 mm) which 'maximized' minute volumes. CONCLUSIONS: The results suggest that the high airway pressures generated during ASV are the consequence of air entrainment and this effect, although reduced slightly, is maintained in the presence of the model pharynx. In contrast to the previous work, no significant entrainment occurred during BSV. If applicable to patients, these data suggest that ASV HFJV should be avoided in small diameter stenoses, but provides more efficient gas delivery and greater distending pressures with larger stenoses. BSV HFJV produces lower distal pressures and more consistent oxygen concentrations of injected gas across a range of stenosis diameters.     

Convective mixing mechanisms in high frequency intermittent jet ventilation

A liquid flow visualization technique was used to identify the location of neutrally buoyant bead clouds injected into airway models during flows simulating high frequency intermittent jet ventilation (HFIJV) in neonatal lungs. The motions of these bead clouds show that the convective or bulk mixing that occurs during HFIJV is made up of two parts; a turbulent convective exchange with the atmosphere caused by the jet in the trachea and a streaming motion along the airways driven by an interaction between the jet and the expansion and contraction of the airways due to their compliance. These convective streaming motions combine with molecular diffusion to produce augmented diffusion which transports O₂ and CO₂ between the trachea and the peripheral alveoli. Optimizing HFIJV (as well as other forms of HFV) depends on maximizing these airway convective streaming flows which depend on many more lung and fluid mechanical parameters than are necessary to describe conventional mechanical ventilation.     

High frequency jet ventilation

High frequency jet ventilation for thoracic surgery offers some practical advantages over intermittent pressure ventilation using bronchial tubes. Satisfactory blood gases were obtained in 50 patients and good operating conditions were provided.     

Gas flow distribution in distal high frequency jet ventilation and lung thorax compliance

To investigate the influence of changes in thorax and lung compliance on ventilation during distal High Frequency Jet Ventilation (HFJV), similar ventilator settings were compared before and after changing the compliance in two groups of anaesthetized mongrel dogs. Each period of distal HFJV was preceded by adequate Intermittent Positive Pressure Ventilation (IPPV) to assure a start with baseline values. In Group 1 (n = 7), thorax compliance was changed by chest strapping, while in Group 2 (n = 7) lung compliance was changed by inducing acute lung injury by injection of oleic acid into the right atrium. Gas flow distribution in the ventilatory circuit during distal HFJV was determined before and after the changes in compliance were induced. Comparing similar ventilator settings during distal HFJV in the same dog, a decrease in lung or thorax compliance led to changes in gas flow distribution in the ventilatory circuit. Entrainment was decreased and bypass increased with a negative effect on the gas volume entering the lungs and on gas exchange. The results indicate that distal HFJV should be regarded as pressure-limited ventilation.     

气管导管远、近端复合高频喷射通气对二氧化碳清除和血流动力学影响的比较

选择ＡＳＡⅠ～Ⅱ 级全麻手术患者３６例，随机分为两组，于气管导管的远端和近端分别实施远、近端复合高频喷射通气（ＣＨＦＪＶ）。ＣＨＦＪＶ是在每分２００次高频喷射通气（ＨＦＪＶ）基础上，分别叠加每分 ２～５次潮气量为 １５ｍｌ／ｋｇ的间歇指令通气（ＩＭＶ）。结果：远、近端ＣＨＦＪＶ时 ＰａＣＯ２均比相应的远、近端ＨＦＪＶ明显降低；远端ＣＨＦＪＶ时 ＰａＣＯ２明显低于近端 ＣＨＦＪＶ， 而动脉氧合和血流动力学指标（ＭＡＰ、ＣＯ、ＨＲ、ＳＶ）两者均无明显差异。表明：远、近端ＣＨＦＪＶ的ＣＯ２清除效果均优于单纯的ＨＦＪＶ。远端ＣＨＦＪＶ的ＣＯ２清除效果明显优于近端ＣＨＦＪＶ，且不影响血流动力学指标。     

High frequency jet ventilation in intensive care—a review of 63 patients

High frequency jet ventilation has been used clinically in this unit for over 2 years. During this time we have treated 63 intensive care patients for whom the mean duration of ventilatory support was 3.4 days, which represents more than 5000 patient hours in total, with the Penlon Bromsgrove humidified jet ventilator. The series comprises a wide variety of general intensive care patients; a review of these cases is presented.     

High frequency jet ventilation for bilateral bullectomy

This case report describes the use of high frequency jet ventilation for resection of bilateral lung bullae. Low airway pressures reduced the risk of pulmonary barotrauma. A continuous infusion of ketamine provided acceptable anaesthesia.     

Tracheobronchial dilating effect of high frequency jet ventilation

Effect of high frequency jet ventilation (HJFV) on tracheobronchial tone was examined in anesthetized dogs. Changes in intraluminal pressure of water-filled endotracheal cuff (Pcuff) were used as an indicator of tracheal smooth muscle tone. Animals were initially ventilated with conventional mechanical ventilation (CMV) to maintain normal Pa_{CO 2}. HFJV (2.0Hz.) was then applied to each animal in such a way to maintain the same mean airway pressure and Pa_{CO 2} as in CMV.Immediately after changing CMV to HFJV, Pcuff decreased significantly and remained decreased during the period of HFJV. After changing HFJV to CMV, Pcuff gradually returned to its previous level. Histamine-induced tracheobronchial constriction was partially released by HFJV as shown by a decrease in Pcuff and airway resistance (Raw) and by an increase in static lung-thorax compliance (Cst) measured immediately after the cessation of HFJV.These results suggest that HFJV has a tracheobronchial dilating action, presumably mediated by pulmonary stretch reflex, and this may be one of the mechanisms of an increase in mucous secretion and of other reported favorable effects of HFJV in some types of respiratory failure.(Toyooka H, Amaha K, Yokoyama K.: Tracheobronchial dilating effect of high frequency jet ventilation. J Anesth 4: 206–212, 1990)     

Comparison of conventional intermittent positive pressure ventilation with high frequency jet ventilation

This study was designed to compare the cardiorespiratory effects of high frequency jet ventilation at 150 breaths/minute with and without added positive and expiratory pressure, with conventional intermittent positive pressure ventilation in 20 patients following aortocoronary bypass graft surgery. On comparison with intermittent positive pressure ventilation, there was a decrease in peak airway pressure during high frequency jet ventilation when positive and expiratory pressure of 0 or 0.5 kPa was applied, but not with 1 kPa, and an increase in mean airway pressure with positive end expiratory pressures of 0.5 and 1 kPa. On changing from intermittent positive pressure to high frequency jet ventilation with no added end expiratory pressure, there was an acute decrease in arterial oxygen tension and increases in cardiac output and total tissue oxygen delivery. On changing from intermittent positive pressure ventilation to high frequency jet ventilation with 1 kPa of positive end expiratory pressure, there was an acute decrease in arterial oxygen tension, cardiac output and oxygen delivery, and increases in pulmonary arterial, right atrial and pulmonary capillary wedge pressures. The addition of positive end expiratory pressure did not prevent the acute decrease in arterial oxygen tension which occurred on transfer to high frequency jet ventilation.     

Resonance in the mechanical response of the respiratory system to high frequency jet ventilation

Eight normal domestic pigs (Large White breed) of body weights 17 kg to 62 kg were subjected to high frequency jet ventilation (HFJV) at frequencies of 1 to 10 Hz (60–600 breaths/min). Six animals survived the study. The gain response curves and phase shift response curves obtained for these animals indicate that respiratory system resonance can be excited at HFJV frequencies. Post-mortem examinations of the non-survivors' lungs suggested pulmonary barotrauma. These findings and their clinical implications are discussed