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.     

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。     

Gas flow distribution and tidal volume during distal high frequency jet ventilation in dogs

During distal high frequency jet ventilation (HFJV) in anaesthetized healthy dogs gas flows were recorded at the proximal end of the open tracheal jet tube. Spirometer measurements of minute volumes with and without entrainment were made. During the inspiratory or insufflation period, leakage of jet gas (bypass) could occur depending on the ventilator setting. From the gas flow recordings and the spirometer measurements, jet-, entrainment- and bypass minute volumes were determined. From these the effective minute volume, that is the minute volume of fresh gas entering the lungs, was calculated, as well as tidal volume. The results show that entrainment volumes are relatively small in an open system of distal HFJV and that at the same time bypass can (nearly) completely eliminate the effect of entrainment on tidal volume.     

Effects of helium on high frequency jet ventilation in model of airway stenosis

Background. The addition of helium to the inspired gas may facilitateventilation in the presence of clinically evident upper airwayobstruction. However, there are no data on the effects of usinga helium–oxygen mixture during high frequency jet ventilation(HFJV) in upper airway obstruction. Methods. HFJV at a frequency of 150 min^–1 (driving pressure2 bar, inspiratory time 30%) was applied to a trachea–lungmodel to simulate ventilation through varying degrees of fixedlaryngotracheal stenosis (2.5–8.5 mm). HFJV was deliveredfrom above, through and below the level of stenosis to simulatesupraglottic, transglottic and infraglottic administration.Measurements of distal tracheal pressures were repeated foreach route at steady state for each stenosis diameter usingboth 100% oxygen and helium–oxygen (50% oxygen, 50% helium).The output of the ventilator was measured during operation onoxygen and helium–oxygen. Results. Peak, mean and end-expiratory pressures were greaterduring simulated supraglottic HFJV than during transglotticand infraglottic HFJV, and pressures increased markedly as thediameter of the stenosis decreased for all routes of ventilation(P<0.001). Generated pressures during HFJV using helium–oxygenand 100% oxygen were very similar overall, although reductionsin pressures were observed during ventilation with helium–oxygenvia the transglottic and transtracheal routes at stenosis diameters<4 mm (P<0.05). However, HFJV with the helium–oxygenmixture increased the delivered gas volumes by     

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.     

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     

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.     

Laryngospasm during transtracheal high frequency jet ventilation

A 74-year-old woman developed severe cardiovascular depression during percutaneous transtracheal high frequency jet ventilation for laser surgery of the epiglottis. This was found to be caused by acute airway obstruction secondary to severe laryngospasm. We recommend profound neuromuscular blockade during percutaneous transtracheal jet ventilation, in order to prevent this complication.     

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)     

Combined unilateral high frequency jet ventilation and contralateral intermittent positive pressure ventilation

The anaesthetic management of a patient who required right lower lobectomy for bronchial carcinoma associated with emphysema, pneumoconiosis and a previous thoracoplasty for pulmonary tuberculosis, is described. A technique of unilateral high frequency jet ventilation plus conventional intermittent positive pressure ventilation to the contralateral lung was used.     

主动按压减压结合高频喷射通气用于犬的心肺复苏

目的　评价主动按压减压结合高频通气 (ACD- H)用于心肺复苏的可行性。方法　ACD- H:按压减压与通气同时进行 ,按压与呼气同步 ,减压与吸气同步 ;而主动按压减压结合传统通气技术 (ACD- C) :按压减压连续 5次停 2秒进行一次通气。 9只犬吸入 10 5℃蒸气 4秒致伤后用以上方法复苏。结果　心搏骤停前观察 :ACD- H吸气流速峰值 7.32 L / m in,呼气流速峰值 9.5 0 L / min;潮气量 79.5 0 ml,每分通气量 7.9L / m in,Pa O2 2 2 .2 5 k Pa,Pa CO2 4.93k Pa,明显优于主动按压减压结合持续供氧 (ACD) ,也明显优于单纯的 HFJV及主动按压 (AC)。电致颤心搏骤停后 ,按压与提拉条件不变 ,观测循环指标 :动脉收缩压最低值 ACD- C为 0 ,ACD- H为 18.6 8k Pa,平均值 ACD- C为19.0 7k Pa,ACD- H为 2 2 .81k Pa,两者有非常显著差异 ;心排血量最低值 ACD- C为 0 ,ACD- H为 (0 .81± 0 .45 ) L / min,平均值 ACD- C为 (0 .6 5± 0 .14) L / m in,ACD- H为 (0 .92± 0 .33) L / m in,两者差异非常明显。结论　 ACD- H用于心肺复苏 ,其效果尤于传统方法。     

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.     

高频喷射通气对吸入性损伤犬呼吸气流与气体交换的影响

目的观察犬吸入性损伤时呼吸气流对气体交换的影响。方法用三维粒子动态分析仪测定犬自主呼吸时吸气和呼气流速。将实验动物通入高压蒸气5秒后随机进行五种不同条件高频喷射通气,每种通气方式通气20分钟,并根据公式Re=Vrρ/η计算出雷诺数,同时采取动脉血标本,观察Pa-CO_2、PaO_2PIP的变化。结果①自主呼吸时吸气为层流,呼气可能为层流,也可能为涡流;②高频喷射通气(HFJV)时呼气和吸气均为涡流;③高频双向喷射通气(HFTJV)与HFJV相比,呼气流速显著增加(P<0.05),PaCO_2显著降低(P<0.05),呼气流速与PaCO_2呈负相关(r=-0.9216,P<0.05),同时吸气流速也有增加的趋势。结论 HFJV可维持吸入性损伤犬正常通气,其机制可能与涡流有关。HFTJV是在HFJV基础上增加了反向喷射气流,可以增进呼吸气体速度,促进CO_2排除。     

High frequency jet ventilation: use of the Bain system for entrainment

The use of a Bain system to convey anaesthetic gases for entrainment during high frequency jet ventilation (HFJV) was evaluated by examining the effect of varying the fresh gas flow (Vf) on the end-tidal carbon dioxide (PECO2) in 46 ASA physical status I and II patients undergoing extracorporeal shock-wave lithotripsy (ESWL). Anaesthesia was induced with methohexitone (1-2 mg.kg-1), fentanyl (1-1.5 micrograms.kg-1) and vecuronium (0.1 mg.kg-1). After endotracheal intubation with a Mallinckrodt Hi-Lo Jet cuffed endotracheal tube, the patient was immersed in a water bath and HFJV at 150 breaths per minute was instituted with an Acutronic AMS 1000 jet ventilator attached to the side channel of the Hi-Lo tube. A Bain system was attached to the proximal end of the endotracheal tube to provide gases for entrainment. Anaesthesia was maintained with an intravenous infusion of methohexitone (5 mg.kg-1.h-1) and 50% nitrous oxide in oxygen for both the jetted and entrained gases. PECO2 was determined at 5-min intervals by a single-breath technique using a calibrated Engstrom Eliza capnograph. Thirty patients were randomly allocated to receive Vf's of 50 (Group 1), 75 (Group 2) and 100 (Group 3) ml.kg-1.min-1, respectively. A further eight patients (Group 4) received a Vf of 100 ml.kg-1.min-1 for 15 min, 75 ml.kg-1.min-1 for the next 15 min and 50 ml.kg-1.min-1 thereafter. In a further group of eight patients (Group 5), Vf was initially 25 ml.kg-1.min-1 for 10 min and was then switched off for the remainder of the procedure.(ABSTRACT TRUNCATED AT 250 WORDS)     

高频喷射通气对吸入性损伤犬呼吸气流与气体交换的影响

目的观察犬吸入性损伤时呼吸气流对气体交换的影响。方法用三维粒子动态分析仪测定犬自主呼吸时吸气和呼气流速。将实验动物通入高压蒸气５秒后随机进行五种不同条件高频喷射通气，每种通气方式通气２０分钟，并根据公式Ｒｅ＝Ｖｒρ／η计算出雷诺数，同时采取动脉血标本，观察Ｐａ－ＣＯ２、ＰａＯ２、ＰＩＰ的变化。结果①自主呼吸时吸气为层流，呼气可能为层流，也可能为涡流；②高频喷射通气（ＨＦＪＶ）时呼气和吸气均为涡流；③高频双向喷射通气（ＨＦＴＪＶ）与ＨＦＪＶ相比，呼气流速显著增加（Ｐ＜０．０５），ＰａＣＯ２显著降低（Ｐ＜０．０５），呼气流速与ＰａＣＯ２呈负相关（ｒ＝－０．９２１６，Ｐ＜０．０５），同时吸气流速也有增加的趋势。结论ＨＦＪＶ可维持吸入性损伤犬正常通气，其机制可能与涡流有关。ＨＦＴＪＶ是在ＨＦＪＶ基础上增加了反向喷射气流，可以增进呼吸气体速度，促进ＣＯ２排除。