Nitric oxide and high frequency jet ventilation in a patient with bilateral bronchopleural fistulae and ARDS

PURPOSE: To describe a method of delivering nitric oxide during high frequency jet ventilation. CLINICAL FEATURES: A 63-yr-old man underwent reduction pneumoplasty for bullous emphysema. Postoperatively, ventilation was inadequate, secondary to bilateral high output bronchopleural fistulae. High frequency jet ventilation was initiated and achieved adequate ventilation (pH>7.2). Over the following 24 hr, progressive hypoxemia (SaO2 <86%) developed along with the acute respiratory distress syndrome. Nitric oxide was delivered by continuous flow at the patient Y-connector during combined high frequency jet and conventional ventilation (two conventional low volume breaths/minute). Substantial improvement in oxygenation (FiO2 0.8 0.5, SaO2 >92%) was noted initially and was sustained over 72 hr. Subsequently, the patient was weaned to conventional ventilation without difficulty. Mechanical ventilation was discontinued on postoperative day sixteen. CONCLUSION: The simultaneous use of nitric oxide and high-frequency jet ventilation was used safely and effectively in this patient as a method of support for acute respiratory distress syndrome with co-existing large bilateral bronchopleural fistulae.     

Minimum airway pressure weaning Weaning from mechanical ventilation at 50 breaths/minute by reduction of inflation pressure using a pressure generator

Ten patients, whose lungs were ventilated initially with intermittent positive pressure ventilation at conventional rates after myocardial revascularisation or cardiac valvular surgery, were weaned using a valveless high frequency jet ventilator at a constant rate of 50 breaths/minute. The withdrawal of ventilation was achieved, when clinical criteria permitted, by reduction of the tidal volume preset on the jet ventilator in successive stages; this was effected by stepwise decreases in the jet driving pressure. This new mode of weaning at a constant rate of 50 breaths/minute is associated with minimum peak airway pressures. Synchronisation of the patient's breathing with the valveless ventilator is not required and weaning is tolerated well by the patient. Arterial oxygen tension and saturation were maintained throughout weaning and did not decline after extubation of the trachea.     

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.     

Newer modes of mechanical ventilatory support

Recent modes of ventilatory support aim to facilitate weaning and minimise the physiological disadvantages of intermittent positive pressure ventilation (IPPV). Intermittent mandatory ventilation (IMV) allows the patient to breathe spontaneously in between ventilator breaths. Mandatory minute volume ventilation (MMV) ensures that the patient always receives a preset minute volume, made up of both spontaneous and ventilator breaths. Pressure supported (assisted) respiration is augmentation of a spontaneous breath up to a preset pressure level, and is different from 'triggering', which is a patient-initiated ventilator breath. Other modes or refinements of IPPV include high frequency ventilation, expiratory retard, differential lung ventilation, inversed ratio ventilation, 'sighs', varied inspiratory flow waveforms and extracorporeal membrane oxygenation. While these techniques have useful applications in selective situations, IPPV remains the mainstay of managing respiratory failure for most patients.     

Artificial ventilation of a canine model of bronchopleural fistula

The authors studied the abnormalities of gas exchange and lung mechanics in a canine model of bronchopleural fistula during intermittent positive pressure ventilation (IPPV) and high-frequency oscillatory ventilation (HFOV). The left lower lobe bronchus was opened to atmosphere and it was determined that end expired volume was best maintained at frequencies of 45-50 breaths/min. during IPPV. Comparing alternating periods of IPPV and HFOV in six dogs (Group I) at matched airway opening pressure (Pao), we found that Pao2 decreased significantly to 68 +/- 14 mmHg and 69 +/- 24 mmHg, respectively, on opening the fistula. In a second group of six dogs (Group 2), when Pao was increased by additional bias flow into the ventilatory circuit during both IPPV and HFOV, Pao2 increased significantly to 89 +/- 12 mmHg and 87 +/- 8 mmHg, respectively. Repeating Group 2 studies after induction of oleic acid low-pressure pulmonary edema demonstrated that conventional IPPV was associated with large intrapulmonary shunts. HFOV, however, maintained gas exchange at near baseline values. For both Group 1 and Group 2, the calculated gas flow through the fistula was significantly less at all levels of airway pressure during HFOV. The authors conclude that HFOV offers advantages over conventional IPPV in the maintenance of oxygenation and in the reduction of gas leak through the fistula.     

Effect of oral high frequency ventilation by jet or oscillator on minute ventilation in normal subjects.

Normal subjects were asked to breathe through an open ended tube while high frequency oscillations were superimposed on tidal breathing via a side arm, either an eight inch (20 cm) loudspeaker or a jet ventilator being used. Both systems were comfortable and well tolerated. Spontaneous minute ventilation fell by 19-46% at frequencies up to 33 Hz without a rise in transcutaneous PCO2. Maximum ventilatory savings occurred at 1.6 Hz with the jet ventilator (p less than 0.01) and at a frequency corresponding to respiratory system resonance with the loudspeaker. This suggests that during oral high frequency ventilation pulmonary gas exchange is improved and leads to more efficient carbon dioxide excretion for a given minute ventilation. This technique provides a practical and simple method of supplementing breathing in conscious subjects, and it may also have application in the management of patients with acute or chronic respiratory failure, where intubation and conventional ventilation might be avoided.     

Aspiration in transtracheal jet ventilation

Background: Transtracheal jet ventilation (TJV) has been used successfully for managing difficult airways. However, there are some controversies regarding pulmonary aspiration. It has been shown that TJV caused no aspiration as long as the frequency of ventilation was kept higher than 60/ min. On the other hand, it has been demonstrated that manual translaryngeal jet ventilation at 20 breaths per minute also provided good protection from aspiration even with 30-degree head-up position. The purpose of this study was to reevaluate this controversy with observation of the trachea and the lungs together during TJV.
Methods: Eight mongrel dogs were anesthetized, paralyzed and ventilated transtracheally with jet ventilator at frequencies variying from 600 to 10/min. The airway pressures below and above the jetting port were measured. The mouth of the dog was then filled with barium and chest x-rays were taken 5 minutes after each different jetting frequency.
Results: No tracheal or pulmonary aspiration was observed on chest x-rays as long as the frequencies were set above 80 per minute. With frequencies of 60 per minute, barium was seen in the trachea but at a level above the jetting port. Slowing down the frequency to 10/min did not affect the level of barium.
Conclusion: No aspiration could be visualized on chest x-rays. The mechanism for preventing pulmonary aspiration is thought to be due to forceful continuous gas outflow through the larynx. The epiglottis seems to play no role in this mechanism. The limited tracheal aspiration was probably due to the existence of a negative pressure in the upper airway. Cessation of the TJV will cause a drop in this pressure gradient and results in pulmonary aspiration. It is recommended that the airway above the jetting port be totally cleansed prior to discontinuation of the tanstracheal jet ventilation.     

Inhibition of phrenic nerve activity during positive-pressure ventilation at high and low frequencies

A study was made to determine whether the ventilatory pattern, in terms of ventilatory frequency, insufflation period and end-expiratory pressure, influences the arterial blood gas level at which central inspiratory activity is inhibited, and whether further expansion of the lung changes this activity. This was accomplished by measuring arterial pH and blood gases, and intratracheal, intrapleural and transpulmonary pressures, at the setting of positive-pressure ventilation causing inhibition of phrenic nerve activity in chloralose-anaesthetized cats. Spontaneous breathing movements were prevented by muscle relaxation. Ventilatory frequencies of 15-120 breaths per minute (b.p.m.) were studied at at least two different insufflation times. A volume-controlled ventilator with a large compressible volume was used in the frequency range 15-45 b.p.m. and a constant flow respirator with a low-compressible volume in the range 45-120 b.p.m. A much lower PCO2 was needed for phrenic nerve activity to be inhibited at a ventilatory frequency of 15 b.p.m. than at higher frequencies. At ventilatory frequencies between 30 and 120 b.p.m. inhibition could be achieved at a higher PCO2, within the normal range. The inhibition of phrenic nerve activity tended to be less stable when PEEP was added during ventilation with a long insufflation period, but PEEP did not influence the arterial blood gas level at which inhibition occurred. In the lower frequency range of 15-30 b.p.m., inspiratory activity was observed with bursts at the same rate as the insufflations given by the ventilator. The intratracheal peak pressures at ventilation causing inhibition of phrenic nerve activity decreased with increasing ventilatory frequencies.(ABSTRACT TRUNCATED AT 250 WORDS)     

A low flow open circle system for anaesthesia Part I: Laboratory evaluation at normal and high frequencies

A circle breathing system was connected by deadspace tubing to an open system valveless ventilator. The minimum volume of this tubing, required to prevent dilution of anaesthetic gas in the breathing system by the driving gas of the ventilator, was determined at frequencies of 15, 30, 60, 100 and 150 breaths/minute, with tidal volumes that ranged from 100 to 1100 ml and a fresh gas supply to the circle system of 1, 2 and 4 litres/minute. At 15 breaths/minute, tidal volumes equal to or less than the deadspace volume could be used safely without any mixing with the ventilator driving gas, when a fresh gas flow of 2 litres/minute or above is supplied to the circle system. At 1 litre/minute of fresh gas flow, mixing occurred at tidal volumes less than the deadspace volume. Mixing of gas occurred in the system at frequencies greater than 30 breaths/minute even when the tidal volume was much less than the deadspace volume. However, at high frequencies of ventilation, since the tidal volume requirement decreases, deadspace tubing with a safe internal volume, that is greater than 600 ml, may be used up to 100 breaths/minute.     

Alveolar oxygenation and mouth-to-mask ventilation: effects of oxygen insufflation.

The effect on alveolar oxygen fraction (FAO2) of insufflating oxygen under a mask (or through an inflow nipple provided in the mask) during simulated mouth-to-mask ventilation was investigated using a lung model. A variety of commercially produced masks were evaluated. Two patterns of artificial ventilation were applied: 1. 500 ml tidal volume at 20 breaths per minute, and 2. 900 ml tidal volume at 12 breaths per minute. The ventilating gas mixture was oxygen 16% in nitrous oxide, and oxygen was insufflated at flow rates of 2, 4, 6, 8, 10, 12 or 14 litres per minute. The rate of rise of FAO2 and the equilibrium FAO2 attained were greatest at high oxygen inflow rates. The relationship between oxygen flow and FAO2 was not linear however, and an oxygen flow rate of 10 l/min was adequate to generate FAO2's around 50% with either ventilatory pattern. The equilibrium FAO2 achieved was greater with smaller tidal volumes and with larger mask deadspace. We also found that several breaths were required for equilibration of FAO2 during each trial, supporting recommendations that several breaths should be given on commencement of artificial ventilation during cardiopulmonary resuscitation.     

High frequency jet ventilation and gas trapping

We have compared three types of high frequency jet ventilation (HFJV) with conventional positive pressure ventilation in patients recovering from elective coronary artery bypass surgery. Twelve patients were allocated randomly to receive HFJV at ventilatory frequencies of 60, 100, 150 and 200 bpm from a standard jet ventilator at either the proximal or distal airway (HFJV.p and HFJV.d), or from a valveless high frequency jet ventilator acting as a pneumatic piston (VPP). Trapped gas volume (Vtr), cardiac index (CI) and right ventricular ejection fraction (RVEF) were measured. Vtr was related to the type of HFJV used (P < 0.05) and ventilatory frequency (P < 0.05). CI decreased with increasing rate of HFJV (P < 0.05) and there were significant differences between the three types of HFJV (P < 0.05). RVEF showed a linear relationship with ventilatory frequency (P < 0.05) decreasing most with the VPP. The decrease in RVEF was associated with an increase in right ventricular end-systolic volume (P < 0.05) suggesting that an increase in right ventricular afterload was the cause. The same three types of HFJV were compared using a lung model with variable values of compliance and resistance, to assess the impact of lung mechanics on gas trapping (Vtr, ml). Lung model compliance (C) was set at 50 or 25 ml cm H2O-1 and resistance (R) at 5 or 20 cm H2O litre-1 s, where values of 50 and 5, respectively, are normal. Vtr increased with ventilatory frequency for all types of jet ventilation (P < 0.05), varying with the type of jet ventilation used (P < 0.05).      

Weaning from Mechanical Ventilation by means of Intermittent Assisted Ventilation I.A.V. Case Reports

A new ventilator is described which is capable of interposing controlled breaths synchronized with the patient's own breathing rhythm. This ventilation pattern is called "intermittent assisted ventilation" (IAV). It differs from intermittent mandatory ventilation (IMV) in that each ventilator cycle is triggered by the patient. IAV constitutes a new approach to the problems during the critical period of weaning from mechanical ventilation. Further, this new ventilator provides means for continuous display and recording of airway gas flow and pressures and expired minute volume (EMV) during different types of ventilation, e.g. controlled ventilation, intermittent assisted, and spontaneous ventilation.     

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.     

Limits of high frequency percutaneous transtracheal jet ventilation using a fluidic logic controlled ventilator

A study was undertaken on dogs to find the limit of carbon dioxide exchange with high frequency jet ventilation using a fluidic logic controlled oxygen jet ventilator. Fifteen dogs were ventilated through a transtracheal catheter at respiratory rates up to 600 per minute. The following were recorded: aortic, pulmonary artery, pulmonary arterial wedge, and central venous blood pressures; intratracheal pressure, electrocardiogram; inspiratory and expiratory time of the jet; arterial and central venous blood gases; intermittent cardiac output. Normal gas exchange was found up to a respiratory rate of 400 per minute with low tidal volume and low intratracheal pressures. There were no adverse circulatory effects up to a rate of 400 per minute. At rates of 500 and 600 per minute, cardiac contractility was unaffected, but a decreased heart rate and increased peripheral resistance produced a fall in cardiac output. There was no interference with the resumption of spontaneous ventilation during weaning. In a control series of five dogs, apnoeic oxygenation was used. The PaCO2 was allowed to reach 15.96 kPa (120 torr). High frequency jet ventilation was then started at a rate of 600 per minute and decreased in increments to 100 per minute. Arterial blood gases were continuously recorded through an intra-arterial catheter connected to a mass spectrometer. The PaCO2 gradually declined to normal levels as the rate decreased.     

HIGH FREQUENCY JET VENTILATION: THE INFLUENCE OF GAS FLOW, INSPIRATION TIME AND VENTILATORY FREQUENCY ON GAS TRANSPORT IN HEALTHY ANAESTHETIZED DOGS

High frequency jet ventilation (HFJV) experiments were performedin healthy anaesthetized mongrel dogs via a multilumen trachealjet tube to examine the influence of gas flow, ventilatory frequencyand inspiration time (as a percentage of the total ventilatorycycle) on gas exchange. We compared arterial Po₂, PCO₂ and cardiacoutput during periods of adequate intermittent positive pressureventilation (IPPV) and periods of HFJV. Reducing gas flow bydecreasing the number of activated valves and increasing thefrequency to greater than 4 Hz resulted in less than optimalarterial P0₂ and Pco₂ compared with IPPV. This indicates thatconvection during HFJV is probably essential for efficient gasexchange. Inspiration time proved to be important in determiningefficacy of ventilation for a fixed ventilator minute volume.Cardiac output. during all HFJV settings was equal to or greaterthan cardiac output during IPPV, even at those HFJV settingsthat resulted in a positive end-expiratory pressure.     

Conventional versus high frequency jet ventilation with a bronchopleural fistula

A bronchopleural fistula (BPF) is an aberrant pathway through which inspired gas exits the lungs. A BPF may cause significant respiratory compromise, which in turn may result in the need of mechanical ventilation. The purpose of this study was to compare the efficacy of conventional positive pressure ventilation (CV) with high frequency jet ventilation (HFJV) using increasing increments of positive end expiratory pressure (PEEP) in the management of an induced BPF. A reproducible model of a BPF was surgically created in 10 mongrel dogs. Measurements of blood pressure (BP), cardiac output (CO), mean airway pressure (Maw), peak airway pressure (Paw), and fistula flow (FF) were carried out with the chest closed. Selective occlusion of the BPF allowed for blood gas stabilization at increased values of PEEP. Paired observations were performed at 0, 5, 10, 15, and 20 cm H2O of PEEP, while maintaining PaCO2 between 30 and 50 Torr. There was no difference in BP or CO between ventilation methods even though significantly lower Maw and Paw pressures were obtained using HFJV. While FF increased significantly with each increment of PEEP, there was no improvement in flows obtained using HFJV. This acute model of a BPF demonstrated that increasing PEEP dramatically increases FF irrespective of the method of ventilation.     

Comparison of high-frequency jet ventilation with conventional mechanical ventilation for bronchopleural fistula

In seven patients with acute respiratory failure and a bronchopleural fistula, the authors compared gas exchange and volume of gas lost via the chest tube during conventional mechanical ventilation (CV) and high-frequency jet ventilation (HFJV). After the initial comparison, patients were randomized to HFJV or CV, unless one mode of ventilation was clearly superior based on preestablished criteria. In six of the seven patients, oxygenation deteriorated after the switch from CV to HFJV. The ratio of PaCO2 to FI02 declined from 227 +/- 167 to 133 +/- 100 (mean +/- SD, P less than 0.05), and the PaCO2 increased from 47 +/- 13 to 56 +/- 18 mm Hg (P less than 0.05). The mean chest tube leak did not change significantly. Randomization of the mode of ventilation was not performed in any patient because CV was superior by a priori criteria. We conclude that when acute respiratory failure is complicated by a bronchopleural fistula, HFJV with mean airway pressures comparable to those provided during conventional ventilation does not provide satisfactory gas exchange.     

Gas exchange in low-compression HFPPV is maintained at low distending pressures in the pig

The fact that collateral ventilation normally occurs in the human lung has led to the suggestion that it might contribute to the successful clinical effects of low-compression high-frequency positive-pressure ventilation (HFPPV). As the pig has poor collateral ventilation, pulmonary vasoconstriction has to be part of the regulatory mechanisms matching ventilation-perfusion. A study was made on nine pigs anesthetized with ketamine hydrochloride intravenously to elucidate the maintenance of ventilation-perfusion balance during mechanical ventilation. Comparisons were made between the ventilatory patterns provided by a conventional ventilator (Servo-Ventilator 900C) and an improved prototype of a low-compression system for volume-controlled ventilation (system H). A ventilatory frequency of 20 breaths per min (bpm) with SV-900C (SV-20) and system H (H-20) and of 60 bpm with system H (H-60) was used. The experimental conditions were otherwise identical. Positive end-expiratory pressures (PEEP) were applied to maintain the same mean airway pressure with the three systems. The tidal volume required for normoventilation differed significantly between the three ventilatory patterns, but there were no differences in circulatory and oxygen-transport variables. By measurements of airway pressure and intrapleural liquid surface pressure, it was demonstrated that the distending pressure (at end-inspiration) was significantly lower with a low-compression system (H-20 versus SV-20), especially at a high ventilatory frequency (H-60 versus H-20). Consequently, although the mean airway pressure was set at the same level for the three different ventilatory modalities, the distending pressures required for the same alveolar ventilation and arterial oxygenation differed significantly.(ABSTRACT TRUNCATED AT 250 WORDS)     

MATHEMATICAL MODEL OF JET VENTILATION

The design of jet ventilators has always been empirical becauseno theory linked jet geometry, driving pressure, gas densityand lung mechanics. A mathematical means has been developedlinking these parameters to model jet ventilation. The mathematicalmodel predicts the flow into a physical lung model, but underestimatesflow into the lungs when used to predictthe effects of jet ventilationon an animal model at high rates of ventilation. This is attributedto a reduction in compliance with increasing ventilator/ frequency.     

High frequency ventilation and afferent vagal activity

Recordings were made from pulmonary afferent fibres in the vagus nerves of anaesthetised dogs during conventional and high frequency ventilation. In single and multiple fibre preparations, the mean spike counts per minute at 14 breaths/minute were in the ranges 36.9-155.3 and 755-1921, respectively. These counts decreased by up to 61 and 44% respectively at 100 breaths/minute, and by 27-89% and 22-51% at 200 breaths/minute. At this frequency there was a further decrease of between 19 and 65% when the positive end expiratory pressure was removed. The findings of this study are intuitively acceptable, since pulmonary stretch receptor activity is proportional to tidal volume, and are in keeping with the clinical impression that high frequency ventilation per se does not eliminate respiratory drive.