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BJA Advance Access published online on October 31, 2007
British Journal of Anaesthesia, doi:10.1093/bja/aem312
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© The Board of Management and Trustees of the British Journal of Anaesthesia 2007. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

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

P. W. Buczkowski1,3,*, F. N. Fombon1, E. S. Lin1, W. C. Russell1 and J. P. Thompson2

1 Department of Anaesthesia, Critical Care and Pain Management, University Hospitals of Leicester NHS Trust, Leicester Royal Infirmary, Leicester LE1 5WW, UK
2 Department of Cardiovascular Sciences,Clinical Division of Anaesthesia, Critical Care and Pain Management, University of Leicester,Leicester Royal Infirmary, Leicester LE1 5WW, UK

* Corresponding author. E-mail: piotrbuczkowski{at}hotmail.com

Accepted for publication August 16, 2007.


   Abstract
Top
 Abstract
Introduction
 Methods
 Results
 Discussion
 Supplementary material
 Acknowledgement
 References
 
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.

Keywords: airway, calibre; airway, obstruction; model, jet ventilation; ventilation, high frequency jet; ventilation, respiratory impedance


   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 Supplementary material
 Acknowledgement
 References
 
Management of the airway during anaesthesia in patients with upper airway stenosis is a challenging clinical scenario because delivery of both oxygen and anaesthetic gases is restricted by the stenosis. Adequate ventilation by conventional tracheal tube may not be possible and high-frequency jet ventilation (HFJV) is an alternative.1–5 HFJV may be applied using a small bore catheter from above the stenosis (ASV), passed through the stenosis (TSV),3 or via cricothyrotomy below the level of stenosis (BSV) (sometimes termed transtracheal ventilation).4 5 In previous studies of HFJV in a bench top model of upper airway stenosis, we found much higher distal airway pressures during ASV compared with TSV and BSV.6 7 This was an unexpected finding, as, intuitively, we anticipated distal airway pressures might have been lower during ASV. Alternatively, high-pressure gas delivered below a stenosis, as in BSV, might be expected to be more hazardous with an increased accompanying risk of barotrauma. In this study, we aimed to investigate why distal airway pressures during BSV are substantially lower than those developed in ASV.


   Methods
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 Abstract
 Introduction
 Methods
Results
 Discussion
 Supplementary material
 Acknowledgement
 References
 
The lung–trachea model was as previously described7 and comprised a Siemens Test Lung 190 (6006832E037E) (Siemens AG, Munich, Germany) connected to a corrugated plastic tube (210 mm length, 22 mm internal diameter) representing the trachea (Fig. 1). In the proximal part of the ‘trachea’, a connector of fixed length (10 mm) but differing diameter (2.5, 3.0, 3.5, 4.0, 4.5, 5.5, 6.5, 7.5, 8.5 mm) was attached to simulate varying degrees of airway stenosis. The whole apparatus including the jet cannula and stenosis were mounted securely with fixed brackets to a wooden base to maintain a constant concentric alignment throughout the experiments. Concentric alignment between jet cannula and stenosis was further assured by the use of a calibrated guide wire passed through the jet cannula into the stenosis before each set of readings. The distance between the jet cannula and stenosis was measured and confirmed to be 11 mm before all experiments. The lung–trachea model incorporated ports allowing distal tracheal pressure measurements, application of jet ventilation from below the level of stenosis (BSV), and sampling of the gas from the test lung. It also allowed insertion of a Wright’s respirometer between the lung and the trachea. Detailed configurations of the apparatus are described in the online supplement accompanying this paper. In the second set of experiments, this model was modified by the addition of a funnel-like structure attached to the airway inlet to simulate the pharynx.


Figure 1
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  		Fig 1 Lung–trachea model with dimensions. ASV, TSV, and BSV configurations aimed to simulate supraglottic, transglottic, and transtracheal ventilation, respectively, in the clinical situation. The detachable model pharynx was used in the second set of experiments (Table 1).

 
In order to validate our results, two sets of experiments (Table 1) were performed using the same lung–trachea model and two different jet ventilators: a Monsoon (Acutronic Medical Systems AG, Switzerland) and a Bromsgrove Humidified Jet Ventilator (Penlon Ltd, UK) operating on the same settings: driving gas 100% O2, frequency 150 min–1, inspiratory time 30%, and driving pressure 2 bar. In both sets of experiments, recordings of airway pressures, gas concentrations, and minute ventilation at steady state were repeated seven times for all diameters of stenosis and configurations for administering HFJV. Peak, mean, and end expiratory pressures were recorded using the pressure monitor incorporated into the ventilator, and minute volumes were measured using a Wright’s respirometer situated between the lung and the trachea.


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  		Table 1 Experimental schedule. Using the same simulated upper tracheal model, two sets of experiments were performed in which HFJV was delivered as ASV, TSV, and BSV. In the second set of experiments, the model was modified by the addition of a funnel-like structure surrounding the stenosis to simulate a model pharynx (Fig. 1)

 
The main aim of the first set of experiments was to estimate the degree of air entrainment, whereas in the second set the effect of the simulated pharynx on air entrainment was investigated.

Air entrainment and calculation of entrainment ratio
In this study, the balance gas concentrations were used to obtain an approximation of entrainment ratio (ER) for different configurations. Entrainment was estimated indirectly using analysis of the delivered gas mixture with a Datex-Ohmeda S/5 anaesthetic gas analyser module M-CAiO (Datex/Ohmeda Ltd, Herts, UK). Although not capable of measuring nitrogen, this module can calculate the concentration of non-measurable gases (mainly nitrogen from air) as a ‘balance’ gas. Therefore, balance gas concentration was used as an approximation of the entrained nitrogen concentration and, hence, as an index of air entrainment. In both sets of experiments, we used a gas washout principle with N2O in the first set as previously described6 but, following concerns over gas scavenging in the laboratory, we changed to use CO2 for the second set. The system was continuously flushed with N2O 4 litre min–1 (first set) or CO2 200 ml min–1 (second set) and gas sampled from the model lung for analysis.


   Results
Top
 Abstract
 Introduction
 Methods
 Results
Discussion
 Supplementary material
 Acknowledgement
 References
 
Distal airway pressures recorded in both sets of experiments produced a pattern very similar to that previously described by our group.6 7 Airway pressures increased with decreasing diameter of stenosis for all routes of ventilation. Distal airway pressures were consistently higher during ASV compared with TSV and BSV and increased at smaller diameters of stenosis, particularly at stenosis diameters <4.5 mm (Fig. 2). For the smallest diameters of stenosis (2.5 and 3 mm), TSV was not possible because the catheter used caused almost complete obstruction of airway. This generated such high pressures (>80 mbar) that the cut-off safety mechanism in the ventilator was activated and ventilation ceased before steady state was reached. A similar effect was observed during ASV HFJV with small stenosis diameters (<2.5 mm). The presence of the simulated pharynx made no significant difference to the airway pressures (Fig. 2). Minute volume was highest during ASV compared with TSV and BSV. During ASV, minute volume was highest at around 4.0–5.5 mm stenosis diameters and decreased at smaller and greater diameters (Fig. 3). The addition of a model pharynx reduced minute volume very slightly during ASV but had no effect during BSV (Fig. 4).


Figure 2
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  		Fig 2 Peak distal airway pressures during ASV and BSV were very similar with and without simulated pharynx. Data shown as mean (95% CI).

 


Figure 3
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  		Fig 3 Mean (95% CI) minute volumes during ASV, TSV, and BSV (Experiment 2 set 1;  1). Minute volumes were greater during ASV compared with between BSV and TSV at equivalent stenosis diameters. During ASV, there was a non-linear relationship between minute volume and diameter of stenosis. Minute volume was highest at around 4–5.5 mm stenosis diameters and decreased at smaller and greater diameters. In contrast, minute volume was more or less constant during BSV and TSV.

 


Figure 4
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  		Fig 4 The presence of model pharynx produced little change in minute volume during ASV or BSV. Data shown as mean (95% CI).

 
Balance gas concentrations were negligible during BSV and TSV (Fig. 5). However during ASV, the balance gas concentrations followed a pattern similar to that for minute volume, with a maximum concentration recorded at 4.0–5.5 mm diameters of stenosis. In this case, estimated ER was >20% for the same range of stenosis diameters (data contained in supplement). The addition of a simulated pharynx resulted in a significant reduction in balance gas concentration during ASV (Fig. 6). This reduction was associated with an increase in delivered oxygen concentrations (Fig. 7).


Figure 5
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  		Fig 5 Balance gas concentrations recorded during BSV or TSV were negligible, in contrast to high concentrations measured during ASV (Experiment 3 set 1;  1). Data shown as mean (95% CI).

 


Figure 6
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  		Fig 6 The addition of a model pharynx (in set II) resulted in significant reduction in balance gas concentrations during ASV but had no effect on the (negligible) concentrations during BSV. Data shown as mean (95% CI).

 


Figure 7
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  		Fig 7 Oxygen concentrations recorded during ASV with simulated pharynx (Experiment 3 set II; Table 1). The observed increase in oxygen concentrations during ASV with simulated pharynx was associated with reduction in balance gas concentrations and preserved minute volume (Fig. 4) suggesting the entrainment of oxygen, which was used as the driving gas. Data shown as mean (95% CI).

 

   Discussion
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
Supplementary material
 Acknowledgement
 References
 
When HFJV is delivered distally to an airway stenosis, one might intuitively expect that the distal airway pressures would be higher than when HFJV is delivered from ASV. Our results contradict this assumption. We also found that high distal ‘tracheal’ pressure during HFJV delivered from ASV is associated with increased entrainment of surrounding gas.

The jet catheter, stenosis, and proximal airway can be regarded as an interface between the ventilator and the respiratory spaces of the lung. Distal pressures during HFJV depend on the injected flow, input (inspiratory), and exhaust (expiratory) impedance of the trachea and proximal respiratory tract, the impedance of the distal airways and respiratory spaces of the lung and the flow characteristics of the jet itself. Increasing expiratory impedance or injected flow will increase distal tracheal pressure. Basic hydrodynamic modelling for turbulent jets under different conditions allows the pressures to be calculated and flow patterns described using velocity vector profiles.8 In the case of HFJV, the jet can be classified as a submerged turbulent jet. These principles have been applied to develop a theoretical model for jet ventilation in a closed duct (stall pressure)9 and in a model of the respiratory system.10 Our data suggest that variations in the configuration of the components forming this interface, including the diameter of the stenosis, also affect pressures, patterns of gas flow, and entrainment in the distal trachea; these are considered in turn.

In ASV some gas passes directly through, the remainder spills outside the stenosis increasing the suprastenotic pressure, so that the stenosis effectively becomes a secondary jet feeding into the interface. In this case, the exhaust path for gases is the stenosis aperture, which is only open for exhaust during the rest phase of the jet cycle, when the injection valve is closed. The stenosis thus conducts gas in both directions over the course of a jet cycle, passing gas into the interface during inspiration, and out of the interface during expiration. Expiratory impedance therefore depends on the jet cycle (I:E ratio) and the area of the stenosis aperture. In addition, the suprastenotic pressure will also affect the exhaust impedance since as this increases, the pressure gradient across the stenosis during exhaust decreases, and exhaust flow is impeded. When the jet orifice is located below the stenosis (BSV), the exhaust pathway is again via the stenosis aperture. The suprastenotic pressure in this configuration is approximately atmospheric (compared with ASV where it is increased by reflected jet gases). In contrast to ASV, the stenosis aperture during BSV is open for exhaust throughout the cycle so that exhaust impedance and distal pressure are reduced. During TSV, the stenosis aperture is partially obstructed by the jet catheter. This increases exhaust impedance, more so as the stenosis aperture approaches the cross-section of the jet catheter. Distal pressure therefore depends on the size of the stenosis aperture. With decreased stenosis diameters (<4.5 mm), the obstructive effect of the jet catheter increasingly predominates, so that distal pressure during TSV increases above that during BSV at equivalent stenosis size. As the stenosis area approaches the cross-sectional area of the catheter, it obstructs the stenosis completely and ventilation ceases. At larger stenosis diameters (>5 mm), distal pressure was lower and injected minute volumes reduced than during BSV. This may partly be because an additional length (150 mm) of catheter was added in order to deliver the jet TSV. This would tend to increase input impedance and thereby decrease injected flow. The effects of flow rates, stenosis diameter, and expiratory impedance on distal flow in each configuration are detailed in the supplement.

The variations in recorded minute volume between ASV, TSV, and BSV suggest significantly different gas flow patterns between these configurations. In BSV, the jet was applied to the model via a side port in the trachea. Distal placement of the jet in the trachea reduces entrainment of gases due to the increased flow impedance presented to entrainment.10 Although the stenosis aperture is not obstructed (as it is in TSV by the jet catheter), the stenosis itself still impedes entrainment, as reflected by the balance gas measurements which demonstrated no significant degree of entrainment in BSV or TSV. During TSV, because the catheter used to deliver jet ventilation TSV was flexible, it adopted a lateral position in the airway which has been shown to reduce maximum entrainment flows and to decrease the extent of zone I.11 This may also occur during TSV in clinical practice.

The minute volumes recorded during ASV were significantly greater than those observed in the BSV and TSV configurations and associated with increased gas entrainment. Entrainment occurs because the high velocity of the emerging gases from the jet orifice creates viscous frictional drag effects on surrounding gas. This increases the total pulse volume produced by the jet as demonstrated in the bench models,12 animal models,13 14 and patients.15 The amount of entrainment depends on the configuration of the interface, and although some previous studies have shown that entrainment contributes to 40–50% of tidal volume,16 17 others have found a range of 15–74%.18 19 We found that ER was reduced to <10% at smaller or larger stenosis diameters. The estimated values suggest that entrainment augments minute volumes in ASV by as much as 20% or more at stenosis diameters between 4.5 and 5.5 mm. These are consistent with ER of 20–30% reported during HFJV in animals14 and anaesthetized patients.15 Entrainment is reduced by increases in flow impedance, for example, by a stenosis at the entrance to the duct; the balance gas measurements suggest that the addition of the simulated pharynx has a small additional effect. The suggested mechanism by which the simulated pharynx reduces entrainment at the stenosis is discussed in the supplement.

We found that the stenosis diameter had a significant effect on minute volumes delivered to the distal ‘trachea’. When stenosis diameters are small, approaching the diameter of the jet orifice, entrainment is very restricted even though the injected jet contains air carried in its boundary layer. The model approximates to that of a turbulent jet injecting into a totally closed duct, which does not allow entrainment but does allow exhaust via the stenosis aperture when the jet valve is switched off during each jet cycle. At intermediate stenosis diameter (approximately 5 mm), ER is maximum because the stenosis aperture is large enough to allow entrainment and some exhaust during injection. However, this stenosis diameter is still small enough to impede exhaust and which involves the outermost layers of gas in the trachea and occurs mainly during the rest phase of the jet cycle, so minute volumes are increased compared with the smaller stenosis diameters. Distal tracheal pressures are reduced at intermediate stenosis diameters since gas exhausts during the injection phase and during the exhaust phase of the jet cycle. At greater stenosis diameters (e.g. 8 mm), the impedance to exhaust flow is reduced further during injection, but this increased exhaust flow decreases entrainment due to viscous forces, and the total minute volumes and ERs are reduced. This results in the reduction in minute volume and distal tracheal pressures found at the largest stenosis diameters. This simple description of the gas flow patterns occurring gives some insight into the mechanisms producing the results obtained.

Although we used a commercially available test lung with similar compliance to the human lung, and a ‘trachea’ of adult human proportions, we appreciate the limitations of applying results from this model to clinical practice. Changes in resistance and elastance of a human trachea, pulmonary compliance, the physical properties of a soft tissue stenosis, and the position of the jet cannula in relation to the stenosis may all vary during HFJV. However, using a simple model, we could examine the effect of stenosis diameter and the amount of entrainment during HFJV delivered from various sites in relation to the stenosis without these confounding effects. The stability of the model is confirmed by the rapid onset of steady-state conditions, low variability between repeated measurements, and the compliance of the model lung remained constant over a range of driving pressures during preliminary experiments. Furthermore, this study was designed to investigate the effect of route of administration of HFJV in relation to stenoses of varying diameter. Clearly, the conclusions must be guarded but the results are comparable with previous animal work where increased distal pressures or hyperventilation were demonstrated when applying HFJV BSV.20 21

Another possible weakness is that when estimating ERs, we assumed that entrained gas is air with a balance gas concentration of 80%. Although reasonable overall, this may lead to underestimation of the ERs during ASV. The best index of air entrainment in such circumstances would have been a direct measurement of nitrogen concentration but the specialized equipment required was not available to us. In clinical practice, asymmetrical placement or movement of the jet cannula may occur and alter the relationship or distance between the jet orifice and the stenosis. This is difficult to control in the clinical situation but may influence distal tracheal pressure and the delivered minute volume; further studies should aim to investigate these factors.

The main considerations during HFJV are to maintain adequate oxygenation (which depends on delivering satisfactory distal oxygen concentrations and maintaining an adequate mean distending airway pressure) and to avoid barotrauma (which increase when distal tracheal pressures increase uncontrollably or unexpectedly). If extrapolated to HFJV in humans, our data suggest that when using ASV, unexpectedly high distal tracheal pressures can occur with small stenoses particularly when the stenosis diameter (D) approaches the diameter of the jet cannula (d). At larger stenosis diameters (D > 2d), the delivery of injected gases is enhanced by entrainment, but this effect also reduces the oxygen concentration obtained by dilution of the injected gas with entrained gas. Pressures are further reduced as the exhaust impedance to gases from the trachea is reduced at larger stenosis diameters (D > 3d). Therefore, HFJV via the ASV route should be avoided in small diameter stenoses, but with larger stenoses it provides more efficient gas delivery with greater distending pressures, which may be required in patients with low respiratory compliance. In clinical practice, the dilution effect due to entrainment could be reduced by insufflating additional oxygen at low pressure into the suprastenotic space.

If these findings extend to clinical practice, TSV and BSV configurations are likely to produce similarly low distal tracheal pressures, and consistent delivered oxygen concentrations since entrainment is minimal. However, it should be emphasized that TSV may be hazardous with small stenosis diameters (D < 2d) because of obstruction of the stenosis by the jet catheter leading to uncontrolled increases in distal tracheal pressure. BSV has the obvious disadvantage of requiring a cricothyrotomy or tracheotomy, but this is likely to be the safest option from the point of view of low tracheal pressures and consistent oxygen concentrations of injected gas.


   Supplementary material
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Supplementary material
Acknowledgement
 References
 
Supplementary data on the model configuration, peak airway pressures for all routes of HFJV, details of the calculation of entrainment ratios, and consideration of the effect of expiratory impedance on distal tracheal pressure are available at British Journal of Anaesthesia online.


   Acknowledgement
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Supplementary material
 Acknowledgement
References
 
We are grateful to Mr Paul Maslowksi, Medical Engineering Specialist, UHL NHS Trust, for assistance with the figures.


   Footnotes
 
3 Present address: Department of Anaesthesia, Derby Hospitals NHS Foundation Trust,Derbyshire Royal Infirmary, London Road, Derby DE1 2QY, UK Back

{dagger} These data were presented in part to the American Association of Anesthesiologists Meeting, Las Vegas, October 2004 and 3rd Biannual Meeting of the European Society for Jet Ventilation, Vienna, November 2004. Back


   References
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Supplementary material
 Acknowledgement
 References
 
1 Depierraz B, Ravussin P, Brossard E, Monnier PH. Percutaneous transtracheal jet ventilation for paediatric endoscopic laser treatment of laryngeal and sub glottic lesions. Can J Anaesth (1994) 41:1200–7.[Web of Science][Medline]

2 Hunsaker DH. Anaesthesia for microlaryngeal surgery; the case for subglottic jet ventilation. Laryngoscope (1994) 104:1–30.[Web of Science][Medline]

3 Evans KL, Keene MH, Bristow AS. High frequency jet ventilation—a review of its role in laryngology. J Laryngol Otol (1994) 108:23–5.[Web of Science][Medline]

4 Russell WC, Maguire AM, Jones GW. Cricothyroidotomy and transtracheal high frequency jet ventilation for elective laryngeal surgery. An audit of 90 cases. Anaesth Intensive Care (2000) 28:62–7.[Web of Science][Medline]

5 Layman PR. Transtracheal ventilation in oral surgery. Ann Roy Coll Surg Eng (1983) 65:318–20.[Medline]

6 Ng A, Russell W, Harvey N, Thompson JP. Comparing methods of administering HFJV in a model of laryngotracheal stenosis. Anesth Analg (2002) 95:764–9.[Abstract/Free Full Text]

7 Buczkowski PW, Fombon FN, Russell WC, Thompson JP. Effects of helium on high frequency jet ventilation in a model of airway stenosis. Br J Anaesth (2005) 95:701–5.[Abstract/Free Full Text]

8 Smirnova IP. Turbulent jet discharged into a dead-end channel. In: The Theory of Turbulent Jets—Abramovich GN, ed. (1963) Cambridge, MA: MIT Press. 444–74.

9 Young JD, Dorrington KL. Peak airway pressure during high frequency jet ventilation: theory and measurement. Br J Anaesth (1989) 61:601–5.[CrossRef][Web of Science]

10 Nahum A, Sznajder IJ, Solway J, Wood LDH, Schumacker PT. Pressure, flow and density relationships in airway models during constant flow ventilation. J Appl Physiol (1988) 64:2066–73.[Abstract/Free Full Text]

11 Isabey D, Boussignac G, Harf A. Effect of air entrainment on airway pressure during endotracheal gas injection. J Appl Physiol (1989) 67:771–9.[Abstract/Free Full Text]

12 Seigneur F, Fischler M, Bourreli B, Melchior JC, Lavaud C, Vourc’h G. Air entrainment during high-frequency jet-ventilation. Simulation of a bronchoscopy with a lung model. Bull Eur Physiopath Respir (1986) 22:341–7.[Web of Science][Medline]

13 Spoelstra AJG, Tamsma TJA. High frequency jet ventilation: the influence of gas flow, inspiration time and ventilatory frequency on gas transport in healthy anaesthetized dogs. Br J Anaesth (1987) 59:1298–308.[Abstract/Free Full Text]

14 Paloski WH, Barie PS, Mullins RJ, Newell JC. Effects of changing inspiratory time ratio on carbon dioxide elimination during high-frequency jet ventilation. Am Rev Respir Dis (1985) 131:109–14.[Web of Science][Medline]

15 Jones MJ, Mottram SD, Lin ES, Smith G. Measurement of entrainment ratio during high frequency jet ventilation. Br J Anaesth (1990) 65:197–203.[Abstract/Free Full Text]

16 Spoerel WE, Narayanan PS, Singh NP. Transtracheal ventilation. Br J Anaesth (1971) 43:932–9.[Abstract/Free Full Text]

17 Chakravarty K, Narayanan PS, Spoerel WE. Further studies on transtracheal ventilation: the influence of upper airway obstruction on the patterns of pressure and volume changes. Br J Anaesth (1973) 45:733–7.[Abstract/Free Full Text]

18 Daughan SD, Ozaki GT, Benumof JL. A comparison in a lung model of low and high flow regulators for transtracheal jet ventilation. Anesthesiology (1992) 77:189–99.[CrossRef][Web of Science][Medline]

19 Benumof JL. Transtracheal jet ventilation via percutaneous catheter and high pressure source. In: Airway Management. Principles and Practice—Benumof JL, ed. (1996) Saint Louis, MO: Mosby-Year Book Inc. 445–74.

20 Carl ML, Rhee KJ, Schegeles ES, Green JF. Effects of graded upper-airway obstruction on pulmonary mechanics during transtracheal jet ventilation in dogs. Ann Emerg Med (1994) 24:1137–43.[CrossRef][Web of Science][Medline]

21 Ward KR, Menegazzi JJ, Yealy DM, Klain MM, Molner RL, Goode JS. Translaryngeal jet ventilation and end-tidal PCO2 monitoring during varying degrees of upper airway obstruction. Ann Emerg Med (1991) 20:1193–7.[CrossRef][Web of Science][Medline]


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High frequency jet ventilation above, passed through and below the airway stenosis.
Gerlinde Mausser
British Journal of Anaesthesia, 3 Dec 2007 [Full text]
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Piotr W. Buczkowski, et al.
British Journal of Anaesthesia, 12 Dec 2007 [Full text]
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