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LETTERS TO THE EDITOR

No Need for Claims: Facts Rule Performance of Jet Ventilation

University of Tampere, Medical School and Department of Anaesthesia and Intensive Care Tampere University Hospital FIN-33521 Tampere, Finland

To the Editor:

Nobody would compre the maximum speed of cars at a certain rpm of the motors without looking at horsepower and the gear in use. Recently, two modes of the "promising" (1) jet ventilation for endolaryngeal procedures (2) have been compared, supraglottic (3) and translaryngeal intracheal (4) jet ventilation.

The pressure a jet pump creates not only depends on driving gas velocity and jet diameter, but also on the diameter relation of the jet and the diffuser (5), i.e. the trachea, the cross-sectional shape (6) of the trachea, and the distance of the jet nozzle from the glottis (7). A Venturi effect, however, has no influence on jet performance (8).

With intratracheal jet ventilation, aspiration and air entrainment are virtually absent (9). Barotrauma appeared frequently before the introduction of airway pressure monitoring (10). In our teaching hospital, airway pressure curve monitoring (11) helped avoid barotrauma for almost 20 years. At normal respiratory rate and adequate airway pressures (12), oxygenation and CO₂ eliminiation are no problem because of the circumvented dead space and the jet mixing of the ventilating gas. The comparison at different airway pressures (1) does not show the superiority of one of the studied ventilation modes over the other.

References

1. Bacher A, Pichler K, Aloy A. Supraglottic combined frequency jet ventilation versus subglottic monofrequent jet ventilation in patients undergoing microlaryngeal surgery. Anesth Analg 2000; 90; 460–5.[Abstract/Free Full Text]
2. Spoerel WE, Greenway RE. Transtracheal ventilation. Br J Anaesth 1971; 43: 932–9.[Abstract/Free Full Text]
3. Oulton JL, Donald DM. A ventilating laryngoscope. Anesthesiology 1971; 35: 540–2.[Web of Science][Medline]
4. Carden E, Crutchfield W. Anaesthesia for microsurgery of the larynx: a new method. Can Anaesth Soc J 1973; 20: 378–89.[Web of Science][Medline]
5. Perry RH. Ejector performance. In: Perry RH, Chilton CH, eds. Chemical engineer’s handbook. New York: McGraw-Hill, 1973: 29–32.
6. Baer GA. Die Wirkung verschiedener tracheaquerschnittsformen auf den atemwegsdruck bei experimenteller intratrachealer injektorventilation. Anaesthesist 1985; 34: 124–8.[Web of Science][Medline]
7. Spoerel WE, Greenway RE. Technique of ventilation during endolaryngeal surgery under general anaesthesia. Can Anaesth Soc J 1973; 20: 369–77.[Web of Science][Medline]
8. Scacci R. Air entrainment masks: jet mixing is how they work—the Bernouille and Venturi principles are how they don’t. Resp Care 1979; 24: 928–31.
9. Baer, GA. Intratracheal jet ventilation for endolaryngeal procedures. Acta Universitatis Tamperensis 1985;ser. A, Vol 187.
10. Heifetz M, DeMyttenaere S, Rosenberg B. Intermittent positive pressure inflation during microscopic endolaryngeal surgery. Anaesthesist 1977; 26: 11–4.[Web of Science][Medline]
11. Baer GA. Laryngeal muscle recovery after suxamethonium: detection during intratracheal jet ventilation by pressure curve monitoring. Anaesthesia 1984; 39: 143–6.[Web of Science][Medline]
12. Baer GA, Paloheimo M, Rahnasto J, Pukander J. End-tidal oxygen concentration and pulse oximetry for monitoring oxygenation during intratracheal jet ventilation. J Clin Monit 1995; 11: 373–80.[Web of Science][Medline]

Response

Department of Anesthesiology and General Intensive Care University of Vienna A-1090 Vienna, Austria

In Response:

The only way to assess the performance of jet ventilation techniques is to determine the efficacy of carbon dioxide elimination and oxygenation at a certain driving pressure and inspiratory oxygen fraction (1). In our study, we found that both work best with supraglottic combined-frequency jet ventilation (2). It is simply not true that normal arterial carbon dioxide and oxygen tensions can easily be achieved during microlaryngeal surgery in any patient. There are patients in whom hypercarbia and hypoxia occur even if the driving pressure is set at maximum on the jet ventilator. Therefore, the search for the most efficient ventilation technique is of pivotal clinical importance for such procedures. In our study, we further found that a greater amount of room air entrainment might be responsible for the better performance of supraglottic combined frequency jet ventilation. Whether this is caused by a more pronounced Venturi effect or by a greater amount of "jet mixing," as Dr. Baer refers to, is of academic interest and subject to basic research in this field.

Dr. Baer doubts our finding that airway pressure cannot be mea- sured via the monitoring port of the Mon-Jet catheter (Xomed; Jacksonville, FL). It is correct that airway pressure can be accurately determined during subglottic jet ventilation techniques with additional catheters that are forwarded distal to the jet nozzle. However, at a distance of less than 5 cm proximal to the jet nozzle, airway pressure cannot be measured because of a pressure trough that is generated in this area by the jet stream. By publishing our findings, it was our intention to warn clinicians to rely on airway pressure measurements with the monitoring port of the Mon-Jet catheter to avoid barotrauma.

References

1. Biro P, Eyrich G, Rohling R. The efficiency of CO₂ elimination during high-frequency jet ventilation for laryngeal microsurgery. Anesth Analg 1998; 87: 180–4.[Abstract/Free Full Text]
2. Bacher A, Pichler K, Aloy A. Supraglottic combined frequency jet ventilation versus subglottic monofrequent jet ventilation in patients undergoing microlaryngeal surgery. Anesth Analg 2000; 90: 460–5.

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