Estimation of Arterial P Co 2 During High Frequency Jet Ventilation

Abstract

The arterial to end-tidal PCO2 difference (PaCO2-PE'CO2) was measured in five anaesthetized dogs during controlled ventilation at 0.25 Hz (15 b.p.m.) and during high frequency jet ventilation at 1, 3 and 5 Hz. Because of the slow response of the infra-red carbon dioxide analyser, satisfactory recordings of end-tidal carbon dioxide could not be obtained at frequencies greater than 1 Hz. The interruption of high frequency jet ventilation by conventional ventilation resulted in approximately equal arterial and end-tidal PCO2 values during the first breath, and restoration of the normal arterial to end-tidal PCO2 difference by the third breath. It is concluded that, when high frequency jet ventilation at 1, 3 or 5 Hz is interrupted with normal tidal volumes at low frequencies, the arterial PCO2 can be estimated from recordings of the end-tidal PCO2.

The effect of combined high frequency ventilation with and without continuous positive airway pressure in experimental lung injury

“…The higher ETo, level may reflect the larger amount of fresh gas flow during CHFV modes, but it may also mean that little oxygen is taken up into the lungs during each high frequency wave. Recording ET gases would be valuable in adjusting the ventilator as well with CHFV, but the base level may differ from that seen during CPPV (14).…”

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

“…Efficiency of carbon dioxide elimination was measured by the P,.co, determined by a 'single-breath' technique. Although we did not perform any direct comparisons with arterial carbon dioxide (Paco,) measurements, the validity of this technique has been verified by several previous investigators (17)(18)(19). Our results indicate that when the Bain system is used in the configuration described, overall CO, elimination during HFJV as measured by P,.co, is independent of V, and is unaffected even by discontinuation of Vf.…”

“…Neuromuscular blockade was assessed intermittently with a Bard Model 750 (Bard Biomedical Division, USA) peripheral nerve stimulator and increments of vecuronium (1-2 mg) administered as necessary. P,.co, during the study period was determined by the 'single breath' technique (which has been described and validated by previous workers (9,(17)(18)(19) using a calibrated Engstrom Eliza capnograph (Gambro Engstrom AB, Sweden). This technique involved the temporary cessation of HFJV whilst a maximum inspiration was delivered by manually squeezing the reservoir bag of the Bain system against a partially closed expiratory valve, which was then reopened.…”

Peak Airway Pressure During High Frequency Jet Ventilation: Theory and Measurement

“…Finally, we refer P x to atmospheric pressure Patm by the use of Bernoulli's equation for steady flow in an inviscid incompressible fluid (loss of pressure energy = gain of kinetic energy). As-suming that the entrained gas flows unimpeded from a static reservoir at pressure Patm, we get Patm-P, = (4) Equations (l)-(4) represent a complete model of one-dimensional entrainment flow. For the specific case A x = A 2 the model has been shown previously [7] to predict the performance of oxygen entrainment masks [12] and the effects of back pressure on an anaesthetic machine which was designed for use in the Antarctic [9].…”

“…During high frequency jet ventilation, accurate measurement of arterial carbon dioxide tension using end-tidal carbon dioxide concentrations is not possible because of the small tidal volumes delivered [1] and the slow response of carbon dioxide analysers [2]. Interrupting jet ventilation with a "conventional" positive pressure breath overcomes this problem, but requires a second ventilator [3,4]. If the jet ventilator is designed to deliver intermittent deep breaths using a high driving pressure and long inspiratory and expiratory times, the need for a second ventilator is removed [5].…”