Carbon dioxide monitoring during high-frequency jet ventilation for rigid bronchoscopy

At present, high-frequency jet ventilation (HFJV) is a common and well-accepted method of ventilation during laser therapy performed using a rigid bronchoscope [1]. The ability of jet ventilation to maintain an adequate oxygenation and to provide an effective CO₂ elimination during operative procedures, allowing the bronchoscopist satisfactory operating conditions, is well known [2]. Oxygenation of the patient can be monitored in an easy way by means of a pulse oximetry (measurement of SpO₂); carbon dioxide monitoring is more difficult to evaluate and requires adequate equipment [3].

The aim of this study was to assess the reduction of transcutaneous CO₂ partial pressure, as an approximation for PaCO₂, measured by a new noninvasive technique at the ear lobe during progressive changes of the driving pressure (DP).

Methods

After informed consent, 20 adult patients, scheduled for elective interventional rigid bronchoscopy, were enrolled. Patients undergoing broncoscopy for bronchial cancers involving the carena, post-intubation or post-tracheostomy malacia, and tracheo-bronchial stenoses were treated with laser therapy and/or tracheo-bronchial stent implantation. Total intravenous anaesthesia (TIVA) was conducted with propofol and fentanyl for induction and maintenance, and with rocuronium for muscle relaxation. HFJV was performed with a jet ventilator (Acutronic Medical Systems, Hiezel, Switzerland) via the rigid bronchoscope. A respiratory frequency of 120 cycles/min, an inspiratory duration of 40% and a fraction of inspired oxygen of 50% were set. During the procedure, DP was set at different levels (1.5, 2, 2.5 atm), on the basis of clinical evaluations and of intraoperative CO₂ monitoring. In addition to the usual monitoring, all patients had a transcutaneous sensor in the ear lobe for the noninvasive measurement of arterial oxygen saturation and CO₂ partial pressure (TOSCA System; Linde Medical Instruments, Basel, Switzerland). PtCO₂ values were documented at various DP settings.

Results

The results obtained (Fig. 1) show how the progressive increase of jet DP may avoid the rise of PtCO₂ during bronchoscopy. In particular, a DP of 2.5 atm (P < 0.01) seems to be the best ventilatory setting to assure an adequate PCO₂ elimination (with a CO2 reduction of 8.3% in comparison with a DP of 2 atm).

Figure 1

a, basal; b, 1.5 atm; c, 2 atm; d, 2.5 atm. Wilcoxon test, d significantly different vs b and c (P < 0.01), d vs a not significantly different.

Conclusion

In conclusion, our study confirms that HFJV may assure an effective CO₂ elimination during rigid bronchoscopy and suggests that the TOSCA system allows a reliable estimation of ventilation efficiency, with increased sensitivity during PCO₂ changes and the benefit of avoiding hypercapnia.