High frequency jet ventilation: the influence of different methods of injection on respiratory parameters

A new tracheal tube and methods to facilitate ventilation and placement in emergency airway management

The "jet endotracheal tube" (JET) has been designed to facilitate emergency intubation in apnoeic or paralyzed patients with a difficult airway. We investigated the efficiency of jet ventilation to maintain adequate oxygenation and ventilation using the initially designed JET, either with its distal tip positioned above vocal cord and pointed directly at or 45 degrees to the right of the vocal cord opening midline in 10 adult paralyzed pigs. The effectiveness of using end tidal carbon dioxide pressure (PetCO(2)), chest rise and breath sounds to facilitate tracheal placement of the JET blindly in a simulated difficult airway was studied. All complications of using the JET were noted. Jet ventilation with the distal tip of the JET pointed directly at, not 45 degrees to the right of vocal cord opening midline, provides adequate oxygenation and ventilation during intubation. In a simulated difficult airway, PetCO(2), chest rise and breath sounds were all effective methods to assist placement of the JET blindly, and the combination of all three methods works the best. No serious complications were detected with the use of the JET. Our results suggest that a correctly positioned JET guided by monitoring PetCO(2), chest rise and breath sound provides adequate oxygenation and ventilation during intubation in apnoeic pigs, and facilitates the intubation blindly in a simulated difficult airway. No serious complications were observed using the JET in this study. In patients requiring emergency intubation, a JET with PetCO(2) monitoring catheter and the instructions for use may be a useful addition to the airway management devices.

Extracranial radiosurgery: immobilizing liver motion in dogs using high-frequency jet ventilation and total intravenous anesthesia

PURPOSE

Extracranial radiosurgery requires control of organ motion. The purpose of this study is to quantitatively determine the extent of liver motion in anesthetized dogs with continuous i.v. propofol infusion with or without muscle relaxants and high-frequency jet ventilation.

METHODS AND MATERIALS

Five dogs were used in the experiment. Each dog was restrained while anesthetized in the supine position using an alpha cradle. Surgical metal clips were implanted around the liver periphery so that its motion could be visualized using a fluoroscopic imaging device in a conventional simulator. Initially, two orthogonal simulation films were taken to correlate locations of implanted clips. Two orthogonal views of fluoroscopic images for each anesthetized dog were recorded on a magnetic tape and analyzed from the post-imaging data. Liver motion was documented under the following three conditions: 1) ventilated with a conventional mechanical ventilator, 2) ventilated with a high-frequency jet ventilator, and 3) ventilated with a high-frequency jet ventilator and total muscle paralysis (with vecuronium injection). The maximum liver motion for each dog was analyzed in three orthogonal directions: the inferior-to-superior direction, the anterior-to-posterior direction, and the right-to-left direction.

RESULTS

When the anesthetized dogs were ventilated with a conventional mechanical ventilator, the average liver motions were 1.2 cm in the inferior-to-superior direction, 0.4 cm in the anterior-to-posterior direction, and 0.2 cm in the right-to-left direction, respectively. After the introduction of high-frequency jet ventilation, the average liver motions were reduced to 0.2 cm in the inferior-to-superior direction, 0.2 cm in the anterior-to-posterior direction, and 0.1 cm in the right-to-left direction. The maximum liver motion was dependent on ventilator settings. There was no additional measurable motion reduction with the addition of the muscle relaxant.

CONCLUSION

The liver motion in each anesthetized dog was controlled under 3.0 mm in all directions with the use of high-frequency jet ventilation. No detectable advantage was identified by the injection of muscle relaxant in terms of further reducing the liver motion. The preclinical animal study indicated that the use of high-frequency jet ventilation (HFJV) would be able to limit the liver motion to an extent acceptable for the application of extracranial radiosurgery in humans. Radiosurgery for localized liver tumors warrants further investigation.

Dynamic hyperinflation: comparison of jet ventilation versus conventional ventilation in patients with severe end-stage obstructive lung disease

Positive pressure ventilation in patients with obstructive lung disease may result in over-inflation of the relatively compliant lungs, resulting in dynamic hyperinflation (DHI). Using a crossover trial design, we compared high-frequency jet ventilation (HFJV) versus "optimal" intermittent positive pressure ventilation (IPPV) in ten patients undergoing lung transplantation for severe, end-stage obstructive lung disease. We measured haemodynamics and the degree of DHI after both modes of ventilation. There were no significant differences between IPPV and HFJV, with respect to efficiency of ventilation (PaCO2), haemodynamic effects (stroke volume, blood pressure and cardiac output), or lung hyperinflation (trapped gas volume). This study suggests that HFJV, when compared with optimal IPPV, is no better at minimizing DHI in patients with severe, end-stage obstructive lung disease.

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

The use of a Bain system to convey anaesthetic gases for entrainment during high frequency jet ventilation (HFJV) was evaluated by examining the effect of varying the fresh gas flow (Vf) on the end-tidal carbon dioxide (PECO2) in 46 ASA physical status I and II patients undergoing extracorporeal shock-wave lithotripsy (ESWL). Anaesthesia was induced with methohexitone (1-2 mg.kg-1), fentanyl (1-1.5 micrograms.kg-1) and vecuronium (0.1 mg.kg-1). After endotracheal intubation with a Mallinckrodt Hi-Lo Jet cuffed endotracheal tube, the patient was immersed in a water bath and HFJV at 150 breaths per minute was instituted with an Acutronic AMS 1000 jet ventilator attached to the side channel of the Hi-Lo tube. A Bain system was attached to the proximal end of the endotracheal tube to provide gases for entrainment. Anaesthesia was maintained with an intravenous infusion of methohexitone (5 mg.kg-1.h-1) and 50% nitrous oxide in oxygen for both the jetted and entrained gases. PECO2 was determined at 5-min intervals by a single-breath technique using a calibrated Engstrom Eliza capnograph. Thirty patients were randomly allocated to receive Vf's of 50 (Group 1), 75 (Group 2) and 100 (Group 3) ml.kg-1.min-1, respectively. A further eight patients (Group 4) received a Vf of 100 ml.kg-1.min-1 for 15 min, 75 ml.kg-1.min-1 for the next 15 min and 50 ml.kg-1.min-1 thereafter. In a further group of eight patients (Group 5), Vf was initially 25 ml.kg-1.min-1 for 10 min and was then switched off for the remainder of the procedure.(ABSTRACT TRUNCATED AT 250 WORDS)