Clinical evaluation of high-frequency positive-pressure ventilation (HFPPV) in laryngoscoy under general anaesthesia

Anesthesia for endobronchial laser surgery: a modified technique

We describe a technique for endobronchial surgery with the neodynium:yttium-aluminum-garnet laser, in which an insufflation catheter with side holes placed into the contralateral mainstem bronchus is used for high-frequency positive pressure ventilation. Thirty-five patients (45 procedures) were treated during general anesthesia using a rigid bronchoscope in combination with a fiberoptic bronchoscope. Perioperatively, oxygen saturation (SaO2), mean arterial pressure, and heart rate were recorded. SaO2 during the recovery period was comparable to that during the intraoperative period but was significantly (P < 0.05) higher than that before the induction of anesthesia. There was a considerable (> or = 5%) increase in SaO2 at the end of the treatment in six patients, which indicates that the recanalization of the treated airway was successful. Our data support the assumption that, during endobronchial resection, selective ventilation of the nonaffected lung was adequate; in addition, subcarinal placement of the insufflation catheter with side holes was advantageous. We conclude that this technique contributes to the prevention of lung complications during endobronchial laser surgery.

IMPLICATIONS

We describe a technique in which an insufflation catheter with side holes placed into the contralateral mainstem bronchus largely prevented inhalation of laser smoke and aspiration of blood and debris.

A multilumen catheter guide for difficult airway management. Its uses in anaesthesia and intensive care

A multilumen catheter guide (jet stylet) with an adapter has been used for various manoeuvres in the upper airway. With the split length, procedures such as change of tracheal tube from oral to nasal nasal to oral position, are possible while the patient's lungs are ventilated by means of high frequency jet ventilation. During high frequency jet ventilation for longer periods of time, for example for microlaryngeal surgery, the central channel of the catheter is used as a conduit for jet delivery, whilst the other channels are used for continuous monitoring of airway pressure and concentration of carbon dioxide in the upper airway.

Anesthesia for microlaryngeal surgery: the case for subglottic jet ventilation

Although the techniques for surgery on the endolarynx using suspension and the operating microscope have been fully developed, the safest, and least obtrusive anesthetic technique has yet to be manifested, as evidenced by more than 200 references to anesthesia for microlaryngoscopy in the world literature. This study reviews the physiology, physics, and problems of each anesthetic technique. In light of this review, animal and human studies are reported demonstrating the utility and safety of subglottic ventilation when provided with proper monitoring using an automatic ventilator. A modified Ben-Jet tube is reported, which has a 1-mm ID channel to monitor PCO2 and tracheal pressure. This self-centering 3.0-mm tube, which extends 6 to 8 cm below the glottis, is unobtrusive for the surgeon. The subglottic tube, which is much less likely to be malaligned, is much more acceptable to the anesthesiologist. Anesthesia, by intravenous sedation, utilizes neuromuscular blockade while ventilating through the jet tube powered by an automatic ventilator with an automatic shutdown feature attached to the monitor tube to prevent inadvertent barotrauma. The third phase of this study compared fluoroplastic, used in a prototype jet ventilation tube, with 6-mm Silastic, Red Rubber, and polyvinyl chloride (PVC) tubes when struck by maximum power of CO2, Nd-YAG, and K-532 lasers. The test was performed in a closed chamber in which concentrations of oxygen and nitrogen were controlled. Although damaged by the CO2 laser beam, the fluoroplastic tubes did not continue burning when the laser was turned off in 100% oxygen, even when coated by blood. The other three tubes continued to burn in 23% oxygen. Neither the KTP nor Nd-YAG laser damaged the Teflon tube, while they ignited a sustained flame in 30% oxygen. This study supports the use of fluoroplastic for a laser safe jet ventilation tube. It also demonstrates the danger of tube fires, even in low oxygen concentrations, when using Silastic, rubber, and PVC tubes in laser laryngeal surgery. There was no difference in the flammability of Silastic, rubber or PVC when struck by these lasers in this study. For these reasons, subglottic ventilation using a fluoroplastic, monitored, self-centering, subglottic, jet ventilation tube driven by an automatic ventilator with a shutdown feature, in the event of excessive pressure buildup, is proposed for anesthetizing healthy patients undergoing suspension microlaryngoscopy, and who have no airway obstructing lesion. A large tube with inflatable cuff is indicated when a supraglottic lesion may obstruct the airway.

Tubeless translaryngeal superimposed jet ventilation

Microsurgical endoscopic interventions of the larynx offer an optimal approach to the surgeon by providing an unrestricted operative field. During such operations, ventilating the patient should in no way be impaired. For this reason we have developed a new type of tubeless jet ventilation which consists of both low-frequency and superimposed high-frequency jet ventilation. In addition, we have integrated two specifically sized jets into a Kleinsasser laryngoscope, placing them at different sites. This technique guarantees adequate ventilation with an oxygen-air blend. Due to the Venturi effect, air and tidal volumes are also enhanced when passing through the external open end of the laryngoscope. This type of tubeless jet ventilation was applied to more than 60 patients, using a prototype jet. Anesthesia consisted of a continuous intravenous administration of propofol, with sufentanil and vecuronium given as needed. Clinical results revealed optimal ventilation of all patients without hypercapnia or other complications. Operative conditions for the surgeon were also very satisfactory. Findings demonstrated that this type of tubeless jet ventilation is also particularly suited for laryngeal laser surgery, thus avoiding flammable tubes and noxious anesthetics.

In what respect does high frequency positive pressure ventilation differ from conventional ventilation?

The original rationale for HFPPV was that under certain conditions adequate alveolar ventilation could be achieved with high ventilatory frequencies and small tidal volumes. It was theorized further that increased ventilatory frequencies and low tidal volumes would decrease the airway pressures, barotrauma, and cardiovascular and other systemic consequences seen with conventional mechanical ventilation. The first clinical applications of HFPPV were in bronchoscopy and laryngoscopy for diagnostic and/or therapeutic purposes. Apart from these endoscopic applications, volume-controlled HFPPV has been compared with conventional ventilation in upper abdominal surgery and coronary artery bypass grafting. The possible advantages of HFPPV over conventional volume-controlled ventilation in the intensive care setting are still unclear. Provided that the mean lung volumes are similar, oxygenation in acute respiratory failure is similar with both ventilation methods. Although the role of HFPPV in the management of pulmonary diseases still remains to be clarified, it does provide effective ventilation in selected types of patients needing ventilatory support. New modes of pressure-controlled ventilation have not resolved all clinical problems in severe ARDS and/or acute respiratory failure. The search for means of optimal ventilatory support with minimal complications must continue, as conventional ventilation does not always offer the best treatment.

A new ventilator for physiologic studies during high-frequency ventilation

Research in the field of high frequency ventilation (HFV) has been hampered by the difficulty of collecting and analyzing expired gas, uncontaminated by gas of inspiratory composition, at ventilatory frequencies in the relevant range. A new mechanical ventilator is described, which has been designed to facilitate studies on the respiratory physiology of small animals during HFV. Ventilation is controlled by a single rotary valve, which alternately switches the airway to an approximately constant-flow gas source during inspiration, and to gas measurement and analysis apparatus during expiration, which takes place passively. Theoretical and experimental studies, using the techniques of mechanical and mathematical modelling, are used to measure the performance of the ventilator and to demonstrate that it allows the quantitative collection of expired gas during ventilation at rates up to at least 20 Hz. The advantages and limitations of this approach are discussed.

Constancy of physiological dead space during high-frequency ventilation

A ventilator, specially designed to allow the direct measurement of expired gas volume and composition, was used to maintain gas exchange in anesthetized, paralyzed, New Zealand White rabbits at ventilatory frequencies up to 22 Hz. A total of eleven studies were carried out on seven animals. Determinations of the minute ventilation required to maintain a normal steady-state PCO2, together with the FECO2 and arterial PO2, PCO2, and pH, were made at a number of frequencies. The results so obtained were used to calculate the physiological dead space. It was found that this value remained remarkably constant for each individual rabbit over a range of ventilatory frequencies from 1 to 22 Hz. Our findings in rabbits are in contrast to those of other workers (in dogs) that adequate gas exchange can be maintained at high ventilatory frequencies with the use of tidal volumes much smaller than the volume of anatomical dead space.

Physiologic evaluation of the HFPPV pneumatic valve principle and PEEP. An experimental study

In experiments in dogs the ventilatory and circulatory conditions prevailing with the ventilatory pattern in high-frequency positive-pressure ventilation (HFPPV) were investigated with use of a pneumatic valve principle and a ventilator system of an "open" character. Keeping the gas input constant the importance of insufflation frequency and insufflation time and the reactions to various levels of positive end-expiratory pressure (PEEP) were investigated in terms of changes in arterial pH, Pco2 and Po2. With the volumes of delivered gas kept constant, an increasing insufflation frequency from 60 to 100 per min gave a parallel decrease in tidal volume accompanied by lower maximum intratracheal pressures and a significant decrease in alveolar ventilation. Also taking into account the possibilities of inducing a suppression of the spontaneous respiration, higher ventilatory frequencies than 60 per min do now seem to introduce any further advantages. Including the associated effects on cardiac output and venous admixture, the cardio-pulmonary and circulatory parameters studied did not show any substantial changes with PEEP levels below 7.5--10 cm H2O. Thus the level of PEEP, which often is part of the ventilatory pattern in HFPPV, does not seem to have any untoward influence on the circulation (stroke volume, cardiac output, total peripheral vascular resistance) and oxygen transport (arterial oxygen content and oxygen flux) in normovolaemic dogs.