Cole Ray

Clinical experience with high frequency jet ventilation.

: High frequency jet ventilation (HFJV) has been used in recent years in some forms of respiratory failure, where the presence of barotrauma limited the application of high peak inspiratory pressure. In the present report, the authors describe the clinical experience with 17 patients, who could not be supported with conventional mechanical support and were placed on HFJV. Rates of 100 breath/min, inspiratory/expiratory ratio of 1:2 and cannula size of 1.06--1.62 mm (18--14) gauge were used. Driving pressure required to maintain a PaCO2 of 40--45 torr was 14--45 psig; however, except in 2 patients who developed hemorrhagic tracheitis with subtotal obstruction of both mainstem bronchi, a driving pressure higher than 27 psig was never required, even when PEEP up to 32 cm H2O was used. Of 17 patients treated, 8 survived. In all cases, alveolar ventilation could be maintained within the desired range with high frequency ventilation, even in those patients who eventually died; mechanical support never provided better oxygenation or alveolar ventilation than high frequency ventilation. Hemodynamic function was essentially unchanged with high frequency ventilation; indeed, in three cases, inotropic support with dopamine could be discontinued after initiation of high frequency ventilation.

Technical aspects and clinical implications of high frequency jet ventilation with a solenoid valve

High frequency jet ventilation (HFJV) is an incompletely studied technique of mechanical respiratory support. The authors have built a ventilator based on a solenoid valve, that allows independent selection of respiratory rate and inspiratory/expiratory ratio. The ventilator can be synchronized to the heart rate. Humidification is provided by warm saline dripped in front of the injector nozzle, so that the jet stream itself acts as a nebulizer. Tube diameter, length, and deformability are fundamental determinants of inspiratory flow rate and wave form. Cannula kinking and inadequate humidification were the most significant sources of complications.

Capnography in mechanically ventilated patients

Capnography, the science of CO2 waveforms analysis, can play a role in the management of mechanically ventilated patients. Mass spectrometers are the devices most commonly used to collect sequentially and examine CO2 waveforms from multiple patients in the ICU or operating rooms. We present here a review of some clinical and technical problems, which may be resolved efficiently and expeditiously through the use of mass spectrometry and capnography. Mechanical failures, especially those that lead to rebreathing of exhaled gases, can be readily detected. The patients progress during weaning and the consequences of changes in mechanical assistance can be virtually and noninvasively determined. An expanded role of capnography in mechanically ventilated patients can increase the use of mass spectrometers in the ICU.

Indirect calorimetry in the mechanically ventilated patient

We used indirect calorimetry to measure oxygen consumption (&OV0312;o2) and carbon dioxide production in 29 mechanically ventilated patients. These data were compared to &OV0312;o2 measured simultaneously by a standard thermodilution technique. A good correlation was demonstrated between the methods, but &OV0312;o2 measured by indirect calorimetry was 15% higher than &OV0312;o2 measured by thermodilution.

Filter for prevention of microembolism during massive transfusions.

This concern by cardiovascular surgeons stimulated thoughts of the possibility of pulmonary microembolization following the infusion of bank blood into the venous system. In 1965, Moore5 questioned whether accumulation of material in the lungs when many units of blood are rapidly transfused might cause impaired pulmonary function. Autopsies in another study6 revealed multiple pulmonary emboli in patients who developed pulmonary insufficiency following massive transfusion. Swank7 and Moseley and Dotys have shown that particulate aggregates increase in bank blood with the

Tidal volume and airway pressure on high frequency jet ventilation.

The principle of jet injector indicates that large tidal volumes may be delivered on high frequency jet ventilation (HFJV) without increasing airway pressure. Fifteen dogs were ventilated on HFJV in 2 separate experiments. In the first one, tidal volume was maintained constant at 10 ml/kg, while PEEP, respiratory rate, and cannula size were changed in 16 different experimental conditions. In the second experiment, driving pressure was progressively increased from 5 to 45 psig, and PEEP, respiratory rate, and injector size were changed in 32 experimental conditions. Mean airway pressure, tidal volume, driving pressure, thoracic aortic mean pressure, and abdominal aortic mean pressure were the variables measured. Tidal volume linearly increased with driving pressure, while airway pressure only increased when tidal volume exceeded 25 ml/kg. Blood pressure was inversely related to mean airway pressure.Tidal volume was twice as high with the 1.62 mm injector, as compared to the 1.06 mm injector, although resistances are 6 times higher with the smaller injector. The difference is related to the higher entrainment, which is observed when jet flow velocity increases, as is the case when the injector cannula is smaller. The experiments confirmed that HFJV follows the physical principles of jet mixing and entrainment.

High frequency jet ventilation in experimental airway disruption

Anecdotal observations suggest that high frequency jet ventilation (HFJV) is beneficial in major airway disruption. Quantitative evaluation is, however, unavailable. In 12 healthy mongrel dogs, a tracheal window of increasing size, from 0.5 × 1 cm to 1.5 × 2 cm, was opened. Dogs were supported on volume-cycled ventilation (VCV) and on HFJV, using injector cannulas of 1.06 and 1.62 mm internal diameter. The tracheal window was then closed and an upper lobectomy performed, followed by total pneumonectomy. Arterial blood gases were obtained after 10 min in each experimental condition. VCV could maintain life-supporting blood gases only with the tracheal window of 0.5 × 1 cm. HFJV, delivered with a 1.06-mm injector cannula, was adequate with a tracheal window of 1 × 1 cm, or after a lobectomy. In all experimental conditions, HFJV delivered with a 1.62-mm injector effectively maintained alveolar ventilation and arterial oxygenation.Gas transport on HFJV is based, in part, on the principles of jet mixing and entrainment; increasingly large tidal volumes can be delivered under conditions of low and constant pressure. Air leaks through pathological openings remain constant even when tidal volume is increased, so that alveolar ventilation can be adequately maintained.

High-frequency jet ventilation: technical implications.

A variety of technical decisions are required for the proper selection and safe and efficacious application of high-frequency jet ventilation (HFJV). Criteria for analyzing the performance of an HFJV system are presented, along with discussions of some of the more common respiratory measurements and their applicability to HFJV.

Pneumatic-to-electrical analog for high-frequency jet ventilation of disrupted airways.

A pneumatic-to-electrical circuit anàlog is used to describe 2 separate mechanisms by which high-frequency jet ventilators sustain ventilation and oxygenation in the presence of large airway disruptions. The frequency-dependent mechanism is based on variations in the pneumatic equivalent to capacitive reactance. The pressure-dependent mechanism models lung defects on a voltage-controlled resistor. The electrical circuit model is also used to explain the factors leading to gas trapping and inadvertent positive end-expiratory pressure during high-frequency jet ventilation.

Frequency response of the peripheral sampling sites of a clinical mass spectrometer

Mass spectrometers are used in ICUs and ORs to measure the concentration of medical and anesthetic gases gathered from multiple sites. This investigation was designed to determine the accuracy of a clinical system, which included 12 ICU bedside stations monitored by a medical mass spectrometer (Perkin-Elmer RMS III, Pomona, CA). Each site station was connected to the analyzing unit via two Teflon tubes, one permanently installed, 30-m long, and the second disposable, 2.4-m long. A gas mixture containing 95% O2 and 5% CO2, alternating with room air, was delivered to a solenoid valve and from there to the connecting tubes. Gas flow-rate, delay time, rise time, and peak and trough concentrations were determined for each gas at solenoid cycling frequencies of 25, 50, and 100/min. After the first set of measurements, the 30-m tubes were thoroughly cleaned and all measurements repeated. In addition, the authors also measured CO2 delay and rise times when the gas was delivered to the mass spectrometer through an unused 30-m tube or a new 2.4-m tube. Gas flow-rate increased from 143 +/- 12 ml/min (mean +/- SD) to 238 +/- 9 ml/min after the tubes were cleaned. Delay time was identical for all gases at all solenoid cycling rates but decreased significantly (P less than 0.05), from 11.5 +/- 0.3 to 4.8 +/- 0.7 s after the ceiling tubes were cleaned. As solenoid valve rate increased, the difference between measured and actual gas concentration increased. The lowest accuracy was 63.6 +/- 2.1%, for CO2 at 100 cycles/min.(ABSTRACT TRUNCATED AT 250 WORDS)