Comparison of conventional intermittent positive pressure ventilation with high frequency jet ventilation

This study was designed to compare the cardiorespiratory effects of high frequency jet ventilation at 150 breaths/minute with and without added positive and expiratory pressure, with conventional intermittent positive pressure ventilation in 20 patients following aortocoronary bypass graft surgery. On comparison with intermittent positive pressure ventilation, there was a decrease in peak airway pressure during high frequency jet ventilation when positive and expiratory pressure of 0 or 0.5 kPa was applied, but not with 1 kPa, and an increase in mean airway pressure with positive end expiratory pressures of 0.5 and 1 kPa. On changing from intermittent positive pressure to high frequency jet ventilation with no added end expiratory pressure, there was an acute decrease in arterial oxygen tension and increases in cardiac output and total tissue oxygen delivery. On changing from intermittent positive pressure ventilation to high frequency jet ventilation with 1 kPa of positive end expiratory pressure, there was an acute decrease in arterial oxygen tension, cardiac output and oxygen delivery, and increases in pulmonary arterial, right atrial and pulmonary capillary wedge pressures. The addition of positive end expiratory pressure did not prevent the acute decrease in arterial oxygen tension which occurred on transfer to high frequency jet ventilation.     

Combined unilateral high frequency jet ventilation and contralateral intermittent positive pressure ventilation

The anaesthetic management of a patient who required right lower lobectomy for bronchial carcinoma associated with emphysema, pneumoconiosis and a previous thoracoplasty for pulmonary tuberculosis, is described. A technique of unilateral high frequency jet ventilation plus conventional intermittent positive pressure ventilation to the contralateral lung was used.     

Convective mixing mechanisms in high frequency intermittent jet ventilation

A liquid flow visualization technique was used to identify the location of neutrally buoyant bead clouds injected into airway models during flows simulating high frequency intermittent jet ventilation (HFIJV) in neonatal lungs. The motions of these bead clouds show that the convective or bulk mixing that occurs during HFIJV is made up of two parts; a turbulent convective exchange with the atmosphere caused by the jet in the trachea and a streaming motion along the airways driven by an interaction between the jet and the expansion and contraction of the airways due to their compliance. These convective streaming motions combine with molecular diffusion to produce augmented diffusion which transports O₂ and CO₂ between the trachea and the peripheral alveoli. Optimizing HFIJV (as well as other forms of HFV) depends on maximizing these airway convective streaming flows which depend on many more lung and fluid mechanical parameters than are necessary to describe conventional mechanical ventilation.     

High frequency jet ventilation

A case is described where high frequency jet ventilation was used to avoid the cardiovascular depressant effects associated with conventional ventilation. Early weaning from inotropic and ventilatory support proved possible.     

Volume-controlled high frequency positive pressure ventilation for upper abdominal surgery

Volume-controlled high-frequency positive pressure ventilation was evaluated and compared to intermittent positive pressure ventilation during anesthesia in 74 patients undergoing biliary tract surgery. There were no statistically significant differences in oxygenation or ventilation. Significantly lower airway pressures and lower tidal volumes were recorded during high frequency positive pressure ventilation. This technique was also used in eight morbidly obese patients during gastric stapling surgery, and provided adequate oxygenation and ventilation. Used intra-operatively, it also produced a quiet operative field, which the surgeons appreciated during cannulation of the biliary duct and stapling of the stomach. At the end of the anaesthesia, high frequency positive pressure ventilation was superimposed on spontaneous breathing and operated as a new mode of intermittent mandatory ventilation. This reduced the risk of hypoxia at the time of emergence from anaesthesia and at tracheal suctioning.     

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.     

Hemodynamic effects of high frequency ventilation superimposed on intermittent positive pressure ventilation in dogs

The hemodynamic effects of high frequency ventilation (HFV) superimposed on intermittent positive pressure ventilation (IPPV) in seven dogs before and after thrombin infusion were investigated. HFV was superimposed on a Servo 900 B ventilator by a Siemens Elema HFV prototype unit. Mean arterial blood pressure, heart rate, central venous pressure, pulmonary artery pressure, cardiac output, right and left ventricular pressures, pleural pressure, arterial blood gases, and right and left ventricular ejection fractions were recorded. Measurements were done during IPPV alone and during HFV superimposed on IPPV. The HFV frequencies were 5, 15, and 20 Hz at a constant minute volume of 5 1. When HFV was started, the IPPV minute volume was reduced to one third of the initial volume. No significant changes in the measured parameters were observed during the different ventilatory modes either before or after thrombin infusion which doubled the pulmonary vascular resistance. It is concluded that high frequency ventilation superimposed on IPPV might be a ventilatory mode that offers cardiovascular stability and reduces the risk of barotrauma.     

Efficacy of the laryngeal tube during intermittent positive-pressure ventilation

We studied the efficacy of the laryngeal tube (VBM, Germany) during intermittent positive-pressure ventilation in 50 patients. After induction of anaesthesia and neuromuscular blockade, a size 4 laryngeal tube was inserted for patients of height 155 cm or greater. After insertion of the laryngeal tube, its pharyngeal and oesophageal balloons were inflated to an intracuff pressure of 60 cmH(2)O. An Ambu self-inflating bag was attached to the laryngeal tube and the lungs were ventilated manually at 15 breath.min(-1). It was possible to ventilate the lungs at the first attempt in 47 patients (94%). The airway pressure at which air leaked around the laryngeal tube exceeded 18 cmH(2)O in 41 patients (82%), and was > 30 cmH(2)O in 25 (50%). Median [interquartile range (range)] leak pressure was 30 [20-30 (6 to > 30)] cmH(2)O. Median [interquartile range (range)] tidal volume was 587 [533-653 (133-800)] ml or 8.8 [8.2-10.6 (1.9-12.6)] ml.kg(-1). We conclude that the laryngeal tube has a potential role in airway management during intermittent positive-pressure ventilation for anaesthesia or cardiopulmonary resuscitation.     

Intravenous infusion of propofol for induction and maintenance of anaesthesia during endoscopic carbon dioxide laser ENT procedures with high frequency jet ventilation

Fourteen patients of ASA grades 1 3 were anaesthetised with continuous infusions of propofol and alfentanil for endoscopic carbon dioxide laser ENT microsurgery. Their lungs were ventilated with an oxygen-air mixture using a high frequency jet ventilator. Propofol was given at an initial rate of 120 μg/kg/minute for 10 minutes after a bolus dose of 2.6 mg/kg, and then at 80 fig μg/kg/minute. Alfentanil was given at a rate of 0.5 μg/kg/minute. Arterial pressure decreased significantly after the bolus dose. It increased significantly for a few minutes after laryngoscopy and returned to baseline values during maintenance of anaesthesia. Heart rate increased significantly during induction and until laryngoscopy was performed but it decreased below its initial value after 5 minutes of maintenance. Platelet count and the degree of aggregation did not change during infusion of propofol.     

A new technique for sleeve resection and major bronchial resection using twin catheters and high frequency jet ventilation

A new anaesthetic technique that uses two catheters combined with high frequency jet ventilation for sleeve resection of the major bronchus and carina is described. The advantages and disadvantages are discussed and compared with other techniques.     

High frequency jet ventilation for microlaryngeal laser surgery

The use of a triple lumen central venous catheter, which can be shielded from laser irradiation by metal tape, as a conduit for high frequency jet ventilation in six children, is described. The problems of anaesthesia for laryngeal laser surgery and the advantages of the technique described in this paper are discussed.     

High frequency jet ventilation in intensive care—a review of 63 patients

High frequency jet ventilation has been used clinically in this unit for over 2 years. During this time we have treated 63 intensive care patients for whom the mean duration of ventilatory support was 3.4 days, which represents more than 5000 patient hours in total, with the Penlon Bromsgrove humidified jet ventilator. The series comprises a wide variety of general intensive care patients; a review of these cases is presented.     

High frequency jet ventilation

High frequency jet ventilation for thoracic surgery offers some practical advantages over intermittent pressure ventilation using bronchial tubes. Satisfactory blood gases were obtained in 50 patients and good operating conditions were provided.     

Laryngospasm during transtracheal high frequency jet ventilation

A 74-year-old woman developed severe cardiovascular depression during percutaneous transtracheal high frequency jet ventilation for laser surgery of the epiglottis. This was found to be caused by acute airway obstruction secondary to severe laryngospasm. We recommend profound neuromuscular blockade during percutaneous transtracheal jet ventilation, in order to prevent this complication.