High frequency ventilation

Analytic Reviews : Initiating Mechanical Ventilation

Mechanical ventilation is a central facet of intensive care medicine. Technological progress has led to major advances in this field. Initiation of mechanical ventila tion remains standard; however, many options are now available to continue mechanical ventilation. These mechanical options include assist-control ventilation, intermittent mandatory ventilation, pressure support ventilation, positive end-expiratory pressure, and high- frequency ventilation. The sophistication of ventilators has also allowed more procedures to be performed dur ing mechanical ventilation, including bronchoscopy and transbronchial biopsy. Complications do occur during mechanical ventilation, but can be minimized by vigi lance and use of proper procedures. The recent increase in home care will lead to increased use of alternatives to conventional ventilatory modes. Finally, more well- designed studies are needed as newer techniques are promoted.

[The pharmacokinetics of a fibrin adhesive agent applied to the rat lung]

PURPOSE

Although fibrin adhesive agents are frequently applied in the clinical setting, their pharmacokinetics in vivo remain to be clarified. We examined the pharmacokinetics of a fibrin adhesive agent applied to the rat lung.

MATERIAL AND METHODS

Male Sprague Dawley rats were used. Under general anesthesia, left thoracotomy was performed, and the left lung was incised about 1 cm length and 1 mm depth. This incision was sutured with 9-0 nylon, and a fibrin adhesive agent containing 125I-labeled fibrinogen was applied. On days 1, 3, 7 and 14 after the operation, the left lung, right lung, liver and kidneys were collected. The tissue distribution of radioactivity was examined by determining the 125I levels in each organ as well as calculating the tissue levels of radioactivity.

RESULTS

The tissue distribution of radioactivity in the left lung was significantly higher than those in other organs on days 1 and 3. The tissue levels of radioactivity in the left lung was significantly higher than those in other organs on days 1, 3 and 7. Each value rapidly decreased after day 7.

CONCLUSION

A fibrin adhesive agent applied to the lung significantly remained at a high level through the inflammatory and proliferative phases followed by a prompt decrease before the phase of cicatrization. Therefore it is considered that a fibrin adhesive agent applied to the lung is satisfactory for the healing of wounds.

Advances in pediatric surgical critical care

The advances in pediatric intensive care outlined here point out the differences between children and adults that need to be considered when taking care of children with surgical diseases. In the past, advances in pediatric critical care have not kept pace with advances in adult care, but these and other new techniques have rapidly closed this gap in knowledge.

Effect of sternotomy and cardiopulmonary bypass on airway pressures and respiratory mechanics during high frequency ventilation

The airway pressures at ventilatory frequencies of 15, 60, 100, 120 and 150 breaths per minute were measured in eight adult patients undergoing coronary artery bypass grafting. Measurements were made perioperatively at four stages: precardiopulmonary bypass with the chest closed, precardiopulmonary bypass with the chest open, postcardiopulmonary bypass with the chest open and postcardiopulmonary bypass with the chest closed. In five patients thoracic compliance and airways resistance were also measured at these times. Neither sternotomy nor cardiopulmonary bypass made any significant difference to the airway pressures during normal and high frequency ventilation, nor were lung mechanics affected.

Comparison of the haemodynamic effects of intermittent positive pressure ventilation with high frequency jet ventilation. Studies following valvular heart surgery

The cardiorespiratory effects of intermittent positive pressure ventilation and high frequency jet ventilation with and without positive end expiratory pressure were compared in patients following valvular heart surgery (mitral and/or aortic). Twenty patients received intermittent positive pressure ventilation and high frequency jet ventilation with 0, 0.5 and 1.0 kPa positive end expiratory pressure. High frequency jet ventilation was well tolerated. The addition of 1.0 kPa positive end expiratory pressure was associated with preservation of the arterial oxygen tension without any increase in shunt or significant adverse haemodynamic effect. The results are discussed and compared with a previous study of high frequency jet ventilation following aortocoronary bypass graft surgery.

High frequency ventilation

High frequency ventilation (HFV) presents a new respiratory therapy modality that has taught us much about the theories of gas transport in the lung. Both experimental and clinical applications are summarized. Although the future clinical role of HFV remains uncertain, pediatric applications and investigation continue at the forefront of this new technology.

Relationship between frequency of ventilation, airways and pulmonary artery pressures, cardiac output and tracheal tube deadspace

Intravascular and airway pressures, cardiac output (CO) and blood gas tensions were measured in five adult patients after hepatobiliary surgery. They were ventilated at frequencies of 15, 100 and 200 breaths min-1 (bpm) with the respiratory fresh gas (RFG) supplied at the proximal and distal end of a Mallinckrodt Hi-Lo tracheal tube. The peak airway pressure (P AW) fell from 1.20 kPa at 15 bpm to 0.6 kPa at 100 bpm, rising again to 1.9 kPa at 200 bpm, and both changes were significant (P less than 0.05). The mean pulmonary artery pressure (PAMP) remained in the range 1.87-2.00 kPa (14-15 mmHg) at 15 and 100 bpm but rose to over 2.67 kPa (20 mmHg) at 200 bpm (P less than 0.05). Cardiac output, heart rate and systemic arterial pressure remained unchanged. A small but significant (P less than 0.05) reduction in PaCO2 occurred when the RFG was moved to the distal end of the tracheal tube. A theoretical analysis predicts that the minimal P AW to maintain CO2 hemostasis will occur between 30 to 100 bpm, which is reflected in the results of the present study.