High-frequency ventilation

Published on 07/02/2015 by admin

Filed under Anesthesiology

Last modified 22/04/2025

Print this page

rate 1 star rate 2 star rate 3 star rate 4 star rate 5 star
Your rating: none, Average: 0 (0 votes)

This article have been viewed 1239 times

High-frequency ventilation

Joshua Horowitz, DO and Keith A. Jones, MD

High-frequency ventilation (HFV) is the delivery of small tidal volumes (equal to or less than the anatomic dead space) at rates of 60 to 900 or more cycles per minute. The nomenclature for HFV includes high-frequency positive-pressure ventilation (HFPPV), high-frequency jet ventilation (HFJV), and high-frequency oscillation (HFO). High-frequency chest wall compression is occasionally discussed in the literature under the heading of HFV, but high-frequency chest wall compression is not used to ventilate patients; it is a chest physiotherapy technique used primarily on patients with cystic fibrosis to help them clear secretions.

Table 160-1 compares the major types of HFV. HFPPV can be delivered by a standard mechanical ventilator, though most are not designed to achieve rates greater than 60 to 100/min.

Physiology

Gas transport (i.e., O2 insufflation and CO2 elimination) at ventilation rates greater than 170 breaths/min depends on convection, diffusion, and other complex mechanisms that are very different from those that occur during conventional mechanical ventilation (CMV) and are not well understood. CO2 elimination can and does occur at tidal volumes that are much lower than the volume of air contained in the anatomic dead space. The decrease in airway resistance associated with HFV somehow facilitates penetration of gas to alveoli, alveolar minute ventilation, and CO2 elimination. However, CO2 elimination increases linearly as ventilation rate increases up to only a certain point (3-6 Hz; 180-360 breaths/min); at higher rates, dead-space to tidal volume ratio and alveolar minute ventilation are constant.

HFV does not substantially improve oxygenation, compared with CMV; in both situations, oxygenation correlates with mean airway pressure. However, the ability to maintain lower peak and mean airway pressures with HFV is beneficial for other reasons (e.g., hemodynamic stability). The magnitude of the hemodynamic effects is related to the amount of positive pressure applied to the airway. At lower peak and mean airway pressures, the adverse effects should be fewer; however, the lower levels of adverse effects have not been shown to be consistent. Fluctuations in intracranial pressure with the use of HFV, compared with CMV, are typically lower, but the mean intracranial pressure does not decrease.

Clinical applications

High-frequency jet ventilation

HFJV has several clinical applications. HFJV is often used in laryngeal and tracheal operations because it can be delivered with a cannula or catheter much smaller than a traditional tracheal tube. The use of such a catheter minimizes the intra-airway space occupied by the tracheal tube, thereby increasing the working space available to the otolaryngologic or thoracic surgeon. HFJV also decreases ventilatory excursion, which also improves operating conditions for the surgeon.

Percutaneous transtracheal HFJV can be used to manage the difficult airway in an emergency by inserting a small cannula through the cricothyroid membrane. The cannula can be connected to any of several jet ventilators or to a hand-held flush valve connected to an adequate pressure source—the O2 flush valve on a Dräger anesthesia machine has been found to provide sufficient pressure. Pressing the valve briefly (≤0.3 sec) delivers a pulse of O2 at high pressure that dissipates quickly into the airway—slight expansion of the chest may be observed. If the valve is held open too long (≥0.5 sec), the volume of O2 fills the airway and pressure rises; the high pressure can be communicated directly to the airway and lung, leading to barotrauma.

High-frequency oscillation

HFO has been used for decades, mostly in newborn and premature infants with respiratory distress syndrome. Unlike in HFJV, in which “inspiration” is active and “exhalation” is passive, in HFO, both inspiration and expiration are active processes. As mentioned previously, the mean airway pressure can be increased to improve oxygenation levels. Increasing the amplitude of the gas wave generated by the oscillator increases the rate of CO2 elimination. Several randomized studies and meta-analyses have not demonstrated clear-cut benefits of HFO, as compared with CMV; in most centers with a neonatal intensive care unit, HFO is used as rescue therapy to treat patients with respiratory distress syndrome who do not respond to treatment with CMV. If neonates or infants are not fully supported with HFO or their condition deteriorates further, the use of extracorporeal membrane oxygenation is often considered as the next step.

There are few recent studies of the use of HFO in adults, largely because the ARDS Network has demonstrated that low-volume, pressure-targeted ventilation strategies, compared with CMV strategies, significantly reduce mortality rates in patients with acute lung injury/acute respiratory distress syndrome. In 2006, however, Derdak and colleagues published the results of a large randomized controlled trial comparing HFO with CMV in patients with acute respiratory distress syndrome and showed that the 30-day mortality rate was reduced from 52% in the CMV group to 37% in the HFO group.

Related posts:

Vaporizers Default ThumbnailAnesthesia information management systems Default ThumbnailIssues in ambulatory anesthesia Croup versus epiglottitis Default ThumbnailMultimodal analgesia Default ThumbnailBlood gas temperature correction