High-frequency Flow Interruption Research Articles

Volume Targeted Ventilation and High Frequency Ventilation as the Primary Modes of Respiratory Support for ELBW Babies: What Does the Evidence Say?

Respiratory management of the extremely low birth weight (ELBW) newborn has evolved over time. Although non-invasive ventilation is being increasingly used for respiratory support in these ELBW infants, invasive ventilation still remains the primary mode in this population. Current ventilators are microprocessor driven and have revolutionized the respiratory support for these neonates synchronizing the baby's breath to ventilator breaths. High frequency ventilators with the delivery of tidal volumes less than the dead space have been introduced to minimize barotrauma and chronic lung disease. Despite these advances, the incidence of chronic lung disease has not decreased. There is still controversy regarding which mode is ideal as the primary mode of ventilation in ELBW infants. The most common modes seem to be pressure targeted conventional ventilation, volume targeted conventional ventilation and high frequency ventilation which includes high frequency oscillatory ventilation, high frequency jet ventilation and high frequency flow interrupter. In recent years, several randomized controlled trials and meta-analyses have compared volume vs. pressure targeted ventilation and high frequency ventilation. While volume targeted ventilation and high frequency ventilation does show promise, substantial practice variability among different centers persists. In this review, we weighed the evidence for each mode and evaluated which modes show promise as the primary support of ventilation in ELBW babies.

An in‐line high frequency flow interrupter applied to nasal CPAP: Improved carbon dioxide clearance in a premature infant lung model

Noninvasive respiratory support continues to have high failure rates in small preterm infants. We previously demonstrated significantly improved in vitro CO2 washout by applying oscillations to a high flow nasal cannula system. To develop a high frequency flow interrupter that could be applied to commonly used nasal continuous positive airway pressure (NCPAP) devices and to determine the effect of oscillations on end-tidal carbon dioxide (EtCO2 ) levels in an infant lung model. NCPAP was applied to a premature infant lung simulator using either bubble (BCPAP) or variable-flow (VCPAP) CPAP. Supply gas was interrupted with a solenoid pinch valve. EtCO2 was measured before and during oscillation and repeated at 4, 6, 8, 10, and 12 Hz oscillation and CPAP pressures of 4, 6, and 8 cm H 2 O. BCPAP and VCPAP EtCO2 levels decreased with oscillation (P < .001). BCPAP EtCO2 was significantly dependent on oscillation frequency (P < .001) with decreases of 18% to 47% and maximum effect at 10 Hz. Optimum VCPAP CO2 clearance occurred at 6 Hz with reductions of 30% and 39% at 6 and 8 cm H2 O CPAP respectively. BCPAP and VCPAP mean airway pressures remained unchanged transitioning from nonoscillation to oscillation. Oscillated BCPAP and VCPAP average amplitudes were 8.3 ± 0.5 and 8.4 ± 2.3 SD cm H2 O, respectively. Power spectrum analysis of non-oscillated BCPAP showed bubbling-only dominant peaks at 10 to 12 Hz corresponding with the maximum BCPAP EtCO2 reductions. Application of high frequency oscillation to NCPAP improves CO2 clearance in a premature infant lung model. This simple modification to NCPAP delivery devices may prove to be an effective enhancement of this mode of noninvasive respiratory support.

High-Frequency Percussive Ventilation Using the VDR-4 Ventilator

High-frequency percussive ventilation (HFPV) has been used for patients with severe respiratory compromise refractory to conventional mechanical ventilation. It frequently results in equivalent or improved oxygenation and ventilation at lower peak pressures than conventional ventilation, thus minimizing secondary ventilator-associated lung injury. The only ventilator currently available that delivers HFPV is the volume diffusive respirator (VDR-4; Percussionaire Corp, Sandpoint, Idaho). High-frequency percussive ventilation is delivered via a pneumatically powered, pressure-limited, time-cycled, high-frequency flow interrupter and provides small tidal volumes with 300 to 700 oscillations per minute. Following transition to HFPV, respiratory status often stabilizes or improves within a few hours. The unique gas flow mobilizes significant volumes of pulmonary secretions, further facilitating gas exchange. This article reviews the operating principles of HFPV, the functional components of the VDR-4, and the special nursing care considerations to include sedation, hemodynamic assessment, skin and oral care, nutrition, and weaning from ventilation.

High-Frequency Percussive Ventilation Using the VDR-4 Ventilator

High-frequency percussive ventilation (HFPV) has been used for patients with severe respiratory compromise refractory to conventional mechanical ventilation. It frequently results in equivalent or improved oxygenation and ventilation at lower peak pressures than conventional ventilation, thus minimizing secondary ventilator-associated lung injury. The only ventilator currently available that delivers HFPV is the volume diffusive respirator (VDR-4; Percussionaire Corp, Sandpoint, Idaho). High-frequency percussive ventilation is delivered via a pneumatically powered, pressure-limited, time-cycled, high-frequency flow interrupter and provides small tidal volumes with 300 to 700 oscillations per minute. Following transition to HFPV, respiratory status often stabilizes or improves within a few hours. The unique gas flow mobilizes significant volumes of pulmonary secretions, further facilitating gas exchange. This article reviews the operating principles of HFPV, the functional components of the VDR-4, and the special nursing care considerations to include sedation, hemodynamic assessment, skin and oral care, nutrition, and weaning from ventilation.

Haemodynamics and oxygenation improvement induced by high frequency percussive ventilation in a patient with hypoxia following cardiac surgery: a case report

IntroductionHigh frequency percussive ventilation is a ventilatory technique that delivers small bursts of high flow respiratory gas into the lungs at high rates. It is classified as a pneumatically powered, pressure-regulated, time-cycled, high-frequency flow interrupter modality of ventilation. High frequency percussive ventilation improves the arterial partial pressure of oxygen with the same positive end expiratory pressure and fractional inspiratory oxygen level as conventional ventilation using a minor mean airway pressure in an open circuit. It reduces the barotraumatic events in a hypoxic patient who has low lung-compliance. To the best of our knowledge, there have been no papers published about this ventilation modality in patients with severe hypoxaemia after cardiac surgery.Case presentationA 75-year-old Caucasian man with an ejection fraction of 27 percent, developed a lung infection with severe hypoxaemia [partial pressure of oxygen/fractional inspiratory oxygen of 90] ten days after cardiac surgery. Conventional ventilation did not improve the gas exchange. He was treated with high frequency percussive ventilation for 12 hours with a low conventional respiratory rate (five per minute). His cardiac output and systemic and pulmonary pressures were monitored.Compared to conventional ventilation, high frequency percussive ventilation gives an improvement of the partial pressure of oxygen from 90 to 190 mmHg with the same fractional inspiratory oxygen and positive end expiratory pressure level. His right ventricular stroke work index was lowered from 19 to seven g-m/m2/beat; his pulmonary vascular resistance index from 267 to 190 dynes•seconds/cm5/m2; left ventricular stroke work index from 28 to 16 gm-m/m2/beat; and his pulmonary arterial wedge pressure was lowered from 32 to 24 mmHg with a lower mean airway pressure compared to conventional ventilation. His cardiac index (2.7 L/min/m2) and ejection fraction (27 percent) did not change.ConclusionAlthough the high frequency percussive ventilation was started ten days after the conventional ventilation, it still improved the gas exchange. The reduction of right ventricular stroke work index, left ventricular stroke work index, pulmonary vascular resistance index and pulmonary arterial wedge pressure is directly related to the lower respiratory mean airway pressure and the consequent afterload reduction.

High-Frequency Oscillation and Chronic Lung Disease in Very Low Birth Weight Infants

To the Editor. The study by Rimensberger et al1 suggests that early institution of high-frequency oscillation (HFO) for the treatment of respiratory distress syndrome improves the pulmonary outcome in ventilated very low birth weight infants. Unfortunately, there are flaws in study design that limit the validity of this conclusion. First, the 2 study cohorts were not concurrent. Most of the infants in the experimental cohort treated with HFO were born in 1997 and 1998, whereas those in the historical control cohort treated with conventional mechanical ventilation were born in 1994 and 1995. Subtle differences in clinical management might have been unavoidable in the 2-year period that separates these cohorts and contributed to the difference in the pulmonary outcome. Second, the statistical basis for selecting the specific number of infants in each cohort is not provided. Without appropriate power analysis, the statistical validity of comparisons between cohorts is difficult to confirm. Third, the retrospective nature of the study raises questions about uncontrolled data collection and problems with data retrieval, both inherent problems of a retrospective study design. Fourth, what is most striking is that there is no discussion of the common complications, such as symptomatic patent ductus arteriosus and airway infection, both of which are strong contributors to the development of chronic lung disease. And fifth, there is no discussion of the nutritional management of the infants. Nutrition plays a big role in the process of healing from lung injury. Thus, although the zero incidence of chronic lung disease in very low birth weight infants ventilated with HFO appears to be a remarkable achievement indeed, the enthusiasm for accepting this conclusion is dampened by the flawed study design. The subtle message that a single ventilation strategy can eliminate chronic lung disease, a disease of diverse causes, is misleading. What is …

Partial liquid ventilation: a comparison using conventional and high-frequency techniques in an animal model of acute respiratory failure.

To test the hypothesis that high-frequency ventilation (HFV), when compared with conventional techniques, enhances respiratory gas exchange during partial liquid ventilation (PLV). A four-period crossover design. Animal research laboratory of Children's Health Care-St. Paul. Thirty-two newborn piglets, weighing 1.40 +/- 0.39 kg. Animals were divided into four groups of eight animals: a) PLV with high-frequency jet ventilation; b) PLV with jet ventilation using a background intermittent mandatory ventilation (IMV) rate; c) PLV with high-frequency oscillation; or d) PLV with high-frequency flow interruption using a background IMV rate. After anesthesia, paralysis, and tracheotomy, a normal saline wash procedure produced lung injury. Perfluorocarbon was then instilled via the endotracheal tube in an amount estimated to represent functional residual capacity. Animals received randomly either PLV using conventional techniques or PLV using the selected HFV technique as initial treatment. Then, animals were crossed over to the alternative treatment at equal mean airway pressure, as measured at the endotracheal tube tip. This sequence was repeated for a total of four crossover periods, such that all animals were treated twice with PLV using conventional techniques and twice with PLV using HFV. We measured airway pressures at the endotracheal tube tip, aortic and central venous blood pressures, arterial blood gases, and respiratory system mechanics at baseline, after induction of lung injury, and at specified intervals throughout the experiment. Measurements were made before and 15 mins after crossovers, then ventilators were adjusted to normalize gas exchange. Measurements were again made 30 mins later, at the end of the treatment period. All types of PLV provided adequate gas exchange. Only PLV using jet ventilation with IMV produced gas exchange equal to that seen during PLV using conventional techniques at equivalent mean airway pressure. By the end of the treatment periods, only PLV using high-frequency oscillation continued to require higher airway pressure than PLV using conventional techniques for equivalent gas exchange. Gas exchange was not enhanced during PLV-HFV. Application of HFV with PLV provides no clear acute physiologic advantages to PLV using more conventional techniques.

Smoke inhalation is a multilevel insult to the pulmonary system.

Inhalation injury represents an ongoing threat to patients with thermal injury. The magnitude of the disease severity is related to the multilevel insult to the pulmonary system. Asphyxiants present in inhaled smoke can compromise oxygen delivery, resulting in cell death. Also, early changes in the microcirculation of the lung parenchyma, related to polymorphonuclear cell activation and oxygen free radical production, are responsible for early pulmonary edema. Perhaps the most significant pathologic change caused by smoke inhalation is loss of the respiratory epithelium and the formation of tracheobronchial casts. The recent application of high-frequency flow interruption ventilation and intrapulmonary percussive ventilation has made the largest impact on improved survival in patients suffering from smoke inhalation.

Smoke inhalation is a multilevel insult to the pulmonary system

Inhalation injury represents an ongoing threat to patients with thermal injury. The magnitude of the disease severity is related to the multilevel insult to the pulmonary system. Asphyxiants present in inhaled smoke can compromise oxygen delivery, resulting in cell death. Also, early changes in the microcirculation of the lung parenchyma, related to polymorphonuclear cell activation and oxygen free radical production, are responsible for early pulmonary edema. Perhaps the most significant pathologic change caused by smoke inhalation is loss of the respiratory epithelium and the formation of tracheobronchial casts. The recent application of high-frequency flow interruption ventilation and intrapulmonary percussive ventilation has made the largest impact on improved survival in patients suffering from smoke inhalation.

High frequency ventilator therapy for newborns.

High-frequency ventilation is a general term that refers to a family of ventilator techniques that utilize respirator rates greater than 60 breaths/minute and tidal volumes that are usually less than or equal to the anatomical dead space of the airways. These techniques include high frequency positive-pressure ventilation, high frequency jet ventilation, high frequency flow interruption, high frequency oscillatory ventilation, and high frequency chest wall oscillation. I review the proposed mechanisms of gas transport during high-frequency ventilation and the different ventilators capable of delivering this mode of ventilation. In addition, clinical studies involving infants treated with this new technology are reviewed, along with long-term patient follow-up and reported complications.

High-Frequency Ventilation in Acute Pediatric Respiratory Failure

High-Frequency Ventilation in Acute Pediatric Respiratory Failure

Decreased Pulmonary Damage in Primates with Inhalation Injury Treated with High-Frequency Ventilation

This study compared two forms of high-frequency ventilation (HFV) with conventional volume ventilation (CON) in a primate model of inhalation injury to determine whether ventilatory mode was a determinant of pulmonary damage. The authors previously reported that the prophylactic use of high-frequency flow interruption in patients with bronchoscopically diagnosed inhalation injury requiring mechanical ventilatory support resulted in a significant decrement in mortality. They hypothesized that a reduction in ventilatory mode induced pulmonary damage was in part responsible for their clinical results. Fifteen adult baboons were randomized to one of three ventilatory modes (CON, high-frequency flow interruption [HFFI], or high-frequency oscillatory ventilation [HFO]) after moderate smoke injury. Ventilatory support was tailored to the same physiologic endpoints. After 7 days, the animals were killed and pulmonary pathologic changes were scored and compared. Repetitive physiologic and biochemical data were compared using analysis of variance for repeated measures. Physiologic endpoints were achieved in CON and HFFI, but not in HFO. Hemodynamic variables did not differ between CON and HFFI. The barotrauma index was greater in CON compared to HFFI (p < 0.05), despite similar PO2, FIO2, AA gradient, and PCO2. Animals treated with HFFI had significantly less parenchymal damage than those treated with CON (p = 0.03) or HFO (p = 0.0008). The prophylactic use of HFFI led to a significant decrement in ventilatory mode induced pulmonary damage and offers an explanation for the decreased mortality in inhalation injury patients treated with HFFI.

Necrotizing Tracheobronchitis (NTB) Following High Frequency Ventilation: Role of an Angiotensin Converting Enzyme Inhibitor

The purpose of this investigation was to study the effect of an angiotensin converting enzyme inhibitor (enalaprilat) on the morphologic manifestations of experimentally induced necrotizing tracheobronchitis (NTB). Twenty piglets were anesthetized before saline lung lavage. High frequency flow interrupter (HFFI) ventilation was used with a strategy known to produce NTB. Animals were randomly assigned to receive IV enalaprilat 0.1 mg/kg (ENP-Hi), enalaprilat 0.01 mg/kg (ENP-Lo), or saline (C). After 8 hours of ventilation, the piglets were sacrificed. Total airway injury scores (mean +/- S.D.) were 1.2 +/- 0.7 for ENP-Hi, 0.2 +/- 0.2 for ENP-Lo, and 21.3 +/- 16 for group C. Enalaprilat minimizes NTB lesions in neonatal piglets exposed to high frequency oscillatory ventilation. Although the origin of NTB is multifactorial, airway mucosa ischemia may play an important role. Enalaprilat may compensate for the reduction of mucosal blood flow by limiting formation of angiotensin II and/or preventing degradation of bradykinin.

Different High-Frequency Ventilator Strategies: Effect on the Propagation of Tracheobronchial Histopathologic Changes

To assess the role of high-frequency ventilator strategy in the propagation of airway injury, we compared the tracheobronchial histologic alterations in 20 newborn piglets ventilated for 8 hours with high-frequency flow interruption (HFFI). Ten animals were assigned to HFFI with a strategy of continuous pulsations at a frequency of 10 Hz and a mean airway pressure of 16 cm H2O. Ten piglets were treated at identical settings except for 10 one-second baseline pauses per minute to a positive end-expiratory pressure of 5 cm H2O. A semiquantitative scoring system was used to grade light microscopic tissue alterations in the trachea, carina, and mainstem bronchi. Ultrastructural changes were evaluated with scanning electron microscopy. The HFFI-continuous-treated piglets had significantly more damage in all areas than the HFFI-baseline pause group (P less than .001). The upper tracheas of animals in both groups were altered to a greater extent than the lower tracheas (P less than .007). In addition, numerous "skip" areas of injury were noted throughout the tracheas. High-frequency ventilator strategy is a determinant of the severity of airway histologic changes. Factors that adversely affect tissue oxygenation or cause direct mechanical trauma may also influence the degree of injury. Optimal operating characteristics and limitations of different high-frequency devices must be assessed before their use in human neonates.

Evaluation of lung mechanics in rabbits using short duration flow pulses.

An alternative method of evaluating pulmonary mechanical function that uses short duration flow pulses was applied in five adult rabbits with high frequency flow interruption (HFFI) at 4 cycles per second. Variations in the total pressure across the respiratory system were partitioned into separate lungs and chest wall components, and the mechanical impedance of each component was evaluated in the range of 4 to 40 Hz using cross and power spectral analysis and spectral averaging. The resistances, R, of the respiratory system, lungs, and chest wall were 23.5 (2.3 SD), 18.6 (2.8), and 4.9 (1.5) cm H2O.L-1.s, respectively. These values were similar to R obtained by the conventional method at ordinary rates of ventilation, with the exception of chest wall resistance, which was approximately 50% smaller than R obtained by the conventional method. The compliances of the respiratory system, lungs and chest wall were 1.40 (0.19), 2.88 (0.94), and 2.85 (0.86) ml.cm H2O-1, respectively. In all cases, compliance values obtained by pulse analysis were roughly 70% of the values obtained by the conventional method. The smaller compliance values obtained with the pulse method may reflect the multicompartment behavior of the lungs and chest wall at the high frequencies found in the pulse spectra. We conclude that the response of the respiratory system to short duration flow pulses may be used to evaluate pulmonary mechanical function. The brief duration of the flow pulse suggests that this method may be well suited to evaluate lung function in uncooperative subjects, particularly newborns and premature infants.

Gas exchange during high frequency flow-interruption in rabbits before and after bronchoalveolar lavage.

The performance of a high frequency flow-interrupter (HFFI) type neonatal ventilator was evaluated on nine adult rabbits (control) and on five adult rabbits after bronchoalveolar lavage (BAL). Tidal volumes and airway pressures were measured during conventional ventilation and during HFFI at rates of 4, 6, 8, 10, and 12 cycles/s. Tidal volumes were adjusted to maintain PaCO2 between 35 and 42 mm Hg in control rabbits and 35-55 mm Hg in BAL rabbits; a positive end-expiratory pressure of 4 cm H2O was applied to BAL rabbits to reduce atelectasis and improve gas exchange. The normalized tidal volume required to maintain PaCO2 within the specified range during HFFI varied between 2.02 ml/kg (0.30 SD) and 2.55 (0.41) in control rabbits and between 2.65 (0.57) and 2.97 (0.51) in BAL rabbits. In neither group did the normalized tidal volume vary systematically with the rate of ventilation (p less than 0.05). Mean airway pressures were lower during HFFI than during conventional ventilation in control rabbits but comparable in the BAL group. Peak inflation pressures were greater during HFFI than conventional ventilation in control rabbits but similar in the BAL group. End-expiratory lung volume was not affected by ventilation rate during HFFI in control rabbits. We conclude 1) that HFFI can maintain gas exchange in rabbits suffering from acute respiratory distress with airway pressures that are comparable to those measured during conventional ventilation and 2) the capacity of HFFI to ventilate the lungs with significantly lower airway pressures than conventional ventilation depends, in part, on the condition of the lungs.

Tracheal and bronchial injury in high-frequency oscillatory ventilation and high-frequency flow interruption compared with conventional positive-pressure ventilation

We compared the histopathologic changes in the airways of premature baboons treated with conventional positive-pressure ventilation (PPV) with those seen after high-frequency oscillatory ventilation (HFOV) and high-frequency flow interruption (HFFI). Twenty-six animals were treated with ventilation for 24 hours (five PPV, 10 HFOV, 11 HFFI), and 18 were treated with ventilation for 96 hours (six PPV, six HFOV, six HFFI). A semiquantitative scoring system was used to grade tissue changes in the trachea, carina, and both main-stem bronchi. Alterations were produced by all forms of mechanical ventilation. The degree of injury was similar and relatively mild for the PPV- and HFOV-treated animals at both 24 and 96 hours. Eleven of 17 baboons treated with HFFI ventilation (8/11 at 24 hours; 3/6 at 96 hours) had severe airway damage characterized by diffuse submucosal necrosis, extensive hemorrhage, dense polymorphonuclear leukocyte infiltration, sloughed epithelium, focal basophilia, and intraluminal debris. HFOV resulted in no greater degree of airway damage than did PPV. The use of HFFI, with the particular strategy we employed, resulted in a far greater degree of damage than either PPV (P less than 0.01) or HFOV.

High-Frequency Ventilation and Tracheal Injuries

To the Editor.— We read with interest the study of Mammel et al.1 However, we wish to address several aspects of the report regarding the design of the investigation, their interpretation of the results and of other reports, and the conclusions they make. First, we take exception to the title itself. Unfortunately, many pediatricians and neonatologists do not make any distinction between the various types of nonconventional, high-frequency ventilators. High-frequency ventilation is a generic term encompassing several very different modalities of ventilation including high-frequency positive pressure ventilation, high-frequency flow interruption, high-frequency jet ventilation, and high-frequency oscillatory ventilation.

High-Frequency Ventilation in Newborn Infants

In the past mechanical ventilation always mimicked the tidal volumes and ventilatory frequencies of normal breathing. Recently, there has been great interest in techniques that use rapid rates (60 to 3,000 per minute) and tidal volumes approximating dead space. These techniques are known collectively as high-frequency ventilation, although they differ in circuit design, use, potential complications, and mechanism of gas transport. High-frequency ventilation can be divided into four categories: (1) high-frequency positive pressure ventilation, (2) high-frequency jet ventilation, (3) high-frequency oscillatory ventilation and high-frequency flow interruption, and (4) high-frequency chest wall oscillation. In this review we discuss the similarities and differences of these high-frequency techniques, their clinical applications, and some physiological mechanisms involved in gas transport.