Application of Mid-Frequency Ventilation in an Animal Model of Lung Injury: A Pilot Study

Abstract

BACKGROUND: Mid-frequency ventilation (MFV) is a mode of pressure control ventilation based on an optimal targeting scheme that maximizes alveolar ventilation and minimizes tidal volume (V T ). This study was designed to compare the effects of conventional mechanical ventilation using a lung-protective strategy with MFV in a porcine model of lung injury. Our hypothesis was that MFV can maximize ventilation at higher frequencies without adverse consequences. We compared ventilation and hemodynamic outcomes between conventional ventilation and MFV. METHODS: This was a prospective study of 6 live Yorkshire pigs (10 ؎ 0.5 kg). The animals were subjected to lung injury induced by saline lavage and injurious conventional mechanical ventilation. Baseline conventional pressure control continuous mandatory ventilation was applied with V T ‫؍‬ 6 mL/kg and PEEP determined using a decremental PEEP trial. A manual decision support algorithm was used to implement MFV using the same conventional ventilator. We measured P aCO 2 , P aO 2 , end-tidal carbon dioxide, cardiac output, arterial and venous blood oxygen saturation, pulmonary and systemic vascular pressures, and lactic acid. RESULTS: The MFV algorithm produced the same minute ventilation as conventional ventilation but with lower V T (؊1 ؎ 0.7 mL/kg) and higher frequency (32.1 ؎ 6.8 vs 55.7 ؎ 15.8 breaths/min, P < .002). There were no differences between conventional ventilation and MFV for mean airway pressures (16.1 ؎ 1.3 vs 16.4 ؎ 2 cm H 2 O, P ‫؍‬ .75) even when auto-PEEP was higher (0.6 ؎ 0.9 vs 2.4 ؎ 1.1 cm H 2 O, P ‫؍‬ .02). There were no significant differences in any hemodynamic measurements, although heart rate was higher during MFV. CONCLUSIONS: In this pilot study, we demonstrate that MFV allows the use of higher breathing frequencies and lower V T than conventional ventilation to maximize alveolar ventilation. We describe the ventilatory or hemodynamic effects of MFV. We also demonstrate that the application of a decision support algorithm to manage MFV is feasible.

Feasibility of Mid-Frequency Ventilation Among Infants With Respiratory Distress Syndrome

“…The application of the mid-frequency ventilation strategy has been tested in mathematical models, 23 a highfidelity adult lung simulator, 23 and acute lung injury animal models. 24 The feasibility and efficacy of the mid-frequency ventilation strategy using an algorithm to adjust the ventilator parameters to achieve optimal frequency were evaluated in an acute lung injury piglet model. 24 Although we incorporated the basic principles of mid-frequency ventilation, our study did not use this algorithm to achieve optimal ventilator frequency.…”

“…Mid-frequency ventilation is an alternative mode of ventilatory support aimed at providing the needed minute ventilation at lower tidal volumes and lower peak inspiratory pressures by operating conventional ventilators at higher than normally used ventilator rates. 23,24 In the present paper, we classify mid-frequency ventilation (in its present non-commercial form) as PC-IMVs,s (this classification is very common and has many unique names). 25 The mode is a form of intermittent mandatory ventilation (IMV) because spontaneous breathing is allowed, although it may not occur at high levels of ventilatory support (eg, the mode in this study was synchronized IMV pressure control on a Puritan Bennett 840 ventilator [Covidien, Mansfield, Massachusetts]).…”

“…Mid-frequency ventilation has been stud-ied only using adult lung simulators and animal models of ARDS. 23,24 Randomized crossover studies using conventional ventilators with a mid-frequency ventilation strategy have not been reported. Therefore, we conducted a trial to study the feasibility of using mid-frequency ventilation to reduce surrogate measures of lung injury in preterm infants with RDS receiving mechanical ventilation.…”

Mid-Frequency Ventilation: A Viable Option for Lung Protection?

“…Whether MFV is eventually deployed and proves its worth at the bedside, the work presented here by Mireles-Cabodevila and colleagues 5 provides interesting preclinical data motivated by a strongly mechanistic rationale. It is precisely this type modeling and testing of a clinical problem, once so prevalent in the science of respiratory care, that tests our assumptions, helps develop a solid base for designing clinical studies, and provides insights for improving care delivery.…”

“…4 In this issue of RESPIRATORY CARE, Mireles-Cabodevila and colleagues present experimental work demonstrating the feasibility of significantly reducing V T and excursions of tidal pressures by using ventilator frequencies higher than those customarily targeted. 5 This method, previously described in conceptual fashion by these authors as midfrequency ventilation (MFV), 6 uses algorithm-adjusted pressure controlled ventilation over a frequency range of ϳ50 -70 breaths/min. Because alveolar pressure during pressure controlled ventilation rises and falls quasi-exponentially toward the airway pressure extremes of the tidal cycle, 7 V T declines as progressively increasing frequency allows less time for alveolar pressures to build and fall to their fixed airway pressure targets.…”