Improved Arterial Oxygenation with Biologically Variable or Fractal Ventilation Using Low Tidal Volumes in a Porcine Model of Acute Respiratory Distress Syndrome

Abstract

We compared biologically variable ventilation (V (bv); n = 9) with control mode ventilation (V (c); n = 8) at low tidal volume (VT)--initial 6 ml/kg--in a porcine model of acute respiratory distress syndrome (ARDS). Hemodynamics, respiratory gases, airway pressures, and VT data were measured. Static P-V curves were generated at 5 h. Interleukin (IL)-8 and IL-10 were measured in serum and tracheal aspirate. By 5 h, higher Pa(O(2)) (173 +/- 30 mm Hg versus 119 +/- 23 mm Hg; mean +/- SD; p < 0.0001 group x time interaction [G x T]), lower shunt fraction (6 +/- 1% versus 9 +/- 3%; p = 0.0026, G x T) at lower peak airway pressure (21 +/- 2 versus 24 +/- 1 cm H(2)O; p = 0.0342; G x T) occurred with V (bv). IL-8 concentrations in tracheal aspirate and wet:dry weight ratios were inversely related; p = 0.011. With V (c), IL-8 concentrations were 3.75-fold greater at wet:dry weight ratio of 10. IL-10 concentrations did not differ between groups. In both groups, ventilation was on the linear portion of the P-V curve. With V (bv), VT variability demonstrated an inverse power law indicating fractal behavior. In this model of ARDS, V (bv) improved Pa(O(2)) at lower peak airway pressure and IL-8 levels compared with V (c).

Resolution of pulmonary edema with variable mechanical ventilation in a porcine model of acute lung injury

“…5 In animal models of ARDS, variable ventilation strategies are superior to conventional control mode mechanical ventilation (CMV) or CMV with recruitment maneuvers with respect to lung mechanics, gas exchange, surfactant content, and inflammatory mediators with an overall decrease in distending stress. [5][6][7][8][9][10][11][12] In a recent computed tomography (CT) imaging study, we confirmed BVV induced recruitment of both poorly and non-aerated lung regions. 13 In this study, we hypothesized that the recruitment benefit and periodic low V T breaths seen with BVV could result in enhanced resolution of edema fluid in ARDS.…”

“…These parameters were chosen as multiple previous studies have demonstrated significant BVV advantages with respect to lung mechanics, gas exchange, and inflammatory mediators within this time period with a similar number of subjects, 6,7 and Ware and Matthay 1 were able to demonstrate significant differences in fluid clearance rates in clinical subjects over a similar time frame. Given the more modest effects seen with a less severe injury model, however, significant differences were limited to the CT findings.…”

“…Instrumentation has been reported previously. 7 Total intravenous anesthesia was provided with propofol/ketamine/pancuronium (15/ 3.75/0.1 mgÁkg -1 Áhr -1 ) during the experimental period. The animals were ventilated with an EspritÒ intensive care ventilator (Respironics Inc., Palo Alto, CA, USA) capable of delivering either CMV or BVV.…”

“…6,7 Briefly, breath-to-breath control of the Esprit ventilator is provided by a modulation file and laptop computer. The modulation file is derived from the breathto-breath frequency variability that was obtained from a spontaneously ventilating awake subject, captured by a data acquisition system, and processed.…”

Variable Ventilation from Bench to Bedside

“…Apart from the benefits in gas exchange, the most striking and common finding during variable controlled mechanical ventilation across different studies is the improvement in lung mechanics. In an experimental model of the acute respiratory distress syndrome (ARDS), variable controlled mechanical ventilation improved lung function compared to the ARDS Network lung protective strategy, as well as the open lung approach [14,15]. In addition, it has been shown that variable ventilation may also be used during assisted ventilation by means of random variation of pressure support (variable pressure-support ventilation [PSV]) leading to comparable improvements in lung function compared to conventional PSV [16].…”