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Comparative Study
. 2014 Jan 23;18(1):R22.
doi: 10.1186/cc13706.

Lung protection during non-invasive synchronized assist versus volume control in rabbits

Lucia Mirabella, Giacomo Grasselli, Jack J Haitsma, Haibo Zhang, Arthur S Slutsky, Christer Sinderby, Jennifer Beck
Comparative Study

Lung protection during non-invasive synchronized assist versus volume control in rabbits

Lucia Mirabella et al. Crit Care. .

Abstract

Introduction: Experimental work provides insight into potential lung protective strategies. The objective of this study was to evaluate markers of ventilator-induced lung injury after two different ventilation approaches: (1) a "conventional" lung-protective strategy (volume control (VC) with low tidal volume, positive end-expiratory pressure (PEEP) and paralysis), (2) a physiological approach with spontaneous breathing, permitting synchrony, variability and a liberated airway. For this, we used non-invasive Neurally Adjusted Ventilatory Assist (NIV-NAVA), with the hypothesis that liberation of upper airways and the ventilator's integration with lung protective reflexes would be equally lung protective.

Methods: In this controlled and randomized in vivo laboratory study, 25 adult White New Zealand rabbits were studied, including five non-ventilated control animals. The twenty animals with aspiration-induced lung injury were randomized to ventilation with either VC (6 mL/kg, PEEP 5 cm H2O, and paralysis) or NIV-NAVA for six hours (PEEP = zero because of leaks). Markers of lung function, lung injury, vital signs and ventilator parameters were assessed.

Results: At the end of six hours of ventilation (n = 20), there were no significant differences between VC and NIV-NAVA for vital signs, PaO2/FiO2 ratio, lung wet-to-dry ratio and broncho-alveolar Interleukin 8 (Il-8). Plasma IL-8 was higher in VC (P <0.05). Lung injury score was lower for NIV-NAVA (P = 0.03). Dynamic lung compliance recovered after six hours in NIV-NAVA but not in VC (P <0.05). During VC, peak pressures increased from 9.2 ± 2.4 cm H2O (hour 1) to 12.3 ± 12.3 cm H2O (hour 6) (P <0.05). During NIV-NAVA, the tracheal end-expiratory pressure was similar to the end-expiratory pressure during VC. Two animals regurgitated during NIV-NAVA, without clinical consequences, and survived the protocol.

Conclusions: In experimental acute lung injury, NIV-NAVA is as lung-protective as VC 6 ml/kg with PEEP.

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Figures

Figure 1
Figure 1
Experimental set up and experimental recordings. Left panels show experimental set-up and physical placement of interfaces and right panels show experimental recordings for each mode. Volume control (VC, top) and non-invasive ventilation-neurally adjusted ventilatory assist (NIV-NAVA, bottom). VC setup: ventilator was connected to the endotracheal tube at the tracheostomy to measure ventilator pressure (Pvent). NIV-NAVA setup: Ventilator was connected to the nasal prong (Pprong), where ventilator-delivered pressure was measured. Tracheal pressure (Ptr) was also measured via a side-port at the tracheotomy. PEEP, positive end-expiratory pressure; EAdi, electrical activity of the diaphragm.
Figure 2
Figure 2
Experimental protocol. Animals were randomized to be ventilated with either volume control mode (with neuromuscular paralysis, VC group, left) or with non-invasive ventilation with neurally adjusted ventilatory assist (NIV-NAVA) and spontaneous breathing (NIV-NAVA group, right). Animals were briefly ventilated before an acid-induced acute lung injury (Pre-ALI) and for 6 hours (Post-ALI). In both arms, dynamic lung compliance was measured Pre-ALI, Post-ALI, and after 6 hours. PEEP, positive end-expiratory pressure.
Figure 3
Figure 3
Partial arterial pressure of oxygen/inspired oxygen fraction (PaO 2 /FIO 2 ) ratio and dynamic lung compliance after lung injury and after 6 hours of ventilation. (A) PaO2/FIO2 ratio before acute lung injury (Pre-ALI), Post-ALI, and 6 hours after ALI with non-invasive ventilation with neurally adjusted ventilatory assist (NIV-NAVA, black bars) and volume control (VC, white bars). (B) Reduction in dynamic compliance Post-ALI, and after 6 hours of ventilation with NIV-NAVA (black bars) and VC (white bars) expressed as percent reduction from Pre-ALI. Note that dynamic compliance recovered in the NIV-NAVA group, but not the VC group. Values are mean ± SD. *NIV-NAVA, significantly different from Pre-ALI. $VC, significantly different from Pre-ALI.
Figure 4
Figure 4
Ventilator pressures during volume control (VC), and prong and tracheal pressure during non-invasive ventilation with neurally adjusted ventilator assist (NIV-NAVA). (A) End-expiratory pressure (End Exp P, solid squares) and peak inspiratory pressure (above End Exp P, open squares) during VC in pre-acute lung injury (Pr-ALI) conditions, Post-ALI, and during 6 hours of ventilation. Peak inspiratory pressures increased during hours 5 and 6. (B) End-expiratory tracheal pressure (solid black circles), peak inspiratory tracheal pressure (gray solid circles), and peak prong pressure (open circles) during NIV-NAVA in Pre-ALI conditions, Post-ALI, and during 6 hours of ventilation. Values are mean ± SD. *VC, significantly different from 1 h. Ptr, tracheal pressure; Pvent; ventilator pressure.
Figure 5
Figure 5
Markers of lung injury for volume control (VC) and non-invasive ventilation with neurally adjusted ventilator assist (NIV-NAVA). (A) Values of IL-8 in bronchoalveolar lavage fluid (BAL IL8) were significantly different from control for both VC and NIV-NAVA, but not significantly different from each other. (B) Values of plasma IL-8 after 6 hours of NIV-NAVA were significantly lower at 6 hours of NIV-NAVA. Values are median and 25th and 75th interquartile ranges. *NIV-NAVA, significantly different from pre-acute lung injury (Pre-ALI). $VC significantly different from Pre-ALI. #NIV-NAVA significantly different from 3 hours.
Figure 6
Figure 6
Representative photomicrographs of lungs stained with hematoxylin-eosin. Left panels A and C: animals ventilated with volume-controlled ventilation (VC); right panels B and D: animals ventilated with non-invasive ventilation with neurally adjusted ventilator assist (NIV-NAVA). (A and B) Overview of lungs sections at 200× magnification. (C and D) Close-up of alveoli (400× magnification) showing edema, hemorrhage and neutrophil infiltration.
Figure 7
Figure 7
Lung injury score for volume control (VC) animals and non-invasive ventilation with neurally adjusted ventilator assist (NIV-NVA) animals. (A) During NIV-NAVA (black bars), the lung injury score for the middle portion of the lung showed significantly lower values than the VC group (white bars). (B) Average lung injury score was lower for NIV-NAVA (solid black bar) than the VC arm (white bar). Values are mean ± SD.
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