Very Low Tidal Volume Ventilation with Associated Hypercapnia - Effects on Lung Injury in a Model for Acute Respiratory Distress Syndrome

Abstract

BackgroundVentilation using low tidal volumes with permission of hypercapnia is recommended to protect the lung in acute respiratory distress syndrome. However, the most lung protective tidal volume in association with hypercapnia is unknown. The aim of this study was to assess the effects of different tidal volumes with associated hypercapnia on lung injury and gas exchange in a model for acute respiratory distress syndrome.Methodology/Principal FindingsIn this randomized controlled experiment sixty-four surfactant-depleted rabbits were exposed to 6 hours of mechanical ventilation with the following targets: Group 1: tidal volume = 8–10 ml/kg/PaCO2 = 40 mm Hg; Group 2: tidal volume = 4–5 ml/kg/PaCO2 = 80 mm Hg; Group 3: tidal volume = 3–4 ml/kg/PaCO2 = 120 mm Hg; Group 4: tidal volume = 2–3 ml/kg/PaCO2 = 160 mm Hg. Decreased wet-dry weight ratios of the lungs, lower histological lung injury scores and higher PaO2 were found in all low tidal volume/hypercapnia groups (group 2, 3, 4) as compared to the group with conventional tidal volume/normocapnia (group 1). The reduction of the tidal volume below 4–5 ml/kg did not enhance lung protection. However, oxygenation and lung protection were maintained at extremely low tidal volumes in association with very severe hypercapnia and no adverse hemodynamic effects were observed with this strategy.ConclusionVentilation with low tidal volumes and associated hypercapnia was lung protective. A tidal volume below 4–5 ml/kg/PaCO2 80 mm Hg with concomitant more severe hypercapnic acidosis did not increase lung protection in this surfactant deficiency model. However, even at extremely low tidal volumes in association with severe hypercapnia lung protection and oxygenation were maintained.

Hypercapnia

“…Fuchs et al [27] performed an interesting study comparing progressively lower tidal volumes while permitting the resultant hypercapnia. Compared with 8-10 ml/kg, reductions in tidal volume below 4 ml/kg did not provide additional protection; reassuringly, the severe hypercapnia (i.e., 160 mmHg), which arose at extremely low tidal volume (i.e., 2 ml/ kg), did not reverse the protection.…”

Effects of different ventilation strategies on lung injury in newborn rabbits

“…However, they have also been implicated as the causes of secondary lung injury, such as ventilator‐induced lung injury (VILI) and oxygen toxicity, which contribute to the high mortality rates associated with pulmonary diseases, including acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) 2–4. Some ventilation strategies applied to reduce lung injury include high frequency nasal ventilation,5 ventilation with low tidal volumes and associated hypercapnia 6. Three main mechanisms of lung injury have been postulated: volutrauma, atelectrauma, and biotrauma 3, 7, 8.…”

“…[2][3][4] Some ventilation strategies applied to reduce lung injury include high frequency nasal ventilation, 5 ventilation with low tidal volumes and associated hypercapnia. 6 Three main mechanisms of lung injury have been postulated: volutrauma, atelectrauma, and biotrauma. 3,7,8 Many animal studies suggest that peak inspiratory pressures (PIP), the fraction of inspired oxygen (FiO 2 ), and/or the respiration time (RT) are contributory factors for the development of VILI.…”

Relevância da calibração na acuidade do oxicapnógrafo >i<mainstream>/i< DL500 DeltaLife em cães submetidos à anestesia inalatória

“…Dentre os fatores fisiológicos que impedem o colapso pulmonar têm-se o surfactante natural dos pulmões, que preserva a arquitetura do órgão diminuindo a tensão superficial alveolar, e o estresse dentro dos ácinos, principalmente ao final da expiração (MEAD et al, 1970;FUCHS et al, 2011). A diminuição da amplitude respiratória, como geralmente ocorre na anestesia, pode contribuir para diminuição dessa substância (BENDIXEN et al, 1963;OYARZUN et al, 1991).…”