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. 2016 Feb 3;11(2):e0147807.
doi: 10.1371/journal.pone.0147807. eCollection 2016.

The Effects of Lung Protective Ventilation or Hypercapnic Acidosis on Gas Exchange and Lung Injury in Surfactant Deficient Rabbits

Helmut D Hummler  1 , Katharina Banke  1 , Marla R Wolfson  2 , Giuseppe Buonocore  3 , Michael Ebsen  4 , Wolfgang Bernhard  5 , Dimitrios Tsikas  6 , Hans Fuchs  1
Affiliations

The Effects of Lung Protective Ventilation or Hypercapnic Acidosis on Gas Exchange and Lung Injury in Surfactant Deficient Rabbits

Helmut D Hummler et al. PLoS One. .

Abstract

Background: Permissive hypercapnia has been shown to reduce lung injury in subjects with surfactant deficiency. Experimental studies suggest that hypercapnic acidosis by itself rather than decreased tidal volume may be a key protective factor.

Objectives: To study the differential effects of a lung protective ventilatory strategy or hypercapnic acidosis on gas exchange, hemodynamics and lung injury in an animal model of surfactant deficiency.

Methods: 30 anesthetized, surfactant-depleted rabbits were mechanically ventilated (FiO2 = 0.8, PEEP = 7cmH2O) and randomized into three groups: Normoventilation-Normocapnia (NN)-group: tidal volume (Vt) = 7.5 ml/kg, target PaCO2 = 40 mmHg; Normoventilation-Hypercapnia (NH)-group: Vt = 7.5 ml/kg, target PaCO2 = 80 mmHg by increasing FiCO2; and a Hypoventilation-Hypercapnia (HH)-group: Vt = 4.5 ml/kg, target PaCO2 = 80 mmHg. Plasma lactate and interleukin (IL)-8 were measured every 2 h. Animals were sacrificed after 6 h to perform bronchoalveolar lavage (BAL), to measure lung wet-to-dry weight, lung tissue IL-8, and to obtain lung histology.

Results: PaO2 was significantly higher in the HH-group compared to the NN-group (p<0.05), with values of the NH-group between the HH- and NN-groups. Other markers of lung injury (wet-dry-weight, BAL-Protein, histology-score, plasma-IL-8 and lung tissue IL-8) resulted in significantly lower values for the HH-group compared to the NN-group and trends for the NH-group towards lower values compared to the NN-group. Lactate was significantly lower in both hypercapnia groups compared to the NN-group.

Conclusion: Whereas hypercapnic acidosis may have some beneficial effects, a significant effect on lung injury and systemic inflammatory response is dependent upon a lower tidal volume rather than resultant arterial CO2 tensions and pH alone.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Gas exchange (PaO2 [A], PaCO2 [B]) and acid base characteristics (pH [C], lactate [D]) over experimental time.
Time = 0 refers to time of randomization. BAL = bronchoalveolar lavage. PaO2 was significantly higher in the HH- vs. the NN-group. Arterial pH and lactate were lower in both hypercapnia groups as compared to the NN-group; * = p< 0.05.
Fig 2
Fig 2. Hemodynamic parameters over time: Arterial blood pressure [A], heart rate [B], central venous pressure [C] and cardiac index [D] over experimental time.
Time = 0 refers to time of randomization. BAL = bronchoalveolar lavage. There were no significant differences between groups.
Fig 3
Fig 3. Wet-dry-weight ratio of excised lungs.
* = p< 0.05. NN vs. NH groups: p = 0.07.
Fig 4
Fig 4. Plasma interleukin-8 over time.
* = p< 0.05, NN- vs. HH-groups.
See this image and copyright information in PMC

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