Gas exchange and lung mechanics in patients with acute respiratory distress syndrome: Comparison of three different strategies of positive end expiratory pressure selection

Mechanical ventilation (MV) is a lifesaving supportive intervention in the management of acute respiratory distress syndrome (ARDS), buying time while the primary precipitating cause is being corrected. However, MV can contribute to a worsening of the primary lung injury, known as ventilation-induced lung injury (VILI), which could have an important impact on outcome. The ARDS lung is characterized by diffuse and heterogeneous lung damage and is particularly prone to suffer the consequences of an excessive mechanical stress imposed by higher airway pressures and volumes during MV. Of major concern is cyclic overdistension, affecting those lung segments receiving a proportionally higher tidal volume in an overall reduced lung volume. Theoretically, healthier lung regions are submitted to a larger stress and cyclic deformation and thus at high risk for developing VILI. Clinicians have difficulties in detecting VILI, particularly cyclic overdistension at the bedside, since routine monitoring of gas exchange and lung mechanics are relatively insensitive to this mechanism of VILI. Expired CO2 kinetics integrates relevant pathophysiological information of high interest for monitoring. CO2 is produced by cell metabolism in large daily quantities. After diffusing to tissue capillaries, CO2 is transported first by the venous and then by pulmonary circulation to the lung. Thereafter diffusing from capillaries to lung alveoli, it is finally convectively transported by lung ventilation for its elimination to the atmosphere. Modern readily clinically available sensor technology integrates information related to pulmonary ventilation, perfusion, and gas exchange from the single analysis of expired CO2 kinetics measured at the airway opening. Current volumetric capnography (VCap), the representation of the volume of expired CO2 in one single breath, informs about pulmonary perfusion, end-expiratory lung volume, dead space, and pulmonary ventilation inhomogeneities, all intimately related to cyclic overdistension during MV. Additionally, the recently described capnodynamic method provides the possibility to continuously measure the end-expiratory lung volume and effective pulmonary blood flow. All this information is accessed non-invasively and breath-by-breath helping clinicians to personalize ventilatory settings at the bedside and minimize overdistension and cyclic deformation of lung tissue.

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Positive end-expiratory pressure selection based on best respiratory system compliance or collapse/hyperdistension curves in patients with acute respiratory distress syndrome: lack of correlation with alveolar recruitment

Intensive Care Medicine ◽

10.1007/s00134-017-5022-7 ◽

2017 ◽

Vol 44 (3) ◽

pp. 389-391 ◽

Cited By ~ 2

Author(s):

Po-Lan Su ◽

Wei-Chieh Lin ◽

Yen-Fen Ko ◽

Pei-Fang Su ◽

Chang-Wen Chen

Keyword(s):

Acute Respiratory Distress Syndrome ◽

Respiratory Distress Syndrome ◽

Respiratory Distress ◽

Respiratory System ◽

Distress Syndrome ◽

Alveolar Recruitment ◽

Respiratory System Compliance ◽

Positive End Expiratory Pressure ◽

Pressure Selection

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Physiological Effects of the Open Lung Approach in Patients with Early, Mild, Diffuse Acute Respiratory Distress Syndrome

Anesthesiology ◽

10.1097/aln.0000000000000862 ◽

2015 ◽

Vol 123 (5) ◽

pp. 1113-1121 ◽

Cited By ~ 38

Author(s):

Gilda Cinnella ◽

Salvatore Grasso ◽

Pasquale Raimondo ◽

Davide D’Antini ◽

Lucia Mirabella ◽

...

Keyword(s):

Acute Respiratory Distress Syndrome ◽

Respiratory Distress Syndrome ◽

Respiratory Distress ◽

Tidal Volume ◽

Distress Syndrome ◽

Driving Pressure ◽

Lung Mechanics ◽

Positive End Expiratory Pressure ◽

Open Lung ◽

Open Lung Approach

Abstract Background To test the hypothesis that in early, mild, acute respiratory distress syndrome (ARDS) patients with diffuse loss of aeration, the application of the open lung approach (OLA) would improve homogeneity in lung aeration and lung mechanics, without affecting hemodynamics. Methods Patients were ventilated according to the ARDS Network protocol at baseline (pre-OLA). OLA consisted in a recruitment maneuver followed by a decremental positive end-expiratory pressure trial. Respiratory mechanics, gas exchange, electrical impedance tomography (EIT), cardiac index, and stroke volume variation were measured at baseline and 20 min after OLA implementation (post-OLA). Esophageal pressure was used for lung and chest wall elastance partitioning. The tomographic lung image obtained at the fifth intercostal space by EIT was divided in two ventral and two dorsal regions of interest (ROIventral and ROIDorsal). Results Fifteen consecutive patients were studied. The OLA increased arterial oxygen partial pressure/inspired oxygen fraction from 216 ± 13 to 311 ± 19 mmHg (P < 0.001) and decreased elastance of the respiratory system from 29.4 ± 3 cm H2O/l to 23.6 ± 1.7 cm H2O/l (P < 0.01). The driving pressure (airway opening plateau pressure − total positive end-expiratory pressure) decreased from 17.9 ± 1.5 cm H2O pre-OLA to 15.4 ± 2.1 post-OLA (P < 0.05). The tidal volume fraction reaching the dorsal ROIs increased, and consequently the ROIVentral/Dorsal impedance tidal variation decreased from 2.01 ± 0.36 to 1.19 ± 0.1 (P < 0.01). Conclusions The OLA decreases the driving pressure and improves the oxygenation and lung mechanics in patients with early, mild, diffuse ARDS. EIT is useful to assess the impact of OLA on regional tidal volume distribution.

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Cardiorespiratory Effects of Positive End-expiratory Pressure during Progressive Tidal Volume Reduction (Permissive Hypercapnia) in Patients with Acute Respiratory Distress Syndrome

Anesthesiology ◽

10.1097/00000542-199510000-00010 ◽

1995 ◽

Vol 83 (4) ◽

pp. 710-720. ◽

Cited By ~ 90

Author(s):

V. Marco Ranieri ◽

Luciana Mascia ◽

Tommaso Fiore ◽

Francesco Bruno ◽

Antonio Brienza ◽

...

Keyword(s):

Mechanical Ventilation ◽

Acute Respiratory Distress Syndrome ◽

Gas Exchange ◽

Respiratory Distress Syndrome ◽

Respiratory Distress ◽

Tidal Volume ◽

Distress Syndrome ◽

Alveolar Recruitment ◽

Permissive Hypercapnia ◽

Positive End Expiratory Pressure

Background In patients with acute respiratory distress syndrome (ARDS), the ventilatory approach is based on tidal volume (VT) of 10-15 ml/kg and positive end-expiratory pressure (PEEP). To avoid further pulmonary injury, decreasing VT and allowing PaCO2 to increase (permissive hypercapnia) has been suggested. Effects of 10 cmH2O of PEEP on respiratory mechanics, hemodynamics, and gas exchange were compared during mechanical ventilation with conventional (10-15 ml/kg) and low (5-8 ml/kg) VT. Methods Nine sedated and paralyzed patients were studied. VT was decreased gradually (50 ml every 20-30 min). Static volume-pressure (V-P) curves, hemodynamics, and gas exchange were measured. Results During mechanical ventilation with conventional VT, V-P curves on PEEP 0 (ZEEP) exhibited an upward convexity in six patients reflecting a progressive reduction in compliance with inflating volume, whereas PEEP resulted in a volume displacement along the flat part of this curve. After VT reduction, V-P curves in the same patients showed an upward concavity, reflecting progressive alveolar recruitment with inflating volume, and application of PEEP resulted in alveolar recruitment. The other three patients showed a V-P curve with an upward concavity; VT reduction increased this concavity, and application of PEEP induced greater alveolar recruitment than during conventional VT. With PEEP, cardiac index decreased by, respectively, 31% during conventional VT and 11% during low VT (P < 0.01); PaO2 increased by 32% and 71% (P < 0.01), respectively, whereas right-to-left venous admixture (Qs/Qt) decreased by 11% and 40%, respectively (P < 0.01). The greatest values of PaO2, static compliance, and oxygen delivery and the lowest values of Qs/Qt (best PEEP) were obtained during application of PEEP with low VT (P < 0.01). Conclusions Although PEEP induced alveolar hyperinflation in most patients during mechanical ventilation with conventional VT, at low VT, there appeared to be a significant alveolar collapse, and PEEP was able to expand these units, improving gas exchange and hemodynamics.

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Effects of Inverse Ratio Ventilation versus Positive End-expiratory Pressure on Gas Exchange and Gastric Intramucosal Pco2and pH under Constant Mean Airway Pressure in Acute Respiratory Distress Syndrome

Anesthesiology ◽

10.1097/00000542-200111000-00023 ◽

2001 ◽

Vol 95 (5) ◽

pp. 1182-1188 ◽

Cited By ~ 21

Author(s):

Chung-Chi Huang ◽

Mei-Ju Shih ◽

Ying-Huang Tsai ◽

Yu-Chen Chang ◽

Thomas C. Y. Tsao ◽

...

Keyword(s):

Acute Respiratory Distress Syndrome ◽

Gas Exchange ◽

Respiratory Distress Syndrome ◽

Respiratory Distress ◽

Airway Pressure ◽

Distress Syndrome ◽

Positive End Expiratory Pressure ◽

Mean Airway Pressure ◽

Inverse Ratio Ventilation ◽

Pressure Controlled

Background In patients with acute respiratory distress syndrome, whether inverse ratio ventilation differs from high positive end-expiratory pressure (PEEP) for gas exchange under a similar mean airway pressure has not been adequately examined. The authors used arterial oxygenation, gastric intramucosal partial pressure of carbon dioxide (PiCO(2)), and pH (pHi) to assess whether pressure-controlled inverse ratio ventilation (PC-IRV) offers more benefits than pressure-controlled ventilation (PCV) with PEEP. Methods Seventeen acute respiratory distress syndrome patients were enrolled and underwent mechanical ventilation with a PCV inspiratory-to-expiratory ratio of 1:2, followed by PC-IRV 1:1 initially. Then, they were randomly assigned to receive PC-IRV 2:1, then 4:1 or 4:1, and then 2:1, alternately. The baseline setting of PCV 1:2 was repeated between the settings of PC-IRV 2:1 and 4:1. Mean airway pressure and tidal volume were kept constant by adjusting the levels of peak inspiratory pressure and applied PEEP. In each ventilatory mode, hemodynamics, pulmonary mechanics, arterial and mixed venous blood gas analysis, PiCO(2), and pHi were measured after a 1-h period of stabilization. Results With a constant mean airway pressure, PC-IRV 2:1 and 4:1 decreased arterial and mixed venous oxygenation as compared with baseline PCV 1:2. Neither the global oxygenation indices with oxygen delivery and uptake nor PiCO(2) and pHi were improved by PC-IRV. During PC-IRV, applied PEEP was lower, and auto-PEEP was higher. Conclusion When substituting inverse ratio ventilation for applied PEEP to keep mean airway pressure constant, PC-IRV does not contribute more to better gas exchange and gastric intramucosal PiCO(2) and pHi than does PCV 1:2 for acute respiratory distress syndrome patients, regardless of the inspiratory-to-expiratory ratios.

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