Application of dead space fraction to titrate optimal positive end-expiratory pressure in an ARDS swine model

Abstract

Abstract. This study aimed to apply the dead space fraction [ratio of dead space to tidal volume (VD/VT)] to titrate the optimal positive end-expiratory pressure (PEEP) in a swine model of acute respiratory distress syndrome (ARDS). Twelve swine models of ARDS were constructed. A lung recruitment maneuver was then conducted and the PEEP was set at 20 cm H 2 O. The PEEP was reduced by 2 cm H 2 O every 10 min until 0 cm H 2 O was reached, and VD/VT was measured after each decrement step. VD/VT was measured using single-breath analysis of CO 2 , and calculated from arterial CO 2 partial pressure (PaCO 2 ) and mixed expired CO 2 (PeCO 2 ) using the following formula: VD/VT = (PaCO 2 -PeCO 2 )/PaCO 2 . The optimal PEEP was identified by the lowest VD/VT method. Respiration and hemodynamic parameters were recorded during the periods of pre-injury and injury, and at 4 and 2 cm H 2 O below and above the optimal PEEP (Po). The optimal PEEP in this study was found to be 13.25±1.36 cm H 2 O. During the Po period, VD/VT decreased to a lower value (0.44±0.08) compared with that during the injury period (0.68±0.10) (P<0.05), while the intrapulmonary shunt fraction reached its lowest value. In addition, a significant change of dynamic tidal respiratory compliance and oxygenation index was induced by PEEP titration. These results indicate that minimal VD/VT can be used for PEEP titration in ARDS. IntroductionAcute respiratory distress syndrome (ARDS) is a severe and life-threatening medical condition that is common in critically ill patients and has a high mortality rate (1). It is a main reason for acute respiratory failure, and is characterized by widespread inflammation in the lungs (1,2). ARDS can induce pathophysiological mechanisms of alveolar collapse, hyoxemia, vascular dysfunction and elevated dead space fraction [the ratio of dead space volume to tidal volume (VD/VT)] (3,4).Currently, the lung-protection strategy for ventilation involves the use of high positive end-expiratory pressure (PEEP) levels combined with low tidal volumes to prevent end expiratory alveolar collapse, increase functional residual capacity, reduce VD/VT and attenuate hypoxemia (5,6). However, the application of higher levels of PEEP may not be necessarily beneficial, since it increases the inflation of lung regions. Additionally, it will also increase the risk of hemodynamic abnormalities as well as the lung injury induced by ventilation (7,8). Numerous studies have attempted to define the optimal PEEP level on the basis of a variety of methods during a recruitment maneuver (RM) with decreasing PEEP (9-11).A number of studies have applied the VD/VT method to assess the effects of lung recruitment and PEEP titration in patients with severe ARDS (9-11). VD/VT is a specific value based on the relatively high diffusibility of CO 2 across tissue membranes (12), and the exchange of CO 2 depends strictly on alveolar ventilation volume (13). However, some studies did not find a similar effect on VD/VT during PEEP titration (14,15). Therefore, the applic...

Positive end-expiratory pressure titration with electrical impedance tomography and pressure–volume curve in severe acute respiratory distress syndrome

“…To identify individual optimal PEEP remains a popular research topic in the field of intensive care [27, 28]. Besides widely used PEEP titration methods (e.g., Crs, blood gases), new methods such as esophageal pressure [29] and dead space fraction [30] are proposed. Since the application of PEEP aims at maintaining alveoli open, imaging techniques might be the more intuitive methods to select optimal PEEP.…”

A structured narrative review of clinical and experimental studies of the use of different positive end‐expiratory pressure levels during thoracic surgery

“…As gas exchange is insufficient and the lungs are susceptible to VILI during OLV, 129 monitoring dead space in real time plays an important role in adjusting ventilator settings 130 . Given that the ideal PEEP minimizes dead space fraction to bring ventilation and blood flow into the best state, dead space fraction is an attractive physiological target for PEEP titration 131 …”

“… 130 Given that the ideal PEEP minimizes dead space fraction to bring ventilation and blood flow into the best state, dead space fraction is an attractive physiological target for PEEP titration. 131 …”

Optimal positive end-expiratory pressure obtained with titration of a fraction of inspiratory oxygen: a randomized controlled clinical trial

“…Therefore, optimal PEEP should be individualized and adjusted dynamically according to each patient’s needs ( 5 ). Several techniques have been used to determine the optimal PEEP ( 6 - 10 ). For example, electrical impedance tomography (EIT) can be performed at the bedside ( 5 , 11 , 12 ).…”