End-Expiratory Volume and Oxygenation: Targeting PEEP in ARDS Patients

Effects of end-expiratory lung volume versus PaO2 guided PEEP determination on respiratory mechanics and oxygenation in moderate to severe ARDS

There is no ideal method for determination of positive end-expiratory pressure (PEEP) in acute respiratory distress syndrome (ARDS) patients. We compared the effects of end-expiratory lung volume (EELV)-guided versus PaO₂-guided PEEP determination on respiratory mechanics and oxygenation during the first 48 hours in moderate to severe ARDS.

Twenty-two patients with moderate to severe ARDS admitted to an academic medical ICU were assigned to PaO₂-guided (n = 11) or to EELV-guided PEEP determination (n = 11) group. First, an incremental PEEP trial was performed by increasing PEEP by 3 cmH₂O steps from 8 to 20 cmH₂O and in each step EELV and lung mechanics were measured in both groups. Then, oxygenation and respiratory mechanics were measured under the determined PEEP at 4, 12, 24, and 48th hours.

After the incremental PEEP trial, over the 48 hours of the study period, in the EELV-guided group PaO₂ and PaO₂/FiO₂ increased (p = 0.04 and p = 0.02; respectively), whereas they did not change in PaO₂-guided group (p = 0.09 and p = 0.27; respectively). In all patients, the median value of EELV change (ΔEELV) during incremental PEEP trial was 25%. In patients with ΔEELV > 25% (n = 11) PaO₂, PaO₂/FiO₂ and Cs increased over time in 48 hours (p = 0.03, p < 0.01, and p = 0.04; respectively), whereas they did not change in those with ΔEELV ≤ 25% (n = 11) (p = 0.73, p = 0.51, and p = 0.73; respectively).

Compared to PaO₂-guided PEEP determination, EELV-guided PEEP determination resulted in greater improvement in oxygenation over time. Patients who had > 25% improvement in EELV during a PEEP trial had greater improvement in oxygenation and compliance over 48 hours.

Supplemental data for this article is available online at.

Acute Respiratory Distress Syndrome: Challenge for Diagnosis and Therapy

OBJECTIVE

Acute respiratory distress syndrome (ARDS) is a devastating clinical syndrome whose diagnosis and therapy are still in question. The aim of this review was to discuss the current challenge for the diagnosis and treatment of ARDS.

DATA SOURCES

Data sources were the published articles in English through December 2017 in PubMed using the following key words: "acute respiratory distress syndrome," "definition", "diagnosis," "therapy," "lung protective strategy," "right ventricular dysfunction," and "molecular mechanism."

STUDY SELECTION

The selection of studies focused on both preclinical studies and clinical studies of therapy of ARDS.

RESULTS

The incidence of ARDS is still high, and ARDS causes high intensive care units admissions and high mortality. The Berlin Definition proposed in 2012 is still controversial owing to lack of sensitivity and specificity. ARDS is still under recognition and it is associated with high mortality. Lung protective strategies with low tidal volume (VT) and lung recruitment should consider the physiology of ARDS because ARDS presents lung inhomogeneity; the same low VT might increase local stress and strain in some patients with low compliance, and lung recruitment could injure lungs in ARDS patients with low recruitability and hemodynamic instability. Acute cor pulmonale is common in severe ARDS. ARDS itself and some treatments could worsen acute cor pulmonale. Molecular understanding of the pathogenic contributors to ARDS has improved, but the molecular-associated treatments are still under development.

CONCLUSIONS

ARDS is a devastating clinical syndrome whose incidence and mortality has remained high over the past 50 years. Its definition and treatments are still confronted with challenges, and early recognition and intervention are crucial for improving the outcomes of ARDS. More clinical studies are needed to improve early diagnosis and appropriate therapy.

Assessing Respiratory System Mechanical Function

The main goals of assessing respiratory system mechanical function are to evaluate the lung function through a variety of methods and to detect early signs of abnormalities that could affect the patient's outcomes. In ventilated patients, it has become increasingly important to recognize whether respiratory function has improved or deteriorated, whether the ventilator settings match the patient's demand, and whether the selection of ventilator parameters follows a lung-protective strategy. Ventilator graphics, esophageal pressure, intra-abdominal pressure, and electric impedance tomography are some of the best-known monitoring tools to obtain measurements and adequately evaluate the respiratory system mechanical function.