Cerebrovascular autoregulation and neurocognitive outcome in patients with acute respiratory distress syndrome

Abstract

Background: Acute respiratory distress syndrome (ARDS) is a life-threatening form of respiratory failure. The average hospital mortality for ARDS patients is 40%, and it is higher in patients with hypercapnia. Cerebrovascular autoregulation (CVA) is a protective control mechanism that maintains relatively constant cerebral blood flow despite changes of arterial blood pressure. Carbon dioxide is one of the key influence factors on CVA. The aim of this study was to compare CVA function in ARDS patients with and without early hypercapnia, as well as the association between CVA impairment and neurocognitive outcomes.

Methods: Between December 2018 and November 2019, we conducted a prospective observational cohort study during the acute stage of ARDS. Patients with pre-existing neurological diseases and chronic hypercapnia were excluded. CVA was assessed using the cerebral oxygenation index, which is the correlation coefficient between regional oxygen saturation measured with near-infrared spectroscopy and arterial blood pressure. CVA was measured twice with each measurement lasting 60–90 minutes. The primary endpoint was the percentage of monitoring time with impaired CVA. Patients were divided into two groups based on arterial partial pressure of carbon dioxide (PaCO2) and pH level at ARDS onset: 1) early hypercapnia (PaCO2 ≥ 50mmHg, pH < 7.35) and 2) no early hypercapnia (PaCO2 < 50mmHg). Functional, neurocognitive, and health outcomes were assessed three months after discharge from the intensive care unit (ICU) with the Cerebral Performance Category, the Cognitive Failures Questionnaire, and the 36-item Short-Form Health Survey.

Results: We included 66 ARDS patients and performed 117 CVA assessments. Early hypercapnia was not associated with the percentage of time above a pathologic COx threshold (B=0.023 [95%CI: -0.054; 0.100], p=0.556). Hypocapnia during measurement was associated with impaired CVA (B=0.155 [95%CI: 0.014; 0.296], p=0.032). 21/31 (67.7%) patients who completed follow-up three months after discharge from the ICU had moderate or severe functional disability. The average self-assessed cognitive failure score was 29.73 ± 19.81. In health-related quality of life assessment, physical sum score was 33.2 ± 11.9, and mental sum score was 45.4 ±10.6. No correlation between impaired CVA, cognitive, and health outcomes were observed.

Conclusion: Our results show that hypercapnia during the acute stage of ARDS is not associated with CVA impairment and may be tolerated to a certain extent to achieve lung protective ventilation. However, hypocapnia may compromise CVA function. The potential association between impaired CVA, cognitive, and health outcomes warrants investigation in future studies.