Agreement between arterial and end-tidal carbon dioxide in adult patients admitted with serious traumatic brain injury

BACKGROUND

Low-normal levels of arterial carbon dioxide (PaCO2) are recommended in the acute phase of traumatic brain injury (TBI) to optimize oxygen and CO2 tension, and to maintain cerebral perfusion. End-tidal CO2 (ETCO2) may be used as a surrogate for PaCO2 when arterial sampling is less readily available. ETCO2 may not be an adequate proxy to guide ventilation and the effects on concomitant injury, time, and the impact of ventilatory strategies on the PaCO2-ETCO2 gradient are not well understood. The primary objective of this study was to describe the correlation and agreement between PaCO2 and ETCO2 in intubated adult trauma patients with TBI.

METHODS

This study was a retrospective analysis of prospectively-collected data of intubated adult major trauma patients with serious TBI, admitted to the East of England regional major trauma centre; 2015-2019. Linear regression and Welch's test were performed on each cohort to assess correlation between paired PaCO2 and ETCO2 at 24-hour epochs for 120 hours after admission. Bland-Altman plots were constructed at 24-hour epochs to assess the PaCO2-ETCO2 agreement.

RESULTS

695 patients were included, with 3812 paired PaCO2 and ETCO2 data points. The median PaCO2-ETCO2 gradient on admission was 0.8 [0.4-1.4] kPa, Bland Altman Bias of 0.96, upper (+2.93) and lower (-1.00), and correlation R2 0.149. The gradient was significantly greater in patients with TBI plus concomitant injury, compared to those with isolated TBI (0.9 [0.4-1.5] kPa vs. 0.7 [0.3-1.1] kPa, p<0.05). Across all groups the gradient reduced over time. Patients who died within 30 days had a larger gradient on admission compared to those who survived; 1.2 [0.7-1.9] kPa and 0.7 [0.3-1.2] kPa, p<0.005.

CONCLUSIONS

Amongst adult patients with TBI, the PaCO2-ETCO2 gradient was greater than previously reported values, particularly early in the patient journey, and when associated with concomitant chest injury. An increased PaCO2-ETCO2 gradient on admission was associated with increased mortality.

Brain injury in COVID-19 is associated with dysregulated innate and adaptive immune responses

COVID-19 is associated with neurological complications including stroke, delirium and encephalitis. Furthermore, a post-viral syndrome dominated by neuropsychiatric symptoms is common, and is seemingly unrelated to COVID-19 severity. The true frequency and underlying mechanisms of neurological injury are unknown, but exaggerated host inflammatory responses appear to be a key driver of COVID-19 severity. We investigated the dynamics of, and relationship between, serum markers of brain injury [neurofilament light (NfL), glial fibrillary acidic protein (GFAP) and total tau] and markers of dysregulated host response (autoantibody production and cytokine profiles) in 175 patients admitted with COVID-19 and 45 patients with influenza. During hospitalization, sera from patients with COVID-19 demonstrated elevations of NfL and GFAP in a severity-dependent manner, with evidence of ongoing active brain injury at follow-up 4 months later. These biomarkers were associated with elevations of pro-inflammatory cytokines and the presence of autoantibodies to a large number of different antigens. Autoantibodies were commonly seen against lung surfactant proteins but also brain proteins such as myelin associated glycoprotein. Commensurate findings were seen in the influenza cohort. A distinct process characterized by elevation of serum total tau was seen in patients at follow-up, which appeared to be independent of initial disease severity and was not associated with dysregulated immune responses unlike NfL and GFAP. These results demonstrate that brain injury is a common consequence of both COVID-19 and influenza, and is therefore likely to be a feature of severe viral infection more broadly. The brain injury occurs in the context of dysregulation of both innate and adaptive immune responses, with no single pathogenic mechanism clearly responsible.

Can process mapping and a multisite Delphi of perioperative professionals inform our understanding of system-wide factors that may impact operative risk?

OBJECTIVES

To examine whether the use of process mapping and a multidisciplinary Delphi can identify potential contributors to perioperative risk. We hypothesised that this approach may identify factors not represented in common perioperative risk tools and give insights of use to future research in this area.

DESIGN

Multidisciplinary, modified Delphi study.

SETTING

Two centres (one tertiary, one secondary) in the UK during 2020 amidst coronavirus pressures.

PARTICIPANTS

91 stakeholders from 23 professional groups involved in the perioperative care of older patients. Key stakeholder groups were identified via process mapping of local perioperative care pathways.

RESULTS

Response rate ranged from 51% in round 1 to 19% in round 3. After round 1, free text suggestions from the panel were combined with variables identified from perioperative risk scores. This yielded a total of 410 variables that were voted on in subsequent rounds. Including new suggestions from round two, 468/519 (90%) of the statements presented to the panel reached a consensus decision by the end of round 3. Identified risk factors included patient-level factors (such as ethnicity and socioeconomic status), and organisational or process factors related to the individual hospital (such as policies, staffing and organisational culture). 66/160 (41%) of the new suggestions did not feature in systematic reviews of perioperative risk scores or key process indicators. No factor categorised as 'organisational' is currently present in any perioperative risk score.

CONCLUSIONS

Through process mapping and a modified Delphi we gained insights into additional factors that may contribute to perioperative risk. Many were absent from currently used risk stratification scores. These results enable an appreciation of the contextual limitations of currently used risk tools and could support future research into the generation of more holistic data sets for the development of perioperative risk assessment tools.