Association of abnormal carbon dioxide levels with poor neurological outcomes in aneurysmal subarachnoid hemorrhage: a retrospective observational study

Abstract

BackgroundIn patients with aneurysmal subarachnoid hemorrhage (SAH), an association between hypocapnia and poor clinical outcomes has been reported. However, the optimal arterial carbon dioxide tension (PaCO2) remains unknown. The present retrospective study aimed to examine the association of abnormal PaCO2 levels with neurological outcomes and investigate the optimal target PaCO2 level in patients with SAH.MethodsWe retrospectively selected consecutive adult patients hospitalized in the intensive care unit (ICU) for SAH between January 2009 and April 2017. Univariate and multivariate analyses were performed to identify the independent predictors of unfavorable neurological outcomes (i.e., modified Rankin scale score of 3–6 on hospital discharge).ResultsAmong 158 patients with SAH, 73 had unfavorable neurological outcomes. During the first 2 weeks in the ICU, the median number of PaCO2 measurements per patient was 43. The factors significantly associated with unfavorable neurological outcomes were age, Hunt and Kosnik grade, maximum lactate levels during the first 24 h, and maximum (odds ratio [OR], 1.12; 95% confidence interval [CI], 1.03–1.21; p < 0.01) and minimum PaCO2 levels (OR, 0.81; 95% CI, 0.72–0.92; p < 0.01). Receiver operating characteristic curve analysis revealed that the cutoff range of PaCO2 was 30.2–48.3 mmHg. Unfavorable neurological outcomes were noted in 78.8% of patients with PaCO2 levels outside this range and in 22.8% of patients with PaCO2 levels within this range.ConclusionsBoth the maximum and minimum PaCO2 levels during ICU management in patients with SAH were significantly associated with unfavorable neurological outcomes. Further prospective studies are required to validate our findings and explore their clinical implications. Our findings may provide a scientific rationale for these future prospective studies.Electronic supplementary materialThe online version of this article (10.1186/s40560-018-0353-1) contains supplementary material, which is available to authorized users.

High-normal PaCO2 values might be associated with worse outcome in patients with subarachnoid hemorrhage – a retrospective cohort study

“…A selection bias has been introduced by including ventilated patients only. The rate of patients with a mRS scale score of 5 and 6 is higher compared to other studies [19,36]. Only 11.3% of the patients had a favorable outcome while other publications could demonstrate a good clinical outcome with mRS < 3 in 59.5% [3].…”

“…These mechanisms are not closely linked to systemic P a O 2 and P a CO 2 which might explain our results. Keeping in mind that our P a CO 2 values were mainly in the normal range, a different study showed that the maximum P a CO 2 values were significantly different comparing patients with and without DCI [19]. We do not have data on microcirculation in our study, consequently the occurrence of a reversed Robin-Hood-phenomenon in SAH patients currently remains a hypothesis, which needs to be confirmed in future trials.…”

“…Most importantly, clinical outcome was not an outcome of the study and hypercapnia in our study persisted over longer periods of time and is therefore not comparable to brief episodes of hypercapnia with P a CO 2 values returning to baseline within one hour. The detrimental effects of hypercapnia have been demonstrated by a recent study that examined the outcome of patients with aneurysmal SAH and focused on the hyperventilated and hypoventilated patients [19]. 158 patients were retrospectively analyzed.…”

“…On the other hand, hypercapnia causes dilatation of arterial cerebral vessels with enhanced cerebral blood flow (CBF) putatively improving cerebral oxygenation. A recent retrospective study on patients with SAH discovered that patients with arterial partial pressure of carbon dioxide (P a CO 2 ) values above 48 mmHg had a lower rate of favorable clinical outcome [19]. It therefore remains doubtful whether the positive effects of hypercapnia through increased CBF leading to increased brain oxygenation which might prevent ischemic lesions outweigh the detrimental effects.…”

“…It therefore remains doubtful whether the positive effects of hypercapnia through increased CBF leading to increased brain oxygenation which might prevent ischemic lesions outweigh the detrimental effects. Prolonged hypocapnia induced by hyperventilation, on the other hand, has been shown to be harmful for patients with SAH as well [6,12,19]. An induced reduction of P a CO 2 below 35 mmHg does not improve clinical outcome in these patients.…”