The cover illustration for Sandra Bjerkne Wenneberg’s doctoral thesis. "Thunderclap headache" is a typical symptom when a brain aneurysm bursts. Illustration by Azra Moric.

Sandra Bjerkne Wenneberg: Researching secondary brain injuries after aSAH stroke


When a brain aneurysm bursts, it leads to a life-threatening bleeding event. In the immediate aftermath, patients are at risk of developing secondary brain injuries, which may result in long-term functional and cognitive problems. Sandra Bjerkne Wenneberg is researching new methods to detect such brain injuries early on.

Dissertation Defense: October 6, 2023
Doctoral Thesis: Short and long-term outcomes after subarachnoid hemorrhage
Research Area: Anesthesiology and Intensive Care
Sahlgrenska Academy, The Institute of Clinical Sciences


Aneurysmal subarachnoid hemorrhage (aSAH) is a form of stroke caused by the rupture of a brain aneurysm. A typical symptom is the so-called ”thunderclap headache.”

During the bleeding event, pressure inside the skull increases, leading to a risk of oxygen deficiency in the brain. This sets off a chain of reactions that, over the next days and weeks, may cause secondary brain injuries known as Delayed Cerebral Ischemia (DCI). Without early treatment, these injuries can become permanent.

”Patients experiencing this acute brain bleed are typically a bit younger than those affected by, for example, ischemic strokes, which are primarily caused by blood clots. A majority of aSAH patients are at risk of long-lasting issues, particularly cognitive impairment,” says Sandra Bjerkne Wenneberg, a specialist in anesthesia and intensive care at Sahlgrenska University Hospital.

She continues: ”What is somewhat unique about aSAH is that, a few days or weeks after the acute onset, about one-third of patients develop secondary ischemic injuries, DCI, which significantly increases the risk of death or severe residual symptoms.”

Sandra Bjerkne Wenneberg.

”More studies are needed”

What is your research about?
”Patients receiving care after aSAH are closely monitored, but better methods are needed to detect the development of DCI early on. This is essential for optimizing treatment. We have examined two potential methods: heart rate variability and inflammatory markers in blood samples.”

What did the heart rate variability (HRV) studies reveal?
”When the body is under stress, as it is during a brain bleed, the natural variation in heart rate decreases. We observed that HRV decreased more in patients who died within the first year after the stroke compared to those who survived. However, unfortunately, our method couldn’t reliably predict the development of DCI.”

Figure 7 in the thesis. Heart rate variability (LF/HF ratio) for patients developing DCI (dashed red line) compared to non-DCI patients (dashed blue line). Detailed caption and source reference are provided at the bottom.

And what did the measurements of inflammatory markers in the blood show?
”We didn’t find a clear link between the onset of DCI and the markers we examined. However, we could see that patients with worse outcomes one year after the brain bleed had higher levels of inflammatory markers in the acute phase. More studies are needed to continue identifying and developing effective methods for predicting and preventing the development of DCI.”

”Can feel somewhat helpless”

What made you decide to focus your doctoral project on this type of stroke?
”During our specialist training, we have an extended placement in neurointensive care. Compared to ischemic strokes, patients with aSAH are a small group overall, but they constitute a significant patient category in neurointensive care. These patients often experience a sudden onset in the prime of their lives, and many are affected for the rest of their lives,” says Sandra Bjerkne Wenneberg. ”As a doctor, you can sometimes feel somewhat helpless when patients develop secondary injuries while under our care, and we don’t have sufficiently good methods to detect them early. After discussions with my future supervisors, I had the opportunity to explore potential new methods for detecting the development of DCI.”

Figure 11 in the thesis. Distribution of total MFS scores at 1, 3, and 5 years after aSAH stroke. A total score of ≥ 10.5 indicates the presence of mental fatigue. MFS; Mental Fatigue Scale.

Mental fatigue after five years

You also studied the long-term effects of brain bleeding. What can you tell us about that?
”We did a follow-up study through telephone interviews and questionnaires at one, three and five years after the acute phase. Many had physically recovered but were still dealing with cognitive issues that made it challenging to return to work and affected their daily lives and family. One particularly persistent symptom was mental fatigue. It may not be visible on the outside, but it can have far-reaching effects on patients’ daily lives. Despite many reporting improvements in their symptoms, around half still experienced mental fatigue after five years.”

Text: Jakob Lundberg

Caption for Figure 7 and source

Heart rate variability (LF/HF ratio) for patients developing Delayed Cerebral Ischemia (DCI) compared to non-DCI patients. The dashed lines indicate the mean ratio for patients developing DCI (red) and patients without DCI (blue). The LF/HF increased over time for both populations; however, patients developing DCI had a significantly higher increase (p=0.012).

Source: Bjerkne Wenneberg, S et al., Acta Anaesthesiol Scand. 2020, Creative Commons BY 4.0 License.