Surgery-Induced Strokes: Understanding The Risks And Causes

Strokes are a major cause of disability and the third leading cause of death globally, after heart disease and cancer. While strokes are a known risk factor for heart surgery, they can also occur during and after lower-risk surgeries. Perioperative strokes refer to strokes that occur during surgery or within 30 days after surgery, and evidence shows that they can happen to people without heart conditions who are not considered high-risk.

Research has found that the combination of surgery and anesthesia is an independent risk factor for the development of incident (first-time) ischemic strokes. The risk of perioperative stroke varies based on patient risk factors, the type of surgery, and intraoperative factors such as hypotension and hypoxia.

Certain types of surgeries carry a higher risk of perioperative stroke, including cardiac, neurological, and vascular procedures, with rates ranging from 2.2% to 5.2%. Additionally, the risk increases with patient age, with octogenarians having a six-fold higher risk compared to younger populations. Other specific risk factors include kidney disease, COPD, tobacco use, and elevated blood pressure.

Understanding the mechanisms underlying strokes associated with surgery and anesthesia requires further investigation. However, alterations in the coagulation system and hemostasis due to stress responses related to surgery have been proposed as potential explanations.

Perioperative stroke risk factors

Perioperative stroke refers to a stroke that occurs during surgery or within 30 days after surgery. While it is uncommon during low-risk non-vascular surgery, it can negatively impact recovery and functional outcomes if it does occur. The reported risk of perioperative stroke varies with the type of surgery, ranging from approximately 0.1–1.9% in non-cardiac, non-neurologic, and non-major surgery to up to 10% in patients undergoing high-risk cardiac or brain surgery.

Non-Modifiable Risk Factors

Age

The risk of perioperative stroke increases with age, with octogenarians having a six-fold higher risk compared to younger populations. Older age is also associated with a higher odds of perioperative stroke, with each 10-year increase in age contributing to higher odds.

Sex

Being female is a risk factor for perioperative stroke in both cardiovascular and non-cardiovascular surgeries. The reason for this sex difference is not clearly understood, but it may be related to the more rapid progression of atherosclerosis in elderly women after menopause.

History of Stroke or Transient Ischemic Attack

A history of stroke or transient ischemic attack is an important risk factor for perioperative stroke. This includes individuals with a previous stroke or those who have had stroke symptoms.

Migraine

There is growing evidence of an association between migraine and ischemic stroke, with some studies suggesting that migraine may be a risk factor for perioperative stroke.

Modifiable Risk Factors

Severe Carotid Stenosis

Severe carotid stenosis, or narrowing of the arteries in the neck, may limit cerebral perfusion and increase the risk of perioperative stroke. However, the optimal timing and requirement for carotid revascularization before surgery remain debated.

Timing of Surgery After Previous Stroke

A history of stroke increases the odds of 30-day mortality in patients with non-cardiac surgery. While it is recommended to delay elective non-neurological non-cardiac surgery after a stroke, the optimal timing is unclear. Expert opinion suggests that waiting for at least one month may allow for the restoration of cerebral autoregulation and decrease the risk of perioperative stroke.

Intraoperative Hypotension

Most anesthetic agents can induce hypotension, which is a risk factor for perioperative stroke, especially in patients with significant large vessel stenosis. A sudden drop in blood pressure can decrease cerebral perfusion and lead to brain ischemia and perioperative stroke.

Intraoperative Hypoxia

Poor systemic oxygenation during surgery, particularly in patients undergoing cardiopulmonary bypass, may be a risk factor for perioperative stroke. Lower nadir PaO2 values have been associated with an increased risk of postoperative stroke.

Surgery and anaesthesia as a cause of stroke

Perioperative stroke is a rare complication, but it can have devastating consequences for patients, surgeons, and anaesthesiologists. Perioperative stroke refers to a stroke that occurs during surgery or within 30 days after surgery. It is an uncommon occurrence during low-risk, non-vascular surgery, with an incidence of approximately 0.1-1.9%. However, the risk increases significantly for patients undergoing high-risk cardiac or brain surgery, with up to 10% of patients experiencing a perioperative stroke.

Several factors contribute to the risk of perioperative stroke, including age, sex, history of stroke or transient ischaemic attack, and specific types of surgery. Older individuals, especially those over 65, are at a higher risk. Being female is also a risk factor for perioperative stroke, possibly due to the more rapid progression of atherosclerosis after menopause. A history of stroke or transient ischaemic attack is another important factor.

Certain types of surgery carry a higher risk of perioperative stroke. Cardiac surgery, including aortic surgery, mitral valve surgery, and coronary artery bypass graft surgery, is associated with a higher risk. Neurosurgery, such as external carotid-internal carotid bypass surgery, carotid endarterectomy, or aneurysm clipping, also increases the likelihood of perioperative stroke. The combination of concomitant carotid and cardiac surgery further elevates the risk.

Anaesthesia itself is also a significant risk factor for perioperative stroke. A study published in the journal "Anesthesia" found that surgery and anaesthesia were a substantial risk factor for stroke, even when excluding patients with cardiac, vascular, neurologic, and other high-risk conditions. The type of anaesthesia used may also influence the risk, with general anaesthesia being more commonly associated with perioperative stroke than central neuroaxis blockade.

The mechanism underlying the association between surgery and anaesthesia and perioperative stroke is not fully understood. However, alterations in the coagulation system and stress responses related to surgery may play a role. Perioperative changes in hemostasis, including increased plasma concentrations of coagulation factors and decreased concentrations of coagulation inhibitors, can create a "hypercoagulable state," increasing the potential for thromboembolic events such as stroke.

In summary, while perioperative stroke is uncommon during low-risk surgeries, it becomes a more significant concern for high-risk cardiac and neurological procedures. Age, sex, medical history, and the type of surgery are important factors in assessing the risk. Additionally, the role of anaesthesia in perioperative stroke suggests that the combination of surgery and anaesthesia is an independent risk factor.

Stroke prevention methods

Strokes are a devastating complication of cardiac surgery and the third leading cause of death in the U.S. They can be caused by a blockage, leading to an ischemic stroke, or by bleeding in the brain, leading to a hemorrhagic stroke. Ischemic strokes constitute an estimated 87% of all stroke cases.

The American Heart Association and the American Stroke Association have issued guidelines to reduce the incidence of stroke, urging people to:

• Not smoke
• Maintain a healthy weight
• Exercise
• Eat a diet rich in fruits and vegetables
• Maintain healthy levels of cholesterol and blood pressure

Additionally, here are some methods to prevent strokes during surgery:

• Carotid Endarterectomy Surgery (CEA): This procedure involves making an incision in the carotid artery in the neck and removing plaque to restore normal blood flow. The artery is then repaired with sutures or a graft. While this surgery has potential complications, including a 1-3% risk of stroke, it can help prevent strokes by improving blood flow to the brain.
• Carotid Angioplasty and Stenting (CAS): This is a newer, less invasive treatment option that may be suitable for patients who are at too high a risk for traditional surgery. It involves inserting a tiny, slender metal-mesh tube, called a stent, into the carotid artery to increase blood flow blocked by plaques. CAS has a shorter occlusion time, shorter anesthesia, and a smaller incision compared to CEA. However, there is still a slight risk of stroke due to plaque disruption or blood clots.
• Epi-aortic Scanning: This method is effective in identifying aortic atheroma, which is the foremost cause of post-coronary artery bypass graft strokes. It is a cheap and effective tool for reducing the incidence of perioperative brain damage.
• Beta-Blockers: While beta-blockers can help reduce heart rate and sympathetic activity, leading to a lower risk of cardiac arrhythmia and myocardial infarction, they have not been found to significantly reduce the risk of stroke. In fact, extended-release metoprolol has been associated with an increased risk of stroke in patients undergoing non-cardiac surgery.
• Intra-arterial Mechanical Thrombectomy: This procedure involves using a small microcatheter to deliver a thrombolytic medication directly to the occluding thrombus in the brain. It is more specific than intravenous thrombolysis and has a longer time limit for implementation. However, it is typically only offered by Comprehensive Stroke Care Centers.
• Clot Retrieval Devices: Devices such as the Merci Retriever, approved by the FDA in 2004, are used to remove blood clots from the arteries of stroke patients. A small incision is made in the patient's groin, and a catheter is fed until it reaches the arteries in the neck. A straight wire inside the catheter pokes out beyond the clot and coils into a corkscrew shape, allowing the clot to be pulled out safely.
• Anticoagulants and Antiplatelet Agents: These medications are used to prevent strokes in high-risk patients, especially those who have experienced a transient ischemic attack (TIA) or ischemic stroke. Anticoagulants thin the blood and prevent clotting, while antiplatelet drugs make platelets less sticky and less likely to form clots.

It is important to note that the risk of perioperative stroke varies depending on the type of surgery and the patient's individual risk factors. Age, sex, history of stroke or TIA, cardiac surgery, and neurosurgery are all factors that can increase the risk of stroke during or after surgery.

High-risk surgeries

While any surgery can carry a risk of stroke, certain procedures are considered high-risk and have been associated with a higher incidence of perioperative strokes. Perioperative strokes refer to strokes that occur during surgery or within 30 days after surgery. Here are some of the high-risk surgeries and factors that contribute to an increased risk of perioperative strokes:

Cardiac Surgery:

Cardiac surgeries, such as coronary artery bypass graft (CABG) surgery, aortic valve replacement, mitral valve replacement, and proximal aorta replacement, carry a higher risk of perioperative strokes. The reported risk of stroke varies depending on the specific procedure, ranging from 1.2% for CABG to 6.6% for proximal aorta replacement. The manipulation of the aorta and other surgical techniques involved in these procedures can increase the risk of cerebral embolism. Additionally, aortic atherosclerosis, which is common in patients undergoing cardiac surgery, is also linked to an increased risk of cerebral embolism.

Neurosurgery:

Neurosurgical procedures, including external carotid-internal carotid bypass surgery, carotid endarterectomy, and aneurysm clipping, are associated with a higher risk of perioperative strokes. For example, the reported risk of stroke after carotid endarterectomy is around 2-5%. The risk factors associated with neurosurgery include the patient's age, sex, history of stroke or transient ischemic attack, and specific intraoperative events.

Age:

Advanced age is a significant risk factor for perioperative strokes. The risk of stroke increases with age, with octogenarians having a six-fold higher risk compared to younger individuals. This is an important consideration when evaluating the risks associated with elective surgeries in older adults.

Pre-existing Health Conditions:

Individuals with certain pre-existing health conditions are at a higher risk of perioperative strokes. These conditions include kidney disease, COPD, tobacco use, elevated blood pressure, hypertension, diabetes mellitus, ischemic heart disease, atrial fibrillation, and mitral valve disease. It is crucial to carefully evaluate these risk factors when considering surgery, especially in patients with multiple risk factors.

Anesthesia:

The combination of surgery and anesthesia itself has been identified as an independent risk factor for perioperative strokes. This risk is present even after excluding high-risk surgeries such as cardiac, neurologic, and vascular procedures. The type of anesthesia used can also influence the risk, with general anesthesia being more commonly associated with perioperative strokes than central neuroaxis blockade.

Previous Stroke History:

A history of stroke is a significant risk factor for perioperative strokes. The risk of stroke after surgery is higher in individuals with a recent history of stroke, and the timing between the stroke and surgery can impact the likelihood of a perioperative stroke. It is generally recommended to delay elective surgeries by at least one month after a stroke to allow for the restoration of cerebral autoregulation and reduce the risk of perioperative stroke.

In conclusion, while any surgery carries some risk of stroke, the procedures and factors mentioned above are considered high-risk and warrant special consideration. It is important for patients to be educated about these risks and for healthcare providers to carefully evaluate and manage these risks to ensure the best possible outcomes.

Stroke treatment methods

Treating Ischemic Strokes

Ischemic strokes are the most common type of stroke, accounting for around 87% of all strokes. They occur when blood clots or other particles block blood vessels in the brain. The main treatment for ischemic strokes is a thrombolytic drug called tissue plasminogen activator (tPA). This drug must be administered within 3 hours of the onset of stroke symptoms to improve the chances of recovery. Other blood-thinning medications, such as aspirin or clopidogrel, may also be given to prevent blood clots from forming or growing larger.

In some cases, a procedure called thrombectomy may be performed to remove the clot from the blood vessel. This involves inserting a catheter into the upper thigh and guiding it to the blocked artery in the neck or brain. Angioplasty and stenting procedures may also be used to open up the blocked artery by inserting a balloon or a small mesh tube.

Treating Hemorrhagic Strokes

Hemorrhagic strokes occur when an artery in the brain leaks blood or ruptures. Lowering blood pressure is crucial in treating hemorrhagic strokes to reduce the strain on blood vessels in the brain. Any anticoagulant or blood-thinning medications that may have contributed to the bleeding are discontinued.

Several procedures may be used to treat hemorrhagic strokes, including aneurysm clipping surgery, blood transfusion, coil embolization, and draining excess fluid that has built up in the brain. In cases of severe swelling, surgery may be performed to temporarily remove part of the skull to relieve pressure on the brain.

Rehabilitation

Regardless of the type of stroke, rehabilitation is an important part of the recovery process. This may include speech therapy, physical therapy, and occupational therapy to help the patient regain their speech, movement, and daily living skills. Support from family and friends can also help relieve fear and anxiety following a stroke.

Frequently asked questions