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DANGERS OF STROKE DURING CARDIOVASCULAR OPEN HEART SURGERY AND PREVENTATIVE PRECAUTIONS

  By Jamie Lin

Open Heart Surgery is a high risk procedure that involves cutting open the cardio to fix the issues within it.  Complications of the surgery can result in permanent disabilities if not proceeded carefully. One of the most dangerous complications after cardiac surgery is the possibility of stroke. This is a symptom that can cause brain death and paralyzation of the body for the remainder of the individuals lifetime. However, this devastating complication can be prevented if careful precautions are taken. To prevent stroke from occurring during cardiovascular open heart surgery, cardiologists can tighten control of blood pressure and monitor blood flow to the brain during surgery.

Overview of the Causes and Effects of Stroke on a Patient Undergoing Cardiovascular Surgery

The two main issues leading to stroke during the cardiovascular procedure are the formation of microemboli and hypoperfusion of the brain. Commonly seen occasions of microembli are  “patients with undertreated atrial fibrillation, and indicate the need for more aggressive blood thinning to prevent strokes…a large number of these microemboli may cause damage in the form of a transient ischemic attack (TIA), sometimes referred to as a microstroke or ‘warning stroke’" (Cedars Sinai). Atrial Fibrillation, or A-Fib often occurs in older groups such as grownups around fifties and sixties, where an irregular and rapid heartbeat causes poor blood flow in the individual. The microemboli within the blood thinning medications that is often used in cardiovascular surgeries can lead to a blockage of blood flow in the brain. A cardiothoracic anesthesiology professor at Stanford University studying subsequent brain images  summarizes after his experiment that “48% of cardiac surgical patients with postoperative stroke had infarction in the watershed regions of the brain and that hypotension was a risk factor for stroke” (Cheung et al.).  The death of tissue, or an infarction is the main culprit for stoke after surgery. Often these tissue deaths occur in the watershed regions of the brain, which eventually turns into microembli, blocking the blood supply from circulating in the cerebal system.

Not only are hypoperfusion and microemboli deadly to remove in the surgical process, patients that suffer from perioperative stroke caused by the two conditions often face longer hospital stays, an increase of lifelong disability, or possibly even death. Perioperative stroke “might affect control of the muscles in the mouth and throat, making it difficult for you to talk clearly, swallow or eat,''(Pruthi). Due to the high risk complications during or after cardiovascular open heart surgery, the conditions listed above can cause unimaginable changes to the patients day-to-day lifestyle. “Even after adjustment for comorbidities, patients experiencing a stroke in the hospital are more likely to have longer hospitalizations, worse outcomes, including higher mortality, and a lower probability of discharge home compared with patients who have a stroke in the community” (Benesch). Stroke after surgery can result in not only result in disabilities, it can also culminate to complications during or after the cardiological surgery. To prevent stroke from occurring, blood pressure management is an important aspect needed to be monitered during surgery.

Prevention of Stroke During Cardiovascular Surgery by Managing Blood Pressure During Surgery

The pressure of circulating blood in the circulatory system can become unstable during a surgical procedure. The blood pressure should be controlled within a reasonable amount in order for the surgery to proceed safely. In findings by the IARS,“the risk of death was higher for patients who spent more time with blood pressure outside the range of 75 to 135 mm Hg during surgery, and 85 to 145 mm Hg before and after surgery. For each systolic blood pressure swing of greater than 60 mm Hg, the risk of death was increased by 16 percent.” In cardiovascular surgery, a healthy blood pressure would have to be maintained in a slightly broader range in order to reduce the likelihood of stroke occurring. This is because the anesthesia that numbs your body effects the circulatory system, temporarily reducing the amount of oxygen you recieve. Data collected by Dr. Solomon Aronson, who has earned his medical degree with honors in research from the medical college of Wisconsin, reveals that “cumulative perioperative blood pressure excursion (area under the curve) beyond a systolic blood pressure range more than 135 or less than 95 mmHg predicted adverse outcome after cardiac surgery, was confirmed (odds ratio [OR]= 1.03 per mmHg min, 95% CI 1.007–1.044, P < 0. 006; table 2)” (Aronson). This research conducted by Aronson provides evidence that patients with a systolic pressure(pressure of heart contraction) outside the protected range have a higher chance of acquiring stroke after cardiovascular surgery.  The systolic pressure can increase due to many circumstances, including but not limited to prior health conditions, low potassium, low oxygen levels and anesthesia. 

Causes of blood pressure increasing during cardiovascular open heart surgery are being under anesthesia during surgery and low oxygen levels. Rena Goldman mentions in her article “What Causes High Blood Pressure After Surgery?’ that the reason behind the blood pressure increase during anesthesia is “the upper airways of some people are sensitive to the placement of a breathing tube.” (Goldman).  Blood pressure can elevate when an individual feels uncomfortable or tense, and a breathing tube down an individuals throat is definitely an uncomfortable experience. Goldman points out that not only is the insertion of a breathing tube increase blood pressure, the lack of oxygen in certain parts of the body can have the same effect. “Less oxygen being in your blood leads to a condition called hypoxemia. Your blood pressure can increase as a result” (Goldman). When the oxygen cells in the blood are low(hypoxemia), the pressure from the arteries carrying oxygen and nutrients to the lungs can increase significantly due to the high blood pressure impairment in blood vessels. This pressure causes the blood supply to be squeezed into a narrow spot, overloading the pressure onto one vessel. Although undergoing anesthesia can result in hypertension, certain drugs can be injected to control the pressure and maintain it at a safe level.

 

Blood pressure can be controlled with certain drugs and medicine to maintain the arterial pressure, reducing the risk of hypertension. Dr. Aronow, a director of cardiology research explains that the drug Clevidpine “is a rapid-acting, dihydropyridine L-type calcium channel blocker with a half-life of about 1 minute that reduces arterial pressure by direct arterial vasodilation with selective action on arteriolar resistance vessels and does not cause reflex tachycardia and tachyphylaxis” (Aronow 27). Clevidipine is commonly seen used to control blood pressure during surgery to maintainthe arterial pressure is controlled at a safe range. Maintaining a “mean arterial pressure at 60-65 mm Hg during cardiopulmonary bypass (higher in case of high stroke risk), considering LAA closure and/or Afib ablation at the time of surgery” is curcial to preventing stroke (Gaudino). The patient undergoing  surgery would not experience any severe complications during or after the surgery if the pressure is maintained properly. However, almost all risks of hypertension can avoided be altogether if the cerebral blood flow to the brain is monitored properly during the cardiovascular procedure.

 

Prevention of Stroke During Cardiovascular Surgery by Monitoring Blood Flow to the Brain

Blood flow to the brain delivers necessary energy the brain needs to function, and needs to be maintained under a steady rate no matter what occurs.  “Circulating blood supplies your brain with oxygen it needs to function properly'' is important for humans because ‘blood delivers oxygen and glucose to your brain. Although your brain is a small part of your body’s total weight. It requires a lot of energy to function” (Weatherspoon). Brain death can occur when the cerebral membrane doesn’t get the nutrients delivered by the blood supply, forming a cavity that blocks the blood vessel that delivers the nutrients to the rest of the brain. When the cerebral circulation is impaired or damaged, “less oxygen and glucose reach your brain. This can cause brain damage and neurological problems. Some conditions include: stroke, cerebral hemorrhage” (Kinman). To prevent the dangers of brain death, steady blood flow can be monitored with a brain monitor to make sure that any blood clot occurring in the cardiovascular surgery is taken care of immediately.

In order to ensure that blood is properly flowing during cardiovascular surgery, patients are monitored with a hybrid B-NIRS neuromonitor. “The development of a hybrid B-NIRS/DCS system has been previously reported and demonstrated continuous monitoring of cerebral blood flow, cerebral oxygen saturation, and metabolism in both animal models and infants in the neonatal intensive care unit” (Rajaram). The Brain Near-Infrared Spectroscopy, or B-NIRS, is a method of brain imaging that measures the amount of infrared light(heat) absorbed by the brain to determine the number of oxygenated and deoxygenated red blood cells in the brain. This allows brain infarction(stroke) to be detected during the surgery, reducing the likelihood of it progressing further in the patient’s body. This machine is also capable of “provid[ing] non-invasive and continuous monitoring of CBF and oxCCO throughout cardiac surgery with CPB,” Dr. Rajaram explains. By using a brain monitor to surveil patients in cardiovascular open heart surgery, we can detect the rate of CBF (the rate of delivery of blood from an artery to a tiny blood vessels in a tissue) in the patient and determine if a stroke is occuring during surgeries with the help of cardiopulmonary bypass. CPB, or cardiopulmonary bypass a technique in which a  heart-lung machine provides patients with cardiac and pulmonary support in place of the patient's own heart and lungs. The B-NIRS is a good way to ensure the safety of a patient during the surgery process so that the brain will not lack the necessary resources it needs.

If blood flow to the brain is not managed during cardiovascular surgery, the brain will lack the necessary resources it needs to function, leading to the dangerous consequence of stroke. “Because the brain relies on only two sets of major arteries for its blood supply, it is very important that these arteries are healthy. Often, the underlying cause of an ischemic stroke is carotid arteries blocked with a fatty buildup, called plaque. During a hemorrhagic stroke, an artery in or on the surface of the brain has ruptured or leaks, causing bleeding and damage in or around the brain.” (AANS; Association of Neurological Surgeons). It is important for the surgeons to constantly monitor the readings on the echocardiogram to make sure that stroke doesn’t occur in the process of surgery. No matter what type of heart surgery the patient undergoes, “it is [always] crucial that proper blood flow and oxygen be restored to the brain as soon as possible. Without oxygen and important nutrients, the affected brain cells are either damaged or die within a few minutes. Once brain cells die, they cannot regenerate, and devastating damage may occur” (AANS). When operating in a cardiovascular open heart surgery, it is important to be wary of dangers that come with the operation. Precautions such as blood pressure control tightening and monitoring neurological blood flow to the brain should always be taken in order to prevent stroke from occurring during or after surgery. This will lower mortality rates and provide a safer surgical environment for patients in the future. 

Work Cited

Cover image- https://wallpaperaccess.com/heart-anatomy