Among the millions of surgeries done today, Coronary Artery Bypass graft surgery (CABG) is one of the most performed. “Approximately 800,000 patients each year undergoing the procedure worldwide”1. When an individual has coronary artery disease (CAD), it means the narrowing of the coronary arteries by fat deposits. The coronary arteries are vessels that supplies nutrients and oxygen to the cardiac muscle. When the lumen of these vessels are narrowed, the amount of oxygen and nutrient supply is limited. With a decreased oxygen supply, the heart suffers greatly. Depending on how long the blockage is present and how much, the individual might suffer ischemia, myocardial infarction, chest pain, and irregular heart rate, shortness of breath, abnormal heart rhythms and fatigue.
Coronary Artery Bypass graft surgery is used to treat narrowed or blockage coronary arteries. During the procedure, a healthy vein from the leg or the Lima artery could be used to bypass the infected area. The new anastomosis will supply blood to the heart muscle. A vein is a free graft which can be attached proximally and distally while the Lima artery can only be attached proximally.
Over the years, there have been an improvement in the surgical techniques which have led to the reduction of the mortality rate. Even with the decrease in mortality rate, there are still other risk involved like neurologic injury, emboli, infection, bleeding, death, system inflammatory response and irregular/abnormal heart rhythms.
Coronary artery bypass graft surgery has many complications but brain injury and emboli production remains at the top of the list. The emboli produced from the use of the heart and lung machine plus the manipulation of the aorta can cause ischemia, heart attacks and stroke. About “1% to 2% of the patients with the neurologic injury may experience coma or encephalopathy while 0.4 to 5.7% experience strokes and ischemic attacks. Secondly, the injury may cause an impairment of the brain functions like “attention, concentration, short-term memory, fine motor function and the speed of mental and motor responses”1. Depending on the time when each CABG patient was assessed, the brain dysfunction may vary from 30% to 80%.
The aim of both articles is to state the differences between On-pump and Off-pump bypass and neurologic damage. Informed consents were obtained from the patients for both experiments.
According to the “Neurocognitive function and cerebral Emboli: randomized study of On-pump versus off pump coronary artery bypass surgery”1 fewer embolic is produced with Off-pump than with On-pump bypass. Between August 2002 and March 2004, 212 patients were selected to undergo bypass surgery at the Saint George’s hospital in London. Participants who had a history of cardiac surgeries, heart attacks, not English speaking, terminal diseases, poor heart functions, strokes or are mentally unstable were excluded for the study. 104 of the patients are to undergo On-pump bypass and 108 of the patients to undergo off pump.
Each patient is to be tested for the micro emboli count at discharge and at 6weeks post-surgery. Before surgery, each patient went through several test including the transcranial Doppler Ultrasonography to monitor the blood flow and oxygen in the brain. A week before their surgeries, each patients was given an exam to test their mental state (“memory, attention, vasomotor skills, cognitive speed and executive functions”1. The test is to be repeated at discharge, 6 weeks and 6 months. During the procedures, the patients were anesthetized with fentanyl, isoflurane.
On-pump CABG was done using the roller pump membrane oxygenator and the patient was kept and hypothermia. The pressures were at 60mm and flow at 2.4l throughout the duration of the case. The cross clamp was placed during the distal anastomoses then the partial clamp during the proximal anastomoses. The cell saver was used to reduce the amount of micro emboli in the system.
Off pump CABG, median sternotomy is carried out, patients kept at normothemia, pressures at 70mmHg throughout the length of the case, the proximal and distal anastomoses done using the partial clamp.
The results from the stroke and mortality rate showed the following: “cerebellar and brainstem cerebrovascular accident” 1, 1st patient from the on-pump group and two from the off pump group died on the ninth day post-surgery. Due to a “rupture of the chronic aortic dissection”1, 1 patient from the off pump group died on the 2nd day after surgery and another died from respiratory failure on the 13th day post-surgery. 6 months post-surgery, 3 patients from the on-pump group had died and 1 from the off-pump group. It had a p value of 0.72 which was insignificant. 30 day post-surgery, the on pump group had 3 non fetal strokes and I in the off pump group. The p value was 0.11 which was insignificant.
In the on pump group, more micro emboli was produced during the removal of the cross clamp and partial clamp which showed an increased rate of ES detection but not difference between the right and left. The p value of 0.3 which was insignificant. In the off pump group, the most micro emboli was produced when the partial clamp was removed which also showed an increase in the ES detection. No difference between the right and left side of brain either. The p value was 0.5 which was also insignificant. Overall, the most micro emboli was produced after the clamp removal in the on pump CABG rather than the off pump CABG.
Another exam was given to test the mental state of the patients. The results are to be compared to the first test that was done prior to the surgery. The results for both the off and on pump patients were same as the initial test.
In conclusion, production of emboli is a 100 times more in on pump CABG than for off pump. Neurological functions are better after an off pump than with on pump. There is significant difference after discharge but no significant difference at 6 weeks or 6 months.
According to the paper “Evaluation of brain injury after coronary artery bypass grafting. A prospective study using neuropsychological assessment and diffusion weighted magnetic resonance imaging”2, decreased neurological functions after bypass can be due to age, severity of disease and the bypass pump. The micro emboli from the pump and aorta are the main cause of the brain injury. Several methods are now been used to detect brain damage. Among them, the advanced magnetic resonance is been used for an early detection of brain ischemia. Each patients that undergoes the surgery will go through a series of test before, at discharge and at 3 months.
35 patients were chosen to undergo the CABG but those who with history of mental instability, terminal diseases, not fluent in German and those who cannot do an MRI were excluded. The patients were given assessments to test their mental capabilities like “attention, rate of information processing, memory and verbal learning”2.
The surgeries were performed in the same manner. Anesthetized using sufentanyl and isoflurane, open chest, 32 degree Celsius, PRBC administered for a higher HCT and the heart lung machine used was the roller pump.
Among the 35 patients that underwent the surgery, only 29 was able to complete the 3 months follow up. One patient was lost 24 hours post surgery, one who underwent off CABG died from a cerebral artery infarction on the 3rd day, one from renal failure and the last three did not complete the 3 months followed up as required.
Once the testing was completed, the length of operation was between 38 to 160 minutes and the number of grafts done were 1 to 5. Among the 29 patients, 22 of them had a 76% chances for atherosclerosis, 76% of them at risk of hypertension, 76% hyperlipidemia and finally the chances for diabetes was 35%. No significant differences nor evidence of any abnormalities seen between the two groups.
According to the paper “The Brain: what happens to a Linebacker’s Neurons”3. Given the number of times they run into each other, brain injury is only a matter of time. The players are given teasers for the benefit of their gray matter. The results are compared from the time they were drafted and after a number of years. The test will tell how damage the brain is.
Several people suffer brain damage each year which are caused by many factors like trauma to the head. At times, people experience mild brain damage and don’t even know. Mild damages can lead to serious consequences like dementia.
An experiment was done by Douglas Smith to understand how people survive the daily trauma. He cultured rat neurons in a petri dish filled with silicon. As each day passed the neurons grew axons which connected with each other. Smith then applies a certain amount of air to the disc to see how the neurons would react. He discovered that the neurons are able to expand then return to their original length without problem. Each expanded from mild trauma changes the structure. This was because the neurons were not made up of bones but of microtubules that are able to slide by each other. The microtubules also serve as a track for the movement of protein and when the path is destroyed, there is accumulation of protein that causes swelling. When Smith delivered a sharp puff of air, the axons expanded so quickly that they developed kinks in the microtubules. The kinks later on causes swelling in the brain and the neurons are destroyed. There are enzymes in the brain that are constantly building new neurons from old ones. When the trauma occurs, these enzymes instead breaks down the axon. When the axon later on relaxes, the damage has already been done.
Many times, damaged axons try to repair themselves by growing extra channels for movement to sodium ions. As more trauma occurs, it continually builds more channels till the channels become defective and starts letting in calcium ions. This continues flow leads to the death of the axon.
Football players experience mild but constant brain trauma that causes the axon to malfunction slowly. They are given mental test at each interval to detect any damage.
Once the brain is damaged, there is not much doctors can do and neither are there drugs to treat the affected area. Three trials have been done but failed. In a later research, the anticancer drug was found to prevent the microtubules from forming knots which decreases the chances of the axon dying.
As a perfusionist, the best ways to prevent brain injury during on-pump cases is to always keep the mean arterial pressures above 65mmHg, make sure the patient is receiving adequate perfusion, high flows according to the patient’s height and weight, cool the patients down to decrease the metabolism, monitoring the brain stats. Adequate perfusion can be determined by urine production, CO2 saturations, blood gases, head stats. As for the off pump cases, the only ways the perfusionist can help the patients is by running blood gases and making sure the value are ok.
There is not much perfusionist can do for football players because the injury sustained is caused by constant crashing on the field. The mild injuries sustained at each moment will eventually leads to something even greater in the long run.
No, both injuries are completely different. The only similarity between the two groups is the brain damage they incur. The cardiac patients incur damages by lack of sufficient blood supply (ischemia) and oxygen (hypoxia) to the brain. There is intensive damage at one moment in the cardiac patient which can go on without notice till it is too late while for the football player, brain damage occurs over time. The axon are given time to repair themselves.
No both injuries are same because the individuals still experience a decline in neurocognitive functions. There are only differences among the two. One occurs over a length of time while the one in mere 3 to 6 hour interval.
- Knipp, Stephan C., Nadine Matatko, Hans Wilhelm, Marc Schlamann, Parwis Massoudy, Michael Forsting, Hans Christian Diener, and Heinz Jakob. “Evaluation of Brain Injury after Coronary Artery Bypass Grafting. A Prospective Study Using Neuropsychological Assessment and Diffusion-weighted Magnetic Resonance Imaging☆.” European Journal of Cardio-Thoracic Surgery 25.5 (2004): 791-800. Web.
- Motallebzadeh, Reza, J. Martin Bland, Hugh S. Markus, Juan Carlos Kaski, and Marjan Jahangiri. “Neurocognitive Function and Cerebral Emboli: Randomized Study of On-Pump Versus Off-Pump Coronary Artery Bypass Surgery.” The Annals of Thoracic Surgery 83.2 (2007): 475-82. Web.
- Carl Zimmer. “The Brain: What happens to a Linebacker’s Neuron?” 2010