As much as possible, there should be no drama in the OR. For pediatric spine surgeons who must contend with problems arising during spinal deformity surgery, however, things can quickly get out of hand. While deformity surgeons do have an early warning system of sorts—intraoperative spinal cord monitoring—it is not foolproof. And then there is the situation where the surgeon doesn’t perform many pediatric deformity cases. The potential consequences for the patient? Paralysis.
A study published earlier this year in the Journal of Bone and Joint Surgery shed light on spinal cord monitoring, intraoperative injury, and what might be done to address the problem. Dr. Michael Vitale, Chief of Pediatric Spine at Morgan Stanley Children’s Hospital, Columbia University Medical Center, and lead author on the study, states, “Fortunately, neurological problems are very rare during spinal deformity surgery. State of the art techniques of intraoperative electrophysiological monitoring have improved the safety of these procedures. Despite all safeguards, however, there is some small unavoidable risk of a neurological complication, especially in the more severe cases of spinal deformity. My colleagues and I wanted to better elucidate the risk factors and provide possible solutions…these are high stakes situations so we are hoping to contribute to a standardization of approach.”
Source: Journal of Bone and Joint SurgeryThe spine surgeon’s best friend during deformity surgery is the technology that tells him or her that something is neurologically amiss. Dr. Vitale explains, “Since the mid-1980s we have evolved sophisticated ways of monitoring spinal cord functioning in the OR that tell us whether an electrophysiological event is occurring. Sensory monitoring is the standard of care now, while motor evoked potential (MEP) monitoring—something that can be crucial—is not as widely used.”
So when the alarm bells go off, what are they drawing attention to? “During surgery there may be a neurologic injury arising from direct trauma or stretching of the spinal cord; there may also be an insult to the spinal cord where there is inflammation and swelling that threatens the blood supply in the spinal cord.”
As we perform increasingly complex spinal deformity surgeries and apply powerful correction measures, it may be that we are stretching the limits of what the spinal cord can tolerate. That is why state of the art monitoring is important.
“Despite some controversy about costs and the need for special skills when implementing the motor evoked potential monitoring, use of MEP can make a big difference. There were a number of cases in our study that wouldn’t have been detected by sensory monitoring alone.”
Elaborating on the benefits of combined sensory and motor evoked potential monitoring, Dr. Vitale says, “By using both monitoring techniques we are able to keep an eye on a larger proportion of patients. Patients who have other problems—mostly neurological issues—can be difficult to monitor so being able to do both types of monitoring allows the neurologist to obtain more accurate information. Interpretation of these data is complex, however, and to a great extent depends on the skills of those doing the monitoring. The process requires close communication between anesthesia and the neuro-monitoring team.”
Opening a window into his research, Dr. Vitale states, “Of 151 pediatric patients with spinal deformity who were monitored with both sensory and motor based techniques, 12 had electrophysical signs of impending problems. Eight patients experienced these changes due to curve correction, two had hypotension, in one case there was direct spinal cord trauma, and in another there was improper positioning of a pedicle screw. Early recognition of potential problems in these cases allowed swift action and there were no lasting neurological problems as a result.”
“Also, we found that the rate of true electrophysical events was dramatically higher in the patients with cardiopulmonary comorbidities than it was in the patients with no comorbidities. We don’t fully understand what is different about the physiology of these patients, but it may be that they have special problems with blood flow to the spinal cord or problems with oxygenation.”
The overall recommendation? High stakes, thus set a low threshold. Dr. Vitale: “Due to the serious nature of the consequences, it is best to establish a low threshold for defining a relevant electrophysiological change. Having said that, however, ‘low threshold’ is not well defined. Basically, any reduction in the amplitude of sensory or motor evoked potential should be taken seriously. This will allow the surgeon to intervene immediately and avoid what could be serious neurologic complications.”
So the good news is that it is possible to take corrective action.
“In the event of an electrophysiological change the surgeon must step through the appropriate algorithm of responses which should allow him or her to reverse the problem. You begin by increasing the blood pressure, then increasing the oxygen carrying capacity via a blood transfusion, increasing the temperature, reversing the correction, removing the instrumentation, waking up the patient, and finally, neurological imaging.”
As in other areas of medicine and life, there is probably a relationship between volume and outcomes. According to Dr. Vitale, “There is a fair amount of spine surgery going on in low volume centers around the country. The possible negative consequences of these deformity surgeries is a strong argument for having high volume centers where the surgeons aren’t strangers to these cases. The fact is that these intraoperative events are relatively rare, so budding surgeons aren’t exposed to them in their training. Those surgeons who have not performed many of these surgeries need to have a game plan in the event of such complications.”
Those in charge of finances may also be proponents of these surgeries occurring in high volume centers. “The monitoring equipment is several thousand dollars. The real expense, however, is in having a team of technicians and neurologists who are skilled in the execution and interpretation of the data. Undertaking this monitoring doubles the amount of information to be combed through, and requires training and experience. As we enter an era of increased cost consciousness it becomes a challenge to convince hospitals to institute these systems.”
“The bottom line, ” says Dr. Vitale, “is that we are now able to do much bigger cases without incident because of this monitoring. For those patients whose lives have been marred by spinal deformities, this is good news indeed.”
Dr. Randall Betz, Chief of Staff and Medical Director of the Spinal Cord Injury Unit at Shriners Hospital for Children in Philadelphia, is also glad have such monitoring at his side in the OR. And having practiced for nearly 30 years, Dr. Betz was there when things weren’t so smooth. “In the ’80s you didn’t know if someone was paralyzed until you woke them up. If the situation was detected, and able to be reversed, it would take about three hours to do so. Sensory and motor evoked potential monitoring has resulted in a significant reduction in permanent spinal cord injury. If you are dealing with a loss of blood to the spinal cord then every minute makes a difference. With motor evoked monitoring you are alerted to a problem almost immediately; the process is such that electrodes stimulate the brain and shoot an electrical impulse down the spine at set intervals.”
While invaluable, says Dr. Betz, such monitoring is merely a guidepost. “Monitoring tells you that there is a problem…it doesn’t enlighten you as to what the problem is. Is blood pressure an issue? Have you overstretched the spinal cord? Has the surgeon caused trauma with an instrument? You must walk through the appropriate algorithm and then if you can’t determine the issue, you need to do an MRI and find out, for example, if there was a fragment of bone or a blood clot. The most common issue is blood pressure; typically, if you elevate the blood pressure with medication then the monitoring returns to normal. There was a trend to lower the blood pressure to cut down on blood loss, but for these severe deformities associated with neurological events we usually run the blood pressure higher because the spinal cord seems to tolerate manipulation better because it is being perfused with blood (oxygen). Another ‘lesson learned’ is that if there is a neurological event and you have to stop the surgery you should keep the blood pressure above 90 for 24/48 hours. This allows the spinal cord to remain perfused with blood (oxygen).”
If given his druthers, and perhaps a substantial research grant, Dr. Betz would make some changes to the current systems. “The type of deformity correction now available to patients is amazing.”
But the fact is that we are stretching the spinal cord, sometimes taxing it. The nerve fibers aren’t fond of being stretched; the stretching also wrings out the blood supply. Improvements in the systems would make the process safer for patients and more manageable for surgeons. For instance, ideally there would be continuous monitoring so that you don’t have to stop periodically.
“Also, we do get some false positive alarms, so more precision would be beneficial. Perhaps the most useful improvement would be if a system could notify us as to exactly what the problem is. Knowing whether we’re looking at a blood pressure issue or a cord stretch event would save time and thus increase safety.”
Get the paperwork ready…a grant proposal just may be on the horizon.
