Study Examines Risks of Prolonged Ventilation After Thymus Surgery
In patients with myasthenia gravis (MG) with an associated thymus tumor, being male, having poorer lung function, more severe disease, receiving into-the-vein anesthetics, and spending a longer time in surgery are all associated with a higher risk of prolonged ventilation following thymus removal surgery.
The study with that finding, “Risk factors of prolonged ventilation after thymectomy in thymoma myasthenia gravis patients,” was published in the Journal of Cardiothoracic Surgery.
MG is an acquired autoimmune disease characterized by muscle weakness driven by an impairment in nerve-muscle communication. Up to 30% of MG patients have a tumor in the thymus, an organ that is part of the immune system and is thought to be involved in the disease. Up to 60% of patients with these tumors, also known as thymomas, are diagnosed with MG.
“These constitute a real subtype of disease named thymoma associated with myasthenia gravis (TAMG),” the researchers wrote, adding that in these cases, thymus removal surgery (thymectomy) is the preferred method of treatment, as it has been linked to a high rate of symptom remission.
Yet, symptoms do not resolve quickly after surgery in all cases. It may take weeks to months for some patients to achieve full remission. Some patients also may not deal well with the physical stress of anesthesia and surgery and may require prolonged ventilation after the procedure.
Prolonged ventilation is influenced by many factors, including preoperative state, as well as other perioperative risk factors. Weaning MG patients off ventilation is particularly challenging, with a 25–40% failure rate.
Here, researchers retrospectively reviewed information collected for MG patients who underwent thymectomy from January 2010 through December 2019 at Peking University People’s Hospital in China. Their goal was to identify risk factors associated with a need for prolonged ventilation after thymectomy, as well as create a model capable of accurately predicting which patients were at greater risk of requiring ventilation after surgery.
Investigators analyzed the records of 112 patients — 62 women and 50 men, with a mean age of 54 years, and an average disease duration of 60 days. From these, 63 patients had mild clinical symptoms and 49 had more serious symptoms, according to the Osserman classification.
Researchers divided patients into two groups, depending on the time they were taken off ventilation. From the 112 patients included in the study, 74 were placed in group 1, which included those who were taken off ventilation within 24 hours after surgery. The remaining 38 participants were placed in group 2, which included those who needed more than 24 hours of ventilation following surgery.
Seven of the 38 patients in group 2 needed more than seven days of ventilation, and 13 failed to come off of ventilation.
Patients in group 1 had shorter MG duration and less-severe symptoms than those in group 2. Patients in group 2 also had poorer lung function — showcased by a lower vital capacity — than those in group 1.
Nearly half (49.1%) of the patients included in the analyses received immunosuppressive medications prior to undergoing surgery.
A total of 96 of patients included in the study had video-assisted surgery. Sixteen had transsternal thymectomy, which is a more complex and invasive procedure that involves making an incision in the chest and exposing the thymus. A total of 11 of the 16 patients who had transsternal thymectomies were from group 2.
The risk of prolonged ventilation was much higher for who had open chest surgery, with 28.9% of those in this group requiring prolonged ventilation, as compared to 6.8% of patients who had video-assisted surgery.
Statistical analyses also revealed that being male, having poorer lung function, more severe symptoms, being given into-the-vein anesthetics exclusively, and spending more than three hours in surgery were all linked to a higher risk of prolonged ventilation following thymectomy.
Researchers used these risk factors to create a predictive model capable of estimating the risk of prolonged ventilation in TAMG patients. After doing so, they came up with a model that was able to identify TAMG patients at risk of requiring prolonged ventilation with an accuracy of 83.5%.
“Our study suggested that the sex, [lung function], Osserman classification, anesthesia method, operation time may influence the extubation for MG patients after thymectomy. And we also developed and validated a [predictive model], hoping it will be useful for the clinical decision,” the researchers wrote.