Elsevier

World Neurosurgery

Volume 84, Issue 2, August 2015, Pages 555-560
World Neurosurgery

Original Article
Pharyngeal Motor Evoked Potential Monitoring During Skull Base Surgery Predicts Postoperative Recovery from Swallowing Dysfunction

https://doi.org/10.1016/j.wneu.2015.04.023Get rights and content

Objective

Monitoring pharyngeal motor evoked potential (PhMEP) with a modified endotracheal tube is useful for predicting postoperative swallowing dysfunction. However, the relationship between intraoperative PhMEP findings and recovery from postoperative swallowing dysfunction has not been clarified. The aim of this study was to determine whether PhMEP monitoring predicts swallowing dysfunction not only immediately after surgery but also in the postoperative recovery period.

Methods

We analyzed PhMEPs in 36 patients during treatment for skull base tumors. Recovery from postoperative swallowing dysfunction was evaluated when oral intake was started postsurgery and drip or tube feeding was discontinued. The correlation between the final to baseline PhMEP ratio and postoperative recovery times from swallowing dysfunction was examined.

Results

The PhMEP ratio significantly correlated with postoperative swallowing function immediately after surgery (P < 0.001). The period before starting oral intake in patients with a PhMEP ratio >50% (mean ± standard deviation [SD], 3.8 ± 4.3 days) was shorter than those with a PhMEP ratio ≤50% (mean ± SD, 14.7 ± 11.8 days; P < 0.01). Drip or tube feeding was removed from patients with a PhMEP ratio >50% significantly earlier (mean ± SD, 13.7 ± 19.2 days) than those with a PhMEP ratio ≤50% (mean ± SD, 38.3 ± 27.3 days; P < 0.05). Both univariate and multivariate analysis showed that only the PhMEP ratio was predictive of early recovery from swallowing dysfunction.

Conclusions

PhMEP monitoring allowed us to predict not only immediate swallowing dysfunction but also recovery from the dysfunction in the postsurgery period.

Introduction

Intraoperative monitoring of swallowing function is important in patients undergoing skull base surgery when the glossopharyngeal and vagus nerves are involved in the tumor. Motor function of these nerves can be monitored using needle electrodes placed in the vocal cords or pharyngeal wall, as well as surface electrodes on an endotracheal tube adhering to the vocal cords 1, 7, 8, 11, 12. However, these devices are usually used for recording compound muscle action potentials obtained from direct electrical stimulation of the glossopharyngeal and vagus nerves during intraoperative neurophysiologic monitoring.

Recently, we have demonstrated that monitoring pharyngeal motor evoked potential (PhMEP) using a modified endotracheal tube placed on the posterior pharyngeal muscles can be useful in predicting postoperative swallowing function during skull base surgery 3, 4. Patients with reduced PhMEP amplitude after tumor resection often experience deteriorated swallowing function immediately after surgery compared with those with preserved PhMEP amplitude. However, the correlation between intraoperative PhMEP findings and the postoperative course of swallowing function is not clear. The aim of this study was to determine whether PhMEP monitoring predicts outcomes of swallowing function not only immediately after surgery but also in the period of recovery from swallowing dysfunction.

Section snippets

Patients

We assessed data from 38 consecutive patients with skull base tumors treated surgically at the University of Niigata from February to October 2013, in whom PhMEP monitoring was performed. Two patients had severe preoperative swallowing dysfunction and were excluded. Therefore, the study included 36 patients (15 males and 21 females). Twenty-one of the 36 patients described here were included in a previous study (3) and 15 new patients were added. The cranial base tumors were as follows: jugular

Swallowing Function Immediately After Surgery

Seven of the 36 patients had mild preoperative dysfunction (1 point); all of them reported mild swallowing dysfunction but had no objective palsy of the glossopharyngeal or vagus nerve. Five of the 7 patients had jugular foramen schwannomas, 1 had a foramen magnum meningioma, and 1 had a petroclival meningioma. Magnetic resonance imaging revealed that all 7 patients had tumors affecting the lower cranial nerves. In 3 of the patients, their immediate postoperative swallowing function

Discussion

In the present study, we demonstrated that PhMEP amplitude ratios negatively and weakly correlated with the time to the end of drip or tube feeding and the beginning of oral intake in patients who underwent skull base surgery. If the PhMEP ratios were >50%, patients were able to start oral intake within 4 days after surgery. In contrast, it took approximately 2 weeks postsurgery to start oral intake in patients with PhMEP ratios ≤50%. For recovery from swallowing dysfunction, considered to be

Conclusions

PhMEP amplitude after removal of a skull base tumor was significantly correlated to earlier recovery from swallowing dysfunction by both univariate and multivariate analysis. Patients with preserved PhMEP ratios >50% during surgery had faster recovery than those with PhMEP ratios <50%. PhMEP monitoring is useful for predicting swallowing function outcomes not only immediately after surgery but also the period of recovery from swallowing dysfunction.

Acknowledgments

The authors thank Motohiro Soma and Kiyoe Nonaka for their technical support.

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