This study demonstrated that radiating pain during an epidural procedure was not statistically significantly associated with persistent paresthesia. While at the same time, we found that cases with surgical site at the extremities, with longer duration of anesthesia, with postoperative headache, and who took longer to visit the postoperative anesthesia consultation clinic were all prone to have postoperative persistent paresthesia.
Radiating pain during an epidural procedure was not statistically significantly associated with persistent paresthesia, which may imply that this radiating pain was just a warning of nerve injury not a sign of neuronal injury. However, we must remember that this result was based on the theory that needle-related neurologic complications are likely to be avoided if the inserted needle is retracted promptly when the radiating pain is elicited . Patients who canceled epidural anesthesia due to radiating pain were excluded from the study. In addition, we did not know exactly how many patients canceled epidural anesthesia for this reason. Such cases should not be ignored, though they have been very infrequent. The reason why we did was because it was difficult to extract them as cases of general anesthesia combined with epidural anesthesia. They were treated as cases of general anesthesia without epidural anesthesia from the viewpoint of our anesthesia registration. Therefore, it is still unknown whether severe radiating pain causing cancelation of epidural anesthesia could result in persistent paresthesia. In the study population included in our final analysis, however, we can say that radiating pain during an epidural procedure was not strongly associated with persistent paresthesia.
Some authors have suggested that the risk of neurologic complications associated with epidural catheter placement or spinal drain placement in anesthetized patients is small [6, 7]. However, considering that an isolated radiating pain unlikely causes permanent neurologic complication if the rule of promptly retracting the inserted needle by this alert is strictly respected, it is more acceptable that epidural procedure should be performed in awake status, as much as possible.
By the way, we had not provided cervical epidural anesthesia to any patients with a surgical site at the extremities. Thus, patients with upper extremity surgeries were excluded in this analysis. Therefore, it follows that lower extremity surgeries per se were associated with persistent paresthesia. This is just right because patients usually complain about paresthesia at surgical sites for a while. The postoperative questionnaire simply asked “Do you have any uncomfortable feeling at your legs?” This may be why patients’ response to the question was straight. In addition, the use of pneumatic tourniquet during orthopedic surgery could have influenced the incidence. Furthermore, postoperative longer fixation may be a plausible explanation in some cases.
Longer duration of anesthesia was also associated with persistent paresthesia. It has been suggested that the majority of intraoperative nerve injuries are associated with intraoperative positioning . Therefore, it is reasonable that the longer the duration of anesthesia is, the more frequently intraoperative nerve injury can occur.
Headache was significantly associated with postoperative paresthesia. Headache treated in this study was not restricted to post-dural puncture headache (PDPH). Therefore, it does not directly mean that PDPH was closely associated with persistent paresthesia induced by nerve injury during epidural procedure. It has been reported that several patients experience postoperative depression [9, 10]. Population-based studies and clinical investigations found high rates of comorbidity between headache or paresthesia and depressive status having the characteristics of mood and anxiety disorders [11, 12]. These might have resulted in the present finding.
The number of days taken to visit the postoperative anesthesia consultation clinic was also associated with persistent paresthesia. It is obvious that patients with persistent paresthesia were sicker than patients without paresthesia. Therefore, it is supposed that it took more time for sicker patients to recover to the status that they could visit a post-anesthesia consultation by themselves. Otherwise, longer bed rest may have caused the longer nerve compression time, and it may have worsened the degree of nerve injury.
The current study had several limitations that merit discussion. First, this study was retrospective in nature; thus, unmeasured variables could still confound the results. We used data from the institutional registry of anesthesia, which includes minimal essential information about each case, but does not include precise details. Therefore, we did not obtain several variables which might have affected postoperative persistent paresthesia. For example, it was reported that multiple needle-insertion attempts were risk factors for neurologic deficits after epidural anesthesia . However, the current study did not include information on the number of attempts. Second, this study relied on patient self-reports to determine symptoms. Therefore, postoperative paresthesia may include paresthesia induced by neural anesthesia, surgical tissue damage, or unsatisfactory patient positioning . Therefore, it may be difficult to distinguish these etiologies. Third, a considerable number of patients were excluded from the study. However, the excluded patients might not have affected the results because the exclusion was performed according to the objective criteria, and the missing data were at least missing at random. Fourth, there should have been some deviations from our institutional anesthesia protocol because the methods of anesthesia were basically left to the preference of the anesthesia attendant. However, our hospital is a teaching hospital. Therefore, it is reasonable to think that the deviation from the standard protocol was not so large even though there were some deviations. Finally, the present study represents an audit of clinical practice at an individual institution, and our findings might not be generalizable to the practice of anesthesiology as a whole.