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PAIN MEDICINE

Reversal of an Unintentional Spinal Anesthetic by Cerebrospinal Lavage

Ban C. H. Tsui, MD MSc, FRCP(C)^*, Stephan Malherbe, MB ChB, MMed, FCA(SA)^*, John Koller, MD FRCP(C)^*, and Keith Aronyk, MD FRCS(C)

Departments of *Anesthesiology and Pain Medicine and Neurosurgery, University of Alberta, Edmonton, Alberta, Canada

Address correspondence and reprint requests to Ban C. H. Tsui, MD, MSc, FRCP(C), Department of Anesthesiology and Pain Medicine, University of Alberta Hospitals, 3B2.32 Walter Mackenzie Health Science Centre, 8440-112 St., Edmonton, Alberta, Canada T6G 2B7. Address e-mail to btsui{at}ualberta.ca

	Abstract

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In this case report, we describe the use of cerebrospinal fluid lavage as a successful treatment of an inadvertent intrathecally placed epidural catheter in a 14-yr-old girl who underwent a combination of epidural anesthesia and general anesthesia for orthopedic surgery. In this case, a large amount of local anesthetic was injected (the total possible intrathecal injection was 200 mg of lidocaine and 61 mg of bupivacaine), resulting in apnea and fixed dilated pupils in the patient at the end of surgery. Twenty milliliters of cerebrospinal fluid was replaced with 10 mL of normal saline and 10 mL of lactated Ringer’s solution from the "epidural" catheter. Spontaneous respiration returned 5 min later, and the patient was tracheally extubated after 30 min. No signs of neurological deficit or postdural puncture headache were noted after surgery.

IMPLICATIONS: Cerebrospinal lavage may be a helpful adjunct to the conventional supportive management of patients in the event of an inadvertent total spinal.

	Introduction

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Inadvertent subarachnoid catheter placement is a major complication of epidural blockade. There are numerous reports of unrecognized subarachnoid catheters even after negative aspiration of cerebrospinal fluid (CSF) and negative epidural test doses with local anesthetics and epinephrine (1–4). This report describes the successful treatment of an inadvertent intrathecally placed epidural catheter.

	Case Report

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A 14-yr-old (46.2-kg) girl was scheduled for elective major orthopedic surgery for spastic diplegia. General anesthesia was induced with propofol and rocuronium. An epidural catheter was placed at the L3-4 interspace without any difficulty. After negative aspiration for blood and CSF, a test dose of 5 mL of lidocaine 2% with 1:200,000 epinephrine was administered without a noticeable change in heart rate or blood pressure. Five minutes later, an initial loading dose consisting of 5 mL of lidocaine 2% with 1:200,000 epinephrine and 5 mL of bupivacaine 0.5% was administered. Ninety minutes later, an epidural infusion of bupivacaine (0.1%) with fentanyl (1 µg/mL) was commenced at a rate of 16 mL/h. The procedure was uneventful and lasted 3 h. The patient did not receive any additional muscle relaxant or opioid during the surgery. General anesthesia was maintained with desflurane 4% in a 50%:50% mixture of oxygen and nitrous oxide. Vital signs remained stable throughout the procedure, with a blood pressure range of 80–90/30–40 mm Hg and a heart rate range of 75–90 bpm.

After discontinuation of the volatile anesthetics, the patient continued to require ventilatory support despite an end-tidal desflurane concentration of <0.2%. She had fixed and dilated pupils, and the epidural infusion was immediately stopped at this time (135 min after it was started). Aspiration of the epidural catheter revealed free-flowing, glucose-positive, clear fluid, and the diagnosis of a total spinal was made. After consultation with a neurosurgeon, 20 mL of CSF was slowly withdrawn from the epidural catheter 10 min after discontinuation of the epidural infusion. A combination of 10 mL of normal saline and 10 mL of lactated Ringer’s solution was then injected slowly via the epidural catheter. Spontaneous respiration returned 5 min later. During the following 15 min, the patient started to open her eyes and had a return of normal strength, as evidenced by a strong handgrip. The patient was tracheally extubated 30 min after the epidural infusion was terminated.

The patient woke with good initial analgesia but complained of pain 20 min later. Subsequent postoperative pain was managed with morphine patient-controlled epidural analgesia. The patient was discharged 5 days later with no signs of neurological deficit or postdural puncture headache.

	Discussion

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This report describes the use of CSF lavage as a successful treatment for an inadvertently intrathecally-placed epidural catheter. Our case raises two important questions. First, did the rapid recovery in our patient result from the actual removal of bupivacaine and fentanyl from the subarachnoid space or from simple dilution of the local anesthetic as a result of saline instillation? Second, why did our patient remain hemodynamically stable despite an initial loading dose of 200 mg of lidocaine and 25 mg of bupivacaine and an infusion of 36 mg of bupivacaine and 36 µg of fentanyl into the subarachnoid space?

Subarachnoid placement, as a result of migration of the tip of the epidural catheter either during initial insertion or during the course of epidural analgesia, is rare (the incidence is approximately 0.6%) and difficult to detect (1–4). There are numerous case reports of subarachnoid injections after negative aspiration and negative test doses. Despite the injection of a large test dose and initial dose of local anesthetic (200 mg of lidocaine and 25 mg of bupivacaine) after negative aspiration, no clinical signs such as changes in blood pressure and heart rate alerted us of a total spinal in our anesthetized patient. Signs of a total spinal (unconsciousness and fixed dilated pupils) were evident only at the end of the procedure, which was later confirmed by positive aspiration of CSF. We believe that the most likely explanation in this case is that the epidural catheter tip may have migrated into the intrathecal space during the course of the epidural infusion. Therefore, it was difficult to determine exactly what volume of local anesthetic was injected into either the intrathecal or the epidural space. One possible explanation is that most of the initial dose of local anesthetic was administered into the epidural space in our patient.

Techniques such as the use of low-current epidural stimulation (Tsui test) to confirm the location of epidural catheters have recently been described to identify subarachnoid placement of epidural catheters (5–7). With the Tsui test, inadvertent subarachnoid placement during an attempted epidural block could be detected by observing a bilateral motor response to a low electrical current of <1 mA applied via the epidural catheter. In retrospect, if the stimulation test had been performed, it could have clarified whether the catheter was initially placed in the subarachnoid space or whether it had migrated into the subarachnoid space during the course of the epidural infusion.

Flushing the epidural catheter with normal saline and lactated Ringer’s solution in our patient appeared to facilitate sensory and motor block recovery. Case reports have described the successful treatment of patients who had received inadvertent large intrathecal doses of lidocaine and morphine by simply withdrawing CSF (8–11). In one case report (8), 51% and 39% of intrathecally injected lidocaine was recovered by withdrawing 20 and 30 mL of CSF, respectively, in two different patients. A possible explanation for this large yield of recovered drug may be that the CSF volume in the lumbosacral area is relatively small. In an average 70-kg adult, the mean lumbosacral CSF volume is approximately 25 to 30 mL, although the total volume of CSF is approximately 150 mL (12,13). We speculated that since the lumbosacral CSF volume in our 46-kg patient was approximately 20 mL, it is likely that the removal of 20 mL of CSF (the approximate volume of her spinal CSF) also removed a large portion of the local anesthetic. Continuous spinal anesthesia with an appropriate dose of isobaric local anesthetic usually produces a segmental block rather than a generalized total spinal (13–15). This implies that most of the spinally infused drug stays in the vicinity of the infusion site. Therefore, there has to be a concentration gradient along the CSF, rather than an even distribution of the local anesthetic throughout the CSF. In our case, a large amount of local anesthetic was injected, resulting in a large enough concentration of local anesthetic in the brainstem to cause apnea and fixed dilated pupils. It has to be reemphasized, however, that the concentration of local anesthetic at the infusion site was likely much larger than in the brainstem.

Another possible reason for the relatively fast recovery after aspiration of CSF in our patient is that the catheter could have been in a sacral position. Studies using spinal column models have shown that insufficient spread of local anesthetic can occur if the catheter is positioned caudally, especially if the local anesthetic is injected slowly (14,15). Under such circumstances, the local anesthetic can accumulate in the caudal end of the dural sac with minimal cephalad spread, thus allowing a relatively large yield of local anesthetic when the CSF is aspirated. Although the actual level of the catheter tip was not known in our patient, the relatively stable blood pressure and heart rate were comparable with the clinical picture of a restricted block.

One of most important benefits of CSF lavage is that it removes and dilutes the injected drug, thus limiting the possibility of neurological damage. Such a maneuver is routinely used to reduce the morbidity and mortality caused by inadvertent intrathecal injections of excessive vincristine (10). In the absence of any known antidote or reversal for an excessive local anesthetic spinal dose, lavage may be an effective way to reverse a total spinal and possibly limit central nervous system toxicity from the excessive local anesthetic (8–11). Inadvertent intrathecal injections of large doses of lidocaine, bupivacaine, and 2-chloroprocaine have been reported to cause serious neurological complications, such as cauda equina syndromes (16–18). In a 1980 editorial (9), CSF lavage was recommended as part of the management of an inadvertent spinal anesthetic when a relatively large dose of local anesthetic was injected intrathecally. We performed CSF lavage in our patient (the total possible dose injected intrathecally was 200 mg of lidocaine and 61 mg of bupivacaine) to reduce the risk of serious neurological complications with the additional possible benefit of reducing the risk of a postdural puncture headache. In one study (19), the immediate injection of 10 mL of preservative-free normal saline intrathecally, after a wet tap, was shown to be safe and to significantly reduce the incidence of postdural puncture headache. Fortunately, no postdural puncture headache or any other neurological complications occurred in our patient. The maximum allowable local anesthetic infusion for the epidural space was used in this case. In retrospect, we should have limited the initial loading dose and titrated the infusion rate to clinical effect.

Normal saline, lactated Ringer’s solution, and Plasma-lyte have been used as perfusate for CSF lavage and endoneurosurgery (10,20,21). Perfusion of the cerebral ventricles with large volumes (400–1000 mL) of normal saline produces central nervous system side effects, such as headaches, high fever, and neck stiffness, but does not increase the overall morbidity (20,21). The volume, rather than the type of perfusate, used is probably the critical factor. Therefore, anesthesiologists should weigh the possible side effects and benefits of CSF exchange, select the type of solution, and limit the volume to be exchanged. In this case, a combination of 10 mL of normal saline (Na 154 mEq/L; osmolality, 308 mOsm/L; pH 5.5) and 10 mL of lactated Ringer’s solution (Na 130 mEq/L; osmolality, 272 mOsm/L; pH 6.5) was used in an attempt to replace the CSF with a similar physiological solution. In retrospect, Plasma-lyte (Na 140 mEq/L; osmolality, 294 mOsm/L; pH 7.4), a commercially available solution, may have been a preferred alternative (21).

In conclusion, this case indicates that CSF withdrawal potentially hastens recovery from an excessive spinal block. It is therefore reasonable to consider the replacement of 20–30 mL of CSF with 30–40 mL of preservative-free normal saline, lactated Ringer’s solution, or Plasma-lyte via the epidural catheter in the event of life-threatening extensions of total spinals to possibly 1) shorten the recovery time, 2) minimize the potential neurotoxic insult, and 3) reduce the incidence of postdural puncture headaches. Finally, this maneuver may be a helpful adjunct to the conventional supportive management of patients in the event of an inadvertent total spinal.

	Acknowledgments

 
Supported in part by a Clinical Investigatorship Award, Alberta Heritage Foundation for Medical Research, Alberta, Canada.

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