Why do thoracic epidurals fail? A literature review on thoracic epidural failure and catheter confirmation

Abstract

Thoracic epidural anesthesia (TEA) has been the gold standard of perioperative analgesia in various abdominal and thoracic surgeries. However, misplaced or displaced catheters, along with other factors such as technical challenges, equipment failure, and anatomic variation, lead to a high incidence of unsatisfactory analgesia. This article aims to assess the different sources of TEA failure and strategies to validate the location of thoracic epidural catheters. A literature search of PubMed, Medline, Science Direct, and Google Scholar was done. The search results were limited to randomized controlled trials. Literature suggests techniques such as electrophysiological stimulation, epidural waveform monitoring, and x-ray epidurography for identifying thoracic epidural placement, but there is no one particular superior confirmation method; clinicians are advised to select techniques that are practical and suitable for their patients and practice environment to maximize success.

Key Words: Thoracic epidural; Failure rate; Placement; Electrophysiological stimulation; Epidural waveform monitoring; X-ray epidurography

Core Tip: Thoracic epidural anesthesia is a valuable technique for perioperative analgesia in abdominal and thoracic surgeries, but it is associated with a significant failure rate. Factors such as mis-identifying vertebral level, catheter migrations, anatomic factors and equipment failures can all cause suboptimal outcomes. Techniques such as electrophysiological stimulation and waveform monitoring enable the clinicians to confirm catheter level and location in the epidural space, respectively, but provide no information on the spread pattern. X-ray epidurography, on the other hand, provides information on catheter location and spread pattern but requires special equipment and training to perform.

INTRODUCTION

While thoracic epidural anesthesia (TEA) is a well-established method for providing effective perioperative analgesia in major thoracic and abdominal surgeries, it is associated with a high failure rate[1]. It remains the gold standard for managing thoracotomy pain and is crucial in enhanced recovery protocols like esophagectomies[2-5]. Apart from providing excellent analgesia, thoracic epidurals offer benefits in attenuating the surgical stress response, which can trigger harmful inflammation, coagulation abnormalities and immunosuppression. These factors can lead to complications such as myocardial ischemia, thromboembolism, muscle catabolism, and post-operative infections. While systemic opioids also provide effective analgesia and attenuate the stress response, their side effects, such as respiratory depression, can limit the dose and result in suboptimal analgesia[6].

In this systematic review, we examined the evidence behind epidural failure and methods for confirming the position of the thoracic epidural catheter.

THORACIC EPIDURAL FAILURE

TEA has a significant failure rate (32%)[2-4]. In the MASTER study[7] with 915 patients, where mortality and other postoperative outcomes were assessed between patients receiving epidural and systemic analgesia, only 50% of the patients achieved satisfactory epidural analgesia for the intended duration. The definition of epidural failure varies in the literature, from "insufficient analgesia" to "catheter dislodgment, migration of the catheter, or any reason for early discontinuation of epidural analgesia from the intended duration"[2-5]. Primary failure occurs when either analgesia does not take place or is incongruent with the surgical site. Such failure may include a catheter in paravertebral, pleural or intravascular space; a catheter at the wrong epidural level; equipment failure such as debris in the catheter, airlocks, knotting or kinking and anatomic factors such as midline fat pedicles and adhesion preventing adequate local anesthetic spread. Summary of the causes and factors contributing to thoracic epidural failure are shown in Table 1.

Table 1 Causes and factors contributing to thoracic epidural failure.

Causes of epidural failure	Factors contributing to failure
Incorrect catheter placement	Misplacement into paravertebral space, pleural space, or intravascularly
	Catheters placed at the wrong level
Equipment failure	Debris in the catheter
	Disconnections, air locks, or knotting and kinking of the catheter
Epidural space characteristics and complexities	Midline fat pedicles and adhesions impeding adequate spread of local anesthetics

Catheters placed at the incorrect level may lead to incongruent analgesic coverage from the surgical site. In an imaging study by Motamed et al[8], it was found that initial incorrect catheter placement accounted for half of the failed epidurals. Another study by Hamilton et al[9] demonstrated that catheters could migrate during normal patient movement. In this study of 60 patients undergoing lung surgery with a pre-operative thoracic epidural catheter, chest radiographs taken before and after the operation revealed that the catheter had migrated by more than one vertebral level in 24% of cases.

Another important cause of wrong epidural level is mis-identifying commonly used landmarks including vertebra prominent at C7, scapular spine at T3 and inferior border of the scapula at T7. In a study by Teoh et al[10] with 210 patients, the anesthesiologists used a vertebral prominent and inferior border of the scapula to identify T7 and the results were compared with radiography. T7 level was correctly identified 29% of the time using the vertebra prominent and only 10% of the time using the inferior scapular landmark. The C7 landmark correctly identified T7 within 1 interspace 78% of the time, while the inferior scapular landmark achieved this in only 42% of cases. Importantly, neither the C7 nor the tip of the scapula was reliable in patients with a body mass index greater than 25. Tran et al[11] investigated the reasons for thoracic epidural failure in their teaching center. They emphasized that accurate placement of an epidural catheter is a skill that needs to be mastered and suggested that 60-90 placements are necessary to reach a technical plateau. Factors affecting correct catheter placement included the experience of the operator, patient positioning, body habitus, and spinal and surface anatomy palpation. Their recommendations included using fluoroscopy and ultrasound to address the complex anatomy of the thoracic spine and confirming the correct identification of the thoracic epidural space with objective, real-time modalities such as neurostimulation and waveform analyses.

An audit of 600 patients[12] who had epidurals placed for post-operative analgesia revealed that in one-third of cases, the epidural failed for the intended duration. Various reasons were documented, including technical issues related to catheter dislodgement, leaking epidurals, patchy or unilateral blocks, and catheter occlusion leading to early catheter removal.

Local anesthetic spread in the epidural space can affect the efficacy of analgesia. Yokoyama et al[13] investigated the correlation between the sequentially injected contrast dye and lidocaine in 90 patients with epidurograms. The spread pattern was correlated with the dermatome blockade, as assessed with a pinprick. This technique allows the prediction of the dermatomal distribution of the block. The study also revealed a mean distance of 1 segment between the predicted level of the catheter tip and the level shown by the epidurograms, with up to a 3-segment difference observed, which could contribute to epidural failure. Additionally, the study described the order of contrast spread, from longitudinal to lateral and then circumferential.

Yeager et al[14] described the placement of all non-obstetrical epidural catheters under fluoroscopic guidance. They injected contrast dye immediately after catheter placement and obtained an epidurogram. This retrospective review of 303 patients found that increased cephalad-caudad spread was associated with lower epidural infusion rates on post-operative day 1, unilateral dye distribution correlated with unilateral blocks, and higher catheter sites were associated with lower pain scores.

A list of studies discussing thoracic epidural failure are shown in Table 2.

Table 2 Studies discussing thoracic epidural failure.

Ref.	Factors contributing to epidural failure
Porteous et al[5]	Equipment failure, such as debris in the catheter, incorrect catheter placement, epidural space characteristics and complexities
Motamed et al[8]	Anatomical variances, coiling and kinking of the catheter
Hamilton et al[9]	Changes in the position of epidural catheters associated with patient movement
Tran et al[11]	Primary failure of thoracic epidural analgesia in training centers
Yeager et al[14]	Malposition of epidural catheters
Tsui et al[15]	Incorrect catheter placement
Balki et al[16]	Incorrect catheter placement
Ghia et al[17]	Incorrect catheter placement
Lennox et al[18]	Incorrect catheter placement
Sánchez et al[20]	Incorrect catheter placement
Johnson et al[21]	Incorrect catheter placement

THORACIC EPIDURAL CATHETER CONFIRMATION

Electrophysiological stimulation, epidural waveform monitoring, and X-ray epidurography are common methods used to confirm the position and placement of the catheter tip. Table 3 provides a summary.

Table 3 Techniques for confirming thoracic epidural catheter position.

Technique	Description	Advantages	Disadvantages
Electrophysiological stimulation	Connecting nerve stimulator to catheter	High sensitivity and effectiveness in confirming position	Requires specialized adaptor
	Applying current and assessing motor response	Correlation with adequate postoperative analgesia	Discomfort to awake patient
	Bilateral stimulation indicates proximity to nerve root		Does not give information on local spread
	Limb or truncal response indicates epidural space
Epidural catheter waveform	Connecting catheter to pressure transducer	Simple technique using readily available equipment	Does not provide information about catheter level or injectate spread
	Confirming epidural space when pulsatile waveform is obtained
Contrast epidurography	Taking X-ray after injection of radio-opaque contrast	Confirms epidural position and assesses catheter level and spread pattern	Involves X-ray, may not be suitable for all patients
	Assessing contrast spread and catheter placement	Identifies anatomical variances and coiling/kinking	Time-consuming. Required training for epiduralgram interpretation
	Evaluating bilateral spread and vertebral levels		Risk of transiently raising spinal cord pressure with large volumes

Electrophysiological stimulation

Electrophysiological stimulation to confirm catheter position was first described by Tsui et al in 1998[15]. This technique involves connecting the nerve stimulator end (cathode) to the existing epidural catheter via an electrocardiographic adaptor and flushing it with saline. The anode terminal end is connected to the deltoid, and a 1-10 mA current is applied. Nerve stimulation utilizes a pulse width of 200 ms at a frequency of 1Hz, and a truncal or limb motor response indicates that the catheter is in the epidural space. Bilateral stimulation with a current of less than 1 mA suggests proximity to the nerve root, subarachnoid space, or subdural space.

Over the years, multiple studies and case reports in adults and children have confirmed the high sensitivity of this test in confirming the correct position of lumbar and thoracic epidural catheters, with sensitivity ranging between 80% and 100% (citation needed).

Balki et al[16] conducted a prospective observational study comparing the responses of a standard local anesthetic test dose with the thoracic epidural electrical stimulation test (EEST) in patients undergoing abdominal surgery. They studied 68 thoracic epidurals and demonstrated that EEST is a sensitive and effective test for confirming the correct position of a thoracic epidural catheter, which is correlated with its ability to provide adequate postoperative epidural analgesia. However, this technique has some disadvantages, including the need for a specialized adaptor and discomfort to the awake patient[16]. Additionally, this technique does not provide information about the spread of the injectate.

Epidural catheter waveform

The technique of using epidural catheter waveform to identify the catheter in the epidural space was first reported by Ghia et al[17] in 2001. They described a pulsatile epidural pressure waveform that is synchronous with the heartbeat. In their technique, the epidural needle was connected to a pressure transducer flushed with saline, and entry into the epidural space was confirmed when the waveform was obtained. In 2006, Lennox et al[18] modified the technique by connecting the catheter to the transducer after the conventional loss-of-resistance technique.

The main advantage of this technique is its simplicity, as it can be performed using a readily available pressure transducer. However, while it confirms the presence of the epidural space, it does not confirm the catheter's level or the spread of the injectate. Chauvin et al[19] studied the accuracy of epidural waveform analysis (EWA) in assessing the functionality of thoracic epidural catheters in the immediate postoperative period. They concluded that EWA provides a useful adjunct for assessing epidural functionality.

Contrast epidurogram

Epidurography involves taking an X-ray of the spine after the injection of radio-opaque contrast. This technique was first described in 1967 by Sánchez et al[20]. The positions of catheters in 90 patients were investigated, and they were described as "going straight, curled up, and winding". In some cases, the catheters had completely passed out of the epidural space. Epidurography is considered the gold standard in pain medicine for confirming the epidural position of the needle before injecting steroids, to accurately identify and document the vertebral level due to the risks associated with injecting steroids and arachnoiditis[21,22]. If the catheter is located within the epidural space, the radiograph shows a patchy honeycombed appearance of contrast with nerve root filling and if it is placed subdurally, the contrast has a flat, glass-like appearance in the central canal[21,22].

This technique allows confirmation that the catheter is in the epidural space and provides an assessment of the catheter's level, observation of any anatomical variances, assessment of contrast spread bilaterally and across vertebral levels, and evaluation of whether the catheter is coiled or kinked. However, it involves an X-ray, which may not be suitable for all patients and can be time-consuming. There is also a risk of transiently raising the pressure of the spinal cord if large volumes or high-viscosity contrast agents are administered.

Summary of studies done on confirming thoracic epidural catheter position are shown in Table 4.

Table 4 Studies done on confirming thoracic epidural catheter position.

Ref.	Techniques for confirming catheter position
Teoh et al[10]	Surface anatomy as a guide to vertebral level for thoracic epidural placement
Yokoyama et al[13]	Evaluation of contrast medium distribution and blockade extent during epidural anesthesia
Yeager et al[14]	Fluoroscopy-assisted epidural catheter placement
Tsui et al[15]	Confirmation of catheter placement using nerve stimulation
Balki et al[16]	Epidural electrical stimulation test
Ghia et al[17]	Confirmation of catheter position using epidural pressure waveform and computed tomography catheter gram
Lennox et al[18]	Use of pulsatile pressure waveform as a marker for confirming the location of the thoracic epidural space
Sánchez et al[20]	Radiological visualization of catheters placed in the epidural space

CONCLUSION

TEA is a valuable technique for perioperative analgesia in abdominal and thoracic surgeries, but it is associated with a significant failure rate. Factors such as mis-identifying vertebral level, catheter migrations, anatomic factors and equipment failures can all cause suboptimal outcomes. Techniques such as electrophysiological stimulation and waveform monitoring enable the clinicians to confirm catheter level and location in the epidural space respectively but provide no information on spread pattern. X-ray epidurography on the other hand provides information on catheter location and spread pattern but requires special equipment and training to perform. As per the current evidence[23,24] it is suggested that fluoroscopy, EWA, and possibly electrical stimulation, could decrease the primary TEA failure to 2% but there are no one superior confirmation method, clinicians are advised to select techniques that are practical and suitable for their patients and practice environment to maximize success. Further research and clinical experience are needed to refine these techniques and develop standardized protocols for confirming catheter position and optimizing TEA success rates.