Ultrasound-Guided Caudal Epidural Anesthesia in Adults for Anorectal Procedures.

INTRODUCTION: Caudal epidural is a commonly performed regional anesthetic technique in children. In adults, the high-failure rates associated with landmark-based techniques deter its widespread use. Fluoroscopy-guided caudal epidural steroid injections are widely used as a treatment modality in chronic back pain. Ultrasound (US) guidance has been shown to be equally effective as fluoroscopic-guided caudal injections. We aimed to assess the feasibility of US guided caudal epidurals as a sole anesthesia technique in adult patients undergoing minor anorectal procedures. SUBJECTS AND METHODS: Fifty consecutive adult patients undergoing elective minor anorectal procedures were recruited for this study. Eligible patients received US-guided caudal epidural and success rates, surgical patient and surgeon's comfort were assessed using validated tools. Any adverse events were also observed.
RESULTS: The block was successful in all patients. One patient had pain in the perianal region requiring skin infiltration. All patients were either highly satisfied or satisfied of the procedure. Surgeons rated the surgical conditions as highly satisfied (90%), satisfied (8%), or unsatisfied (2%). Two patients rated the caudal injections were of moderate pain, rest all rated it as mildly painful. One patient experienced a single episode of urinary incontinence.
CONCLUSION: US-guided caudal epidural can be considered as an option for anorectal procedures of short duration with acceptable success rates, surgical conditions, and patient comfort. Copyright:

INTRODUCTION

Caudal epidural anesthesia is a commonly used technique in the pediatric patients. In adults, currently, the route is mainly employed for treating low back pain, under fluoroscopic guidance. One of the main reasons for unpopularity of this technique in adults is the high-failure rates experienced with landmark-based approach, due to anatomic variations.[1] Ultrasound (US) guidance during caudal injections demonstrate improved success rates, apart from reduced numbers of attempts, blood aspiration, bone contact, and inadvertent subcutaneous injections.[2] The treatment effect, complication rates, and adverse events were comparable to fluoroscopic technique,[3] while the time required for the procedure is lesser with US guidance.[4]

Minor anorectal surgeries are commonly performed as day care procedures. Even though spinal anesthesia, modified into a saddle block is a widely used technique, epidural anesthesia offers certain unique advantages such as minimal motor blockade, early mobilization, lesser degree of hypotension, and lesser chances of postdural puncture headache. Other potential advantages of the caudal route include ease of positioning and selective blocking of sacral nerves. There is a gap in our knowledge whether US-guided caudal epidural can be used routinely as a sole anesthetic technique in adult patients. The aim of the study was to assess the success rates, surgical comfort, and patient comfort with US-guided caudal anesthesia. The current study was done to assess the feasibility of a larger trial (CTRI no: 2020/01/022896) comparing US-guided caudal epidural with saddle block in terms of hemodynamic effects, time for discharge apart from the success rates, and surgical comfort.

SUBJECTS AND METHODS

Fifty consecutive adult patients scheduled for minor (estimated duration less than an hour) anorectal elective procedures (hemorrhoidectomy, perianal fistula, fissurectomy, polypectomy, etc.) were recruited for the study after obtaining Institutional Ethical Committee approval. Informed written consent was obtained from the participants. The inclusion criteria were adult patients of either sex, American Society of Anesthesia (ASA) physical statuses 1 and 2, and those scheduled for elective anorectal procedures of short duration. The exclusion criteria were bleeding diathesis, prolonged surgeries, ASA physical status 3 and 4, inability to lie in prone position, previous spine surgeries, or any other obvious anatomical abnormality in the caudal area.

All patients were premedicated with midazolam 1 mg intravenously and intravenous infusion of ringer lactate was started. Patients were then placed in the prone position. Monitoring was done with pulse oximetry, noninvasive blood pressure, and 3 lead electrocardiogram. The procedure was performed by the first author, with more than 15 years of experience in caudal epidurals and routinely performs US-guided caudal epidural injections for low back pain. A screening scan was done by initially placing a linear high-frequency probe (Aeroscan CD25 Pro, KonicaMinolta) in the transverse view across the sacrum to view the sacral median crest, and the probe was slid caudad to view the sacral hiatus, sacro coccygeal ligament, and dorsal surface of the sacrum – appearing like a frog's face. The probe is then rotated to a sagittal orientation to view the hiatus and sacrococcygeal ligament [Figure 1]. After asepsis and skin infiltration, a 23 G spinal needle using an in-plane approach to pierce the sacrococcygeal ligament. The needle tip was confirmed using a transverse view, and few milliliters of drug was injected in a pulsatile manner, and the expansion of the epidural space was observed. Color Doppler was used to detect the flow of the drug and absence of extravasation [Figure 2]. A total volume of 15 mL of drug (10 mL 0.5% bupivacaine and 5 mL of NS) was injected.

Figure 1

Sonographic images showing longitudinal (a) and transverse (b) view of the sacral hiatus. The needle track can be appreciated in the transverse (c) and sagittal view inside the hiatus (d), the needle is slightly off the midline and few inadvertent air bubbles can be appreciated

Figure 2

Colour Doppler showing appropriate flow pattern

The patients were turned into the supine position, and following parameters were monitored. Hypoesthesia to pin-prick sensation was checked every 5 min in S1 dermatome as an indicator of onset of sensory loss. Patients were asked to grade the procedural comfort according to the verbal response scale (no pain, mild, moderate, and severe pain). After shifting them to the operating room, lithotomy position was applied. Intraoperatively, the hemodynamic parameters were noted. Any discomfort either during positioning and surgery was noted and if significant, supplemental analgesia or general anesthesia was planned to be administered according to the anesthesiologist's preference. After the surgery, the surgeons, blinded to the anesthesia technique were asked to grade the quality of surgical field on a 4-point Likert scale (highly satisfied, satisfied, somewhat satisfied and unsatisfied), and the patient was asked to grade the surgical comfort on a similar scale. This scale has been validated by previous studies.[56]

RESULTS

The mean age of the study patients was 43.4 years, with a range of 19–67 years [Table 1]. Weight varied from 43 kg to 100 kg with a mean of 64.6 kg. Most patients (n = 42) were males. The caudal space was easily identified and needle positioning was achieved in the single attempt in all patients. After the scout scan, all procedures were performed within 2 min. Two patients had thickened sacrococcygeal ligament which offered considerable resistance during penetration. In one patient, the drug spread was observed predominantly caudally; hence, the needle was further inserted cephalad by 1 cm and appropriate flow pattern as judged by color Doppler achieved. All patients demonstrated hypoesthesia in S1 dermatome within 15 min (mean 12.8 min, with a range of 5–15). Two patients who had demonstrable thickened sacrococcygeal ligament which offered considerable resistance to needle penetration reported the anesthetic procedure as “moderately painful,” others rated the procedural pain as mild. Positioning was possible in all patients. One patient demonstrated discomfort to pin prick on perianal region after positioning hence needed local infiltration. Further insertion of speculum and procedure was without any discomfort. Two patients demonstrated a sensory level of T6 and motor blockade along with hypotension requiring a single dose of intravenous mephentermine 6 mg. Both were elderly (65 and 67 years of age, respectively) and recovered without any sequelae. A different patient had one episode of urinary incontinence 3 h after the procedure which resolved without any interventions.

Table 1

Observation and results

Parameter	Value
Age (years), mean (range)	43.4 (19-67)
Weight (kg), mean, (range)	64.6 (43-100)
Scout scan (normal, abnormal)
Normal (n)	47
Thick sacrococcygeal ligament (n)	2
Narrow hiatus (n)	1
Number of attempts
One attempt	50
Procedural time (mean±SD, seconds)	69.3±10.3
Drug spread
Acceptable (n)	49
Needed adjustment (n)	1
Onset of sensory (min), mean, (range)	11.4 (4.5-15)
Needed supplementation
No (n)	49
Yes (n)	1
Surgical comfort
Highly satisfied, n (%)	45 (90)
Satisfied n (%)	4 (8)
Somewhat satisfied (n)	0
Unsatisfied n (%)	1 (2)
Patient comfort - caudal injection (n)
No pain	0
Mildly painful	48
Moderately painful	2
Severe pain	0
Patient comfort surgery
Highly satisfied, n (%)	48 (96)
Satisfied, n (%)	2 (4)
Somewhat satisfied (n)	0
Unsatisfied (n)	0
Adverse events
Urinary disturbance (n)	1
High sensory level (n)	2

SD=Standard deviation

DISCUSSION

Caudal epidural anesthesia for anorectal surgeries is indeed an old technique. In fact, the caudal approach predates the lumbar route for accessing the epidural space.[78] Continuous caudal epidural for labor analgesia also has been performed in the past with good results.[9] Several recent case reports of successful caudal anesthesia in adults exist.[1011] Landmark-based caudal epidural in adults is associated with lower success rates (68%–75%) than children.[12] The subjective feel of a loss of resistance, the “whoosh test” (auscultation of the thoracolumbar region while injecting 2 mL of air) and palpation for subcutaneous injection, all have low sensitivity and specificity.[13] The depth of the sacral canal and length of the sacrococcygeal ligament might influence proper needle placement.[14] US is also a useful screening tool to detect the abnormalities in the sacral hiatus and assess the feasibility of caudal epidural injections for back pain.[15] Very few studies have analyzed US-guided caudal epidural in adults as a sole anesthetic technique.

In our study, none of the patients had significant sonographic anomaly impeding caudal approach apart from thickened sacrococcygeal ligaments (n = 2), narrow hiatus as judged by the transverse scan (n = 1). In an Iranian study on 240 patients, the authors report a 0.8% incidence of sonographically detected sacral anomaly precluding caudal epidural and varying depths and angulations according to the patient body habitus and pelvis inclination.[15] The sample size of our current study is only fifty; however, these factors will be analyzed in greater detail in our ongoing trial with a larger sample size. We did not measure the dimensions of the sacral hiatus as this was not part of the study design. The block was successful in all patients and one patient requiring skin infiltration. In many instances, the patient was positioned even before the completion of the sensory block, a situation encountered by similar studies.[8] Positioning was possible in all patients and surgeons rated all but one patient (”unsatisfied”) having adequate surgical conditions (”highly satisfied” or “satisfied”). All patients rated the intraoperative period as “highly satisfied” (n = 48) or “satisfied” (n = 2).

Accidental intrathecal injection due to variable termination of filum terminale and intravascular injections are the serious complications of caudal epidurals. It has been suggested that the needle should not be inserted too cephalad into the sacral canal to avoid dural puncture.[16]. Injecting just after penetrating the sacrococcygeal ligament has been shown to be produce higher success rates than inserting the needle further in to the sacral canal,[17] a fact reinforced by our study. In one patient, we did insert the needle into the sacral canal by approximately 1 cm, (tip was still caudal the acoustic shadow of the hiatus) to achieve a cephalad drug spread as judged by the Doppler.

Two elderly patients experienced a high sensory level, warranting dose reduction in the elderly. The spread of injectates into the epidural space is governed by complex factors, including surface area of the lumbosacral dura and fat content,[18] whereas spinal canal dimensions may not always decrease with age as believed.[19] Urinary disturbance in the form of overflow incontinence was present in one patient, and the patient regained bladder control during next voiding. Some of the other possible complications of caudal epidural include inadvertent intrathecal or intravascular injection, spread of the drug in subcutaneous of presacral region, rectal perforation, etc., Some of these complications can be avoided by not inserting the needle too cephalad, careful aspiration, always keeping the tip of the needle in vision and using color Doppler to assess the spread of the drug. All these precautions were taken, and none of these complications were observed. Apart from the small sample size, surgeries were performed by different surgeons which could be a confounding factor in assessing the surgical comfort which, along with the patient comfort are the subjective scales.

CONCLUSION

US-guided caudal anesthesia for adult anorectal surgeries present an attractive option for day care surgeries. This small-scale trial done as a feasibility study for a larger trial clearly shows the practicality and ease of this technique with acceptable success rates, patient comfort, and acceptable surgical conditions.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.