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Conventional Landmark-Guided Midline Versus Preprocedure Ultrasound-Guided Paramedian Techniques in Spinal Anesthesia

Kallidaikurichi Srinivasan, Karthikeyan MBBS, FRCA, FCARCSI, MRCPI, MD*; Iohom, Gabriella MD, PhD*†; Loughnane, Frank FFARCSI*; Lee, Peter J. FFARCSI, MD*†

doi: 10.1213/ANE.0000000000000911
Regional Anesthesia: Research Report

BACKGROUND: Multiple passes and attempts while administering spinal anesthesia are associated with a greater incidence of postdural puncture headache, paraesthesia, and spinal hematoma. We hypothesized that the routine use of a preprocedural ultrasound-guided paramedian technique for spinal anesthesia would reduce the number of passes required to achieve entry into the subarachnoid space when compared with the conventional landmark-guided midline approach.

METHODS: One hundred consenting patients scheduled for elective total joint replacements (hip and knee) were randomized into group C (conventional) and group P (preprocedural ultrasound-guided paramedian technique) with 50 in each group. The patients were blinded to the study group. All spinal anesthetics were administered by a consultant anesthesiologist. In group C, spinal anesthetic was done via the midline approach using clinically palpated landmarks. In group P, a preprocedural ultrasound scan was used to mark the paramedian insertion site, and spinal anesthetic was performed via the paramedian approach.

RESULTS: The average number of passes (defined as the number of forward advancements of the spinal needle in a given interspinous space, i.e., withdrawal and redirection of spinal needle without exiting the skin) in group P was approximately 0.34 times that in group C, a difference that was statistically significant (P = 0.01). Similarly, the average number of attempts (defined as the number of times the spinal needle was withdrawn from the skin and reinserted) in group P was approximately 0.25 times that of group C (P = 0.0021). In group P, on an average, it took 81.5 (99% confidence interval, 68.4–97 seconds) seconds longer to identify the landmarks than in group C (P = 0.0002). All other parameters, including grading of palpated landmarks, time taken for spinal anesthetic injection, periprocedural pain scores, periprocedural patient discomfort visual analog scale score, conversion to general anesthetic, paresthesia, and radicular pain during needle insertion, were similar between the 2 groups.

CONCLUSIONS: Routine use of paramedian spinal anesthesia in the orthopedic patient population undergoing joint replacement surgery, guided by preprocedure ultrasound examination, significantly decreases the number of passes and attempts needed to enter the subarachnoid space.

Published ahead of print August 11, 2015

From the *Cork University Hospital, Wilton, Cork, Ireland; and University College Cork, Ireland.

Accepted for publication May 8, 2015.

Published ahead of print August 11, 2015

Funding: Departmental funding.

The authors declare no conflicts of interest.

Reprints will not be available from the authors.

Address correspondence to Karthikeyan Kallidaikurichi Srinivasan, MBBS, FRCA, FCARCSI, MRCPI, MD, Department of Anesthesia, Cork University Hospital, Wilton, Cork, Ireland. Address e-mail to ksrinivasan@outlook.com.

Spinal anesthesia is widely performed using a surface landmark-based “blind” technique. Multiple passes and attempts while administering spinal anesthesia are associated with a greater incidence of postdural puncture headache, paraesthesia, and spinal hematoma.1–5

Real-time and preprocedural neuraxial ultrasound techniques have been used to improve the success rate of spinal anesthesia. Information on the use of real-time ultrasound-guided spinal anesthesia has, to date, been limited to case series and case reports.6–8 Its use may be limited by the requirement for wide-bore needles and the technical difficulties associated with simultaneous ultrasound scanning and needle advancement.9 The use of preprocedural ultrasound has been shown to increase the first-pass success rate for spinal anesthesia only in patients with difficult surface anatomic landmarks.10 No technique has been shown to improve the success rate of dural puncture when applied routinely to all patients.11

Studies on preprocedural ultrasound-guided spinal techniques have focused on a midline approach using a transverse median (TM) view. The parasagittal oblique (PSO) view consistently offers a better ultrasound view of the neuraxis compared with TM views.12 However, no studies have been conducted to assess whether these superior PSO views translate into easier paramedian needle insertion.

We hypothesized that the routine use of preprocedural the ultrasound-guided paramedian spinal technique results in fewer passes required to enter the subarachnoid space when compared with the conventional landmark-based midline approach.

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METHODS

This was a prospective, randomized, controlled study performed from February 2014 to May 2014. After approval by the Clinical Research Ethics Committee of Cork Teaching Hospitals (ref no. ECM 4[j] 04/02/14), all consented patients scheduled to undergo elective total knee or total hip arthroplasty with spinal anesthesia were included in the study. A written informed consent was obtained from all patients. Those with contraindications to spinal anesthesia (allergy to local anesthetic, coagulopathy, local infection, and indeterminate neurological disease) were excluded from the study.

The patients were randomized using random number-generating software (Research Randomizer version 4.0) to undergo either conventional landmark-guided spinal anesthesia (group C) or preprocedural ultrasound-guided paramedian spinal anesthesia (group P). Group allocation was concealed by enclosing the codes in a sealed opaque envelope seen by the attending anesthesiologist immediately before performing the procedure. In both groups, spinal anesthesia was performed by 1 of 3 consultant anesthesiologists, each having performed >75 neuraxial ultrasound scans before the study. On arrival to the anesthesia induction room, baseline monitoring (noninvasive blood pressure, pulse oximetry, and 3-lead electrocardiography) and IV access were established. Patients in both groups were then positioned sitting on a level trolley with feet resting on a foot rest. They were given a pillow to hug and were requested to maintain an arched back posture with an assistant holding the patient to aid positioning. No sedation was given before or during the administration of spinal anesthesia.

In group C, the anesthesiologist palpated the landmarks after positioning and graded the ease of palpation on a 4-point scale (easy, moderate, difficult, or impossible) as described in previous studies.10 The selection of interspinous space was left to the discretion of the anesthesiologist. Strict asepsis was observed throughout the procedure with the anesthesiologist, scrubbed before the procedure, wearing a mask and sterile gloves. The skin was prepared with 2% chlorhexidine (ChloraPrep 3 mL applicator; CareFusion Corporation, San Diego, CA) after which 2 to 5 mL of 1% lidocaine was used to infiltrate the skin. The anesthesiologist performing the spinal technique was allowed to choose the appropriate needle length (90- or 119-mm 25-G Whitacre needle), gauge (25-G or 22-G), depth, and angle of insertion. The type and dose of local anesthetic injected for spinal anesthesia were at the discretion of the attending anesthesiologist. After completion of spinal anesthetic injection, and positioning the patient in the lateral decubitus position, ultrasound was used to identify the interspinous level at which the injection was administered.

In group P, a portable ultrasound unit (SonixTablet, Peabody, MA) with a curved 2- to 5-MHz probe was used for initial preprocedural marking. A paramedian sagittal oblique view of the neuraxis was obtained, and the sacrum was identified, after which the interlaminar space between L5 and S1 was noted. Subsequent interspinous spaces were identified by counting the interlaminar spaces in a cranial direction. The interspinous space at which the clearest image of the anterior complex (ligamentum flavum dura complex [LFD]) and posterior complex (posterior longitudinal ligament [PLL]) was obtained was selected. At the selected interspace, and with the probe positioned to obtain the clearest ultrasound image, a skin marker was used to mark the midpoint of the long border of the probe and the midpoints of the short borders of the probe (Fig. 1). The medial angulation of the probe was also noted to facilitate guiding the insertion of the spinal needle. At the same horizontal level as the midpoint of the long border of the probe, the midpoint of the line drawn between the 2 short border midpoints of the probe was used as paramedian insertion point for the spinal needle (Fig. 2). A TM view at the same level was also obtained, and the midline was marked. This marking was used to aid the medial angulation of the spinal needle (Fig. 1). Both PSO and TM views were graded as good (both LFD and PLL visible), intermediate (either LFD or PLL visible), and poor (both LFD and PLL not visible).12 After skin marking, care was taken to make sure that the needle entry site was free of ultrasound gel before needle insertion. In group P, the anesthesiologist did not palpate the landmarks for grading until the spinal injection was complete. Spinal anesthesia was performed in the same aseptic manner as mentioned earlier.

Figure 1

Figure 1

Figure 2

Figure 2

In both groups, the anesthesiologists were given the option to use alternative methods if 3 attempts were unsuccessful. For patients in group C, another interspinous space could be used or ultrasound used. For patients in group P, a midline approach or a conventional landmark palpation technique could be used.

The outcomes were noted by a single observer for all patients. Because of the nature of the study, the observer could not be blinded to the groups. In addition to demographic details from the patients (age, sex, and height), type of surgery and history of lumbar spine surgery were recorded. History of a difficult neuraxial block was also recorded in both groups. This was obtained from previous anesthetic records. Our hospital uses a standardized electronic anesthesia record that requires description of the grade of difficulty of spinal performance as “easy,” “difficult,” or “failed.” Only evidence previously documented by the anesthesiologist noting the difficulty of the procedure (spinal, epidural, or combined spinal epidural anesthesia) was included.

A timer was used to record the various time intervals. Time for identifying landmarks in group C was defined as time from which the anesthesiologist started palpating to identify the landmarks for the completion of the process, as declared by the anesthesiologist. In group P, it was defined as time from which the ultrasound probe was placed on the skin to the anesthesiologist declaring that the markings were completed. Time taken for performing spinal anesthetic was defined as time taken from insertion of the introducer needle to the completion of injection. The number of passes (defined as the number of forward advancements of the spinal needle in a given interspinous space, i.e., withdrawal and redirection of spinal needle without exiting the skin) and number of spinal needle insertion attempts (defined as the number of times the spinal needle was withdrawn from the skin and reinserted) were noted.10 The number of passes and attempts were recorded either until the completion of spinal anesthetic or until the anesthesiologist converted to an alternate technique.

Any radicular pain, paraesthesia, or blood in the spinal needle was also noted. All patients who experienced paraesthesia or radicular pain were followed over the next 24 hours, and any patients with persistent symptoms were further evaluated as per department protocol. The use of a long needle, that is, 119-mm 25-G Whitacre needle, was also recorded.

In both groups after administration of spinal anesthesia, patients were positioned on either left or right lateral position, depending on the site of surgery and the type of bupivacaine used (plain or hyperbaric). After positioning, and before administration of sedation, patients were asked for their periprocedural pain scores (patients were specifically asked to rate the pain in their back during administration of spinal anesthesia) measured using an 11-point verbal rating scale (0 = no pain, 10 = most pain imaginable) and periprocedural discomfort scores measured using an 11-point verbal rating measured (0 = no discomfort, 10 = most discomfort imaginable). Level of block (loss of cold sensation tested with ethyl chloride spray) was noted 15 minutes after spinal anesthetic injection. Type and dose of sedation (midazolam with or without propofol infusion) were left to the discretion of the anesthesiologist.

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Study Outcomes

The primary outcome was the difference in number of passes between the 2 groups. Secondary outcomes included the following:

  1. Number of spinal needle insertion attempts
  2. Time for identifying landmarks
  3. Time taken for performing spinal anesthetic
  4. Level of block
  5. Incidence of radicular pain, paraesthesia, and blood in the spinal needle
  6. Periprocedural pain
  7. Periprocedural discomfort score
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Statistical Analysis

Based on a previous study, we assumed that the average number of passes per spinal anesthetic for an experienced anesthesiologist would be 3.3 ± 3.1 (mean ± SD).13 We hypothesized that by using a preprocedural paramedian spinal, the number of passes could be reduced to 1.3. A total of 38 patients in each group would have been needed to achieve a power of 0.8 and type 1 error of <0.05. We randomized 50 patients per group to allow for dropouts. All data were analyzed based on intention to treat. Data were analyzed for normal distribution using the Shapiro-Wilk test. Categorical data were analyzed using the χ2 test or Fisher exact test as appropriate. Normally distributed parametric data were analyzed using Student t test. All tests were 2-tailed.

For nonnormally distributed count data (passes and attempts) that cannot have a value of zero and had negative binomial distribution, zero truncated negative binomial regression was used to examine the group effect. For other variables that were nonnormally distributed, especially if the data could not be approximated by log-normal distribution, a bootstrap independent samples test was applied, because it is considered a better approach compared with the Z-score procedure.14 Results for time variables were based on 5000 bootstrap samples. For the variable dose of intrathecal bupivacaine, the 99% confidence interval (CI) was based on 5000 bootstrap samples; variances in some samples were zero; therefore, the P value was estimated from 1000 bootstrap samples.

Time variables were reported with 10th and 90th percentile to provide information on the spread. Student t test for unequal variance (Welch method) gave 99% CI within 1.5 seconds for time taken to identify landmarks and 16.2 seconds for time taken for spinal anesthetic administration when compared with bootstrap.

For patient characteristic variables and primary outcome variable, a 2-tailed P < 0.05 was considered significant and 95% CIs were reported. For all other outcome variables, a 2-tailed P value <0.01 was considered statistically significant and 99% CIs were reported. SPSS (IBM SPSS Statistics for Windows, Version 21.0, Armonk, NY) and STATA 12.1 (StataCorp LP, College Station, TX) were used for statistical analysis.

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RESULTS

One hundred patients were assessed for suitability. All patients gave their consent to take part in the study, and 50 were randomized to each group. All patients received the allocated intervention. No patients were lost to follow-up, and data acquisition was complete (Fig. 3). In one patient, spinal injection was performed in the lateral position because of a vasovagal episode after local anesthetic infiltration. This patient’s data were included in the analysis.

Figure 3

Figure 3

The distribution of demographic data of the patients (age, sex, and height), type of surgery, history of lumbar spine surgery, history of difficult dural tap, and grading of palpated landmarks was similar between the 2 groups with the exception of weight (Table 1). The mean weight in group C was 84.8 kg (SD = 14.4) vs 78.1 kg (SD = 17.8) in group P (P = 0.04), but there was no difference in body mass index between the 2 groups.

Table 1

Table 1

The mean number of passes (the primary outcome variable) in group C was 8.2 (SD 12.3) vs 4 (SD 4) in group P (Table 2). The average number of passes in group P was approximately 0.34 times that of group C, and this difference was statistically significant (P = 0.01). The average number of attempts in group P was approximately 0.25 times that of group C (P = 0.0021; Table 2). Because of the distribution (negative binomial) and type (count) of data, we used a zero truncated, negative binomial regression model and hence one should be mindful of the small sample size (n = 100) when interpreting the results. On comparing variables for successful dural puncture (Table 3), 84% of patients in group P had a successful dural puncture on the first attempt compared with 60% in group C (χ2 test, P = 0.0075). On subgroup analysis of number of passes at each level in group P, L5 to S1 had a tendency toward a smaller number of passes (mean 2 ± 1) compared with L4 to L5 (mean 4.27 ± 4.1) and L3 to L4 (mean 5.15 ± 5.01) although not statistically significant (P = 0.15). There was no evidence of differences among the 3 anesthesiologists in terms of number of passes (zero truncated binomial regression, P = 0.97, likelihood ratio χ2 = 0.06) or attempts (zero truncated binomial regression, P = 0.36, likelihood ratio χ2 = 0.83).

Table 2

Table 2

Table 3

Table 3

Alternative techniques were used in 6 patients in group C (technique used—ultrasound-guided paramedian spinal) and 2 patients in group P (technique used—midline approach by conventional palpation). There was no significant difference between the 2 groups in requirement for alternative techniques (Fisher exact test, P = 0.27). Despite the use of alternative techniques, dural puncture could not be achieved in 3 of the 6 patients in group C. Successful dual puncture was achieved in both patients in group P in whom an alternative technique was used.

It took the operator on average 81.5 seconds longer (99% CI, 68.4–97 seconds) to identify the landmarks in group P than in group C (P = 0.0002). The dose range of intrathecal bupivacaine was between 14 and 18 mg. Other parameters were comparable between the groups (Tables 4 and 5). All 5 patients in the study who had radicular pain or paraesthesia during needle placement were followed up for 24 hours postsurgery, and none of them had persistent symptoms.

Table 4

Table 4

Table 5

Table 5

Of the 5 patients in group C who required general anesthesia (GA), failure to perform spinal anesthesia was the reason in 3 patients. Of the other 2 patients who required GA, 1 had pain on incision and 1 developed abdominal pain during the surgery. Of the 4 patients in group P who needed GA, 3 patients reported pain on incision and 1 patient became difficult to sedate 30 minutes into the surgery.

The interspinous level at which the spinal was performed was significantly different between the 2 groups with P = 0.0025 (Table 6). Four patients in group C had their spinal performed at L2 to L3 versus none in group P (Fisher exact test; P = 0.05).

Table 6

Table 6

Table 7

Table 7

There was no difference within the quality of ultrasound views (Table 7) and number of passes or attempts for both TM (P = 0.49, P = 0.19) and PSO (P = 0.43, P = 0.32) views.

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DISCUSSION

The use of a preprocedural ultrasound-guided paramedian spinal technique resulted in a >50% reduction in the number of passes required for success compared with a conventional landmark-based midline approach in patients undergoing total hip or total knee arthroplasty. In addition, a preprocedural ultrasound-guided paramedian spinal technique significantly reduced the number of attempts and increased the first attempt success rate in achieving dural puncture. The number of passes was greater in our control group compared with the referenced study.13 This might be because of a number of reasons. First, the patient population was different. Mean age and body mass index in our study were 65.2 years and 30 kg/m2, respectively, versus 56.2 years and 23.8 kg/m2 in the referenced study. Second, in the study by Kim et al.,13 the number of passes was self-reported, whereas in our study, it was recorded by an independent observer. This is important, because it has been shown that the self-reported number of passes is always lower than the actual number of passes.

To date, the routine use of preprocedure ultrasound in the general adult or obstetric populations has not been shown to improve the number of passes or attempts needed to achieve successful dural puncture.11,15 We note a reduction in number of passes required to enter the subarachnoid space because of the following probable reasons. First, the age of our population group was, on average, 64.3 years (SD = 12.8), and spinal anesthesia has been shown to be more difficult in an older population compared with a general adult population.16 Second, we used a paramedian approach to the neuraxis (guided by ultrasound), which has not been studied so far. In the presence of interspinous ligament calcification and an inability to achieve adequate flexion (both of which are common in the elderly), this paramedian approach might be valuable. It has also been shown that both the length and the width of the lumbar spinous process increase significantly with aging, which further narrows the interspinous space available for a midline approach.17 The interlaminar space is least affected by changes attributable to aging and offers a potential window for spinal anesthesia. The same reasons explain why the PSO view consistently yields a clearer image of LFD and PLL compared with TM view.12,18,19 Although a paramedian approach for epidural catheter placement has technical advantages compared with the midline approach,20 previous studies on the landmark-guided paramedian versus midline approach to spinal anesthetic have yielded mixed results.21–23 It is conceivable that the advantages of the paramedian approach were more pronounced in our orthopedic population. Third, we used both the probe angle and the midline marking to aid paramedian insertion of the spinal needle. Using a midline approach, the needle angle is only guided by the operator remembering the angle of the probe. Because even small changes in angle of needle insertion and entry point can cause significant changes to where the tip of the needle finally ends up, we believe the addition of another skin marking at the midline to guide the angle of the needle might have played an important role.

Finally, studies that showed no difference on routine scanning investigated first-pass success rates between the 2 groups (success at first attempt and first pass). We chose to look specifically at the number of passes required in each group. We believe that using only first-pass success rates may risk overlooking important between-group differences.

Establishing landmarks took on average 81.5 (99% CI, 68.4–97.1) seconds longer in group P. In a study by Chin et al.,10 using similar endpoints, this process in the ultrasound group took 240 seconds longer. The difference might be because of the fact that in their study, scanning was done in patients with difficult surface landmarks, and it involved marking 3 interspinous spaces. Our study population included all patients, and we marked only one interspinous space, because we wanted it to reflect real-time practice. Likewise, we found no difference in the time taken to perform spinal anesthetic, probably reflecting its routine use in all patients.

The study does have limitations. First, neither the observer nor the attending anesthesiologists were blinded to the study group. The fact that the ultrasound group would have skin markings and the difference in the direction of needle insertion would have made blinding very difficult. A potential for bias cannot be excluded. Second, the procedure is heterogeneous with multiple factors affecting the number of passes, including individual anesthesiologist preference and style of practice and the number of attempts and/or time taken before using alternate methods. This reflects daily clinical practice. Having a single anesthesiologist perform all procedures might limit the differences because of the aforementioned reasons, but it might also be more apt to reflect individual bias and lack of validation. Third, neuraxial ultrasound has limitations. TM views for a midline approach to dural puncture have a positive predictive value of up to 85% but a negative predictive value of just 30%.12 Also, ultrasound views are generally more difficult to acquire in the elderly because of anatomical changes (facet hypertrophy, interspinous, and supraspinous ligament calcification).24 In addition, the necessity to remember the angle of approach of the needle and the inaccuracies of skin markings can further decrease the utility of ultrasound views in patients with a longer distance between skin and dura mater.

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CONCLUSIONS

The use of paramedian spinal anesthesia in an elderly orthopedic population, guided by preprocedure ultrasound examination, significantly decreases the number of passes and attempts needed to reach the subarachnoid space.

Spinal anesthesia is still largely a blind procedure. An ultrasound beam may prove better than a needle for locating the target.

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ACKNOWLEDGMENTS

The authors would like to acknowledge our statistician Margaret M. Cole (MSc, Graduate School of Medicine and Health, University College Cork) for her invaluable contribution and guidance on the completion of this manuscript.

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DISCLOSURES

Name: Karthikeyan Kallidaikurichi Srinivasan, MBBS, FRCA, FCARCSI, MRCPI, MD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: Karthikeyan Kallidaikurichi Srinivasan has seen the original study data, reviewed the analysis of the data, approved the final manuscript, and is the author responsible for archiving the study files.

Name: Gabriella Iohom, MD, PhD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: Gabriella Iohom has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Name: Frank Loughnane, FFARCSI.

Contribution: This author helped design the study and conduct the study.

Attestation: Frank Loughnane has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Name: Peter J. Lee, FFARCSI, MD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: Peter J. Lee has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

This manuscript was handled by: Terese T. Horlocker, MD.

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