A cohort study of anatomical landmark-guided midline versus pre-procedure ultrasound-guided midline technique of spinal anesthesia in elderly patients undergoing orthopedic surgery.

BACKGROUND AND AIMS: The primary objective of the study was to compare the number of attempts and number of passes of spinal needle insertion and secondary objective was to compare complications, bloody tap, and patient discomfort in anatomical landmark-guided versus pre-procedure USG-guided midline technique of spinal anesthesia in elderly patients posted for orthopedic surgery.
MATERIAL AND METHODS: In this a prospective observational cohort study, 60 patients of either sex, ASA grades I-III, and aged more than 65 years were randomly allocated to 2 groups of 30 patients each. In group AG (Anatomical landmark guided), standard landmark technique was used. In group UG (Ultrasound guided), pre-procedure ultrasound guided marking for insertion point of a spinal needle was done before giving spinal anesthesia. Patients in both the groups were compared on the basis of number of attempts, number of passes, vascular injury (bloody tap), pain score, complications, and procedure time.
RESULTS: Successful dural puncture on the first needle insertion attempt was achieved more in UG group (90%) than in AG group (50%) (P < 0.05). Dural puncture was not achieved in only 3.3% patients in the UG group even after three midline attempts at spinal needle insertion. Mean of the number of passes was more in AG group (1.90) than in UG group (1.07) (P < 0.05). VAS (Visual Analogue Scale) score was 0.4 in AG group and 0.3 in UG group (P > 0.05). Group UG had shorter procedure time (2.25 min) than AG group (4.35 min).
CONCLUSION: Preprocedure ultrasound imaging is a very useful tool to facilitate the performance of central neuraxial blockade in patients with difficult anatomical landmarks, especially in elderly patients. Copyright:

Introduction

A report in India by Kaniset al in 2004 estimated an annual incidence of 600,000 osteoporotic hip fractures,[1] and this was expected to increase significantly. Spinal anesthesia is the most preferred technique for elderly patients with multiple comorbidities as it decreases the chances of deep vein thrombosis, surgical site infection, and reduces intraoperative bleeding.[23] Traditionally, spinal anesthesia has been accomplished using the surface anatomical landmark-guided technique by palpation of tips of the spinous process and the intercristal line.[4] Directing the needle into the vertebral canal is sometimes difficult in elderly patients because of narrow interspinous and interlaminar spaces, ossification of ligaments, and hypertrophy of facet joints. Therefore, the failure rate of spinal anesthesia in elderly patients is as high as 4–17%.[56] The highest level of technical difficulty is evidenced by prolonged procedure times and multiple needle passes.[7] Multiple attempts result in increased incidence of complications like postdural puncture headache, bloody tap, and neurological injury. Preprocedure ultrasound scanning of spine before spinal anesthesia or spinal anesthesia given under real-time ultrasound guidance helps to overcome all these limitations over conventional anatomical landmark technique. Very limited data are available in the literature about the use of ultrasound in elderly patients.

The present study was designed to test the hypothesis that the success rate of preprocedure USG-guided midline technique and blind anatomical landmark-guided midline technique of spinal anesthesia would be different in elderly patients posted for orthopedic surgery.

Material and Methods

This was a prospective observational cohort study conducted in 60 patients of either sex, ASA grades I–III, and aged more than 65 years, undergoing elective lower limb orthopedic surgery during a period of 1 year (CTRI/2017/11/010567). The sample size was calculated as in [Table 1].

Table 1

Calculation of sample size

Two-sided significance level (1-alpha)	95
Power (1-beta, % chance of detecting)	90
Ratio of sample size Unexposed/Exposed	1
Percent of unexposed with outcome	38
Percent of exposed with outcome	80
	Fleiss with CC
Sample size - exposed	30
Sample size - nonexposed	30
Total sample size	60

Before starting the study, institutional review board approval was obtained. Written informed consent was taken from all the patients. Patients less than 65 years, ASA grades IV and V, having bleeding tendency and coagulopathy, local infection at spine, known allergy to local anesthetic, obesity, and spinal deformity were excluded from the study.

Inside the operation theater, standard ASA monitors were applied to the patient and intravenous access was obtained. The patients were randomly divided into 2 groups of 30 each. In group AG, spinal anesthesia was given using conventional surface anatomical landmark-guided midline technique. In the ultrasonography (UG) group, the ultrasound imaging of the lumbar spine in the sitting position was performed by an anesthesia fellow. Actual procedure was assisted by fellow guide experienced with the use of ultrasound machine for >5 years. A low-frequency (2–5 MHz) curved array probe was used. The sonographic appearance of the lamina produces a pattern that resembles the head and neck of a horse, which Karmakar and colleagues[8] referred to as the “horse head sign” [Figure 1].

Figure 1

Horse-head like appearance of lamina (horse head sign)

When the transducer was moved slightly lateral from the paramedian sagittal plane at the level of the lamina, the articular processes of the vertebra were seen. The articular processes appear as one continuous, hyperechoic wavy line with no intervening gaps at the level of the lamina. The articular processes in a sagittal sonogram produce a sonographic pattern that resembles multiple camel humps, which were referred to as the “camel hump sign” as described by Karmakar et al.[8] [Figure 2]. Further when the transducer was moved more laterally, transverse processes in the appearance of trishula were seen which is described as “Trident sign” [Figure 3].

Figure 2

Camel-hump like appearance of articular processes (camel hump sign)

Figure 3

Trident sign (transverse process)

In the UG group, ultrasound probe was placed first on sacrum which corresponded to the white hyperechoic line on ultrasound [Figure 4]. When the probe was moved cranially the first gap seen was L5–S1 gap. The probe was then slid upward to mark L4–L5 and L3–L4 interlaminar spaces. At each level, the probe was turned horizontally to see transverse midline interlaminar view [Figure 5]. The space in which we could see the anterior complex was chosen to give spinal anesthesia; at that level, skin marks were made at the midpoint of the probe's long and short edges [Figure 6]. The intersection of these two marks provided an appropriate needle insertion point for a midline approach. The angulation of the probe corresponded to the needle trajectory.

Figure 4

White hyperechoic line on ultrasound (Sacrum)

Figure 5

Transverse midline interlaminar view (AC – Anterior complex, PC – Posterior complex, AP – Articular process, TP – Transverse process)

Figure 6

Markings at midpoint of the probe's long and short edges

Spinal anesthesia drug was given in both the groups after observing a clear flow of CSF. Both the ultrasound scanning and spinal anesthesia were performed by the same operator. After three attempts of midline technique, paramedian technique of spinal anesthesia was tried. We changed the interspinous space when a bloody tap occurred. Success was defined by motor and sensory block up to T10 dermatome within 30 min of injection of the drug. We observed the patient for 24 h after giving spinal anesthesia for any significant sensory or motor deficit. Data were collected in terms of the number of attempts, number of passes, bloody tap (yes/no), patients comfort (visual analogue scale), complications, and procedure time (in min – time from entry of spinal needle till free flow of cerebrospinal fluid from the needle).

Statistical analysis

Data were compiled in MS Office Excel sheet and appropriate statistical tests (unpaired t-test, percentage analysis, and Chi-square test of significance) were applied to analyze the data. For all analysis, P < 0.05 was considered statistically significant. Association between the number of attempts and bloody tap was studied using Chi-square test. Association between the number of passes, procedure time, and VAS score was studied using Mann–Whitney test.

Results

60 patients were included in the study. No patients were lost to follow-up and there was no protocol violation. Successful dural puncture on the first needle insertion attempt was achieved more in the UG group than in the AG group (90% vs. 50%). In the UG group, successful backflow of CSF occurred in 27 patients in first attempt, compared to 15 in the AG group. Dural puncture was not successful even after three midline attempts of spinal needle insertion in ten (33%) patients in the AG group and one (3.3%) patient in the UG group. In these patients the paramedian technique was used. The difference in the number of attempts between the two groups was statistically significant (P = 0.002) [Figure 7].

Figure 7

Comparison between number of attempts in anatomical landmark- and USG-guided group (One = Single attempt, Two = Two attempts, Three = Three or more than three midline attempts)

Mean of number of passes was more in the AG group (1.9 ± 1.7) than in the UG group (1.1 ± 0.6, P = 0.029). Only one patient had a bloody tap without any neurodeficit postoperatively. VAS score was 0.4 ± 1.1 in the AG group and 0.3 ± 0.9 in the UG group (P = 0.960). None of the patients experienced complications like paresthesia, spinal hematoma, or headache. The mean procedure time (from entry of spinal needle till flow of cerebrospinal fluid from the needle) was 4.4 ± 3.7 min in the AG group which was more than the mean time in the UG group (2.3 ± 1.7, P = 0.002).

Discussion

Regional anesthesia is the technique of choice in geriatric patients undergoing orthopedic surgery.[8] Because of degenerative changes in the spine, anatomical landmarks are difficult to palpate. It is also difficult to get successful CSF flow due to ossification of ligaments. Hence, the ultrasound-guided imaging and marking followed by spinal needle insertion is the recent technique for difficult central neuraxial blockade.[91011] It also reduces the number of complications. There are many studies which describe its use for labor epidural,[1213] but very minimal data are available for its use in elderly patients undergoing orthopedic surgery. UG helps in the identification of interspinous space as visualization of anterior complex serves as a surrogate marker. Hyperechoic anterior complex signifies that ultrasound beam has penetrated the vertebral canal through the interspinous and interlaminar spaces.[14] USG helps to predict the degree of technical difficulty before the actual spinal block is performed. Thus, USG plays a vital role in decision-making before the spinal block.[15] USG is also useful to predict the depth to reach lumbar intrathecal and epidural spaces in order to decrease the number of puncture attempts.[16]

We failed to get a successful dural puncture in first attempt by midline technique in only one patient in the UG group and ten in the AG group probably because of old age-related changes in spinal anatomy. A single attempt by paramedian approach was successful in all these patients. We also noticed that in three patients in the UG group the marked point did not correlate with any anatomical landmark. Rabinowitz et al.[17] and Blomberg et al.[18] proved that the paramedian technique of spinal block was superior to midline technique in elderly patients. But this finding was not reproduced in other studies. In the present study, preprocedure scanning in the UG group required more time to mark puncture point, which was not needed in the AG group but this time was partially compensated by the shorter procedure time in the UG group. Thus in the UG group, the number of attempts, number of passes as well as procedure time decreased compared to AG group.

In the UG group, spinal block was performed by the clinical fellow with the help of experienced anesthesiologist who has worked with USG for more than 5 years, which results ultimately in decreasing number of complications such as paresthesia and bloody tap, thus improving patient comfort. This result was consistent with the findings of Chin et al.[16] Perlas et al.[19] concluded that neuraxial ultrasound increases the efficacy of lumbar epidural or spinal anesthesia by decreasing the risk of technical failure and the number of needle punctures required, which was consistent with our data. Lee et al.[20] showed that USG helps in detecting abnormal spine sonoanatomy and reduces complications. After marking the puncture point, we get an idea where exactly we have to insert spinal needle. The angle of needle direction either cephalad or caudad is decided by the angle to which the probe is tilted to obtain the optimal image.

There are some limitations of our study including: (1) both the observer and performer were not blinded (2) anesthesiologists who performed the spinal anesthesia were not constant although all of them were experienced ones; (3) we used a curvilinear probe with lower resolution as the spine was at a greater depth; at this depth, attenuation of image is common making it difficult to identify structures; (4) USG has a learning curve. The actual procedure was not guided by real-time imaging. We did not study the use of USG in the paramedian technique.

Conclusion

We from the results of the present study, it may be concluded that preprocedure ultrasound imaging facilitates the performance of central neuraxial blockade in patients with difficult anatomical landmarks, especially in elderly patients. We believe that it is a very useful tool as an increasing number of geriatric patients are coming for orthopedic surgeries.

USG-guided regional anesthesia is an evolving and exciting field, providing further improvement in the point of care (POCUS) anywhere and anytime.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.