Dural sac cross-sectional area is a highly effective parameter for spinal anesthesia in geriatric patients undergoing transurethral resection of the prostate: a prospective, double blinded, randomized study

The Relationship of Spinal Anesthesia Dosing Based on Thecal Sac Area to Anesthetic Failure in Lumbar Surgery

BACKGROUND AND OBJECTIVES

Greater thecal sac volumes are associated with an increased risk of spinal anesthesia (SA) failure. The thecal sac cross-sectional area accurately predicts thecal sac volume. The thecal sac area may be used to adjust the dose and prevent anesthetic failure. We aim to assess the rate of SA failure in a prospective cohort of lumbar surgery patients who receive an individualized dose of bupivacaine based on preoperative measurement of their thecal sac area.

METHODS

A total of 80 patients prospectively received lumbar spine surgery under SA at a single academic center (2022-2023). Before surgery, the cross-sectional area of the thecal sac was measured at the planned level of SA injection using T2-weighted MRI. Patients with an area <175 mm2, equal to or between 175 and 225 mm2, and >225 mm2 received an SA injection of 15, 20, or 25 mg of 0.5% isobaric bupivacaine, respectively. Instances of anesthetic failure and adverse outcomes were noted. Incidence of SA failure was compared with a retrospectively obtained control cohort of 250 patients (2019-2022) who received the standard 15 mg of bupivacaine.

RESULTS

No patients in the individualized dose cohort experienced failure of SA compared with 14 patients (5.6%) who experienced failure in the control cohort (P = .0259). The average thecal sac area was 187.49 mm2, and a total 28 patients received 15 mg of bupivacaine, 42 patients received 20 mg of bupivacaine, and 10 patients received 25 mg of bupivacaine. None of the patients experienced any adverse outcomes associated with SA. Patients in the individualized dose cohort and control cohort were comparable and had a similar distribution of lumbar procedures and comorbidities.

CONCLUSION

Adjusting the dose of SA according to thecal sac area significantly reduces the rate of SA failure in patients undergoing lumbar spine surgery.

Correlation of thecal sac cross sectional area to total volume

BACKGROUND

Spinal anesthesia (SA) has been increasingly utilized in lumbar surgery due to its various advantages over general anesthesia (GA), however failure of the first dose requiring intraoperative conversion to GA occurs in as many as 3.6% of SA patients. Some studies have reported that a larger thecal sac volume may dilute the anesthetic and play a role in first dose failure. Unfortunately, easy determination of thecal sac volume has not been reported in the literature. Thus, we sought to determine whether cross-sectional area obtained from MRI accurately predicts the volume of the thecal sac.

METHODS

We conducted a retrospective review of 80 patients who underwent lumbar surgery with spinal anesthesia. T1 and T2-weighted MRI sequences were used to measure thecal sac area at each level between L1-S1. The volume of the thecal sac was calculated using HorosTM. A statistical model was derived relating the area at each level to the thecal sac volume. Of the 80 patients, 20% were reserved and utilized to test the accuracy of the statistical model.

RESULTS

The area of the thecal sac positively correlated with volume at each lumbar level. The area of the thecal sac at the L4-L5 level most accurately represented total thecal sac volume (R2 = 0.588, RMSE = 2.76).

CONCLUSION

Cross-sectional area of the L4-L5 spinal level obtained from MRI sequences may be utilized as a proxy for thecal sac volume.

A Second Prone Dose Algorithm for Patients Undergoing Spinal Anesthesia During Thoracolumbar Surgeries

BACKGROUND

Spinal anesthesia is safe and effective in lumbar surgeries, with numerous advantages over general anesthesia (GA). Nevertheless, 1 major concern preventing the widespread adoption of this anesthetic modality in spine surgeries is the potential for intraprocedural anesthetic failure, resulting in the need to convert to GA intraoperatively.

OBJECTIVE

To present a novel additional prone dose algorithm for when a first spinal dose fails to achieve the necessary effect.

METHODS

A total of 422 consecutive patients undergoing simple and complex thoracolumbar surgeries under spinal anesthesia were prospectively enrolled into our database. Data were retrospectively collected through extraction of electronic health records.

RESULTS

Sixteen of 422 required a second prone dose, of whom 1 refused and was converted to GA preoperatively. After 15 were given a prone dose, only 2 required preoperative conversion to GA. There were no instances of intraoperative conversion to GA. The success rate for spinal anesthesia without the need for conversion rose from 96.4% to 99.5%. In patients who required a second prone dose, there were no instances of spinal headache, deep vein thrombosis, pneumonia, urinary tract infection, urinary retention, readmission within 30 days, acute pain service consult, return to operating room, durotomy, or cerebrospinal fluid on puncture.

CONCLUSION

Use of an additional prone dose algorithm was able to achieve a 99.5% success rate, and those who received this second dose did not experience any complications or negative operative disadvantages. Further research is needed to investigate which patients are at increased risk of inadequate analgesia with spinal anesthesia.

Dural sac cross-sectional area measured using ultrasound to modify the dosage of local anaesthetic in spinal anaesthesia for transurethral resection of prostate surgery: A prospective, double blind, randomised controlled study

BACKGROUND AND AIMS

The area of lumbar spinal canal decreases with age, and hence the level of sensory blockade is higher in the elderly after spinal injection. The present study optimised the dose of local anaesthetic in elderly patients based on the lumbar dural sac cross sectional area (DSCSA) determined using ultrasound.

METHODS

Sixty patients of age above 60 years undergoing transurethral resection of prostrate (TURP) surgery in a tertiary care hospital were included in the study. Patients were categorised into two groups of 30 each based on a computer-generated random number table. In the control group (C), 2 ml of 0.5% hyperbaric bupivacaine was given and in the ultrasound group (U), the drug dose was modified according to DSCSA which was measured using the formula area = p (diameter/2) ².

RESULTS

The DSCSA and bupivacaine dosage were significantly lower in group U compared to control group (P = 0.0001). The maximal level of cephalad spread of sensory blockade was significantly lower in ultrasound group, than in control group (P = 0.002). The two-segment block regression time and motor recovery time was less in group U. Higher mean arterial pressure (105.8 ± 9.66 mmHg; P = 0.007), and a lower decrease from baseline (14.15 ± 7.55%; P = 0.041) was noted in group U after subarachnoid block.

CONCLUSION

The estimation of DSCSA is an effective parameter and can be used to modify the dose of local anaesthetic for subarachnoid block in elderly patients undergoing TURP surgery.