Minimum effective dose of plain bupivacaine 0.5% for ultrasound-guided spinal anaesthesia using Taylor's approach

Inadequate Spinal Anesthesia in Lumbar Spine Surgery Is Related to Volume of the Thecal Sac

BACKGROUND

Spinal anesthesia (SA) is used in lumbar surgery, but initial adequate analgesia fails in some patients. In these cases, spinal redosing or conversion to general endotracheal anesthesia is required, both of which are detrimental to the patient experience and surgical workflow.

METHODS

We reviewed cases of lumbar surgery performed under SA from 2017-2021. We identified 12 cases of inadequate first dose and then selected 36 random patients as controls. We used a measurement tool to approximate the volume of the dural sac for each patient using T2-weighted sagittal magnetic resonance imaging sequences.

RESULTS

Patients who had an inadequate first dose of anesthesia had a significantly larger dural sac volume, 22.8 ± 7.9 cm3 in the inadequate dose group and 17.4 ± 4.7 cm3 in controls (P = 0.043). The inadequate dose group was significantly younger, 54.2 ± 8.8 years in failed first dose and 66.4 ± 11.9 years in controls (P = 0.001). The groups did not differ by surgical procedure (P = 0.238), level (P = 0.353), American Society of Anesthesia score (P = 0.546), or comorbidities.

CONCLUSIONS

We found that age, larger height, and dural sac volume are risk factors for an inadequate first dose of SA. The availability of spinal magnetic resonance imaging in patients undergoing spine surgery allows the preoperative measurement of their thecal sac size. In the future, these data may be used to personalize spinal anesthesia dosing on the basis of individual anatomic variables and potentially reduce the incidence of failed spinal anesthesia in spine surgery.

Comparing the minimum local anesthetic dose of ropivacaine in real-time ultrasound-guided spinal anesthesia and traditional landmark-guided spinal anesthesia: a randomized controlled trial of knee surgery patients

Background

Through previous studies and clinical practice, we have found that real-time ultrasound-guided (UG) spinal anesthesia (SA) and traditional landmark-guided (LG) SA each require a different minimum local anesthetic dose (MLAD) of ropivacaine. For this study, we used Dixon’s up-and-down sequential method to analyze and compare the MLAD of different ropivacaine concentrations required for the UG and LG SA methods.

Methods

A total of 120 patients undergoing knee surgery were consecutively recruited and randomly divided into four groups (30 patients per group). These groups were categorized as follows: Group I: high ropivacaine ultrasound-guided (HRUG), Group II: low ropivacaine ultrasound-guided (LRUG), Group III: high ropivacaine landmark-guided (HRLG), and Group IV: low ropivacaine landmark-guided (LRLG). SA was established by a bolus administration of up-and-down doses of 0.75% or 0.5% plain ropivacaine. Initial doses of 16, 18, 12, and 14 mg were administered to groups I–IV, and after that, increased or decreased by 1.5 mg according to dose effectiveness. Upon identifying the intervertebral puncture level, a lumbar X-ray was performed with metal markers, and actual radiographic findings were identified and compared to the initial markings.

Results

For UG groups, the MLAD in the LRUG group was significantly higher than in the HRUG group [20.192 mg (95% CI, 19.256–21.174) versus 17.176 mg (95% CI, 16.276–18.124), respectively; P<0.001]. For LG groups, the MLAD in the LRLG group was significantly higher than in the HLRG group [14.478 mg (95% CI, 13.364–15.500) versus 13.201 mg (95% CI, 11.959–14.571), respectively; P=0.047]. When comparing both high ropivacaine groups (HRGs: I/III) to the low ropivacaine groups (LRGs: II/IV), we found that both UG subgroups (I/II) had a significantly higher MLAD than LG subgroups (III/IV) (P<0.001). US identified L4–5 in up to 90% of cases. Comparatively, palpation was successful in only 33.3% of patients. The rates of cephalad localization by US and palpation were 6.67% vs. 66.67%, respectively (P=0.002).

Conclusions

We found a higher MLAD of ropivacaine was required for UG SA at the L4–5 level due to the method providing a more accurate (less cephalad) localization than traditional LG SA.

Trial Registration

Chinese Clinical Trial Registry ChiCTR2000033158.

Minimum local anesthetic dose of ropivacaine in real-time ultrasound-guided intraspinal anesthesia for lower extremity surgery: a randomized controlled trial

Background

Despite the many advantages real-time ultrasound-guided lumbar anesthesia has over traditional lumbar anesthesia, it seemingly involves a much higher dose of ropivacaine. This study aimed to determine the minimum local anesthetic dose (MLAD) and the 95% confidence interval of ropivacaine at different concentrations in real-time ultrasound-guided lumbar anesthesia for lower extremity surgery.

Methods

A total of 60 patients who were consecutively scheduled for selective lower extremity surgery were enrolled. The patients were randomly divided into two groups, which each received different concentrations of ropivacaine at different initial dosages when Dixon's up-and-down sequential method was applied. The high ropivacaine group and the low ropivacaine group received 0.75% and 0.5% ropivacaine, respectively. The patients' baseline characteristics, the MLAD, and the 95% confidence interval were assessed. The highest level of sensory block, time to reach the T10 sensory block, duration for sensory blocks higher than T10, highest plane for sensory block, and onset time and duration for motor block were recorded. Comparisons were also made between the patients' vital signs and adverse reactions.

Results

The minimum local anaesthetic dose (MLAD) and 95% confidence interval in the high ropivacaine group and the low ropivacaine group were 17.176 (16.276 to 18.124) and 20.192 (19.256 to 21.174) mg, respectively. Moreover, motor block maintenance was greatly reduced in the 0.5% ropivacaine compared to the 0.75% ropivacaine group (P=0.0309).

Conclusions

In real-time ultrasound-guided intraspinal anesthesia for lower extremity surgery, both 0.75% and 0.5% ropivacaine provide satisfactory anesthesia. Our results suggest that shortened motor block duration can hold benefits for patients including earlier mobilization and a quicker rehabilitation process.