Epidural pressures and spread of 2% lidocaine in the epidural space: influence of volume and speed of injection of the local anesthetic solution

Programmed intermittent epidural bolus for labour analgesia: a randomized controlled trial comparing bolus delivery speeds of 125 mL·hr-1 versus 250 mL·hr-1

PURPOSE

Programmed intermittent epidural bolus (PIEB) provides better analgesia for labour pain than continuous epidural infusion does. Nevertheless, commonly used PIEB regimens are associated with high sensory block. We hypothesized that a PIEB technique with slower bolus delivery speed would produce lower sensory levels.

METHODS

We recruited term nulliparous women with singleton pregnancies during the first stage of labour. All participants had an American Society of Anesthesiologists Physical Status score of II-III, had epidural catheters placed at L3/4, and had epidural analgesia maintained with PIEB 10 mL every 40 min using 0.0625% bupivacaine with fentanyl 2 µg·mL^-1. Women were randomized to receive PIEB delivered at 250 mL·hr^-1 (G250) or 125 mL·hr^-1 (G125). The study was completed six hours after the loading dose or at full cervical dilatation, whichever occurred first. The primary outcome was the presence of sensory block to ice ≥ T6 in at least one assessment during the study period (maximum six hours).

RESULTS

We analyzed data from 90 women. The proportion of women presenting sensory block ≥ T6 at any time was not different between G125 and G250 groups (60.0% vs 64.4%; difference, -4.4%; 95% confidence interval [CI], -24.5 to 15.6; P = 0.66). The median [interquartile range] highest sensory block level was also not different between G125 and G250 groups (T6 [T7-T5] vs T5 [T7-T5], P = 0.39). Women in the G125 group had a lower incidence of hypotension than women in the G250 group did (11.1% vs 33.3%; difference, -22.2%; 95% CI, -38.8 to -5.67; P = 0.01). Quality of analgesia and patient satisfaction were not different between groups.

CONCLUSION

The maintenance of epidural analgesia with a PIEB delivery speed of 125 mL·hr^-1 did not produce lower sensory block levels when compared with 250 mL·hr^-1. The slower injection speed regimen was associated with lower incidence of hypotension, but this secondary finding warrants confirmation in a future trial.

TRIAL REGISTRATION

www.ClinicalTrials.gov (NCT03236298); registered 1 August 2017.

Epidural space "ballooning" during local anaesthetic injection in infants and children: An ultrasound observational study

BACKGROUND

Infants and children require a larger dose of a local anaesthetic (LA) to establish epidural analgesia than adults, but the reason for this remains unclear. We hypothesised that prominent ventro-dorsal expansion of the epidural space limits cranio-caudal spread of LA in infants. Accordingly, we studied the dimensions of the epidural space with real-time ultrasound (US) before and after epidural injection.

METHODS

Ninety-six infants and children aged 0-12 years who underwent abdominal surgery under combined epidural and general anaesthesia were examined in this prospective observational study. Using a micro-convex probe, US recordings of the posterior epidural space were performed while a LA (0.5 ml kg^-1 ) was infused at 0.54 ml s^-1 . The width in the ventro-dorsal dimension (VDD) of the posterior epidural space before and after injection was recorded; the change in VDD was defined as "ballooning". Correlations between "ballooning" and patient age, body mass index, and volume and rate of LA administration were analysed.

RESULTS

"Ballooning" correlated positively but weakly with age (R²  = 0.25; p < .001) and the infused LA volume (R²  = 0.32; p < .001). The "magnitude of ballooning" ("ballooning" per ml of injected LA) correlated negatively but weakly with age (R²  = 0.27; p < .001).

CONCLUSIONS

"Magnitude of ballooning" of the epidural space become inconspicuous with growing during epidural injection. This effect may slow the cranio-caudal spread of LA and explain partially why larger volumes of LA are required to effect a block in children.

Epidural pressure changes following caudal blockade: a prospective, observational study

PURPOSE

Recent case reports raise the question as to whether anesthetic agents injected into the epidural space could lead to a 'compartment syndrome' and neurovascular sequelae. Single-shot caudal epidural anesthesia has been established as a safe technique, but changes in pressure in the caudal epidural space have not been described. Our aim was to study pressure changes to provide preliminary information for future studies design.

METHODS

We prospectively measured the pressure changes in the caudal epidural space in 31 pediatric patients. The pressures were measured at loss of resistance, immediately after the bolus dose of local anesthetic (1 ml/kg), and at 15-s intervals up to 3 min.

RESULTS

The pressure at loss of resistance was 35.6 ± 27.8 mmHg. A pulsatile waveform was observed once the epidural space was accessed. The pressure after administration of the local anesthetic bolus (1 ml/kg 0.2 % ropivacaine/bupivacaine with 1:200,000 epinephrine) was 192.5 ± 93.3 mmHg. The pressure decreased to 51.5 ± 39.0 mmHg at 15 s, 26.9 ± 9.9 mmHg after 2 min, and 24.7 ± 11.7 after 3 min. The return to baseline occurred at approximately 45-60 s.

CONCLUSIONS

Following the administration of the local anesthetic into the caudal epidural space, there was a marked, but transient, increase in the pressure within the epidural space. It appears unlikely that a slow epidural catheter infusion could lead to a sustained increase in epidural pressure.

Epidural loss-of-resistance biomechanics: an open pilot cadaver study

Purpose

We measured dynamic biomechanics of loss-of-resistance (LOR) epidural placement in prone cadavers, focussing on the period immediately following LOR, to estimate forces acting on the tissue of the epidural space.

Methods

An epidural syringe with 17G Hustead needle was instrumented to track force on the plunger, pressure in the chamber, and movement of barrel and plunger. Insertions were attempted in five formalin-preserved cadavers from T2–3 to L4–5, using LOR with saline or air, and confirmed with X-ray.

Results

Sixteen insertions were successful. Soft tissues in formalin-preserved cadavers are much harder than in living humans. With continuous pressure on the plunger, fluid thrust through the needle at the point of LOR was significantly greater (P = 0.005) with saline (mean ± standard deviation [95% confidence intervals]: 19.3 ± 14.9 [8.3 to 30.3] N); than with air (0.17 ± 0.25 [0 to 0.39] N). Stress exerted on epidural tissue was similar (air = 7792 ± 920 [6986 to 8598] Pa; saline = 7378 ± 3019 [5141 to 9614] Pa); and in both cases was greater than the stress exerted by cerebrospinal fluid pushing outwardly on the dura (4800 Pa).

Conclusion

Formalin-preserved cadavers are too stiff to make them an experimental model from which we can generalize to live humans, although we were successful in entering the epidural space and testing the instrumentation for further studies on live animals or humans. Continuous pressure on the plunger while advancing the epidural needle may “blow” the dura away from the needle tip and help prevent dural puncture. Better results are seen with saline rather than air.

Hip-flexed postures do not affect local anaesthetic spread following induction of epidural analgesia for labour

Hip-flexed postures enlarging the pelvic diameter are used to improve the obstetric course of labour. Although most investigations show that lateral and sitting positions do not affect the spread of epidural analgesia, the effect of recently introduced hip-flexed postures has yet to be confirmed. This prospective randomised study included 93 parturients. Ropivacaine 0.1% 12 mL plus sufentanil 0.5 micrograms/mL was administered epidurally over a period of 6 min in one of four postures: sitting, right hip-flexed left lateral position, left hip-flexed right lateral position and supine 30 degrees lateral tilt as a control group. Left and right cephalad and sacral epidural spread were measured every 2 min over a period of 30 min. Pain relief, motor blockade and maternal and fetal side effects were noted. The total epidural spread was 15+/-0.3 dermatomes and the upper level of thermo-algesic blockade T7-T8 (range T3 to T10) in all groups. There were no differences between groups in left or right total spread or upper level of epidural blockade, time to maximal block or pain relief. There was no motor block nor any maternal or fetal side effects. The power of the study (1 - beta) was 93%. We conclude that, for the three hip-flexed postures tested, position does not influence local anaesthetic spread or symmetry of thermo-algesic blockade after induction of obstetric epidural analgesia.