Epidural Volume Extension (EVE)

Epidural Volume Extension (EVE) technique injects normal saline into the epidural chamber immediately after injection of local anesthesia into the intrathecal (or after subarachnoid/spinal block). Normal saline injection would widen the epidural space thus making the spread of local anesthesia in previous intrathecal injections and the distribution of cerebrospinal fluid to be higher (more cephalad), or it could be said that this EVE technique utilizes the volume effect of normal saline that decreases the volume of intrathecal space. The EVE technique may be useful for reducing the dose of local anesthesia injected intrathecally while still achieve an adequate block height for surgery, as well as for faster recovery of motor blockades. Unfortunately, for the risk of hypotension, the EVE technique does not significantly reduce this risk. Hypotension persists even though the hemodynamics (arterial blood pressure drop mean) is observed to be more stable.


Introduction
Epidural block provides anesthesia for either surgical or analgesic treatment in post-surgery and intrapartum pains.The presence of adipose tissue in epidural space affects the spread of injected local anesthetic agent, even it remains obscure if this prolongs the block duration (for its function as reservoir) or reduces the amount of available local anasthesia agents, thereby slowing the onset, or both.Notably, the onset of epidural block in the targeted dermatome is detectable in 5 -15 minutes (Chloroprocaine) and 15 -20 minutes (Bupivacaine, Ropivacaine, and Levobupivacaine).This onset is considered quite slow and wastes the time for starting a surgery in an emergency situation. 1n the last two decades, the combination of epidural and subarachnoid/spinal blocks is expected to solve the slow onset issue.This technique is known as Combined Spinal-Epidural (CSE).Faster onset is not the only benefit of CSE technique.The other benefits are: low failure rate, more intense motoric blockade compared with only epidural block, epidural catheter enables the blockade extension and supplementation when subarachnoid/spinal block is inadequate, including to enable the administration of low-dose local anesthetic agent on cesarean section for preventing the tendency of anesthesiologist to administrate a high dose to ensure the block's completion (the presence of epidural catheter becomes a kind of "protective net" for anesthesioloigist to administrate lowe dose).

Epidural Volume Extension (EVE) : Technique and Mechanism
Medulla spinalis is the extention of medulla oblongata.Medulla spinalis has three layers : dura mater, arachnoid mater and pia mater.These three concentrically arranged membranes form compartments, namely: the epidural space, the subdural space and the subarachnoid space.The subarachnoid space is formed by the arachnoid mater and pia mater.Here there are spinal nerves, dorsal and ventral nerve roots, and cerebrospinal fluid.The epidural space is the potential space between the dura mater and attached to the ligamentum flavum.Here there are fat, epidural veins, nerve fiber roots, and connective tissue. 1 The Epidural Volume Extension (EVE) technique involves injecting normal saline into the epidural space immediately after intrathecal injection of local anesthesia (or after subarachnoid/spinal block).Theoretically, normal saline injection would widen the epidural space in order to make the spread of local anesthesia on the previous intrathecal injection and the distribution of cerebrospinal fluid to be higher (more cephalad), or in other words, this EVE technique utilizes the volume effect of normal saline which suppresses the volume of the intrathecal space.The first affecting factor is the fluid used to cause the volume effect.The selection of normal saline to produce a volume effect is based on safety considerations; no side effect of saline is found when large volume is used.Other fluids that have been studied for comparison with normal saline are 6% hydroxyethyl starch (Hespan) and low-dose local anesthesia.The use of Hespan presents an optimal hemodynamic profile (outcome) with normal saline. 6The volume of normal saline used is quite variable, between 5 -20 ml.Kane, et al (2018) through their systematic review and meta-analysis, discovered that a volume of 10 ml is the most consistent for causing a volume effect, or in other words, proved to increase the level of sensory blockade.In parturients, this volume could be smaller, which is up to 5 ml.
Normal saline injection is performed after intrathecal local anesthetic injection, rapidly for 10-15 seconds, and immediately.There is no standardization of how long "immediately" is meant.Existing studies inject normal saline between immediately up to 10 minutes.However, immediate injection and before the patient in supine position has been proved to give the best volume effect.This shows that the EVE technique is basically a time-dependent phenomenon, the sooner normal saline is injected, the better the results.The increase in block height ranged from 3-4 dermatomes from the level that was declared adequate for the operation, however in some studies, there was no increase in block height at all. 7,8,9egarding the local anesthetic used, the questions that must be answered include: what type of drug is it, how much is the dose, how much is the concentration, and how is the baricity.So far, Bupivacaine and Levobupivacaine are the two most frequently studied agents for the use in EVE technique.The greatest variation was found in the concentration and dose used.Existing studies have used hyperbaric Bupivacaine 0.5% at a dose of 6 -18 mg, where 9 mg was the most common, and Levobupivacine 0.15 -0.5% at a dose of 6 -12 mg. 8 In other study, Naaz et al (2020) used 0.75% Ropvacaine without comparing it to other agents.The need for analgesic supplementation in the group using normal saline for EVE compared to the control group (without EVE) was found to be not statistically significant.However, when small doses of local anesthetic are added to the EVE solution, it is found that the need for analgesic supplementation may decrease. 5,8covery from motoric blockade is one of the outcomes measured.In patients with EVE, recovery from motoric blockade assessed by the Bromage score occurs more rapidly.Recovery from motoric blockade, according to researchers, supports the implementation of Enhanced Recovery After Surgery (ERAS): beneficial for early mobilization and faster removal of urinary catheters.The onset of sensory blockade (adequate for surgery) in both groups (EVE and without EVE) was found to be the same.

5,11
The most important outcome assessed was the incidence of hypotension in EVE.
Can EVE reduce the incidence of hypotension?The systematic review and meta-analysis conducted by Heesen et al (217) and Terri et al (2018) showed statistically, the risk of hypotension was not significantly reduced in patients treated by EVE. 5,11Another study, namely the Randomized Controlled Trial, Naaz, et al (  2020) found that although the magnitude of hypotension that occurred was the same between the EVE and non-EVE groups, the EVE group was observed to be hemodynamically more stable (Graph 1) and still achieve the intended block height target, compared to using a higher dose in the same patient, therefore the researchers recommend this technique if you look for the better hemodynamic stability caused by the use of a lower dose of local anesthesia.
Naaz, et al (2020) used a study design on geriatric patients over 60 years old who were undergoing lower limbs orthopedic surgery.In the treatment group, 10 ml of normal saline was injected within 5 minutes after giving 3 ml of Ropivacaine 0.75% intrathecally; while in the control group, normal saline was not injected.The researcher entered the operating teather after the patient was in supine position.Hemodynamic monitoring (systolic blood pressure, diastolic and heart rate) was performed every 5 minutes for 30 minutes after intrathecal injection and thereafter every 15 minutes until surgery was concluded. 10aphic 1.Comparison of Mean Arterial Pressure to Time (Naaz, et al, 2020)  • Sample Total = 1670 people 5 -10 ml normal saline • 7,5 -12,5 mg 0,5% hyperbaric Bupivacaine • 6 -12 mg 0,15 -0,5% Levobupivacaine • 8 studies achieved T4 • 4 studies achieved T5 • 2 studies achieved T4-T5 • 3 studies achieved T6 • 13 studies achieved 0-4 dermatoms above the adequate block height for surgery Regarding the hypotension risk, conclusion from existing researchers have not shown that EVE technique reduces the risk of hypotension incidence, yet it could provide a more stable hemodynamic (even if hypotension occurs, the drop in blood pressure is not sudden).
This conclusion is based on the significantly limited amounts of studies.The sample amounts of low and high heterogeneity, along with high technique variations become the limitations of the studies which discuss on EVE technique.More future studies are expected to explain the relationship between the outputs found.

Figure 1 .
Figure 1.Epidural Volume Extension (EVE) Mechanism.The black arrows show the cerebrospinal fluid flow (including local anesthesia) after saline injection into epidural space 5

Table 1 .
Factors which Affect the Height of Subarachnoid/Spinal Block 4 Tabel 2. Comparison of Researches on EVE Published in the Last 5 Years 10Below is the table of the comparison between researchers on EVE published for last 5 years.55 DOI: 10.22146/jka.v11i1.12598e-ISSN 2354-6514 ConclusionEVE technique is expected to be useful to reduce the local anasthesia dosage by intratecal injection while keep achieving adequate block height for surgery, and for faster recovery from motoric blockade.