Epidural volume extension: a review

Current status of the combined spinal-epidural technique in obstetrics and surgery

Epidural and spinal blocks are well-accepted neuraxial techniques but both have several disadvantages. Combined spinal-epidural (CSE) can combine the best features of both techniques and reduce or eliminate these disadvantages. It provides the rapidity, density, and reliability of subarachnoid block with the flexibility of catheter epidural technique to extend the duration of anesthesia/analgesia (and to improve spinal block). It is an excellent technique for determining minimum intrathecal drug doses. Although most commonly employed in obstetric practice, CSE is also used in a wide variety of non-obstetric surgical procedures including orthopedic, vascular, gynecological, urological, and general surgical procedures. The needle-through-needle technique remains the most commonly used method to perform CSE. Several technical variations including Sequential CSE and Epidural Volume Extention (EVE) are commonly used particularly in obstetric and high-risk patients such as those with cardiac disease where a slower onset of sympathetic block is desirable. The risks of complications such as epidural catheter migration through the dural hole, neurological complications, and subarachnoid spread of epidurally administered drugs are possible but have not been a clinically relevant problem in the 40+ years of their existence. In obstetrics, CSE is used for labor pain because it produces rapid-onset analgesia with reduced local anesthetic consumption and less motor block. The epidural catheter placed as part of a CSE is more reliable than a catheter placed as part of a conventional epidural. Less breakthrough pain throughout labor is noted and fewer catheters require replacing. Side effects of CSE include greater potential for hypotension and more fetal heart rate abnormalities. CSE is also used for cesarean delivery. The main purpose is to decrease the spinal dose so that spinal-induced hypotension can be reduced. However, reducing the spinal dose requires an epidural catheter to avoid intra-operative pain when surgery is prolonged.

Clinical utility of epidural volume extension following reduced intrathecal doses: a randomized controlled trial

Background and objectives

Epidural Volume Extension (EVE) involves instillation of normal saline into the epidural space soon after an intrathecal injection, with the aim to augment the sensory block height. Its clinical relevance lies in the possibility of using reduced intrathecal dose and yet achieving the desired sensory block level. Intrathecal dose is a known determinant of the level of sensory block. Whether EVE is dependent on intrathecal dose is not known.

Methods

We conducted a randomized, controlled, double-blind study to compare the maximum sensory level (S_max) achieved with or without application of EVE to two different reduced intrathecal doses. Eighty four adult male patients of ASA status I or II with body weight between 50–70 kg and height in the range of 150–180 cm, scheduled for orthopedic lower limb surgery using combined spinal epidural anesthesia were randomized to receive, either intrathecal dose (5 or 8 mg) with or without EVE, in accordance to group allocation.

Results

S_max was lowered by application of EVE to 5 mg intrathecal bupivacaine (T_8.9 ± 4.3 vs. T_6.4 ± 1.9 with and without EVE respectively; p = 0.030). S_max was similar when EVE was applied to 8 mg intrathecal bupivacaine than without it (T_5.8 ± 1.8 vs. T_6.4 ± 2.2 respectively; p =  0.324).

Conclusion

EVE should not be applied to 5 mg plain bupivacaine during a combined spinal epidural block in patients undergoing lower limb orthopedic surgery as it may result in a decrease in the maximum sensory level.

Inadvertent high spinal anesthesia as sequelae to epidural injection of normal saline

Here we present a case of high spinal blockade in a patient belonging to ASA Grade I which lead to need for endotracheal intubation. A 35 year old healthy male, weighing 59 kg, of height 165 cms presented with a post traumatic raw area over the left lower limb. A reverse sural graft along with skin grafting (from the thigh) was planned. In OR, the patient was placed in sitting position and the extradural space was identified by ‘loss of resistance to air’ technique at the L2-L3 intervertebral space. The catheter could not be threaded into the extradural space, hence 5ml of 0.9% saline was injected. However, still the catheter could not be negotiated. Further attempts to identify the extradural space at the L1-L2 and L3-L4 interspace levels were made. During these attempts a total of 18 ml of 0.9% saline was injected into the extradural space. Within 2 minutes blood pressure fell to 90/60 mmHg. Injection mephenteramine (3 mg) was given intravenously and a slight head up tilt was applied. After 2 more minutes the patient started complaining of tingling in his hands and difficulty in breathing. Oxygen 100% was administered via a face mask attached to the anesthesia circle system. In view of onset of respiratory failure, general anesthesia was induced. Thiopentone (200 mg) and Suxamethonium (75 mg) were given intravenously, the patient's trachea was intubated and his lungs ventilated with 40% oxygen, 60% nitrous oxide and 0.2-0.4% Isoflurane, without additional neuromuscular blockade. The arterial saturation promptly returned to 97% and, immediately after intubation, the heart rate was found to be 103 beats/min and the arterial BP 162/102 mmHg. At the end of surgery, spontaneous ventilation returned and the patient was allowed to breathe 100% oxygen via the tracheal tube until he awoke, when his trachea was extubated.

Minimum effective volume of normal saline for epidural volume extension

BACKGROUND

Rescue strategies like changes in tilt of table are used to raise the level of an inadequate sensory block following intrathecal injection. Epidural volume extension (EVE) refers to an injection of normal saline through epidural catheter following an intrathecal block. It results in a rapid increase in the sensory level of subarachnoid block. Thus, it has been postulated that EVE may be used as a rescue strategy for an inadequate post-spinal sensory block. However, the minimum effective volume (MEV) of normal saline for EVE induced increase in level of spinal block has not been researched till date. We proposed to determine the MEV of normal saline required for EVE induced increase in post-spinal block sensory level.

MATERIALS AND METHODS

This prospective sequential allocation study was conducted in consenting adult males after institutional ethical committee approval scheduled for lower limb surgery under combined spinal epidural (CSE) anesthesia, who had an inadequate level of sensory block. Herein, an inadequate level was defined as lower than T10 at 10 min after the intrathecal injection, with no ascent for two consecutive readings taken 2 min apart. The EVE was performed with normal saline injected through epidural catheter, and was considered successful if the level of sensory block increased by two or more dermatomal segments within 5 min of the injection. The volume of normal saline for EVE was decided by using the up-and-down method, with the first patient receiving 10 mL and a dosing interval of 1 mL in subsequent patients. The analysis was done using the formula of Dixon and Massey, which enabled calculation of the MEV with 95% CI. Quantitative parametric data is represented as mean ± SD and nonparametric data as median (range).

RESULTS AND CONCLUSION

The MEV of normal saline to raise the level of sensory block by two or more dermatomal segments within 5 min of EVE is 7.4 mL (95% CI: 5.5-9.9 mL).