Algorithm for the anesthetic management of cesarean delivery in patients with unsatisfactory labor epidural analgesia

Category 1 cesarean delivery (Figure 1)

The first management decision is based on the airway examination and the anesthetist's assessment as to whether the in situ epidural catheter is likely to provide adequate surgical anesthesia. Due to time constraints, this assessment should be based simply on the existence or not of a discernable neuraxial block.

Figure 1. Schematic of Category 1 cesarean delivery algorithm.

If there is a discernable bilateral block, a bolus dose of 15–20 mL of a rapid-acting local anesthetic should be injected though the epidural catheter (Figure 1a). According to a recent meta-analysis²⁰, a mixture of lidocaine and epinephrine with fentanyl injected into the epidural catheter can achieve one of the fastest sensory blocks in approximately 3 minutes. Alkalinization of the epidural solution with sodium bicarbonate (1mEq/10 mL) can significantly speed the onset of epidural anesthesia²¹, however it requires increased preparation time²² and can lead to medication errors, especially in the stressful environment of an emergent cesarean delivery²².

Administering a bolus can be justified because administration of supplemental local anesthetic in a higher volume can facilitate spread in the epidural space into previously spared areas²³, while carrying a relatively small risk of unintentional intravascular (1:5000)²³ or intrathecal injection (1:2900)²⁴. In contrast, administering general anesthesia for cesarean delivery has a much higher risk (1:238)²⁵ of failed intubation. Therefore, especially in patients with predicted difficult airways, every effort should be made to avoid general anesthesia. Preoxygenation and preparation for general anesthesia can begin once the patient is in position, even while dosing the epidural anesthetic.

Given the time constraints, a quick reassessment of the neuraxial block should be performed at the time the surgeon is ready to make the incision (Figure 1b). Loss of sensation to light touch bilaterally at the dermatomal level of T5 or above is the most reliable method to ensure satisfactory surgical anesthesia. Assessment using other modalities such as loss of sensation to cold and pin-pricks are less reliable^26,27. In addition, before incision, the surgeon should be asked to test the dermatomal level of the neuraxial block by sharp-touch.

If satisfactory epidural surgical anesthesia cannot be achieved, general anesthesia should be induced to guarantee effective surgical anesthesia and cesarean delivery (Figure 1c). In order to increase the safety of conversion to general anesthesia, the patient’s position should be optimized for intubation, efficient pre-oxygenation performed, and airway backup equipment should be available.

Category 2 cesarean delivery (Figure 2)

A more thorough assessment of the neuraxial block can be performed and should include the height, density and distribution of analgesia (unilateral or bilateral). Should a block be present, fractioned doses of a mixture of local anesthetics and opioids should be administered though the epidural catheter in an attempt to rescue the epidural block (Figure 2a). Caution should be used not to exceed local anesthetic toxic levels. The epidural block level should be reassessed (Figure 2b) and if found to be unsatisfactory, an immediate conversion to general anesthesia should occur (Figure 2c).

Figure 2. Schematic of Category 2 cesarean delivery algorithm.

In patients with no evidence of neuraxial blockade, spinal anesthesia may be considered (Figure 2d), as this has been described to be almost as quick as a general anesthetic in experienced hands. Kinsella et al.²⁸ described a “rapid sequence spinal” technique; a non-touch technique allowing only limited attempts, no local skin infiltration, and necessitating 8 minutes (on average) to complete. This is a newly described and not yet universally accepted technique. Criticisms of this “rapid sequence spinal” technique include the lack of aseptic preparation and the inability to establish a prior rapport in an anxious patient^29,30.

Alternatively general anesthesia could be used, as this is the quickest approach to reliably anesthetize the patient for cesarean delivery. Clinical situations that would favor immediate conversion to general anesthesia include the presence of an analgesic window; neuraxial dermatomal levels below T12; a unilateral block that differs by more than two or three dermatomal levels or insufficient analgesic density with uneven distribution of numbness to soft touch.

Category 3 and 4 cesarean delivery (Figure 3)

In a situation where there is no maternal or fetal compromise, a complete evaluation of the degree of the motor and sensory block can be performed. Epidural sensory block should be assessed for the highest dermatomal level at which the patient is able to detect a change in sensation to light touch, bilateral distribution and potential analgesic windows. The degree of epidural motor block can be assessed using a modified Bromage score (1 = able to raise legs above table, 2 = able to flex knees, 3 = able to move feet only, 4 = no movement in legs or feet).

Figure 3. Schematic of Category 3 and 4 cesarean delivery algorithm.

In patients with residual block there are three management options:

Option A – Trial of epidural (Figure 3a). The most common situation encountered in clinical practice is a patient with some degree of sensory and/or motor block. In this situation, fractioned epidural administration of one quarter to one third of the final anticipated dose is indicated in order to ascertain whether the anesthesia will be effective before injecting the entire dose. If this trial of epidural fails, one can proceed to either a combined spinal epidural (CSE) anesthetic (Figure 3-1), continuous spinal (Figure 3-2), or general anesthesia (Figure 3-3).

A CSE allows the use of a lower intrathecal dose with the additional flexibility of supplementation of the block through an epidural catheter. Portnoy and Valdhera¹⁰ recommend decreasing the dose of local anesthetic injected intrathecally by 20–30% to avoid a high spinal block. Intrathecal doses of bupivacaine as low as 4.5–6.5 mg have been used successfully for cesarean delivery^31,32. A standard dose spinal anesthetic at this stage could result in an unpredictable cephalad extension of the neuraxial block (vide infra)³³.

Although controversial, a continuous spinal catheter is a viable option for cesarean delivery after failed epidural analgesia³⁴. The advantage of a continuous spinal technique lies in the immediate confirmation of a successful block, and the ability to use careful titration of local anesthetics in boluses or as a continuous infusion. 5.0 mg of 0.5% preservative-free bupivacaine, plus 15 µg fentanyl can be initially injected intrathecally, followed by 2.5 mg boluses of 0.5% bupivacaine every 5 minutes until a T5 dermatomal level is achieved³⁴.

General anesthesia would assure a reliable anesthetic for cesarean delivery.

Option B - Remove the epidural catheter and perform a CSE or a de novo epidural (Figure 3b). An alternative to option A is to remove the epidural catheter as soon as the decision to perform a cesarean delivery is made and then replace the epidural catheter or administer a CSE. This option should be considered especially in patients where previous attempts to rescue labor epidural analgesia have been performed (withdrawal of the epidural catheter by 1 cm followed by top-up with local anesthetics and opioids).

Option C - Allow the residual block to recede and perform a single shot spinal anesthetic (Figure 3c). This option may be recommended especially in patients presenting with unilateral block and a very high level of sensory block on one side. One should wait until the residual epidural block wears off before a spinal anesthetic is performed. It has been recommended to wait at least 30 minutes after the last epidural bolus before initiating a spinal anesthetic¹⁰. This is because there is an associated risk of a subsequent high block especially after administration of a recent epidural bolus just prior to a spinal anesthetic^20,35. The described cephalad spread of the block can result from the compression of the spinal space by the previously injected epidural solution and/or the leakage of the epidural solution into the intrathecal space¹⁰.

General anesthesia may become the preferred choice if the mother or fetus’ condition change, the total dose of local anesthetic administered approaches the potential for toxicity, or after multiple failed attempts at neuraxial anesthesia.

In patients with no residual block a spinal anesthetic can be safely performed.