Obstetric Anesthesia53
Neostigmine is an anticholinesterase that enhances analgesia by indirectly increasing spinal levels of acetylcholine.
At a spinal dose of 10 mcg, neostigmine fails to enhance labor anal-
•
gesia but produces severe nausea.
At epidural doses up to 500 mcg, preliminary studies indicate that
•
it enhances labor analgesia without producing nausea, but is still under investigation and cannot be recommended for routine use at this time.
54Pain Relief for Labor and Delivery
extend 11–15 mm past the tip of the epidural needle (Figure 3.2a and 3.2b ; Figure 3.3c ). Although epidural needles with separate spinal and epidural catheter lumens are available, to theoretically minimize the risk of unintentionally placing a spinal catheter, they are expensive.
Further studies have failed to demonstrate an increased risk, especially when the CSE is technically easy. As a result, the “needle through needle” approach is recommended (Figure 3.2b ).
A standard epidural needle is used to identify the epidural space.
•
A long spinal needle is inserted through the lumen of the epidural
• needle.
Spinal medications are administered via the spinal needle into the
•
intrathecal space, and the spinal needle is removed.
The epidural catheter is inserted as usual.
•
Anesthetic Technique
The contraindications to regional analgesia and anesthesia and the guide- lines for regional anesthesia previously described ( Tables 3.1 and 3.2 )
Table 3.10 Summary of Spinal Analgesia from Various CSE Solutions
Drugs Dose Duration (min) Side Effects ∗
Fentanyl 25 mcg 90
Fentanyl 25 mcg 108
Bupivacaine 2.5 mg Sufentanil 10 mcg 105 Sufentanil 10 mcg 150 Bupivacaine 2.5 mg
Sufentanil 10 mcg 188 Motor block
Bupivacaine 2.5 mg Epinephrine 200 mcg
Sufentanil 5 mcg 205 Sedation
Bupivacaine 2.5 mg Hypotension
Clonidine 50 mcg
Sufentanil 5 mcg 205 Sedation
Bupivacaine 2.5 mg Hypotension
Clonidine 50 mcg Nausea
Neostigmine 10 mcg
∗ Nearly all patients administered spinal opioids experience pruritus although it rarely requires treatment.
Obstetric Anesthesia55
also apply to CSE techniques. Procedurally, CSE and epidural tech- niques are similar, with only a few exceptions (also see recommended technique described in Table 3.11 ).
The sitting position, rather than the lateral decubitus position, is recommended for CSE placement. The sitting position offers several advantages.
Identifi cation of the midline is easier, which is essential for success-
•
ful dural puncture.
The position increases lumbar intrathecal pressure, making the
•
dura more taut and increasing the likelihood of a successful dural puncture.
(a)
(b)
Figure 3.2 (a) An epidural needle and a spinal needle from a standard CSE kit are pictured. The epidural needle is a 17g winged needle with a 9 cm barrel. The hub is specially designed to receive this particular spinal needle, which is a 27g 4 –11/16" Whitacre needle. (b) The tips of the epidural and spinal needle using the recommended “needle through needle”
technique are pictured. Once the epidural space has been located with the epidural needle, the spinal needle is inserted through the lumen of the epidural needle. It is recommended that the spinal needle tip extend 11–15 mm past the tip of the epidural needle to facilitate dural puncture.
The tip of the spinal needle pictured extends 11 mm past the tip of the epidural needle.
56Pain Relief for Labor and Delivery
Either air or saline can be used for loss of resistance. After placing the spinal needle, secure the spinal needle by pinching both the spinal and epidural needle hubs between the thumb and index fi nger during aspiration and injection, to reduce needle movement and the failure rate.
The dura does not hold the spinal needle fi rmly in place as does the
•
ligamentum fl avum during a one-shot spinal technique.
Since CSE solutions are hypobaric, aspiration of spinal fl uid 1 ml makes the injectate more isobaric, and theoretically limits cephalad spread.
Once the epidural catheter is inserted and the epidural needle
•
removed, have the patient assume the lateral decubitus position and secure the catheter.
A spinal test dose may be administered to rule out an intrathecal cath- eter. Some clinicians prefer to avoid the use of this test dose, feeling it may result in an unnecessarily dense block. The epidural infusion can be initiated immediately.
Table 3.11 Recommended Technique for CSE
Labor Analgesia Sitting position
•
Sterile prep and drape, any interspace between L
• 2 and S 1
LOR with air or saline
•
CSE kit (spinal needle tip should extend 11–15mm past epidural
•
needle tip)
Small gauge pencil tip spinal needle (25–27 g)
•
Firmly secure spinal and epidural needle hubs with index fi nger and
• thumb Spinal injectate:
•
Bupivacaine (0.25
• % ) 1.75–2.5 mg (0.7–1 ml) + Fentanyl 15–20 mcg (0.3–0.4 ml)
If possible, aspirate CSF to total 2 ml prior to injection
•
Remove spinal needle, insert multiport epidural catheter 5–6 cm,
•
remove epidural needle
Have patient assume lateral position
•
Secure catheter
•
Test dose (if desired):
• 2 ml 2
• % lidocaine (40 mg), or 3 ml 1.5
• % lidocaine (45 mg) + epi 15 mcg
Begin epidural maintenance infusion as described in Table 3.5
•
Obstetric Anesthesia57 If using PCEA, ask the patient to press the demand button approxi-
•
mately 45 min after spinal injection; this augments the epidural dose and increases the likelihood of the patient remaining pain free when the spinal analgesia recedes.
Initiation of CSE with the spinal injection noted in Table 3.11 ( bupivacaine/fentanyl) will produce about 90–120 minutes of analgesia.
The onset of analgesia is approximately 5–7 minutes faster than epidural analgesia.
The rapid onset of profound analgesia improves patient satisfaction
•
compared to epidural techniques.
The low drug doses minimize side effects such as motor block and
•
hypotension.
Initiating the epidural infusion soon after the spinal injection elimi-
•
nates the need for independent dosing of the epidural catheter.
Less than 20
• % of patients should require interventions for inade- quate analgesia.
The primary drawback of the CSE technique is that the correct epidural catheter placement remains unproven for some time after the spinal injection. As a result, the routine use of CSE anes- thetics in parturients at high risk for operative delivery is not recommended. Inducing traditional epidural analgesia in high-risk patients is recommended, since a well-functioning epidural catheter reduces the need for general anesthesia should urgent cesarean section be required.
When to Consider Avoiding CSE Morbid obesity
•
Severe preeclampsia
•
History of previa or abruption
•
Abnormal presentation
•
Multiple gestation
•
Fetal macrosomia
•
Abnormal fetal heart rate tracing
•
Anticipated diffi cult airway
•
Reasons for CSE Failure
Assuming the use of appropriately sized spinal and epidural needles, the most likely reason for failure to obtain CSF is deviation from the midline ( Figures 3.3 ).
58Pain Relief for Labor and Delivery
Should CSF fail to return when the spinal needle is passed, the following steps can be performed:
Remove the spinal needle.
•
Withdraw the epidural needle 1–2 cm.
•
Reassess the angle of epidural needle placement and redirect either
•
right or left, using LOR to re-enter the epidural space in a slightly different position.
If still unsuccessful following the second attempt, abandon the CSE
•
technique and proceed with an epidural technique.
(a)
(d) (e)
(c)
(f) (b)
Figure 3.3 The fi gure illustrates a successful dural puncture, and a number of possible scenarios that lead to CSE failure or the inability to aspirate spinal fl uid. (a) A successful dural puncture, (b) The dura is “tented”
rather than punctured. (c) A short spinal needle fails to reach the dura.
(d) Lateral deviation of the epidural needle causing the spinal needle to miss the dural sac. (e) Similar to (d) except that the dura is punctured laterally, which may result in the inability to aspirate CSF. (f ) “Tenting”
of the dura with a “too short” spinal needle. Further advancement of the epidural needle may result in the dura rebounding over both the spinal and epidural needle tips, causing an accidental “wet tap” with the epidural needle.
Obstetric Anesthesia59 If CSF is observed but cannot be aspirated, this is most likely due to lateral penetration of the dura.
Attempt to aspirate while rotating the spinal needle.
•
If still unsuccessful but there is no persistent paresthesia, it is rec-
•
ommended to inject the spinal solution and proceed with epidural catheter placement.
If the patient fails to develop spinal analgesia (which should be
•
rapidly apparent), dose the epidural catheter.
Complications
In general, the risks associated with CSE and epidural analgesia are similar. Although concerns of meningitis, high spinal block, abscess, permanent neurologic injury, hematoma, and metallic fragments introduced into the spinal space have been suggested as possible complications of the technique, the incidence of these complica- tions has not increased since the advent of CSE. The incidence of post-dural puncture headache should not be signifi cantly different from standard epidural techniques with the use of very small gauge spinal needles.
Some series have indicated that use of the CSE technique actually
•
avoids inadvertent dural punctures with the epidural needle by using the spinal needle as a “fi nder needle” to confi rm correct epidural needle placement.
Initial reports of fetal bradycardia associated with CSE led to speculation that fetal heart rate changes were related to uterine hypertonicity, induced by a precipitous decrease in circulating mater- nal epinephrine as a consequence of rapid onset analgesia.
Clinical studies, however, suggest that the incidence of fetal brady-
•
cardia is similar with both CSE and epidural anesthetics, and approx- imates 10 % .
Fetal bradycardia following either technique is usually self-limiting
•
and generally persists only a few minutes. Ensuring left uterine dis- placement, administering oxygen and supporting maternal blood pressure, if necessary, are recommended.
It is imperative that interspaces below the L 2 spinous process be used during CSE placement, to minimize the risks of perma- nent neurologic injury; spinal cord damage can occur if interspaces above L 2 –L 3 are used (see also Positioning and Choice of Interspace above).
60Pain Relief for Labor and Delivery