This technique, fi rst used in obstetrics in the 1940s, is used only in select circumstances. Interest in it reemerged in the late 1980s when small gauge intrathecal microcatheters were introduced, but neural injuries resulted in their withdrawal from the market in some coun- tries. Currently, both purpose-designed microcatheters (available in some countries) and standard epidural “macrocatheters” are used.
The latter approach is popular in tertiary units as an alternative to reinsertion of the catheter into the epidural space when the epidural needle has punctured the dura and arachnoid mater (a “wet tap”).
Advantages, Disadvantages and Applications The advantages of continuous spinal anesthesia (CSA) are:
Successful block can be established in patients with abnormal or
•
altered neuraxial anatomy, in whom epidural or single-shot spinal anesthesia has a substantial risk of failure (e.g., severe scoliosis or previous vertebral canal surgery).
A safe, reliable anesthetic can be performed when attempts to
•
achieve epidural or spinal anesthesia have previously failed (e.g., in a morbidly obese woman).
The ability to titrate drug in women at high risk for morbidity from
•
high block, or from general anesthesia (e.g., severe asthma or impossible intubation).
Obstetric Anesthesia115 Stable hemodynamics in those likely to tolerate sympathetic-
•
induced cardiovascular changes poorly (e.g., certain cardiac diseases, pulmonary hypertension, aortic stenosis, cardiomyopathy, adult congenital heart disease).
Effective anesthesia for operative delivery after an epidural catheter
•
has been placed intrathecally for labor analgesia.
The disadvantages include:
Diffi culty with microspinal catheter placement, contributing to a
•
high overall failure rate (as high as 20 % in some reports, though with frequent use the failure rate falls).
The possibility of catheter misuse, in particular, unintentional
•
injection of epidural drug doses resulting in high or “total spinal”
block.
A high incidence of PDPH, though the incidence is lower among the
•
morbidly obese.
The risk of microcatheter breakage during insertion or withdrawal,
•
possibly necessitating surgical removal.
Equipment and Technique Equipment
There are two main types of catheter and kits:
An epidural catheter (20 or 22 gauge) inserted through an epidural
•
needle (unintentionally or deliberately) placed into the subarach- noid space (designated a “macrocatheter”). Pediatric epidural cath- eters, 24 gauge, which pass through a 20 gauge Tuohy needle, can also be used.
Catheter-over-needle kits available with 22 or 24 gauge catheters
•
mounted over an internal needle or stylet, which can be withdrawn after placement. The catheter is introduced with a Crawford style needle placed in the epidural space.
Insertion Technique
Technical issues with placement are common, irrespective of the proceduralist’s experience. Successful and safe insertion depends on:
Accurate needle placement
•
Insertion of only 3–4 cm of catheter (the direction and fi nal tip loca-
•
tion cannot be predicted)
Rapid injection of drugs (local anesthetic maldistribution is more
•
likely with slow injection)
Titration of bolus doses (e.g., bupivacaine 1.25–2.5 mg in volumes of
•
0.25–0.5 ml)
116Anesthesia for Cesarean Delivery
Dose requirements vary widely (range for surgical anesthesia
•
with bupivacaine may be 5–17.5 mg).
For safety, pay attention to detail with respect to use of small
•
syringes, fi lling of the dead space within the catheter (and fi lter, if used) and frequent block assessment.
Drug Selection
Plain 0.5 % bupivacaine is usually titrated to the desired level or effect.
Hyperbaric solutions can be used but may contribute to maldistribu- tion of local anesthetic in the CSF. Opioid adjuncts as used for single- shot spinal anesthesia are often a good idea.
Local Infi ltration or Field Block
In developing countries in particular, some obstetricians gain experience in performing cesarean delivery under progressive local anesthetic infi ltration of the abdominal wall (Figure 4.8 ), with or with- out instillation of local anesthetic into the peritoneal cavity and wound, or fi eld block of the lower abdomen (bilateral iliohypogastric and ilioinguinal nerve blocks). As large volumes of local anesthetic are required, solutions of low to medium concentration are used, and total dose must be considered. Maximum recommended doses of bupivacaine (up to 150 mg) or ropivacaine (300 mg) are very unlikely to result in plasma concentrations reaching the toxic range. Sedation, including subanesthetic doses of ketamine, may be added.
The transversus abdominis plane (TAP) block also appears to be a suitable technique, but has not yet been evaluated as a component of anesthesia.
Dealing with Failed Regional Anesthesia
Management of Failed Block before Surgery Failed Spinal Anesthesia
Technical failures (failed or abandoned insertion, or inadequate block) are infrequent. Inability to obtain a satisfactory spinal block (incidence approximately 0.5 % –4 % for spinal anesthesia and 0.5 % –2 % for CSEA) may be due to several factors:
Delivery of an inadequate dose of local anesthetic (dose selection
•
errors, loss from the syringe-needle connection or deposition out- side the dura).
Maldistribution of local anesthetic due to anatomical factors (high
•
CSF volume, subarachnoid and extradural cysts, arachnoid adhesions
Obstetric Anesthesia117
and trabecula, previous surgery or severe scoliosis), poor patient positioning, or low injection level
Mistaking infi ltrated local anesthetic for CSF, leading to injection in
•
the wrong anatomic compartment or space Other rare causes.
•
A good assistant who helps position the patient optimally is very help- ful. Manipulation of patient position post-injection (e.g., changing sides for unilateral or asymmetric spread or head-down posture) can also be an important factor in obtaining a good block.
Strategies to “rescue” a bilateral but low spinal block include:
Repositioning the patient head-down with her hips fully fl exed
•
(although caution is required with these maneuvers, and sensory distribution should be checked very frequently to avoid a high block).
Insertion of an upper lumbar or low thoracic epidural catheter,
•
after which often only a small volume of local anesthetic (3–5 ml) will be suffi cient to establish surgical anesthesia.
Dosing the epidural catheter if a CSEA was performed.
•
6 7 12 8 11 10
9 5
2 IB IA
IC ID
IE
3 4 1
Figure 4.8 Method of local fi eld block of the lower abdominal wall.
Reprinted with permission from Ranney B. and Stanage WF.
Advantages of local anesthesia for cesarean section. Obstet Gynecol . 1975;45(2):165.
118Anesthesia for Cesarean Delivery
Failed Epidural Anesthesia
This is more common than failed spinal anesthesia (incidence 5 % –15 % ) and is predicted by factors such as:
Unsatisfactory analgesia previously, during labor
•
A large number of supplementary bolus doses during labor
•
Failure to add opioid to the local anesthetic
•
Morbid obesity.
•
If time allows a “top-up,” up to 85 % of these cases will ultimately develop satisfactory epidural anesthesia. Strategies to improve the quality or height of the block include:
Withdraw the catheter slightly (about 1 cm) before re-dosing (pro-
•
vided at least 4 cm of catheter remains in the epidural space).
Re-dose with a high concentration of local anesthetic.
•
Add adjuncts such as lipophilic opioid (e.g., fentanyl 50 mcg) and/or
•
clonidine 75–150 mcg.
The decision to abandon use of the epidural catheter and perform a repeat regional anesthetic technique, or to change to general anesthesia, must be based on personal experience, individual risk- benefi t assessment, the urgency of delivery and the woman’s wishes.
An essential part of the consent process is to warn women that regional analgesia and anesthesia may fail or prove to be unsatisfactory intraoperatively, despite having established an apparently satisfactory surgical anesthetic.
Management of Intraoperative Pain
Despite good somatic (abdominal wall) block, visceral pain, particu- larly from pelvic organs such as the ovary, fallopian tubes, or the peritoneum, is not uncommon during cesarean delivery, even in the presence of apparently adequate sensory anesthesia to light touch, pinprick or cold at mid-thoracic dermatomes. The incidence of pain is lower with spinal compared with epidural anesthesia, but with either can reach 20 % –50 % (typically 5 % –20 % if neuraxial opioid has been used), especially when surgery takes more than 45–60 minutes. The anesthesiologist must be prepared to deal with pain in an unsedated and anxious patient, and with their support person.
Assessment of the patient is imperative.
The patient should already have been aware that the experience
•
will involve sensation, and the block distribution must be re-checked and documented.
Obstetric Anesthesia119 The timing of pain in relation to surgery is important.
•
Pain during initial incision is highly indicative that general anesthe-
•
sia will be required.
Pain arising during pelvic organ inspection and peritoneal closure
•
is not uncommon and can normally be managed satisfactorily.
The severity of pain (e.g., on a verbal numerical 0–10 rating score)
•
and the location of the pain should be noted.
Surgical exteriorization of the uterus increases the likelihood of
•
intraoperative pain.
Up to 5
• % of women experience upper chest or shoulder pain in the skin distribution of the cervical nerve roots of the phrenic nerve (C 3 –C 5 ). This is thought to result from irritation of the subdiaphagmatic peritoneum by blood and amniotic fluid.
Shoulder tip pain can be reduced by head-up table tilt and some- times counter-irritation, with vigorous rubbing of the painful shoulder.
Psychological support and reassurance can be crucial.
•
Reassure the woman that the pain will be dealt with, that mild
•
pain is often short-lived and resolves fully, and let the patient know how you intend to treat it.
Ascertain her feelings about the proposed treatment, maintain
•
rapport, and if pain is severe, immediately raise the possibility of conversion to general anesthesia.
Use distraction techniques, especially by encouraging maternal–
•
infant contact and interaction.
Inform the obstetrician of the situation and the plan. Unless
•
at the time of delivery, consider asking them to stop surgical manipulation briefl y in order to gain control.
Consider a small dose of an analgesic drug and also an anxiolytic
•
drug if the patient is obviously fearful. Anxiolysis with 50 % –70 % nitrous oxide in oxygen via the anesthetic circuit, or intravenous midazolam 1–2 mg, can be helpful.
Document the events and management.
•
Follow up with the patient, and counsel the woman postoperatively.
•
There are a number of analgesic options, which can be used if necessary.
Start with IV opioid (e.g., fentanyl 25–100 mcg or remifentanil 0.01–
•
0.02 mcg/kg/min).
120Anesthesia for Cesarean Delivery
Inject epidural local anesthetic (especially if near the end of surgery
•
or at a time of possible block regression).
Give epidural adjuncts (fentanyl or sufentanil, clonidine), recogniz-
•
ing that these and local anesthetic will take 5–15 minutes to take effect.
Ask the obstetrician to inject local anesthetic (e.g., 20–30 ml 0.5
• %
ropivacaine) either into the peritoneum (for adnexial or generalized abdominal or pelvic pain) or beneath the rectus sheath (for somatic abdominal wound pain during closure).
As a last resort, consider IV ketamine (e.g., 5 mg repeated as
•
required until sedated). Care must be taken not to give so much that general anesthesia is induced and airway refl exes are lost.
Specific consent from the patient should be obtained before administration because of potential oversedation and the undesira- ble psychomimetic effects.
Management of Failed Regional Anesthesia due to Complications
The anesthesiologist must be prepared for complications of regional anesthesia that require intervention (see the following and Chapter 13).
This includes induction of general anesthesia during the operation.
Some like to keep drugs for induction and intubation of the patient (e.g., sodium thiopental and succinylcholine) at hand. If propofol is prepared, it should be used within 4 hours because it supports bacterial growth.