This guide is intended for the use of anaesthetists and anesthesiologists who are already experienced in performing epidural anaesthesia for Caesarean section, and wish to convert to spinal (intrathecal, subarachnoid) anaesthesia. The technique described has been used by the author for over 100 consecutive cases, with a 100% success rate. While he believes that this technique represents good practice of anaesthesia, and can be supported by current literature and by comparison with the practice in other Canadian hospitals, no specific guarantees are given.
I was taught to use general or epidural anaesthesia for Caesarean section. After reading an article by Brownridge I wanted to try using spinals, but the technique was out of favour. There were concerns about historical medico-legal problems, hypotension and post-dural puncture headache. I finished my training (C.V.) in Toronto in 1990 without ever seeing a Caesarean section under spinal anaesthesia.. Once I obtained a staff position, I decided I had to learn the technique so that I would have it in my bag of tricks for the "Urgent C-Section / Difficult Intubation" case I figured I would eventually come across. I read what I could find, then taught myself a way to do the block. It worked better than I dreamed possible. Compared to an epidural, a spinal:
Once I had mastered the technique, and determined that
postoperative analgesia with intrathecal morphine was as safe and
effective as with epidural morphine
(Chadwick), I changed almost all
my elective awake Caesarean sections from epidurals to spinals. The
difference is amazing! The surgeons are delighted, the patients are
much happier, and my colleagues have adopted my technique. None of us
would go back to epidurals, and we wonder why we took so long to
rediscover spinal anaesthesia for Caesarean section.
Spinals have become the anaesthetic of choice for Caesarean section
in the major Canadian teaching centres. However, when I did a survey
in the fall of 1994, 52% of Ontario hospitals were not using spinals
for Caesarean section (Oyston). I
hope that this article will encourage more anaesthetists to use the
technique.
I used to worry about a list including a Caesarean section under
epidural. I knew that the technique could occasionaly be difficult,
that the dose of drug necessary could cause life-threatening side
effects, and that the quality of the block was often only just
adequate, especially in anxious patients where additional intravenous
situation is relatively contra-indicated by concern for the foetus.
Now I look forward to doing these cases under spinal. A quick, easy
block, using a small dose of local anaesthetic, will reliably produce
an excellent block.
The following criteria must be met:
In practice, if the patient already has a working epidural in
situ, I will top it up. Almost all other cases get a spinal. Most
"emergency" cases allow enough time that, with the agreement of the
surgeon, I will still perform a spinal. Although this is
controversial, Beilin has shown
that 80 - 88% of American anesthesiologists would do a spinal for
"emergent" Caesarean section. It usually takes less time than a
thorough pre-oxygenation or a full surgical scrub.
A spinal produces a more rapid onset of block, including a more rapid
sympathetic block, which causes peripheral vasodilatation and
hypotension which is frequently more severe than that associated with
epidural anaesthesia. Care is needed in patients who are less able to
tolerate this situation (e.g. pre-eclampsia, aortic stenosis,
Eisenmengers' syndrome
(Smedstad)). In these
circumstances, the anaesthetic technique must be tailored to the
individual case, and many would suggest that if the patient wishes to
be awake, a slow gentle introduction of epidural anaesthesia, perhaps
with invasive haemodynamic monitoring, is preferable to spinal
anaesthesia, as it gives greater control. However,
Wallace has shown that a combined
spinal/epidural technique is safe in pre-eclampsia.
Check: Make sure that a working anaesthesia machine is available, complete with a method of ventilating the patient with oxygen, suction, intubation equipment, and standard anaesthetic and resuscitation drugs.
Have ephedrine drawn up. I make up a 10 ml syringe with 50 mg of ephedrine made up to 10 mls with saline.
Positioning: I prefer sitting up, with the patients' ankles at the foot of the bed, knees spread out, curved over a pillow or with her hands in front around her knees. A skilled assistant is a great help. Others use a lying position, usually right side down, as the patient will be tilted left side down during the surgery. However, even left side down can be used. Inglis showed that the sitting position is quicker, and that these patients require less ephedrine.
Prep and Drape: I put on a hat and mask, wash my hands and glove. I recommend a formal scrub and gown until one is quick at the procedure. The patient is prepped with povidone iodine and draped, using the Baxter Spinal Anesthesia Tray (Baxter Healthcare Corp., Deerfield, IL 60015 USA).
Drugs: I use 0.75% heavy bupivacaine 1.5 mls (11.25 mg) with 0.33 mls (0.33 mg) of preservative-free epidural morphine (1.0 mg per ml) for most cases, unless the patient is under 5 feet 4 inches tall, in which case I use 1.25 mls bupivacaine with 0.25 mls morphine. Morgan describes a range of alternative doses. Some people prefer a lower dose of morphine, or use fentanyl or sufentanil. Use a filter needle to draw up the drugs.
The Needle: I use a #27 gauge 3.5 inch (0.41 mm x 8.89 cm) Whitacre needle (Becton Dickinson and Company, Franklin Lakes, NJ 07417 USA). Use the smallest needle possible, and use a "tearing" rather than "cutting" tip. The 24 gauge Sprotte needle is acceptable (Mayer), but some find the long opening, set further back from the tip of the needle, a disadvantage. Most reports suggest a low incidence of spinal headache with 25 gauge needles, but I had three consecutive mild spinal headaches with my first three cases using 25 gauge Whitacre needles! I therefore changed to 27 gauge, and have had no further problems. I have a 98% success rate with this size of needle. Smith reported a 4% spinal headache rate and no failures with a 25G needle, and no spinal headaches but an 8% failure rate with 27G needles.
The Block: Identify the L3/4 interspace (or the
one above or below, if easier). Infiltrate the skin with 1%
lidocaine. I use a 21 gauge 1.5 inch (3.8 cm) needle to do this, then
leave the needle in place to act as an introducer. This
eliminates one needle prick. Using this needle, stay in the midline,
pointing slightly towards the patient's head (roughly 80 to 85 degree
angle to skin), and insert the needle almost to the hub in the
average sized patient. Now, take the spinal needle and insert it
through the introducer. This is easier if you let the needle rest on
the lowest part of the inside of the rim of the introducer, which
then stabilises it in the midline, so that you only have to get the
position right in the vertical plane to enter the introducer needle's
aperture. Push the spinal needle in slowly and gently. The "feel" is
minimal, but often the denser ligamentum flavum and the "pop" as the
arachnoid are pierced can be detected. With the needles I use, I
usually find CSF after about 2.5 to 3 inches have been inserted into
the introducer. It is rarely necessary to aspirate to get CSF. I
attach the syringe, aspirate about 0.2 mls of CSF, inject about half
the local anaesthetic, then aspirate, inject the rest, and aspirate
again. If the aspiration test fails at any stage, I can at least
estimate the amount of drug given, and add more to make up the
estimated deficit.
Immediately after injecting, I put a small dressing on the puncture
site and have the patient lie down with a wedge under the right hip.
If you give the right dose of the right drug into the right place, the block WILL work. Testing is hardly necessary, and I often omit it. However, testing has some uses, such as teaching the anaesthetist how much drug is needed, catching the rare block which is too high or too low before it becomes a problem, and reassuring the patient, the surgeon, and the anaesthetist!
I use an alcohol wipe to test. I ask the patient if it feels cold on her arm. Most say "Yes" but some cannot tell. I then wipe it up the abdomen, starting from the inguinal region and heading up to the nipple in mid-clavicular line, and ask the patient to tell me when it feels cold. If it never feels cold, I try on the shoulder. Most patients can say where the block has got to. If it is above the umbilicus at five minutes, I position the patient slightly head up. (The surgeons I work with all do Pfannensteil incisions.) This method is non-invasive and introduces the patient to the idea that one type of sensation (cold) can be blocked without another (touch). The block comes on more rapidly than surgeons can scrub, prep, drape, and catheterise the patient. Most surgeons will test by pinching the site of incision with a clamp. Patients are not usually aware of this happening.
Patients receive oxygen (2 litres per minute) by nasal prongs until delivery, when it is discontinued if all is stable.
Hypotension is a frequent problem. I sometimes give 10 mg ephedrine prophylactically, and sometimes add 10 mg to the IV bag. Others will give intramuscular ephedrine prophylactically, but this seems rather uncontrollable. At the first suggestion of nausea I give 10 mg ephedrine IV before even checking the blood pressure.
Very few patients require any additional sedation. Rarely, I will give 50% nitrous oxide by mask. Exceptionally anxious patients may need IV benzodiazepines, but most can be emotionally supported and presuaded to put up with any discomfort, at least until the baby is born. Supplemental narcotics should be avoided, as they increase the risk of postoperative respiratory depression.
This is our standard form:
[SPACE for PATIENT ID LABEL]
Epidural/Spinal morphine .....mg was given at .......[TIME]
The following orders are in effect for 18 hours after bolus dose:
Signed .................MD (Anaesthetist) Date.............
Spinal anaesthesia is an excellent technique for Caesarean
section. It has become the routine in Canadian teaching centres, and
deserves to be used even more widely in community hospitals.
All obstetric anaesthetists should learn the technique.
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Dr Kari Smedstad (Chief of Obstetrical
Anaesthesia, McMaster University, Hamilton, ON) and |
ABOUT THE AUTHOR
Dr John Oyston, MB BS,
FFARCS, is a certified specialist
anaesthetist, currently working in the Anaesthesia
Department of Orillia
Soldiers' Memorial Hospital, in
Orillia, Ontario, Canada. He can be reached by e-mail to
oyston@oyston.com.
