Measuring regional anaesthesia

I think one of the more trying aspects of obstetric anesthesia is ensuring adequate regional anaesthesia for surgical delivery. Inadequate regional anaesthesia remains a top cause of medicolegal hassle, but surprisingly what little there is in the literature assessing for adequate anaesthesia is vague and imprecise. We read expressions such a "block to T4 with cold", or "T5 level to pin-prick". But does this mean the described dermatome is altered, or is it the first one unaffected? Is the sensory modality altered or absent at this dermatome? And what do we use: pin, cold or light touch? A local guru says only test with an ice block if the surgeon is going to operate with one, but we cannot test with a scalpel and scissors!
Most of the published work in recent years has been by Ian Russell in Hull, UK. He concluded in IJOA 1994 that no patient with a loss of light touch to a "Neurotip" at the T6 dermatome and above had pain or discomfort during CS. A light touch level can be several segments below a cold or pin-prick level, and Russell's own work finds that it takes over 20 minutes for light touch block to reach T5. His own words in this July 2004 paper are: "Surgery was allowed to start when T6 was either blocked to touch, or expected to be blocked to touch before surgery had reached the peritoneal cavity". So it seems Russell himself has an optimistic approach to his regional anaesthesia. Of his 102 subjects, 4 had intraoperative pain, and all 4 had low light touch levels with higher cold and pinprick levels, but his interquartile graph indicates that 25% had light touch levels below T5, and at 10 minutes (the mean time of surgical incision) 25% had light touch block below T7. So it seems to me that a failure of anaesthesia predicts a low light touch block, rather than the other way around.

Steve Yentis has a recent editorial in IJOA 2005, and also conributes to the topic, but to me he just makes it all a bit more confusing and uncertain. He describes his idea of assessing "wide-eyed" sensation to cold, and a "true" level at which sensation begins to change from normal. He rightly points out that personality, systemic and spinal drugs, the obstetrician, and the circumstances of delivery all contribute to how a patient will respond to surgery under regional anaesthesia. He concludes that he aims for a "true" level of T1, or higher. In practical terms this means sensation should be changing over the upper breast and even the axilla for effective regional anesthesia for CS.

So what do we do? It's all a bit confusing, and I know the local Guru often refers to the gods of regional anaesthesia. But I give a solid dose and aim for motor block of the lower limbs and alteration of pin and cold over the upper breasts and an absent pin up to and including T6 before the knife. In emergent conditions I rely on an ascending block, and with sensory changes occuring over the breasts and motor block of the legs I am optimistic of effective regional anesthesia.

Intrathecal Morphine for Major Abdominal Surgery

Last week there was an anaesthesia clinical meeting at the Hospital of Miracles and Incurables. It included a presentation on anaesthesia for liver resection. A particular issue in Nick's excellent talk was postoperative analgesia for what is obviously an operation that needs it. While thoracic epidural analgesia is an effective tool, it is fraught by the deranged coagulation that occurs after liver resection, and which often persists until the time of desired removal. Despite this concern, Nick and his team in the UK used epidurals on many liver resection cases; effective analgesia without sequelae was the result in over 100 of them. The local team prefers to avoid epidurals, and it seems the patients kind of manage on "multimodal" intravenous analgesia, although the impression is that the postoperative period can be miserable for these patients. Unfortunately Nick didn't discuss intrathecal morphine through a preoperative single shot injection. This form of analgesia has been described and used in all manner of major operations and is widely used many in parts of the world, although not so much in Australia. However, there has, and is, a little hotbed of intrathecal morphine use, by yours truly. I have used it for several years, particularly for elderly women having major oncology surgery who seem particulary at risk of epidural haematoma because of osteoporotic spinal stenosis. And Di Pietri et al in Anesthesia Analgesia April 2006 find in their RCT on liver resection patients that the analgesia from 0.2 mg of intrathecal morphine and IVPCA is not inferior to thoracic epidural anlgesia. It is arguable to what extent a small spinal needle is less likely to cause haematoma than a large epidural needle and catheter, although it both plausible and supported by the prospective Swedish survey by Moen et al. Certainly the intrathecal technique avoids confusion about the cause of motor block and there is no need to be concerned about the timing of the withdrawal of a catheter. Respiratory depression seems only a remote possibility with a 0.2 mg dose. So it is a choice to be considered!

Diclofenac and dystocia

It was quite a busy night last night, and it included two caesarean sections for obstructed labour. Both women had been labouring all day since elective inductions, both had received several hours of oxytocin infusion, and both delivered babies over 4 kg. The caesars went fairly will with epidural anaesthesia, but both uteri needed more massage than usual, and I administered generous doses of oxytocin and ergometrine. After the skin closures I declined the use of rectal diclofenac. This was met with some surprise because it seems in this part of the world rectal diclofenac is given almost routinely after caesarean section. But diclofenac is a COX-2 inhibitor, and thus antagonises the production of endogenous prostaglandin F2alpha which is essential in mediating myometrial contraction. PGF2a is even more crucial after oxytocin-augmented labour because oxytocin receptors become massively down-regulated during continuous intravenous infusion and the uterus is then resistant to further doses of intravenous oxytocin. And when the uterus is acidotic and truamatised from the long and obstructed labour and subsequent surgery it does not a tocolytic drug as well, which is what diclofenac and other COX-2 inhibitors are. So I leave out the diclofenac after obstructed labour and oxytocin infusion and ensure there is ready access to opioid analgesia. Postpartum haemorrhage from uterine atony remains a major cause of maternal morbidity and mortality and it shouldn't be iatrogenic.

Induction drugs for the bleeding patient

There have been a few bleeding patients in recent days. One was a postpartum haemorrhage from an atonic uterus, another was an ectopic pregnancy. I was also part of a clinical meeting discussion about a case of a bleeding gastric ulcer presenting for laparotomy and oversew. The presenter of this case believed that the induction of anaesthesia should be delayed until invasive lines had been placed and until after the patient was resuscitated with fluid and blood. The concern was the patient would "crash" on induction. Presumably this means profound and irreversible hypotension would occur due to the myocardial depressive and vasodilating effects of intravenous anaesthesia. My feeling is that the sooner a bleeding vessel is ligated the better, and I would be keen to get surgery underway ASAP. Lines can be placed later (we know the pressures are low!), the airway of the obtunded patient becomes protected, and we can deal with a still patient much easier than a distressed one. But how do we get to that point without crashing? Propofol with fentanyl or alfentanil are very popular induction drugs, but together they are potent hypotensive agents. They are even more so in the setting of acute hypovolaemia because of the contraction of the central volume. Reich et al in Anesthesia Analgesia Sept 05 identified propofol and fentanyl as drugs that increased the risk of hypotension in older ASA 3+ patients and those with MAP < 70 compared to thiopentone and etomidate. And importantly, induction hypotension was associated with later morbidity and mortality. I have had personal experience with this effect of propofol and fentanyl, and I suspect that the more lipophilic or non-ionised the opioid the greater is the potential hypotensive effect, thus care should be taken with alfentanil and remifentanil as well. So overall, I believe thiopentone (perhaps with a dose as little as 1mg/kg) without opioid is a better choice than propofol for the emergent and unstable bleeding patient needing rapid sequence induction and intubation. The opioid can wait until there is a response to a noxious stimulus.

bis business

A question at the QA meeting today was: does the induction of GA for emergency CS mandate the application of BIS before induction? I say NO: there is enough to do to ensure a safe induction and intubation, such as a brief equipment check and adequate preoxygenation. With adequate doses of thiopentone and volatile anaesthetic with N2O awareness should be unlikely, and even though it has been an often cited problem, I have not had any direct or acquainted experience with awareness at CSection. And and a real rapid sequence induction is that: you pick your dose of thiopentone and stick with it and follow it immediately with suxamethonium and intubate ASAP. There is no opportunity to titrate to a BIS number, and I believe it can be a distration from the real business of ensuring adequate ventilation and oxygenation. And why cause more stress by applying a device that feels like ECT?

Clopidogrel and epidurals

April 2006 "Anaesthesia" has a survey by Pennefather et al. It finds that nearly half of UK anaesthetists would place an epidural in a patient of clopidogrel, and a third would place one on clopidogrel and aspirin. This is despite the American Society of Regional Anaesthesia recommending at least a 7 day clopidogrel-free period! It is not clear if this attitude to this potent antiplatelet drug is borne out of ignorance or considered informed opinion, but I find it quite extraordinary that when the risk of epidural haematoma may be as high as 1:1500 in postmenopausal women that UK anaesthetists would be pushing on with epidurals in antiplateleted patients. Can we at least be reassured that they usually do not have spinal haematoma?

Spinal disease and obstetric neuraxia analgesia

The most common issue I deal with in antenatal consultions is whether a woman's previous or current spinal disease complicates the use of neuraxial analgesia and anaesthesia for labour and delivery. Many cases are simply scoliosis or postural problems, and I often feel that other professionals such as chiropractors, physiotherapists, osteopaths and orthopaedic surgeons have made an unneccessary fuss over what should be fairly benign condtions. Such women may well have ongoing back pain, and are likely to still have it after delivery. And it may well be worse, particulary after the traivails of child-bearing and the subsequent child-carrying. Howell and others in BMJ 2002;325:357 conclude in their prospective study that low back pain commonly occurs after delivery, but epidural labour analgesia does not cause it. An epidural can be readily offered to such people, but it is prudent to discuss postpartum back pain and to suspect that the performance of the block may be hampered by posture and degenerative changes. Previous surgery, or clearly diagnosed spinal disease is a more complex matter. Sometimes a patient carries a warning from another practitioner "don't have an epidural or spinal", and of course this directive immediately excludes a way of providing anaesthesia with a low risk of airway crisis. Previous spinal surgery does not contraindicate the use of neuraxials, although it may make it more difficult to perform and to achieve a satisfactory block due to altered or obliterated anatomy. Intrathecal dosing may achieve a more satisfactory and reliable effect, and some use intrathecal catheters. I have avoided intrathecal catheters: case reports of inadvertant dosage and meningitis and my personal observations of hypotension, sedation and motor block in the labour ward have dulled my enthusiasm. I try to achieve labour analgesia with high-volume-low-concentration epidural bupivacaine and fentanyl, and use single shot intrathecal doses for operative delivery. If there is an abnormal spinal cord or spinal nerves (such as spina bifida or cord tethering) neuraxials are usually should be avoided because of the risk of intraneural injection. But often we are confronted with "I've got spina bifida occulta" after we have been called give epidural relief in active labour rather than an antenatal consultation. This is usually a diagnosis from Xrays done for low back pain.The books say 10% of the population have SBO, and nearly all have them have not been Xrayed, and are blissfully unaware of their disability. We have surely done many epidurals and spinals on such patients, without problems, and we can usually proceed with those with knowledge of SBO in a similar fashion. However, when the SBO is not really occulta -that is there is a lump, or hairy knot, or a dimple, or haemagioma- a neuraxial should be avoided unless there is reassuring imaging.