Abstractions

I quite like viewing the abstracts from the major international meetings. In particular the clinical investigations often have a freshness a practicality that you don't find in the published articles. From the abstracts of the ASA in New Orleans 2009 are some interesting conclusions:

• 5% glucose after laparoscopic surgery reduced PONV.
• Crystalloids may be better than colloids for spinal anaesthesia cesarean section
• In the UK there has been a 200% increase in RA to GA conversions for CS
• They are ultrasounding the airway now instead of a Mallampatti score
• ED 95 of intrathecal bupivacaine for CS in morbidly obese is even higher than non-obese (!)
• Avoid RA in parturients with Budd-Chiari malformation
• TAP blocks on cesarean patients who also had 150 mcg intrathecal morphine was of no benefit

and more!

What makes a good anaesthesiologist

From the BBC

An Australian psychology expert who has been studying emotions has found being grumpy makes us think more clearly.

In contrast to those annoying happy types, miserable people are better at decision-making and less gullible, his experiments showed.

While cheerfulness fosters creativity, gloominess breeds attentiveness and careful thinking, Professor Joe Forgas told Australian Science Magazine.

Explains a few things about our specialty, and me too I suppose.

Oxycodone Musings

More oxymoronics from me:

this time on oxycodone

BIS biz

Often seems another distracting number which doesn't add to the scheme of anaesthesia, but BIS can be a handy tool of reassurance when there may be doubts about adequate cerebral perfusion. In particular it can indicate adequate cerebral perfusion and function when position and high venous pressure might compromising. Recent cases when it has reassured me have been a thoracic level laminectomy and a prolonged gyne laparoscopy when the relatively low positions of the head caused estimated venous pressures of 20 - 30 cmH2O. In addition to measures to maintain arterial pressure and minimise cerebral vasodilatation normal BIS values and waveform indicated we could safely persevere with surgery in the desired position.

Oxytocin Musings

Some musings on oxytocin



http://docs.google.com/Doc?docid=0Af2UxQuLjznjZGhzYmp4eHNfMzI3Zmt0OWRmZnE&hl=en_GB

Porcine influenza

H1N1 is everywhere now and we're all pretty sanguine about it. But pregnancy appears to be a real risk factor for serious morbidity and mortality. We should have it on the differential diagnosis list for pregnant women with premature labour with fever: it may not be chorioamnionitis. Pregant contacts of flu cases should be given osteltamivir, and the pregnant woman with flu symptoms should be closely watched for worsening pneumonia.

F%&*!2! Fentanyl!

Ever since I started practising anaesthesia in 1991 fentanyl has been part and parcel of almost every anaesthetic I have given or observed. At the very least 50 – 100 mcg is used to attenuate the airway and cardiovascular response to airway management. More fentanyl can be used for further intraoperative analgesia and sometimes it becomes a total fentanyl affair with PCA continued postoperatively. Even neuraxial anaesthesia usually has fentanyl as part of it.

But it seems this potent µ receptor could be causing underappreciated trouble. The potent lipophilic opioid agonists (fentanyl, remifentanil etc) induce acute opioid tolerance which results in more severe postoperative pain which is more resistant to morphine analgesia.

This phenomenon has been well studied in rats using doses (per body mass) that are far in excess of human clinical practice and it seems it is due to changes that occur in the NMDA and GABA receptor processes.

But even modest clinical doses in humans seem to contribute to this unwanted effect. Sukhani (Anesthesia-Analgesia Nov 1996) compared anaesthesia for gynaecologic laparoscopy with 100mcg fentanyl versus 15 – 30 mg ketoralac without fentanyl. Pain, nausea and time to discharge was longer in the 100 mcg fentanyl group even though this group had lesser intraoperative propofol.

In more contemporaneous techniques, anaesthesia for laparoscopic cholecystectomy was compared by Collard in Anesthesia-Analgesia (Nov 2007). Desflurane anaesthesia was administered with either fentanyl, esmolol or remifentanil. The esmolol group had the superior postoperative course with significantly less need for analgesia and antiemesis and a more rapid discharge. The remifentanil group had the worse outcomes for analgesia, emesis and discharge time. Xuerong et al (Anesth Analg Dec 2008) found higher morphine consumption in abdominal hysterectomy patients who received 3 intravenous doses of 1 mcg/kg of fentanyl with spinal anaesthesia compared to controls and those who also or only received ketamine or lornoxicam.

Remifentanil may not be the wonder “nitrous-oxide killer” after all. The literature now abounds with the effect of remifentanil on morphine tolerance and hyperalgesia and a report of its use for a laparoscopy (Rev Esp Anestesiol Reanim. 2008 Jan;55(1):40-2) reports an extreme case of postoperative hyperalgesia.

Morphine, presumably because of its lesser potency and lipophilicity does not cause such a degree of rapid acute tolerance, but of course its tendency to cause PONV still limits in applicability in some situations.

Ketamine seems to counter the acute tolerance of the lipophilic opioids and I wonder if this is what its true analgesic effect is. It may be better avoiding lipophilic opioids altogether and using anaesthetics (including regional anaesthesia and intravenous lignocaine) to anaesthetise and alpha and beta blockers to attenuate haemodynamic stress. Magnesium may be valuable. Perhaps analgesics should be kept in reserve until pain is expressed or soon before pain is expected to be expressed.