Random notes from ASA Conference 2007 September

Saturday 15th September 2007

Analgesia in labour

Significant association to post-op pain

• Young age
• Female gender
• Level of pre-op pain
• Incision size
• Type of surgery

 

Mode of delivery (vaginal vs Caesarean section) makes no difference with regard to:

• Pain at 2 months
• Post partum depression

 

Severe pain post op correlates with risk of chronic pain

 

Calculation of dosage

• Propofol - use actual weight
• Suxamethonium - use actual weight
• Fentanyl - use actual weight
• Morphine - use ideal weight

 

Myometrial afferent nerves regress during pregnancy

 

Most pain is from cervix and lower segment, from:

• Spontaneous activity
• Increased response to stimulation
• (Possibly due to oestrogen)

Hypotension in obstetric spinals

Hypotension in obstetric spinal anaesthesia occurs in 80-90%

 

Ephedrine vs Phenylephrine

• Ephedrine
  * Longer duration
  * More beta agonist effect
  * Crosses placenta more than phenylephrine
• Phenylephrine
  * Shorter duration - easier to titrate
  * Alpha agonist
  * Less foetal acidosis
  * Less N&V

 

Foetal acidosis

Ephedrine crosses placenta more than phenylephrine (possibly due to higher lipid solubility)
--> Causes increased metabolism
--> Increased O2 demand
--> Increased risk of foetal acidosis

Weight and pregnancy

Underweight (<50kg)

Increased risk of

• IUGR (intra-uterine growth retardation)
• Prematurity
• Low fertility

Obesity (BMI > 30)

Increased risk of

• Infertility
• Higher miscarriage if IVF is used
  * Not when conception was natural
• Congenital malformation
• Essential hypertension
• DM and gestational diabetes
• Obstructive sleep apnoea, which in itself also leads to
  * Pregnancy-induced hypertension
  * IUGR
• Increased pre-term birth
  * Odds ratio of <32 weeks = 1.6
• Intra-partum complication
  * Increased incidence of induction of labour
  * Increased rate of caesarean section
• Failure of epidural
  * 42% vs 6% in non-obese
• High rate of difficult intubation
• Longer surgery time
• Increased risk of bleeding

 

Sunday 16th September 2007

NSAID and Paracetamol

Presented by Dr Steve Jones

Number needed to treat (NNT)

• Diclofenac 100mg = 1.9
• Parecoxib IV 40mg = 2.2
• Morphine IM 10mg = 2.9
• Paracetamol 1g = 3.8
• Codeine 60mg = 16.7

 

Selective and non-selective NSAIDs have similar efficacy

 

NSAID

NSAID decreases morphine consumption and its associated side-effects

• Nausea decreases by 12% (NNT = 16)
• Vomit decreases by 32% (NNT = 15)
• PONV decreases by 33% (NNT = 12)
• Sedation decreases (NNT = 15)

35% improvement in pain score

20-40% decrease in morphine consumption

 

Paracetamol

Morphine consumption decreases by 20%

10% improvement in pain score

20% decrease in morphine consumption (but not statistical significant)

 

Combination with NSAID is more effective

Paracetamol + Tramadol

Paracetamol 650mg NNT = 4.6

Tramadol 75mg NNT = 5.3

Paracetamol 650mg + Tramadol 75mg NNT = 2.6

 

Side effects associated with NSAIDs

NSAID increases risk of severe bleed (0% vs 1.4%) (NNH = 59)

COX2 increases risk of renal failure (0% vs 1.4%)

NSAID increases risk of GI bleed (but not statistical significant)

 

Chronic pain

Possible decrease in chronic pain with NSAID

e.g.

In ACL repair, celecoxib 200mg PO BD for 14 days

In posterior spinal fusion, celecoxib 400mg pre-op + 200mg BD x 5 days
* 10% vs 30% with pain at 1 year's time.

NMDA antagonists

Presented by Eric Visser

NMDA receptors

Mg2+ blocks NMDA channel

Ketamine attaches to PCP site on NMDA channel

NMDA antagonists include:
* Dextromethorphan
* Mg2+
* Ketamine

Ketamine

Ketamine 0.1 - 0.2 mg/kg/hr

Decreases opioid consumption by 30%

But, no reduction in opioids side effects
* Except for N&V

No benefit from mixing ketamine and opioid in PCA
* Need to keep infusion separate (due to different requirements)

Side effect of ketamine infusion

Hallucination 7% (NNH 27)

Nightmare 4% (NNH 62)

Side effects can be reduced with anaesthetics and benzodiazepine

Clinical significance

Despite reduced opioid consumption, opioid SE is not reduced (except for N&V)

Therefore, while effect of ketamine is statistically significiant,
--> Effect not clinically significant

Ketamine infusion should not be used routinely.