Article Notes
Why is this important?
Buprenorphine (Subutex, Tamgesic, Suboxone, Norspan) is a partial opioid agonist with high mu-receptor affinity, though limited by a ceiling effect. Because of its favourable safety profile it is used for opioid dependence, chronic and, increasingly, acute pain.1
Patients historically often have regular buprenorphine (BUP) ceased post-operatively when needing opioid analgesia. It was assumed that because of it’s high mu-receptor affinity, BUP blocks the efficacy of additional opioid analgesics. In reality, ceasing buprenorphine creates more complexity and may precipitate acute withdrawal.
Be smart
Haber, DeFries & Martin point out that despite the high receptor affinity of BUP, there are still additional receptors remaining for full-agonist opioids to bind and activate. This is supported by the literature (Kornfeld 2010 & Harrison 2018). Even in the post-operative period buprenorphine can be easily continued, although with patients sometimes needing higher doses of acute opioid analgesics (Goel 2019 & Hansen 2016).
“Temporarily discontinuing buprenorphine introduces unnecessary complexity to a hospitalization, places the patient at risk of exacerbation of pain, opioid withdrawal...“
Bottom-line
If buprenorphine is regularly being taken then it should not be ceased for hospital admission. Additional short-acting opioids can be added if needed. Doses required may be higher, but this is primarily due to opioid tolerance rather than receptor competition with BUP. Alternatively, a maintenance BUP dose can be split into 3-4 divided doses and/or increased to cover acute analgesic needs.
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Buprenorphine is also a kappa and delta receptor antagonist, a weak partial NOP/Nociceptin receptor agonist, and has potent local anaesthetic effects. It behaves as a full agonist for analgesia in the opioid-naive, but a partial agonist for respiratory depression. ↩
Daniel Jolley
What’s all the fuss?
Significant observational evidence suggested an association between mortality and deep anaesthesia, in particular a 2017 meta-analysis. However it has been suspected that anaesthetic depth may merely be a surrogate marker for intraoperative hypotension, a well-established risk factor for post-operative mortality and morbidity.
With this large RCT, the Balanced Anaesthesia Study Group has shown that deep general anaesthesia is not associated with an increase 1-year mortality.
What did they do?
The researchers conducted an ambitious, large (6,644 patients), multi-center, randomised controlled trial. Patients aged ≥60 years undergoing major surgery (expected ≥2h surgery and ≥2d hospital stay) were randomised to receive volatile general anaesthesia targeting BIS 50 or BIS 35.
To minimise intra-operative blood pressure as a confounder, anaesthetists were required to specify a target MAP before BIS-group allocation.
They found...
Not only was there no mortality difference between the BIS 50 and BIS 35 groups, there were also no major or moderate morbidity differences, or difference in recovery or length of stay. BIS targets were adequately achieved, though not perfect, and MAP was clinically similar for both groups.
Context is everything
This is about as high-quality as a large, modern study looking at longer-term outcomes can get. It is widely applicable to most populations and common general anaesthetic scenarios, except for a few important caveats:
- Very few ASA 4 (5%) patients were enrolled.
- Only volatile-maintenance anaesthesia was studied not propofol/TIVA.
- We can draw no conclusion regarding the consequences of extreme-depth (ie. BIS << 35).
- The actual depth difference between the BIS-35 and BIS-50 groups was not as much as perhaps ideal: mean BIS 39 vs 47 respectively...
Final thought
...there was (only) one case of awareness in the light-depth BIS 50 group, despite 39% of patients receiving volatile < 0.7 MAC.
Daniel Jolley
Pholcodine, rocuronium and suxamethonium, showing common tertiary/quaternary ammonium epitopes.Australia and New Zealand both experience an unusually high incidence of perioperative anaphylaxis, particularly to neuromuscular blocking drugs. The opioid-based anti-tussive pholcodine has been implicated in increasing population hypersensitivity to muscle relaxants.
Although historically difficult to identify accurate denominator numbers for incidence calculations, more recent data shows that the anaphylaxis risk for rocuronium is particularly high in Australia & New Zealand and may in fact be roughly comparable to the local risk of suxamethonium anaphylaxis, at 1 in 2,000-3,000 exposures.
Rocuronium also has a higher risk of anaphylaxis than it’s aminosteroid-sibling vecuronium, and up to a ten-times greater risk than the benzylisoquinolinium atracurium (~1 in 22,500, depending on population). Cisatracurium demonstrates the lowest incidence of anaphylaxis (~1 in 50,000).
Daniel Jolley
This retrospective, observational cohort study over 6 years from Auckland, New Zealand identified a 10 fold higher incidence of anaphylaxis for rocuronium than for atracurium.
Also of note, the rate of anaphylaxis to rocuronium was similar to that for suxamethonium.
Anaphylaxis incidence for the three muscle relaxants were approximately:
- Atracurium – 1 in 22,500
- Rocuronium – 1 in 2,500
- Suxamethonium – 1 in 2,000
Daniel Jolley