Article Notes
- Remifentanil infusions above 0.20-0.25 μg/kg/min are associated with hyperalgesia (OIH = Opioid Induced Hyperalgesia) and tolerance (AOT = Acute Opioid Tolerance) respectively.
- Some of these effects can be mitigated by multimodal analgesia (notably ketamine), and possibly by gradual weaning of a remifentanil infusion.
- The findings have been predominately identified in rats and volunteer human studies. The clinical and longterm significance is still uncertain.
- Although OIH and AOT arise from different physiological mechanisms, they are clinically difficult (if not impossible) to differentiate.
- The clinical priority for management is prevention.
POISE showed that for every 1000 patients receiving metoprolol, 15 were prevented from suffering a myocardial infract, 3 from requiring cardiac revascularization along with 7 new cases of atrial fibrillation, but at a cost of causing an excess 8 deaths, 5 strokes, 53 hypotensive events and 42 episodes of bradycardia.
The harm associated with perioperative beta-blockade, at least in the form of non-titrated extended-release metoprolol, is greater than the demonstrated benefit. For every two cases of myocardial infract avoided there is one excess death.
Researchers induced awake paralysis in 10 volunteers using separately both suxamethonium and rocuronium. Both the BIS A2000 (2003) and BIS Vista monitor (2013) were tested.
BIS decreased immediately after paralysis and did not fully recover until muscle recovery. BIS values decreased to as low as 44, despite the subject being awake.
In more than half of the 20 trials the BIS value decreased to below 60 at some point. In one case this lasted for almost 4 minutes, representing 76% of the total paralysis time for that subject.
This controlled study randomised 212 children to either deep plane-of-anesthesia or awake, and either supine or lateral position, for removal of their laryngeal mask at the completion of surgery.
"Deep anesthesia" was defined as ET-sevoflurane 2.2%, stable for 1 minute. The "awake" group had their LMA removed by the PACU nurse after eye opening and/or obeying commands.
Airway complications included desaturation < 90%, stridor, laryngospasm, retching/vomiting, excess secretions and biting. A secondary outcome was also studied, assigning a 'clinical significance score' to the range of complications.
Deep removal in the lateral position was associated with the fewest complications. Deep removal when supine was associated with the most complications.
This study was a follow-up to a two-centre observational audit from 2008.
Van Decar et al. on the diagnosis and management of intra-operative diabetes insipidus concludes:
For the average adult patient, urine output >125 mL/h is consistent with polyuria. Urinary osmolality and specific gravity should be obtained and levels <300 mOsm/kg and <1.003, respectively, are consistent with hypotonic urine.
It is prudent to rule out other causes of polyuria including hyperglycemia, uremia, or iatrogenic causes including diuretic or mannitol administration.
Serum electrolytes and osmolality should also be obtained, and a high sodium (>146 mmol/L) and plasma osmolality (>300 mOsm/kg) are typically seen with DI.
Treatment should focus on replacement of free water deficit with a balanced salt solution, pharmacotherapy including DDAVP or vasopressin as appropriate, and close monitoring of patient’s fluid and electrolyte status.
The association of anesthesia in the sitting beach-chair position with intra-operative stroke, continues to be controversial. Although some studies have identified this as a risk, it is still a rare complication, albeit devastating.
Expert opinion suggests intra-arterial blood pressure monitoring is best practice, but most importantly with consideration for actual cerebral perfusion pressure given the sitting position.
Some research suggests regional anaesthesia, possibly combined with spontaneous ventilation GA (rather than relaxation GA with IPPV) offers unique benefits that better maintain cerebral oxygenation, although the exact difference is unclear.
Similarly, the benefit and role of non-invasive cerebral perfusion monitoring has not been conclusively shown, although it appears logical that it may offer benefit in these patients.
Case studies of patients suffering cerebral ischaemia under beach-chair, do point to combinations of poor intra-operative blood pressure management and possibly pre-existing mild cardiovascular disease (eg. hypertension) as contributing to some degree.
A case report describing the first-reported, successful and safe use of Xenon-based anesthesia in an MH-susceptible 31 year old male.
The authors conclude that this case, along with previous investigation of Xe in susceptible-swine animal models and in vitro human muscle biopsy testing, show that Xenon is likely safe for use in MH-susceptible individuals.