Page 44 - CASA Bulletin of Anesthiology 2021, Vol 8, No. 6 (1)

CASA Bulletin of Anesthesiology

Figure 4: Average pain score over the 35 days post each infusion for each of the 20
patients. Each color represents a different patient.
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Dosing Guidelines

Determining a proper dosing regimen for ketamine infusions is difficult due to the wide
range of total doses and infusion/bolus regimens reported in studies. In the aforementioned
studies dosing has ranged from a low dose one time bolus of 0.4 mg/kg to a high dose infusion
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over days at 7 mg/kg/hr. In addition, there are few studies on dose response relationships that
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compare different doses of ketamine, instead of comparing ketamine versus placebo. One study
on refractory neuropathic pain in cancer patients already on morphine, found that there was more
relief with higher dosing, but also more side effects, and pain relief was only measured for up to
3 hours. Still, there are some papers that have attempted to give cursory recommendations on
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dosing.
Maher and colleagues concluded that evidence supports a dose response relationship. In this
literature review they provide a table of many of the large studies with dosing regimens and pain
outcomes. They claim level 2 evidence supports that higher dosing over longer periods of time
with more frequent administration is more effective, secondly rate is irrelevant, and lastly
regardless of dosing, side-effects are common, so adjunct medication like clonidine and
midazolam are helpful.
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Noppers and colleagues concluded infusions less than 2 hours were unlikely to provide relief
after 48 hours. Infusions over 10 hours had a 95% chance of significant pain relief after 48 hours,
and infusions over 30 hours had nearly a 99% chance. The Consensus Guidelines take a much
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more reserved approach, recommending to start with a single outpatient infusion of 80 mg
lasting more than 2 hours and reassess before initiating further treatment (grade C
recommendation).
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Conclusions

Based on the evidence, much higher dosing is likely needed for long-term relief from chronic
pain, as compared with depression (which is often 0.5 mg/kg over 40 minutes). This may make it
less suitable for the outpatient setting, although the study by Schwartzman and colleagues was
successful as high dose outpatient treatment. These studies can be difficult to blind since
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ketamine has such profound psychomimetic effects. Patients receiving adjunct medications, such
as midazolam and clonidine, may help with this by decreasing side-effects and giving the
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