American Society of Regional Anesthesia and Pain Medicine November 2017 - 45

Ketamine Infusion on Regular Wards: A Myth or Reality?

T

he clinical use of ketamine for sedation, catalepsy, somatic
analgesia, bronchodilation, and sympathetic nervous system
stimulation began in 1970; however, its use has been
limited mostly to pediatric and trauma anesthesia because it can
cause side effects, especially the psychotropic effects.1 Because
of its strong analgesic effect, ketamine has recently emerged
as a promising adjunct for pain management as an alternative
to narcotic medications to end the dreaded opioid epidemic.
Ketamine works mainly as an N-methyl-D-aspartate (NMDA)receptor antagonist but also enhances descending inhibition and
has anti-inflammatory properties.1-5 The NMDA antagonism helps
to attenuate central sensitization and palliate neuropathic pain,
which are believed to play significant roles in the development and
propagation of chronic pain states.6-8

In recent years, a relatively large body of evidence has accumulated
showing the beneficial effects of intravenous ketamine infusion in
patients with chronic refractory pain states, including fibromyalgia,
neuropathic pain, phantom limb pain, postherpetic neuralgia,
complex regional pain syndromes (CRPS), diabetic neuropathy,
sickle cell pain during acute crises, and central pain related to
stroke or spinal cord injuries.9-13 However, to date, no guideline
has been developed for its use or a protocol to standardize doses
and duration because of the lack of quality studies and sufficient
evidence.
INFUSION PROTOCOLS
Because of the potential side effects of tachyarrhythmias,
hypertension, and psychomimetic effects, ketamine continuous
infusion was, historically, mostly limited to intensive or intermediate
care settings and thus associated with high costs. Ketamine,
however, can be administered safely on a nonacute, inpatient ward.
Following are the infusion protocols that have been implemented
at the University of Chicago
Medical Center and University
of Virginia Health System.
When used in subanesthetic
doses, ketamine is considered
safe and side effects are
generally well tolerated1 or
readily treatable. No major
complications have occurred
in our patients so far.

Sarah Choxi, MD
Clinical Associate
Department of Anesthesia and
Critical Care
University of Chicago
Chicago, Illinois

Xiaoying Zhu, MD, PhD
Assistant Professor
University of Virginia Health System,
Department of Anesthesiology, Pain
Management Center
Charlottesville, Virginia

Section Editor: Lynn Kohan, MD

syndrome, and pain related to vaso-occlusive sickle cell crisis.
Infusions are dosed based on ideal body weight and started at 1
mcg/kg/min and titrated to effect or best tolerated dose without
significant cardiovascular or central nervous system side effects
up to a maximum dose of 5 mcg/kg/min for a course of 1-5 days.
During this time, patients are closely monitored with routine
vital signs of blood pressure, pulse, respiratory rate, pain score,
and sedation level assessed 1 hour post dose following the first
dose or dose increase and then every 4 hours and continuous
pulse oximetry throughout infusion. The acute pain service is
alerted for systolic blood pressure greater than 160 mm Hg,
respiratory rate less than 10 breaths/min, any acute change in
mental status (eg, blunted affect, emotional withdrawal, thought
disorder, delirium), or any
difficulty in arousal despite
continuous stimulation.
Laboratory test results and
electrocardiograms are
checked periodically upon
the discretion of the acute
pain service attending.
Oxygen therapy via nasal
cannula is available to
maintain oxygen saturation above 92% with a bag valve mask
available at the bedside in case of severe hypoxia. Supportive
medications such as naloxone, lorazepam, and prochlorperazine are
readily available. At time of initiation, strong consideration is given
to decreasing or modifying opioid and nonopioid analgesics with
concomitant use of ketamine intravenous infusions.

"To date, no protocol has been developed
to standardize doses and duration of
ketamine infusion because of the lack of
quality studies and sufficient evidence."

University of Chicago. Patients are admitted to the inpatient
ward, where low-dose ketamine infusions outside of the intensive
care unit are managed by the acute pain service staffed by
faculty physicians trained in pain medicine and anesthesiology.
Conditions commonly treated with intravenous ketamine infusions
include neuropathic pain, CRPS, refractory headache or back pain
in patients with Chiari malformations, refractory abdominal pain
from inflammatory bowel disease or celiac artery compression

University of Virginia. At University of Virginia Health System,
ketamine infusions are also performed on an inpatient ward and

American Society of Regional Anesthesia and Pain Medicine
2017

45



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