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University of North DakotaUND Scholarly Commons
Nursing Capstones Department of Nursing
6-15-2017
Utilizing Dexmedetomidine During an AnteriorCervical Discectomy and FusionDanielle L. Kiedrowski
Follow this and additional works at: https://commons.und.edu/nurs-capstones
This Independent Study is brought to you for free and open access by the Department of Nursing at UND Scholarly Commons. It has been accepted forinclusion in Nursing Capstones by an authorized administrator of UND Scholarly Commons. For more information, please [email protected].
Recommended CitationKiedrowski, Danielle L., "Utilizing Dexmedetomidine During an Anterior Cervical Discectomy and Fusion" (2017). NursingCapstones. 185.https://commons.und.edu/nurs-capstones/185
Running head: DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
Utilizing Dexmedetomidine During an Anterior Cervical Discectomy and Fusion
by
Danielle L. Kiedrowski
Bachelor of Arts in Nursing, Concordia Moorhead, 2010
An Independent Study
Submitted to the Graduate Faculty
of the
University of North Dakota
in partial fulfillment of the requirements
for the degree of
Master of Science
Grand Forks, North Dakota
December
2017
DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
2
PERMISSION
Title Utilizing Dexmedetomidine During an Anterior Cervical Discectomy and Fusion
Department Nursing
Degree Master of Science
In presenting this independent study in partial fulfillment of the requirements for a graduate
degree from the University of North Dakota, I agree that the College of Nursing and Professional
Disciplines of this University shall make it freely available for inspection. I further agree that
permission for extensive copying or electronic access for scholarly purposes may be granted by
the professor who supervised my independent study work or, in his absence, by the chairperson
of the department or the dean of the School of Graduate Studies. It is understood that any
copying or publication or other use of this independent study or part thereof for financial gain
shall not be allowed without my written permission. It is also understood that due recognition
shall be given to me and to the University of North Dakota in any scholarly use which may be
made of any material in my independent study.
Signature ____________________________
Date _____________________________
DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
3
ABSTRACT
Title: Utilizing Dexmedetomidine During an Anterior Cervical Discectomy and Fusion
Background: Dexmedetomidine, is a highly selective 2-adrenoreceptor agonist containing
sedative, amnesic, analgesic, anxiolytic, and sympatholytic properties. Spine surgery can be very
challenging and specific anesthetic considerations should be applied when planning an anesthetic
plan. Safe neurophysiologic monitoring and pain management are two areas in which
dexmedetomidine can assist to allow for improved patient outcomes.
Purpose: Discover the evidence supporting the use of dexmedetomidine and spine surgery.
Process: The author’s literature search was performed through the University of North Dakota
Health Sciences Library. PubMed was selected as the search engine, as the intended use is for
medical professionals including the author’s profession of nurse anesthesia. PubMed also was
thought to have the most relevant and up-to-date journal articles concerning the wanted literature
search. The search box was selected and the first search term “dexmedetomidine” was placed.
This produced over 3,400 results which convinced the author to decrease the search results with
a filter and utilize the Medical Subject Headings (MeSH) database. The filter applied included
full text, English language, human subjects, and published within last five years. MeSH database
link was selected under the More Resources column. Additional search terms included “spine”
(with the addition of surgery under controlled vocabulary in MeSH), “anterior cervical
discectomy and fusion”, “myelomalacia”, “neurophysiologic monitoring”, “evoked potentials”,
and “opioid”. The most relevant journal articles pertaining to the author’s wanted literature
search included the search terms “dexmedetomidine” and “spine surgery”.
Results: Dexmedetomidine does not affect evoked potentials, it reduces the amount of volatile
and intravenous anesthetic, and minimizes the impedance of anesthetics on neurophysiologic
monitoring. It was also discovered that opioid use was decreased intraoperatively as well as
postoperatively with dexmedetomidine use. Thus, the negative side effects of opioids are
lessened, which may improve patient satisfaction. Adjuncts such as ketamine and lidocaine to
dexmedetomidine also became apparent to assist in additional pain relief intraoperatively.
Implications: The use of dexmedetomidine is beneficial for individuals undergoing spine
surgery, specifically an anterior cervical discectomy and fusion. It may also be helpful among
other surgeries such as minimally invasive spine surgery, laparoscopic cholecystectomies,
uterine artery embolization for fibroid tumors or adenomyosis, as well as for chronic pain and
opioid dependent patient populations (Bakan et al., 2014; Dunn, Durieux, & Nemergut, 2016; C.
H. Kim et al., 2013; K. H. Kim, 2014).
Keywords: Dexmedetomidine, spine surgery, anterior cervical discectomy and fusion,
myelomalacia, neurophysiologic monitoring, and evoked potentials.
DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
4
Utilizing Dexmedetomidine During an Anterior Cervical Discectomy and Fusion
Surgery of the spine is highly invasive which presents challenges to the medication
regimen that is administered to maintain safety with untainted neurophysiologic monitoring
ability, patient comfort, and stable hemodynamics. It is imperative for anesthesia professionals to
have the knowledge regarding anesthetics (intravenous and volatile) and opioid requirement as it
pertains to the surgical procedure. For example, spine surgeries often “require larger doses of
opioids and higher concentration of anesthetic agents to suppress the hypertensive response,
which can interfere with neurophysiological monitoring” (Mariappan, Ashokkumar, &
Kuppuswamy, 2014, p. 192). Both inhaled and intravenous anesthetics can hinder evoked
potentials, displaying as false readings mimicking the appearance of spinal cord compromise
thus requiring an anesthetic plan that provides comfort and safety. Given that, balanced
anesthesia is the goal of anesthesia professionals, it is vital that these concerns are considered
when developing an anesthetic plan of care for these patients.
Case Report
A 47-year-old, 160 cm, 79.8 kg male presented for an anterior cervical discectomy and
fusion of the 4th and 5th cervical vertebrae. His medical history included seizures, anxiety,
hypertension, hydronephrosis, developmentally delayed from neonatal meningitis, impaired
mobility and activities of daily living, gait instability, and dysphagia. Past surgical history
included a ventriculoperitoneal shunt placement with two revisions and recent laminectomies of
the 2nd to 6th cervical vertebrae. The laminectomy surgery was post-operatively complicated with
pneumonia, treated then discharged home. Subsequently, the patient presented with increased
gait instability, left sided weakness, dysphagia, and worsening incontinence following his recent
laminectomies of the 2nd to 6th cervical vertebrae indicating the need for an additional spine
DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
5
surgery. Pre-operative magnetic resonance imaging (MRI) scan of the cervical spine displayed
worsening disc herniation at the 4th and 5th cervical vertebrae and myelomalacia of the spinal
cord at the 5th cervical vertebrae warranting the plan for an anterior cervical discectomy and
fusion of the 4th and 5th cervical vertebrae. His current medication regimen included guaifenesin-
dextromethorphan, miconazole powder, acetaminophen, triamcinolone acetonide, aspirin,
carbamazepine, divalproex sodium, epinephrine pen, lacosamide, lorazepam, magnesium
hydroxide, melatonin, oyster shell calcium + vitamin D, paroxetine, risperidone, and senna-
docusate. Allergies included bee stings, amoxicillin, and augmentin. Given the patient’s medical
history and current health status, he was considered an American Society of Anesthesiologists
physical status level 3.
Pre-operative airway evaluation demonstrated a Mallampati III, with visualization of only
soft palate and uvula base, a thyromental distance less than 6 cm, an inter-incisor distance less
than 4 cm, and limited atlanto-occipital joint mobility suggesting a potential difficult airway. The
anesthesia team planned a modified rapid sequence induction and the use of the GlideScope
(Verathon Inc., Bothell, WA) for intubation to minimize cervical vertebrae movement as well as
the potential for difficult placement of the endotracheal tube. Pre-operative vital signs included a
blood pressure of 148/80 mmHg, heart rate 82 in normal sinus rhythm, oxygen saturation of 98%
on room air, and afebrile with a temperature of 98.7. The patient’s chart was further reviewed
then the patient and guardian were informed of the anesthetic risks and benefits of general
anesthesia and consented.
In the surgical holding room, an 18-gage intravenous (IV) access was established and
Lactated Ringers (LR) fluid was initiated. Upon arrival to the operating room, standard monitors
were applied, midazolam 2 mg IV was given for anxiolysis, and oxygen supplementation at 10
DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
6
liters/minute of flow via facemask for 5 minutes was started. A modified rapid sequence
intravenous induction was utilized. Induction medications included fentanyl 100 mcg, lidocaine
40 mg, rocuronium 5 mg, propofol 150 mg, and succinylcholine 140 mg. Once the patient
achieved unconsciousness and negative eyelid movement with eyelash stimulation, artificial
ointment was applied to bilateral lower conjunctiva then the eyelids were closed and secured
with tape. Next, a GlideScope (Verathon Inc., Bothell, WA) Macintosh size 3 was introduced
into the mouth and placed into oropharynx providing a full grade I view of the vocal cords onto
the video monitor. An 8.0 mm cuffed endotracheal tube with stylet was advanced through the
larynx successfully on first attempt. Placement was confirmed by the presence of end-tidal
carbon dioxide (ETCO2) as well as auscultation of bilateral breath sounds in upper and lower
lung lobes. The endotracheal tube was secured and the patient was placed on synchronized
intermittent mechanical ventilation. General anesthesia was maintained with 1% sevoflurane
inspired concentration in an oxygen and air mixture of 1 L/min each, a propofol infusion at 50
mcg/kg/min, and a dexmedetomidine infusion at 0.5 mcg/kg/hr. No dexmedetomidine loading
dose was given. Slight hypotension was encountered mid-way during the case so the propofol
infusion was decreased to 25 mcg/kg/min.
The surgical procedure was uneventful and neurophysiological monitoring remained
stable throughout the case. Upon conclusion of the case, the patient successfully followed
commands by opening eyes and lifting head, a regular breathing pattern was noted with 600 ml
of tidal volume, and the trachea was extubated. A simple mask with oxygen 6 liters/min was
applied. Hemodynamics remained stable and was transferred to the post-anesthetic recovery unit
without complications. The post-operative evaluation was also stable without anesthetic
complications. The patient was admitted as pre-operatively planned for close monitoring. Post-
DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
7
operative day 1, the patient’s baseline left-sided weakness was still present but improvement was
noted to the patient’s ambulation as compared to preoperatively. The patient’s post-operative
hospital length of stay totaled 8 days. During the hospital course, the patient developed
worsening dysphagia resulting in a failed swallow evaluation. A nasopharyngeal feeding tube
was initially placed but then later required a gastrostomy tube with interventional radiology. The
patient required chest physiotherapy during his hospital stay to assist the prevention of
pneumonia as the patient failed to successfully complete incentive spirometry. Also, the patient
developed intermittent fevers and bowel distension, both of which resolved spontaneously
without treatment. Patient was successfully discharged to a group home with this gastrostomy
tube but had improved left sided-weakness and ambulation. The patient was scheduled to follow
up with speech therapy two weeks following his hospital stay for his dysphagia.
Discussion
Dexmedetomidine
Mechanism of action. Dexmedetomidine, is a highly selective 2-adrenoreceptor
agonist, binding to the 2 and 1 receptors in a 1620:1 ratio (Mariappan et al., 2014). In
comparison, clonidine, another selective 2-adrenoreceptor agonist has selectivity towards 2
receptors in a 200:1 fashioned ratio (Mariappan et al., 2014). Dexmedetomidine produces
sedative, amnesic, analgesic, anxiolytic, and sympatholytic properties without causing
respiratory depression (Sen, Chakraborty, Santra, Mukherjee, & Das, 2013).
Indications. The United States Food and Drug Administration (FDA) approved
dexmedetomidine for sedative infusions for 24 hours or less in the Intensive Care setting when
the patient is intubated and mechanically ventilated (Hospira, 2016). Additionally,
DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
8
dexmedetomidine has been approved for “sedation of non-intubated patients prior to and/or
during surgical and other procedures” (Hospira, 2016, p. 3).
Side effects. The side effects associated with dexmedetomidine include hypotension,
bradycardia, sinus arrest, transient hypertension, and dry mouth (Hospira, 2016).
Dexmedetomidine is also associated with tolerance, tachyphylaxis, acute respiratory distress
syndrome, respiratory failure, and agitation when the infusion exceeds 24 hours (Hospira, 2016).
Dose. A loading dose is recommended as 1 mcg/kg to be given over 10 minutes, then the
initiation of a maintenance dose infusion rate of 0.2 to 0.7 mcg/kg/hour for sedation for the
intensive care setting or 0.2 to 1 mcg/kg/hour for adult procedural sedation and titrated for
desired clinical effect (Hospira, 2016).
Cost. For a 100-ml bottle with the concentration of 4 mcg/ml, the cost is $75.26 (K.
Kern, personal communication, January 4, 2017).
Pharmacokinetics.
Absorption. Currently, dexmedetomidine is only registered for intravenous
administration but further research is being conducted evaluating off-labeled uses of oral,
intramuscular, intranasal, and buccal routes of administration (Weerink et al., 2017). A four-
period, cross-over design, randomized open study was conducted with 12 healthy male subjects
evaluating the bioavailability among extravascular routes of dexmedetomidine (Anttila, Penttilä,
Helminen, Vuorilehto, & Scheinin, 2003). When dexmedetomidine is administered orally, it
undergoes significant first pass effect with approximately 16% bioavailability and complete
bioavailability with intramuscular administration (Anttila et al., 2003). Additionally, intranasal
and buccal route, alternative noninvasive administration techniques were also evaluated, both
illustrating an 82% mean bioavailability, which would be helpful for the uncooperative patient
DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
9
population when intravascular placement is impossible (Anttila et al., 2003; Yoo et al., 2015).
Distribution. Distribution is rapid, it may cross the placenta as well as distribute into
breast milk and has been assigned as a pregnancy category C (Hospira, 2016). The steady-state
volume of distribution is 118 liters with a half-life of 6 minutes. When dexmedetomidine is
administered intravenously for up to 24 hours between the dosages of 0.2-0.7 mcg/kg/hour, it
demonstrates linear pharmacokinetics (Hospira, 2016). Protein binding is approximately 94%
(Hospira, 2016).
Metabolism. Dexmedetomidine is metabolized through hepatic processes via N-
glucoronidation, N-methylation, and cytochrome P2A6 (Hospira, 2016).
Elimination. Terminal elimination half-life of 2 hours and undergoes clearance of
approximately 39 L/h (Hospira, 2016). Excretion of dexmedetomidine occurs 95% through urine
and 4% through feces (Hospira, 2016).
Pharmacodynamics.
Sedative effects. The mechanism is not well understood however the sedative effects are
thought to occur from the stimulation of 2-receptors in the locus coeruleus among central
presynaptic and postsynaptic receptors promoting an endogenous physiologic sleeping pattern
(Weerink et al., 2017).
Analgesic effects. It is believed that the analgesic effects occur from dexmedetomidine
binding to the central and spinal cord 2-receptors resulting in decreased release of substance P
and glutamate thus potentially resulting in opioid-sparing effects (Weerink et al., 2017).
Cardiovascular effects. Dexmedetomidine binds 2-adrenoreceptors found within the
peripheral and central nervous systems in pre-, post-, and extra-synaptic sites reducing the
release of norepinephrine and the plasma norepinephrine concentration (Penney, 2010). There
DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
10
are three 2-adrenoreceptors: 2a, 2b, and 2c. Hemodynamic effects are dose dependent.
Hypertension and bradycardia are commonly seen when high dosages of dexmedetomidine are
administered, especially following the loading dose of 1 mcg/kg over 10 minutes (Weerink et al.,
2017).
This hyperdynamic vasoconstrictive response is thought to be caused by the stimulation
among 2b-receptors within the vascular smooth muscle resulting in increased blood pressure
and a decrease of heart rate from the baroreceptor reflex (Penney, 2010; Weerink et al., 2017).
As the plasma concentration of dexmedetomidine diminishes, for instance once the loading dose
is completed, the 2-receptors within the vascular endothelial cells respond by causing a
vasodilation response resulting in the common side effect of hypotension associated with
dexmedetomidine (Weerink et al., 2017). It is also believed that centrally located 2a and 2c
adrenoreceptors may contribute to the hypotension associated with dexmedetomidine (Penney,
2010). “If necessary, high plasma concentrations can be avoided by decreasing loading dose
sizes or by increasing time over which the loading dose is administered” (Weerink et al., 2017, p.
13). Sympatholytic properties that dexmedetomidine possesses include a decrease in heart rate,
mean arterial blood pressure, cardiac output, and norepinephrine release from binding to 2-
receptors both centrally and peripherally (Jamaliya et al., 2014). Dexmedetomidine has also been
used in conjunction for spine surgery as a hypotensive agent to a decrease in blood loss as well
as improve surgical field visualization (Jamaliya et al., 2014).
Respiratory effects. Dexmedetomidine minimally suppresses respiratory drive in which
the response to carbon dioxide is still present mimicking a natural sleeping pattern (Weerink et
al., 2017).
Spine Pathophysiology and Surgery
DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
11
Myelomalacia. Spinal cord injury resulting in softening of the spinal cord through
compression, ischemia, or hemorrhage is termed myelomalacia (Zhou, Kim, Vo, & Riew, 2015).
Clinical manifestations of this disorder may be displayed as weakness, sensory loss, and poor
coordination or dexterity (Smorgick et al., 2015). The patient discussed in the case report
displayed this abnormality of myelomalacia of the spinal cord at the 5th cervical vertebrae. This
patient’s clinical manifestations that corresponded with myelomalacia includes gait instability
and left sided weakness. Myelomalacia is reversible if interventions are implemented early with
decompression surgery.
According to Potter & Saifuddin (2003), myelomalacia is the most common disorder
among spinal cord injury patients represented by a 55% prevalence. Furthermore, Zhou et. al.
(2015) completed a retrospective study evaluating 23,139 patients undergoing cervical MRI’s,
964 patients were diagnosed with cervical myelomalacia calculating to approximately 4.2% of
this population. In addition, they found that myelomalacia was higher among the male gender at
5.6% (576/10,196) compared to 3.0% (388/12,943) (Zhou et al., 2015). Further, as a person ages,
the prevalence for myelomalacia also increases until 80 years of age. The highest prevalence for
myelomalacia was among individuals between 70 to 79 years of age with a 7.6% prevalence then
interestingly enough decreases after age 80 at 5.1% (Zhou et al., 2015).
Anterior cervical discectomy and fusion. Discectomy is a procedure that is completed
to alleviate compression of the spinal cord or nerve roots by removing herniated disks or
osteophytes (Jaffe, Schmiesing, & Golianu, 2014). Fusions are also commonly completed during
spine surgery by placing a bone graft or prosthesis to support the disc space preventing collapse
of the disc space and deformity as well as restoring the natural curvature of the spine (Jaffe et al.,
DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
12
2014). Most commonly the patient assumes prone position for spine surgeries but if an anterior
approach is determined such as in the cervical vertebrae region the patient assumes supine.
In the case report, the patient’s cervical discectomy and fusion was determined in which
the anterior approach was decided, implicating the supine position. Due to the more predictable
anatomic path of the left recurrent laryngeal nerve, injury risk is reduced when the left side of the
neck is utilized for the anterior approach (Jaffe et al., 2014). Exposure of the anterior cervical
spine is accomplished by dissecting a route between the carotid sheath and the esophagus then
the disc is removed microscopically after fluoroscopic confirmation (Jaffe et al., 2014).
Complications. Complications associated with anterior cervical spine surgery include
venous air embolisms, esophagus perforation, retraction nerve injury, hypotension, airway
obstruction from edema, hematoma, neurologic deficit, and tension pneumothorax (Jaffe et al.,
2014). According to a retrospective cohort study evaluating 183 elective anterior cervical
discectomy and fusion patients by Basques and colleagues, patients with a history of nonspinal
malignancy, pulmonary disease, and corpectomy are at risk for increased length of stay thus
placing these individuals at a higher risk for additional complications (Basques, Bohl,
Golinvaux, Gruskay, & Grauer, 2014). These additional complications include pneumonia,
venous thromboembolisms, and delirium (Basques et al., 2014). In contrast, “[a]ge, elevated
BMI, ASA class, smoking history, diabetes, heart disease, number of levels fused, and the use of
an iliac crest bone graft did not correlate with extended length of stay” (Basques et al., 2014, p.
945). Thus, at lower risk of further complications.
Anesthetic Considerations
Evoked potentials. One major concern during spine surgery is the neurophysiologic
status of the patient. Neurophysiologic monitoring with the use of evoked potentials is
DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
13
commonly used to enhance patient safety during spine surgery (Rozet et al., 2015). Evoked
potentials are frequently used for spine surgery including somatosensory evoked potentials
(SSEPs) and motor evoked potentials (MEPs) (Rozet et al., 2015). SSEPs assess the dorsal
sensory portion and MEPs evaluate the anterior motor portion of the spinal cord. These two
neurophysiologic monitoring modalities evaluate spinal cord compromise by measuring the
amplitude and latency during evoked potentials, thus assessing the intactness of the spinal cord
during surgery (Mahmoud et al., 2010). Amplitude depression, prolonged latency, and decreased
motor response indicates neurologic injury and requires immediate intervention (Mahmoud et al.,
2010). Specifically, in SSEPs, criteria for significant change occurs when a 50% decrease of
amplitude and/or a 10% increase of latency is detected and the cause should be examined (Bithal,
2014). For MEPs, a 50% decrease in amplitude and diminished motor response indicates
significant change also requiring attention (Bithal, 2014). Hence, it is important for the
anesthesia professional to consider evoked potentials when developing an anesthetic plan.
Intravenous and volatile anesthetics suppress evoked potentials by interrupting the quality
and accuracy of neurophysiologic monitoring (Rozet et al., 2015). A common intravenous
anesthetic utilized intraoperatively for spine surgery is propofol, due to its high safety profile and
rapid emergence (Sen et al., 2013). It is believed to enhance the interaction of gamma-
aminobutyric acid (GABA), an inhibitory neurotransmitter, with the GABA receptor, resulting in
sedation by cell membrane hyperpolarization and synaptic inhibition (Mariappan et al., 2014;
Bithal, 2014). Propofol displays a decrease in amplitude of SSEPs as well as suppresses MEPs
when given in high dosages or in bolus doses which may result in complete interruption of
neurophysiologic monitoring (Bithal, 2014). Determining an appropriate intravenous anesthetic
dose is challenging when evoked potentials are included within the surgical plan.
DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
14
Further, according to Bithal (2014), all volatile anesthetics are associated with dose
dependent amplitude depression, prolonged latency, and motor suppression. Isoflurane
suppresses evoked potentials the greatest, however, monitoring of SSEPs may be still possible
when a goal of minimum alveolar concentration (MAC) value of 0.5-1.0 is implemented.
Likewise, sevoflurane and desflurane may be included in the anesthetic plan if the MAC value is
less than 1.5. Moreover, MEPs are deterred at lower MAC values with all halogenated volatile
anesthetics, yet still allows monitoring of MEPs when the MAC value is less than 0.5% (Bithal,
2014).
If volatile anesthetic technique is utilized within an anesthetic plan when EPs are
executed, the anesthesia provider must communicate with the neurophysiology team as to
whether SSEPs and/or MEPs will be applied. As a rule of thumb, a goal MAC value of 0.5
would be safe for either SSEPs or MEPs.
A combination of volatile and intravenous anesthetic plan was utilized for the case report.
As described in the case report, the anesthesia was initiated and maintained with 0.5 MAC of
sevoflurane along with intravenous anesthetic of propofol and adjunct dexmedetomidine
infusions. The propofol infusion was decreased to alleviate hypotension.
Due to intravenous and volatile anesthetic interruption to evoked potentials, it is
recommended that an anesthetic-sparing technique is employed when evoked potentials are
utilized (Rozet et al., 2015). Dexmedetomidine is known to decrease anesthetic dosages without
hindering neurophysiologic monitoring and weakening sedation. According to Rozet et al.,
dexmedetomidine does not prolong latency or decrease amplitude of SSEPs, MEPs, and VEPs
when used at clinical doses (2015). In a double-blind, placebo-controlled trial of 40 adult patients
undergoing elective spine surgery with total intravenous anesthetic with propofol and
DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
15
remifentanil, assessed adjunct dexmedetomidine and evoked potential response (Rozet et al.,
2015). This study discovered that dexmedetomidine did not alter EPs at clinically relevant
dosages and declared its use to be safe during spine surgery when EPs are used (Rozet et al.,
2015). Dexmedetomidine also enhances the hypnotic effect of propofol allowing for reduced
doses of this anesthetic while still allowing accurate neurophysiologic monitoring.
Furthermore, Sen and colleagues (2013) performed a randomized control trial of 70
patients undergoing elective spine surgery evaluating propofol requirements during induction
and maintenance anesthetic phases. Half of the patients received dexmedetomidine with propofol
and the other half omitted dexmedetomidine. This study found a 48.08% decrease in mean
requirement of propofol during induction and a 61.87% decrease during the maintenance phase
of anesthesia when dexmedetomidine was used (Sen et al., 2013). The requirement of volatile
anesthetic is also reduced with the use of a dexmedetomidine infusion.
Similarly, a randomized controlled trial consisting of 48 patients undergoing abdominal
surgery, dexmedetomidine allowed a 39% reduction in sevoflurane based anesthetic (Harsoor et
al., 2015). Alike, Mizrak and colleagues reported a double-blind, placebo-controlled study
assessing dexmedetomidine administration prior to induction and the effects on sevoflurane
MAC concentration during an inhalation induction on 60 adult patients undergoing intubation for
general anesthesia (2013). Induction time was decreased by approximately 75% and significantly
decreased the sevoflurane end-tidal concentration (Mizrak et al., 2013). Also, a 28% reduction of
sevoflurane concentration was noted when a dexmedetomidine infusion was applied within a
randomized, double-blind controlled trial among 40 patients undergoing general anesthesia for
abdominal surgery (Harsoor, Rani, Lathashree, Nethra, & Sudheesh, 2014). In a concise manner,
DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
16
dexmedetomidine, reduces intravenous and inhaled anesthetics preventing anesthetic interference
while promoting the ability to safely monitor and detect negative neurologic outcomes.
Other anesthetic considerations related to neurophysiologic monitoring include avoiding
neuromuscular antagonists if motor evoked potentials are used. Neuromuscular antagonists
disturb and prevent the conduction of motor evoked potentials thus preventing the ability to
neurophysiologically monitor (Jaffe et al., 2014). Also, the neurophysiology team should be
updated if any changes to anesthetic depth, anesthetic medications, blood pressure, PCO2, and
PO2 occur as these may cause false readings of spinal cord compromise (Jaffe et al., 2014).
Pain Management. In addition to the anesthetic-sparing effects, dexmedetomidine also
has opioid-sparing effects (Dunn et al., 2016). Spine surgery is very stimulating and may require
large doses of opioids (Garg et al., 2016). Often, the patient population that presents for spine
surgery frequently suffers from chronic pain and are treated with long-term opioid medication
regimens making pain management perioperatively difficult due to opioid tolerance (Dunn et al.,
2016). Opioids may provide pain relief; however in large dosages, opioids have been found to
cause hyperanalgesia (Mariappan et al., 2014). Hyperanalgesia results in patient tolerance
consequently increasing the requirement of opioids to provide adequate pain control thus
increasing the risk of negative opioid side effects. These side effects include itching, respiratory
depression, nausea/vomiting, and constipation. Interestingly, the patient described in the case
report did not take chronic opioids in which did not fit the typical spine surgical patient and
contrasts with this patient profile.
According to a cross-sectional study evaluating 1,857 adults with a history of spine
related pain and the prevalence of chronic neuropathic pain from spinal cord or nerve root
compression or damage revealed a 53.3% prevalence of neuropathic pain (Yamashita, Takahashi,
DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
17
Yonenobu, & Kikuchi, 2014). Thus, the incidence of chronic pain is high within the spine
surgical patient population and must be considered within the anesthetic plan.
Likewise, a prospective study involving 67 anterior cervical discectomy and fusion
patients were evaluated investigating pain, range of motion, motor function, and sensory function
pre-operatively and post-operatively assessing the influence of these factors on patient
satisfaction (Hessler et al., 2012). It was found that range of motion, motor function, and sensory
function did not significantly impact patient satisfaction. However, improvement of pain
displayed a significant role in patient satisfaction as well as the patient’s perception of success of
the surgery (Hessler et al., 2012). Pain-reducing regimens during and after surgery should be the
aim of anesthesia providers to reach highest patient satisfaction and improve quality of life.
Dexmedetomidine contains analgesic properties therefore reducing opioid requirements
intraoperatively as well as post-operatively. With the reduction of opioids, hyperanalgesia,
tolerance, and side effects that are associated with opioids and can be reduced with the use of
dexmedetomidine. Moreover, Arain, Ruehlow, Uhrich, & Ebert (2004) conducted a randomized
control trial of 34 inpatients scheduled for elective surgery evaluating the use of
dexmedetomidine and morphine requirements post-operatively. Two groups were divided evenly
between patients receiving a dexmedetomidine infusion or a morphine infusion intraoperatively.
A 66% decrease of opioid requirement post-operatively was noted among the dexmedetomidine
group (Arain, Ruehlow, Uhrich, & Ebert, 2004).
Similarly, Garg and colleagues conducted a prospective randomized double-blind placebo
controlled study involving 66 patients undergoing spine surgery and found a 54% decrease in
opioid requirement post-operatively when dexmedetomidine was used (Garg et al., 2016).
Furthermore, Kim and colleagues (2013) performed a prospective randomized study
DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
18
investigating opioid consumption and opioid-related side effects among 50 patients undergoing
uterine artery embolization. The 50 patients were divided into two groups: a dexmedetomidine
infusion was started 30 minutes prior to the procedure and continued 6 hours after, while the
other group received a placebo of matching normal saline volume (Kim et al., 2013). Both
groups were given patient controlled analgesia (PCA) with intravenous fentanyl. A lower pain
score, less rescue analgesics, as well as a decrease of 28% of fentanyl was found when a
dexmedetomidine infusion was utilized (Kim et al., 2013). Multi-modal approaches with
dexmedetomidine infusions also assists in opioid-sparing anesthetic plans improving patient
comfort and pain management (Garg et al., 2016).
Adjuncts. A promising analgesia relieving adjunct to dexmedetomidine is ketamine.
Ketamine, a N-methyl-d-aspartate (NMDA) receptor antagonist, may be added as an adjunct to
dexmedetomidine to assist in pain management as well as reduce anesthetic requirements.
Sedation from ketamine is due to the functional dissociation of the thalamo-neocortical system
and limbic system causing depression of the thalamus and cerebral cortex while simultaneously
activating the limbic system resulting in additional anesthetic-sparing capability (Mion &
Villevieille, 2013). Plus, it contains analgesic properties due to binding of opioid receptors,
subsequently providing supplementary opioid-sparing ability (Mion & Villevieille, 2013). “By
blocking the NMDA receptor, ketamine holds obvious promise for attenuating these centrally
mediated pain processes, thereby reducing acute pain and potentially preventing chronic pain”
(Gorlin, Rosenfeld, & Ramakrishna, 2016, p. 162).
Ketamine may be a beneficial adjunct to dexmedetomidine to assist in the opioid tolerant
and chronic pain population. In 2011, a systematic review of 70 studies, evaluated intravenous
ketamine for perioperative analgesia (Laskowski, Stirling, McKay, & Lim, 2011). This
DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
19
systematic review revealed that within placebo groups, 78% experienced more pain even with
increased amounts of opioids than ketamine groups (Laskowski et al., 2011). Additionally,
among the ketamine treated groups, there was a reduction in opioid consumption post-
operatively, improved quality of pain control, as well as delayed time to the first post-operative
analgesic requirement (Laskowski et al., 2011).
Further, in a prospective, double-blinded, and placebo-controlled study of 102 opiate
dependent patients receiving major lumbar spine surgery determined that there was a 37%
reduction of opioids in the acute post-operative phase (Loftus et al., 2010). Also, a decreased
intensity of pain in post-anesthetic care unit and 6 weeks following surgery was discovered,
along with a decreased amount of morphine analgesia needed during the post-operative period up
until the first follow up visit (Loftus et al., 2010).
Concerted dexmedetomidine and ketamine infusions appear to be a novel practice. A case
report by Penney (2010) discussed the combination of dexmedetomidine and ketamine infusions
for a 15 year old female undergoing scoliosis repair surgery. It discussed the potential future for
these two medications in spine surgery in neurophysiologic monitoring. Evoked potentials were
not interrupted and in fact, with the addition of ketamine, motor-evoked potentials were
enhanced (Penney, 2010). Additionally, analgesia properties of both medications presented an
avenue for supplementary pain relieving methods.
Relatedly, Nama, Meenan, & Fritz (2010), examined a case report of a 47 year old female
suffering from complex regional pain syndrome whom was also treated with the combination of
dexmedetomidine and ketamine infusions. This combined infusion was given for 19 hours to
which the patient experienced complete relief of pain due to the synergist analgesic effect while
eliminating the negative side effects of both medications (Nama et al., 2010). All in all, ketamine
DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
20
as an adjunct to dexmedetomidine and spine surgery would assist in providing additional
analgesia coverage especially for those opioid dependent individuals but warrants additional
research.
However, the many positive effects of dexmedetomidine, it is still necessary to
continually assess the patient for negative side effects such as hypotension and bradycardia
(Garg et al., 2016). Ketamine may also be helpful in countering these negative side effects.
Tachycardia, increases in blood pressure, and cardiac output are common with ketamine,
preventing hypotension and bradycardia from dexmedetomidine (K. H. Kim, 2014; Tobias,
2012). Likewise, dexmedetomidine prevents tachycardia, hypertension, and salivation associated
with ketamine (K. H. Kim, 2014; Tobias, 2012).
Similarly, many studies have evaluated dexmedetomidine and ketamine use in procedural
sedation among the pediatric population. For example, Tobias (2012) reviews four large case
series (n >10) and eight small (n <10) or single case series involving dexmedetomidine-ketamine
infusions for procedural sedation with infants and children. It was also found that the
combination of ketamine and dexmedetomidine offset the negative side effects of both
medications.
Bronchodilatory properties are also present with ketamine as well as allows maintenance
of respiratory drive and airway reflexes. To note, ketamine is contraindicated in ischemic heart
disease, hypertension (pulmonary/systemic), elevated intracranial pressure, elevated intraocular
pressure, globe injuries, psychosis, hepatic dysfunction, liver transplant, porphyria,
pheochromocytoma, and seizure patient populations (Gorlin et al., 2016). As previously
discussed, the case report patient did not receive adjunct intravenous ketamine due to the
patient’s history of seizures.
DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
21
Like dexmedetomidine and ketamine, lidocaine may also deliver supplementary pain
relief especially for those individuals whom suffer from chronic pain and opioid use. Lidocaine,
a sodium channel blocker, may also assist in pain management as an adjunct to
dexmedetomidine. When administered intravenously, lidocaine provides anti-inflammatory,
analgesic, and anti-hyperanalgesic properties (Farag et al., 2013). A randomized control trial
consisting of 116 adults undertaking complex spine surgery were evaluated on pain, opioid
consumption, and quality of life following surgery (Farag et al., 2013). One group received
intravenous lidocaine intraoperatively and during the post-anesthetic care unit at a rate of 2
mg/kg/hr or received a placebo (Farag et al., 2013). Those individuals belonging to the lidocaine
group voiced improved pain scores in comparison to the placebo group (Farag et al., 2013).
Likewise, in 2014, a randomized control trial of 80 patients undergoing a laparoscopic
cholecystectomy were placed into two groups: opioid-free anesthesia (dexmedetomidine,
lidocaine, and propofol infusions) and opioid-based anesthesia (remifentanil and propofol
infusions) (Bakan et al.). The authors concluded that opioid-free anesthesia had considerably
lower pain ratings, consumption of rescue analgesics, and less antiemetic use (Bakan et al.,
2014).
Similarly, another study that evaluated lidocaine as an adjunct infusion to total
intravenous anesthesia with propofol-sufentanil was a retrospective review 129 cases whom
underwent spine surgery (Sloan, Mongan, Lyda, & Koht, 2014). It was discovered that sufentanil
and propofol dosages were decreased among groups receiving the lidocaine adjunct, specifically
five 5-ml ampules of sufentanil and one hundred and four 50-ml bottles of propofol (Sloan et al.,
2014).
DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
22
Additionally, 51 lumbar surgical patients were included in a randomized, double-blinded,
placebo-controlled trial evaluating the effect of lidocaine on postoperative pain (K. T. Kim et al.,
2014). With the use of a lidocaine infusion pre- and intraoperatively, for up to 48 hours pain
post-operatively was reduced as well as opioid consumption for 24 hours following surgery (K.
T. Kim et al., 2014). To note, lidocaine should be avoided among individuals that have a
hypersensitivity to amide local anesthetics.
All evidence considered, great possibility is among these adjuncts for additional pain
management medications, however, more research is needed in this topic of adjunct use with
dexmedetomidine.
Evidence Based Recommendations
Practice.
Method of Anesthetic. Propofol is superior over volatile anesthetics as there is less
potential of interruption of SSEPs and MEPs (Rozet et al., 2015). Specifically, MEPs are easily
depressed with volatile anesthetics (Mahmoud et al., 2010). Therefore, it is suggested that
volatile anesthetics are avoided and total intravenous anesthesia is recommended during spine
surgeries when evoked potentials are used (Bithal, 2014; Mahmoud et al., 2010; Rozet et al.,
2015). However, a combination of volatile anesthesia with intravenous anesthesia is still
possible. Approach each case individually and communicate with the neurophysiological team
regarding the goals for monitoring. For example, if only SSEPs are to be conducted, evoked
potentials can generally still be accurately monitored if the minimum alveolar concentration is
less than 1.5 (isoflurane) or less than 1.0 (desflurane or sevoflurane) (Bithal, 2014). Likewise,
when MEPs are implemented, a lower MAC should be maintained at 0.5 or less to avoid
hindrance (Bithal, 2014). Maintaining a MAC of 0.5 or less is would allow either SSEPs or
DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
23
MEPs to be safely monitored. Also, consider induction paralytic for intubation. Again, open
communication with the neurophysiologic team is vital to prevent inaccurate readings. Discuss
when MEPs will be applied and consider duration of action of paralytic during intubation.
Administration of Dexmedetomidine. An infusion of dexmedetomidine is to not exceed
24 hours. It is recommended to administer a dexmedetomidine loading dose of 1 mcg/kg over 10
minutes and prior to starting a continuous infusion of 0.2 mcg/kg/hour to 1 mcg/kg/hour to avoid
significant hypotension and bradycardia (Garg et al., 2016; Hospira, 2016). Most importantly,
incorporating dexmedetomidine into an anesthetic plan should be individualized and not
generalized to all patient populations.
Adjuncts. Intravenous opioids minimally alter SSEPs and MEPs and may be safely used
as continuous infusions during neurophysiologic monitoring (Bithal, 2014). Although more
research is needed, regarding ketamine dosing with the use of dexmedetomidine; sub-anesthetic
of plain ketamine for perioperative analgesia is suggested by Gorlin et al. (2016). Dosing is
based on length of case and if the patient will continue to receive ketamine post-operatively
(Gorlin et al., 2016). If the surgical case is less than 60 minutes, 0.1-0.3 mg/kg IV bolus is
recommended with induction (Gorlin et al., 2016). If the case is longer than 60 minutes and there
is no plan for a postoperative infusion of ketamine, 0.1-0.3 mg/kg IV bolus with induction and
0.1-0.3 mg/kg repeated every 30-60 minutes but avoid re-dosing within 30 minutes of emergence
(Gorlin et al., 2016). If the patient will be receiving a ketamine infusion post-operatively, 0.1-0.3
mg/kg IV bolus with induction then infused continuously at a rate of 0.1-0.2 mg/kg/hr and may
continue infusing for 24-72 hours (Gorlin et al., 2016). Once 24 hours is achieved with the
continuous ketamine infusion, it is suggested to reduce infusion dose to 10 mg/hour or less
(Gorlin et al., 2016). According to numerous studies, lidocaine loading dose during induction is
DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
24
1.5 mg/kg and recommended maintenance continuous infusion dose ranged from 1.5 to 2
mg/kg/hr (Bakan et al., 2014; Farag et al., 2013; Harsoor et al., 2015; K. T. Kim et al., 2014).
Anterior cervical discectomy and fusion. During the pre-operative period, every patient,
but especially individuals undergoing spine surgery should be assessed for pre-operative
neurologic signs and symptoms and the anesthesia provider should document these deficits (Jaffe
et al., 2014). Also assess and document the patient’s neck range of motion, note if there is pain
present with manipulation. Head movement should be limited with airway manipulation and
securement during intubation and intraoperatively (Jaffe et al., 2014). Due to the area of the
surgical field of an anterior cervical discectomy and fusion, edema may be present and it is
recommended to ensure the patient reaches awake extubation criteria (Jaffe et al., 2014).
Methods to assess airway patency prior to extubation include deflating the cuff with the
endotracheal tube remaining in the trachea and assess air movement around the endotracheal
tube or a bougie or placement of an airway exchange device preceding to extubation (Jaffe et al.,
2014). Additionally, the patient’s arms are tucked and limits intravenous access to the anesthesia
provider so ensure the intravenous catheter is infusing adequately following repositioning of the
arms.
Research. There is lack of research regarding the prevalence of myelomalacia. In
addition, the combined use of intravenous dexmedetomidine-ketamine, dexmedetomidine-
lidocaine, and dexmedetomidine-ketamine-lidocaine intraoperatively is lacking and warrants
additional evidence especially amid the adult population. Also, bradycardia is more common
following the loading dose (Blaudszun, Lysakowski, Elia, & Tramèr, 2012). This suggests the
omission of the dexmedetomidine bolus may be advantageous in preventing bradycardia.
However, additional evidence is needed for this finding to be generalizable.
DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
25
Conclusion
In summary, anesthetic (intravenous and volatile) and opioid requirements during spine
surgery are decreased due to the analgesic and synergistic sedative properties that are present
within dexmedetomidine. Dexmedetomidine is a great adjunct to use for spine surgery to
enhance safety intraoperatively and increase patient satisfaction postoperatively. Ketamine and
lidocaine may also assist in further pain control.
Of course, the administration of dexmedetomidine should be evaluated by the anesthesia
professional in an individualized manner and carefully monitored. Further research would be
beneficial in the practice of dexmedetomidine in other procedures or surgeries. Disseminating
the benefits of dexmedetomidine, practice recommendations, and current research will improve
anesthetic practice as well as patient outcomes.
DEXMEDETOMIDINE AND ANTERIOR CERVICAL DISCECTOMY
26
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Appendix A
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