NYSORA - The New York School of Regional Anesthesia: Sedation-Analgesia During Local and Regional Anesthesia

Sedation-Analgesia During Local and Regional Anesthesia
================================================================================
Richard Claudio  on 2009-03-15 23:28:00
 
Author: Paul F. White, PhD, MD, FANZCA
Affiliation: Professor and McDermott Chair of Anesthesiology, Department of
Anesthesiology & Pain Management, UT Southwestern Medical Center, Dallas, TX
For: Regional Anesthesia: Principles & Practice. Admir Hadzic, MD (Editor)
TABLE OF CONTENTS
Introduction
Components of monitored anesthesia care
Use of adjunctive sedative-hypnotic drugs
Role of opioid and non-opioid analgesics
Miscellaneous techniques used to supplement local anesthesia
Cost-benefit of monitored anesthesia care
INTRODUCTION
During local and regional anesthesia, it is a common practice to administer
both sedative and analgesic medications to enhance patient comfort during the
operation. Use of local anesthetic infiltration and peripheral nerve blocks
(PNBs) techniques in combination with intravenous (IV) sedative-hypnotic and
analgesic drugs is commonly referred to as monitored anesthesia care (MAC). In
many centers around the world, over 50% of all ambulatory (day-surgery)
procedures are performed utilizing these techniques (Table 1).1 When patients
undergo surgical procedures under local anesthesia with IV sedation-analgesia
in the operating room (OR), the old terminology used to describe the care of
these patients was “conscious sedation.” As the term implies, conscious
sedation was a minimally-depressed level of consciousness that retained the
patient’s ability to maintain an airway independently and continuously, and
to respond appropriately to physical stimulation and verbal commands. The
American Society of Anesthesiologists (ASA) avoids this term in their Practice
Guidelines for Sedation and Analgesia by Non-anesthesiologists2 because it is
imprecise and instead refers to this practice of anesthesia as MAC.
Table 1. Surgical procedures commonly performed under local anesthesia with
intravenous sedation-analgesia techniques.1
Peripheral nerve blocks
*ilioinguinal/hypogastric (e.g., herniorrhaphy) 	*paracervical (e.g.,
dilation/curettage, cone biopsy) 	*dorsal penile (e.g., circumcision)
	*peroneal/femoral/saphenous/tibial/sural (e.g., podiatric)
	*femoral/obturator/lateral femoral cutaneous/sciatic (e.g., leg) 	*brachial
plexus/axillary/ulnar/median/radial (e.g., arm/hand) 	*peribulbar/retrobulbar
(e.g., ophthalmologic procedures) 	*mandibular/maxillary (e.g., oral surgery)
	*intravenous regional (Bier block) (e.g., arms, legs)
	*intercostal/paravertebral (e.g., breast surgery)
Tissue infiltration and wound instillation
*cosmetic procedures (e.g., blepharoplasty, nasal, septum, endosinus)
	*excision of masses and biopsies (e.g., breast, axilla, lipomas) 	*field
blocks or instillation technique (e.g., hernia repair, vasovasotomy)
	*laparoscopic procedures (e.g., cholecystectomy, tubal ligation)
	*arthroscopic procedures (e.g., knee, shoulder, wrist, ankle)
Topical analgesia
*eutectic mixture of local anesthetics (EMLA(R)) (e.g., skin lesions)
	*lidocaine spray (e.g., bronchoscopy, endoscopy, hernia repair) 	*lidocaine
gel or cream (e.g., circumcision, urologic, oral surgery) 	*lidocaine –
bupivacaine (Duocaine(R)) (e.g., cataract surgery) 	*tetracaine (e.g., cataract
and plastic surgery) 	*cocaine paste (e.g., nasal, endosinus surgery)
Back to top
COMPONENTS OF MONITORED ANESTHESIA CARE
Figure 1: The dose-dependent spectrum of central nervous system depression
produced by sedative-hypnotic drugs. MAC=monitored anesthesia care; LOC=loss of
consciousness and LPR=loss of protective reflexes1
According to the ASA,2 MAC is the term used when an anesthesiologist monitors a
patient receiving local anesthesia alone or administers anesthetic drugs to
patients undergoing diagnostic or therapeutic procedures with or without local
anesthesia. The ASA defines MAC “as instances in which an anesthesiologist
has been called upon to provide specific anesthesia services to a particular
patient undergoing a planned procedure in connection with which a patient
receives local anesthesia or, in some cases, no anesthesia at all. In such a
case, the anesthesiologist is providing specific services to the patient, is in
control of his or her vital signs, and is available to administer anesthetics or
provide other medical care as appropriate.” The standard of care for patients
receiving MAC should be the same as for patients undergoing general anesthesia
or central neuroaxis blockade, and should include a complete preoperative
assessment, intraoperative monitoring, and postoperative in the recovery room
prior to discharge.
Vigilant monitoring is required because patients may rapidly progress from a
“light” level of sedation to “deep” sedation and ultimately,
unconsciousness (Fig. 1).1 As a result, patients may be at risk for airway
obstruction, oxygen desaturation, and even aspiration.3 Therefore, supplemental
oxygen is commonly administered with end-expiratory CO2 monitoring for assessing
ventilatory rate, presence of airway obstruction and apnea.4 Although cerebral
monitoring (e.g., EEG bispectral index) has been used successfully to assess
the sedative effects of both midazolam5 and propofol6 during procedures
performed using local anesthesia and PNBs, the confounding effects of the
surgical stimulus and patient discomfort on the cerebral index can make it
difficult to interpret the findings.7 In addition, background noise in the OR
can effect the cerebral index at “light” levels of sedation.8 Nevertheless,
some investigators have suggested that the BIS is useful for monitoring the
central nervous system during surgery under local or regional anesthesia with
IV sedation.9
A wide variety of pharmacologic agents are commonly administered during
administration of local anesthesia or PNBs, as well as during surgical
procedures under local anesthesia (or PNBs) to produce sedation, analgesia, and
anxiolysis, while optimizing the surgical conditions and insuring
cardiorespiratory stability and a rapid recovery of cognitive functioning
without untoward side effects (Table 2).10 Systemic opioid and non-opioid
analgesics are used to reduce discomfort associated with injection of local
anesthetics and prolonged immobilization, as well as procedural related pain
which is not amendable to local anesthesia (e.g., endoscopy).
Clinical Pearls
*Sedative-hypnotic drugs as well as narcotics are commonly used perioperatively
to make regional anesthesia more tolerable for patients by reducing anxiety and
providing an appropriate degree of sedation, amnesia and analgesia.
Sedative-hypnotic drugs are also commonly used to make procedures more
tolerable for patients by reducing anxiety and providing an appropriate degree
of intraoperative sedation and amnesia. During longer surgical procedures,
patients may become restless, bored, or uncomfortable when forced to remain
immobile. Therefore, sedative-hypnotic drugs, as well as non-pharmacologic
approaches (e.g., music), may prove beneficial because they allow patients to
rest during the operation. Patients’ anxiety can be reduced by using
benzodiazepines, as well as by good preoperative communication, keeping the
patient warm and covered, and allowing the patient to listen to relaxing music
during the procedure. This article will discuss the commonly used adjunctive
techniques to enhance patient comfort during local and regional anesthesia.
Table 2: Sedative-analgesic drugs and non-pharmacologic techniques used for
minimizing perioperative discomfort during local and regional anesthesia10
Sedative-hypnotics
*midazolam, 2-5 mg PO/IM/IV 	*thiopental, 75-150 mg IV 	*methohexital, 20-50 mg
IV 	*etomidate, 10-15 mg IV 	*propofol, 50-100 mg IV
Local anesthetics
*lidocaine, 0.5-2% SQ/IV 	*bupivacaine, 0.125-0.5% SQ 	*levobupivacaine,
0.125-0.5% SQ 	*ropivacaine, 0.25-0.75% SQ 	*EMLA cream, lidocaine 25 mg/g,
prilocaine 25 mg/g, TC
Opioid analgesics
*fentanyl, 0.75-1.5 mcg/kg, IV 	*alfentanil, 10-20 mcg/kg, IV 	*remifentanil,
0.5-1 mcg/kg, IV 	*sufentanil, 0.1-0.2 mcg/kg IV 	*dextromethorphan, 40-120 mg
PO/IM/IV
Nonsteroidal anti-inflammatory drugs
*ketorolac, 15-30 mg PO/IM/IV 	*diclofenac, 50-100 mg PO/IM/IV 	*ibuprofen,
300-800 mg PO 	*naproxen, 25-500 mg PO 	*celecoxib, 200-400 mg PO
Non-pharmacologic techniques
*music and “white” noise 	*electroanalgesia, TC
Miscellaneous compounds
*acetaminophen, 0.5-2 g PO/PR/IV 	*propacetamol, 0.5-2 g IV 	*ketamine, 10-20
mg PO/IM/IV 	*clonidine, 0.1-0.2 mg PO/TC/IM/IV 	*dexmedetomidine, 0.5-1
mcg/kg, IM/IV 	*gabapentin, 600-1200 mg bid PO 	*pregabalin, 150-300 mg bid PO
Routes of administration: PO=oral, PR=per rectum, SQ=subcutaneous/tissue,
IM=intramuscular, IV=intravenous and TC=transcutaneous
Back to top
USE OF ADJUNCTIVE SEDATIVE-HYPNOTIC DRUGS
Many different sedative-analgesic drugs have been used for premedication
(including barbiturates, benzodiazepines, opioid analgesics and alpha-2
agonists) (Table 3).10 Midazolam remains the most popular premedicant because
of its predictable sedative, anxiolytic and amnestic properties unrespective of
the route of administration (i.e., oral, topical, or parenteral).11-14 In
addition, a wide variety of drug delivery systems such as intermittent boluses,
variable-rate infusions, target-controlled infusions, as well as
patient-controlled sedation-analgesia techniques have been utilized during
procedures under local and regional anesthesia.15,16
Although benzodiazepines (e.g., diazepam, midazolam) were formerly the most
popular sedatives for “conscious sedation,”17,18 their use has declined
with the introduction of more titratable IV sedative-hypnotics (e.g.,
methohexital, etomidate, propofol) and analgesics (e.g., alfentanil,
remifentanil).15,19 Methohexital, a shorter-acting barbiturate than thiopental,
was the IV sedative-hypnotic of choice prior to the introduction of propofol.
Etomidate, a popular IV induction agent for cardiovascular surgery, can be
administered by continuous infusion (5-20 mcg*kg-1*min-1) and may be
particularly useful for sedation of elderly patients and those with significant
underlying cardiac disease due to its minimal cardiovascular depressant
properties. However, when combined with opioid analgesics, etomidate is
associated with an increased risk of postoperative nausea and vomiting (PONV).
Clinical Pearls
*Propofol is probably the IV sedative-hypnotic of choice for intraoperative
sedation for many patients having surgery under regional anesthesia
Propofol, the IV sedative-hypnotic of choice at the present time, has been
found to be equivalent to both midazolam and methohexital for providing
adequate sedation and amnesia during superficial procedures under local
anesthesia and PNBs.20-23 Importantly, compared to other available
sedative-hypnotic drugs, use of propofol is associated with less residual
postoperative sedation, amnesia, and nausea and vomiting, as well as ease of
fast-tracking (i.e., bypassing the PACU), leading to a reduced recovery time to
a “home readiness” state. Although use of the benzodiazepine antagonist,
flumazenil, reduces the residual sedative-amnestic effects of midazolam, and
allows the early recovery profile after midazolam sedation to compare favorably
to propofol.24 However, the short duration of action of the reversal drug can
lead to varying degrees of resedation in the postdischarge period.
Clinical Pearls
*The most popular sedative technique consists of a small dose of midazolam (1-2
mg) for premedication (or induction of sedation), and propofol (0.5-0.75 mg/kg
followed by a variable-rate infusion at 25-100 µg/kg/min
The most popular sedative technique consists of a small dose of midazolam (1-2
mg) for premedication (or induction of sedation), and propofol (0.5-0.75 mg/kg
followed by a variable-rate infusion at 25-100 µg/kg/min).20,25 Methohexital
has also been used successfully during MAC by intermittent boluses (10–20 mg)
or as a variable-rate infusion (20-60 µg*kg-1*min-1).19,26 Although residual
sedation appears to be somewhat greater with methohexital than propofol, there
were no differences in the recovery times to ambulating and discharge home when
comparing infusions of methohexital (40 µg/kg/min) and propofol (50 µg/kg/min)
during a MAC technique.26 In addition, there was a significantly higher
incidence of pain on injection in the propofol infusion group. Therefore,
methohexital remains a cost-effective alternative to propofol for sedation
during MAC despite the fact it is less convenient to use because it has to be
reconstituted. Careful titration of these IV anesthetics is essential to
maintain the desired level of sedation while avoid ventilatory depression
during surgery, and ensuring a prompt recovery of cognitive functioning after
surgery.
In an effort to enhance patient comfort, both opioid and non-opioid analgesics
have been used to supplement the sedative hypnotics.27-31 Although fentanyl
remains the most commonly used opioid analgesic, remifentanil has become
increasingly popular because its faster onset and recovery characteristics may
minimize the potential for adverse drug interactions in the postoperative
period. However, careful titration is necessary when remifentanil is combined
with midazolam and propofol to avoid ventilatory depression and apnea.30-35 Of
interest, some investigators have suggested that remifentanil fails to improve
the quality of propofol sedation36 A variety of nonsteroidal anti-inflammatory
drugs (NSAIDs) (e.g., ibuprofen, ketorolac, piritramide, celecoxib) may also
prove useful in preventing pain and discomfort which is refractory to local
anesthetics.37-40 However, with effective local anesthesia, the addition of an
NSAID provides only minimal intraoperative improvement in the local analgesic
effect.27,38,41
Table 3. Sedative-anxiolytic- drugs used for premedication in patients
undergoing local and regional anesthesia10
Dosage range (and route)
Onset (min)
Key points
Barbiturates
Amobarital
100-200 mg PO
10-20
Delays early recovery
Butalbital
50-100 mg PO
20-40
Variable response
Chloral hydrate
0.5-1 g PO
20-40
Variable response
Secobarbital
200-300 mg PO
15-30
Delays early recovery
Zaleplon
5-20 mg PO
20-40
Variable response
Zolpidem
5-10 mg PO
15-30
Variable response
Benzodiazepines
Midazolam
7.5-15 mg PO
15-30
Large first-pass effect
5-7 mg IM
5-10
Water-soluble, non-irritating
1-2 mg IV
1-3
Rapid-onset, excellent amnesia
Diazepam
5-10 mg PO
30-60
Long-acting metabolites
Temazepam
15-3- mg PO
15-30
Similar to midazolam
Triazolam
0.12-0.25 mg PO
15-30
Prominent sedation
Lorazepam
1-2 mg PO
45-90
Prolonged amnestic effect
Opioid analgesics
Alfentanil
250-500 µmg
2-3
Minimal residual analgesia
Fentanyl
50-100 µmg
3-5
Mild sedation
Remifentanil
40-80 mg