Biomedical Engineering Reference
In-Depth Information
summary
A variety of anesthetic modalities can be employed when trea-
ting children with laser surgery depending on the need and
preferences of the physicians, the patient, and the families. The
choice of agents and technique should be based on the needs of
the individual child (82) and the surgical requirements while
balancing the risks and benefits of the various techniques.
The major hemodynamic effect of propofol is arterial hypo-
tension (up to 30%) with minimal change in heart rate.
Both decreased systemic vascular resistance and direct myo-
cardial depression have been implicated as important factors
in producing hypotension after large bolus doses of propofol
(67). The cardiovascular effects are accentuated and may
be significant in the presence of hypovolemia (excessive
nothing-by-mouth status) and preexisting cardiovascular
disease and in elderly patients. Most investigators seem to
agree that the clinical significance of these changes in young,
healthy, normovolemic patients is negligible (73). Once
again, dosage should be titrated for the individual patient and
surgical procedure.
Propofol has a profound respiratory depressive effect, inclu-
ding a decrease in tidal volume, minute ventilation, and a
depressed ventilatory response to hypoxemia (74) and hyper-
carbia. Apnea (20-30 seconds) may occur after a large bolus,
stressing the importance of infusion rate titration to allow
spontaneous ventilation without supplemental oxygen. The
expertise and equipment necessary to monitor and maintain
the airway, including supplemental oxygen and ventilatory
support, are implicit in the use of this drug (75).
Several minor disadvantages accompany this technique. IV
access must be established in small children with each treatment.
With an uncooperative or very frightened child, low-dose IM
ketamine, 2-3 mg/kg, with atropine, 0.02 mg/kg, is used as a pre-
induction sedative to facilitate establishment of IV access. Pain
on injection of propofol into a vein in the dorsum of the hand is
common (30-45%). The incidence of pain can be decreased
(6-12%) if injection is made into a large vein of the forearm or
antecubital fossa (71,75). The incidence of injection pain can be
decreased with a dose of IV lidocaine, modified Bier block (76),
or addition of 1 mg/mL lidocaine to the propofol emulsion will
significantly reduce the incidence of injection pain.
Nonetheless, the aforementioned emulsion formulation is
capable of supporting rapid growth of bacteria if contami-
nated. Therefore, strict aseptic techniques must be maintained
when handling propofol. In addition, it is recommended that
unused drug be discarded at the end of the procedure or at
6 hours, whichever occurs sooner.
Overall, propofol is a desirable sedative agent because of its
rapid induction, rapid redistribution, rapid recovery with
clear emergence, and a low incidence of nausea and vomiting
(67). Studies also suggest that propofol can be used safely in
malignant hyperthermia-susceptible patients (77-79). For
these reasons, propofol anesthesia is popular among children
and their parents.
Adults
As with children, many laser treatments in adults can be painful
and uncomfortable, although some treatments can be accom-
plished without anesthesia or with limited application of topi-
cal agents. Nonetheless, more painful procedures may require
more invasive anesthetic techniques (83,84). For example,
facial laser resurfacing is a highly stimulating and often painful
procedure requiring a combination of anesthetic modalities.
Furthermore, the anesthetic goal during surgery is to render
the patient insensitive to pain over the treated area, motionless
during the procedure, and amnestic for the time spent in the
operating suite. Specific pharmacologic agents are selected to
meet these clinical objectives. Anxiolytics, hypnotics, dissocia-
tive agents, narcotics, and nonsteroidal antiinflammatory drugs
(NSAIDs), as well as inhaled anesthetics, all may play a role in
meeting anesthetic goals. The advantages and disadvantages of
various techniques are discussed below.
General Anesthesia
General anesthesia with ET intubation may be administered
quickly and is usually safe when proper monitoring occurs.
General anesthesia ensures airway control and allows the
administration of adequate narcotic analgesia without con-
cern for respiratory depression. However, not all facilities are
equipped to provide general anesthesia, and because of poten-
tial complications while the patient is unconscious, the patient
or physician may be reluctant to use this technique.
Intravenous Anesthesia
Advances in anesthetic airway management, specifically the
development of the laryngeal mask airway (LMA), have
allowed for increased flexibility in office-based practice. For
example, LMA allows facial laser resurfacing to be safely per-
formed using IV and/or inhaled agents while maintaining
spontaneous ventilation and airway control. If necessary, the
technique of IV anesthesia combined with the use of an LMA
can provide safe and effective anesthesia for laser facial resur-
facing without the need for an anesthesia machine.
Although some surgeons have utilized a combination of
local and regional anesthetic techniques, total IV anesthesia
offers several advantages since infiltration of local anesthetics
may often distort facial anatomy and increase postoperative
discomfort. In addition, any movement of the patient may
alter the surgical result and increase the risk of complications.
Given these risks, total IV anesthesia provides a cost-effective
method to provide anesthesia with minimal risk to patients
undergoing laser facial resurfacing. Sore throats, however,
related to LMA use, are common (85). Despite this minimal
risk, proper patient monitoring and availability of airway
management equipment, emergency airway and cardiac medi-
cations, and a defibrillator should be ensured. A potential IV
anesthesia regimen is discussed below.
Inhalation Anesthesia
When general anesthesia has been selected as the anesthetic
technique, no single approach will be effective for all chil-
dren in all situations. Inhalation induction of anesthesia
may be preferred for small infants and children with abnor-
mal airways. Nausea and vomiting may occur, but recovery
is usually uneventful. Anesthetic agents such as isoflurane
sevofl urane, and desfl urane have a longer induction period
and produce a higher incidence of coughing and breath
holding (80). Both appear to have significant advantages
over present agents (81). A detailed discussion is beyond the
scope of this chapter.
