Anesthesia Student Survival Guide.pdf - Index of

46 ● AnesthesiA student survivAl Guide
the maintenance of spontaneous ventilation is required, the patient is already
hypotensive, or the patient’s ability to sustain hemodynamic stability is in question
for any reason. Propofol decreases the body’s normal response to both
hypoxia and hypercarbia, and up to 35% of patients experience apnea after an
induction dose. Propofol decreases blood pressure by decreasing cardiac contractility,
systemic vascular resistance, and preload. It is generally thought of as
having the most profound cardiodepressant effects of all the induction agents.
From a neurologic standpoint, propofol has moderate anticonvulsant
activity. It reduces both intracranial pressure and cerebral blood flow. However,
due to greater effects on systemic blood pressure, propofol can actually decrease
cerebral perfusion pressure when given in large doses. Another advantage of
propofol is that it is generally thought of as affording less residual cognitive
disarray when compared to other induction agents.
In addition to negative side effects of propofol already mentioned, pain
on injection is seen in up to 67% of patients. Pain can be lessened with concomitant
administration of 1% lidocaine. In addition, patients may experience
mild muscle twitching and hiccupping. Favorable propofol side effects include
antipruritic and antiemetic properties.
Thiopental is a barbiturate that shares many characteristics with propofol
(enhances GABA transmission). It is rapid in onset, and has both cardiovascular
and respiratory depressant properties. Many favor propofol because of the
prolonged cognitive disarray observed in some patients after administration
of thiopental. Thiopental is also possibly cerebro-protective, and it is used in
many brain surgery cases. Thiopental solution is very alkaline, and can form a
precipitate that will occlude IV catheters if mixed with acidic solutions or drugs
(such as paralytic agents). Thiopental induces the enzyme ALA synthetase (the
rate limiting step in porphyrin synthesis), and is therefore contraindicated in
patients with inducible porphyrias. Repeated doses may result in a delayed
emergence because of high protein binding and a low hepatic extraction ratio.
Etomidate is an imidazole which increases GABA transmission and has the
advantages of minimal cardiac and respiratory depression. Its onset and duration
of action are similar to propofol, but etomidate is considered a safer drug to
use for patients in a compromised hemodynamic state. Trauma patients, elderly
patients, and patients who are severely volume depleted or are on vasopressors
are typical candidates for an etomidate induction. After a single bolus, the
clinical effect of etomidate is terminated by redistribution and rapid hepatic
metabolism. A concern exists regarding transient adrenal suppression after