- As noted earlier, the
cardiovascular effects of an epidural block or
similar to the use of intravenous beta and alpha
adrenergic receptor blockers. Treatment should be
directed towards the reversal of beta and alpha
blockade. The most commonly use sympathetic drugs
are:
phenylephrine
|
norepinephrine
|
epinephrine
|
ephedrine
|
dopamine
|
dobutamine
|
isoproterenol
|
- The spectrum of adrenergic activity
ranges from nearly pure alpha agonist
(phenylephrine) to nearly pure beta-agonist
(isoproterenol)
 A frequently and easily used drug is
ephedrine.
- Its alpha and beta effects are
primarily secondary to the release of
norepinephrine from sympathetic nerve
endings.
 Those
patients that are catecholamine-depleted
either from their disease or
pharmacologically induced with reserpine
or Aldomet (alpha-methyldopa)-like drugs
may not respond to ephedrine.
There may be minimal direct effect of
ephedrine.
- Patients
with an existing beta blockade (metoprolol,
atenolol, propranolol, labetalol, etc.) to
control hypertension or angina may require higher
doses to achieve an effect.
The effects of intravenous ephedrine are
immediate and last for 5-15 minutes.
Tachyphylaxis may occur
- Ephedrine doses of 10 and
15 mg were given without significant
effect.
|
- The increased bradycardia
maybe in part due to the unopposed cholinergic
activity of the vagus nerve. The anticholinergic
drugs most commonly used are atropine and
glycopyrrolate.
-
Atropine crosses the blood-brain barrier
and in higher doses can cause delirium.
- Glycopyrrolate doses of
0.2, 0.2, and 0.4 mgs were administered
with a minimal increase in heart rate to
55 bpm. Fewer beats without P waves were
noted. The blood-pressure remained at
85-90/60.
|
- In spite of the lack of
response to the ephedrine and glycopyrrolate, the
working diagnosis remained sympathectomy from
epidural blockade. One could elect to increase
the dose of ephedrine or try different drug.
 Dopamine and epinephrine
both a significant dose-related alpha and
beta adrenergic receptor activity- Dopamine has beta
stimulation at the 2-5 ug/kg/minute range
with alpha stimulation at the 5-10
ug/kg/minute range.
- Epinephrine has beta
stimulation at the 1-3 ug/min range with
alpha stimulation at higher doses
- Dopamine at 5 ug/kg/minute
was administered with minimal change in
hemodynamics. The dose was increased to
10 ug/kg/minute. candy effects of the
increase dose of dopamine was slight. Can
the heart rate continued at 50-55 bpm and
the blood-pressure held at 90-95/60.
|
- The closure of the
surgical wound is now complete and the decision
to continue to ventilate postoperatively was
made. The plan was to extubate after hemodynamics
have stabilized. The patient was turned supine
and the double lumen tube was replaced with a
single lumen tube. the patient remained sedated
with intravenous propofol.
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