4. Anti-Hypertensive Drugs and Anaesthesia

Question 1

β-adrenoceptor blockers

Answer 1

: patients should continue taking these drugs and in some
cases may be prescribed them de novo.

Question 2

Diuretics

Answer 2

Thiazides, such as bendrofluazide,
which act on the distal tubule; and

loop diuretics typically furosemide,
which act on the loop of Henle

These drugs decrease the active
reabsorption of sodium and chloride by binding to the chloride site of the electroneutral
Na+/Cl− co-transport system to inhibit its action.

Anaesthetic implications: potassium loss can be significant, particularly in the
elderly. Electrolytes should be checked prior to anaesthesia, and consideration
should be given to withholding the drugs on the day of surgery.

Question 3

Calcium channel antagonists

Answer 3

L-type calcium channels and are of three main classes:
phenylalkylamines (verapamil),
dihydropyridines (nifedipine, amlodipine)
benzothiazepines (diltiazem

All three groups bind to the α1-subunit of the calcium channel and inhibit the slow
inward calcium current in cardiac and smooth muscle cells

Verapamil has primarily cardiac effects
acts as a negative inotrope and chronotrope.

Nifedipine and related drugs are more selective for vascular smooth muscle
and so are usually used to treat hypertension.

channel blockers are all negative
inotropes, but because they offload the myocardium by vasodilatation, cardiac output
is usually maintained.

Question 4

Anaesthetic implications: CCB

Answer 4

there may be some synergistic action with volatile anaesthetic agents,

which also affect slow Ca2+ channels in the myocardium and elsewhere.

Nifedipine and verapamil may also potentiate the actions of nondepolarizing
muscle relaxants.

Question 5

Angiotensin-converting enzyme (ACE) inhibitors:

Answer 5

the renin– angiotensin system

Angiotensin acts on receptors to mediate vasoconstriction (its
pressor activity is 40 times as powerful as that of noradrenaline),

it also stimulates noradrenaline release from sympathetic nerve terminals,
sodium reabsorption from proximal tubules

aldosterone secretion from the adrenal cortex.

ACE inhibitors include ramipril, captopril, enalapril, lisinopril and perindopril

significant fall in BP in hypertensive subjects and
reduce cardiac load by affecting both capacitance and resistance vessels

no influence on cardiac contractility, although they do act preferentially on
angiotensin-sensitive vascular beds in the myocardium, brain and kidney. Cough is
a common side effect of their use, due to bradykinin accumulation

Question 6

Anaesthetic implications ACE

Answer 6

significant intraoperative hypotension may follow the concomitant administration of a
general or regional anaesthetic in patients who are continuing to take an ACE
inhibitor.

If the ACE inhibitor has not
been omitted, then volume loading and vasopressors may be needed to maintain
normal arterial blood pressure,

Question 7

Angiotensin antagonists:

Answer 7

pure antagonists of the angiotensin II receptor (examples
include losartan, valsartan, irbesartan, candesartan) should in theory have a similar
spectrum of benefit as ACE inhibitors. They have a better side effect profile and do
not cause persistent cough, although they are less effective in the treatment of heart
failure.

Anaesthetic implications: these are broadly similar to those that apply to ACE
inhibitors, although, if not discontinued prior to surgery, they are even more likely
to cause profound and refractory intraoperative hypotension.