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9780521704632c16 CUFX213A/Peck 9780521618168 December 28, 2007 13:34
16 Antihypertensives
Central nervous system – cerebral blood flow is not reduced as long as the preload
is maintained with intravenous fluid and the mean blood pressure remains above
approximately 50 mmHg. The cerebral metabolic rate is unchanged and it does
not cross the BBB to any extent.
Respiratory – histamine release may induce bronchospasm.
Parasympathetic – owing to parasympathetic ganglion blockade the following
effects are seen: constipation, urinary retention, dry mouth, mydriasis, increased
intra-occular pressure and variable tachycardia. These may complicate recovery
from anaesthesia.
Miscellaneous – it inhibits plasma cholinesterase and prolongs the effects of depo-
larizing and non-depolarizing muscle relaxants, although this is variable.Kinetics
Data are limited but it is mainly excreted unchanged in the urine. There may be some
plasma hydrolysis. It crosses the placenta and has been associated with meconium
ileus in neonates.Hexamethonium (C6)
This quaternary ammonium compound has similar effects to trimetaphan. It is no
longer used in the UK.Diuretics
See Chapter 21.Adrenoceptor antagonists
See Chapter 13.Ca^2 +channel antagonists
See Chapter 15 and 16.