Læknaneminn - 01.10.1996, Blaðsíða 89

Curtis P. Snook
Overdoses and
poisonings:
physiological responses
I. INTRODUCTION TO THE TOXIDROMES
Therapeutic decision making for the poisoned or
overdosed patient must often precede specific knowled-
ge of the poison based on history and laboratory
results. Some of the therapies used assist in the di-
agnosis, since the patient’s response provides in-
formation about the poison involved. Many of these
therapies are safe to use, and are, therefore, used
“generically” or according to pre-established protocols
in certain types of patients. Some of these will be
discussed in the lecture “Preliminary Care and Treat-
ment in Overdose and Poisoning”.
Therapies associated with significant risk or expense,
or those required for rare types of poisoning and over-
dose, are not given routinely. Their use is dictated by
clinical and/or laboratory identification of the toxin or
class of toxin involved and the urgency of need in the
specific patient.
How, then, do clinicians make therapeutic decisions
when historical or laboratory information is unavaila-
ble, inadequate, or too slow in coming? In this situ-
ation their decisions ,must be based on an understand-
ing of human physiology and its response to a toxic
insult. Drugs or toxins, alone or, as is often the case, in
combinations can leave physiologic fmgerprints which
betray their presence. While these fingerprints are subt-
ly different for agents considered individually, in gener-
al terms they occur in the form of syndromes or groups
of symptoms which are observed to occur together in
response to exposure to one of a pharmacologically
similar group of agents. In the clinical context of over-
Curtis P. Snook er M.D., Sérfraðingur á Slysadeild Sjúkrahúss
Reykjavíkur.
dose or poisoning we refer to these syndromes as toxic
syndromes or toxidromes.
Specifically, the recognition of toxidromes requires
an understanding of how different drugs or toxins in-
fluence the autonomic nervous system and what symp-
toms and signs result from this influence. There are
Opposing
SYMPATHETIC (Fight/Flight) <—> PARASYMPATHETIC (RestDigest)
t t
Transmitters Transmitter
Preganglíonic: Acetylcholine Postganglionic: Norepinephrine Adrenal medulla: Epinephrine Thalamus: Dopanmine Acetylcholine t t t
t t
Receptors Receptors
/' X / tx
a„ a2 |3„ P2 Muscarinic y Nicotinic t Antagonists / X Atropine d-Tubocurarine
Figure 1. The Autonomic Nervous System-
also specific single symptoms which provide powerful
clues in identifying certain drugs or toxins. An exam-
ple of such a symptom is a seizure.
II. THE AUTONOMIC NERVOUS SYSTEM
A review of the autonomic nervous system at this
point is necessary before the known toxidromes can be
understood. Figure 1 outlines this system.
LÆKNANEMINN
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2. tbl. 1996, 49. árg.