Page 1737 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

1206 PART 11: Special Problems in Critical Care

patient, though hemodynamic compromise is less likely if not TABLE 124-21 Antidotes
actively removing plasma volume (by ultrafiltration). Finally, air
embolism is an extremely rare consequence of HD. Drug/Poison Antidotes
Acetaminophen Acetylcysteine
Peritoneal Dialysis: Intoxicant removal across the peritoneal membrane Anticholinergics Physostigmine
is generally only one-eighth to one-fourth as efficient as hemodialysis,
even when maximizing solute exchange volume and frequency. This Anticholinesterases Atropine
technique is therefore never the preferred method for extracorporeal Benzodiazepines Flumazenil
drug removal, unless other considerations supervene (eg, use as an β-Blockers Glucagon
adjunctive measure or in the absence of available HD or HP).
Black widow spider bite Equine-derived antivenin
Hemoperfusion: Hemoperfusion (HP) is defined as direct contact of blood Calcium-channel blockers Calcium chloride, glucagon
with a sorbent system. Currently available systems perfuse a cartridge
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packed with coated AC (carbon). Blood perfusing such a cartridge is Carbon monoxide Oxygen
exposed (via a highly porous coating) to a large sorbent surface area, thus Coral snake (Eastern and Texas) bite Equine-derived antivenin
maximizing drug adsorption. Activated charcoal adsorbs both water- Cyanide Amyl nitrite, sodium nitrite, sodium
soluble and lipid-soluble substances and can remove essentially all of an thiosulfate, hydroxycobalamine
adsorbing substance from blood perfusing the cartridge. Thus it is not
unusual to achieve drug clearances of 200 to 400 mL/min, particularly early Digoxin Digoxin-specific antibodies
in the treatment period, before cartridge saturation begins. Polymer coating Ethylene glycol Ethanol, 4-methylpyrazole
reduces adsorption of larger compounds (>3500 Da). The drug adsorption Heavy metals (arsenic, copper, gold, lead, Dimercaprol, Ethylenediamine
process competes with plasma proteins and tissue stores to greatly augment mercury) tetra-acetic acid (EDTA), penicillamine
removal of bound drug beyond the level achievable by HD. Hypoglycemic agents Dextrose, glucagon
Complications of HP include:
Iron Deferoxamine mesylate
1. Cartridge saturation: The extraction ratio (EX) of a substance by
HP (or HD) is the amount of the solute removed as a fraction of the Isoniazid Pyridoxine
maximum it is theoretically possible to remove: EX = (A − V)/A, Methanol Ethanol, folic acid, 4-methylpyrazole
where A and V are the cartridge inlet and outlet blood concen- Methemoglobinemia Methylene blue
trations, respectively. This ratio declines during an HP treatment Opioids Naloxone
session as the cartridge becomes saturated; as noted above, this
occurs during HD only if a sorbent-based dialysis system is used. Rattlesnake bite Equine-derived antivenin
2. Hematologic: Thrombocytopenia commonly occurs due to platelet
adsorption, inducing up to a 30% decrement in platelet count, which with iron or with aluminum. CAVH has also the advantage that trained
usually recovers within 24 to 48 hours. Leukopenia and coagulation personnel can perform this technique without the assistance of a pump.
factor depletion also occur, to a lesser extent. Antidotes: An antidote is any substance that increases the mean lethal
3. Metabolic: Cartridge adsorption can cause hypoglycemia and dose of a toxin, or that can favorably affect the toxic effects of a poison.
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hypocalcemia. Table 124-21 lists antidotes for specific drugs/poisons.
4. Technical: Access complications can occur as for HD. Hypothermia
is an additional risk, because HP pumps do not warm blood as the INDICATIONS FOR ICU ADMISSION
HD apparatus does. Particle embolization (prevented by a filter in
the line returning effluent blood to the patient) and development of In the current health care environment, the practice of routinely admit-
pyrogenic reactions are of largely historic interest at this point. ting poisoned patients to the medical intensive care unit or a cardiac-
monitored bed is being questioned. In one retrospective study, Brett
Most drugs are extractable by HP, which is particularly suitable for and colleagues identified several factors that predicted the need for ICU
extracorporeal removal of toxins that are of high molecular weight, admission: partial pressure of arterial carbon dioxide (P CO 2 ) ≥45 mm Hg,
highly protein bound, or lipid soluble. Drugs poorly extracted by HP the need for intubation, seizures, QRS duration ≥0.12 seconds,
include heavy metals (lithium and bromide), some alcohols (ethanol second- or third-degree atrioventricular block, other cardiac arrhyth-
and methanol), carbon monoxide, and some illicit drugs (cocaine, mias, systolic blood pressure <80 mm Hg, and unresponsiveness to
phencyclidine, and others). Efficacy of intoxicant removal is diminished verbal stimuli. If none of these factors was present, no ICU interven-
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for substances with a large Vd (ie, highly lipid soluble and/or extensively tions (intubation, vasopressors, antiarrhythmics, dialysis, or hemoperfu-
tissue bound), which may be more effectively removed by hemofiltration. sion) were required. Other considerations include a Glasgow Coma Scale
score <12, progressive metabolic acidosis, and a cyclic antidepressant or
Hemofiltration: Hemofiltration (HF) achieves drug removal by convec- 97,98
tion, transporting drugs and other solutes through a highly porous phenothiazine overdose with signs of anticholinergic cardiac toxicity. 99
Cyclic antidepressants in particular may cause delayed cardiac toxicity.
membrane by bulk flow with filtered plasma water. Such membranes are
generally permeable to substances with weights of up to 6000 Da, includ- Severe hyperkalemia, extreme body temperatures, and need for continu-
ous infusion of naloxone are also reasons to admit to an ICU. Often, staff-
ing virtually all drugs, and in some cases HF membranes are permeable to
substances weighing up to 20,000 Da. 90-92 There are increasing numbers ing issues including the availability of a “sitter” in cases of attempted suicide
have an important impact on the disposition of the patient.
of case reports of extracorporeal intoxicant removal using hemofiltration,
by either the arteriovenous (continuous arteriovenous hemofiltration;
CAVH) or venovenous (continuous venovenous hemofiltration; CVVH) SPECIFIC INTOXICATIONS
with a large Vd, slow intercompartmental transfer, or avid tissue ■ ACETAMINOPHEN
method.
Hemofiltration is potentially useful for removal of substances
93,94
binding. Specific highly porous HF cartridges are also particularly use- In 2008, alone or in combination with other drugs, acetaminophen
ful for removal of large-molecular-weight solutes or complexes, such as accounted for over 180,000 exposures, making it the most common phar-
combined digoxin-Fab fragment complexes or deferoxamine complexes maceutical overdose reported to poison control centers. Approximately

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