Page 1733 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

1202 PART 11: Special Problems in Critical Care

can occur in the absence of a documented increased osmol gap. Thus, TABLE 124-18 Drugs Commonly Included in Urine Toxicology Screens
measuring serum levels of these alcohols is important in any patient in (Available in 2-3 Hours)
whom inebriation, acidosis, or other clinical features suggest intoxica-
tion with these agents. Acetaminophen
Amoxapine
Oxygen Saturation Gap: An elevated arterial oxygen saturation gap is
defined by a >5% difference between saturation calculated from an Barbiturates other than phenobarbital
arterial blood gas and saturation measured by cooximetry. Elevated Benzodiazepine metabolites
oxygen saturation gap is seen in carbon monoxide poisoning and Nordiazepam
with methemoglobinemia. These toxins interfere with oxygen bind-
ing to hemoglobin and thereby significantly decrease oxygen content Oxazepam
). It is important to Cannabinoids (marijuana)
without lowering arterial oxygen pressure (Pa O 2
note that oxygen saturation measured by pulse oximetry is falsely high Carbamazepine
in these settings. Hydrogen sulfide and cyanide interfere with cellular
utilization of oxygen, leading to an abnormally high venous oxygen Chlorpromazine
saturation and “arteriolization” of venous blood. Cimetidine
Additional Laboratory Tests: Additional useful laboratory data include Codeine
urine ferric chloride analysis, which provides rapid evidence of salicy- Cocaine metabolites
late or phenothiazine intake; a pregnancy test in women of child- Desipramine
bearing age; and abdominal radiography, which may detect retained
pills (such as iron) or show evidence for body packing (see below). Dextromethorphan
Sustained-release preparations may be detected more easily through Diphenhydramine
digital enhancement of the radiograph. 45 Doxepin
■ TOXICOLOGY SCREENING Doxylamine

Toxicology screening provides direct evidence of ingestion, but it rarely Ephedrine
impacts initial management, and supportive measures should not await Erythromycin
results of such analysis. In Brett’s review of 209 cases of intentional drug Glutethimide
overdose, toxicology analysis supported the clinical suspicion in 47% Guaifenesin
46
of cases. Clinically unsuspected drugs were detected in 27% of cases, but
unexpected findings altered management in only three cases. Kellerman Hydrocodone
and coworkers reviewed urine toxicology screens in 361 of 405 consecu- Hydromorphone
tive ED patients with suspected drug overdose. Management changes Imipramine
47
followed drug screening in only 16 (4.4%) of cases.
Toxicology screening provides evidence for select intoxications quickly Lidocaine
(see below) and may establish the grounds for treatment with a specific Meperidine
antidote or method for enhancing elimination. Toxicology screening Meprobamate
also identifies drugs that should be quantitated to guide subsequent
management. If at all possible, samples should be collected before Methadone
48
administration of medications that might confuse toxicologic analysis. Methamphetamine
Understanding the limitations of toxicology screening is important, Methaqualone
including which drugs are (and which drugs are not) included in routine
screening panels. These panels are institutionally variable. Most institu- Morphine
tions offer urine screening for commonly abused drugs only, preferring Nortriptyline
to send more extensive screening panels to outside laboratories. Other Opiates
institutions routinely perform extensive urine and blood analysis on all
patients in selected categories (eg, trauma patients). Urine screens used Orphenadrine
in the ED are aimed at detecting common drugs of abuse (Table 124-17). Pentazocine
Results are generally available in 30 minutes. Many more drugs are Phenacetin
included in the expanded screening panel (Table 124-18), the results Phencyclidine
of which should be available in several hours. Table 124-19 lists some
drugs not included in routine drug screening. Phenethylamine
Phenmetrazine
Phenobarbital
Phentermine
TABLE 124-17 Drugs Commonly Included in Urine Substances of Abuse Screens
Phenothiazine metabolites
Amphetamines
Prochlorperazine
Barbiturates
Promethazine
Benzodiazepines
Trifluoperazine
Cannabinoids
Trimeprazine
Cocaine
Triflupromazine
Opioids
Phenylpropanolamine
Phencyclidine (PCP) (Continued)

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