Poisoning

Published on 22/03/2015 by admin

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Last modified 22/03/2015

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170 Poisoning

Overview of Approaches for Evaluation and Treatment

image Gastrointestinal Decontamination

The theory of gastric decontamination (GID) is that removal of toxins from the stomach (where absorption is poor) before they move into the small bowel (where absorption is more rapid) decreases the toxicity of the poisoning. Because of controversies regarding the role of gut decontamination, senior toxicologists from the American Academy of Clinical Toxicology and the European Association of Poison Centres and Clinical Toxicologists (EAPCCT) agreed to collaborate on the production of Position Statements on GID treatments. These statements, published in 1997, are systematically developed guidelines founded on a criteria-based critical review of all relevant scientific literature.1 The Position Statements were updated in 2004. GID Position Statement summaries are presented in this chapter.

Single-Dose Activated Charcoal

Activated charcoal is made when coconut shells, peat, wood, or other materials undergo controlled pyrolysis and are subsequently activated by heating in steam or air at high temperatures. Activation creates multiple internal pores and the small particle size necessary for adsorption. The particles have a large surface area and are capable of adsorbing poisons with varying affinities. Although in vitro studies demonstrate adsorption of many drugs to activated charcoal, animal studies reveal variable reductions in the systemic uptake of marker substances.9 Volunteer and clinical studies have not demonstrated that single-dose administration of activated charcoal improves outcome. Contraindications to the administration of activated charcoal include decreased level of consciousness and unprotected airway, ingestion of caustic substances or hydrocarbons, gastrointestinal pathology, and medical conditions that could be further compromised by the administration of activated charcoal. Complications include aspiration and direct administration of charcoal into the lung.10

Because activated charcoal is an inert substance, it is thought that lung injury after aspiration of activated charcoal is caused by gastric contents. Aspiration of gastric contents causes neutrophils to release neutrophil elastase, which increases pulmonary vascular permeability.11 In comparison, intratracheal administration of activated charcoal does not increase elastase in the bronchoalveolar fluid.12 Activated charcoal can activate alveolar macrophages, which are a potent source of oxygen radicals, proteases, and other inflammatory mediators. Charcoal also causes obstruction of small distal airways Overdistention of alveolar segments in areas not occluded by charcoal leads to volutrauma in those areas, which increases microvascular permeability.13 Although case reports reveal long-term pulmonary pathology after aspiration or instillation of activated charcoal,14,15 the true incidence of chronic problems after charcoal aspiration is unknown.

image Enhanced Elimination

Multiple-Dose Activated Charcoal

Multiple-dose activated charcoal is the repeated oral administration of activated charcoal to enhance drug elimination. If the drug concentration in the gut is lower than that in the blood, the drug will passively diffuse back into the gut. The concentration gradient, intestinal surface area, permeability, and blood flow determine the degree of passive diffusion. As the drug passes continuously into the gut, it is adsorbed onto the charcoal particles, a process called gastrointestinal dialysis. Multiple-dose activated charcoal also interrupts the enterohepatic and enterogastric circulation of drugs. Drugs with a prolonged elimination half-life, a small volume of distribution (less than 1 L/kg), and little protein binding are the most amenable to this sort of management.19

The initial dose of charcoal is 50 to 100 g, and this treatment is followed every 1, 2, or 4 hours by a dose equivalent to 12.5 g/h. More frequent, smaller doses may prevent vomiting. Addition of a cathartic (e.g., sorbitol) can be considered for the initial one or two doses. Continuous use of a cathartic can cause diarrhea and fluid and electrolyte imbalances. Multiple-dose activated charcoal can be continued until the patient improves clinically. Contraindications include an unprotected airway, intestinal obstruction, and an anatomically abnormal gastrointestinal tract. Complications include bowel obstruction and vomiting with subsequent aspiration.19

image Selected Antidotes

Stabilization of the patient always should precede administration of antidote(s). The effects of the toxin can outlast the effects of the administered antidote. Patients receiving antidotes should be observed in a critical care setting.

Dextrose

Up to 8% of patients with altered mental status are hypoglycemic.21 Hypoglycemia can be a result of drug or toxin exposure, nutritional deprivation, or a medical complication (e.g., sepsis, hyperthermia). Glucose should be checked at the bedside for all patients with altered mental status.

Naloxone

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