Chapter 4 Taking a Toxicological History
History taking is especially important in cases of suspected animal poisoning. Taking a complete toxicological history refines and focuses the trajectory of the interview in an attempt to detect the involvement of any potential poison. Let us begin this discussion by reviewing the basic history-taking techniques (Box 4-1).
Box 4-1 Key Items in the Toxicological History
For a variety of reasons, owners may give histories that are inaccurate, highly unreliable, and sometimes purposely deceitful. Veterinarians must realize that many owners may feel guilty about the duration a condition has existed, how long it has been since the last veterinary visit, how long an animal is left alone each day, how the animal actually came across a poison and how long it took the owner to realize it, or the level of care with which toxic substances are stored or disposed of in the home. Owners frequently say things they think the veterinarian wants to hear in an attempt to be seen as a more responsible pet owner. Owners often deliberately falsify a history (as in the case of an animal’s ingestion of an illicit drug) because of fear of legal repercussions and potential grounds for prosecution. Furthermore, the veterinarian must recognize the fears, anxieties, and emotional distress of many people as they face a potentially devastating health problem in their companion animal. The veterinarian must be a calming influence if a reliable account of events is to be obtained. If it is not possible to obtain an adequate history from the pet owner, it may be necessary to question other family members, neighbors, and friends. Finally, owners have different emotional make-ups, different educational backgrounds, different intellectual levels, and different economic realities. Language differences, physical disabilities, and other barriers may prevent the veterinarian from communicating effectively. If the owner’s primary language is not English, there may be a person fluent in the owner’s language in the veterinarian’s practice. A local person may be available who can act as an interpreter for the hearing impaired. Veterinarians must be inventive and flexible in their approach to listening to and communicating with their clients. Clinicians must consciously strive to eliminate any preconceptions that they may have about owners that will bias the history and affect their diagnostic ability.
The task of the veterinarian is to translate the owner’s account into a comprehensive medical history. Remember that clients have not been schooled to give an accurate history in a precise chronological order, and they may have failed to recognize important changes in vital signs or the onset of clinical signs that veterinarians are trained to identify. Just as the clinician must avoid having his or her own preconceptions, incorrect perceptions of owners that their animal has been poisoned must be identified because these can lead veterinarians to search for a toxicological cause of a problem that is in fact nontoxicological in origin. Veterinarians must never suggest that a client’s animal has been poisoned unless there is adequate evidence to support such a conclusion. Last, it is up to the clinician to organize the history in an orderly and logical manner and to establish the exact chronology of events leading up to the animal’s clinical presentation. For some veterinarians, a standardized history form is an effective aid in obtaining a complete, thorough, and objective history.
Taking a toxicological history differs a little from the standard clinical history in that it attempts to more specifically establish the time of onset of clinical signs and link them with exposure to a particular toxin. Classically, in suspected poisoning cases, the clinician is faced with one of three scenarios: (1) the animal has been exposed to a known toxin; (2) the animal has been exposed to an unknown substance that may be a toxin, or (3) the animal displays signs of disease of an uncertain or undetermined cause for which toxins must be considered as part of the differential diagnosis. The toxicological history focuses on the animal. The following questions must be answered: Are there predisposing factors that make the animal more sensitive to exposure? Is the situation compatible with a toxic exposure? Is there a potential source of toxins? Have there been any recent chemical applications?
It is of tremendous help if the owner can bring in the original container of the toxic substance. For most suspected poisonings, the exact quantity of toxin ingested is unknown. However, by examining the container in which the poison was stored and questioning the owner, the amount of toxin previously present in the container may be determined. Using this information, the largest amount the animal could have ingested can be estimated. This amount can be compared with the known lethal dosage for that size of animal. Not only amounts, but also active ingredients, potential antidotes, and related manufacturer information sometimes can be obtained from the package. The first line of defense in management of poisonings is the telephone. For this reason, all telephone personnel at animal hospitals should be trained as much as possible in the most common small animal poisonings, their relative toxicities, how they are managed, and what to tell people about the treatment (Box 4-2).
