Chapter 4 Taking a Toxicological History
History taking is a vital skill. Combined with performing a thorough physical examination, obtaining an appropriate minimum database, and establishing a differential diagnosis, it allows the clinician to potentially arrive at a correct diagnosis. It is a technique that must be continually improved and perfected, both consciously and constantly.
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).
If any part of veterinary medicine is an art, it is the act of securing from an owner the facts surrounding an animal’s clinical signs. The clinician must be sympathetic, gentle, and patient in an effort to quickly establish the trust of the person. Such trust will facilitate spontaneous volunteering of important information by the owner. If a person feels intimidated by the veterinarian, he or she may not offer pertinent observations that are crucial to the case, and valuable time will be lost. If the history is to provide any type of working diagnosis, the veterinarian’s interview must be meticulous, caring, and thorough in scope.
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.
The history and all initial data obtained should be recorded at the time of the original presentation. The animal’s records are a medicolegal document that can be subpoenaed, and they should be treated accordingly. Suspected poisoning cases have a particularly high potential for legal action because of possible liability and criminal activity. The recorded history should be organized, legible, and complete. A good rule of thumb is to not take any records that are incomplete or disorganized or that you would be ashamed to have reviewed by your peers or officers of the court.
The history must be organized concisely and logically and must include any and all introductory data. Such data include species, breed, age, sex, reproductive status, vaccine history, previous or current medical problems, current medications, diet, home environment, presence of other animals in the house and any potential appearance of clinical signs in them, recent boarding or kennel history, any recent impoundment and potential exposure to sick or unvaccinated animals, and any recent application of herbicides, pesticides, household cleaners, finishing products, paints or stains (or spills thereof), or use of automotive products or any solvents. Previous or referring veterinarian’s notes or any laboratory data outlining previous medical problems or any recent veterinary treatments should be identified, examined, and added to the record. Additional helpful information can be obtained by calling the previous or referring veterinarian. This technique provides an opportunity for the interviewer to obtain supplemental information relevant to the present problem or to underscore the significance of previously obtained data. Next, the chief complaint should be identified, its duration noted, and the physical examination initiated.
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?
Despite the often unreliable and possibly unknown nature of the owner’s account of events leading to a suspected poisoning, veterinarians must try to obtain as definitive a history as possible. Just as veterinarians must not be misled when owners are convinced that their animals have been poisoned when other causes are actually responsible, clinicians must also never forget that preexisting infections or metabolic, congenital, and neoplastic conditions can mimic the clinical signs of a poisoning or can predispose the animal to a toxicosis. The correlation of an accurate history with the physical examination is crucial. Veterinarians must know the vital signs for the species they care for and must be able to recognize the telltale clinical signs and the characteristic “fingerprints” of specific poisonings.
Despite any possible flaws in the owner’s account of the history, the history represents a record of events before and during the onset of the illness. Veterinarians must obtain and organize this information in a logical and orderly manner. Specific criteria characteristic of a toxicological history include what poison or poisons are involved, when the exposure occurred, how much poison the animal was exposed to, and the route of the exposure (e.g., dermal, oral, inhalation, intravenous, subcutaneous, or intraperitoneal). An important further question is whether other animals at home could also have been exposed.
It is important to review the animal’s entire environment. Is the patient an indoor-only cat? An outdoor-only dog? What are the animal’s normal daily activities? Is it free to roam? How long is it gone each day? This line of questioning will provide helpful information, particularly since many clients may not recognize the potential toxicological hazards present in their house and yard unless specifically asked. Likewise, information about weather conditions and season and the activities, hobbies, and occupations of the owner may all be important and can provide important clues to the cause of an animal poisoning.
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).
Box 4-2 Initial Telephone Contact