Toxicological emergencies

30 Toxicological emergencies


Suspected or witnessed poisoning is a common reason for presentation of small animals to emergency clinics, with dogs being much more commonly affected than cats. This chapter presents a general approach to the poisoned patient before going on to describe some of the more commonly implicated poisons in greater detail using a number of case examples.



Approach to the Poisoned Patient



Telephone communication


Initial telephone communication is perhaps no more important than in the intoxicated patient. The important questions to ask are summarized in Box 30.1.




On the basis of the information obtained, a recommendation should be made as to whether the animal needs to be presented to the practice or may be managed conservatively at home. In some cases, the animal will be exhibiting marked clinical signs and questioning should be kept to a minimum with immediate transport to the practice being the only appropriate recommendation. In other cases, it is necessary to obtain further information before a recommendation can be made.



Further information


The purpose of seeking additional information about the poison in question is to ascertain if possible the severity of exposure that has or may have occurred (see Box 30.2).



A number of sources of information are available with respect to veterinary toxicology that includes:





The internet: only reliable up-to-date sources should be used (e.g. www.vin.com, www.ivis.org). The internet is also useful for determining ingredients and concentrations in cases where for example only a proprietary product name is available.

Some information that may be useful when calculating exposure dosages is presented in Box 30.3.




Home management


If the decision is made for the animal to be monitored at home, the owner must be thoroughly briefed both on what signs to observe the animal for and the typical time frame for their onset and progression. In general, if there is any doubt as to the animal’s condition, veterinary examination should be recommended. Owners should be advised on appropriate measures to implement during transportation (e.g. keeping unconscious animals warm or keeping seizuring animals cool and protected from injury).



Inducing emesis at home


In some cases in which poison ingestion has occurred within a suitable period of time, it may be appropriate for the owner to induce emesis at home, for example if financial concerns or practical constraints preclude presentation to the practice. In addition, if a considerable delay is anticipated prior to presentation, and the owner has ready access to an appropriate emetic, inducing emesis prior to departure from home may be advisable to minimize further absorption of the poison in transit. The owner must be questioned carefully to ensure that contraindications to inducing emesis do not exist; these are summarized in Box 30.4.



Agents that may be used to induce emesis at home are shown in Table 30.1.


Table 30.1 Agents for inducing emesis at home























Agent Dose Comments
Soda crystals (washing soda) 1 crystal



Syrup of ipecacuanha (7%) D: 1–2 ml/kg p.o.
C: 3.3 ml/kg p.o.



Hydrogen peroxide (3%) D, C: 1–3 ml/kg


Table salt (sodium chloride) Not recommended



C, cats; D, dogs.




General Clinical Approach


See Box 30.5.




History




All the information in Boxes 30.1 and 30.2 should be obtained at the appropriate time. In some emergency patients, clinical signs and progression are compatible with possible intoxication without an immediately suggestive history. In such cases, the owner must be carefully and thoroughly questioned to establish whether a potential source of poison exists that the owner has not considered.



Initial management of ingested poisons


As for all emergency patients, a major body system (cardiovascular, respiratory, neurological) examination (see Ch. 1), including measurement of rectal temperature, should be performed and immediate measures taken to correct potentially life-threatening problems. Intravenous fluid therapy (see Ch. 4) may be required to correct hypovolaemia and/or dehydration. Fluid therapy is also indicated in the management of poisons that are nephrotoxic (e.g. nonsteroidal antiinflammatory agents) and those that are largely dependent on renal excretion. Oxygen supplementation is indicated in patients with respiratory compromise, for example from aspiration following vomiting, and in the context of certain poisons such as carbon monoxide.




Treatment of seizures and muscle tremors


A variety of poisons include neurotoxicity amongst their mechanisms of action – examples include metaldehyde, pyrethroids, strychnine, caffeine, theobromine, organophosphates and tremorogenic mycotoxins. Seizures and/or muscle tremors are common signs of poisoning requiring symptomatic treatment (see Ch. 24).


In patients intoxicated with tremorogenic poisons (e.g. metaldehyde, permethrin), it can be difficult to differentiate severe muscle tremors from seizure activity. However, if the poison in question is known to be one associated with severe tremors or sufficient clinical suspicion exists, the use of methocarbamol may be indicated and may avoid the need for anaesthesia. This is a centrally acting muscle relaxant related to guaiphenesin whose precise mechanism of action remains unclear. The manufacturer’s recommended dose in dogs and cats is 44–220 mg/kg i.v. with a typical upper limit of 330 mg/kg in a 24 hour period. However, to the author’s knowledge, an injectable preparation of this agent is not currently available in the United Kingdom. In the absence of methocarbamol, the management of patients with tremors is the same as for those with seizures.



Hyperthermia is a potentially serious development in patients suffering from seizures or muscle tremors. Hypothermia may also occur following bathing or sedation. Close monitoring of rectal temperature for either development and appropriate intervention (see Chs 16 and 17) is therefore required.



Gastrointestinal decontamination (GID)


Toxin exposure is usually via ingestion and gastrointestinal decontamination (GID) is frequently indicated. This consists of emptying of the stomach followed by administration of an adsorbent to minimize absorption of any poison remaining in the gastrointestinal tract.




Activated charcoal

Activated charcoal acts as an adsorbent binding to toxins and allowing their passage through the gastrointestinal tract while preventing or minimizing further systemic absorption. It is typically administered once gastric emptying has been performed and should be given as soon as possible. If an emetic has been employed for gastric emptying, enough time must be allowed for the emetic effects to subside before activated charcoal is administered. In some cases activated charcoal is administered initially via stomach tube at the end of gastric lavage. The recommended dose in dogs and cats is 1–5 g/kg to be repeated as necessary (typically every 4–6 hours) until black faeces are detected. Doses up to 8 g/kg have been used. Activated charcoal is often successfully administered in food to dogs. However, compliance is likely to be much poorer in cats. Various proprietary preparations are available with accompanying dosing guidelines, including powdered formulations (e.g. BCK Granules®, Fort Dodge) that can be added to food or made into a slurry and administered by mouth, and suspensions (e.g. Charcodote®, Pliva Pharma Ltd).


Different substances are bound to different degrees by activated charcoal. However, unless contraindicated, the use of activated charcoal in almost all cases of oral poisoning is probably reasonable and may also help following topical poisoning (see below). Activated charcoal should not be used following ingestion of caustic or corrosive substances, in patients that are vomiting or seizuring, or where there is any possibility of gastrointestinal perforation. Vomiting and constipation following administration of multiple doses are the main complications reported.




Topical poisoning


Washing the patient is recommended to minimize irritation of and absorption via the skin; this should also minimize absorption through ingestion following grooming. Washing is usually done using mild soap or detergent, followed by copious rinsing with water and then drying the animal as thoroughly as possible. Powdered toxins may be vacuumed off before washing. All individuals involved in handling the animal should take care to wear gloves and preferably an apron so as to avoid self-contamination. In some cases it may be appropriate for the owner to wash the animal at home. However, in compromised or noncompliant animals, veterinary care is recommended.


Clipping the coat of long-haired patients may help to maximize decontamination. Chemical restraint may be preferable during washing to allow protection of the eyes and in some cases general anaesthesia with endotracheal intubation is safest to minimize the risk of aspiration. Vital parameters including rectal temperature should be monitored closely throughout.


Oily substances may be more successfully removed using commercial hand-cleaning degreaser formulations (e.g. Swarfega Hand Cleaner® products) but it is important to ensure that such preparations are thoroughly washed off the animal subsequently.


The use of activated charcoal is generally recommended following topical poisoning. This is to minimize gastrointestinal absorption that may occur following ingestion from grooming. In addition, some poisons undergo enterohepatic circulation following absorption from the skin and thereby become available in the gastrointestinal tract.


In cases in which the skin has come into contact with an acidic or caustic substance, the affected area should be lavaged very thoroughly (’the solution to pollution is dilution’) using normal saline or indeed warm water. The same is true in cases of ocular contamination and in both cases the animal should be given appropriate analgesia and chemically restrained to allow comprehensive lavage to be performed. Damaged skin is highly susceptible to mechanical injury and gentle lavage is therefore mandatory.





Specific Poisons



Pyrethrins and pyrethroids



Theory refresher


Pyrethrins are naturally occurring insecticidal esters of chrysanthemic acid and pyrethric acid extracted from the Chrysanthemum cinerariaefolium plant; pyrethroids (e.g. permethrin) are synthetic pyrethrins. Many topical and household insecticidal preparations containing these compounds are marketed for the control of flea and lice infestations amongst others in dogs and cats. These preparations are widely available from a variety of outlets.







Case example 1







Metaldehyde



Theory refresher


Metaldehyde is a cyclic tetramer of acetaldehyde that is commonly used as a pesticide against slugs and snails (molluscicide). Commercial pellet preparations usually contain 1.5–8% metaldehyde w/w (see Box 30.3) in a cereal base. The pellets are often blue or green in colour and the cereals and other additives make slug/snail baits palatable to dogs. Cats as usual are more discerning and metaldehyde poisoning has only been reported in a few cases. Liquid preparations containing higher concentrations of metaldehyde are also available, as are granular and powdered preparations. Metaldehyde baits sometimes contain additional herbicides and pesticides, most commonly carbamate insecticides.






Case example 2





Sep 3, 2016 | Posted by in SMALL ANIMAL | Comments Off on Toxicological emergencies
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