Pie plant (more commonly known as 'rhubarb') is a herbaceous flowering plant that can be found in mainly temperate climates around the globe. It is extremely popular with cooks, with its stalks making a tasty filling for many varieties of dessert. However, the leaves of the rhubarb are quite poisonous to both humans and animals, with felines being no exception to the rule.

Fortunately, the symptoms produced by rhubarb poisoning are quite visible, meaning that owners can typically identify that there is a problem early on, and make a note of the progression of the symptoms. This information can be especially useful when trying to diagnose the issue.

Within a short time after consuming rhubarb leaf matter, the cat will begin to exhibit signs of digestive discomfort. Owners can identify nausea by looking out for the cat displaying an aversion to food, sensitivity to touch, and a willingness to isolate itself from other members of the household. Within a few hours the cat will begin to start retching and gagging before attempting to expel the toxins it has eaten. Owners can differentiate this from normal stomach upset and regurgitation of indigestible matter by the sustained nature of the vomiting. Continuous vomiting can be surprisingly dangerous to an animal the size of a cat, due to the sheer quantity of liquid that is expelled from the body in a relatively short space of time. This can quickly lead to dehydration, which can worsen the symptoms of the poisoning in addition to posing its own health risks. To avoid this, owners should make extra drinking water readily available and accessible for their cat.

Almost immediately after eating the rhubarb, the cat will show signs of physical irritation. One way that this can present itself is by swelling of the face and tongue, as the tissues react to the chemicals contained within the rhubarb. Sometimes, this swelling can cause blockage of the throat as the tongue begins to obstruct the airway and cause the cat to produce a wheezing noise when inhaling. This is often accompanied by redness around the nose and mouth, which can be more or less intense depending on how much of the plant was eaten. Owners may also notice the cat drooling. This is because saliva will also be produced in great quantities as the cat attempts to alleviate the irritation by flushing the offending chemicals out of its mouth. 

Muscle tremors are also a common symptom of rhubarb poisoning, with the cat's forelimbs often displaying the majority of the involuntary movement. This can also cause a general loss of coordination and difficulty walking and climbing. Additionally, owners could also notice that the cat might seem quite weak compared to its normal self, with the animal finding it hard to navigate over obstacles and manipulate objects with its usual level of ease.

The toxins present in rhubarb can have a direct effect on the health of the kidneys, as they form the body's primary means of defense against harmful substances being absorbed via the digestive system. In sufficient quantities, the rhubarb toxins can impair the function of the kidneys and even cause them to fail. This can cause a variety of symptoms, including diarrhea, a buildup of harmful substances in the blood, and damage to other organs. In extreme cases, this can even lead to death.

The leaf of the rhubarb plant contains a chemical referred to as 'oxalic acid'. The main function of this chemical is to act as a deterrent against potential predators who would otherwise regard rhubarb as a good source of food. The acid work by directly attacking the tissues it comes into contact with, causing the irritation to the sensitive tissues of the mouth and face as well as causing digestive discomfort and vomiting. Once absorbed by the body, oxalic acid also has an impact on coordination and is the root cause of the aforementioned muscle tremors. However, oxalic acid's most dangerous property is the fact that it is highly nephrotoxic, meaning that it highly damaging to liver tissue, carrying potentially lethal consequences.

Typically, a vet will first perform a physical examination of the cat in order to confirm and evaluate their symptoms. This is often accompanied by a blood test in order to judge the extent of any damage to the kidneys. The vet will also have some questions with regards to the timeline of and circumstances surrounding the poisoning, as this information can be especially helpful when trying to identify the root cause of the illness.

The primary mode of treatment for most common plant poisonings is to start the cat on fluid therapy. This will alleviate the effects of dehydration by directly injecting liquid into the cat's body, whilst simultaneously flushing the toxins from its system by provoking urination. The vet may also opt to give the cat a dosage of precipitated chalk as a means of reducing the levels of acidity in the stomach, thereby preventing further damage and making recovery easier. It might also be necessary to follow this with a dose of activated charcoal in order to absorb any leftover oxalic acids lingering in the digestive tract.

The majority of cats poisoned by rhubarb will recover within roughly two weeks. However, this does not mean to say that aftercare is not needed. Owners should be sure to make plenty of liquids available to the cat in the days following the poisoning, as well as serving them a bland diet in order to give their stomach a chance to recover. The cat's activity should also be restricted in order to conserve their energy. In severe cases, a follow-up appointment with the vet may be needed. This will allow a blood test to be done in order to gauge the recovery rate of the kidneys.