Drips, it has to be said, can seem scary. They’re clear bags full of liquid. There are different mixtures of liquid for different occasions, as advertised on the side of the bag. The liquid runs through a tube, down a needle (cannula) and usually into the bloodstream. Drips are something that we usually associate with serious illness or hospital care; in fact, ‘on a drip’ is something that people mention when they want to let everyone know that it’s serious.

But other than that, what does it mean? What’s the point of putting a pet ‘on a drip’? Here, we try to unravel the reasons behind the plastic tubes.

Maintaining water balance

The main product in most drips is water: the same molecule that you and I drink. 

When we drink it, it is absorbed from the guts and taken up into the blood. Some of it is used by the body and some of it is excess; healthy kidneys filter out water at the right sort of speed to keep a good balance.

A drip simply puts the fluid into the vein more quickly than we could if the animal drank it. 

Sometimes, drips are given because an animal can’t take water in quickly enough; sometimes, water is actively lost. Perhaps the kidneys aren’t working for example, and fluid is escaping into the urine (where working kidneys would recycle it). Or perhaps the animal is vomiting and losing more water than it can keep down.

But is it as simple as that? Of course not. 

Acidity regulation

Vomiting changes the levels of different chemicals in blood. Vomit is acidic and losing vomit can make the blood more alkaline, for example. 

An animal’s blood needs to be kept at the right level of acidity. Other examples are when the kidneys don’t work, or in hyper-ventillation when carbon dioxide is lost very quickly, or when acidic or alkaline waste products are building up in the blood. The flow of charged particles through the bloodstream can luckily be changed with a drip, controlling the acidity whenever the body can’t take care of this for itself. 

Salt and blood pressure

Unlike water in pipes, water in veins doesn’t stay where it’s put; the fluid component moves through the walls of the blood vessels and in and out of surrounding tissues and cells.

There is very clever chemistry involved in keeping the right amount of water inside the blood vessels, and letting the right amount move into cells. The movement of water around the body is controlled using salt. Salt has clever water-controlling properties; without salt, the water would leave the vessels and flood into the surrounding tissues instead. On the other hand, if we put too much salt in the bloodstream, fluid from the body would move into the veins, leaving the outer tissues dehydrated. 

Salt content is controlled by the kidneys and closely connected to blood pressure. Sometimes a drip can give the salt levels a helping hand.

Maintaining blood pressure under anaesthesia

This is listed separately because we’re often asked about it. When there is plenty of water in an animals’ veins during an anaesthetic, the drug can be cleared from the body much faster. Further, the drip can prevent drops in blood pressure associated with being under anaesthetic. This helps to minimise any impact on the kidneys. It is therefore common practise to offer a drip during surgery and a good idea, even in fit animals, to take it. 

Flushing out poisons

Some chemicals that end up in our blood are poisonous, whether coming in from outside (Warfarin, for instance) or made by the body (Ketones in diabetes). The solution to pollution is often dilution: these toxins can be watered down as much as possible in the body and then flushed out through the kidneys. If the kidneys are supported by fluids, particular substances that are poisonous to kidneys are likely to be more diluted and thereby cause less damage on the way out. 

Putting in medicines

Drips provide a direct portal to the blood for the input on chemicals. An anaesthetic put straight into the blood will often work straight away. Furthermore, if such anaesthetics are dripped in slowly, the level of anaesthetic can be controlled; drip the anaesthetic in faster to make the pet ‘deeper’ or more slowly to make the anaesthesia ‘lighter.’ This can also be used to great effect in controlling fitting dogs.

Further, radio-opaque dyes can be dripped into a pet’s blood and an X-ray taken before they leave the body, enabling vets to see the path of the body’s circulation. This is particularly useful when blood vessels don’t take the usual routes, for example where there’s a shunt (an extra path) that misses out the liver. Drips can also provide a well-controlled means of administering certain types of drugs. These can include insulin or some types of chemotherapy. They can also be used to deliver blood products and transfusions into the veins, or to help the circulation to by-pass the heart or the kidneys during radical surgery.

Transport of oxygen

Giving fluid can also help Oxygen to move more freely around the body. 
All in all, IV fluids have a vast range of uses and they can be quite difficult to follow. The main thing to understand is that it isn’t always as simple as just treating dehydration. The best way that we can advise to find out what a vet is trying to achieve with a drip is to ask them. Vets spend a lot of time thinking about drips; we’ll probably only be too pleased to tell you.