In recent years, the number of rodent species (including guinea pigs) kept as pets has grown considerably and the demand for appropriate veterinary care for these species has also increased (Hawkins and Graham, 2007). There is considerable concern in both pet owners and the veterinary industry that many do not survive general anaesthesia. This often means that veterinary surgeons are reluctant to perform relatively routine procedures when presented with a guinea pig at a clinic, potentially leading to these patients not receiving gold standard care when it comes to veterinary medicine.
Guinea pigs have a relatively high risk of anaesthetic complications, with a perioperative mortality rate of 3.80% compared with 0.24% for cats and 0.17% for dogs (Brodbelt et al, 2008). This study revealed that all exotic species have a higher risk of anaesthetic complications than more commonly treated domestic pets.
This may be because many exotic species presented in practice have underlying disease or are extremely debilitated by the time they make it to see a veterinarian. This is largely because many are prey species and it has been historically in the their best interests to hide disease to avoid predation.
These patients will therefore often have a higher American Society of Anesthesiologists (ASA) classification (Table 1). Although many young patients for neutering may well be ASA I-II, many of those presented are at least ASA II-III or higher, which explains their higher mortality rate to some extent. However, there are factors that we can change to decrease the chances of anaesthetic-related deaths or complications.
| American Society of Anesthesiologists (ASA) Physical Status Scale (2016) | |
|---|---|
| Class I | Minimal risk |
| Class II | Slight risk, minor disease present |
| Class III | Moderate risk, obvious disease present |
| Class IV | High risk, significantly compromised by disease |
How can we reduce risks?
Before even considering an anaesthetic, patients should undergo a full clinical examination and history taking with an experienced veterinary surgeon.
Many veterinarians can be unsure of the normal physical characteristics of the species, such as physical features like bald patches behind the ears or that the lower incisors are longer than the upper incisors (Harkness et al, 2002), which could easily lead to misdiagnosis. Ensuring that a veterinary surgeon is confident with these species is vital as over-interpreting normal findings could result in unnecessary anaesthesia or an incorrect diagnosis.
A general level of competency in medical and surgical management of these species can be reasonably expected by owners. If this is not the case, it is the veterinarian's duty to inform the owner or seek help from a colleague. Veterinary surgeons should recognise when a case or a treatment option is outside their area of competence and be prepared to refer it to a colleague, organisation or institution that they are satisfied is competent to carry out the investigations or treatment required (Royal College of Veterinary Surgeons, 2016).
Veterinary nurses should understand the normal, healthy guinea pig and its welfare needs. They should know that these patients are social, prey species and their optimal environmental temperature is 18–26°C (65–79°F) (Banks et al, 2010). They are constant grazers who require an unlimited supply of fibre to ensure healthy, motile guts and wear of their continually growing teeth.
Given these considerations, patients should be housed in a separate ward to cats and dogs where possible and offered a hide box or covered area to minimise stress. Housing with companions should also be considered; as a social species, these animal prefer to have company. Food should be offered before anaesthesia rather than fasting, which is used in many carnivorous patients. These may sound like simple needs, but anaesthetising a patient that is stressed and already into some degree of gut stasis will increase the risks.
Prestabilisation
If a guinea pig is debilitated, it may advisable to stabilise it for several days before a procedure. As already mentioned, these patients can be presented in an extremely debilitated condition even when the owner has noticed only small changes in behaviour or eating habits.
These patients often need supportive care to treat gut stasis and dehydration before an anaesthetic can be considered. Drugs such as ranitidine and cisapride can be administered to aid gut motility and a regimen of syringe feeding regularly throughout the day should be undertaken if the patient has reduced food intake.
Anti-inflammatories such as meloxicam are often advised in the presence of gut stasis, and sometimes antibiosis if the patient has an infection. Antibiotic choice should be guided by culture and sensitivity where possible and selected appropriately for the infection.
Fluids
Guinea pigs require a large maintenance rate of fluids of 100 ml/kg/24 hours, due to their high glomerular filtration, respiratory and metabolic rates. Fluids are extremely important pre, peri and postoperatively in all rodents, especially guinea pigs. Periods of anorexia, respiratory disease and other factors will mean guinea pigs require fluids to maintain their cardiovascular system. Anaesthetising a dehydrated patient could lead to hypotension, hypoxia and potential renal insufficiency. A common sense approach to this should be adopted, perhaps questioning whether a cat or dog in a similar state of illness would receive fluids.
Because of the species' small size, routes for the administration of fluids are limited. The best and most effective route would be intravenous; however, due to the size of guinea pigs, even a 26G catheter will often not fit down the lumen of the vein. If the patient is large enough, it may be possible to use a cephalic or saphenous vein, but this is often extremely difficult. The intraperitoneal route is usually contraindicated due to the large amount of abdominal contents and the risk of puncturing vital structures. The subcutaneous route is therefore generally used (Figure 1). This has always been regarded as a slow route of fluid administration. However, administration of a recombinant human formulation of hyaluronidase at the infusion site can speed up the absorption of subcutaneous fluid up to five times faster than without the enzyme, making the technique more clinically practical (Spandorfer, 2011).
During anaesthesia or in emergency situations, the intraosseous route can be a useful alternative and, although often these catheters are not well tolerated by healthy patients, they can be an asset if a guinea pig is critically ill.
The oral route of administration should not be forgotten. In dehydrated patients, the gut contents often become dehydrated and increasing oral fluids can help rehydrate these and improve peristalsis.
Drugs selection
Care should always be taken when selecting drugs for patients. Rather than giving each rodent species the same combination or dosage of drug, each patient should be treated as an individual and factors such as age, disease status and the procedure being performed should always be considered. Although drug dosages in rodents are often at a higher milligram per kilogram dosage than are commonly used to in cats and dogs, care should be taken with cardiovascular and respiratory depressants such as medetomidine, acepromazine and opioids.
Anaesthetic monitoring
Guinea pigs require very close monitoring before, during and after an anaesthetic. Guinea pigs — like many other rodent species, and species such as rabbits — often have a shorter period between apnoea and cardiac arrest, and the sooner the response to an anaesthetic crisis, the more positive the outcome will be.
Several factors should be taken into consideration during the anaesthetic.
Postoperative monitoring and care
The postoperative period has been found to be the highest risk period for dogs, cats and rabbits (Brodbelt et al, 2008), so it could be assumed that this is the case with guinea pigs too.
This could be due to the less intense approach to monitoring in the postoperative period or perhaps that the anaesthesia is likely to exacerbate any underlying illness such as respiratory disease. Patients should therefore always be monitored closely in the postoperative period, with temperature, pulse, respiration rates and demeanour being observed regularly. Placing the patient into an incubator is advisable as these patients will still be at risk of losing body heat even after anaesthesia (Figure 5). If this is not possible, other warming aids should be used. Raising the thorax above the abdomen again is advantageous, especially if the patient is recumbent on recovery.
It is important that guinea pigs begin eating soon after anaesthesia to reduce the risk of ileus (Longley, 2008). Postoperative gut stasis is common in rabbits, guinea pigs and chinchillas, usually due to a combination of pain, stress, drugs and length of time when they have been unable to eat (i.e. under general anaesthesia). Therefore, a selection of fresh, favourite foods should be offered to the patient as soon as possible and syringe feeding should be started (Figure 6). Gut stimulants can be administered during the postoperative period and for several days at home if necessary.
In exotic small mammals, behavioural signs of pain are subtle, and both veterinary surgeons and nurses are often unfamiliar with normal behaviours (Wenger, 2012). Detrimental effects of untreated pain include inducing a catabolic state, reduced appetite or anorexia, delayed wound healing, lowered immune responses and prolonged hospital stays. Pain can also reduce gastrointestinal motility and peristalsis due to the stress response. Untreated pain increases morbidity and potentially increases mortality in many species, but likely more so in prey species (Barter, 2011). It is important to ensure that guinea pigs receive adequate analgesia postoperatively even if this means a longer stay in hospital for injectable medications.
Over the following hours and days, postoperative faecal output should be monitored closely. If the patient lives with a companion, then separating them via a grid divider or placing the recovering guinea pig in a wire cage into the enclosure for periods of time ensures the veterinary nurse and/or the owners can monitor this while still maintaining the guinea pig's bond with its companion(s). Giving them plenty of time to eat away from any competition is important, too, as fights about food can become heated so a recovering guinea pig is less likely to have adequate access to food sources. If the owner is not confident or is unable to monitor their pet closely, it is advisable to hospitalise the guinea pig until it is eating adequately so that it can be nursed and syringe fed until this point.
Conclusion
Care should always be taken with anaesthetising any patient. However, more research and preparation may be required for guinea pigs if they are not seen often in a practice. The physiological make up of this species should always be taken into account and individuals should always be fully assessed for clinical disease before anaesthesia. Both the preparation and recovery period can involve more intense nursing due to the nature of these species. If some of the advice here is considered, the risks involved in anaesthetising guinea pigs can be reduced somewhat with much happier and healthier outcomes.