Urogenital Disease and Anaesthesia

Introduction

Surgery on the urogenital is a daily procedure as many small animals are neutered, and large animals males are castrated frequently. Because these are elective procedures, the patients are often healthy and so normal protocols can be used. However, there can often be non routine reasons to perform surgery on the urogenital tract, such as pyometra or emergency caesarean sections. These procedures in themself provide additional risks to anaesthestising patients, but also other disease processes can affect anaesthesia in patients, for example renal failure.

Renal Failure

Renal failure can present as either acute or chronic meaning that management of such cases in preparation for anaesthesia may vary. In an ideal situation, the patient would be stabilised and underlying cause treated and/or managed before any anaesthetic procedure is carried out. However, in emergency cases, this is not always possible and so careful selection agents is required.

The kidney not only plays a role in the excretion of waste products, including some anaesthetic agents, it also plays a major part in regulating blood volume. Both these functions play a role in anaesthesia and so when the kidney function is altered, this will impact upon anaesthesic procedures. This means it is of great importance to detect any problems with renal function before deciding on a protocol for use in these patients. This should be done via a thorough physical exam with appropriate further testing such as full haematology, biochemistry and urinalysis. Blood pressure should also measured in these patients and necessary treatment before any procedure is performed. Intravenous access is always necessary in these patients to allow for fluid administration throughout the anaesthestic, and these should continue postoperatively also. During the procedure, blood pressure should also be closely monitored, preferably via in invasive method to allow most accuracy. If possible, local anaesthetic techniques, particularly epidurals should be used for analgesia to help prevent changes in renal blood pressure.

Urethral Obstruction and Bladder Rupture

Blocking of the urinary tract is a common cause of post renal failure in small animals. The blocked cat commonly presents in general practice, and considered an emergency often requiring sedation or general anaesthesia. However, these patients pose a number of problems due to the abnormalities in electrolytes and acid base balance. The most common abnormality detected is hyperkalemia. This is commonly detected on biochemistry, but if this is not available, it may be detected on an ECG trace if the hyperkalemia is severe enough. Care should be taken in choose the agents used in these patients as adverse effects on the cardiovascular system may exacerbate any haemodynamic problems present.

Pyometra

Pyometras are the most common cause for emergency ovariohysterctomies in small animals. These patients can present in various conditions, with patients having minimal metabolic disturbances to those with severe imbalances. Due to this variety in presentation, preoperative treatment can also vary from patient to patient, as some only require fluids to correct a mild dehydration, while others need fluids with addtional electrolyte to correct any imbalances and disturbances. The severity of the patient should be assessed on physical examination, full haematology and biochemistry and further testing as required.

Premedication in these patients can also vary depending on the state of the patient, as those that are severely affected may not require any premedication with patients appearing otherwise healthy can be premedicated routinely. Monitoring throughout the procedure should be the same as for any major surgery and commonly fluids are administered throughout. The patient should also be monitored closely for any signs of endotoxaemia, which may complicate the condtion of the patient further. Postoperatively, the most important consideration is analgesia. Fluid therapy should continue post operatively and in some severe cases, parenteral feeding may be necessary until the patient has recovered enough to start eating and/or has stopped vomiting.

Caesarean Section

During pregnancy, there are a number of physiological changes in the mother, which if a caesarean section is performed, need to be taken into consideration. There are changes to the respiratory, cardiovascular, neurological and gastrointestinal systems. Another important consideration is placental transfer, which includes anaesthetic agents both intravenous and inhalation agents. The amount of agent that is transfered over the placenta depends on:-

• Placental blood flow
• Maternal protein binding
• Placental uptake
• Foetal metabolism
• Pharmacokinetic properties of the drug

When selecting agents to be used in either an elective or emergency caesarean section, the following should be considered:-

• Duration of action of agent - Ideally short duration agents should be used.
• Dose used - Use the lowest possible dose to get the desired effect.
• Local anaesthesia - Use techniques whenever possible.
• Close monitoring
• Oxygen supplementation.

It is important, as with any procedure to intubate quickly and secure the airway to prevent aspiration by the mother, particularly in those patients presenting for emergency surgery. In these cases, it is also sensible to use a protocol which the anaesthetist is used to, even if not the ideal protocol for this procedure and it is often safer. The use of premedication can vary from patient to patient depending upon their presentation, as in any surgery, a healthy animal for an elective procedure is likely to require a premedication while a dull and depressed patient may not. Fluid therapy is commonly used, and analgesia is important post operatively.