Ureteral obstruction has been previously considered an uncommon occurrence in cats. With wider availability of advanced imaging, particularly ultrasonography, the diagnosis of ureteral obstruction appears to be increasing in incidence (Kyles et al, 2005).

Ureteral obstruction occurs secondary to an intraluminal obstruction, a mural lesion, or extraluminal compression.  Mural lesions include neoplasia, fibrosis, congential and acquired stricture and polyps. Extraluminal compression most often occurs secondary to neoplasia arising from the ureter, the bladder, or the retroperitoneal space however there is also a report of an occurrence secondary to retroperitoneal infarction and fibrosis (Ragni and Fews, 2008). Examples of intraluminal obstruction include calculi, debris, and spasm of the ureter. 

Intraluminal obstruction may occur unilaterally or bilaterally. Ureteral obstruction regardless of the underlying cause leads to restriction of urine flow, and if left untreated, obliteration of the renal parenchyma secondary to pressure.  The physiology of ureteral obstruction has been studied in dogs and revealed that the prognosis for recovery of renal function is dependent on both the degree of obstruction and the time that obstruction is in place. After four days of obstruction the prognosis for return of renal function is excellent, after 14 days there will only be a recovery of approximately half of the normal glomerular filtration rate, and after 40 days there is little or no recovery if the obstruction is corrected (Kyles, 2006). 

This highlights the need for prompt diagnosis and intervention. Unilateral obstructions are difficult to diagnose as renal function remains normal due to the efforts of the contralateral kidney. Unfortunately if the first obstruction is unilateral the cat is often left undiagnosed until a second obstruction occurs in the contralateral kidney resulting in renal failure (Evans et al 2007).

Clinical signs of cats presenting with ureteral obstruction may be vague. Presenting complaints include lethargy, vomiting, inappetance, and weight loss. The most common finding on physical examination is abdominal/spinal pain.  In cases where there has been previous undiagnosed obstruction one large kidney may be palpated and the contralateral kidney may be unable to be detected (“big kidney-little kidney” presentation). 

In the author’s opinion, any cat that upon abdominal palpation one large kidney and one small kidney are palpated should have renal imaging performed. Pyrexia and dehydration may also be clinical examination findings in cases where ureteral obstruction is occurring as a consequence of debris generated by pyelonephritis. In cats presenting with ureteral obstruction for the first time, physical examination findings may be very subtle and a high index of clinical suspicion needed for diagnosis.

Biochemical changes of ureteral obstruction can range from unremarkable through to severe azotemia (from acute renal failure). Bilateral obstructions usually have significant azotemia as neither kidney can function. Unilateral obstructions usually have unremarkable biochemical changes if the contralateral kidney is unaffected where as they will have severe azotemia if the contralateral kidney is non-functional. Clinical pathology may demonstrate severe renal dysfunction but cannot differentiate ureteral obstruction from other forms of acute renal failure. Common laboratory findings include severe azotemia, hyperphosphatemia, and hyperkalaemia.

Any cat presenting with these clinical pathology changes should be considered an emergency.  While there are many causes of acute renal failure it is the authors opinion that imaging of the urinary tract should be mandatory for any cat with acute renal failure. Urine specific gravity (USG) is often suboptimal in these cats (< 1.035).  Urine sediment should be examined for concurrent bacterial infection and urine should be sent for culture and sensitivity.

Definitive diagnosis of ureteral obstruction may be made via several different imaging modalities.  Ureteral calculi are often visible on plain abdominal radiographs.  A retrospective study revealed that sonography and survey radiography used in combination was able to diagnose 90% of ureteral calculi (Kyles et al, 2005). 

Sonography will reveal dilation of the renal pelvis greater than 3mm.  Occasionally the cause of obstruction may be visualised sonographically, for example the visualization of a bladder mass or calculus within the proximal ureter.  In the absence of visualisation of the cause of suspected obstruction, an antegrade positive contrast pyelogram should be performed.  Intravenous urography does not usually provide suitable images. A three-way tap is connected to: a 3ml syringe filled with suitable contrast material (eg Urograffin or Omnipaque) an empty 3ml syringe (for fluid collection) and a long 22 guage needle (2 ¼ inch).

Under ultrasound guidance the needle is inserted through the greater curvature of the kidney into the renal pelvis.  Urine is aspirated from the renal pelvis into the empty syringe and retained for sediment analysis and culture and sensitivity.  Once urine is collected, the 3-way tap is turned and contrast is injected into the renal pelvis.  Lateral and dorsoventral abdominal radiographs are then performed. Where ureteral obstruction exists there will be abrupt termination of the contrast column. In some cases, particularly those where obstruction is secondary to pyelonephritic debris the obstruction may be flushed under pressure into the bladder.  Other methods of diagnosis include advanced imaging such as CT, MRI and nuclear scintigraphy.

Treatment of ureteral obstruction varies depending on the underlying cause. The following notes discuss treatment of treatment of intraluminal obstruction secondary to calculi or debris only.

Intraluminal ureteral obstruction may be treated medically or surgically. 

First and foremost pain relief is MANDATORY for cats with ureteral obstruction. It is amazing how many angry aggressive cats seemingly change personality overnight with the administration of pain relief. The most common analgesics used for ureteral obstruction at The Cat Clinic are the opiates methadone (used in intermittent bolus dosing) and fentanyl patches (Durogesic patch, 12.5microgram or 25 microgram depending upon the size of the cat).

The mainstay of medical therapy involves judicious use of intravenous fluids and agents to dilate the ureter to promote passage of the obstruction. There are two distinct groups of cats that are medically treated. The first group are those presenting with their first episode of obstruction, or those cats who have compromise of the contralateral kidney and are azotemic but not hyperkalaemic on presentation. The second group of cats are those who present in acute renal failure with hyperkalaemia. These cats have either bilateral obstruction or unilateral obstruction with little or no function of the contralateral kidney.

At The Cat Clinic non-hyperkalaemic cats are treated with intravenous fluids and ureteral dilating agents initially.  Cats that do have compromise of the contralateral kidney are at risk for oliguric or anuric renal failure.  As such body weight should be closely monitored (the author recommends every 4-6 hours). Obviously another method of monitoring urine output is to place an indwelling urinary catheter and monitor urine output. 

The authors do not routinely place urinary catheters in these cats for the following reasons; these cats are usually relatively bright and sedation/anaesthesia is often required for catheter placement, and the placement of a urinary catheter opens up a potential site of infection. Cats are maintained on intravenous fluids for a maximum of three days.  Agents used to stop ureteral spasm, dilate the ureter or increase urine flow include amlodipine, amyltriptaline, glucagon and diuretics. Further study into the clinical efficacy of these drugs is needed.

Daily monitoring of packed cell volume (PCV), total protein (TP), creatinine and serum electrolytes (sodium, potassium, and chloride) should be performed.  It is vital to track changes in electrolytes in these cats.  The majority of cats are re-imaged via sonography on day three. 

Our criteria for successful medical therapy are 1. Reduction in creatinine to normal or previously determined baseline level and 2. Reduction in size of renal pelvis. 

If the patient has not responded to therapy within three days then surgical intervention should occur.  Cats that progress to hyperkalaemic acute renal failure within this three day period should be considered candidates for surgery post stabilisation.

Cats presenting with hyperkalemic acute renal failure are candidates for surgery following stabilisation.  Intravenous fluid therapy should be commenced with non-potassium containing fluids. Close attention should be paid to the body weight and hydration status of the cat as it is very easy to fluid overload these cats. Depending on the level of hyperkalaemia and the state of the patient, additional therapy for hyperkalaemia may need to be instituted. Therapies include the administration of regular insulin and glucose intravenously and sodium bicarbonate. Calcium gluconate may utilised for its cardioprotective qualities where appropriate.

After the initial period of stabilisation the decision must be made whether the patient is stable enough for a long surgical period, or if peritoneal dialysis or percutaneous nephrostomy tube placement should be attempted. This decision is based upon individual patient factors.

There are several different surgical techniques for relief of ureterliths. The choice of technique is dependent upon the location of the obstruction.  In humans there are three specific sites where ureteroliths tend to lodge. As yet it is not yet determined if such sites exist in cats (Kyles, 2006). Obstructions in the proximal ureter are usually removed via uretotomy.  Given the size of the feline ureter magnification is essential during surgery. 

At The Cat Clinic, an operating microscope is routinely used for this surgery.  Ureteroliths in the distal ureter may be treated via uretotomy or ureteroneocystostomy (transection and then reimplantation of the ureter into the bladder).  The most common post operative complications seen at The Cat Clinic is uroabdomen (Evans et al, 2007). This is also the most common surgical complication seen at the University of California, Davis (Kyles et al, 2005). Other reported complications include pulmonary oedema, septic peritonitis, and persistant ureteral obstruction. Nephrostomy tubes divert urine away from ureterotomy site and allow for rapid reduction in azotemia. At The Cat Clinic, experience with uroabdomen has led us to routinely place nephrostomy tubes however surgeons at UC Davis feel this is not necessary with improved surgical technique. Nephrostomy tubes are associated with complications including obstruction of the tube, dislodgment of the tube, urine leakage, and infection.

Other therapies for resolution of ureteral obstruction include the use of extracorporeal shock wave lithotripsy. The University of California, Davis had been using this treatment method with informed consent of the owner of the patient.  However it is associated with high rates of complications including sudden death, pancreatitis, diarrhea, and cardiac arrythmias. The researchers also found that feline ureteroliths were generally “harder to fracture” than canine ureteroliths and thus this treatment methodology is not favoured (Hardie and Kyles, 2004). There has also been a case report of endoscopic retrieval of a ureteral calculus (Kuntz, 2005).

Kyles et al 2005 reported twelve month survival rates of 66% for those cats treated medically, and 91% for those cats treated surgically. This study also reported that of 35 cats monitored post obstruction 14 had a recurrence of ureterolithiasis. This occurred a median of 12 months post first obstructive episode. 

At The Cat Clinic approximately 1 in 3 cats treated for an episode of ureteral obstruction will have a recurrence of clinical signs.  Data is not yet available with regard to long term survival.

Ureteral obstructions can be treated medically and surgically with good outcomes, however recurrence is very common (Kyles et al, 2005, Evans et al, 2007).  With non specific clinical signs a high index of suspicion may be needed for diagnosis. Prompt diagnosis and intervention minimises long term damage to the affected kidney. Diagnosis is aided by imaging techniques such as radiography and sonography.  It is important that any cat with signs of an acute abdomen be imaged.

References:

Evans, N.A. Gunew, M. Marshall, R. Ureteral obstructions can be treated medically and surgically with good outcomes.  Proceedings of the Australian College of Veterinary Scienctists 2007.

Hardie, E.M. and Kyles, A.E.  2004.  Management of ureteral obstruction
Vet Clin North Am Small Anim Pract. 34(4):989-1010.

Kuntz, C.A.  2005.  Retrieval of ureteral calculus using a new method of endoscopic assistance in a cat.  Aust Vet J.  83(8):480-2.

Kyles, A.E., Hardie, E.M., Wooden B.G., Adin C.A., Stone E.A., Gregory C.R., Mathews K.G., Cowgill L.D., Vaden S., Nyland T.G., Ling, G.V.  2005.  Clinical, clinicopathologic, radiographic, and ultrasonographic abnormalities in cats with ureteral calculi: 163 cases (1984-2002).  J Am Vet Med Assoc. 226(6):932-6.

Kyles, A.E., Hardie, K.M., Wooden, B.G., ., Adin C.A., Stone E.A., Gregory C.R., Mathews K.G., Cowgill L.D., Vaden S., Nyland T.G., Ling, G.V.  2005.  Management and outcome of cats with ureteral calculi: 153 cases (1984-2002).  J Am Vet Med Assoc. 226(6):937-44.

Kyles, A. E.  2006.  Renal and Ureteral Obstruction.  Proceedings if the British Small Animal Veterinary Congress 2006.

Ragni, R.A., Fews, D. 2008.  Ureteral obstruction and hydronephrosis in a cat associated with retroperitoneal infarction.  J Feline Med Surg. In press.

Minimally Invasive Surgery In Cats

Rhett Marshall BVSc MACVSc
The Cat Clinic
189 Creek Road,
Mt Gravatt, 4122.

Minimally invasive surgery (MIS) is a collective term for surgical techniques designed to minimise the extent of an anatomic approach while maintaining precision and efficiency. MIS is a new and rapidly advancing field in veterinary medicine, with new techniques and applications being published in nearly every monthly veterinary journal. The benefits of MIS in decreasing peri-operative pain and decreasing morbidity has well been accepted in human medicine and now also confirmed in animals. Reducing or minimising pain in animals has been a priority for modern veterinary clients and has fueled the pursuit of these veterinary laparoscopic and thoracoscopic techniques that cause minimal invasion.
Laparoscopy
Viewing the internal structures of the abdominal cavity via laparoscopy involves "insufflation’ of the abdominal cavity with carbon dioxide gas. This gas is used because it in non-flammable (when cautery is used), non toxic and inexpensive. Modern CO2 insufflating devices have a pressure limit (12-15mm Hg) that cannot be exceeded so that overdistention of the abdomen is prevented. Insufflation allows displacement of the abdominal wall from the underlying viscera so that instruments may be manipulated without trauma to the abdominal organs. A cannula is placed in the abdominal wall and a rigid telescope (laparoscope) inserted through and into the peritoneal cavity. Once the telescope is in place, biopsy forceps or surgical instruments can be introduced into the abdomen through adjacent cannulas to perform various diagnostic or surgical procedures.
Structures that can be visualized include the liver, gallbladder, kidneys, bladder, stomach, pancreas, spleen, small intestine, cecum, colon, uterus, ovaries, vas deferens, adrenal glands and diaphragm.
The advantages of laparoscopy compared with conventional open surgical exploratory laparotomy include improved patient recovery because of smaller surgical sites and lower postoperative morbidity with a lower infection rate and less postoperative pain. The complication rate of laparoscopy is low. A review of 360 consecutive cases of diagnostic laparoscopy performed by Eric Monnet at Colorado State University found a complication rate of less than 2%. Serious complications include anesthetic- or cardiovascular-related death, bleeding, or air embolism .

Few contraindications exist due to the minimal invasiveness of laparoscopy. Ascites, abnormal clotting times, poor patient condition or obesity are the only relative contraindications. Absolute contraindications to laparoscopy include septic peritonitis or conditions where obvious conventional surgical intervention is indicated. Patients who are a poor anesthetic or surgical risk are not suitable candidates and are even less suitable for conventional surgery.

The basic equipment required for diagnostic laparoscopy include

1. telescope (0 or 30°)
2. videocamera and monitor
3. 2 cannulae (access into abdomen)
4. veress needle (for initial safe insufflation)
5. light source
6. light guide cable
7. carbon dioxide insufflator (to continuously inflate the abdomen)
8. palpation probe
9. oval biopsy forceps
10. punch biopsy forceps
11. grasping forceps
12. scissors
13. device for photographic documentation (optional)

Most major video endoscopy equipment required for laparoscopy, thoracoscopy, and arthroscopy may be used interchangeably. Things such as the light source, light guide, monitor, telescope (arthroscope), camera and printer may be interchanged and significantly reduce set up costs if you already have these large ticket items. Purchased new, this basic equipment could cost more than $60,000. Good quality second hand units are readily available from endoscopic suppliers such as Austvet or on e-bay and may cost as little as $10,000.

All types of modern MIS systems involve a video camera, light source and monitor. The video camera will be the most important determinant of your image quality on the monitor and often represents the largest investment. Camera image quality and is determined by how many chips they have. The more chips, the better the image and unfortunately the more expensive. The least expensive single chip cameras are adequate for routine procedures while modern 3 chip cameras provide increased image quality. Xenon fiber optic light sources are most commonly used for MIS as they are brighter and are necessary to provide adequate lighting in body cavities. A single chip camera with a Xenon light source would serve most practitioners well as it can be used for both soft tissue or arthroscopic procedures. The light guide cable connects the telescope to the light source so must also be compatible at both ends.

Telescopes and other minimally invasive surgical instruments (needle holders, curettes, forceps, etc) are more specifically designed for laparoscopy, thoracoscopy or arthroscopy. Telescopes are classified by their diameter and their length; the larger the diameter of the telescope, the more light and the better the image. Telescopes also come in zero-degree (looking straight ahead) to thirty-degree field of view. Angled scopes allow the operator an increased field of view, but can be confusing to beginners. Telescopes cost about $4000-6000 new and $1800-2500 second hand . The diameter of the telescope and instruments must correspond with the trocar-cannula units.

The procedure
The animal is clipped, prepared and draped for abdominal surgery. A Veress needle is used to safely penetrate the abdominal wall, then attached to insufflation tubing which connects to the automatic carbon dioxide insufflator. Carbon dioxide is considered to be the gas of choice for insufflation because of safety in preventing air emboli and spark ignition during cauterisation. After insufflation of the abdominal cavity, the trocar-cannula unit is placed through the abdominal wall and the trocar removed. Most cannulae contain an internal one-way valve that prevents loss of insufflated gas once the trocar is removed after abdominal entry. The cannula remains in place traversing the abdominal wall and creates a portal for the introduction of the telescope or instruments into the abdominal cavity.

The telescope and instruments can then be moved between cannulas as required. When finished, the telescope and instruments are removed, the insufflation tube detached so abdomen decompresses, cannulas removed and sutures placed in the muscle and skin as required.

Whats different in cats?
Their abdominal wall is very thin making it difficult and somewhat dangerous to normally insert a trocar-cannula. The thin muscle wall provides little grip to the cannulas making them easy to accidentally pull out while working. Cats require less intra-abdominal pressure to maintain a good surgical field (4-6mmHg compared to 8-15mmHg in the dog) and more readily develop complications such as reduced cardiac output from pneumo-peritoneum. Maximal insufflation allowed is hence lower for cats (10mHg for cat vs 15mmHg for dogs). The small dimensions of a cats abdomen and thorax requires telescopes and instruments with shorter working lengths (14-18cm compared to 20-30cm for dogs)

To optimise results, we use

1. 3.5mm Endotip cannulas – the cannula screws through abdominal wall rather than blindly stabbing a sharp trocar to gain access. These threaded cannulas also resist falling out of muscle wall during use and are simply unscrewed after use leaving undamaged muscle fibres.
2. 2.7mm telescope with 14cm working length
3. 3mm instruments with uni-polar coagulation
4. maximal insufflation of 6mmHg

Is there a place for laparoscopy in cats?
Client acceptance is excellent, the biopsy specimens are high quality and cats clearly benefit from reduced trauma. While the applications of laparoscopic surgical procedures continues to grow, it is likely that the main application of laparoscopy in cats will be diagnostic sampling. Initial set up costs is the major deterrent in veterinary medicine and this can be reduced by purchasing second hand equipment.

Thoracoscopy

Visualisation of lungs, pericardium, heart and major blood vessels, thoracic duct, mediastinum, lymph nodes and the pleural and peritoneal surfaces of the thoracic cavity can be performed with minimal invasiveness by placing a cannula in the chest wall and inserting a rigid telescope.
Thoracoscopy has been used in diagnosing spontaneous pneumothorax, pericardial effusions, pulmonary disease, pleural diseases, neoplasia (including determining margins and respectability), and determining the etiology of refractory pleural effusions. The most common minimally invasive thoracic surgical procedure currently being performed in small animals is creation of a pericardial window. Other thoracic procedures being performed include partial and total lung lobectomies, thoracic duct occlusion, PRAA transection, ligation of PDA, mediastinal mass removal and debridement for pyothorax.

The thorax can be entered trans-diaphragmatically (under xyphoid) or intercostally using a screw in Endo-tip cannula. The trans-diaphragmatic approach allows a long axis view of the thoracic cavity and is best for exploration and biopsy. Once a cannula is introduced, a pneumothorax developes causing the lungs to partially collapse and allows visualisation. Mechanical ventilation is therefore required. Additional cannulas are inserted under thoracoscopic visualisation and instruments inserted as required. Once the telescope is in place, biopsy forceps or surgical instruments can be introduced through adjacent cannulas to perform various diagnostic or surgical procedures within the thorax. Once examination and operative procedures have been completed the instruments and cannulas are removed, air removed from the pleural space and the lungs re-expanded.

Thoracoscopy offers many significant advantages over a conventional open thoracotomy.  As such, it will likely become the gold standard for both diagnostic investigations and many surgical procedures performed in the thoracic cavity.

Summary
Minimally invasive thoracic and abdominal surgery is far less invasive than open surgical procedures and has much lower morbidity and mortality yet allows greater visual exploration of the chest and abdomen than can be done with a laparotomy or thoracotomy. General anesthesia is required for performing minimally invasive surgery but the duration and depth of anesthesia can be much less than for open surgery. An owners reluctance for surgery may play an important role in the decision to select a minimally invasive technique.

Constipation And How Best To Manage It In Cats

Constipation or difficulty passing faeces is a severely debilitating disease seen commonly in cats of all ages and is life-threatening if left untreated. Effective management requires recognition of the aetiology and choosing the appropriate therapy for both cat and owner.

Clinical examination reveals colonic impaction with varying degrees of dehydration, weight loss, debilitation and abdominal pain. Pelvic fracture malunion may be detected on rectal examination in cats with previous pelvic trauma. Rectal examination is also useful in identifying other unusual causes of constipation, such as foreign bodies, rectal diverticula, strictures, inflammation, or neoplasia. Chronic tenesmus may be associated with perineal herniation in some cases. A complete neurologic examination with special emphasis on caudal spinal cord function should be performed to identify neurologic causes of constipation, e.g., spinal cord injury, pelvic nerve trauma, and Manx sacral spinal cord deformity.

While it is important to consider an extensive list of differential diagnoses in an individual animal, it should be kept in mind that most cases are idiopathic, orthopedic, or neurologic in origin. A recent review suggests that 96% of cases of obstipation are accounted for by idiopathic megacolon (62%), pelvic canal stenosis (23%), nerve injury (6%), or Manx sacral spinal cord deformity (5%).

Table 1. Common Differentials for Feline Constipation

The pathogenesis of idiopathic megacolon has been variably attributed to a primary neurogenic or degenerative neuromuscular disorder. Recent studies suggest that cats affected with idiopathic megacolon have impaired colonic smooth muscle function without significant abnormalities of smooth muscle cells or of myenteric neurons on histologic evaluation. These studies suggest that the disorder of feline idiopathic megacolon is a generalised dysfunction of colonic smooth muscle, and that treatments aimed at stimulating colonic smooth muscle contraction might improve colonic motility.

A complete blood count, serum chemistry, urinalysis and T4 level should be performed in all cats presented for constipation so that metabolic causes of constipation, such as dehydration, hypokalemia, and hypercalcemia may be detected. Serum T4 concentration and other thyroid function tests should also be considered in cats with recurrent constipation and other signs consistent with hypothyroidism.

Abdominal radiography should be performed in all constipated cats to characterise the severity of colonic impaction, and to identify predisposing factors such as intraluminal radio-opaque foreign material (e.g., bone chips), intraluminal or extraluminal mass lesions, pelvic fractures, and spinal cord abnormalities. The radiographic findings of colonic impaction cannot be used to distinguish between constipation, obstipation and megacolon in idiopathic cases.

Further diagnostic tests may be indicated in some cases. Extraluminal mass lesions should be further evaluated by abdominal ultrasonography and guided biopsy, whereas intraluminal mass lesions are best evaluated by colonoscopy. Colonoscopy requires general anesthesia and evacuation of impacted feces. It is used to evaluate the colon and anorectum for suspected inflammatory lesions, strictures, sacculations, and diverticula and. CSF analysis and myelography are indicated for neurogenic causes of constipation.

Successful management of constipation involves safely removing initial impacted faeces and then selecting therapies aimed at allowing effective defaecation on its own. Therapies are classified as either medical or surgical and are selected based on things such as the aetiology, severity, patient compliance and owner compliance.

Medical Therapy
Mild to moderate or recurrent episodes of constipation require medical intervention. Most cats can be managed as outpatients with dietary modification, water enemas, oral or suppository laxatives, and/or colonic prokinetic agents.

Mild constipation can usually be managed using rectal suppositories alone or combined with an oral laxative. A compliant cat and willing owner are required for success. Several types of suppositories are available and include dioctyl sodium sulfosuccinate (emollient laxative), glycerin (lubricant laxative), and bisacodyl (stimulant laxative).
Mild to moderate or recurrent episodes of constipation may require administration of enemas and/or manual extraction of impacted faeces. Several types of enema solutions may be administered, such as warm tap water (5-10 mL/kg), warm isotonic saline (5-10 mL/kg), dioctyl sodium sulfosuccinate (5-10 mL/cat), or lactulose (5-10 mL/cat). Enema solutions should be administered slowly with a well-lubricated 10-12F rubber catheter or feeding tube.

Cases unresponsive to enemas may require manual extraction of impacted faeces. Cats should be adequately rehydrated and then anesthetised and intubated to prevent aspiration should colonic manipulation induce vomiting (many cats vomit watery faeces on recovery from a water pic enema). Warm water is infused into the colon through a water pic enema while the faecal mass is manually broken up by abdominal palpation. Whelping forceps may also be introduced rectally (with caution) to break down the faecal mass. A water pic enema safely and rapidly removes faeces reducing the risks of prolonged anesthesia and colonic perforation. This method has never failed in our clinic and as such I believe surgical removal of faeces via colotomy has no place in feline medicine. Laxative and/or prokinetic therapy may then be instituted once the faecal mass has been removed.

Many constipated cats will respond to bulk-forming laxatives. These are dietary fiber supplements of poorly digestible polysaccharides and celluloses derived principally from cereal grains, wheat bran, and psyllium. Dietary fiber is preferred as it is well tolerated, more effective, and more physiologic than other laxatives. Fiber supplemented diets are available commercially (eg Hills R/D and W/D) or owners may add psyllium (1-4 tsp per meal), wheat bran (1-2 tblsp per meal), or pumpkin (1-4 tblsp per meal) to their normal canned cat food. Cats should be well hydrated before commencing fiber supplementation to maximise the therapeutic effect and to minimise the impaction of fiber in the constipated colon.

A final group of laxative is the poorly absorbed polysaccharides. Lactulose is the most effective agent in this group and probably the only one worth mentioning. The organic acids produced from lactulose fermentation stimulate colonic fluid secretion and propulsive motility. Lactulose administered at a dosage of 0.5 mL/kg every 12hrs fairly consistently produces soft feces in cats. Most cats with recurrent or chronic constipation can be well managed with lactulose. The dosage may have to be tapered in individual cases if flatulence and diarrhea become excessive.

The stimulant laxatives are a diverse group of agents that have been classified according to their ability to stimulate propulsive motility. Bisacodyl, at a dosage of 5 mg q 24 h PO, is the most effective stimulant laxative in the cat. It may be given individually or in combination with fiber supplementation for long-term management of constipation. It is suggested that daily administration of bisacodyl be avoided because injury to myenteric neurons can occur with chronic usage. We do not routinely use stimulant laxatives in our clinic.
Prokinetic Drugs

1.  Cisapride enhances colonic propulsive motility through activation of colonic smooth muscle 5-HT receptors in a number of animal species. In vitro studies have shown that cisapride stimulates feline colonic smooth muscle contraction. The commercial formulation of cisapride (Prepulsid) was withdrawn from human markets several years ago, but the drug is readily available through compounding pharmacies. Laboratory studies have shown that classic histamine H-2 receptor antagonists ranitidine and nizatidine, stimulate feline colonic smooth muscle contraction in vitro but it is not yet clear how effective these drugs are in vivo. While cisapride was unavailable, we used ranitidine 15mg bid with apparent success.

2.  Tegaserod (Zelnorm®-Novartis Corporation) is a potent partial non-benzamide agonist at 5-HT4 receptors and a weak agonist at 5-HT1D receptors. Tegaserod has prokinetic effects in the canine colon although the motor mechanisms responsible are unclear. Its safety and efficacy in cats is unknown and the author has no personal experience using this drug in cats so caution should be exercised.

In vitro studies suggest that tegaserod does not delay cardiac repolarization or prolong the QT interval of the electrocardiogram as had been occasionally reported with cisapride.
Clinical efficacy has been demonstrated in human constipation-predominant irritable bowel syndrome (IBS) and the drug was approved for the treatment of this disorder in the U.S. in 2002.Gastric and intestinal effects of tegaserod have not been reported in the dog, so this drug may not prove as useful as cisapride in stimulating proximal gastrointestinal motility.

3.  Prucalopride (Janssen Pharmaceutical) is a potent partial benzamide agonist at 5-HT4 receptors, but is without effect on other 5-HT receptors or cholinesterase enzyme activity. Unlike tegaserod, prucalopride also appears to stimulate gastric emptying in dogs.
In lidamidine-induced delayed gastric emptying in dogs, prucalopride (0.01-0.16 mg/kg) dose-dependently accelerates gastric emptying of dextrose solutions.

Prucalopride dose-dependently (0.02-1.25 mg/kg) stimulates giant migrating contractions (GMC's) and defecation in the dog. The prucalopride effect is observed most prominently in the first hour after administration, suggesting that the prucalopride effect is a direct effect on the colon rather than on total gut transit time. Prucalopride also enhances defecation frequency in healthy cats. Cats treated with prucalopride at a dose of 0.64 mg/kg experience increased defecation within the first hour of administration. Fecal consistency is not altered by prucalopride at this dosage. Prucalopride has not yet been approved in the U.S.

4.  Misoprostol is a prostaglandin E1 analogue that reduces the incidence of nonsteroidal anti-inflammatory drug-induced gastric injury. The main side effects of misoprostol therapy are abdominal discomfort, cramping, and diarrhea. Dog studies suggest that prostaglandins may initiate a giant migrating complex pattern and increase colonic propulsive activity. Given its limited toxicity, misoprostol may be useful in dogs and cats with severe refractory constipation. Misoprostol was recently shown to stimulate feline colonic smooth muscle contraction in vitro.

Surgical Therapy
Most surgical therapies for constipation in the cat are related to the management of idiopathic megacolon, although causes such as pelvic outlet obstruction, complications of neutering surgery, perineal herniation, and malunion pelvic fractures may also require surgical intervention. Cats with megacolon which are refractory to medical therapy or unable to be medicated, should have their colon surgically removed via a total or sub-total colectomy. A sub-total colectomy involves removal of the majority of the colon except for the ileocolic valve and the proximal colon followed by anastomosing the proximal colon to the distal colon or rectum. A total colectomy involves removal of the entire colon, the ileocolic valve, cecum and distal ileum followed by ileorectal anastomosis.

Sub-total colectomy is an easier and faster surgery to perform than a total colectomy and stools return to normal faster after surgery with sub-total (1-2 weeks) compared with a total (4-10 weeks). A study of 25 cats treated with either total or sub-total colectomy failed to show a difference in long-term recurrence rates so currently, the recommended best surgical therapy for megacolon is sub-total colectomy with the ileocolic junction preserved. In my experience, recurrent constipation is more likely to recur with this technique. Hence I perform a total colectomy in young cats, Burmese cats and cats with idiopathic dilated megacolon to ensure optimal long-term results.

Surgical correction of pelvic canal stenosis may be performed by pelvic osteotomy or pubic symphyseal distraction and may be sufficient alone for some cats suffering from pelvic canal stenosis. Pelvic osteotomy without colectomy has been recommended for cats with pelvic fracture malunion and megacolon of less than 6 months duration. A colectomy can be performed if osteotomy is not curative. Pelvic osteotomies are technically very difficult making some surgeons prefer colectomy.

We often perform a somewhat elective colectomy very early with little or no medical management. Using a 3 year old Burmese cat with faecal impaction from megacolon as an example, if treated medically would need iv fluids, an anaesthetic, water pic enema and hospitalisation which on average may cost $500. Then it is discharged with increased dietary fibre and medicated twice daily with 5mg cisapride bid ($1.30/capsule) and 2mls duphalac. The cost of cisapride alone is $950/year. So if there are no relapses and no revisit consultations, in the first year a constipated cat may cost $1500 and need to be orally medicated twice daily and be forced to eat a high fibre.  If the same 3 year old Burmese cat with faecal impaction and megacolon was taken straight to colectomy, it would have iv fluids, an anaesthetic, colectomy, 2-3 nights in hospital and be discharged on antibiotics for 7 days and likely never need medicating again. The cost for a colectomy at our clinic is about $1500. Thus there are very clear reasons why colectomy is often the best initial therapy.

Procedure for sub-total colectomy

1. pre-anaesthetic iv fluids at 2 x maintenance
2. pre-medicate with methadone and midazolam, induce with alfaxan, intubate and maintain on isoflourane/oxygen
3. start intravenous fentanyl CRI which continues for 6-8hrs post-surgery
4. prophylactic antibiotics of either cephazalothin or amoxicillin/gentamycin iv
5. place transdermal fentanyl patch behind neck (Durogesic 25ug)
6. doppler blood pressure measured every 5-10 minutes
7. routine caudal laparotomy, colon exteriorised, caudal mesenteric vessels ligated with vascular staples or 2-0 silk, proximal and distal colon manipulated into anastomosis position and arcuate vessels appropriately ligated with 4-0 pds, doyen bowel clamps placed just cranial and caudal to where arcuate vessels were ligated, bowel resected with metzenbaums and disposed of
8. end-to-end anastomosis of proximal to distal colon using 4-0 pds and a simple continuous suture pattern
9. clamps are released and anastomosis tested for leakage
10. abdomen flushed with warm sterile saline 3 times and closed routinely with 3-0 pds
11. repeat prophylactic antibiotics on recovery and again in 6 hrs, change to clavulox the following morning
12. cats are offered food and encouraged to eat as soon as recovered from anaesthesia (approx 60 mins)
13. cats remain in hospital until eating, normothermic and no significant fluid loss in faeces. This is typically 2-3 days.
14. fentanyl patch removed and discharged on clavulox orally for 7 days and sutures out 10 days post surgery

Cats have a very favorable prognosis for recovery following colectomy, although mild to moderate diarrhea may persist for weeks to months postoperatively in some cases. In the majority of cases, the long-term outcome following subtotal colectomy is considered excellent.

Perineal Hernia

Perineal hernia is a rare disease in cats and is characterised by tenesmus and constipation. It occurs due to a weakness of the muscles and fascia of the pelvic diaphragm allowing deviation or dilation of the rectum into the perineum or less commonly, caudal displacement of abdominal organs. Unlike dogs, abdominal contents are rarely herniated. Instead there is lateral bulging of the rectum containing faecal balls and this bulging is also termed anal sacculation or pre-anal faecolith. This can cause marked and continual discomfort requiring manual extraction and is a common reason for presentation.

A presumptive diagnosis is often made based purely on the owner’s history. The bulk of the faeces is usually in the litter tray but small faecal balls are also found dropped all around the house. Owners may wrongly interpret this as intentional inappropriate toileting. When defaecating, cats with perineal hernias can either have trouble getting started (as the first piece of faeces fails to exit through the anal sphincter and doubles back on itself) or finished (the last piece of faeces fails to exit and forms a pre-anal faecolith). These cause significant pain and cats often run around the house screaming and biting at their back end until it either pops out or is extracted by a veterinarian (usually under sedation or GA). A definitive diagnosis is made by demonstrating marked lateral rectal deviation in the area between anal sphincter and ischium. A diagnosis of perineal hernia can be easily made by digital rectal examination but is often overlooked due to a lack of recognition of the disease entity.
We have found siamese cats to be over represented and male cats more commonly affected. This breed association has not previously been recognised in the literature. Primary or idiopathic perineal herina occurrs in younger cats (mean=2.8yrs, range=1.5-4yrs) while perineal hernia associated with megacolon occurrs in older cats (mean=11.9yrs, range=8.5-15.3yrs). Perineal hernia can be associated with previous tail amputation or perineal urethrostomy although we have never seen a case of the latter. We have seen perineal hernia with caudal displacement of the urinary bladder in two Burmese cats also suffering cutaneous asthenia.

Medical management of perineal hernia is similar to that used for constipation (see below) and unfortunately is usually unsuccessful. Surgical management is regarded as the treatment of choice and may involve colectomy, internal obturator transposition herniorrhaphy, or both. Primary or idiopathic perineal hernia is best corrected using an internal obturator transposition herniorrhaphy. 

A colectomy should be performed first in cats with perineal hernia associated with megacolon as this may resolve clinical signs for many years. If a herniorrhapy is performed first in these cases, they are unable to pass faeces at all and require a colectomy for relieve. Careful assessment of cats with perineal hernias associated with megacolon is essential so the correct surgical procedure be performed. It has been a steep learning curve and even when armed with this knowledge, the author admits to performing many surgeries in the wrong order.