Treatment of Urinary Emergencies
Jennifer J. Devey, DVM, Diplomate ACVECC
Saanichton, British Columbia
The two most common medical emergencies presenting to the private practitioner involving the urinary tract are renal failure and urethral obstruction. These two diseases are lifethreatening.
Renal Failure
Causes
Renal failure can be caused by ischemia, infection, trauma, toxins and drugs. A certain percentage of renal failure patients never have the underlying etiology discovered. Ischemia can be caused by hypovolemia (hemorrhagic shock, systemic inflammatory response syndrome, sepsis), excessive vasodilation (anesthesia) or trauma. Drugs that can cause renal failure include antibiotics (aminoglycosides, cephalosporins), nonsteroidal antiinflammatory drugs, and chemotherapeutic agents.
Diagnosis
Initial tests should include a blood pressure and laboratory tests including a hematocrit, complete blood cell count, chemistry profile, blood gas, and urinalysis. Additional tests may include a urine culture, blood titres, coagulation panel, abdominal radiographs, thoracic radiographs, abdominal ultrasound, contrast studies of the urinary tract, and biopsies. Knowledge of the urine specific gravity prior to fluid therapy is very important. In general a lack of ability to concentrate the urine (less than 1.045 in cats and less than 1.030 in dogs) indicates approximately 66% of the kidneys are non functional, and the presence of azotemia indicates that approximately 75% of the kidneys are not functioning.
Treatment
The primary goals of therapy are the following:
- Normalize renal blood flow
- Establish urine output
- Normalize electrolytes and acid-base status
- Diagnose the cause of the real failure and provide specific treatment
- Provide nutritional support
Restoring Normal Renal Blood Flow
Mean arterial blood pressure must be maintained at greater than 60-65 mm Hg to ensure adequate renal perfusion. This means that both systolic and diastolic pressure must be measured. Pulse palpation can be very inaccurate and should not be relied upon. Blood pressure can be measured indirectly using an oscillometric device or a Doppler ultrasonic flow detector. Diastolic pressures can be measured with reasonable accuracy in many patients with a Doppler; however, the ear must become attuned to the differences in flow sounds. If diastolic pressure is not being measured it is essential that systolic pressures be maintained as close to normal as possible. Systolic pressures less than 110 mm Hg can be associated with mean arterial pressures less than 60 mm Hg.
Blood pressure can be normalized in most patients using fluid therapy. A combination of crystalloids and colloids should be used. In order to ensure blood volume (preload) is optimized, a jugular catheter should be placed so that central venous pressure can be measured. If a jugular catheter is not an option then the jugular veins should be clipped and carefully assessed for distention and filling. This is quite subjective but can be used to help guide fluid therapy. Flat jugular veins or CVP less than 1-2 cm H20 are consistent with hypovolemia. Distended jugular veins or CVP greater than 8-10 cm H20 indicate fluid overload.
If the patient has cardiac dysfunction then a positive inotrope such as dobutamine may be indicated. Pressors should be avoided unless they are specifically indicated to counteract excessive vasodilation since the blood pressure may improve at the expense of perfusion to splanchnic organs (including the kidneys).
Fluid Therapy
Fluid therapy must be closely tailored to the animals needs and should be based on cardiac status, volume status (venous), dehydration, sodium concentration, potassium concentration, albumin, and type of renal failure (polyuric, oliguric or anuric).
If the patient is hypovolemic from loss of blood then colloids will be required. Attempting to restore significant hypovolemia using crystalloids only will lead to tissue edema since approximately 80% of the volume of crystalloid infused will be in the interstitial space within an hour. Hypovolemic or dehydrated patients with hypoalbuminemia (less than 20 g/l) also will require colloid administration to prevent the development of tissue edema. Synthetic colloids such as hydroxyethyl starches often will be required in these patients. Care should be taken to ensure the patient does not become volume overloaded.Patients with significant hypoalbuminemia (less than 20 g/L), those with coagulopathies, or those patients predisposed to coagulopathies may need fresh frozen plasma. The hemoglobin should be maintained at approximately 10 g/dL using blood products in the case of acute anemia.
Dehydration should be restored using crystalloids. Generally buffered electrolyte solutions are indicated. Fluids containing potassium must be avoided in the hyperkalemic patient until urine output is restored and the potassium level is starting to decrease. Patients who are hypernatremic may require fluid with low sodium concentration or even no sodium. Care should be taken to ensure the sodium in hypernatremic patients is not lowered faster that 0.5 mEq/L per hour to avoid central nervous system disorders. Patients who developed the dehydration rapidly should be rehydrated over 4-8 hours. Those with chronic dehydration should be hydrated over 12-24 hours. Hourly maintenance requirements should be added to this amount along with ongoing losses. Ongoing losses in patients with polyuria can be significant and urine output in these patients must be measured to ensure fluid requirements are not underestimated. Anuric patients may not even tolerate the amount of fluids required to restore dehydration until urine output is restored. If diuresis is the end goal then fluid will need to be adjusted to ensure urine output is greater than 2 ml/kg/hr.
The amount of fluids required to restore hydration always should be calculated since lack of calculation may lead to significant underestimation of the patient’s needs. For instance a polyuric 5 kg cat that is estimated to be 10% dehydrated has a fluid deficit of 500 ml. Maintenance requirements are approximately 10 ml/hr. Based on an assumption of 2-4 ml/kg/hr if the patient is polyuric adds an additional 10-20 ml of fluid required per hour. Assuming the patient’s hydration is to be restored over 12 hours this cat has a fluid requirement of 60-70 ml/hr to meet the desired goals.
Restoring Urine Output
Urine output in hypovolemic or hypotensive patients hopefully will be restored once perfusion to the kidneys is improved. If the patient is not responding several options are available. Mannitol is a hyperosmotic agent that causes an osmotic diuresis, which flushes the tubules. It also has benefits as a free radical scavenger. The dose can be repeated if it is effective and it can be followed with a constant rate infusion at 1 mg/kg/min until it is no longer effective. It should be used with extreme caution, (and preferably not used) in patients that are hypervolemic since volume overload will result if diuresis does not result. Dextrose at 5% -20% concentrations can be used as an osmotic diuretic if mannitol is not available. The dextrose will be metabolized ultimately making this perhaps a safer choice than mannitol.
Furosemide is a loop diuretic that is most effective when given as a constant rate infusion. A bolus dose of 1-2 mg/kg can be given intravenously followed by a constant rate infusion of 1 mg/kg/hr. If there is no response after 4 hours it is less likely to be effective.
Dopamine at dopaminergic doses (0.5-3 mcg/kg/min) is designed to impact dopaminergic receptors in the kidneys and improve renal perfusion and thus renal function. There is no clear evidence this occurs. The cat lacks the appropriate dopaminergic receptors in the kidneys and one study showed no improvement in urine output, sodium excretion or glomerular filtration in cats given dopamine.
Acid-Base Abnormalities
Patients in renal failure may have significant acid-base abnormalities. Acidemia related to perfusion abnormalities should correct once perfusion is restored. Sodium bicarbonate administration in the acute renal failure patient should be reserved for patients with a pH less than 7.2 with a concurrent bicarbonate level less than 11 mEq/L since side effects include hyperosmolality, overshoot alkalosis, paradoxical cerebrospinal fluid acidosis, and left shift of the oxyhemoglobin dissociation curve.
Dogs and cats with chronic renal failure often lose large amounts of bicarbonate in their urine due to kidney dysfunction. This is more common in the cat than the dog. These cats must be supplemented with bicarbonate or their values will never return to normal. In the author’s experience these cats often require much higher doses of bicarbonate than is typically recommended. In addition the anorexia and nausea seen in cats often improves once the acidemia is improved. These cats often will require oral supplementation to maintain normal acid-base status. Bicarbonate is typically supplemented at 0.3 x kg body weight x deficit (18- measured bicarbonate level) with ¼ of this dose given over 1 hour and the remainder over the next 12 hours. If blood gas assessment is readily available this dose can be given more quickly. If blood gases are not available but total carbon dioxide levels are the bicarbonate can be estimated by the total carbon dioxide minus 1. Bicarbonate supplementation should not be provided if measured levels are not available since the side effects can seriously outweigh the benefits.
Hyperkalemia
Patients in anuric renal failure will develop hyperkalemia. Hyperkalemia should be treated if it is lifethreatening as determined by evidence of significant electrocardiographic abnormalities in combination with clinical signs. Electrocardiographic abnormalities include bradycardia, peaked T waves, shortened QT interval, and a wide QRS complex. Eventually the P wave will disappear and when severe hyperkalemia will cause a sine wave appearance to the electrocardiogram. There are three treatment options available for hyperkalemia. Calcium gluconate at 0.5-1.0 ml/kg intravenously will counteract the effects of the hyperkalemia immediately but the effects will be only last 15-20 minutes. Sodium bicarbonate at 1 mEq/kg will drive the potassium intracellularly and provide a rapid, but short lived effect. Insulin given at 0.5 u/kgwill drive the potassium intracellularly and will have a more prolonged effect. Dextrose can be given at 1-2 g per unit of insulin followed by a 2.5% dextrose infusion for several hours. It is very likely that dextrose alone, without insulin administration, is sufficient in most patients since administration of dextrose should trigger an immediate secretion of endogenous insulin. Ultimately unless the animal is able to urinate the hyperkalemia will persist. If anuria persists dialysis is indicated.
Antiemetics
Vomiting can be a substantial problem in patients with renal failure. If large volumes of fluid are being vomited a nasogastric tube should be placed for gastric decompression. This tube can then be used for delivering microenteral nutrition. Uremia triggers vomiting centrally and central acting antiemetics are likely to be the most effective at controlling vomiting. Constant rate infusions of metoclopramide (1-2 mg/kg/d) can be used but are less likely to be effective than other medications due to their minimal central effect.
Gastric Protectants
Uremia can be associated with gastric erosions and ulcerations. Administration of H-2 blockers or omeprazole and sucralfate may be indicated and are definitely indicated if there is evidence of hematemesis. Raising the pH of the gastric fluids may lead to bacterial overgrowth and a higher risk for pneumonia secondary to aspiration so antacids should not be used prophylactically in the author’s opinion. Enteral nutrition has been shown to be as effective as, if not more effective than, antacids at preventing gastric ulceration.
Other Treatments
Nephrotoxic drugs should be discontinued and specific treatment aimed at the cause of the renal failure should be instituted as soon as possible. Hyperphosphatemia may resolve with fluid therapy; however if the hyperphosphatemia persists then phosphate binders should be administered orally once the patient is eating.
Patients with chronic renal failure may be hypertensive. Amlodipine, a calcium channel blocker, has been found to be the most effective in treating hypertension caused by renal disease. Blood pressures greater than 200 mm Hg systolic can lead to retinal detachment and should be aggressively managed. This may require the administration of intravenous medications.
Oral ulcers are not uncommon in patients with renal failure. Oral rinses using 0.005% chlorhexidine can help prevent infection. Rinses with topical anesthetic agents have also been used anecdotally by the author to try and minimize the pain associated with the ulcers.
Diltiazem has recently been recommended as an agent to help with renal failure associated with ischemia. It appears to decrease the intracellular calcium levels following ischemia thus decreasing the production of reactive oxygen species. It also prevents apoptosis. The dose recommended is 0.3-0.5 mg/kg over 10 minutes followed by 1-5 mcg/kg/min for 48-96 hours or as long as it takes to decrease the serum creatinine concentration to normal. The dose should be decreased if bradycardia or hypotension develop.
Angiotensin-converting enzyme (ACE) inhibitors (enalopril) are recommended as treatment for protein-losing glomerulonephropathy. The drug appears to attenuate glomerular hypertrophy and preserve glomerular function. In addition it may help control hypertension. Angiotensin-converting enzyme inhibitors should be used with caution in the acute stages of renal failure since the drug can decrease glomerular filtration rate and worsen azotemia. It can also cause hypotension and should be avoided in hypotensive patents.
Antibiotics should be administered based on culture and sensitivity results; however, occasionally, antibiotics may need to be administered without confirmation. Prophylactic antibiotics should be avoided in patients with indwelling urinary catheters since these patients are predisposed to infection and the use of antibiotics will lead to microbial resistance.
Analgesics should be provide to all patients showing signs of pain. Nonsteroidal antiinflammatory agents should be avoided. Opioids should be given intravenously to effect. Constant rate infusions may be required.
Nutrition
Enteral nutrition should be provided whenever possible. If patients are nauseous microenteral nutrition (0.1-0.25 ml/kg/hr of an electrolyte solution with 5% dextrose) may be all that the patient will tolerate. To avoid human and food aversion from developing a nasoesophageal (cat and dog) or nasogastric tube (dog) may need to be placed to allow for effective delivery of the nutrition. As soon as the animal will tolerate clear liquids, more complex liquid diets, followed by gruel diets and then canned diets can be given. High dietary protein levels currently are recommended in renal failure since glomerular filtration rate is improved and increased excretion of toxins have been noted. Parenteral nutrition may need to be provided if the patient is not able to meet an adequate nutritional level.
Close Monitoring
The value of repeat physical examinations cannot be underestimated. Vital signs may need to be recoded as frequently as every hour in less stable patients to every 4-6 hours in more stable patients.
Blood pressure and heart rate should be maintained in as normal a range as possible. If initial measurements were not normal then heart rate and blood pressure should be measured on an hourly basis until the values have normalized. At this time measurement should be continued every 4-6 hours.
Hypothermia can develop in patients due to opioid administration, poor temperature regulation, and infusion of large volumes of room temperature fluids. Cats may have low rectal temperatures related to poor perfusion. Providing these cats with supplemental heat may not be indicated since core temperatures may be normal.
Fluid overload is always a concern in oliguric renal failure patients. Signs of fluid overload include chemosis, serous nasal or ocular discharge, distended jugular veins, elevated central venous pressure, increased respiratory rate and effort, pulmonary crackles, and tissue edema. Central venous pressure ideally should be monitored in order to avoid fluid overload. The patient can be weighed twice daily to help track fluid gains.
An indwelling urinary catheter should be placed if oliguria is a concern, and urine output should be quantitated on an hourly basis initially. Once the animal is improving urine output can be measured every 2-4 hours. If a urinary catheter is not placed then bedding should be weighed to estimate urine output (1 ml = 1 g). Fluids should be adjusted based on output. Normal urine output is considered to be 1-2 ml/kg/hr although this number may be high in cats. Oliguria is defined as urine output less than 0.25-0.30 ml/kg/hr. Animals with indwelling urinary catheters are predisposed to urinary tract infections. Ensuring the catheter is connected to a sterile closed collection system, daily cleaning of the vulva or prepuce with a surgical scrub, placement of broad spectrum antibiotic ointment around the urethral orifice, minimizing the disconnection of the closed collection system, and use of exam gloves by personnel when handling the urinary system will minimize this risk.
Laboratory tests should be monitored every 4 to 24 hours depending on the tests and the status of the patient. Hematocrit, total solids, albumin (in patients predisposed to hypoalbuminemia), blood gases, electrolytes, serum urea nitrogen, creatinine, phosphorus, urine dipsticks and urine sediments should be serially monitored. Other tests may be indicated based on the cause of the animal’s renal disease and overall health status.
Urethral Obstruction
Causes
Feline urethral obstruction can be caused by crystalline plugs or calculi whereas canine urethral obstructions are usually caused by calculi. Almost all feline urethral obstructions can be relieved using retropulsion and flushing; however, many canine obstructions will require surgery to relieve the obstruction. Trauma and neoplasia can also cause obstructions; these patients will generally require surgical management of their problem.
Diagnosis
Diagnosis of urethral obstruction is usually based on a physical examination findings of a large bladder than cannot be expressed. Cats, if diagnosed early, may have a small bladder, but one that is very turgid when palpated. The tip of the urethra of the cat may be discoloured and occasionally the obstruction can be seen near the tip.
Laboratory diagnostic tests include a hematocrit and total solids, electrolytes, glucose, blood gas and renal parameters. Since these patients will need to be heavily sedated or anesthetized a baseline blood pressure is indicated along with an electrocardiogram. An electrocardiogram is strongly advised if the patient is hyperkalemic. Cystocentesis of a very distended bladder should be performed with extreme caution since this can lead to a uroabomen. A urinalysis can be collected following relief of the obstruction.