Urinary obstruction in our canine patients is not as common as their feline counterparts, but is still considered a life-threatening emergency and should be treated with urgency.
Urinary obstruction can occur when there is a partial or total blockage of the urethra to the bladder. When this happens, electrolytes, especially potassium, can become imbalanced and will cause multiple problems, which can include death. There are multiple causes of urinary obstruction in dogs, including urinary calculi, neoplasia, polyps, strictures, or even congenital abnormalities. There are also other causes of urinary retention, including prolonged distention of the urinary bladder, reflex dyssynergia, and some side effects of mediations.
Presentation
Owners often bring their pet in during early signs of urethral obstruction. These signs can include increased or decreased urination, reduced volume, pressure or flow, lethargy, discomfort, or lack of appetite.
When the pet is in later stages of urinary obstruction, they can come in with lethargy, inappetence, pain, dyspnea, bradycardia, obtunded, or even deceased.
A history is also important in diagnosing these patients. Canine patients may be wanting to go outside more often. Multiple urinary tract infections may also have been diagnosed in the past. Owners may notice no to little urine flow, hematuria, or prolonged straining to urinate or discomfort.
Diagnosis
Upon physical exam, these patients may have a distended abdomen with a turgid bladder. Their heart rate may be low depending on how long they have been obstructed. Physical exam should include a rectal exam to palpate for obvious urethroliths or masses. The penis may be inflamed or have blood or bruising from self-trauma. Depending on the severity of the blockage, the patient may have hypotension, bradycardia, hypothermia, and tachypnea.
Radiographs should be performed to see if there are any obvious masses or stones causing a blockage. Some stones are not radiopaque, and so should not be ruled out solely on radiographs.
An abdominal-focused assessment with sonography for trauma (AFAST) and a thoracic-focused assessment with sonography for trauma (TFAST), should be performed to assess heart function and any abdominal abnormalities.
Bloodwork should be performed to assess electrolyte status. An elevated potassium level can cause many issues such as bradycardia and death.
Treatment
Stabilization of these patients is very important. An intravenous catheter should be placed. Blood can be taken from that catheter to minimize trauma to that patient (Do not flush your catheter if you decide to do so). Once the blood is taken, a PCV/TP, glucose and “stat” bloodwork should be done. The “stat” bloodwork should include pH and electrolytes. An ECG should be performed to assess heart function.
Let’s talk electrolytes
Potassium plays a big role in how the heart functions. The sodium-potassium pump is the mechanism that helps with ion transport in the heart. If you have too much potassium, the heart will not beat appropriately or at all.
On the electrocardiogram (ECG), there may be “high-tented” T-waves, absent P-waves, prolonged P-R interval, and bradycardia. These abnormalities usually do not show up until their potassium levels are greater than 6 mmol/L, but can occur with lower potassium levels depending on the patient. Acidosis and azotemia can also be found with the initial stat bloodwork. Hyperkalemia should be corrected first.
Treating hyperkalemia
Treating hyperkalemia is the most important thing to be instituted before the patient is to undergo sedation or anesthesia for an unblocking procedure. There are multiple ways to treat hyperkalemia.
- IV crystalloid fluids. Minor hyperkalemia treatment can be treated with intravenous crystalloid fluids. There is some controversy whether 0.9 percent NaCl or other electrolyte balance isotonic fluid is better for these patients. Isotonic fluids will help with intravascular volume and dilute the potassium in the serum and support heart pumping function. It is critical to assess the heart before giving these patients fluids to avoid fluid overload, especially if a heart condition is undetected. Signs of fluid overload are “crackles” on lung auscultation, nasal discharge, coughing, and dyspnea.
- Insulin and dextrose. The most common way to treat hyperkalemia is with regular insulin and dextrose. The dose of regular insulin is 0.5units/kg. Insulin shifts potassium into the cells, which in turn decreases serum potassium. A 0.5-1 ml/kg bolus dose of 50 percent dextrose solution diluted 1:1 with 0.9 percent NaCl should be given after the regular insulin. After the bolus, the patient should be placed on a 1.25-2.5 percent dextrose CRI for four to six hours. This is because the regular insulin will still work in the body for multiple hours after administration.
- Calcium gluconate, albuterol, and sodium bicarbonate are also some treatments for hyperkalemia. Calcium gluconate can be administered at 10-20 mg/kg IV slowly over 15-20 minutes. An ECG must be applied while calcium gluconate is given to avoid bradycardia and arrhythmias if given too quickly. Calcium gluconate does not have an effect on potassium levels, but it will protect the heart by increasing the threshold for the cell’s membrane potential. This results in a normal difference between the resting membrane potential and the action potential. After obstruction, the potassium levels will decrease.
Albuterol can also be a treatment for patients that are hyperkalemic. It can drive potassium into the cells, which in turn decreases serum potassium.
Cystocentesis can also be used in special situations. While a controversial topic as it can possibly cause bladder rupture, it offers some benefits. Cystocentesis can relieve some pressure in the abdomen.
Sodium bicarbonate is usually the last resort when it comes to treating hyperkalemia, which can cause hypocalcemia, hypernatremia, alkalosis, and seizures. It should also be given to patients that are acidemic and hyperkalemic.
Fixing the issue
Once fluids and the hyperkalemia are addressed, the obstruction must be resolved. There are multiple ways to do this, which include catheterization, retrograde urohydropropulsion (if uroliths are present), or urethral stents.
Urinary catheterization is the easiest way to relieve a urinary obstruction, but it may be difficult if a urethrolith or mass is in the way. Urethroliths should not be pushed back to the urinary bladder using the catheter. When the urinary catheter is removed, the patient could re-obstruct with the urethrolith. Once the urinary catheter is placed, the cause of the obstruction must be fixed. Urohydropropulson, cystotomy, or laser lithotripsy can remove the stones. Inflammation of the urethra is a common side effect after removing the catheter and should be monitored.
When a mass is causing the obstruction, a stent may have to be placed. Urethral strictures may require a urethrostomy procedure.
A complication of any of these procedures is a uroabdomen. Urethral tears and slow bladder leaks from cystocentesis can be causes.
Post-obstruction
After the patient is unobstructed, they must stay on fluids for at least one to five days. Post-obstructive diuresis is a process where the body response is to remove the excess fluid and solutes from the body. This can result in dehydration if the patient is not on fluids.
Bloodwork should be done to assess electrolytes at least twice a day. Sometimes these patients need to be on supplemental potassium because the kidneys and fluids dilute the serum potassium that the body needs.
At-home care
Discharge instructions to the owner are dependent upon the procedure that was done. It is always a good thing to remind yourself that they may have never experienced this before with their pet. So, it is always good to explain everything and have everything that was spoken of written down so they can use it for future reference. It is important to remind the owner of symptoms of re- obstruction so they can come into the clinic before their pet becomes obstructed again.
Tami Lind, BS, RVT, VTS (ECC), is the current ICU and ER supervisor at Purdue University Veterinary Teaching Hospital. Lind has been at the university for 10 years. She went to veterinary technology school at Purdue and graduated in 2010 with her bachelor’s degree in veterinary technology and has never left. She started as a veterinary technician in the ICU and has been the supervisor at Purdue since 2012.