Chapter 36
Anesthetic Considerations for Post-Renal Urinary Tract Disease
Oh, for a steady stream!
Ann B. Weil
Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Purdue University, USA
- Q. What are the most important considerations for anesthetizing a patient with a post-renal urinary tract problem?
- A. Some examples of post-renal urinary tract disease requiring general anesthesia include:
- blocked cats
- dogs with urethral obstruction
- dogs and cats with ruptured bladders.
These patients will present with a wide range of morbidity and clinical problems associated with their disease process. The patient may be a healthy young cat with an acute urethral obstruction, or it may be nearly moribund from an untreated complete obstruction. One must take into consideration the overall health of the patient first, with the knowledge that post-renal urinary problems often present as emergency cases. These conditions can produce significant electrolyte changes, metabolic disturbances, and hypovolemia that must be addressed when making an anesthetic plan [1]. These patients are also very painful and their analgesic needs must be addressed. It may not be possible to completely normalize the patient prior to general anesthesia, presenting a challenge to the anesthetist.
- blocked cats
- Q. What abnormalities might be present?
- A. Animals with a urethral obstruction or a ruptured bladder may be hypovolemic, azotemic, acidotic, hyperglycemic, and have a variety of electrolyte abnormalities. If a complete obstruction is present, they may be unable to pass any urine, making fluid therapy a challenge as you don’t want to rupture the bladder. In order to relieve the obstruction, however, this patient will require sedation and/or general anesthesia with its attendant cardiovascular depression, so adequate circulating fluid volume is important. The patient should be stabilized with cautious intravenous fluid therapy so that it can undergo general anesthesia to relieve the obstruction as soon as possible. There are a variety of “recipes” available for expeditious fluid therapy, including mixtures of crystalloids and colloids. The emphasis should be on quick stabilization of the patient so the obstruction can be relieved. Azotemia will only resolve with IV fluid administration and resolution of the obstruction so that the intratubular pressure in the kidney is reduced and GFR can be improved [2]. Fluid administration should at least address the volume deficit of the patient and be continued during the procedure at a rate of 3–5 ml/kg/h with the obstruction relieved as quickly as possible to avoid bladder rupture.
- Q. What electrolyte abnormalities should I anticipate?
- A. These patients may suffer from hyperkalemia, hyperphosphatemia, hyponatremia, hypermagnesemia, and hypocalcemia [1]. Of these disturbances, hyperkalemia (K+ >5.5 mEq/l) is the most immediate life-threatening concern and should be corrected prior to general anesthesia if at all possible. Other electrolyte abnormalities should be corrected with ongoing fluid therapy throughout the peri- and post-operative period.
- Q. How do you handle a hyperkalemic patient?
- A. Treatment of hyperkalemia can depend on the level of the disturbance. Conditions such as ruptured bladders have a high likelihood of hyperkalemia. Patients suffering urethral obstruction may or may not be hyperkalemic, depending on the duration of the obstruction and whether it is partial or complete, but serum potassium concentration should be measured in every patient with urethral obstruction. Moderate to significant hyperkalemia (K+ >6 mEq/l) should be addressed prior to general anesthesia, due to the significant myocardial depression imposed by both general anesthetics and hyperkalemia. An ECG monitor should be used to evaluate for unstable electrical activity, but it is important to remember that the classic arrhythmias may not be seen due to the interactions of the other electrolyte abnormalities [3]. Control of CO2 with the aid of mechanical ventilation (reducing acidosis) can also be helpful in managing hyperkalemic patients, in addition to medical therapy. This is because H+ and K+ are exchanged across cell membranes in order to normalize pH. If serum [H+] is high, as in respiratory acidosis 2o to hypoventilation, the physiologic response is to move K+ out of cells and into the vasculature in exchange for H+
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
