Anesthesia for Transurethral Resection of the Prostate

TRANSURETHRAL RESECTION OF THE PROSTATE

Preoperative Considerations

Benign prostatic hyperplasia (BPH) frequently leads to bladder outlet obstruction in men older than 60 years. Although increasingly being treated medically, some men require surgical intervention. Transurethral resection of the prostate (TURP) is the most common surgical procedure performed for bladder outlet obstruction due to BPH, and indica-tions for TURP in this setting include obstructive uropathy, bladder calculi, and recurrent episodes of urinary retention, urinary tract infections, and hematuria. Patients with adenocarcinoma of the prostate may also benefit from TURP to relieve symptomatic urinary obstruction.

TURP requires regional or general anesthe-sia, and patients should be evaluated for coexistent major organ dysfunction. Despite advanced age (over half of TURP patients are older than 70 years) and prevalence of significant comorbidity in over two thirds of TURP patients, perioperative mortality and medical morbidity (most frequently myocardial infarction, pulmonary edema, and kidney failure) for this procedure are both less than 1%.

The most common surgical complications of TURP are clot retention, failure to void, uncontrolled hematuria requiring surgical revision, urinary tract infection, and chronic hematuria, although other, more rare, complications may include: TURP syn-drome, bladder perforation, sepsis, hypothermia, and disseminated intravascular coagulation (DIC). A blood type and screen  is ade-quate for most patients, although crossmatched blood should be available for anemic patients and for patients with large glands in which extensive resection is contemplated. Prostatic bleeding can be difficult to control through the cystoscope.

Intraoperative Considerations

TURP is performed by passing a loop through a special cystoscope (resectoscope). Using continuous irrigation and direct visualization, prostatic tissue is resected by applying a cutting current to the loop. Because of the characteristics of the prostate and the large amounts of irrigation fluid often used, TURP

can be associated with a number of serious compli-cations ( Table 31–1).

A. TURP Syndrome

Transurethral prostatic resection often opens the extensive network of venous sinuses in the prostate, potentially allowing systemic absorption of the irrigating fluid. The absorption of large amounts of fluid (2 L or more) results in a constellation of symptoms and signs commonly referred to as the TURP syndrome (Table 31–2). This syndrome pres-ents intraoperatively or postoperatively as headache, restlessness, confusion, cyanosis, dyspnea, arrhyth-mias, hypotension, or seizures, and it can be rapidly

fatal. The manifestations are primarily those of circulatory fluid overload, water intoxication,and, occasionally, toxicity from the solute in the irri-gating fluid. The incidence of TURP syndrome is less than 1%.Electrolyte solutions cannot be used for irriga-tion during TURP because they disperse the electro-cautery current. Water provides excellent visibility because its hypotonicity lyses red blood cells, but significant water absorption can readily result in acute water intoxication. Water irrigation is gener-ally restricted to transurethral resection of bladder tumors only. For TURP, slightly hypotonic nonelec-trolyte irrigating solutions such as glycine 1.5% (230 mOsm/L) or a mixture of sorbitol 2.7% and mannitol 0.54% (195 mOsm/L) are most commonly used. Less commonly used solutions include sorbitol 3.3%, mannitol 3%, dextrose 2.5–4%, and urea 1%.

Because all these fluids are still hypotonic, signifi-cant absorption of water can nevertheless occur. Solute absorption can also occur because the irriga-tion fluid is under pressure, and high irrigation pres-sures (bottle height) increase fluid absorption.

Absorption of TURP irrigation fluid is depen-dent on the duration of the resection and thepressure of the irrigation fluid. Most resections last 45–60 min, and, on average, 20 mL/min of the irri-gating fluid is absorbed. Pulmonary congestion or florid pulmonary edema can readily result from the absorption of large amounts of irrigation fluid, particularly in patients with limited cardiac reserve. The hypotonicity of these fluids also results in acute hyponatremia and hypoosmolality, which can lead to serious neurological manifestations. Symptoms of hyponatremia usually do not develop until the serum sodium concentration decreases below 120 mEq/L. Marked hypotonicity in plasma ([Na ⁺] <100 mEq/L) may also result in acute intravascular hemolysis.

Toxicity may also arise from absorption of the solutes in these fluids. Marked hyperglycinemia has been reported with glycine solutions and may con-tribute to circulatory depression and central nervous system toxicity. Plasma glycine concentrations in excess of 1000 mg/L have been recorded (normal is 13–17 mg/L). Glycine is known to be an inhibitory neurotransmitter in the central nervous system and has also been implicated in rare instances of tran-sient blindness following TURP. Hyperammonemia, presumably from the degradation of glycine, has also been documented in a few patients with marked central nervous system toxicity following TURP. Blood ammonia levels in some patients exceeded 500 µmol/L (normal is 5–50 µmol/L). The use of large amounts of sorbitol or dextrose irrigating solutions can lead to hyperglycemia, which can be marked in diabetic patients. Absorption of manni-tol solutions causes intravascular volume expansion and exacerbates fluid overload.

Treatment of TURP syndrome depends on early recognition and should be based on the severity of the symptoms. The absorbed water must be elimi-nated, and hypoxemia and hypoperfusion treated. Most patients can be managed with fluid restric-tion and intravenous administration of furosemide. Symptomatic hyponatremia resulting in seizures or coma should be treated with hypertonic saline . Seizure activity can be terminated with small doses of midazolam (2–4 mg). Phenytoin, 10–20 mg/kg intravenously (no faster than 50 mg/ min), should also be considered to provide more sustained anticonvulsant activity. Endotracheal intu-bation may be considered to prevent aspiration until the patient’s mental status normalizes. The amount and rate of hypertonic saline solution (3% or 5%) needed to correct the hyponatremia to a safe level should be based on the patient’s serum sodium con-centration . The rate of hypertonic saline solution administration should be sufficiently slow as to not exacerbate circulatory fluid overload.

B. Hypothermia

Large volumes of irrigating fluids at room tempera-ture can be a major source of heat loss in patients. Irrigating solutions should be warmed to body temperature prior to use to prevent hypothermia. Postoperative shivering associated with hypother-mia may dislodge clots and promote postoperative bleeding, as well as add deleterious physiological stress to the patient with coexisting cardiopulmo-nary disease.

C. Bladder Perforation

The incidence of bladder perforation during TURP is less than 1%. Perforation may result from the resectoscope going through the bladder wall or from overdistention of the bladder with irrigation fluid. Most bladder perforations are extraperitoneal and are signaled by poor return of the irrigating fluid. Awake patients will typically complain of nausea, diaphoresis, and retropubic or lower abdominal pain. Large extraperitoneal and most intraperitoneal perforations are usually even more obvious, present-ing as sudden unexplained hypotension or hyperten-sion, and with generalized abdominal pain in awake patients. Regardless of the anesthetic technique employed, perforation should be suspected in set-tings of sudden hypotension or hypertension, par-ticularly with acute, vagally mediated bradycardia.

D. Coagulopathy

DIC has on rare occasion been reported following TURP and may result from the release of throm-boplastins from prostate tissue into the circulation during the procedure. Up to 6% of patients may have evidence of subclinical DIC. A dilutional thrombo-cytopenia can also develop during surgery as part of the TURP syndrome from absorption of irriga-tion fluids. Rarely, patients with metastatic carci-noma of the prostate develop a coagulopathy from primary fibrinolysis due to secretion of a fibrino-lytic enzyme. The diagnosis of coagulopathy may be suspected from diffuse, uncontrollable bleeding but must be confirmed by laboratory tests. Primary fibrinolysis should be treated with ε-aminocaproic acid (Amicar), 5 g followed by 1 g/h intravenously. Treatment of DIC in this setting may require hepa-rin in addition to replacement of clotting factors and platelets, and consultation with a hematologist should be considered.

E. Septicemia

The prostate is often colonized with bacteria and may harbor chronic infection. Extensive surgical resec-tion with the opening of venous sinuses can allow entry of organisms into the bloodstream. Bacteremia following transurethral surgery is common and can lead to septicemia or septic shock. Prophylactic anti-biotic therapy (most commonly gentamicin, levo-floxacin, or cefazolin) prior to TURP may decrease the likelihood of bacteremic and septic episodes.

F. Choice of Anesthesia

Either spinal or epidural anesthesia with a T10 sen-sory level, or general anesthesia, provides excellentanesthesia and good operating conditions for TURP. When compared with general anesthesia, regional anesthesia may reduce the incidenceof postoperative venous thrombosis. It is also less likely to mask symptoms and signs of TURP syn-drome or bladder perforation. Clinical studies have failed to show any differences in blood loss, postop-erative cognitive function, and mortality between regional and general anesthesia. The possibility of vertebral metastasis must be considered in patients with carcinoma, particularly those with back pain, as metastatic disease involving the lumbar spine is a relative contraindication to spinal or epidural anes-thesia. Acute hyponatremia from TURP syndrome may delay or prevent emergence from general anesthesia.

G. Monitoring

Evaluation of mental status in the awake or moder-ately sedated patient is the best monitor for detec-tion of early signs of TURP syndrome and bladder perforation. Tachycardia or decrease in arterial oxy-gen saturation may be an early sign of fluid over-load. Perioperative ischemic electrocardiographic changes have been reported in up to 18% of patients. Temperature monitoring is standard of care for gen-eral anesthesia, and it should also be used in cases of lengthy resections under spinal or epidural anes-thesia to detect hypothermia. Blood loss is particu-larly difficult to assess during TURP because of the use of irrigating solutions, so it is necessary to rely on clinical signs of hypovolemia . Blood loss averages approximately 3–5 mL/min of resection (usually 200–300 mL total) but is rarely life-threatening. Transient, postoperative decreases in hematocrit may simply reflect hemodilution from absorption of irrigation fluid. Less than 2% of patients require intraoperative blood transfusion; factors associated with need for transfusion include procedure duration longer than 90 min and resec-tion of more than 45 g of prostate tissue.