KIDNEY INJURY

The most common indication of kidney injury on assessment in the emergency department is the presence of gross or microhematuria. Dipstick and urinalysis methods of determining the presence of hematuria have proved to be satisfactory for screening, with greater than 97.5% sensitivity and specificity,¹ and should initiate the process of staging by radiographic evaluation. The presence of hematuria does not correlate with the degree of injury, however.

There is ongoing evidence that adult patients sustaining blunt trauma can be selectively imaged on the basis of presence of hematuria and hemodynamic status. Based on the large experience of McAninch and colleagues,¹ as well as others, in working with patients with blunt trauma with microscopic hematuria and no evidence of shock, imaging is not required to assess urologic injury. Mee and colleagues² studied 1007 patients with blunt trauma and found that patients with gross hematuria or microscopic hematuria (>5 red blood cells per high-powered field [RBCs/hpf]) and shock (SBP <90 mm Hg) are most likely to have significant injuries, and radiographic imaging is mandatory. The selection criteria to determine need for imaging is based on blood pressure findings recorded at any time during the patient’s initial evaluation, including paramedic assessment in the field.

These criteria do not apply to pediatric patients. The criteria for imaging in the pediatric population are different than for adults. This stems from the fact that there is not a well-established definition of shock in prepubertal children. Certainly, children with gross hematuria, regardless of hemodynamic stability, should be imaged. This will also allow for the detection of any congenital anomalies, such as ureteropelvic junction obstruction. Recent literature has been supportive of sparing imaging in stable children with only microhematuria. Brown et al.³ revealed only a 4.6% significant renal injury rate in children with blunt trauma and microhematuria, defined as more than 3 rbc/hpf. Using more than 50 rbc/hpf as a criterion for imaging children with blunt trauma, Morey et al.⁴ found only 1 in 147 patients with significant renal injury.

In addition, all patients with penetrating injuries and any degree of hematuria should be imaged or explored. At most major trauma centers, hemodynamically stable patients will undergo computed tomography (CT) scan of the abdomen and pelvis to rule out any abdominal injury. This incidentally allows visualization of the kidneys. The sensitivity and cost-effectiveness of the CT scan as a single imaging modality have for the most part replaced the routine use of IVP to exclude collecting system injury. Appropriate grading of renal injuries is crucial in determining management and expectant outcomes. The rate of urologic complications increases with increasing renal trauma grade. This can range from 0% complications with grade I injuries to 100% with grade V renal injuries. Performing follow-up CT scans in patients with grade III or higher injuries will detect 90% of delayed urologic complications.⁵

Blunt traumatic injuries as a result of automobile accidents, falls, or blows to the abdomen may cause significant damage to the kidney and represent at least 80% of all renal injuries seen in most urban hospitals. In rural hospitals, 90%–95% of kidney injuries are caused by blunt trauma. Bed rest and observation are successful in managing 95% of patients with blunt traumatic injuries. Santorelli et al.⁶ showed that solid organ injuries secondary to blunt trauma, including renal injury, can be managed nonoperatively in hemodynamically stable patients with approximately a 90% success rate. Urologic complications occur in about 11% of patients managed expectantly.⁷ These include delayed bleeding,⁸ post renal hypertension, arteriovenous fistula, and urinary extravasation.⁹ Similar findings are found in the pediatric population. Margenthaler et al.¹⁰ reported an 87% success rate with nonoperative management in pediatric blunt renal injury, including 26% of patients with high-grade injury. Only two of the seven children requiring surgery had failed conservative management. No patient with follow-up developed hypertension. The patient should be maintained on strict bed rest until gross hematuria has cleared, at which point ambulation should be allowed to a limited extent. The patient must be carefully monitored for hematocrit and evidence of retroperitoneal bleeding. If gross hematuria returns after ambulation is allowed, reassessment of the injury is indicated.

Penetrating injuries account for approximately 20% of renal injuries in urban settings. These injuries generally occur from gunshot wounds and stab wounds. All penetrating renal injuries require operative exploration, unless the staging process indicates that the renal injury is minor. Indications for renal exploration in patients with renal injury are excessive and persistent retroperitoneal bleeding, pulsatile retroperitoneal hematoma, urinary extravasation in the presence of other significant injuries, significant amount of nonviable tissue, and vascular injury. Clinical judgment must be exercised in applying these indications for operation. The risk of late complications, such as hematuria, arteriovenous fistula, scarring or renal hypertension, after conservative management, has been cited as a reason for prompt exploration. Velmahoes et al.¹¹ evaluated the role of selective exploration of renal gunshot wounds and assessed the clinical and radiographic criteria of such a policy. Patients who underwent nephrectomy were more often hemodynamically unstable, had more severe kidney injuries, and had a higher Injury Severity Score (ISS) than patients who had renal reconstruction. In cases of renal exploration, proximal vascular control was practiced only in the presence of central injuries, provided that the patient was hemodynamically stable. This policy resulted in 38% of patients avoiding unnecessary renal exploration.

Grade IV renal injuries can be particularly challenging. Associated injuries are common, occurring in 80% of patients. These associated injuries are often the reason for laparotomy, with subsequent repair of the renal injury. In a patient who is hemodynamically stable after blunt injury, extravasation of urine would not necessitate renal exploration when additional indications for operation are not present. In fact, less than 10% of blunt traumatic renal injuries require exploration. A large retroperitoneal hematoma incidentally discovered during laparotomy calls for intraoperative excretory urography, which will give information regarding the injured kidney as well as whether the contralateral kidney is normal. If excretory urography reveals an abnormality, renal exploration is indicated. Carefully preoperative staging of the injury with use of CT (excretory urography optional) helps to identify patients who are candidates for nonoperative management. In the San Francisco experience of 113 grade IV renal injuries, 78% were explored, with only a 9% nephrectomy rate. Specific renal complications were rare (4%), with an overall complication rate of 23% in those patients managed conservatively. This was similar to those managed operatively, with a 4% renal complication rate, and an overall rate of 30%.¹²

The operative approach for exposure of an injured kidney is a transabdominal incision, which allows the surgeon to expose the renal vessels and control them with vessel loops. One of the main causes for total nephrectomy after trauma is uncontrollable renal bleeding. A retroperitoneal incision is made over the aorta just above the level of the inferior mesenteric artery. Dissection superiorly over the aorta should allow location of the left renal vein and both renal arteries. Applying vascular clamps to the individual vessel should control any massive bleeding if necessary. This method of control has been shown to significantly reduce nephrectomy.¹³ Reflecting the colon off the hematoma should adequately expose the kidney, and the hematoma can be entered without fear of exsanguinating hemorrhage. Repair of the injured kidney is successful in 90% of cases. Total nephrectomy secondary to trauma is seldom necessary.

All nonviable tissue should be removed. Active bleeding at the margins indicates viability of the tissue. Hemostasis can be obtained by use of fine figure-of-8 chromic sutures on individual bleeding points. If the collecting system is violated, it should be closed with absorbable suture and made watertight. This can be confirmed by injecting methylene blue into the renal pelvis. The parenchymal defect should be covered with any preserved renal capsule, omental pedicle graft, or fibrin sealant. Partial nephrectomy may be appropriate in some cases. The presence of concomitant bowel injury should not change management of the renal injury.

Patients who undergo operative repair should be allowed to ambulate as soon as gross hematuria has cleared. The mean hospital stay for patients who have had renal injuries repaired surgically is less than 7 days. Patients who have gross hematuria and are managed nonoperatively should be hospitalized initially, and remain at bed rest until the gross hematuria is cleared. Once ambulation is allowed, the patient can be discharged if no further bleeding occurs, with restricted activity once at home. Patients with microscopic hematuria should be well staged and can be discharged home with restricted activity levels. Patients should be followed with periodic urinalysis and blood pressure determinations for several months. Follow-up excretory urography or CT scan will provide anatomic information on the healed renal unit, and/or diuretic renal scans will provide functional data. These should be done 2–3 months after injury.