Role of Renal Sonography in the IntensiveCare Unit

Shih-Wen Huang, MD, Chien-Te Lee, MD, Chi-Hsiu Chen, MD, Chung-Hua Chuang, MD,Jin-Bor Chen, MD

Division of Nephrology, Department of Internal Medicine, Chang-Gung Memorial Hospital, 123, Ta-Pei Road,Niao-Sung Shang, Kaohsiung Hsien 833, Taiwan

Received 28 October 2003; accepted 20 August 2004

ABSTRACT: Purpose. This study was conducted toevaluate the role of portable renal sonography in theintensive care unit (ICU).Methods. We conducted a retrospective study of

402 ICU patients who underwent renal sonography.We recorded demographic data, underlying disease,type of ICU, renal function test results, etiology ofrenal failure, need for dialysis, and outcome forpatients with acute renal failure (ARF). The indicationsfor and results of sonography were analyzed.Results. The most common indication for a renal

sonographic examination was ARF (320/402, 79.6%).Hydronephrosis was found in 5 patients with ARF.Chronic renal failure was confirmed by sonographyin 40% of the patients with an indeterminate cause ofrenal failure. In 33% of cases of complicated urinarytract infections, sonography revealed abnormalities.Renal sonography was also useful for follow-upassessment of patients treated with percutaneousnephrostomy and patients with a history of renaltumor, hydronephrosis, adrenal tumor, hematuria ofunknown cause, or fever of unknown origin.Conclusions. Since renal disease is common in

the ICU, renal sonography is a convenient anduseful diagnostic tool in this setting. ª 2005 WileyPeriodicals, Inc. J Clin Ultrasound 33:72–75, 2005;Published online in Wiley InterScience (www.inter-science.wiley.com). DOI: 10.1002/jcu.20087

Keywords: renal ultrasonography; renal failure, acute;intensive care unit; renal failure, chronic

In general, sonography can aid in the evaluation ofurologic system anatomy and be used to differ-

entiate the causes of renal failure, detect neoplasms,diagnose nephrolithiasis, and detect complicated

infections. Although CT andMRI both serve a simi-lar function, sonography is more advantageous forintensive care unit (ICU) patients not only becauseof thismethodology’s cost, safety, and simplicity butalso—and particularly—because it can be per-formed at the bedside. This is of particular benefitto patients with acute renal failure (ARF), whichaffects 5–7% of all hospital patients and 16–23% ofpatients in the ICU.1–3 The incidence of hydro-nephrosis diagnosed by sonography is low in ARFamong ICU patients.4 However, sonography canoften provide evidence of chronic renal failurethat may be useful in clinical management5 anddemonstrate incidental lesions of the kidneys andretroperitoneum.

Our study aims to clarify the benefits of renalsonography in the ICU.

PATIENTS AND METHODS

We retrospectively reviewed the charts andrecords from renal sonography of patients whowere admitted to 1 of 4 ICUs in our hospitalbetween March 1999 and August 2002. The ICUsincluded were the medical intensive care unit(MICU), the coronary care unit (CCU), the neuro-logical intensive care unit (NICU), and the surgi-cal intensive care unit (SICU). The examinationswere performed by nephrologists at the bedsideusing a high-resolution ProSound SSD-5500 scan-ner (Aloka, Tokyo, Japan) with a 3.5-MHz curved-array probe. The machine was transported to theICU whenever renal sonography was indicated.The nephrologists released their reports on theday of the procedure.

A number of variables were recorded, includ-ing patient age and sex, the type of ICU, the

Correspondence to: C.-T. Lee

� 2005 Wiley Periodicals, Inc.

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underlying diagnosis that required ICU admis-sion, and any complications. The indications forthe sonography, the organs examined (adrenalgland, kidney, bladder, and prostate), and sono-graphic findings were recorded. For patients withARF, the etiology of the ARF, the renal functiontest results on the day of sonography (blood ureanitrogen and creatinine), the need for dialysis,and patient outcome were also recorded.

All data are presented as mean ± standarddeviation (SD). The Student’s t-test was used tocompare ARF patients, who were divided into dial-ysis and nondialysis groups. Analysis of the mor-tality rates of different groups was performedwith the Fisher’s exact test. A p-value less than0.05 was deemed statistically significant.

RESULTS

A total of 402 patients (men, 50.2%) were enrolledin this study. The patient age range was 19–97years, with the mean age 68 ± 13 years. Therewere 227 patients from the MICU, 39 from theCCU, 39 from the NICU, and 97 from the SICU.Most patients (389/402, 96.8%) had respiratoryfailure and assisted ventilation. The indicationsfor renal sonography were ARF (320 patients;79.6%); urinary tract infection (30 patients;7.5%); the need to differentiate between acuteand chronic renal failure (20 patients; 5.0%); his-tory of chronic renal failure (17 patients; 4.2%);and gross hematuria (6 patients; 1.5%). Rarerindications (<1%) included dysfunction of a per-cutaneous nephrostomy (PCN; 3 patients), sus-pected adrenal tumor (2 patients), renal tumor(2 patients), previous hydronephrosis (1 patient),and fever of unknown origin (1 patient).

In patients with ARF, the most common sono-graphic findings were parenchymal renal disease(293/320, 91.6%) as indicated by increased corticalechogenicity. Moderate to severe hydronephrosiswas found in 5 patients: 1 with a sonographicallydetected retroperitoneal hematoma (renal func-tion recovered completely after hematoma resolu-tion), 2 with underlying advanced cervical cancer(renal function improved after PCN), and 2 withunknown unilateral etiology and no further exam-ination because of their unstable hemodynamicstatus (both finally died). Patients with ARF hadan age range of 21–97 years, with a mean 68 ± 14years. The total mortality rate was 70.9% (227/320). The ARF group included 230 nonsurgicalICU patients (172 MICU patients, 34 CCUpatients, and 24 NICU patients), and 90 SICUpatients. The mortality rate was 73.5% in thenonsurgical ICU group (169/230) and 64.4% in

the SICU group (58/90). The difference in mortal-ity rate was not statistically significant. Hemodi-alysis was initiated in 185 patients (185/320, 57.8%),16 of whom had end-stage renal disease and hadbeen on chronic maintenance hemodialysis beforeentering the ICU. The dialysis group had moresevere renal failure than the nondialysis group(data not shown). The mortality rate in the dialysisgroup was significantly higher than that of the non-dialysis group (76.8% versus 62.9%, p < 0.01).

Among the 20 patients examined sonograph-ically to distinguish between acute and chronicrenal failure, 8 were found to have bilateral smallkidneys. In the group of 17 patients with a historyof chronic renal failure, sonography confirmed thediagnosis in 11 (64.7%). Of 30 patients examinedbecause of a complicated urinary tract infection,abnormalities were found in 10 (33%), includinga renal calculus in 4 patients, hydronephrosis in4 patients, pelviectasis in 1 patient, and a renaldiverticulum and prostate mass in 1 patient.

To search for the etiology and location of unex-plained gross hematuria, both the kidney and thebladder were examined in 6 patients. Nephro-lithiasis was found in 1 patient. Diffuse thickenedbladder mucosa consistent with chronic cystitis wasfound in another patient. Three patients wereexamined because of poor PCN function. One exam-ination revealed a residual renal abscess and theother 2 found residual hydronephrosis. Sono-graphic follow-up of previous CT-proven renaltumors was performed in 2 patients. Two patients(1 with unexplained elevated cortisol and the otherwith refractory hypertension) underwent sonogra-phy to localize an adrenal lesion. Unilateral adrenalmasses were found in both patients. Elevatedserum adrenocorticotropic hormone was noted inthe patient with a high cortisol level, and abdominalCT revealed bilateral adrenal hyperplasia. A finaldiagnosis was not made in the other patient. Thefollow-up examination of the patient with pre-viously diagnosed hydronephrosis found bilateralsmall kidneys and multiple renal calculi. In thepatient with fever of unknown origin, renal sono-graphy revealed parenchymal renal disease, renalcalculus, and a renal cyst.

DISCUSSION

Sonography is noninvasive, has low cost, andwhen compared to intravenous pyelography, CT,or MRI is more convenient for ICU patients. Thissimple procedure can also provide much informa-tion about renal and bladder disease, as well asretroperitoneal abnormalities.

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In our study, ARF was the most common indi-cation for renal sonography in the ICU. It is gen-erally accepted that the value of using sonographyfor the evaluation of ARF is mainly to excludeobstructive uropathy, which occurs in 5–25% ofall patients.6,7 Since the etiologies of ARF in ICUand non-ICU patients were quite different, theapplications of renal sonography in the ICU maybe different. In the study of Liano et al,8 only 2 of253 ICU patients (0.8%) had ARF and obstructiveuropathy, while 14.7% of 495 non-ICU patientswere given that diagnosis. In the present study,we identified 5 patients (5/320, 1.6%) with moder-ate to severe hydronephrosis by sonography. Thisfinding is similar to that of Keyserling et al,4 whoconcluded that implementation of routine renalsonography in such patients adds little to the diag-nostic workup. Though the prevalence of obstruc-tive uropathy is low in ICU patients, we believethat sonography is needed because of the criticalimportance of knowing that hydronephrosis is notpresent and to aviod the risk of missing a diagnosisof hydronephrosis.9 Sonography is also useful indetecting pre-existing renal disease.

Kidney size is an important factor in clinicalassessment, particularly to differentiate acutefrom chronic renal failure in patients who presentfor the first time with poor renal function. Thekidney size is usually normal in prerenal ARF andmay even increase in primary acute renal disease,such as acute tubular necrosis or acute glomeru-lonephritis.6 Conversely, a small kidney with athin and echogenic cortex usually indicates irre-versible damage, negating the need for furtherdiagnostic workup.7,10 Among the patients withARF in this study, we identified 6 with smallkidneys, another 8 patients with small kidneyswere found among the 20 undergoing sonographyto differentiate between ARF and chronic renalfailure (for an accuracy rate of 40%). The detec-tion of chronic renal failure is important in clin-ical care and management.

Urinary tract infection is one of the most com-mon hospital-acquired infections and also is themost frequent nosocomial infection in theICU.11,12 Most patients in ICUs are catheterizedor may experience occasional urinary retention,both of which frequently contribute to urinarytract infection. The progression to a complicatedinfection often occurs in patients with predispos-ing factors, such as obstruction, diabetes, a com-promised immune system, or chronic debilitatingdisease. Imaging studies assist in the evaluation ofthe extent of disease and therefore play a majorrole in directing theraphy.13 Renal sonographycan help diagnosis of complicated urinary tract

infections, including renal and perirenal abscesses,pyonephrosis, emphysematous pyelitis, and emphy-sematous pyelonephritis, particularly in ICUpatients.14 In our series, sonography detected uri-nary tract abnormalities in these patients.

Hematuria is a common finding in both outpa-tients and ICU patients, and it has a variety ofetiologies.15 Further studies may be unnecessarybecause hematuria often subsides after correctionof the underlying disease, such as infection ordisseminated intravascular coagulopathy. How-ever, if the hematuria persists or recurs, thensonography is the first-line imaging modality forinvestigating the urinary tract.16 PCN is oftenperformed for the treatment of renal abscess orhydronephrosis. Renal sonography is a useful toolfor evaluating the PCN site, as well as for imagingany residual lesion.17

In our study, sonography was used to diagnoseadrenal tumors in 2 patients. Although CT has ahigher diagnostic accuracy than sonography,18,19

adrenal sonography is a logical tool for the initialevaluation of ICU patients.

In conclusion, renal sonography is an importantdiagnostic tool in the ICU. Since renal complica-tions frequently develop in ICU patients, thisexamination can be useful in the diagnosis of kid-ney and urinary tract diseases, as well as for ima-ging retroperitoneal lesions in both adrenal andperirenal regions.

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