Evaluation of the Acute Abdomen

Evidenced-based Testing Strategies

Thomas W. Lukens MD PhD FACEPMetroHealth Medical CenterCleveland, OHAssociate Professor of Emergency Medicine Case Western Reserve University School of Medicine

Greetings from Cleveland, OH

The Acute AbdomenPain less than one weekSudden onsetSurgery neededPeritonitisSevere pain

Any condition that needs rapid decision making and/or operative intervention

ABDOMINAL PAINEmergency Department:

Undifferentiated patientsA collection of symptoms and signs are gathered to predict the conditional probability of a diagnosis Traditional teaching is the reverse

Few evidenced based studies in undifferentiated conditions

ABDOMINAL PAINEmergency Department Series

Discharge Diagnosis 1972 1977 1993 Undifferentiated (UDAP) 41% 39% 25% GI causes 13% 19% 18% Gastroenteritis 7% 12% 5% Surgical GI 10% 18% 8% UTI 11% -- 11% Pelvic Disorder 12% -- 12% Admission rate 27% 42% 18%

Ref: Brewer, Am J Surg, 1976; Jazon, AC Scand, 1982; Powers, AJEM, 1995

Acute AbdomenTestingHistory and Physical ExaminationSerial examinationsLaboratory WBCUrinalysis/pregnancy testPlain RadiographyCTUltrasoundColor flow DopplerNuclear MedicineMRI

Acute AbdomenHistory & Physical ExaminationIntraabdominal3 Gs-- GI, GU, GYN VascularExtraabdominalCardiovascularMetabolicAbdominal wallNeurogenic

Acute AbdomenHistory & Physical ExaminationAccuracy is lacking at timesAtypical presentationsMissed findingsAppendicitis 50-87% sensitivefalse positive = negative laporatomyfalse negative = perforationAcute Abdominal Aneurysm (AAA)< 50% sensitiveDiverticulitis - 34% sensitivityLR+ = 2-3, LR- = 0.4Bergeron, Am J Surg, 1999;177:460, Chervu Surg 1995;117:454,Korner, World J Surg 1997;21:313

Likelihood ratiosA way to measure performanceLR of positive test: sensitivity of test/1-specificityLR of negative test: 1-sensitivity/specificityLR+ - the likelihood of the test being positive in a patient with the disorder, compared to the likelihood of a positive test in someone without the disorderLR- the likelihood of a negative test in someone with the disorder compared to a negative test in one without the disorder

Likelihood ratiosCalculating probabilitiesLR times the (estimated) pretest probability = post test odds of the diseaseAppendicitis- all ED abdominal pain patients Estimated pretest probability ~ 4%LR+ of the test ~4, LR- is 0.3If all received the test for appendicitis (4 X 1:25) = ~16% chance that a positive test is actually detecting appendicitis inthe patient. If negative test (0.3 x 1:25), there is still a 1.2% probability of patient having appendicitis (lowered pre-testprobability by about a third)

Not a particularly accurate test in undifferentiatedpatients

Acute AbdomenLaboratory testingWBC - limited utilityWBC > 11,000 LR+ = ~ 2 < 11,000 LR- = ~ 0.5 WBC alone doesnt distinguish patients with surgical disease from non-specific abdominal painUrinalysis AAA - misleading Hematuria in up to 30% with AAAMost common misdiagnosis in AAA- kidney stoneRenal colic - hematuria LR+ ~ 2 , LR- = 0.3

Acute AbdomenLaboratory testingLiver function testsNormal in up to 40% with acute cholecystitisNot specific for any disease entityAmylase/LipaseOften normal in active pancreatitisSensitivity ~60%

Acute AbdomenImagingPlain films- provide little in addition to H & PFew specific findingsSensitive for free air 90-95%Bowel obstruction- 70% sensitive (LR+ ~3, LR- 0.6)Appendicitis LR+ = 1LR- = 0.4 CholecystitisLR+ = 2LR- = 0.5

Frager, AJR, 1994,162:37, Gruber, Ann Emerg Med, 1996,28:273, Izbicki, Eur J Surg,1992,158:227,

Acute AbdomenImaging-CTCT- test of choice in most abdominal conditions LR+ LR-Appendicitis Unenhanced focused 29 0.1 Contrast focused 49 0.02 Abdomen/pelvis (contrast) 18 0.1Small bowel obstruction 22 0.1 low grade 3 0.5Diverticulitis 98 0.02

Acute AbdomenImaging-CT LR+ LR-AAA 19 0.03Renal colic (Unenhanced) 32 0.02Mesenteric ischemia CT angiography 5 0.3MRA enhanced gadolinium 8 0.2Biliary tract (stones) 28 0.2Common duct 8 0.3MR cholangiography 32 0.05

Acute AbdomenImaging-Ultrasound LR+ LR-Biliary tract (stones)30 0.1Cholecystitis29 0.1Common duct obst11 0.1Common duct stone 8 0.2HIDA scan 10-20 0.05AAA (nonleaking) 9 0.1Diverticulitis18 0.2Appendicitis11 0.5Ectopic TVS (BHGC>1500)80 0.2

Appendicitis - CTLiberal use of CT has lowered negativeappendectomy rate to 5.4% Peck, Am J Surg 2000;180:133CT for appendicitis has lowered hospital stay by 1/2 Raptopoulos, Radiology 2003;226:521

Appendicitis - most common operation butaccuracy hasnt changed significantly inpast decade (data through 1999) Flum, JAMA 2001;286:1748

Appendicitis - CTUse in equivocal cases- not high or lowprobability patients- not routinely Ujiki, J Surg Research 2002;105:119Call for a surgeon not a CT- more costeffective and accurate to have the surgeonsee the patient first Morris. Am J Surg, 2002;183:547

Acute Abdominal Pain -ImagingHistory & examination and simple lab tests have about a 50-60 % accuracy (initial to final diagnosis) Technological advances in imaging are responsible for our increased accuracy in diagnosing patients with acute abdominal painHelical CTUltrasound by EM physicians 24/7MRI

Good judgment comes from experience, and a lot of that comes from bad judgment. Will Rodgers