1.Differential Acute Abdomen: 
-Perforation: sudden onset, pain is constant, generalized, and very severe; classic peritonitis signs-- no movement, rebound, guarding. Examples: perforated gastric ulcer, perforated bowel.
-Obstruction: sudden onset, colicky pain, location and radiation indicates its source; patient is moving all over the table, can't get comfortable. If there is a bowel obstruction, there may also be distention, nausea, vomiting, anorexia. Examples: biliary colic, nephrolithiasis, small bowel obstruction
-Inflammation: gradual onset (gradual buildup over 6-12 hours), pain is constant, starts generalized and localizes. Peritoneal signs are found where the process is occurring, usually there are systemic signs of fever/leukocytosis except pancreatitis. Examples: appendicitis, pancreatitis
-Ischemia: gradual onset, severe pain out of proportion to exam, blood in the gut (the only process that combines acute abdomen with GI bleed). Get a lactate.
2. When facing an acute abdomen, first rule out everything that is not surgically managed, then go for an ex-lap to find and fix the problem.
-Lower-lobe pneumonia: CXR
-MI: EKG, enzymes
-PE: d-dimer
-Primary peritonitis (i.e. infection of extant ascites: treat with abx)
-Pancreatitis: amylase, lipase
-Nephrolithiasis: KUB or CT
-Diverticulitis: CT (manage with IVF, NPO, antibiotics, go the OR if things worsen)
3. Jaundice may be hemolytic, hepatic, or obstructive: 
-Hemolytic: bilirubin high but not very high (<10 not >30), indirect fraction elevated. Next step: labs to figure out the cause of the hemolysis (haptoglobin, autoimmune workup, pregnancy test, genetic workup for G6PD, LDH deficiency, thalassemia)
-Hepatic: both indirect and direct bilirubin elevated, AST/ALT often very high, alk phos not very high. Next step: labs to determine the cause of the hepatitis (viral serologies, labs for wilson's, tylenol levels)
-Obstructive: direct bilirubin elevated, alk phos through the roof. Next step: ultrasound to look for dilated bile ducts, examine gallbladder for stones and for thickness; stones in CBD are rarely seen. Thick gallbladder full of stones, think choledocolithiasis: do ERCP to remove stone, do sphincterotomy, schedule later cholecystectomy. Thin gallbladder: think cancer, do CT scan to look for cancer (head of pancreas, cholangio, duodenal ampulla). If the CT scan is positive for a mass, do a percutaneous biopsy; if it's negative, do an ERCP/EUS to get a closer look, as they can see smaller masses that would be missed on CT.
4. Cancers leading to obstructive jaundice:
-Head of Pancreas, poor prognosis even with whipple;
-Ampullary (obstructive jaundice + GI bleed), good cure rate with whipple
-Cholangiocarcinoma: very high alk phos, good prognosis if extra-hepatic or small
5. Range of cholestatic processes: 
-Acute Biliary Colic: stones that temporarily impact cystic duct, pain attacks that last 10-30 minutes. Triggered by fatty meals, accompanied by nausea and vomiting but no systemic signs. Treat with anticholinergics. Diagnosed by visualizing stones on u/s. Schedule elective cholescystectomy.
-Acute Cholecystitis: stones in the cystic duct that remain lodged until an inflammatory process develops in the gallbladder. Pain progresses to constant, modest systemic signs, modest peritoneal signs. No LFTs, u/s shows thickened gallbladder, pericholecystic fluid, stones in GB. Treat with bowel rest- NG, NPO, IV fluids, antibiotics. If things improve, schedule elective cholecystectomy. If they do not improve, do emergency cholecystectomy or percutaneous transhepatic cholecystostomy for those who cannot tolerate surgery.
-Acute ascending cholangitis: stones have reached CBD, are partially obstructing, and there is an ascending infection. Strong systemic signs of infection-- fevers to 105, chills, high leukocytosis, sepsis-like picture. Labs show elevated bilirubin and very elevated alk phos. Treat with IV antibiotics and emergent CBD decompression-- ERCP or percutaneous transhepatic cholangiogram (to put in a drain), schedule cholecystectomy soon.
6. Range of pancreatic processes:
-Acute edematous pancreatitis: occurs after heavy meal or bout of pancreatitis, constant pain radiating to back, with n/v, mild peritoneal signs over epigastric region, elevated serum amylase/lipase, elevated hematocrit. Treat with bowel rest, will resolve in ddays
-Acute hemorrhagic pancreatitis: begins with edematous form, but with a lower hematocrit, + other Ranson's criteria (elevated WBC, low Ca, elevated glucose, and then sepsis-like picture with pre-renal labs, metabolic acidosis, hypoxia). Finally multiple abscesses develop.
-Acute suppurative pancreatitis (pancreatic abscess): develop fever and leukocytosis ~10 days after the onset of symptoms, treat with percutaneous drainage.
-Pancreatic pseudocyst: occurs 5 weeks after acute pancreatic incident (pancreatitis, trauma). Collection of pancreatic fluid in cyst, compressive symptoms of stomach (early satiety, mass on deep palpation, vague discomfort), diagnose with CT. For cysts that are <6cm or <6 weeks old, can be observed. For larger or older cysts, manage with drainage (percutaneous, endoscopic) or surgical removal.
7. Causes of surgical hypertension: 
-Primary aldosteronism: either adrenal cortical adenoma or hyperplasia. Key to diagnosis: hypokalemia and hypertension in someone not on diuretics; mild hypernatremia, metabolic alkalosis. Hyperplasia will respond appropriately to position, adenoma will not. Renin is low in both.
-Pheochromocytoma: diagnose with 24 hour urine VMA or metanephrines, or octreotide/MBIG scan.
-Renal artery narrowing (fibromuscular dysplasia in the young, bad PAD in old): stent in young, may not be worth operative risk in old.
-Aortic coarctation: correct when there is a >50mmHg gradient, or signs of angina, syncope, CHF.
8. Post-op low urine output: in the face of good perfusion (ie. not shock) it's either inadequate volume or intrinsic renal failure. Test with 500mL or 1L fluid bolus-- if the UOP goes up, it was inadequate volume. If it doesn't change, it may be renal failure. Also can test with FeNa
9. Electrolytes:
-Hypernatremia: due to loss of free water. Replenish with D5 half NS if it was grandual onset, D5W if it was fast-onset.
-Hyponatremia: too much water. Either too much ADH in the context of normal volume, or loss of volume (diarrhea) without replenishing isotonically. In the former, fluid-restrict; in the latter, infuse isotonic fluid- LR, NS.
10. Lung lesions;
-Coin lesion on x-ray, in someone >50 has an 80% chance of being malignant. First step: compare with previous CXR. Next step: CT (chest + liver) & sputum cytology + maybe PET. After this you start getting into invasive tests, so you have to decide if the tumor is operable (mets to mediastinum/carina/liver/other lung) and if the person could survive treatment (FEV1, then determine % lung contribution with vent-perfusion scan, if FEV1 remaining <800, don't do surgery). Then, next step: percutaneous biopsy (peripheral) or bronchoscopic biopsy (central). Next step: thoracotomy/wedge resection.