Small Bowel Obstruction (Sawyer 4/15/2020)

Big thanks to Dr. Russ Sawyer for an excellent presentation this week on Small Bowel Obstruction (SBO) during Grand Rounds. We are all getting better and better at this Zoom platform!

Cliff notes version of what primary care providers should know about SBO:

1. Lactate is highly sensitive for SBO (but not that specific)
2. The money is in the CT scan (CT is BOTH sensitive and specific)
• with IV+oral contrast is are ideal, but IV contrast only is probably okay
3. Many SBO patients don't need surgery (you actually can let the sun set on an SBO)
• In fact, all patients NOT acutely ill (w/fever, leukocytosis, tachycardia) deserve a trial of non-operative management
• SBO patients with a BM in last 24 hours likely will not need surgery
4. Gastrograffin challenge is an effective way to differentiate patients who may need surgery vs. those who definitely don't. 
• 90cc PO or via NGT x 8 hours in early/minimal symptom SBO (see below for details)

And now for the more robust version of my notes for those of you more in depth readers. . .

SBO is super common, >$1.5 billion per year in the US go to management of SBO

Classification of SBO

• functional (i.e. adynamic ileus)
• mechanical (acute vs. chronic, partial vs. complete) 
• adhesions (account for 80% of SBO)
• hernia (internal, groin, ventral)
• malignancy
• inflammatory disorders (IBD, ischemic bowel)

Pathophysiology of SBO

obstruction prevents people from passing food and air --> interluminal fermentation causes gas to accumulate--> bowel edema--> diminished absorption and decreased motility--> can gt transudative losses into the abdominal cavity (free fluid in the peritoneum)

Stats reminder from Dr. Sawyer, which is always helpful to review

Sensitivity: "positivity in disease" (how much you trust a positive result to mean the patient actually has that condition)

Specificity: "negativity in health" (how much you trust a negative result to mean that the patient actually does NOT have that condition).

(We are talking a fair bit about sensitivity and specificity this day with COVID testing. This is an excellent reminder!)

Clinical History

• Acute abdominal pain (92%), usually precedes the onset of nausea/emesis
• Nausea 
• Emesis (82%-- more common than nausea)
• Abdominal distention

Risk factors

• Prior abdominal or pelvic surgery (even a simple appendicitis many years ago)
• Abdominal wall or groin hernia (even internal hernia)
• IBD
• Prior irradiation of the abdomen

Physical exam

• Dehydration (even if not apparent on labs), often notable on physical exam (dry mucous membrane, decreased skin turgor)
• Abdominal distention (most important finding on exam)
• Surgical scars
• Tympanic abdomen
• High pitched bowel sounds or more commonly a rush of bowel sounds

Labs

• Leukocytosis is common
• Electrolyte abnormalities (hyperNa, hypoK)
• Lactate is helpful. It's extremely SENSITIVE 90-100%, Specificity 40-80%. This means that a positive lactate gives high likelihood of surgical SBO, but a normal lactate does not rule out an SBO

Imaging: "Everything in SBO comes down to imaging"

• Plain film (KUB): not very specific or sensitive (equivocal 20-30% of the time, misleading in 10-20%), consider skipping it and going straight to the CT
• CT with IV contrast (+oral contrast if possible-- oral contrast commits patient to 4 hours in the ER, often get get enough info with just IV contrast), 
• >90% sensitive, 95% specific. So you can pretty much trust the CT. 
• If the radiologist sees it, it's there. If the radiologist doesn't see it, it's not there.
• CT can usually tell grade, severity and even etiology (adhesion vs. malignancy)
• However, intra-operative location is only correct 60-70% of the time
• MRI (if CT contraindicated, e.g. pregnancy)

Surgical vs. Non-surgical Management:

Patients with SBO should be evaluated for surgical intervention WHEN/IF they are acutely ill with fever, leukocytosis, tachycardia, metabolic acidosis, ongoing pain.

HOWEVER, without the above findings (or with only a few of them) MOST patients should undergo initial non-operative management (this includes both partial AND complete SBO). How so?

Management of early/minimal symptom SBO (with Gastrograffin)
For patients who meet these criteria, Dr. Sawyer and team are working on a protocol to be started soon

If patient meets the following criteria:

1) SBO on CT, 2) distention w/o emesis (x8 hours, or at least minimal emesis, only need NGT if emesis), 3) BM in the last 24 hours, 4) minimal leukocytosis (<14), lactate (<4), THEN you can give them a gastrograffin challenge

How do I do a gastrograffin challenge for minimal symptom SBO?

1. Give patient 90cc of full strength gastrograffin (via NGT or PO);  order from pharmacy (not radiology)
2. Wait 6-8 hours for BM (up to 24 hours). If they have plenty of BMs, they passed! You don't even need to do KUB
3. If no stool in 8 hours, get KUB to look for gastrograffin. 
4. If it has made it to the colon, can pull NGT, start clear liquids and probably let them go home. 
5. If no contrast in cecum, repeat KUB next day. If in the colon, start clear liquids. If not, call surgery.

How does gastrograffin work? For this purpose, it is actually being used therapeutically (rather than diagnostically). Gastrograffin pulls fluid into the lumen and "flushes things through", decreasing the bowel wall edema and improving the SBO.

Who NOT to give gastrograffin challenge to? 

• infection (e.g. appendicitis, diverticulitis)
• cancer
• incarcerated hernia
• pregnancy
• abdominal surgery in last 6 weeks

Prevention of SBO:

There is not great data on any intervention or product done intraoperatively to prevent adhesions and prevent SBO. However, if a patient has had a first episode of SBO or recurrent SBO, Dr. Sawyer recommends:

• low fat diet (maintains intestinal transit time)
• clear liquids are tolerated well (4-6 days): patients with SBO do not need to go home on a regular diet, once a patient feels true hunger, it's time to eat

Recurrence

• 20% recurrence after first episode
• after 3 episodes, their risk of recurrence is greater than 80%, need to consider surgery to lyse adhesions (depending on interval between the recurrences)