01Approach to the Critical Patient/attcp42

Immediate priorities

›Airway and hemodynamic threats

›Acute gastric dilation with aspiration risk

›Massive bilious emesis

›Inability to protect airway

›If airway compromise present, proceed to definitive airway management

›Hemodynamic instability from dehydration

›SBP < 90 mmHg

›HR > 120 bpm with orthostatic changes

›Metabolic derangements from protracted vomiting

›Hypokalemia

›Hypochloremic metabolic alkalosis

›Bowel ischemia concern

›Severe constant pain with peritoneal signs

›Absent bowel sounds or bloody emesis

Monitoring and targets

›Resuscitation targets

›IV access with fluid resuscitation

›Normal saline or lactated Ringer bolus 20-30 mL/kg for hemodynamic instability

›Reassess after each bolus

›Electrolyte correction

›Potassium replacement IV when < 3.0 mmol/l

›Chloride and bicarbonate normalization targets

›Urine output target >= 0.5 mL/kg/hour

›Foley catheter if monitoring required

›Dehydration severity estimation

›Nasogastric decompression

›NGT insertion for significant gastric dilation

02History/hx68

Presenting symptoms

›Core gastrointestinal symptoms

›Postprandial epigastric pain

›Crampy or pressure-like

›Onset typically 30-60 minutes after eating

›Nausea and vomiting

›Bilious character typical

›Large volume emesis

›Early satiety

›Inability to complete meals

›Sense of epigastric fullness

›Positional features

›Supine position worsens symptoms

›Decreases aortomesenteric angle

›Increases duodenal compression

›Prone or left lateral decubitus provides relief

›Key diagnostic clue

›Knee-to-chest position also relieves symptoms

Weight and nutritional history

›Weight loss characterization

›Amount and timeline of weight loss

›Rapid loss most common precipitant

›Even modest losses in vulnerable patients

›Current BMI

›Median BMI approximately 17.8 kg/m2 in surgical series

›BMI < 15 kg/m2 as high-risk threshold

›Dietary intake and restrictions

›Eating disorder behaviors

03Physical Exam/exam54

Vitals and hemodynamic assessment

›Hemodynamic snapshot

›Heart rate

›Tachycardia from dehydration or pain

›Orthostatic change > 20 bpm

›Blood pressure

›Orthostatic hypotension

›SBP drop > 20 mmHg on standing

›BMI calculation

›Low BMI in most cases

›Nutritional status estimation

Abdominal examination

›Inspection and auscultation

›Abdominal distension

›Epigastric prominence

›Visible peristalsis in thin patients

›Bowel sounds

›High-pitched proximal to obstruction

›Absent sounds suggest ileus or ischemia

›Succussion splash

›Retained gastric contents

›Positive when heard with gentle rocking

›Palpation

›Epigastric tenderness

›Mild to moderate

›Worsened by palpation of upper abdomen

›Hayes maneuver

›Infraumbilical pressure applied cephalad and dorsally

04Differential Diagnosis/ddx45

Life threats

›Immediate dangers to exclude

›Mesenteric ischemia

›Constant pain out of proportion to exam

›ICD-10 K55.1

›Volvulus

›Coffee bean sign on plain film

›ICD-10 K56.2

›Perforation from gastric distension

›Free air on imaging

›ICD-10 K31.1

Mechanical obstruction mimics

›Other causes of duodenal obstruction

›Annular pancreas

›Congenital ring of pancreatic tissue

›Double bubble sign on plain film

›Duodenal web or atresia

›Intrinsic obstruction

›ICD-10 Q41.0

›Small bowel obstruction

›CT transition point not at SMA crossing

›ICD-10 K56.60

›Malrotation with Ladd bands

›Abnormal duodenojejunal junction on upper GI series

›ICD-10 Q43.3

Functional and inflammatory mimics

›Non-mechanical causes

›Gastroparesis

05Laboratory Tests/lt48

Core metabolic panel

›Electrolytes and renal function

›Comprehensive metabolic panel

›Hypokalemia from protracted vomiting

›Hypochloremia and metabolic alkalosis

›BUN and creatinine for dehydration severity

›Phosphate and magnesium

›Baseline before initiating nutritional rehabilitation

›Refeeding syndrome risk assessment

›Glucose

›Hypoglycemia in severely malnourished patients

›Starvation ketosis marker

Nutritional and inflammatory markers

›Nutritional status

›Albumin

›Low in chronic malnutrition

›Not reliable acute marker due to half life

›Prealbumin

›More sensitive nutritional marker

›Half life 2-3 days

›Hepatic transaminases

›Elevated in severe malnutrition

›Refeeding-related hepatotoxicity monitoring

›Inflammatory markers

›Complete blood count

›Leukocytosis when perforation or ischemia

›Anemia from malnutrition or chronic illness

›CRP or ESR

06Diagnostic Tests/dt60

Scoring Systems

›No validated disease-specific scoring system exists for SMA syndrome

›Diagnosis requires clinical and radiologic correlation

›Aortomesenteric angle < 25 degrees diagnostic threshold

›Aortomesenteric distance < 10 mm diagnostic threshold

›Malnutrition screening tools as adjuncts

›MUST (Malnutrition Universal Screening Tool)

›NRS-2002 for hospitalized patients

›Refeeding syndrome risk stratification

›NICE criteria for high-risk identification

›BMI < 16 kg/m2 or > 15% weight loss over 3-6 months

MRI

›MRI abdominal role

›MR angiography for vascular anatomy

›Aortomesenteric angle and distance measurement

›Radiation-free alternative to CT

›MRCP for biliary and pancreatic evaluation

›Annular pancreas differentiation

›Excludes other congenital anomalies

›Limitations

›Limited availability in acute setting

›Motion artifact from vomiting or poor cooperation

›Not first-line in ED setting

CT

›CT abdomen and pelvis with contrast

›Diagnostic findings

›Aortomesenteric angle measured between aorta and SMA on sagittal reconstruction

›Normal angle 38-65 degrees; SMA syndrome < 25 degrees

07Disposition/dispo39

Admission indications

›Inpatient admission criteria

›Complete or near-complete obstruction

›Inability to tolerate any oral intake

›Significant gastric dilation on imaging

›Hemodynamic compromise

›Orthostatic hypotension or tachycardia

›Electrolyte derangements requiring IV replacement

›Severe malnutrition

›BMI < 14-15 kg/m2

›Refeeding syndrome risk requiring monitoring

›Comorbid eating disorder with medical instability

›Medical admission for stabilization prior to psychiatric placement

ICU or step-down indications

›Higher acuity criteria

›Acute gastric perforation or ischemia

›Immediate surgical involvement

›ICU post-operative care

›Severe electrolyte derangements

›Potassium < 2.5 mmol/l

›Phosphate < 0.32 mmol/l in refeeding context

›Refeeding syndrome manifestations

›Cardiac arrhythmias

›Acute respiratory failure from hypophosphatemia

Discharge criteria and follow-up

›Outpatient management criteria

›Partial obstruction with ability to tolerate liquids

›Adequate oral hydration possible

08Treatment/t100

Immediate medical management

›Fluid and electrolyte resuscitation

›IV fluid choice

›Normal saline 0.9% for volume resuscitation

›Potassium chloride additive when hypokalemia

›Potassium replacement

›40 mEq/L KCl in IV fluids for mild-moderate hypokalemia

›Maximum 20 mEq/hour IV infusion rate

›Cardiac monitoring during rapid replacement

›Metabolic alkalosis correction

›Volume replacement corrects chloride depletion

›Avoid bicarbonate administration

›Gastric decompression

›Nasogastric tube placement

›Low intermittent suction at 80-120 mmHg

›Monitor aspirate volume and character

›Continue until bilious output < 200 mL/day or relieved

Antiemetic therapy

›Antiemetics for nausea and vomiting

›Ondansetron IV

›4-8 mg IV every 6-8 hours

›Preferred 5-HT3 antagonist

›QT prolongation monitoring if high risk

›Prochlorperazine IV

›10 mg IV every 6-8 hours

›Akathisia and extrapyramidal side effect risk

›Diphenhydramine 25 mg IV co-administration reduces EPS risk

›Metoclopramide IV

›10 mg IV every 6-8 hours

›Prokinetic and antiemetic

›Contraindicated in complete mechanical obstruction

›Limit to 12 weeks cumulative use due to tardive dyskinesia risk

Acid suppression

›Proton pump inhibitor therapy

›Pantoprazole IV

›40 mg IV daily

›For prevention of stress and stasis ulceration

›Transition to oral once tolerating PO

›Omeprazole PO

›20-40 mg PO daily when tolerating oral

›Continue until obstruction resolved

Nutritional rehabilitation

›Enteral nutrition

›Nasojejunal tube feeding

›Tube advanced past ligament of Treitz under fluoroscopy or endoscopy

›Positioning past obstruction allows caloric delivery

›Standard polymeric formula at 25-30 kcal/kg/day target

›Initial rate and advancement

›Start at 20-30 mL/hour

›Advance by 20 mL/hour every 8-12 hours as tolerated

›Wan et al. Ann Nutr Metab 2020 demonstrated efficacy of enteral approach

›Parenteral nutrition

›TPN indications

›Enteral access not feasible

›Severe aspiration risk precluding NJ tube

›Short-term bridge to surgical correction

›TPN composition targets

›25-30 kcal/kg/day total energy

›1.2-1.5 g/kg/day protein

›Electrolyte supplementation based on daily labs

›Refeeding protocol

›Start low and go slow

›10 kcal/kg/day initial in high-risk patients

›Increase by 5 kcal/kg every 2-3 days

›Thiamine supplementation

›200-300 mg IV daily before initiating nutrition

›Prevents Wernicke encephalopathy in malnourished patients

›Phosphate monitoring and replacement

›Check every 12-24 hours first week

›Replace IV if < 0.6 mmol/l

Positional therapy

›Conservative positioning measures

›Meals in left lateral decubitus position

›Increases aortomesenteric angle

›Postprandial positioning for 30-60 minutes

›Prone positioning after meals

›Lifts mesenteric root anteriorly

›Reduces duodenal compression

›Avoid supine eating and immediately post-meal recumbency

›Worsens aortomesenteric angle narrowing

›Patient education essential

Surgical management

›Indications for surgery

›Failure of 4-6 weeks conservative management

›No weight gain or symptom improvement

›Persistent CT evidence of obstruction

›Complete obstruction not responding to NGT decompression

›Complications

›Perforation

›Bowel ischemia

›Preferred surgical procedure

›Laparoscopic duodenojejunostomy

›Bypass of obstructed segment

›Side-to-side anastomosis proximal to obstruction and jejunum

›Jain et al. Surg Endosc 2021: 86% no recurrence at mean 41-month follow-up

›Bozzetti et al. J Laparoendosc Adv Surg Tech 2026 recent case series

›Strong procedure (duodenal mobilization)

›Division of ligament of Treitz and repositioning

›Less commonly performed

›Higher recurrence compared to duodenojejunostomy

›Open duodenojejunostomy

›When laparoscopic approach not feasible

›Prior multiple abdominal surgeries

›Hemodynamic instability

›Comparable long-term outcomes

›Kirby et al. Ann R Coll Surg Engl 2017 single centre experience

09Special Populations/sp70

Pregnancy

›Pregnancy-specific considerations

›Increased risk in third trimester

›Uterine displacement of abdominal contents

›Altered duodenal position

›Nutritional demands increased

›Weight gain target 11-16 kg total for normal BMI

›Fetal growth restriction if obstruction prolonged

›Imaging approach

›Ultrasound preferred initial imaging

›MRI without gadolinium acceptable in second and third trimester

›CT only if life-threatening complication suspected

›Treatment modifications

›Antiemetics in pregnancy

›Ondansetron: commonly used but controversial in first trimester

›Metoclopramide: generally considered safe in pregnancy

›Prochlorperazine: avoid in first trimester

›Nutritional support

›NJ tube feeding preferred over TPN when possible

›Higher caloric target in pregnancy 30-35 kcal/kg/day

›Surgical approach in pregnancy

›Delay if possible until post-partum

›Laparoscopy feasible in second trimester if required

›Multidisciplinary planning with obstetrics

Geriatric

›Older adult features

›Different precipitants

›Cancer cachexia most common trigger

10Background/b73

Epidemiology

›Incidence and prevalence

›Rare condition

›Incidence 0.013%-0.3% in population

›Higher in postoperative spinal surgery series (0.5%-2.4%)

›Demographics

›Peak age 10-39 years

›Female predominance 3:2 ratio

›Mathenge et al. Clin Anat 2014 comprehensive review

›Associated conditions

›Eating disorders

›Anorexia nervosa most prevalent comorbid

›ARFID and bulimia also reported

›Staller et al. Lancet Gastroenterol Hepatol 2023

›Post-surgical states

›Spinal surgery commonest iatrogenic cause

›Bariatric surgery and esophageal surgery

›Military and athletic populations

›Schauer et al. Mil Med 2013 military trainee case

›Rapid physical conditioning with weight loss

Pathophysiology

›Anatomic mechanism

›Normal aortomesenteric anatomy

›SMA arises from aorta at L1 vertebral level at 38-65 degree angle

›Retroperitoneal fat pad maintains distance 10-28 mm

›Compression mechanism

›Third portion of duodenum crosses between aorta posteriorly and SMA anteriorly

›Loss of mesenteric fat narrows the angle below 25 degrees

›Distance decreases below 10 mm (often 2-8 mm)

›Contributing anatomic variants

›Low SMA takeoff from aorta

›Short mesenteric root

›High ligament of Treitz

›Duodenal malrotation

›Physiologic consequences

›Proximal duodenal obstruction

›Gastric and duodenal dilation

›Bilious vomiting from high-level obstruction

›Nutritional cycle

›Obstruction causes reduced intake

›Reduced intake causes further weight loss

›Further weight loss worsens compression

›Complications of chronic dilation

›Stress ulceration from stasis

›Aspiration pneumonitis from emesis

›Acute gastric dilation with ischemia risk

Therapeutic Considerations

›Conservative management evidence

›Nutritional rehabilitation primary goal

›Weight restoration widens aortomesenteric angle

›Wan et al. Ann Nutr Metab 2020 retrospective series on enteral therapy

›Response timeline

›Improvement typically within days to weeks of adequate nutrition

›4-6 weeks trial before surgical consideration

›Positional therapy adjunct

›Not curative alone but reduces symptoms during rehabilitation

›Patient adherence essential

›Surgical outcomes

›Laparoscopic duodenojejunostomy preferred

›Sun et al. Surg Endosc 2015: minimally invasive case series and review

›Jain et al. Surg Endosc 2021: 86% symptom-free at 41-month follow-up

›Low morbidity and mortality in experienced hands

›Laparoscopic vs open

›Laparoscopic associated with shorter hospital stay

›Comparable long-term efficacy

›Strong procedure outcomes

›Higher recurrence than duodenojejunostomy in most series

›Reserved for selected anatomic situations

›Eating disorder treatment integration

›Simultaneous medical and psychiatric treatment required

›Treating only SMA syndrome without eating disorder leads to recurrence

›Hundman et al. J Natl Med Assoc 2025 eating disorder masking case series

›Recio-Barbero et al. Front Psychiatry 2019 delayed diagnosis review

›Multidisciplinary team approach

›Gastroenterology, surgery, dietitian, psychiatry

›Inpatient eating disorder units with medical monitoring capability

11Patient Discharge Instructions/pdi35

copy discharge instructions

›Superior mesenteric artery syndrome home care

›Eat small, frequent, calorie-dense meals 6-8 times per day

›Avoid large meals that cause gastric distension

›Liquid or semi-liquid foods easier to tolerate initially

›Positional eating strategies

›Sit upright or lean slightly forward while eating

›Lie on left side or prone for 30-60 minutes after meals

›Never lie flat on back immediately after eating

›Weigh yourself daily at same time

›Weight gain is the treatment goal

›Report any continued weight loss to your doctor immediately

›Warning signs to return to ER immediately

›Vomiting and unable to keep down any fluids

›Risk of severe dehydration

›Severe or worsening abdominal pain

›Constant pain not relieved by position change

›Green or yellow (bilious) vomiting that is new or worsening

›Dizziness, fainting, or feeling very weak

›Signs of dehydration or electrolyte imbalance

›Abdominal bloating and firmness that is rapidly getting worse

›Blood in vomit or stool

›Follow-up appointments

›Gastroenterology or surgery clinic within 1-2 weeks

›Bring food diary and weight log

›Dietitian appointment within 1 week for nutritional plan

›Psychiatry or eating disorder clinic if recommended

›Essential for recovery if eating disorder present

12References/r27

Guidelines and key sources

›Key evidence sources

›Pottorf BJ et al. Laparoscopic Management of Duodenal Obstruction Resulting From Superior Mesenteric Artery Syndrome. JAMA Surgery 2014

›Case series establishing laparoscopic approach

›Aortomesenteric angle and distance diagnostic criteria

›Agrawal GA, Johnson PT, Fishman EK. Multidetector Row CT of Superior Mesenteric Artery Syndrome. J Clin Gastroenterol 2007

›CT measurement protocol reference

›Warncke ES et al. Superior Mesenteric Artery Syndrome: A Radiographic Review. Abdom Radiol 2019

›Radiographic review including UGI fluoroscopy

›Le D et al. Point-of-Care Ultrasound Findings in the Diagnosis and Management of SMA Syndrome. Am J Emerg Med 2022

›POCUS utility in ED setting

›Wan S et al. Superior Mesenteric Artery Syndrome Improved by Enteral Nutritional Therapy. Ann Nutr Metab 2020

›Enteral nutrition retrospective series

›Jain N et al. SMA Syndrome: Management Perspective With Laparoscopic Duodenojejunostomy and Long-Term Results. Surg Endosc 2021

›86% symptom-free at 41-month follow-up

›Staller K, Abber SR, Burton Murray H. Intersection Between Eating Disorders and GI Disorders. Lancet Gastroenterol Hepatol 2023

›Eating disorder and GI comorbidity evidence review

›Biank V, Werlin S. Superior Mesenteric Artery Syndrome in Children: A 20-Year Experience. JPGN 2006

›Pediatric case series reference

›Ganss A et al. Superior Mesenteric Artery Syndrome: A Prospective Study. J Gastrointest Surg 2019

›Surgical series with median BMI data

Coding references

›ICD-10 codes

›K31.5 obstruction of duodenum

›Primary code for SMA syndrome

›K31.1 adult hypertrophic pyloric stenosis

›Differential in proximal gastric obstruction

›K55.1 chronic vascular disorders of intestine

Evidence & Review

Evidence & Review