OSA

1
OSA the Perioperative Orthopaedic Patient
2
Who Has OSA?
3
OSA

• Underdiagnosed
• OSA is linked to increased risk for HTN, C-V
  events including nocturnal arrhythmias, including
  afib V-tach, MI, stroke, DM.
• Considered an independent risk factor for
  increased postoperative morbidity.
• Those with OSA frequently have multiple
  co-morbidities COPD, HTN, DM, CAD, obesity.

4
OSA Obesity

• Attributed to a concommittant rise in prevalence
  of obesity. A 10 increase in body weight can
  increase your risk of OSA by 6 fold.
• Caused by fat deposits around your upper airway
  and decreased chest excursion from abdominal
  obesity.

5
In one study Obesity is 5X more prevalent among
the those with OSA (Memtsoudis et al).

• http//youtu.be/A9lLSw9Rtjs

6
OSA

• OSA is a partial or complete airway obstruction
  resulting in repetitive incomplete or complete
  cessation of airflow during sleep a/w strenuous
  breathing against resistance followed by period
  of desaturation, hypercarbia and then subsequent
  arousal.

7
OSA Video
http//www.mayoclinic.org/diseases-conditions/slee
p-apnea/multimedia/obstructive-sleep-apnea/vid-200
84717 - 31k
8

• OSA Can provoke long term C-V consequences such
  as right ventricular dysfunction, atrial
  fibrillation, heart failure and stroke.
• OSA can also cause a higher incidence of
  complications in the perioperative period
  including
• post op delirium
• hypoxia
• aspiration pneumonia
• ARDS
• PE
• Intubation/mechanical ventilation and increased
  use of ICUs

9
Diagnosis

• Timely diagnosis is difficult
• While PSG remains the gold standard for
  diagnosis, it requires an overnight stay, complex
  equipment, expensive, need available
  facilities.
• Screening Instruments help estimate the risk of
  OSA
• - American Society of Anesthesiologists (ASA)
  check list
• - Berlin Questionnaire
• - Stop Model/Stop-Bang Questionnaire.
• These look at SS of OSA snoring, observed
  apnea,, obesity, neck circumference.
• Chung, et al. evaluated use of serum HCO3 as an
  indicator of chronic metabolic compensation for
  chronic recurrent respiratory acidosis (HCO3 gt
  28mmol) a score of gt 3 on the STOP-BANG
  questionnaire increased specificity to 85.

10
Stop-Bang Questionnaire

• 1. Snoring Do you snore loud enough to be heard
  thru closed doors? Yes/No
• 2. Tired Do you often feel tired, fatigued,
  sleep during day? Yes/No
• 3. Observed Has anyone observed you stop
  breathing during sleep? Yes/No
• 4. Pressure Do you have HBP? Yes/No5. BMI BMI
  gt 35? Yes/No
• 6. Age gt 50 y/o? Yes/No
• 7. Neck Circumference Greater than 40cm? Yes/No
• 8. Gender Male? Yes/No

• High Risk of OSA yes to 3 or more questions
  Indicates high probability of OSA
• Low Risk of OSA yes to less than 3 questions

• Chung, F., Subramanyam, R., Liao, P., Sasaki, E.,
  Shapiro, C. Sun, Y. High STOP-BANG score
  indicates a high probability of obstructive sleep
  apnea. British Journal of Anesthesia, 2012.
• 108(5), 774.

11
ASA GuidelinesAmerican Society of
Anesthesiologists

• Preoperative Evaluation interview, MR review,
  PE, PSG,Anesthesiologists should work with
  surgeon to develop a protocol where pts with
  possibility of OSA are evaluated long before day
  of surgery.
• Preop initiation of NIPPV (noninvasive positive
  pressure ventilation ) if severe OSA. Mandibular
  advancement devices and preop weight loss should
  be considered.

12
ASA Guidelines (continued)American Society of
Anesthesiologists

• Use regional anesthesia spinals and peripheral
  nerve blocks peripheral nerve catheters. Also
  agreement that excluding opioids from spinals
  reduces risk.
• Recommendation is to avoid general anesthesia and
  intubation.
• Use local anesthesia when possible.
• Caution against concomitant use of
  Benzos/barbituates which increase risk of
  respiratory depression.
• Avoid PCAs with basal infusions.

13
ASA Guidelines (continued)American Society of
Anesthesiologists

• Use NSAIDS as much as possible.
• Patient positioning lateral, prone or 45 degree
  sitting. Avoid supine.
• Recommend continuous pulse oximetry until room
  air sats are above 90 during sleep. Use of
  supplemental O2, as warranted.
• Risk factors for postop respiratory depression
• Severity of OSA
• Systemic use of opiods
• Use of sedatives
• Potential for apnea during REM rebound on POD
  3-4.

14
Implications

• Patients with OSA are at increased risk of
  perioperative complications. Results in need for
  more intense monitoring and strategies to prevent
  adverse events.
• Implementation of a sedation scale. Sedation
  precedes respiratory depression 2/2 opioid
  administration. Sedation and respiratory
  assessments should be done Q1-2h in the first 24h
  of surgery depending on risk factors and
  presurgical screening. Increases demand on
  nursing resources.
• Use of opiod analgesics, anxiolytics (Xanax),
  antihistamines (Benadryl, scopolamine) and
  antiemetics can increase risk of postop
  respiratory and cardiac complications.

15
Implications (continued)

• Information regarding the effects of length of OR
  time, and EBL is not available from most of the
  studies because a lot of the studies are
  retrospective and taken from databases, and this
  information is frequently not available.
• Information regarding readmission rates are not
  available from most of the studies because a lot
  of the studies are retrospective and taken from
  databases, and this information is frequently not
  available.
• The use of simple screening tools now allows us
  to estimate the likelihood someone has OSA, but
  what then is the next step?? Delay surgery? Or
  proceed knowing the risk of complications is
  higher? Refer pt for workup and treatment before
  surgery? Rate of noncompliance with treatment is
  high. How long should a pt be treated with PAP
  before proceeding with surgery?
•  

16
Implications (continued)

• There is little data to support the use of PAP in
  the acute postoperative setting in improving
  outcomes, and cost is high so adherence is low.
• Be aware that patients are at risk for prolonged
  apnea during sleep for up to 1 week after
  surgery due to interruptions in REM sleep. It
  is imperative they use their CPAP during this
  time. REM sleep can be lost during the
  initial postop period. REM sleep may return
  in a rebound fashion with decreased pharyngeal
  tone, hypoxemia and prolonged apnea.

17
References

• American Society of Anesthesiologists Task Force
  on the Perioperative Management of patients with
  obstructive sleep apnea. Practice guidelines for
  the perioperative management of patients with
  obstructive sleep apnea an updated report by the
  American Society of Anesthesiologists Task Force
  on Perioperative management of patients with
  obstructive sleep apnea. Anesthesiology 120 (2).
  268-286. (2014)
• Chung, F., Subramanyam, R., Liao, P., Sasaki, E.,
  Shapiro, C. Sun, Y. High STOP-BANG score
  indicates a high probability of obstructive sleep
  apnea. British Journal of Anesthesia, 2012
  108(5), 774.
• Memtsoudis, Stavros G., Besculides, Melanie C.,
  Mazumdar, Madhu. A rude awakening- the
  perioperative sleep apnea epidemic. The New
  England Journal of Medicine, 2013 368
  2352-2353.
• Memtsoudis, Stavros Spencer, Liu S. Yan, Ma
  Chiu, Ya Lin Walz, J. Matthias Gaber-Bayllis,
  Licia K. Mazumdar, Madhu. Perioperative
  Pulmonary outcomes in patients with sleep apnea
  after noncardiac surgery. Anesthesia
  Analgesia, 2011. 112(1) 113-121.
• Roop, Kaw Pasupuleti, Vinay Walker, Esteban
  Ramaswamy, Anuradha Foldvary-Schafer, Nancy.
  Postoperative complications in patients with
  obstructive sleep apnea. Chest, 2012. 141(2)
  436-441.
• Studndner, Ottokar Opperer, Mathias
  Memtsoudis, Stavros G. Obstructive sleep apnea
  in adult patients considerations for anesthesia
  and acute pain management. Pain Management,
  2015. 5(1) 37-46.
• Veney, Amy J. Promoting safety of postoperative
  orthopaedic patients with obstructive sleep
  apnea. Orthopaedic Nursing, 2013. 32(6)
  320-324.

18
Post-Op Hypovolemic Shock
http//youtu.be/d2mVKblkGcQ
19
Post-op Hypovolemic Shock

• Pathophysiology
• (Martel et al)

20
Post-Op Hypovolemic Shock
(Martel et al)

• Signs and symptoms

System Early Shock Late Shock
CNS Altered Mental Status Obtunded
Cardiac Tachycardia Orthostatic hypotension Cardiac failure Arrhythmias Hypotension
Renal Oliguria Anuria
Respiratory Tachypnea Tachypnea Respiratory failure
Hepatic No change Liver Failure
Gastrointestinal No change Mucosal Bleeding
Hematological Anemia Coagulopathy
Metabolic None Acidosis Hypocalcemia Hypomagnesium
21
Post-Op Hypovolemic Shock

• Early Treatment
• ORDERO OxygenateR Restore circulating
  volume (Crystalloid solutions, blood
  transfusions)D Drug TherapyE Evaluate
  response to therapy (VS, Urine output,
  mental status, CBC, CMP, PTT PTINR)R Remedy
  underlying cause

22
Post-Op Hypovolemic Shock

• Late Treatment
• O OxygenateR Restore circulating volume
  (Crystalloid solutions, blood
  transfusions)D Drug Therapy Vasoactive agents
  Dopamine/ Norepinephrine) considered stress
  dose steroids or antibioticsE Evaluate
  response to therapy (VS, Urine output, mental
  status, CBC, CMP, PTT PTINR)R Remedy underlying
  cause

23
Post-Op Hypovolemic Shock

• Case Study DF
• ED Presentation and Care
• HPI 85 y/o female fell at home found by aide, on
  ground with leg behind her. Hx dementia pt was
  treated at scene by EMS with zofran 4 mg and
  Morphine sulfate 10mg IVP
• PMH Dementia, asthma, CHF, COPD, PSH rt rev THA
• Social hx 60yr smoking hx, lives w dtr, no ETOH
• PE 50 kg, T 97.9 P 118 R 16 BP 100/57 oxygen
  saturations 93 2L NC rt leg deformity, pulses
  with doppler ECG at fib w VR 113

24
Post-Op Hypovolemic Shock

• Case Study DF

System ED/2000 UNIT/0600 ICU/0800
CNS Dementia-awake unresponsive unresponsive
Cardiac HR 118 BP 100/57 Hgb 11.9 wbc 11.8 CK 160, SR HR 112 BP146/115 Hgb 10.7 wbc AT Fib w RVR HR 110 BP 102/64 CK-437 AT Fib w RVR
Renal NC BUN 19 CR1.5 BUN 27 CR 2.6 BUN 29 CR 3.0
Respiratory 16 O2 sat-94 3L 8-12 BG-Ph 7.157 O2 sat-100 NRB R-12 BG Ph 7.2 O2 sat-99 6L
Hepatic SGOT-22 SGOT- 30 SGOT-48
Gastrointestinal NPO NPO NPO
Metabolic Na 142 K 4.6 Na 147 K 6.2 Na 144 K 4.9
25
Post-Op Hypovolemic Shock
26
Post-Op Hypovolemic Shock
27
Post-Op Hypovolemic Shock
28
Post-Op Hypovolemic ShockCase Study

• Floor care
• O OxygenateR Restore circulating volume
  (Crystalloid solutions, blood transfusions)
  none ordered D Drug Therapy none ordered E
  Evaluate response to therapy (VS, Urine output,
  mental status, CBC, CMP, PTT PTINR)R Remedy
  underlying cause

29
Post-Op Hypovolemic ShockCase Study

• ICU care
• O OxygenateR Restore circulating volume
  (Crystalloid solutions, blood transfusions)
  Normal Saline D Drug TherapyE Evaluate
  response to therapy (VS, Urine output,
  mental status, CBC, CMP, PTT PTINR)R Remedy
  underlying cause

30
Post-Op Hypovolemic Shock

• Conclusions
• Think about hypovolemia-early signs
• Aggressive fluid resuscitation
• Monitor IO especially urine output
• Report abnormal findings
• Think about bleeding

31
References

• Barbosa, N, Moraes, B, Souza, N, Rocha, F,
  Cavalho Barzil J Hemostatic resuscitation in
  traumatic hemorrhagic shock case report
  Anesthesiology 2013 Jan-Feb63(1) 99-102
• Bartellas, E, Klien, M, Lane, C, Sprague, A,
  Wilson, A. Hemorrhagic Shock, SOGC Clinical
  Practice Guidelines. The Journal of Obstet
  Gynaecol Can 201224 (6)504-11
• R. S. Braithwaite, N. F. Col, and J. B. Wong,
  Estimating hip fracture morbidity, mortality and
  costs, Journal of the American Geriatrics
  Society, vol. 51, no. 3, pp. 364370, 2003
• M. Bumann, T. Henke, H. Gerngross, L. Claes, and
  P. Augat, Influence of haemorrhagic shock on
  fracture healing, Langenbeck's Archives of
  Surgery, vol. 388, no. 5, pp. 331338, 2003..
  Martel,M , MacKinnon, C,.
• Lichte, P Kobbe, P Pfeifer, R, Graeme, C Rainer,
  B, Mersedeh, T, Bergmann, C, Kadyrov, M, Fischer,
  H, Gluer, C, Hildebrand, F Pape, H, Pufe, T
  Impaired Fracture Healing after Hemorrhagic
  Shock Mediators of Inflammation
  Volume 2015 (2015), Article ID 132451, 7 pages.
• S.-K. Lee and J. Lorenzo, Cytokines regulating
  osteoclast formation and function, Current
  Opinion in Rheumatology, vol. 18, no. 4, pp.
  411418, 2006.

32
Small Bowel Obstruction
33
Definition

• Small bowel obstructions are caused by a variety
  of pathologic processes.
• An obstruction is a blockage of the intestine
  (small or large) which does not allow the passage
  of food or fluids (mechanical or functional).
• It is a frequent cause of hospitalization and
  surgery consult, representing appx 20 of all
  surgery admission for abdominal pain.

34
Types of SBO

• Mechanical obstruction - is something that
  physically blocks the small intestine.
• Causes
• Intestinal adhesions 1 cause of SBO (small
  fibrous tissue in abdominal cavity)
• Hernia
• Tumors
• Inflammatory bowel disease ie. Crohns Disease
• Twisting of intestine (volvulus)
• Telescoping of the intestine (intussusception)
• Impacted Feces

35
Continued Types of SBO

• Paralytic Ileus/Functional Bowel Obstruction-can
  cause s/s of intestinal obstruction, but doesnt
  involve a physical blockage. It involves an
  impaired gastrointestinal motility dysfunction by
  slowing the movement of food/fluid thru the
  intestine.
• Causes
• Abdominal surgery
• Pelvic surgery
• Infection
• Certain Medications-antidepressants, narcotics,
  anesthesia
• Muscle/Nerve Disorders-ie. Parkinsons Disease
• Constipation is the 1 associated factor for
  ileus after ortho surgery incidence
• The incidence of ileus after lower limb
  reconstruction ranges from 0.3-2.0 w/an even
  higher incidence (5.6) following revision THA
• (Lee et al)

36
Pathophysiology of SBO

• Partial vs Complete
• Significant obstruction is associated with
  increased intestinal contractions proximal to the
  site of the obstruction and are associated with
  abdominal cramps.
• With complete unrelieved obstruction bowel
  contents fail to pass distally, resulting in
  accumulation of fluids causing distention/dilation
  of the proximal bowel.
• As pressure in the bowel proximal to the
  obstruction increases blood flow decreases which
  can result in
• Hemorrhage
• Ischemia/Necrosis
• Infarction of the bowel
• Perforation-as a result of ischemia
• Sepsis/peritoneal infections/shock
• Death

37
Pathophysiology of SBO (continued)

• In simple obstruction the proximal bowel appears
  heavy, edematous, and even cyanosed.
• Acute SBO results in volume depletion and
  electrolyte imbalance.
• Vomiting
• Loss in the peritoneal cavity (fecal fluid)
• Intestinal contents are cut off from the
  absorptive surface of the colon

38
History Taking

• Good history taking on admission is important
• Last bowel movement and usual pattern
• Abdominal history of pelvic/colon disease ie. CA,
  radiation, inflammatory bowel disease
• Has the patient ever experienced any
  complications r/t any previous surgeries in the
  past (ie. SBO)
• Remember abdominal adhesions is the 1 cause of
  mechanical SBO
• Remember Constipation is the 1 cause of
  functional SBO

39
Signs Symptoms

• Small bowel obstruction is considered a medical
  emergency
• Signs Symptoms
• - Nausea
• - Constipation
• - Abdominal Pain - colicky in nature
• - Abdominal distension
• - Vomiting - is a pronounced symptom in SBO
• Other Sign Symptoms that are more ominous-
  Fever- Tachycardia associated hypotension

40
Assessment

• In the focused gastrointestinal assessment
  consider the following
• Vial Signs - fever, tachycardia with associated
  hypotension
• Nausea
• Vomiting
• Bowel Sounds - hypoactive, tinkling, absent
• Abdominal Distension
• Constipation
• Other items to consider are Medications past
  medical history

41
Imaging Work-Up Algorithm
42
Imaging for SBO

• Plain abdominal xrays provide the most valuable
  information in the initial diagnosis of acute
  SBO, in appx 50-60 of cases this type of imaging
  will provide enough information needed for
  clinical decision making (proves to be low cost
  effective).
• Ct scans are used when xrays are equivocal,
  normal, or low grade partial SBO is suspected
  is 85-95 accurate in diagnosis.
• (Silva et al)

43
Radiology Classification of SBOHigh grade vs Low
grade

• High Grade SBO
• Multiple air fluid levels with a width of 2.5 cm
  or more
• Vertical height of more than 2 cm b/t air fluid
  levels
• Distension of small bowel diameter more than 2.5
  cm a small bowel-colon diameter ratio greater
  than 0.5
• Delay in passage of CT contrast
• Low Grade SBO
• Sufficient flow of contrast material through
  obstruction
• Less air fluid levels
• Still will see distension of the small bowel
• (Silva et al)

44
Examples of High grade SBO on Xray

• High-grade SBO. Plain abdominal radiograph shows
  multiple air-fluid levels (arrows), some with a
  width of more than 2.5 cm. In addition, there is
  a differential vertical height of more than 2 cm
  between corresponding air-fluid levels in the
  same bowel loop (circled area). There is also
  distention of the small bowel diameter to more
  than 2.5 cm and a small bowelcolon diameter
  ratio of greater than 0.5.
• (Silva et al)

45
High grade SBO Xray(AlReefi Shukri)
46
Surgical view of High grade SBO(Al Reefi
Shukri)
47
Further Diagnostic Work-Up

• Other Diagnostic Testing
• CBC-leukocytosis
• BMP-if bun creatine are elevated may indicate
  dehydration
• UA
• LFT
• Pancreatic enzymes

48
Further Diagnostic Work-Up(continued)

• Other Differential Diagnosis to Consider
• Gastroenteritis
• Pancreatitis
• UTI
• Cholecystitis
• Inflammatory Bowel Disease
• Appendicitis

49
Treatment of SBO

• Aggressive resuscitative fluid therapy
• Electrolyte imbalance correction
• NPO
• Decompression of stomach-NGT helps prevents
  aspiration
• Foley Catheter for strict IO
• Labs CBC, BMP, LFTs, Pancreatic enzymes, UA
• Analgesics morphine based
• Antibiotic Therapy - broad spectrum used for
  prophylaxis in surgical intervention
• General surgery consult
• Antimetics zofran, reglan, tigan, compazine
• Stay away from scopolamine patches (can cause
  constipation, decreased gut motility, and even
  bowel stasis by mechanism of anticholinergic
  effect)
• (Kulaylat Doerr)

50
Prognosis of SBO

• With proper diagnosis txmt of SBO the prognosis
  is good. Complete obstructions treated
  successfully non-operatively have a higher
  incidence of reoccurrence than do those treated
  surgically.
• Mortality Morbidity are dependent on early
  recognition correct diagnosis of obstruction.
  If untreated or strangulation occurs-death is
  100. If surgery is performed within 36 hrs
  mortality decreases to 8.
• Factors associated with death post-operative
  complications include
• - age
• - comorbidity
• - txmt delay
• (Nobie et al)

51
Case Presentation 1

• K.W. a 66 yr female admitted for an elective
  right THA , last BM was 3 days PTA
• PMHX HTN, DM, hypercholesterolemia, CAD, gerd,
  constipation, hypothyroidism, OA
• PSX Hx TKA, hysterectomy, goiter removal, right
  thumb sx
• Recd from recovery with N/V, recd spinal
  anesthesia non duramorph
• Continued to have N/V up until day of discharge
  on POD 2 which had resolved prior to dc had
  recd mutliple IV boluses, reglan, no abdominal xr
  was done.
• Assessment bs x 4, flatus per pt, abd soft,
  nontender, nondistended.
• Zofran. flatus per patient. No BM on day of DC.
  Had recd K-dur x 1 for hypokalemia on POD 1
• Readmitted POD 4 with a SBO thu the ED.
• Assessment abd mildly distened, mild diffuse
  tenderness no rebound tenderness or guarding. No
  flatus since dc, no bm, continues w/NV

52
Case Presentation 1(continued)

• Abdominal xr revealed a high-grade SBO may be
  early w/ileus. leukocytosis. Electrolyte
  imbalance. Further information gathering from
  the patient revealed that she experienced a SBO
  w/her hysterectomy yrs ago.
• Medications upon admission consisted of
  percocet, senna S, zetia, lipitor, insulin,
  toradol, synthroid, benicar, cozaar, protonix,
  miralax, xalerto, livalo, dexilant, dilaudid

53
Case Presentation 1(continued)

• Txmt consisted of conservative mgt w/fluids,
  pain mgt, antiemetics, NGT, NPO, strict IO,
  serial lab draws xr. Patient failed
  conservative mgt underwent an exp. Lap on POD
  9 w/extensive lysis of adhesions over 2 hrs,
  small bowel resection. Patient continued to fail
  txmt was taken back 9 days later for a 2nd exp
  lap at that time sustained a bowel perforation,
  further bowel resection, G-tube insertion,
  sepsis, ICU mgt for septic shock. TPN lipids
  for nutrition. DC appx 1 month later on the 2nd
  admission.
• Patient returned to ED w/abdominal pain 2
  additional times w/o evidence of SBO

54
Case Presentation 2

• C.B. a 74 yr female admitted for elective left
  TKA recd. Spinal anesthesia with a femoral nerve
  block
• PMHx AFIb w/cardoversion, HTN,
  hypercholesterolemia
• PSX Hx TKA, Shoulder sx, finger sx, back sx,
  cataract sx
• Day of admission no NV, abd was soft, non
  distended, non tender, hypoactive bs, last BM
  was the day PTA
• Patient experienced pain control issues and
  narcotic strength was increased to percocet
  10/325
• POD 1 NV, no flatus, continued w/hypoactive
  bs. Labs wnl. Recd multiple IV boluses reglan
• POD 2 in AM nausea resolved but in PM
  returns. flatus per pt. No BM. Abd xr reveals
  gas filled on dilated transverse/descending
  colon-non obstructive bowel gas pattern. No
  mention of an ileus. NGT was inserted, made NPO,
  continual IV fluids. Consult for general sx
  placed.
• POD 3 abd xr repeated reveals mildly dilated
  loop small bowel LUQ likely representing ileus
  a large amt of stool. Ducolax suppository was
  given resulting in lg BM, NGT clamped, DC
  tolerated clear liquid diet.
• POD 4 DC home. Narcotics were changed to ultram
  upon dc

55
Conclusions

• SBO is considered a medical emergency
• Intervene early be aggressive
• Consider all hx of pt when clinical picture
  isnt making sense ask again
• Evaluate all medications
• Do a very focused GI assessment
• Tx constipation early in ortho post-op pt
• Notify physician early ask for them to
  evaluate pt status

56

• Questions??????
• Thank You!!!

57
References

• Al Reefi, M.A. Shukri, N. Missed small bowel
  obstruction that complicated an acute
  appendicitis A Misdiagnosis. Grand Rounds.
  Specialities Case Report Article Type
  Specialities Paediatric Surgery, 26 March 2013
  e-med Ltd. Vol 13, pg 36.44.
• Kulaylat, M. N. Doerr, R. J. Surgical
  Treatment Evidence-Based Problem-Oriented
  small bowel obstruction, 2001.
  www.nebl.nlm.nih.gov/book/NBK6873/accessed April
  12, 2015.
• Lee T.H., Lee, J.S., Hong, S.J., Jany Young J.,
  Jeon, S. R., Byrum, D.W., Park Young, W., Kim
  S.I., Choi, H.S., Lee, J.C., Lee, J.S. Risk
  Factors for Post-Operative Ileus Following
  Orthopedic Surgery The Role of Chronic
  Constipation. J. Neurogastroenterol Motil., 2015
  Jan 21(1) 121-125.
• Nobie, Brian A. Small-Bowel Obstruction.
  Medscape Reference Drugs, Diseases
  Procedures. Updated Jan 20, 2015.
• Silva, A. C, Pimenta, M., and Guimaraes, L.
  Small Bowel Obstruction What to Look For.
  RadioGraphics. March-April 2009, 29 (2).