Viva 5

A 78-year-old lady with a background of obesity (135kg, BMI 39), AF and hypertension has been admitted to the ICU following an elective anterior lumber interbody fusion (ALIF). She has remained in ICU for the last seven days because of difficult pain control. She has also not opened her bowels since her procedure. She has been complaining of abdominal pain, nausea and vomiting. 

On examination, her abdomen is soft but distended, diffusely tender on palpation, tympanic but not peritonitic on percussion, and the bowel sounds are scant.

Other observations:

• Resp rate 20
• SpO₂ 96% on 30% FiO₂ via high flow nasal prongs (40L/min flow)
• NIBP 175/90, HR 100-120 (AF)
• Urine output 30-60ml/hr
• Temp 37.9 ºC

Biochemistry is as follows:

• Na⁺ 146 mmol/L
• K⁺ 3.4 mmol/L
• Cl^- 110 mmol/L
• HCO₃^- 20 mmol/L
• Mg²⁺ 0.65 mmol/L
• iCa²⁺ 1.21 mmol/L
• PO₄^- 0.55 mmol/L
• Urea 16.2 mmol/L
• Creat 135 μmol/L

What are the most likely causes of her constipation?

(This is not a real CICM viva)

This is a multifactorial thing. There are several contributing factors:

• Surgery which requires a lot of abdominal content retraction
  • Made worse by obesity, which means a lot of content to retract, and also probably some 
• Pain means opioids
• Spinal surgery means immobility
• Electrolyte abnormalities
• AF raises the possibility of embolic gut ischaemia, as anticoagulation would surely have been paused for this procedure
• The lowish urine output high urea creatinine and sodium suggest the patient is somewhat dehydrated

What complications can you expect from her constipation?

• Vomiting and aspiration
• Increased intra-abdominal pressure
  • Thus, reduced renal function
  • Also, poor ventilation
• Reduced nutritional intake
  • Thus, poor wound healing
• Bacterial hyperproliferation and translocation through the gut mucosa
• Bowel obstruction
• Bowel perforation
• Gut ischaemia
• Inability to absorb oral medications (the BP suggests that normal antihypertensive meds are not well absorbed)

Is this ileus? What is ileus? How is this different from just constipation, or bowel obstruction?

• Constipation in the historic literature has been defined as "failure of the bowel to open for three consecutive days" (eg. used by Mostafa et al, 2001). ESICM support this cut-off, but suggest that ICU patients cannot use the normal colloquial definition of constipation ("uncomfortable or infrequent bowel movements, hard stool and painful defecation") and recommend we instead use the term "paralysis of lower GI tract". CICM still call it constipation in Question 17 from the first paper of 2016. A rose by any other name, etc.
• Ileus (or "paralytic ileus", or  "pseudo-obstruction", as separate from "post-operative ileus" and actual bowel obstruction) is the occurrence of intestinal blockage in the absence of an actual physical obstruction.
• "Ogilvie's syndrome" or colonic pseudo-obstruction obviously is the same as above, but specific to the colon. 

What additional investigations would help decide on the management of this problem?

• Chest Xray: to rapidly exclude bowel perforation, looking for gas under the diaphragm
• Abdominal Xray: findings identical to mechanical obstruction, i.e. dilated bowel loops
• CT of the abdomen: findings: gaseous dilatation of the colon with no stricture, mass or clear transition point. A "smooth transition" may be seen, which is a slight discrepancy in diameter between the proximal and distal bowel loops - less than 50% (Choi et al, 2008).

The imaging demonstrates dilated bowel loops in the small and large bowel, with gas throughout (down to the rectum). 
How will you manage this?

Supportive

• Nil by mouth
• Correct electrolytes
• Ensure the patient is well-hydrated
• Nasogastric tube on free drainage or low wall suction
• Rectal tube to gravity drainage
• Limit anti-motility medications, such as opiates and anticholinergic agents
  • Add non-opioid analgesia, eg. ketamine
• Mobilise the patient and sit them out ouf bed
• Alternative nutrition (i.e. TPN)

Aperients, laxatives:

• Stool softeners:
  • Coloxyl (docusate)
• Stimulant laxatives:
  • Sennocot
• Bulk-forming "soluble fibre" laxatives
  • Soy polysaccharide
  • Hydrolyzed guar (often already mixed with the NG formula)
  • Pectin
  • Psyllium
• Osmotic laxatives:
  • Lactulose
  • Polyethylene glycol
  • Sodium picosulfate (which forms magnesium citrate in the bowel)
  • Magnesium sulfate

• Enemas
  • "Microlax" 5ml sodium citrate/sorbitol enema
  • "Fleet" 118ml sodium phosphate enema

What are the pros and cons of aggressive pro-motility medications in this scenario?

Pharmacological (pro-motility) management

• Oral or nasogastric naloxone
  • Could absorb systemically and reverse the opioid analgesia
  • Needs to have gut transit/stomach emptying to work
• Methylnaltrexone
  • Only helps if the obstruction is mainly opioid-related
• Enemas
  • May lead to excess electrolyte loss or absorption
• Erythromycin
  • QT interval prolongation
• Neostigmine
  • Bradycardia

Pros:

• It is a preventible cause of delayed ventilator weaning and longer ICU stay
• Numerous studies have associated constipation with poorer outcomes
• Management options are largely cheap and benign
• Consequences of untreated constipation may be lifethreatening
• Arguments against the aggressive management of constipation are either theoretical (complaining about study methodology or heterogeneity of definitions) or arising from sloth (the constantly defecating patient is more difficult to care for from a nursing point of view).

Cons:

• Constipation may be relatively harmless.
  • Nassar et al, (2009): not associated with greater intensive care unit or hospital mortality, length of stay, or days free from mechanical ventilation. 
• The definition of constipation is far from scientific, as the three day cutoff is quite arbitrary. It is well known that ICU patients open their bowels infrequently. In the group who were declared "not constipated" by standard criteria (Guerra et al, 2013) the mean time until bowels opened was approximately 2.8 days on average.
• The association of constipation with worse outcomes may be merely reflective of its association with severe illness (i.e. patients whose illness is more severe also have more constipation, and - on an unrelated note- they also die more often and have a longer stay in ICU).
• Abdominal distension may worsen with laxative use
• Fluid losses will increase with more frequent liquid stools
• Electrolyte derangement may develop due to high volume diarrhoea resulting from laxative use
• Liquid stools can become difficult to manage from a nursing workload point of view, as well as in terms of infection control and wound contamination
• Bowel perforation or hyperphosphataemia may result from the excessive use of enemas

How would you administer neostiogmine in this case?

• This is a therapy supported by a small number of RCTs, all of which in turn had a small number of patients, such that when Valle & Godoy (2014) tried to do a meta-analysis on this, they turned up only 127 patients.
• A single dose of neostoigmine seemed to resolve colonic pseudo-obstruction in 89.2% of patients.
• In ICU patients, Van der Spoel et al (2001) used a continuous infusion of 0.4-0.8mg/hr, with similar results (they put 5mg in 50ml syringes and started the infusion at 4ml/hr, in case you are wondering) 
• The use of neostigmine would 

Is there any surgical or interventional management available? What are their advantages and disadvantages?

Lots of available options, all of which end with decompression:

• Sigmoidoscopy
• Colonoscopy 
• Surgical decompression (i.e. laparotomy)

Advantages are:

• You release the pressure, which reduces the extraintestinal effects (eg. abdominal compartment syndrome and respiratory failure)
• The improved perfusion of the gut should lead to improved gut function

The disadvantages are:

• More anaesthetic (therefore, more ileus)
• Unless there are adhesions to release, this does not fix the underlying problem (possibly makes it worse)
• By reperfusing the gut, you could cause a "septic shower", creating haemodynamic instability

Disclaimer: the viva stem above may be an original CICM stem, acquired from their publicly available past papers. Or, perhaps it is a slightly altered version of the original CICM stem. Or, it is a completely original viva stem, concocted by the monstrously amoral author of Deranged Physiology for nothing more than his own personal amusement. In either case, because the college do not make the main viva text or marking criteria available, almost everything here has been confabulated. It might sound like a plausible viva and it could be used for the purpose of practice, but all should be aware that it does not represent the "true" canonical CICM viva station.