Question 16

College answer

Syllabus topic/section:

2.1.6    Gastrointestinal Intensive Care: Enteral and Parenteral nutrition: L1
2.1.21 Applied pharmacology: Gastrointestinal

Discussion: 

In general, most candidates were able to answer this question to a reasonable standard with good answers allocating judicious time to sub-sections that had just 2 marks each and answering the final sub-section on management (worth 4 marks) in more detail.

Candidates that did well in part a) provided a structured outline to their list of aetiologies which helped them to include a broad range of reasons.
Clinical signs consistent with feeding intolerance like distended abdomen, high gastric residual volumes and vomiting are common clinical signs that along with the radiological features on X-Ray and CT were expected. Some candidates completely omitted part b) of the question, it was unclear if this was due to misreading the whole question or lack of knowledge.
Candidates are reminded to read the question carefully and provide FOUR major complications as instructed. Additional complications beyond 4 did not attract marks.
Good answers for part d) included a structured approach to medications which treat both constipation and gut dysmotility, alternative feeding strategies (eg post pyloric) as well as treatment of the underlying cause and precipitating factors/complications.
 

Discussion

a) Causes of poor feeding tolerance:

• Poor cardiac output and poor perfusion
• Tissue oedema
• Raised intraabdominal pressure
• Impaired intestinal nervous system activity due to the effect of opioids and anticholinergic agents
• Electrolyte disturbances (potassium and magnesium especially), acidosis
• Abdominal surgery
• Immobility
• Gravity/pressure effects (eg, due to prone positioning or left lateral position with the antrum dependent)
• Mechanical obstruction or surgical causes

b) Expected clinical signs:

• Abdominal distension
• Abnormal bowel sounds
• Bile-stained NG aspirate
• Large gastric residual volume (>500ml)

Expected radiological findings:

• Large gastric bubble
• Distended stomach and bowel loops
• Differential air-fluid levels or air filled loops
• Enlarged (but not inflamed) gallbladder, suggesting that it has not emptied for some time
• Specific imaging (eg. serial contrast studies to observe the rate of gastric emptying) that demonstrates a retention of contrast
• CT or MR enterography suggestive of poor motility and dysfunctional peristalsis
• Contrast from last week's imaging still visible in the bowel lumen

c) Complications of feed intolerance:

• Inadequate nutrition
• Risk of aspiration
• Increased gut wall stress (and therefore risk of ischaemia and perforation)
• Erratic drug absorption (some tablets will surely be aspirated along with those 500ml 6-hourly residuals)
• Nausea and discomfort
• The ventilator consequences of abdominal distension (i.e. reduced FRC)
• Complications of TPN (lines, infected lines, LFT derangement, etc)
• Toxicity of prokinetics (QT prolongation, dystonic reactions)
• Toxicity of antiemetics
• Increased risk of gut translocation (due to lost enteric trophic stimulus)

d) Management of feed intolerance:

• Address immediately worrying possibilities:
  • Exclude surgical causes for feed intolerance, eg. bowel obstruction or ischaemia
• Reverse the reversible physiological contributors:
  • Correct acidosis and electrolyte disturbance
  • Address tissue oedema
  • Correct shock and acidosis
• Encourage gut perfusion:
  • Extubate the patient, or at least wean them to a spontaneous mode to permit movement of the diaphragm, which should reduce abdominal venous congestion
  • Decompress the distended gut by NG drainage
• Minimise the negative/maximise the positive contribution from drugs:
  • Transition to non-opioid and opioid-sparing agents
  • Consider delirium management options which do not have anticholinergic effects
  • Start prokinetics (reasonably benign):
    • erythromycin and metoclopramide 
• Maximise the potential for gut transit:
  • Position the patient as upright as possible
  • Choose the smallest tube possible to reduce the stenting effects on the upper gastro-oesophageal sphincter
  • Use continuous, rather than bolus feeds
  • Reposition the NGT beyond the pylorus
  • Insert an NJT (nasojejunal tube) and keep the NGT to decompress the stomach
• Reassess nutritional goals and aim to have them met within 72 hrs:
  • Determine the nutritional requirements in better detail
  • Use lower volume feeds (higher nutrient concentration)
  • Return half (at least 250ml) of high aspirates
  • Minimise interruptions to continuous feeds
• Add supplemental PN if nutritional goals remain unmet at the end of 1 week, or earlier if the patient is significantly malnourished