Patient preparation and principles of sedation in gastrointestinal endoscopy

Published on 13/02/2015 by admin

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28 Patient preparation and principles of sedation in gastrointestinal endoscopy


A 67-year-old male with a past history of mitral valve stenosis and insulin-dependent diabetes mellitis with moderate renal impairment requests his primary care physician to organise colon cancer screening. An open-access colonoscopy is arranged.

The patient presents for the procedure with moderate dehydration following preparation with three sachets of sodium phosphate solution. The patient is noted to be hypoglycaemic, having taken his usual dose of insulin that morning. He requests antibiotic prophylaxis for the procedure (as he has been told always to request this prior to invasive procedures). He is angry when this is refused and becomes more agitated when the consultant acquiesces and asks the nurse to prepare 1 g of ampicillin.

He is sedated with midazolam and fentanyl. During the procedure he receives oxygen supplementation but no capnography or pulse oximetry. He is uncomfortable during the procedure and complains that he is not ‘asleep’. He is given three further doses of midazolam, initially becoming more agitated, but eventually settling. After several minutes the nurse notes that he does not appear to be breathing. The medical emergency team is called but takes 5 minutes to respond. He is given flumazenil and becomes extremely agitated and tremulous. It is then noted that he takes valium for anxiety and temazepam at night.

This patient, although an extreme example, illustrates some of issues of appropriate preparation for an endoscopic procedure. The patient was given inappropriate bowel preparation, no instruction on the management of his insulin and no information about what to expect during the procedure. The proceduralist was correct not to recommend antibiotics, but his reasoning should have been explained and discussed rather than simply agreeing with the request and ordering penicillin without discussion. He had not had a chance to adequately discuss his history with the proceduralist, who did not know that he was allergic to penicillin, nor that he was on regular benzodiazepines. He was subsequently over-sedated for the procedure and had inadequate non-invasive monitoring.

‘Open access’ endoscopic services are relatively common, but if this type of service is to utilised it is paramount that the proceduralist have effective measures in place in order to obtain appropriate informed consent and identify patients for whom special issues regarding preparation are required. In short, the patient must understand the procedure and the proceduralist must understand the patient.

Preparing Patients for Endoscopy

Bowel preparation for colonoscopy

The quality of the bowel preparation prior to colonoscopy is critical in order to provide good views during endoscopy, and thus minimise the risk of missed lesions due to poor endoscopic views. The importance of this is illustrated by the fact that adequate bowel preparation is often included as a quality indicator in colonoscopy. The preparation is often regarded as unpleasant, and many patients are more concerned about the preparation than the actual procedure. As such, detailed explanation both verbally and written is important in order for this to be performed correctly and safely. If the bowel preparation is inadequate, the procedure may need to be deferred. It is important for patients to be informed that they should drink clear fluids only on the day prior to the procedure in addition to the bowel preparation in order to prevent dehydration, and to improve the effectiveness of the bowel cleansing. In addition, mobilising during the preparation may improve the effectiveness of the preparation, especially in the elderly.

The two main constituents widely used for bowel preparation are non-absorbed, isotonic solutions such as polyethylene glycol and low volume hypertonic solutions such as sodium phosphate and sodium picosulfate. Polyethylene glycol is an osmotic laxative that contains electrolytes in order to balance electrolyte shifts; as such it can be regarded as isoosmotic. It is mixed in a large quantity of water; for example the patient may need to drink a total of 3–4 L of fluid. This is usually taken the day prior to the procedure, but if a morning procedure it should be given as a ‘split’ preparation, where part of the preparation is given on the morning of the procedure. This may improve the effectiveness and tolerability of the preparation; however, it needs to be taken at least 4 hours prior to the procedure in order for the stomach to be empty, to reduce the risk of gastric aspiration.

Sodium phosphate (NaP)-based solutions work via a hyperosmotic mode of action, and can be given in much smaller volumes of water. As such, NaP is often tolerated better by patients. It can be combined with a polyethylene glycol-based regimen in order to improve tolerability and reduce volume. The NaP-based solutions do have some risks, including sudden fluid shifts within the body and precipitating acute phosphate nephropathy. Therefore, it should be avoided in the elderly and in patients with congestive heart failure or renal failure. In addition, caution is required if patients have an increased risk of electrolyte disturbance such as those with cirrhosis, small or large bowel dysmotility or other preexisting electrolyte imbalances.

The sodium picosulfate (Picoprep) preparation has no risk of phosphate nephropathy. Patients should be encouraged to drink fluids liberally during hypertonic-based bowel preparation. Patients with known or suspected inflammatory bowel disease may not be suitable for NaP-based preparations, due to an increased risk of causing preparation-related colonic inflammation compared to polyethylene glycol-based solutions.

Endoscopic retrograde cholangiopancreatography

Patients undergoing ERCP will be exposed to ionising radiation. Therefore women of childbearing age should have pelvic shielding during the procedure. If there is any possibility of pregnancy a serum or urinary β-human chorionic gonadotropin should be checked. Contrast medium in the bowel lumen can obstruct views of the biliary system, so patients who have recently had a CT scan with contrast or a barium study should have a plain abdominal x-ray to ensure the biliary system is not obscured. As iodinated contrast is used to inject into the biliary system, a history of iodine allergy or hyperthyroidism should be elicited, though history of a contrast allergy is not an absolute contraindication as the risk of an allergic reaction during ERCP is extremely low. Patients with biliary obstruction should receive prophylactic antibiotics prior to the procedure. Due to the risk of bleeding with sphincterotomy of the ampulla of Vater, elective patients on clopidogrel should ideally withhold this medication for 7–10 days if feasible. The risk is lower with aspirin (all therapeutic endoscopy can be performed on aspirin). Discussion with the patient’s cardiologist is prudent if there is uncertainty whether it is safe to withhold these medications. Coagulopathy should be reversed if present; patients on warfarin may need to change to low-molecular-weight heparin prior to the procedure depending upon the indication. The decision when to reinstitute anticoagulant therapy following therapeutic procedures such as ERCP and colonic polypectomy is a difficult one and should be individualised in consultation with the patient’s cardiologist.

Antibiotic prophylaxis

Advice regarding antibiotic prophylaxis prior to endoscopic procedures was significantly updated in American Society for Gastrointestinal Endoscopy guidelines (2008) based on the recognition from the American Heart Association that bacterial endocarditis from endoscopic procedures was exceedingly rare. For the majority of patients undergoing endoscopic procedures, including those with prosthetic heart valves or congenital cardiac abnormalities, antibiotic prophylaxis to prevent bacterial seeding was no longer recommended. There are however, certain situations in which the risk of infective complications (which may be local rather than systemic) is increased and antibiotics are warranted; these are listed in Box 28.1.

All patients with cholangitis require antibiotics; patients with biliary obstruction without cholangitis undergoing ERCP require antibiotics only if incomplete drainage is anticipated. Similarly, patients with diffuse sclerosing cholangitis should receive periprocedural antibiotics. There is insufficient evidence to recommend antibiotic prophylaxis for endoscopic ultrasound-guided aspiration of solid lesions, though it is warranted for cystic lesions or pseudocyst drainage.