Normal response to verbal stimulation
Purposeful response to tactile or verbal stimulation (reflex withdrawal to pain is not purposeful)
Purposeful response after repeated or painful stimulation (reflex withdrawal to pain is not purposeful)
Unarousable, even with painful stimulus
No intervention needed
Intervention may be needed
Intervention often needed
May be inadequate
May be impaired
Moderate sedation and analgesia is often referred to as conscious sedation. Many colonoscopies are performed under “conscious sedation.”
Anesthesia providers must be trained to rescue patients from deeper levels of sedation than were intended .
Patients presenting for colonoscopy may be at increased risk of aspiration and aspiration pneumonia, particularly when deep sedation is used .
Deep levels of anesthesia are known to obtund upper airway protective reflexes.
In one study, aspiration occurred in 0.16 % of colonoscopies . Most of these patients received propofol for sedation.
Swallowing impairment occurs with deeper levels of sedation. Aspiration due to swallowing impairment may occur at common infusion targets used during deep propofol sedation .
The swallowing reflex completely returns about 15 min after return of consciousness when propofol is used .
The swallowing reflex is depressed for 2 h after return of consciousness following midazolam use during colonoscopy .
Increased patient age and high BMI are additional risk factors for swallowing impairment with propofol .
Split-dose bowel preparation solutions may be given before colonoscopy. Better bowel preparation is obtained with split-dose regimens as long as the “runaway time” or time since the last dose of oral bowel preparation solution does not exceed 5 h .
Patients receiving split-dose bowel preparation solutions have similar residual gastric volumes to patients that were given single dose solutions the night before examination .
In most patients, a 2 h fasting period should be sufficient after the second dose of bowel preparation solution.
A thorough history will reveal conditions which may predispose the patient to gastric aspiration.
Passive regurgitation with aspiration is a proposed mechanism during colonoscopy .
Initial management of aspiration in a deeply sedated or completely anesthetized patient consists of aggressive suctioning in the head down position and possible tracheal intubation with suctioning prior to initiation of ventilation .
In high risk patients, in addition to strict adherence to fasting guidelines, pharmacotherapy with proton pump inhibitors, H-2 blockers, antacids, and/or prokinetic agents may be warranted.
Endotracheal intubation for airway protection in high risk patients may be indicated.
Difficult Mask Ventilation
As depth of sedation increases, so does the likelihood of requirement of airway and ventilatory intervention.
Screening patients for potential difficulty of mask ventilation cannot be underestimated.
In patients with a difficult mask ventilation, the risk of difficult intubation may be increased four times .
Box 8.1. Difficult Mask Ventilation Predictors
Age older than 55 years
BMI >26 kg/m2
Lack of teeth
Presence of beard
History of snoring or sleep apnea
Mallampati III or IV
Limited mandibular protrusion
Airway mass or tumor
Neck circumference >40 cm
Patient Expectations of Sedation
Many patients expect to be totally unconscious during colonoscopies and are unaware that they may be aware during parts of the procedure.
Patients who have not received pre-procedural counseling about sedation or have never had a colonoscopy in the past are the most likely to have concern about awareness .
In a survey of patients prior to colonoscopy, anxiety about awareness during the procedure was more concerning than respiratory complications, vomiting, incomplete colonic examination, and post-procedural drowsiness .
A discussion about awareness during colonoscopy will improve patient expectations and satisfaction .
Patients should be monitored during colonoscopies according to the standards for basic anesthetic monitoring.
Oxygenation should be assessed continuously with pulse oximetry and exposure of the patient to assess color.
Ventilation should be evaluated by continuous end-tidal carbon dioxide analysis and other qualitative clinical signs which may include chest excursion and auscultation of breath sounds.
Circulation is assessed with continuous display of the electrocardiogram/heart rate and blood pressure determination at least every 5 min.
An EEG based monitor, including the bispectral index (BIS) or patient state index (PSI) monitor, may be helpful for determining depth of sedation. Although optional, use of these monitors may be beneficial in decreasing complications associated with deeper levels of sedation.
Placement of monitoring devices should be simple. The patient is typically in the lateral decubitus position and access to the patient’s airway should not be compromised by the endoscopist.
Depth of Sedation
Several factors must be considered when choosing depth of sedation for colonoscopies. Some of these factors are listed on Box 8.2.
Box 8.2. Depth of Sedation Considerations
In a recent study, depth of sedation during colonoscopy with propofol and fentanyl was examined . “Light” sedation was described as a bispectral index (BIS) of 70–80 and “deep” sedation was described as BIS of <60.
Patients receiving deep sedation had lower levels of recall, less patient movement, more hypotension, and more airway obstruction.
Patients with light sedation were still mostly satisfied despite a higher incidence of recall (12 % versus 1 %).
Recovery was more rapid with light sedation although, at hospital discharge, cognitive impairment was similar in both groups .
Typically, propofol based sedation is associated with deeper levels of sedation than non-propofol based sedation .
Deep sedation, as defined by the administration of propofol, is associated with an increased risk of aspiration, splenic injury, and colon perforation .
Titrating propofol administration to EEG based readings can help providers reduce the amount of time that patients are under deeper levels of anesthesia during colonoscopies. This should lessen the risks associated with deeper levels of sedation (aspiration, hypotension, respiratory depression, etc.), while still being able to utilize the clinical benefits of propofol .
A rapid, short acting benzodiazepine like midazolam is typically combined with a rapid, short acting opiate such as fentanyl.
Midazolam is known to have anxiolytic, amnestic, and sedative properties. It is also a respiratory depressant.
Benzodiazepines have synergetic effects with opiates that result in more profound sedation, respiratory depression, and hemodynamic compromise.
Fentanyl and other opiates offer analgesic and sedative qualities.
Fentanyl is known to cause respiratory depression and nausea, but like midazolam, a reversal agent is available.
Meperidine and morphine have a slower onset and longer duration than fentanyl. This makes fentanyl a more appropriate choice for colonoscopy.
Propofol has been increasingly used for sedation during colonoscopy.
A major advantage of propofol is its rapid onset and rapid offset.
Propofol provides sedation and amnesia; however, minimal analgesia is provided.
Shorter recovery times, return of cognitive function, and antiemetic properties are very useful.
Unfortunately, there is not a reversal agent for propofol.
Levels of consciousness may change rapidly during administration of propofol anesthesia.
Unintentional deep sedation or even general anesthesia, with depression in respiratory, cardiovascular, and neurologic function, may result due to rapidly changing levels of consciousness. Thus, the availability of a qualified anesthesia provider is critical.
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