Drs John Arnold and Anne Roberts, comment about the use of the term, no longer included in the American Society of Anesthesiologists standards.
By Drs John Arnold, staff anaesthesiologist at Sharp Mary Birch Hospital for Women, San Diego, CA, and Anne Roberts, Chief of Interventional Radiology and Executive Vice Chair of the Department of Radiology, UCSD Medical Center, San Diego, CA
The term ‘conscious sedation’, despite its common use in anaesthesia and non-anaesthesia literature, is no longer included in the American Society of Anesthesiologists (ASA) standards. Its use is discouraged because it is imprecise, potentially misleading, and somewhat of an oxymoron. Because sedation and anaesthesia are recognised by the ASA as points on a continuum, a more appropriate term is “moderate sedation”. What follows is the ASA’s description of the four points on the continuum:
Minimal sedation (anxiolysis) – A drug induced state during which a patient responds normally to verbal commands. Although cognitive function and coordination may be impaired, ventilatory and cardiovascular functions are unaffected.
Moderate sedation/analgesia (‘conscious sedation’) – A drug-induced depression of consciousness during which patients respond purposefully to verbal commands, either alone or accompanied by light tactile stimulation. No interventions are required to maintain a patent airway, and spontaneous ventilation is adequate.
Deep sedation/analgesia – A drug-induced depression of consciousness during which patients cannot be easily aroused, but respond purposefully following repeated or painful stimulation. The ability to independently maintain ventilatory function may be impaired. Patients may require assistance in maintaining a patent airway and spontaneous ventilation may be inadequate. Cardiovascular function is usually maintained.
Anaesthesia – Consists of general anesthesia and spinal or major regional anesthesia. It does not include local anaesthesia. General anaesthesia is a drug-induced loss of consciousness during which patients are not arousable, even by painful stimulation. The ability to independently maintain ventilatory function is often impaired. Patients often require assistance in maintaining a patent airway, and positive pressure ventilation may be required because of depressed spontaneous ventilation or drug-induced depression of neuromuscular function. Cardiovascular function may be impaired.
A 2006 review by R Robbertze et al of closed claims for anaesthesia procedures outside the operating room showed that, when adjusted for total number of procedures, the claims for deaths in non-operating room anaesthesia were more than two times those for operating room anaesthesia. They also showed that non-operating room anaesthesia claims had a higher severity of injury and more substandard care than operating room anaesthesia. The most common mechanism of injury was inadequate oxygenation/ventilation. With this background, it is important to emphasise that all patients receiving moderate sedation should have a standard of care similar to that of an operating room.
All programmes for moderate sedation should be monitored by and follow guidelines established by the hospital’s anaesthesia department. This should include a system to periodically evaluate job performance as well as current competencies and skills of those administering moderate sedation. Additional necessary qualifications are certification in Basic Life Support and/or Advanced Cardiac Life Support. In the US, specially trained registered nurses under the direction of the radiologist perform much of the moderate sedation in interventional radiology suites.
Appropriate patient examination
There should be a sufficient number of qualified personnel, in addition to the physician performing the study or therapy, to be present during a procedure using moderate sedation and to do the following:
1. Evaluate the individual receiving care prior to beginning sedation/anaesthesia, ie, complete a history and physical;
2. Perform the sedation/anaesthesia;
3. Perform the procedure (study/therapy);
4. Monitor the individual undergoing sedation/anaesthesia; and
5. Recover and discharge the individual either from the post-sedation or post-anaesthesia recovery area or from the organisation.
Pre-procedure evaluation of the patient includes a history and physical. Pertinent aspects of the patient’s history should include: (1) abnormalities of major organ systems, (2) current medications, (3) drug allergies, (4) previous experience with sedation/analgesia as well as regional and general anaesthesia, (5) pregnancy, (6) history of tobacco, alcohol, or substance abuse, and (7) time and nature of last oral intake. An additional aspect of the patient’s health that should be considered, in view of the current epidemic of obesity, is the individual’s body mass index.
Because most morbidity and mortality for patients receiving anaesthesia in a non-operating room setting is related to inadequate oxygenation and ventilation, often a result of airway obstruction, the patient’s history and physical should emphasise the airway. Patients at high risk include those with previous problems with anaesthesia; stridor, snoring, or sleep apnea; dysmorphic facial features (e.g. Pierre-Robin syndrome); and advanced rheumatoid arthritis.
Some physical exam issues of concern are those patients with significant obesity; short neck; limited neck extension; decreased hyoid-mental distance (<3cm); neck mass; small mouth opening (<3cm); protruding maxillary incisors; macroglossia; tonsillar hypertrophy; and non-visible uvula, among others. Many of these physical attributes may indicate that it would be difficult to secure the airway should the patient suffer an airway obstruction.
Pre-procedure laboratory testing should be individualised to the patient. For young, healthy patients, all that may be needed is a pregnancy test in women. In older patients, consideration should be given to obtaining a recent haematocrit, ECG, BUN, and/or blood glucose.
All patients receiving moderate sedation should follow the ASA Pre-Procedure Fasting Guidelines. For healthy adults without impaired gastric motility, this means a minimum of two hours of fasting following consumption of clear liquids and eight hours of fasting following consumption of a full meal including protein and fat.
Sedation and analgesia
After the patient is evaluated and determined to be a candidate for moderate sedation and consent is obtained, the next step is to perform the sedation and analgesia. Monitors that may be used include electrocardiography, pulse oximetry, and a devise to measure blood pressure. Observational aspects of monitoring include level of consciousness and respiratory rate. Additional monitors to consider are an end-tidal CO2 monitor (helps in the assessment of ventilation) or a processed EEG monitor that aids in measuring the depth of anaesthesia. All vital signs should be recorded at specified intervals. Supplemental oxygen may be administered through a nasal cannula or mask as needed. Once a steady state is achieved, the individual who is performing the moderate sedation may assist the physician doing the procedure with short, interruptible tasks. If the patient slips into a state of deep sedation, the individual giving the sedatives and analgesics should give their undivided attention to the patient and attempt to bring them to a lighter level of sedation/analgesia.
The medications for moderate sedation are relatively few, but practitioners administering them need to be familiar with their pharmacologic profile. Medications should be administered in small, incremental doses through an intravenous line. The primary sedative used today is midazolam (Versed), though diazepam (Valium) is also a potential choice. The use of propofol, a powerful sedative hypnotic used most commonly for induction of general anaesthesia, is controversial in settings outside of the operating room or intensive care setting. The narcotic used most frequently is fentanyl, although morphine, meperidine, or hydromorphone hydrochloride (Dilaudid)? may be better choices in situations requiring post-procedure analgesia. Though they should be rarely necessary, two reversal agents should be immediately available. The reversal agent for benzodiazepines such as midazolam is flumazenil and the reversal agent for narcotics is naloxone.
All settings where moderate sedation is administered should be adequately prepared for a respiratory or cardiac arrest. This includes not only the necessary equipment but also a mechanism for obtaining extra help to manage an arrest.
After the procedure, the patient should be transferred to an appropriate recovery area and monitored until they meet the discharge criteria established by the institution. They should be discharged from the hospital in the care of a responsible adult with instructions and a telephone number to call for emergencies.
The risks of sedation/analgesia may be increased by patient- and procedure- related factors. Uncooperative patients may require sedation to the point of general anaesthesia to remain still for a procedure for which others may need minimal or no sedation. There are extremely invasive procedures that even the most cooperative patient may be unable to tolerate with only sedation and analgesia. When the need for general anaesthesia is anticipated or becomes obvious during a procedure, it is prudent to enlist the assistance of an anaesthesiologist or nurse anaesthetist who is trained to care for patients who are deeply sedated or under general anaesthesia.
Due to staffing issues, it is rare that hospitals will have dedicated anaesthesiologists in the interventional radiology suite. If an anaesthesiologist is needed, the scheduled case will usually need to be arranged around the availability of that physician. Most anaesthesiologists prefer the productivity they can achieve in an operating room setting where cases are closely scheduled with minimal turnover times. If a similar arrangement could be accomplished in an interventional radiology suite, the attractiveness of giving anaesthesia in that setting would increase dramatically.