The ASA Committee on Pain Medicine, in their 2010 Statement on Anesthetic Care During Interventional Pain Procedures for Adults, wrote: “It is the opinion of the Committee that the majority of minor pain procedures, under most routine circumstances, do not require anesthesia care other than local anesthesia.” They also stated: “The use of sedation and anesthesia must be balanced with the potential risk of harm from doing pain procedures in a sedated patient, especially those undergoing cervical spine procedures.” Despite these policy statements, an increasing number of patients receive sedation for interventional pain procedures. Patients increasingly expect to be sedated, particularly since moderate to deep sedation has become the norm for all GI endoscopies. As physicians’ reputations and even reimbursement can be tied to patient satisfaction scores, it may be difficult to turn down patients’ requests for sedation.

The general perception is that sedative and analgesic agents, when used properly, are safe and improve patient satisfaction, reduce procedure times, and stabilize hemodynamic status,¹ but there are significant risks, particularly when administered to patients in the prone position by personnel who are not trained to administer anesthetic agents. This article will present some of the adverse consequences associated with sedation for pain management interventions. Some suggestions for minimizing risk are provided by the authors based on literature review plus academic and private practice clinical experience.

Definitions²

The ASA House of Delegates approved the following definitions for the levels of sedation on October 13, 1999 (and amended them on October 21, 2009):

“Minimal sedation (anxiolysis)

A drug-induced state during which patients respond normally to verbal commands. Although cognitive function and coordination may be impaired, ventilatory and cardiovascular functions are unaffected.

Moderate sedation (’’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. Cardiovascular function is usually maintained.

Deep sedation

A drug-induced depression of consciousness during which patients cannot be easily aroused but respond purposefully after 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.”

Airway Compromise

Moderate to deep sedation poses a risk for airway obstruction and hypoventilation. When administered by non-anesthesia personnel with limited airway management experience, the risks are compounded. The prone position severely compromises one’s ability to regain airway control during periods of obstruction or hypoventilation, and may require cessation of the procedure and repositioning the patient supine. Even short periods of airway obstruction during prone sedation can cause negative pressure pulmonary edema.³

Minimal to moderate sedation is usually administered by non-anesthesia personnel under the direction of a physician, often the individual performing the procedure. By definition, the patient should remain verbally responsive and cooperative throughout. The supervising physician as well as the individual administering medications and monitoring the patient should maintain verbal contact with the patient. Midazolam is the most commonly used sedative/anxiolytic. It should be given in small incremental doses, allowing adequate time between doses to observe the effect of that dose. Small doses of opioid, used to reduce positional or procedural pain, can be effective, but increase the risk of hypoventilation.

The use of propofol to achieve moderate sedation is becoming more widespread because it permits more rapid recovery. However, its use increases the risk of hypotension, hypoventilation, and airway obstruction. Patients sedated with propofol may rapidly progress from a state of moderate sedation to deep sedation or general anesthesia. The 2002 ASA Guidelines for Sedation and Analgesia by Non-Anesthesiologists states, “Even if moderate sedation is intended, patients receiving propofol or methohexital by any route should receive care consistent with that required for deep sedation. Accordingly, practitioners administering these drugs should be qualified to rescue patients from any level of sedation, including general anesthesia.” Small miscalculations in the incremental dose can lead to rapid desaturation and hypotension. In the prone position, airway compromise is more likely and is difficult to manage. The manufacturer’s recommendation for the administration of propofol for MAC sedation is that it “should be administered only by persons trained in the administration of general anesthesia and not involved in the conduct of the surgical/diagnostic procedure.” There are no manufacturer’s recommendations for its use in minimal or moderate sedation. In 2004, the ASA and AANA issued a joint statement supporting the package insert warning label quoted above. A group of 21 European national societies of anesthesia have adopted a consensus statement that bans the use of propofol by non-anesthesiologists.⁴ The ASA Closed Claims Project, investigating reports of out-of-operating-room events, determined that the majority of claims involved respiratory compromise during MAC. A third of these involved the use of propofol combined with other sedatives or analgesics.⁵ Use of capnography in moderate to deep sedation, now an ASA standard, should provide earlier detection of bradypnea or apnea, and guide titration of anesthetic agents.

Even when trained anesthesia personnel are administering sedation or MAC anesthesia, circumstances compromising patient safety can occur. One such condition can occur if the operating physician requests that the anesthesia professional administer propofol or deepen the level of sedation. The operating physician may be unaware of the risks involved with deeper levels of sedation in the prone position, and the anesthesia professional may feel compelled to do so even if it is deemed unsafe, because concern regarding job security may trump safety concerns.

One final concern regarding propofol is the unusual but serious complication of seizure-like phenomena, which are associated with apnea and rapid desaturation.⁶ Prompt control of the airway is essential and could be delayed for the patient in the prone position. The presence of personnel skilled in airway management is critical.

Disinhibition and Agitation

Paradoxical agitation and hyperactivity can occur following the administration of sedative agents. It is most likely to occur during deep sedation,⁷ and is probably rare during minimal sedation (no case reports found). If agitation occurs during needle placement for a neuraxial procedure, injuries may result. Uncontrolled movements can aggravate pre-existing cervical spine pathology. When it is associated with the use of benzodiazepines, administration of flumazenil is likely to reverse the agitation.⁸ When caused by propofol, the only options are to allow spontaneous recovery, or to induce general anesthesia.

Predisposition to Neural Injury

When performing epidural injections in the cervical, thoracic, or high lumbar segments of the spine, direct needle injury to the spinal cord is a potential risk. Needle contact with the cord is likely to elicit a strong paresthesia. The use of moderate or deep sedation may block the patient’s perception of a needle induced paresthesia, increasing the likelihood of accidental injection of material directly into the cord.⁹ Needle penetration of the cord is not likely to produce widespread injury unless significant bleeding occurs. On the other hand, injection into the cord will most likely produce a substantial neurological injury.

Patients with severe spinal stenosis are at risk of neurological injury when epidural pressure is increased, particularly in the cervical spine. In the awake, non-sedated state, injection of small volumes of drug may produce significant discomfort or paresthesia, prompting the physician to limit the volume used. If sedation and analgesics blunt these sensations substantially, larger volumes may be injected, increasing the chance for injury.

When performing radiofrequency denervation procedures, electrical stimulation is often used to minimize the chances of injury to adjacent nerves. Stimulation prior to medial branch RFA will produce both sensory and motor effects on nerve roots supplying the upper or lower extremities if the needle position is incorrect. While motor effects of stimulation are preserved, the sensory effects may be lost during moderate to deep sedation.

Confounding of Diagnostic Information

The use of opioid analgesics as adjuncts to minimal or moderate sedation can compromise information gathered during diagnostic procedures. Opioids will change the threshold pressure at which pain occurs during discography. During diagnostic selective nerve root injection, it is important to determine if the paresthesia elicited during needle positioning or anesthetic injection reproduces the distribution of the patient’s pain. Likewise, during facet or sacroiliac joint injection, it is useful to know if the patient’s clinical pain is reproduced during injection. The use of moderate to deep sedation, particularly when opioids are administered, can significantly blunt these sensations. Continued post-procedure opioid effects will limit the patient’s ability to assess the pain relieving effect of the diagnostic procedure.

Cost

The use of sedation can significantly increase patient care costs. Added facility charges and drug costs are incurred, and the additional recovery time will be billed.

Summary of Authors’ Suggestions

• Avoid sedation for relatively short, uncomplicated procedures unless there is significant anxiety or pain with positioning.
• Avoid deep sedation in the prone position. Maintain continuous verbal contact with prone patients.
• Provide minimal to no sedation for neuraxial procedures at or above the L-2 level.
• Avoid propofol sedation for pain interventions.
• Avoid or minimize the use of opioids for patients undergoing diagnostic interventions.
• Avoid deep sedation for patients undergoing neuroablative procedures that employ electrical stimulation to localize needle position.

Stephen E. Abram, MD
Professor, Department of Anesthesiology
Medical College of Wisconsin, Milwaukee, WI

Michael C. Francis, MD
New Orleans, LA

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References

1. Schaufele MK, Martin DR, Tate JL, et al: Adverse events of conscious sedation in ambulatory spine procedures. The Spine Journal 2011;11:1093–1100.
2. Continuum of depth of sedation definition of general anesthesia and levels of sedation/analgesia. ASA House of Delegates. October 13,1999. Amended on October 21, 2009. Accessed from the world wide web at http://www.asahq.org/For-Members/Standards-Guidelines-and-Statements.aspx on August 22, 2012.
3. Omar H, Kolla J, Anand A, et al: Negative pressure pulmonary edema in the prone position: a case report. Cases J 2009;2:8594.
4. Perel A: Non-Anesthesiologists should not be allowed to administer propofol for procedural sedation: A consensus statement of 21 European national societies of anaesthesia. Eur J Anaesthesiol 2011;28:580-584.
5. Metzner J, Domino KB: Risks of anesthesia or sedation outside the operating room: The role of the anesthesia care provider. Current Opinion in Anesthesiology 2010;23:523-531.
6. Walder B, Tramèr MR, Seeck M. Seizure-like phenomena and propofol: A systematic review. Neurology. 2002;58:1327–32.
7. Braidy HF, Singh P, Ziccardi VB: Safety of deep sedation in an urban oral and maxillofacial surgery training program. J Oral Maxillofac Surg 2011; 69:2112-2119.
8. McKenzie WS, Rosenberg M: Paradoxical reaction following administration of a benzodiazepine. J Oral Maxillofac Surg 2010;68:3034-3036.
9. Hodges SD, Castleberg RL, Miller T, et al: Cervical epidural steroid injection with intrinsicspinal cord damage. Two case reports. Spine 1998;23:2137-2142.