Intravenous sedation is a concept readily grasped by anesthesia providers, but perhaps not so easily comprehended by their clinical colleagues. While it seems like a clear and concise description, the many other terms often used in association with it - "monitored anesthesia care" (also known as "MAC anesthesia"), "conscious sedation," "twilight sleep," "light general" and so on - can create misleading ideas of what this simple expression is intended to convey. The net effect of so many names for the same concept can place anesthesia providers at the intersection of clinical practice and patient care politics. Here's a definition of what IV sedation really is, and what it means.

A sedation refresher course
The American Society of Anesthesiologists classifies sedation into four levels. According to their "Continuum of Depth of Sedation, Definition of General Anesthesia and Levels of Sedation/Analgesia" (www.asahq.org/publicationsandservices/ standards/20.pdf):

• Minimal sedation (anxiolysis) is a drug-induced state during which patients respond normally to verbal commands.
• Moderate sedation or analgesia ("conscious sedation") is a drug-induced depression of consciousness during which patients respond purposefully to verbal commands, either alone or accompanied by light tactile stimulation.
• Deep sedation or analgesia is a drug-induced depression of consciousness during which patients can't be easily aroused but respond purposefully following repeated or painful stimulation.
• General anesthesia is a drug-induced loss of consciousness during which patients aren't arousable even by painful stimulation.

You may have noticed that the term "monitored anesthesia care" doesn't appear in these definitions. That's because as a technique, it's a wider ranging concept than many clinicians realize. The term itself is evidence of a mild political controversy. The ASA coined that term in 1986 in response to the payment policies of Medicare carriers. Anesthesia providers believe that their presence during procedures constitutes anesthesia services, regardless of drugs administered. Medicare carriers, on the other hand, are for-profit insurance companies that receive bonuses from the federal government for decreasing annual reimbursements, and one way for them to do this is to minimize provider payouts.

Given this background of tension between providers and payors, between patient care priorities and business agendas, the ASA's House of Delegates has periodically amended its 1986 statement on MAC to give it general applicability. The 2005 "Position on Monitored Anesthesia Care" (www.asahq.org/publicationsandservices/standards/20.pdf) states that, technically, monitored anesthesia care involves "all aspects of anesthesia care - a pre-procedure visit, intra-procedure care and post-procedure anesthesia management," can involve "varying levels of sedation, analgesia and anxiolysis as necessary" and includes but is not limited to the following services:

• diagnosis and treatment of clinical problems that occur during the procedure,
• support of vital functions,
• administration of sedatives, analgesics, hypnotics, anesthetic agents or other medications as necessary for patient safety,
• psychological support and physical comfort, and
• provision of other medical services as needed to complete the procedure safely.

IV or not IV?
IV sedation, as it is understood in anesthesia practice, is not actually related to concepts such as "conscious sedation." That term is a political sticking point, popularized to justify the administration of anesthetic agents by non-anesthesia providers. It's also a term without significance or currency in anesthesia, since the parameters of sedation provided by trained anesthesia providers aren't limited by the presence or the absence of consciousness. As for "twilight sleep," the term is not descriptive in any meaningful sense, and "light general" is an oxymoron that doesn't deserve comment.

So what, exactly, is IV sedation? What are we trying to accomplish by its administration?

Any definition must encompass all the features of a standard definition of anesthesia, since anesthesia - including IV sedation - occurs over a continuum of responses rather than as a single discrete state. As a result, the effects of IV sedation may or may not be substantially distinguishable from those of general anesthesia, despite political or commercial desires for a quantifiable difference. (This indistinguishability is explicitly recognized in the ASA's MAC definition referenced above.)

And all of the effects of general anesthesia are addressed when providing IV sedation to a patient: amnesia, analgesia, hypnosis, arreflexia and akinesia. Neither we nor our patients want a painful experience; in fact, many pre-operative patients state that they "don't want to hear or remember anything." Vital signs are closely monitored to keep them within acceptable parameters and patient safety is paramount. The length of the procedure and the length of time during which patients will have to lie still directly impacts the depth of sedation administered. Other determining factors include the level of surgical stimulation, the patient's physical condition and drug tolerances, the surgeon's skill with local anesthesia and the anesthesia provider's skill in providing sedation.

Given these constraints, there is no single drug that can produce the above-listed range of effects at no risk to the patient. This inconvenient fact once again opposes political and commercial desires. The anesthetic continuum is dynamic: As physiological parameters vary during a procedure, there will be movement between different stages, and the risk-benefit calculation is continuous for every drug choice we make.

Drug notes
From a technical perspective, there are about as many methods of IV sedation as there are anesthesia providers. When an anesthesia provider decides that IV sedation is the best choice for a patient, the choice of technique and drugs is tailored to each patient's unique situation. This is the hallmark of IV sedation: appropriate evaluation and individualized drug choice, with every contingency pre-planned. It's in this way that IV sedation is not meaningfully different from any other anesthesia service.

Propofol, which is frequently employed for IV sedation, can be used either alone or in combination with any of the many narcotics available. Perhaps dexmedetomidine (alone or with other drugs) or etomidate, ketamine or even thiopental will meet a patient's need. Perhaps you'll select just a small dose of benzodiazepine. The choice of agents depends on the anesthesia provider's experience and the clinical situation, factors that will also impact the relative depth of sedation and whether the patient loses consciousness briefly or at all - although loss of consciousness won't be a central issue for an anesthesia provider.

As always, cautions must be observed. Non-anesthesia providers have advocated propofol for procedural sedation due to its excellent safety record. It should be strongly noted, however, that that safety record was created through its administration by trained anesthesia providers. Substantial literature also exists that makes reference to such anesthetic drugs as dexmedetomidine and ketamine as "sedatives" that offer airway protection with no untoward effects. Anesthesia providers don't share the belief that powerful drugs can be completely benign.

As an anesthetic service, IV sedation is not "one-size-fits-all." There is no single formulation that will meet every patient's individual requirements without risk. Certainly no anesthesia provider would say that IV sedation is necessarily easy to accomplish or that it offers the lowest risk in every clinical situation. In some situations, an anesthesia provider's judgment may be that general anesthesia is the technically easier or more appropriate choice.

The provider's skill
Once you choose sedation, it may remain intravenous in method or it may also include sublingual, oral or inhalational agents as the situation warrants. Customarily, it will still be called "IV sedation," even though it isn't necessarily confined to the IV route or sedative use only. Clinical research clearly demonstrates that an anesthetic service's excellence doesn't rest merely on the choice of pharmacologic agents, but is significantly influenced by the practitioner's abilities. So whether your choice of agents includes meperidine or remifentanil, promethazine or granisetron, thiopental or dexmedetomidine, keep in mind that it's the anesthesia provider's judgment and skill that governs the outcome of the anesthesia.