Merriam-Webster's Unabridged Dictionary defines the adjective conscious as "perceiving, apprehending, or noticing with a degree of controlled thought or observation" and the noun sedation as "the inducing of a relaxed easy state especially by the use of sedatives".  The label conscious sedation (CS) was apparently introduced into medical lingo by Lee in a paper titled "The dental auxiliary and oxygen-nitrous oxide conscious sedation"(1), and the majority of the early (i.e., 1970s) Medline-indexed publications on this topic were from the fields of dentistry and oral surgery.  This is hardly surprising, as dentists and oral surgeons have a long relationship with nitrous oxide, the gas first identified around 1774 by the English chemist Joseph Priestley (1733-1804). While the scientific observation that nitrous oxide can provide analgesia is credited to Humphry Davy (1778-1829), it was an American dentist, Horace Wells (1815-1848) from Hartford, Connecticut, who recognized the medical potential of "laughing gas."  The fact that his 1845 demonstration of the laughing gas effect in the operating theater of Boston's Massachusetts General Hospital was widely perceived as a failure is irrelevant; it was, nonetheless, the birth of what, over the years, would become anesthesia.

The next step towards painlessness, the appreciation of the clinical usefulness of cocaine, came in 1884, when Carl Koller reported on topical anesthesia of the eye.  Shortly thereafter, William Halsted (1852-1922) performed infiltration anesthesia using cocaine.  In 1905, physician Albert Einhorn discovered a nonaddictive local anesthetic: procaine (Novocain).  It became the most popular local anesthetic for the next fifty years or so.

The combination of local analgesia (provided by infiltration with local anesthetics) and systemic effect (analgo-sedation provided by laughing gas in oxygen: Entonox^® ) was the basis for what was to be named "conscious sedation" and successfully practiced by dentists and oral surgeons for some time.

Patients who receive CS are only mildly sedated:  their protective reflexes are not compromised at any time, and spontaneous respiration is reliably maintained throughout the procedure.  The patients are able to speak and respond to verbal cues, communicating any discomfort they might experience to the provider.  CS greatly improves the perceived quality of life during painful procedures, contingent on the provision of adequate analgesia via other means.  This is exactly what happens when a sedative is given prior to a dental procedure, when analgesia is obtained thanks to infiltration of local anesthetics, or during surgery of the hand, when analgesia is obtained by means of an axillary plexus block.  The bottom line is that CS can work only when appropriate analgesia is co-provided.

Nitrous oxide has lost its lustre over the years.  Maybe it is only another case of familiarity breeds contempt, but maybe not:  the fact is that laughing gas, and the machines required  to dispense it safely on demand, are rarer and rarer now a days, and sedation is achieved by administration of a Gamma Amino Butyric Acid - A(GABAA) agonist.  That in itself would not be bad, since GABAA-agonists are more user-friendly than NMDA-antagonists, the group to which laughing gas belongs.  The problem is the enormous economic pressure to use conscious sedation for an ever-increasing number of procedures that do not easily lend themselves to the use of CS because appropriate analgesia can not be obtained locally or regionally.

"Conscious Sedation "is linguistically an oxymoron, a combination of words that seem to contradict one another(2,3).   From a practical point of view, it is the sort of situation where you want to have the cake and eat it, too.  Here is where Marketing 101 kicks in:  if it does not fly (off the shelf), rename it.  So CS redux becomes  "procedural sedation".  While the paternity of the name is unknown to me, it was first used in the title of a PubMed-listed publication in the early 1990s(4).   It took some years until this term stuck, and most of the literature referring to it is from emergency medicine and plastic surgery.

The main problem with CS, however, was not so much the correctness or not of the name; it was the attempt to expand the technique beyond its original limits that was fundamentally flawed. Without appropriate analgesia (to be obtained locally or regionally), mild sedation did not allow the performance of any but the most minor procedures while assuring a comfortable state for the patient.  So, if some diazepam and a touch of meperidine were not enough, then doctors said, "Let's use more of the same".  It worked, in the sense that mild sedation became deep and then deeper (anesthetic) sedation, and unrecognized apnea caused scores of fatalities(5).

At about the same time, somebody must have noticed that sedation is not very good at making people comfortable when they are in pain (that's why normal folks take Panadol, and not Valium, when they have a headache).  The name was extended to procedural sedation and analgesia, which is, like it or not, procedural anesthesia(6,7).

Well, we are getting somewhere (at least language-wise):  what is described is a state of appropriate painlessness and reduced cognitive function sufficient for the patient to tolerate comfortably (one more oxymoron) the planned procedure.  In addition, it must allow for quick patient turnover and rapid discharge.  Procedural anesthesia is being used in the vast majority cases for outpatients; thus the label becomes "outpatient procedural anesthesia (OPA)."  OPA is administered in hospitals and outpatient facilities (ambulatory surgery centers, doctors' offices) to facilitate procedures such as breast biopsy, vasectomy, minor foot surgery, minor bone fracture repair, plastic/reconstructive surgery, dental prosthetic/reconstructive surgery, or endoscopy (stomach, colon and bladder).  The number and types of procedures that can be performed using OPA have increased significantly as a result of new technology, state-of-the art drugs, and budgetary pressure(8).  "What's in a name? That which we call a rose by any other name would smell as sweet"  (Shakespeare, Romeo and Juliet , II, ii, 43).

But what is the fundamental difference between the original concept of CS and that of OPA?  The goal of CS was mild sedation, which, by definition, excluded loss of spontaneous ventilation and protective reflexes.  It did achieve the primary goal "comfort of the patient" but only in combination with adequate local or regional analgesia.  The purpose of OPA is a state of appropriate painlessness and reduced cognitive function sufficient for patients to tolerate the planned procedure comfortably; therefore, by definition it includes the possibility of deep analgesia and sedation, i.e., anesthesia.

The issue CS vs. OPA, or sedationist vs. anesthesiologist, is not a philosophical one:  it is simply that CS did not pass the "reality check" when the attempt was made to over-expand its role.  The Nirvana of a perfect world "where you throw in some benzodiazepine and you can perform almost any procedure on a happy patient, while not having to spend a dime on monitoring equipment and qualified support" just did not materialize.

So if outpatient procedural anesthesia (OPA) it is, what are the consequences?  The short answer is that there are guidelines out there to follow and lawyers to sue you, and none of them in short supply(9,10,11).  Obviously, while OPA will have to be tailored to both procedure and patient, some general rules apply in most, if not all, scenarios:

1.  Informed patient consent is required.
2.  The OPA provider who monitors the patient should  have no other responsibilities during the 
     procedure.
3.  The OPA provider who monitors the patient should remain with the patient at all times  
    during the procedure.
4.  The OPA provider must be qualified.
5.  An OPA protocol  should be filled  out during the procedure.
6.  Monitoring is required.
7.  An IV line should be in place.
8.  Supplemental oxygen must be available.
9.  Resuscitation drugs and equipment must be available in the room where OPA is performed.
10. After OPA, the patient should remain in a dedicated room under supervision for an 
    appropriatelength of time.

While the majority of these guidelines are self-explanatory, two issues require discussion.