Types of Anesthesia
The administration of anesthesia agents to achieve a state of unconsciousness to produce the absence of pain sensation over the entire body. This can be administered by inhalation, intravenously, intramuscularly, rectally, or via the gastrointestinal tract. Basically general anesthesia is a drug induced loss of consciousness during which patients are not arousable even by painful simulation.
IV Sedation is not clearly defined such as the different levels of consciousness outlined by the ASA. We have seen this definition most frequently applied when the administration of anesthetic agents are administered by non-anesthesia providers. The term IV sedation also became more popular when the drug propofol is employed, either alone on in combination an any of the various narcotics available. We have heard the terms “Twilight Sleep” and “Light General”. IV Sedation may not be distinguishable even from general anesthesia as a definition must involve all the features of standard definition of anesthesia such as responsiveness, airway intervention, cardiovascular monitoring, ventilation. There are also many methods of IV sedation as each one is tailored to the patients unique situation. If you were to describe IV Sedation it would be a technique of sedation that is individualized based upon evaluation and drug choice with every contingency pre-planned. The difficulty in pinpointing a definition of IV Sedation stems from the fact that it is not different from any other anesthesia service.
The injection of a local anesthetic into the subarachnoid space around the spinal cord to achieve a level of decreased sensation.
An anesthetic agent that is introduced to an part of the body to produce a level of decreased sensation.
This is defined as the production of insensibility of a part by interrupting the sensory nerve conductivity from a particular region of the body.
The administration of a narcotic drug through an epidural catheter. When this is used as a therapeutic agent for a non surgical condition it should be reported under the appropriate pain management code.
Common Anesthetics Used
This is the most common IV induction agent and serves as the foundation for many moderate sedation regimens. Among its most popular features are:
Potency (it is very potent)
Possesses a clear dose-response sedative effect
Rapid onset of action (produces unconsciousness within one minute)
Clears quickly from the brain so there is no hangover effect
Seems to have antiemetic properties (prevents vomiting)
Promotes a sense of euphoria
Intraoperatively, the rapid clearance from the brain allows practitioners to quickly back out of inadvertent oversedation The final feature introduces the most concerning facet of this drug, its simplicity. Practitioners can easily underestimate propofol’s power rapidly pushing patients from moderate sedation to general sedation unexpectedly. The drug also carries a risk of myocardial depression which increases with higher blood concentrations. One of the most important factors to keep in mind is that IT HAS NO KNOWN REVERSAL AGENT. Immediate airway management could be required.
Ketamine produces a mild disconnected state. It can be used for Intramuscular injection or induction in uncooperative or disabled patients and children. Some may use small doses as additional narcotic to prevent post-op pain and minimize an opiod requirement. This drug also stimulates the cardiovascular system and at higher doses creates a hallucinogenic effect.
Midazolam’s roles in the administration of moderation sedation is to:
induce some amnesia
The fast onset action of this drug provides for quick anxiety reduction as administered in small doses. Keep in mind this is a benzodiazepine which means it slows down the central nervous system producing a state of sleepiness and loss of awareness. It is not an analgesia so it is not used for the treatment of pain. Some practitioners may use it to reduce the propofol requirement during Conscious Sedation. Emergence from higher doses can be slow so its use in the ambulatory setting is limited.
Another common drug, Fentanyl may be used to provide some baseline level of analgesia and patient comfort from emergence. It can even be used with regional anesthesia to alleviate pain. It has faster onset than morphine achieving peak effect in less than 4 minutes and clears quickly from the brain. You may have heard of other drugs such as Sufentanil, Alfentanil and Remifentanil as they are related to Fentanyl.