With so much emphasis on fast-tracking patients through the surgical process, inhalational anesthesia is viewed as the tortoise of ambulatory surgery. Slow, steady, but in this case not winning the race against the hare-like efficiency of conscious sedation and regional blocks.
Inducing your patients with a facemask may never match the throughput times of anesthesia's less-sedative options, but it's still possible to improve the efficiency of general anesthesia. By choosing the right inhalation agent, working to reduce PONV and taking advantage of the latest in brain-wave monitoring, your patients will recover faster and head home sooner.
Hitting the gas
Certain inhalational agents are suited for ambulatory surgery because they allow for rapid induction and rapid recovery. For short cases, the differences between agents are negligible in the hands of an experienced anesthesiologist. The one your staff uses is likely dependent on the personal preference of your anesthesia provider, but here's the inhalational agents commonly used in outpatient surgery today.
- Isoflurane. Before the emergence of desflurane and sevoflurane, isoflurane was the most widely used inhaled agent. Low-priced isoflurane is still used for anesthesia maintenance when combined with a propofol induction, but it is no longer the preferred gas. It has a pungent odor and tends to irritate the airway, making it less accepted by patients and anesthesiologists for mask induction than desflurane or sevoflurane.
- Desflurane. This agent has the lowest solubility in blood and body tissues of all the anesthetics, which allows for greater control over maintenance of anesthesia and the fastest recovery post-op. Some studies have shown the emergence from desflurane anesthesia is quicker than from isoflurane and sevoflurane. Also, patients may recover cognitive motor skills more rapidly when you use desflurane. A common adverse effect of this agent, however, is airway irritation during induction.
- Sevoflurane. Like desflurane, it demonstrates rapid induction and recovery and fast changes in administration. But unlike desflurane - and all other inhalational agents - sevoflurane doesn't cause a reflex response or airway irritation during induction. For those reasons, this agent is very popular in outpatient and pediatric surgery cases.
I prefer to use sevoflurane. It's comfortable to breathe, making it especially effective in cases involving heavy smokers and patients suffering from other lung issues. More importantly, sevoflurane lets me put patients under quickly and recover them rapidly in the PACU.
But what works for me might not work for another anesthesiologist. I know of colleagues who prefer to use isoflurane in ambulatory surgery because it works quickly and is the cheapest of the inhalational agents. It's a game anesthesiologists play along with facility managers - should you go with the more expensive agents (desflurane and sevoflurane), or can you get by with the cheaper drug (isoflurane) without negatively affecting patient comfort or outcome?
I recommend using the more expensive drugs for longer procedures; they let anesthesiologists maintain the anesthesia effectively during the extended time the patient is unconscious. Also, isoflurane's effects become detrimental to rapid recovery after building up in the body during long procedures. When used in short procedures, however, any of the three agents are effective, so go with the cheaper isoflurane.
Decreasing patient recovery time is a key goal in increasing inhalational anesthesia efficiency. A critical part of that goal is controlling pain and PONV - the two most common reasons for delays in discharge.
For controlling pain, I often employ regional blocks and local anesthetic. Narcotics may increase the risk of side effects - PONV, sedation and respiratory depression. Local anesthetics do the job for me. However, I caution all my patients to take their oral pain medications before the local anesthesia wears off. By staying ahead of pain, patients remain comfortable.
Other anesthesiologists, however, use oral medications to great success. There's a whole host of medications out there, from NSAIDs to COX2 inhibitors. Many surgical departments give these pain meds during the pre-op process so they're starting to work as the patient awakens after surgery. Talk to your surgeons and anesthesiologists. Take an informal poll to see which protocol they prefer to follow. There's no right or wrong answer, but I believe narcotics tend to slow down the recovery process and may increase the incidence of post-op PONV.
A greater emphasis on regional anesthesia can facilitate the total elimination of emetogenic opioids or at least a significant reduction in the routine use of opioids.
PONV is an especially important concern in high-risk patients (for example, non-smoking females with positive histories of PONV or motion sickness who are having elective cosmetic surgery longer than two hours). Antiemetics for PONV therapy like Decadron (dexamethasone) and 5HT3 receptor antagonists like Zofran (ondansetron) are far more effective when there is no emetogenic trigger (for example, opioids or inhalational anesthetics or when dealing with a low-risk patient group).
While there isn't a set time to administer dexamethasone or ondansetron, I do so at the beginning of the procedure. Some anesthesia providers give it before they administer anesthesia and some give it post-operatively if the patient begins to feel nauseated. Anesthetists usually give it in conjunction with other antiemetics, and the timing of administration will usually depend on which other antiemetics they gave first or the number of PONV risk factors the patient has.
Head start on recovery
The biggest factor in improving the efficiency of inhalational anesthesia involves giving the appropriate amount of anesthetics in the OR. Titrating anesthesia to a patient during surgery used to be an inexact art, but recent developments in technology have brought it closer to being an exact science.
Twenty years ago, anesthesiologists judged a patient's level of sedation based on vital signs; heart rate, blood pressure and eye movements were closely monitored to determine the depth of unconsciousness. Within the last 10 years, however, we've learned those vital signs don't correlate well with a patient's true level of sedation.
The advent of Bispectral Index monitoring devices is a significant development in improving anesthesia efficiency. But based on recent newspaper headlines and reports on the six o'clock news, you'd think these devices were invented to prevent the occurrences of anesthesia awareness. While BIS monitors clearly help to reduce awareness occurrences, I consider these devices much more valuable for titrating anesthetics. They are efficiency - not awareness - monitors and are an essential tool to improving your patients' recovery times.
Through the use of sensors attached to the patient's forehead, BIS monitors judge the depth of anesthesia based on brain waves (the anesthesiologist's target organ) as opposed to determining sedation levels based on the inaccuracies of vital signs.
BIS numbers range from 0 to 100, with higher numbers signifying a greater level of consciousness (a patient who is fully awake has a BIS reading of 100). A greater dose of anesthetic agents will depress brain waves, resulting in lower BIS readings. Anesthesiologists don't need a great deal of anesthetics to suppress the pain and reflexes of a surgical incision, and BIS monitors let us titrate anesthetics to the specific needs of individual patients. Some elderly patients don't need as much anesthesia as a young football player, and BIS monitors let anesthesiologists take the guesswork out of dosing levels.
The optimal BIS measurement during surgery is between 45 and 60; that's the depth at which patients are adequately anesthetized, but not to a level that's too deep to affect recovery. By constantly measuring brain activity, anesthesiologists get accurate readings of the patient's reaction to the dose of anesthesia. We administer a small amount of anesthetic, watch for its effects on the patient's level of sedation and quickly determine if he needs more or less anesthetic. The BIS monitors let us constantly change the level of medication so we give just the amount patients need. We avoid overdosing and patients come out of sedation quicker because we use less drugs. The result: improved recovery times.
Despite the obvious benefits of using a BIS monitor, they're not yet commonplace in all surgical facilities; only about one-third of ORs in the United States are equipped with one, according to most industry estimates. I believe administrators don't want to add another expense to their capital equipment budget, but a BIS monitor can decrease surgical problems, improve the recovery times of patients and possibly increase the amount of cases you can do in a day. I used a BIS monitor to measure the fast-tracking of surgical patients and published the study's results in Anesthesiology (2004, volume 101, Abstract 291). My fellow researchers and I tracked numerous recovery parameters in patients for several months, both before and after the use of a BIS monitor during surgery. We found patients' recovery times dramatically decreased, fast-tracking increased and the post-op acuity of patients markedly improved.
As you can see, improving efficiencies with inhalational anesthesia starts with a BIS monitor. Providing your anesthesiologists with one will let them titrate anesthetics and improve recovery times. The better your anesthesiologists perform in the OR, the quicker your patients will reach recovery parameters in PACU, and the better your case throughput will be.
Anesthesia News and Notes
' A bill in West Virginia would force office-based oral surgeons to have a nurse anesthetist, another dentist trained in anesthesiology or an anesthesiologist in the procedure room with them when they administered anesthesia. The parents of a 13-year old girl who died while under general anesthesia for an orthodontic procedure spearheaded the bill. Currently, oral surgeons control patient sedation themselves, with the help of a trained dental assistant. Dentists in West Virginia say the bill would make oral surgery too expensive for an office setting. They prefer the state's Dental Board proposal (HB2929) of increasing the training and equipment requirements for dental offices using sedation.
' The FDA approved the use of Zofran (ondansetron) for PONV prevention associated with general anesthesia in children as young as 1 month old. Zofran was previously approved for use in children 2 years old and older.
' Researchers at Duke University Medical Center believe a combination of Versed (midazolam), Pentothal (sodium thiopental) and isoflurane as a means of general anesthesia on pregnant mothers has no negative effects on the fetus's developing brain. Researchers say this anesthetic regimen also appears to improve the oxygenation of the fetal brain, likely because of the presence of isoflurane. The Duke team studied pregnant sheep when the fetus was 17 weeks old - an age that approximates a third-trimester human pregnancy.
- Compiled by Daniel Cook