Outpatient Surgery Magazine

Date Published: 
August 2006

5 Safeguards for IV Anesthesia

Last month marked the 29th anniversary of my start in private practice. My first case was with a plastic surgeon who arrived an hour late, then asked for IV sedation for an eight-hour facial case. I had no idea how to do such a thing. I ended up using 500cc IV bag, 500mg thiopental (Pentothal), 100mg meperidine (Demerol), 60 drop IV set (mini or pedi drip) oxygen by nasal cannula and local by surgeon. Amazingly, the case went well, but the patient was so hung over she had to sleep the night in the hospital. No one was shocked that a patient had to stay overnight after surgery.

Many of the tools that make anesthesia safe today weren’t around in 1977; namely, pulse oximeters (we didn’t get SpO2 until 1984), propofol (Diprivan hit the U.S. market in 1987) and level of consciousness monitors (FDA approved BIS in 1996). But there’s still room for us to make IV sedation safer.

1 Think safety first.
Any suite performing IV anesthesia must be equipped with oxygen, a positive pressure device (an Ambu bag, for example) and a suction device. Further, both a crash cart and defibrillator should be present. Personnel administering IV anesthesia must be prepared to rescue from deeper levels than intended. Specifically, they must be able to recognize airway obstruction and know how to open the airway. They must be able to ascertain whether the patient is breathing. Lastly, they must ensure that the patient has a blood pressure providing circulation of oxygen to the vital organs. These requirements are similar but profoundly different from the ABCs of the ACLS algorithm, which assumes that one comes upon an un-witnessed arrest. But healthcare professionals can never allow for such an eventuality when we assume to provide IV anesthesia to a trusting patient.

2 Understand your agents and their limitations.
Fentanyl (Sublimaze) is only a short-acting opioid in doses of 100ug or less. The short action is based on redistribution, not metabolism. You may administer doses of fentanyl greater than 100ug fentanyl, but you’ll absolutely need to monitor patients for the same duration as those having received meperidine (Demerol) or morphine.

The newest fentanyl cogener, remifentanil (Ultiva), is rapidly metabolized. However, you must take into account the rapid withdrawal of opioid effect upon discontinuance. If you don’t supply post-remifentanil analgesia, patients may suffer needlessly.

The use of opioids, especially post-operatively, is a well-recognized risk factor for PONV.1 Other risk factors merit the highest level of prophylaxis — non-smoking females with positive PONV or motion sickness histories. Highest risk patients should receive multimodal therapy including dexamethasone, ondansetron and droperidol (the latter no longer available in many institutions because of its FDA black box warning). Dimenhydramine (Dramamine) may be a reasonable substitute.2 Other modalities include scopolamine patches and acupressure wristbands.

Midazolam (Versed) as 5mg/cc is two-and-a-half times as potent as diazepam (Valium). The manufacturer unfortunately formulated midazolam in the same concentration as diazepam. Failure to appreciate potency differences has led to respiratory embarrassment of patients.

3 Define the level of sedation or anesthesia to be obtained.
IV anesthesia may include all four levels of sedation and anesthesia described by the ASA position on monitored anesthesia care (visit www.asahq.org for more information).

In the 1890s, Lord Kelvin remarked, “When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced to the stage of science.”

Lord Kelvin’s advice on the subject of temperature measurement, more than a hundred years ago, rings especially true today with respect to measuring the effect on the target organ of anesthesia, the brain. Unfortunately, benzodiazepines (which act primarily on the midbrain) aren’t well measured by any of the current level of consciousness monitors. On the other hand, (cortically acting) propofol is very well measured by BIS and other level of consciousness devices like Entropy.

I remember thinking back in 1977 how wonderful it would be to have a drug we could drip for eight hours that would simply go away at the end of the case. Propofol has achieved wide adoption because of its numerous advantages over either benzodiazepines with or without concomitant opioids. Rapid metabolism, in addition to potent anti-emetic effects, have promoted the widespread use of propofol. Consciousness corresponds with the BIS reading:

* Propofol titrated to BIS 78 to 85 can provide minimal sedation.
* Propofol titrated to BIS 70 to 78 can provide moderate (conscious) sedation.
* Propofol titrated to BIS 60 to 70 can provide deep sedation.
* Propofol titrated to BIS 45 to 60 can provide hypnosis compatible with general anesthesia but only in the presence of systemic analgesia.

Numerical description of the level of hypnosis is more precise than verbal descriptions. Measure the patient’s propofol level.

4 Who’s pushing propofol in your center?
Propofol has a nineteen-fold range of metabolism among individuals.3 What may appear to be a modest dose for one patient can produce loss of airway, apnea and hypotension in a more sensitive patient. None of these undesirable outcomes are beyond management by dedicated anesthesia providers. It’s extremely worrisome for patient safety to have nurses (in endoscopy, in particular) administering propofol without airway management skills or adequate training with which to deal with hypotension. At least one fatality has been reported in this scenario. If it’s economically unfeasible to have dedicated anesthesia providers in the endoscopy suites, then level of consciousness monitors like the BIS should be standard of care, along with the usual vital signs of HR, BP and EKG. Vital signs alone are an extremely poor predictor of the patient’s level of hypnosis.

5 Tread gently.
Not all alcohol drinkers will be resistant to propofol. Not all patients on SSRIs will be more difficult to sedate. Not all recreational drug users will exhibit cross-tolerance. Measuring patient response is infinitely preferable to guessing. Administering a bolus of propofol on the basis of body weight may invite disaster. It’s preferable to incrementally administer propofol. One may give mini-boluses by syringe, dilute some propofol in a bag and infuse with a 60 drop per cc IV set, or even use an infusion pump starting with 50mg/kg/min. Signs to observe for propofol effect are smiling by the patient, relaxation of the orbicularis oris and oculis muscles and the cessation of swallowing. If one elects to use a BIS monitor, trending the EMG as a secondary trace will provide instantaneous information ahead of changes in the BIS number.

1. Apfel CC, Korttila K, Abdalla M, et al.: A factorial trial of six interventions for the prevention of PONV. N Engl J Med 350:2441, 2004.
2. Hasel R. Personal communication 2005.
3. Court MH, Duan SX, Hesse LM, et al.: Cytochrome P-450 2B6 is responsible for interindividual variability of propofol hydroxylation by human liver microsomes. Anesthesiol 94:110, 2001.

Dr. Friedberg (drfriedberg@doctorfriedberg.com) is the author of the upcoming textbook Anesthesia in Cosmetic Surgery, Minimally Invasive Anesthesia for Minimally Invasive Surgery.

Website Development by Regency Web Service

Web Development by Nicholas Alipaz, in conjuction with Regency Web Service