Anesthesiology, Perioperative and Pain Medicine

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Q&A with Stanford Anesthesia's Residency Director

August 2009

Wake-up with inhaled anesthetics

Question
I have been looking for papers regarding turning off isoflurane and starting Desflurane at the end of a case regarding accelerating the wakeups. To me it makes sense, but someone told me this did not matter clinically. Do you know of such a paper describing this? Thank You,

Answer
Research articles on low solubility inhaled anesthetics are often written by investigators funded by Baxter (Desflurane) or Abbott (Sevoflurane) so as usual when reading the literature see who funded the study and how that might affect the findigs. The classic paper on the switching (or crossover) technique you describe is attached.
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The lessons learned are that if one is to substitute desflurane for isoflurane at the end of a case one needs to keep in mind that partial rebreathing through a semiclosed circuit limits elimination of isoflurane more than you may think during the crossover or switching period. A higher fresh gas flow than expected during this crossover period is needed to speed the isoflurane elimination. Alternatively, start the crossover earlier than you might think you need if flows are low to ensure that isoflurane is gone by the end of the case.

Having used isoflurane exclusively for the first part of my career (I like sounding like a veteran of the field) I know I woke patients up just as fast as I do now. This was done by starting to reduce the inspired isoflurane concentration as the end of a case approached. Desflurane and sevovoflurane do provide the practitioner more margin for error, as turning the desflurane or sevoflurane vaporizer off at the very last minute of closure often yields a reasonably fast wakeup. Please keep in mind that studies that show a faster wakeup with desflurane or sevoflurane versus isoflurane use a protocol where the gas is left at the 1 MAC level, for example, until skin closure is finished, and only then is the vaporizer turned off. It is no surprise then that wakeup is faster the lower the blood gas solubility is. This protocol maynot reflect the actual practice by many anesthetists of titrating the inhaled anesthetic concentration down as case is coming to an end.
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Blood pressure in sitting position

Question from resident
Hello, A quick question. I usually level the transducer for an arterial line to the heart. Usually this is also about the position of the brain based on the supine or prone position. Yesterday I did a long case where towards the end they wanted the patient sat up. Previously MAPs had been mid 70's, UOP 1-1.5 cc/kg/hr. I moved the transducer up to heart level with pt sitting up, and MAPs were low 70's. 5 minutes later my attending came in the room and moved the transducer at the level of the head, at which time the patient's MAP was measured as 58-60 which lead to a different perception of what adequate pressure in a patient is. Clearly, a good pressure does not automaticaly mean good flow. I also know the conversion is about 1 mmhg for every 1.4 cm H20. I have had a similar discussion for beach chair position for ortho, but have never done a sitting neurosurg case. I will read about this, but could you give me a broader perspective on your practice.

Answer
Nobody really knows the definitive answer to your good question about where to place the transducer when the patient is not flat, but the issue revolves around whether the circulation above the heart functions as a siphon system or as a waterfall system. The two best sources, besides Dr. Jaffe our esteemed neurosurgical anesthesia faculty, that provide a balanced analysis are:
http://www.apsf.org/assets/Documents//spring2009.pdf
and
http://www.apsf.org/resource_center/newsletter/2008/winter/17_problems_of_posture.htm
Until actual data of some sort sort all this out, my own practice is to measure BP at the level of the most vulnerable tissue--the brain and then aim to maintain MAP within the patients unanesthetized preop BP.
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Visiting Resident from Costa Rica or Spain

Question
Over the past several weeks I have gotten a few questions from residents from other countries interested in doing a rotation here. For example: "Hi, I am a resident of anesthesiology in Costa Rica. I want to know what I have to do to do a 3 month rotation in your hospital? I am interested in neuroanesthesia and obstetric anesthesia.
Thank you."
A second inquiry stated "I don't know who I have to contact with regard to start up arrangements, and what months could be available, and what requirements I must meet as a European doctor from Santiago de Compostela, Spain to learn Anesthesia during two months in the US at Stanford"

Answer
Unfortunately, although Stanford University Medical Center accepts visiting residents from ACGME-accredited programs in the United States and Canada, residents from other countries are not allowed to do clinical rotations at Stanford. There are several reasons for this including the large number of requests that come in. "Observerships" are also not permitted, in part because regulations require an observer in the operating room to introduce themselves as such to the patient. I am sorry,
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