Depth of Anesthesia Monitoring Flashcards
History of Anesthesia
Morton held a ether-dipped handkerchief over the mouth of the pt in the Ether Dome (considered the first successful anesthetic)
N2O at Mass General
Attempted in 1845 but the pt moved and cried out w incision but had no recall. When they used ether the pt had no mvmt but pt was aware and had no pain
Development of Nursing Anesthesia
- Civil War 1864-1865: Union Army Nurse Catherine Lawerence recorded practicing anesthesia in her autobiography
- many other nurses used chloroform
- Franco-Prussian War 1870-1871: Male and Female nurse taught to induce anesthesia and used as anesthetists
- reports more common in 1880s
Key Figures in Nursing Anesthesia
Sister Mary Bernard: entered St. Vincents in PN 1887 and took over anesthesia duties in 1888
Franciscan Sisters of St. Johns: in IL prepared sisters to serve as nurse anesthetists and sent them to other MW hospitals
Sister Mary Erhard: 1886 administered anesthesia on Maui for 42 years
Sisters of St. Francis in Rochester, MN: 1889 St Mary’s Mayo Clinic built and opened. Etith and Dinah Graham directed and supervised nursing and administered anesthesia
The Mother of Nursing Anesthesia
- trained by Dr. William Mayo
- Dinah Graham administered for awhile
- Edith administered until she married Mayo
- Alice Magaw (MoA) her friend and successor took over
- Florence Hendersen introduced to anesthesia dept
- the NAs became integral to success of St. Mary’s hospital and the Mayo brothers became known for their surgery and excellence in anesthesia
- known for making anesthesia safer
- Henderson developed methods of ether administration and assessment criteria
Evolution of NA
1908: Agatha Hodgins at Lakeside Hospital in Cleveland, OH chosen by Dr. Crile as anesthetist.
- Lakeside konwns for its success in surgery and anesthesia
1915: Lakeside School of Anesthesia was founded as fist NA program in Cleveland and led to other NA programs
Who founded the AANA?
Agatha Hodgins of the Lakeside Hospital and School of Anesthesia
WWI
Prior to WWI, few physicians specialized in anesthesia. In 1911 Francias McMechan felt it should be a profession only for physicians
Lakeside Challenge
1916: letter sent to Dr. Crile by Ohio BOM telling him to cease the training of NAs, or lose the nursing school’s accreditation
1917: at a hearing Dr. Crile persuaded the board to lift the order by citing how many other facilities were successfully using nurse anesthetists
• Crile and supporting physicians successfully advocated for the Ohio legislature to legalize the practice of anesthesia by nurses
1919: bill approved that legalized practice of nursing anesthesia under supervision of a physician
Kentucky (Frank v South)
1916: Louisville society of anesthesiologists passed a resolution that only a physician should administer anesthesia, attorney general concurred
– Louis Frank and his nurse anesthetist Margaret Hatfield joined with that state board of health to file a suit against the Kentucky state medical association
• Lost the initial suit, but won in the appeals – Nurse anesthesia is not the practice of medicine
California (Chalmers-Francais v Nelson)
– Dragmar Nelson a nurse anesthetist charged with practice of medicine
– At every level of the California civil court system it was decided in favor of Dragmar Nelson – established legality of nurse anesthesia practice
Breakthroughs in Technology
- pulse ox (standard of care in 1987)
- anesthesia gas analysis
- improved monitoring technology and devices
- fiberoptic imaging
- US guided techniques
- BIS/Entropy monitoring
Why Monitor Depth of Anesthesia?
- to prevent awareness
Awareness
- the unexpected and explicit recall by pts of events that occur during anesthesia
- estimated at 0.0068 to 1%
- may be higher in children
- most pts don’t have pain but have vague auditory recall, a sense of dreaming generally not disturbing
- some experience total pain and recall (traumatic)
- concern for PTSD and other psychological sequelae
Issue of Awareness More Prominent - 2003/2004
- FDA allowed Aspect Medical (makers of BIS) to declare BIS monitors reduce incidence of awareness
- sentinal alert from TJC 2004 on awareness developed Task Force on IntraOp Awareness
- also a hypothesis that DoA monitors help providers titrate meds and reduce oversedation, morbidity, and mortality
Court of Public Opinion
the movie “Awake” in 2007 brought the issue to the publics eye
Major DoA Monitors
- BIS (Aspect Medical)
- Entropy (GE)
- Narcotrend
- Cerebral State Monitor
- SEDLine
- SNAP II
AEP
Goals of DoA Monitors
- Ability to detect level DoA and risk of awareness
- Determine if patient is unnecessarily too deep and at risk of prolonged recovery and increased M and M
- No matter what, the monitor it should work similarly across all patient pops
- Should work the same regardless of meds and anesthetic technique employed
Baseline Principles of EEG Analysis
- 1937: Gibbs et al, discussed the relationship between brain wave patterns (EEG) and neuronal activity changes associated with drug administration *
- Information is collected by frontal electrodes and the signals are processed to yield an “index value” to determine the depth of anesthesia
EEG Activity and DoA
- Cells in cortex provide synaptic activity and results in changes of voltage that can be detected by electrodes placed on the forehead/scalp
- Multiple waveforms with varying frequency ranges correspond to specific neurophysiological processes
- grouped into frequency bands in order of freq:
delta, theta, alpha, beta
Table Explanation of Waves
Delta
<3 Hz
- very low freq, depressed functions (coma, deep GA, hypoxia, ischemia, infarction, poor metabolism), may result from thalamic depression
Theta
4-7 Hz
- low freq, seen under GA. Inhibition of thalamic pacemaker cells
Alpha
8-12 Hz
- med freq, higher amplitude, awake but eyes closed (EEG seen in occipital lobes)
- prominently seen in awake pts
- thought to reflect cyclical activity of thalamic pacemaker cells
Beta
13-24 Hz
- high freq, low amplitudes, awake state
- present in prefrontal regions of brain
- reflect thalamocortical pathways
EEG Waveforms Under Anesthesia
2 EEG Processing Techniques
- Time Domain
- Frequency Domain
Time Domain
- voltage changes plotted against time
- burst suppression is identified in this domain
- complex signals cannot be fully analyzed by using time domai methods alone
Frequency Domain
- advancemnt of microprocessing enabled fast calculations (Fourier transformation) = analysis of freq domain
- freqs present in EEG compared w degree to which these freqs are present
BIS
- bispectrol technology
- proprietary algorithm developed by Aspect Medical and approved in 1996
- frontal EEG recordings converted to a number (BIS Index)
- range 0 (isoelectric) to 100 (awake)
- 40 to 60 good goal
- most widely used DoA monitor in US
Evolution of BIS Graphic (single side EEG to bilateral monitoring)
Principle of BIS
• 2 dimensional spectral analysis (Bispectral)
– Refers to the statistical process
- Quantifying quadratic nonlinearities of the system
- “Represents the degree of phase coupling of two fundamental frequencies and a modulation frequency represented by the sum of the two frequencies”
- CLEAR AS MUD!!!!
– Basic premise is the changes in clinical state are represented by changes in phase coupling
- key point: another tool in the toolbox! Rarely should you make decisions on ONE thing alone, use different tools to make clinical decisions
To BIS or not to BIS?
- should be reliable across all pt pops and all types of anesthetics, but a cantelope on a BIS is a 28
- most beneficial in TIVAs or in the ASC
- GA has a MAC level that corresponds to “depth” and literature shows MAC = little recall
Pros/Cons of BIS
PROs:
- large trials have assessed that it decreases awareness
- BIS algorithm designed for use w Propofol, Versed, and ISO (beneficial for TIVA)
CONs:
- some studies funded by Aspect Medical (makers of BIS)
- BIS index doesn’t accurately reflect all drugs (no change in BIS w N2O, increases w ketamine)
- Artifact from Bovi, Bair Hugger, etc.
BIS Spectrum
- 0 to 100 (higher = more awake)
- low probability of recall w BIS <60
- target range 40-60
- lower isn’t always better, too low = too deep, overly anesthetized
BIS and Awareness Related Outcomes
Studies:
- Ekman (2004): 4945 pts monitored w BIS between 40-60, awareness 0.04% vs 0.18% in control group
- Myles (2004) “B-Aware Study”, 2643 pts at high risk of awareness. Only 2 out of 1225 in BIS group had recall vs 11 in control group
- Avidan (2008) “B-Unaware Study”
Cocrane Data on BIS
- BIS reduces awareness in high risk pts but not in routine cases, therefore BIS is not a standard of care
Too Low of a BIS
- improved outcomes via reducing anesthetic needs 20-25% w reduced recovery time, reduced postop N/V, reduction in long term outcomes…
BUT “prolonged, deep anesthesia” (BIS <45) = significant independent risk factor for 1 year post op mortality
Triple Low
- low BIS
- hypotension
- low end tidal anesthetic concentration
= triple mortality at 30 days
What to do if awareness happens in your patient?
- follow up, listen, acknowledge facts
- pts less likely to sue of provider is open and upfront about situation
