EEG and Electromyogram and Somatic Response

Dr. Loyferman

Increases in Electroencephalogram and Electromyogram Variability Are Associated with an Increased Incidence of Intraoperative Somatic Response

Donald M. Mathews, MD*, Laura Clark, MD†, Jay Johansen, MD, PhD‡, Emilio Matute, MD, PhD§ and Chandran V. Seshagiri, Phd. Anesthesia & Analgesia April 2012 vol. 114 no. 4 759-770

The variability of the Bispectral Index (BIS), the variability of facial electromyogram power (EMG), and the Composite Variability Index (CVI) are 3 new measures of electroencephalogram and EMG variability. CVI is a single measure of the combined variability in BIS and EMG. This multicenter study included 120 patients undergoing elective, noncardiac surgery from 4 different sites. General anesthesia was maintained using propofol and remifentanil at 2 of the sites and sevoflurane and remifentanil at the 2 other sites. Propofol or sevoflurane was adjusted to maintain BIS between 45 and 60. Clinicians were blinded to CVI (v2.0) at all times, and remifentanil infusions were adjusted at the discretion of the clinician. The times of all intraoperative somatic events, defined as movement, grimacing, or eye opening, were recorded. To quantify how effectively each variable discriminated between somatic event segments and nonevent segments, the area under the receiver operating characteristic (ROC) curve for each variable was computed. Finally, BIS, EMG, CVI, and the HR range before each somatic event was observed and the earliest time before the somatic event at which each variable was characterized thus being able to discriminate between the somatic events and a specified set of nonevents.

BIS, EMG, and CVI, measures of electroencephalogram and EMG variability increased when intraoperative somatic events occurred. BIS, EMG, and CVI discriminated between 10-minute segments that contained a somatic event and those segments that did not contain an event better than changes in HR and mean arterial blood pressure. Furthermore, CVI increases before somatic events began earlier than HR changes and may provide caregivers with an early warning of potentially inadequate antinociception.

Simulator Airway Anatomy

Dr. Doody

Anesthesiology. 2012 June; 116(5):1204-1209.

Degrees of Reality: Airway Anatomy of High-fidelity Human Patient Simulators and Airway Trainers.

Schebesta K, Hüpfl M, Rössler B, Ringl H, Müller M, Kimberger O.

In anesthesiology, airway management is a key skill and failing to manage an airway is associated with a high risk of morbidity and mortality.  Today manikins are used for education, training, and research of human airway management.  Schebesta, et al. studied how realistic these patient stimulators and airway-training manikins really are using objective, radiologic measurements.  CT scans of 20 adult trauma patients (average BMI 24) without neck collars, head or cervical trauma, inappropriate image quality, or previously placed airway devices were compared to either a low-fidelity or high-fidelity stimulator.  Low-fidelity describes simulators that facilitate the training of an isolated skill; high-fidelity simulators, in contrast, allow for full immersion into a real scenario and the ability to provide feedback.  The low-fidelity trainers in this study included the Laerdal manikin and the Ambu manikin.  The high-fidelity trainers included the SimMan, SimMan 3G, HPS, and HAL human patient stimulators.  Comparisons using 14 predetermined distances, two cross-sectional areas, and three volume parameters were made between the airways of the actual patients and the training devices.

The anatomy of the training devices does not reflect the upper airway anatomy of actual patients.  The most realistic airway trainer was the HPS Human Patient Stimulator which had 32% of its parameters with the 95% CI of human airway measurements.  As the pharyngeal airspace (retroglossal and hypopharyngeal sections) is of major importance for airway management, this measure was defined as the primary outcome parameter.  The measurements of the pharyngeal airspace were much larger in the high-fidelity trainers (smallest being 30.6 cm³) than actual patients (13.5 ± 7.7 cm³).

A wide pharyngeal airspace, as found in all manikins in this trial, could lead to an inappropriately easy airway management and thereby would bias the results of simulation based research.  These major differences question the appropriateness of simulator-based research translating into the care of actual patients.  The assumption that simulator acquired skills can transfer to a clinical setting should also be reconsidered.  These anatomical abnormalities in the training devices could be perceived as unrealistic to experienced trainees preventing adequate immersion in the training, and with inexperienced trainees, an unrealistic airway may lead to them to acquire inappropriate techniques.  Research into constructing more anatomically similar airways between human and stimulators should be strong encouraged.

Cerebral Oximetry

Dr. Chang

Cerebral Oximetry: Monitoring the Brain as the Index Organ

Anesthesiology. January 2011, Volume 114, Issue 1, pages 12-13.

Note: the influence of this article comes from observing increased use of cerebral oximetry at a top-rated U.S. institution with a high volume of on-pump cardiac surgeries. (HC)

A prospective evaluation of 1,178 consecutive adult patients undergoing on-pump cardiac surgery, showed by Heringlake et al., presented compelling evidence that baseline cerebral oxygen saturation (Sco₂) is an independent risk factor for 30-day and one-year mortality.

A general idea behind cerebral oximetry goes as such: cerebral autoregulation reflects the coupling of cerebral oxygen delivery to cerebral metabolic rate and occurs primarily via modulation of cerebral blood flow in the presence of decreased cerebral arterial oxygen content. This is postulated either due to hypoxemia or moderate hemodilution. This study alluded to the failure of oxygen supplementation to increase Sco₂ beyond a cut-off value of about 50% indicated the potential for significantly higher morbidity and mortality.

One challenge of cerebral oximetry is the fact that perturbations in Sco₂, although highly sensitive, are conversely relatively nonspecific. Like any other perioperative parameter, it is for the clinician to determine whether a decrease in Sco₂ reflects a derangement of systemic perfusion, regional cerebral hypoperfusion, relative hypoxemia, increased cerebral metabolic rate, or some other such combination of factors. The numeric value should complement the larger clinical picture.

Now the study by Heringlake et al. looked at on-pump cardiac surgeries. Another study referenced in the article looked at a cohort of pediatric patients. If the observations can further be confirmed in various settings, the idea to employ this device as a sensitive, yet simple addition to the preoperative assessment of the non-cardiac patient may demonstrate similar findings and efficacy in the operating room.

Technology: Cerebral Oximetry, Dr. Waxer

Nathan Waxer, DO

Cerebral Oximetry Emerging Applications For an Established Technology
Frost, Elizabeth A.M. M.D. Anesthesiology News April 2012

Summary:
Cerebral Oximetry has been studied for more than 30 years and been
commercially available for greater than 2 decades. Cerebral oximetry
is derived from both venous and arterial blood and thus values fall
between the two (60-80%).

Cerebral oximetry, however, has only been recently used to investigate
changes in oxygen delivery to the brain and may have use in "first
alert" monitoring of impending organ dysfunction.

The brain may be an index organ for how well the vital organs of the
body are perfused.  If we are able to monitor the oxygenation of the
brain, it could then be used to infer the perfusion of other vital
organs.  Cerebral oximetry may be a useful technique for predicting
mortality from cardiac arrest, demonstrating a correlation between
cardiac function and perfusion to the brain. Also cerebral oximetry a
documented decrease in rSO2 directly after a procedure that could
affect the perfusion to the brain could help prove that a neurologic
deficit was not related to anesthesia.