Depth of Anesthesia

Monitoring in Cardiac

Surgery

Adam Dryden MD, FRCPC

University of Ottawa Heart Institute

Depth of Anesthesia

Monitoring in Cardiac

Surgery

Because it’s not all about the heart.

“The anesthetist and surgeon could have before them on tape or screen a continuous record of the electric activity of both heart and brain.”

Disclosures

None

Objectives

• Review the general principles of monitoring

• Highlight the commercially available monitors

• Determine whether depth of anesthesia monitoring can

allow us to prevent awareness

• Evaluate whether titrating anesthesia to a processed

EEG value can promote positive outcomes

• Share our experience with processed EEG at the Ottawa

Heart Institute

GENERAL PRINCIPLES OF

MONITORING

Are you asleep?

Barash, 2013

Are you asleep?

Purdon et al, 2015

General Principles of Monitoring

Awake?

Aware?

Are you asleep?

Awake?

Aware?

Power analysis

Power analysis

a b gqd

Power analysis in 3D!!! Or 4D?

Ok… Density Spectral Analysis

Anesthetic Signatures on DSA

Purdon et al, 2015

Limitations of (Processed) EEG

• Muscular activity

• Medical devices

• Pacemakers, electrocautery, surgical navigation systems, forced air

warmers

• Changes in cerebral metabolism

• Cardiac arrest, hypovolemia, hypotension, hypoglycemia,

hypothermia

• Seizures (or other abnormal EEG states)

• Medication limitations

• Ketamine, nitrous oxide, etomidate, ephedrine

BIS = Depth of Anesthesia?

Whitlock et al, 2011

MAC != Effect Site != Anesthetic Depth

Barash, 2013

COMMERCIALLY AVAILABLE

MONITORS

Commercially Available Monitors

• Bispectal Index

• Covidien (Boulder, CO)

• Sedline

• Masimo (Irvine, CA)

• State Entropy

• GE Healthcare (Helsinki, Finland)

• Narcotrend

• Narcotrend-Gruppe (Hannover, Germany)

Bispectral Index

Sedline

State Entropy

Narcotrend

PREVENTING AWARENESSFirst… Do No Harm.

Awareness

• Incidence is likely 1-2/1000

• Cardiac surgical procedures

• Obstetrical surgical procedures

• ASA III or IV

• Use of neuromuscular blocking agents

• ? Older

• ? Longer case

Sebel et al, 2004

Pollard et al, 2007

B – Aware

• Awareness: BIS 0.17% vs Routine 0.91%

• NNT of 138

• Anesthetic technique differences

•Less midazolam in the BIS group (2mg vs 2.5mg)

•Lower target plasma propofol concentration (2mg/L vs 2.4mg/L)

• No significant differences in nearly all post operative parameters and

complications

Myles et al, 2004

BAG - RECALL

• Goal was to determine whether BIS guided anesthetic management

was superior to end tidal anesthetic concentration (ETAC) for

awareness prevention

•Alarms used to guide therapy

• BIS was not superior to ETAC for preventing awareness

•BIS 0.24% compared to ETAC 0.07%

• No difference in median BIS

• No difference in median ETAC

Avidan et al, 2011

MACS

• Patients with no particular risk for awareness were included

• Very large (n=21,601) effectiveness study

• Planned for 30,000 patients – terminated for futility at interim endpoint

• Based on randomization, practitioners received alerts

• MAC < 0.5 (age adjusted)

• BIS > 60

Mashour et al, 2012

• Significant differences

when analyzed by intention

to treat vs post hoc

grouping

• Technical malfunction

MACS

Mashour et al, 2012

The Holy Grail of Cochrane

• Decreases the risk of awareness

in high risk patients

• But ETAC may be as effective

• No clinically relevant difference in

discharge readiness

• Less anesthetic use

• Especially consistent and relevant

for TIVA

• Impact of BIS on outcome was not

evaluated

Punjasawadwong et al, 2014

PROMOTING OUTCOMES

The Holy Grail of Cochrane, Round 2

• Non Cardiac Surgery

• Probably reduces risk of

postoperative delirium in first 7

days

• NNT – 17

• Moderate quality evidence

• No support for other outcomes

• All cause mortality

• Length of stay

Punjasawadwong et al, 2018

B – Aware

• Long term follow-up was done with included patients

•Median follow-up time of 4.1 years

• No difference in post-30 day death rates in the BIS

monitored compared to routine care

• Patients who had BIS < 40 for more than 5 minutes were

less likely to be alive at follow-up (HR=0.66, p=0.003)

Leslie et al, 2010

B – Unaware – Duration of BIS < 45

Kertai et al, 2010

Burst Suppression and Delirium

• A single centre prospective observational study

• 81 patients enrolled with identical anesthetic management

•Divided into delirious and non-delirous groups

• No difference in mean BIS values

• No other statistically significant risk factors identified

• Burst suppression duration was associated

• Burst suppression ratio was associated

Soehle et al, 2015

High BIS vs Low BIS – Possible?

• Anesthetic management at discretion of provider

• Except no nitrous oxide

Short et al, 2014

BIS AND THE OTTAWA HEART

INSTITUTE

Our Experience – Use of Processed EEG

344 408 639 1014 958 1133 1148 1260 1322 1633 1510 758

239

946

37.5 37.337.8

39.139.8

42.041.2

42.141.3

41.842.5

43.3

29.88

28.2

0

200

400

600

800

1000

1200

1400

1600

1800

2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018

25

27

29

31

33

35

37

39

41

43

45Number of BIS Cases

Number of Sedline Cases

Yearly Average BIS

Yearly Average PSI

Our Experience – Average BIS

0

100000

200000

300000

400000

500000

600000

0

100

200

300

400

500

600

0 10 20 30 40 50 60 70 80 90 100

Average BIS

All BIS Values

Summary

• Depth of anesthesia is not a number

• The use of depth of anesthesia monitors, in high risk

patients, can prevent awareness

• Preventing excessive anesthetic depth is an area of very

active investigation

My Conclusions, Predictions and Bias

• The threshold value for “deep anesthesia” is suspect…

•Burst suppression/suppression ratio may prove to be useful signal

• Low numerical depth of anesthesia indicates frailty

• The expected low BIS in a critically ill patient

• The unexpected low BIS in a “well” appearing patient

• Excessive anesthetic depth is harmful

• Neurologic specific outcomes

• Outcomes related to vasoactive agent use

• Will be easier to demonstrate in vulnerable patients

• Sedation and anesthetic depth perioperatively is as, or

more important than intraoperatively

Questions

References1. Avidan MS, Jacobsohn E, Glick D, Burnside BA, Zhang L, Villafranca A, et al. Prevention of intraoperative awareness in a high-risk surgical population. N Engl J

Med. 2011;365(7):591-600.

2. Barash PG. Clinical anesthesia. Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins; 2013.

3. Kertai MD, Pal N, Palanca BJ, Lin N, Searleman SA, Zhang L, et al. Association of perioperative risk factors and cumulative duration of low bispectral index with

intermediate-term mortality after cardiac surgery in the B-Unaware Trial. Anesthesiology. 2010;112(5):1116-27.

4. Leslie K, Myles PS, Forbes A, Chan MT. The effect of bispectral index monitoring on long-term survival in the B-aware trial. Anesth Analg. 2010;110(3):816-22.

5. Mashour GA, Shanks A, Tremper KK, Kheterpal S, Turner CR, Ramachandran SK, et al. Prevention of intraoperative awareness with explicit recall in an

unselected surgical population: a randomized comparative effectiveness trial. Anesthesiology. 2012;117(4):717-25.

6. Maheshwari A, McCormick PJ, Sessler DI, et al. Prolonged concurrent hypotension and low bispectral index ('double low') are associated with mortality, serious

complications, and prolonged hospitalization after cardiac surgery. Br J Anaesth. 2017;119(1):40-49

7. Myles PS, Leslie K, McNeil J, Forbes A, Chan MT. Bispectral index monitoring to prevent awareness during anaesthesia: the B-Aware randomised controlled

trial. Lancet. 2004;363(9423):1757-63.

8. Nitzschke R, Wilgusch J, Kersten JF, Trepte CJ, Haas SA, Reuter DA, et al. Bispectral index guided titration of sevoflurane in on-pump cardiac surgery reduces

plasma sevoflurane concentration and vasopressor requirements: a prospective, controlled, sequential two-arm clinical study. Eur J Anaesthesiol.

2014;31(9):482-90.

9. Pollard RJ, Coyle JP, Gilbert RL, Beck JE. Intraoperative awareness in a regional medical system: a review of 3 years' data. Anesthesiology. 2007;106(2):269-

74.

10. Punjasawadwong Y, Phongchiewboon A, Bunchungmongkol N. Bispectral index for improving anaesthetic delivery and postoperative recovery. Cochrane

Database Syst Rev. 2014;6:CD003843.

11. Punjasawadwong Y, Chau-In W, Laopaiboon M, Punjasawadwong S, Pin-On P. Processed electroencephalogram and evoked potential techniques for

amelioration of postoperative delirium and cognitive dysfunction following non-cardiac and non-neurosurgical procedures in adults. Cochrane Database Syst

Rev. 2018;5:CD011283.

12. Purdon PL, Sampson A, Pavone KJ, Brown EN. Clinical Electroencephalography for Anesthesiologists: Part I: Background and Basic Signatures.

Anesthesiology. 2015;123(4):937-60.

13. Sebel PS, Bowdle TA, Ghoneim MM, Rampil IJ, Padilla RE, Gan TJ, et al. The incidence of awareness during anesthesia: a multicenter United States study.

Anesth Analg. 2004;99(3):833-9.

14. Short TG, Leslie K, Campbell D, Chan MT, Corcoran T, O'Loughlin E, et al. A pilot study for a prospective, randomized, double-blind trial of the influence of

anesthetic depth on long-term outcome. Anesth Analg. 2014;118(5):981-6.

15. Sigl JC, Chamoun NG. An introduction to bispectral analysis for the electroencephalogram. J Clin Monit. 1994;10(6):392-404.

16. Soehle M, Dittmann A, Ellerkmann RK, Baumgarten G, Putensen C, Guenther U. Intraoperative burst suppression is associated with postoperative delirium

following cardiac surgery: a prospective, observational study. BMC Anesthesiol. 2015;15:61.

17. Whitlock EL, Torres BA, Lin N, Helsten DL, Nadelson MR, Mashour GA, et al. Postoperative delirium in a substudy of cardiothoracic surgical patients in the

BAG-RECALL clinical trial. Anesth Analg. 2014;118(4):809-17.

18. Whitlock EL, Villafranca AJ, Lin N, Palanca BJ, Jacobsohn E, Finkel KJ, et al. Relationship between bispectral index values and volatile anesthetic

concentrations during the maintenance phase of anesthesia in the B-Unaware trial. Anesthesiology. 2011;115(6):1209-18.

Selected References

Short TG, Leslie K, Campbell D, Chan MT, Corcoran T, O'Loughlin E, et al. A pilot study for a

prospective, randomized, double-blind trial of the influence of anesthetic depth on long-

term outcome. Anesth Analg. 2014;118(5):981-6.

Whitlock EL, Torres BA, Lin N, Helsten DL, Nadelson MR, Mashour GA, et al. Postoperative

delirium in a substudy of cardiothoracic surgical patients in the BAG-RECALL clinical trial.

Anesth Analg. 2014;118(4):809-17.

Kertai MD, Pal N, Palanca BJ, Lin N, Searleman SA, Zhang L, et al. Association of

perioperative risk factors and cumulative duration of low bispectral index with

intermediate-term mortality after cardiac surgery in the B-Unaware Trial. Anesthesiology.

2010;112(5):1116-27

Purdon PL, Sampson A, Pavone KJ, Brown EN. Clinical Electroencephalography for

Anesthesiologists: Part I: Background and Basic Signatures. Anesthesiology.

2015;123(4):937-60.