From flow chart to 3 × 3 matrix: visualizing anesthetic depth and hemodynamics as a complement to Lee, Egan, and Johnson’s framework

Donald H. Lambert; Laura Lambert; Hanzhang Zhao; Mauricio Gonzalez

doi:10.4097/kja.25958

To the Editor,

We commend Lee, Egan, and Johnson for their contribution to intraoperative monitoring strategies, particularly their decision flow chart (Fig. 1A) published in the Korean Journal of Anesthesiology, which integrates hemodynamic parameters with processed EEG indices to guide anesthetic management [1]. Their framework significantly advances structured, physiology-informed decision-making in the operating room to prevent intraoperative hypotension (IOH), a critical concern for all patients, especially older adults [2,3].

Complementary to their work, we propose an alternate visual representation, the Proper Anesthetic Depth (PAD) Matrix (Fig. 1B), which we suggest offers enhanced clarity and usability at the bedside. This Matrix simplifies the interplay between Mean Arterial Pressure (MAP) and the SedLine^TM Patient State Index (PSi^TM) or the Bispectral Index, (BIS^TM), presenting a color-coded grid that delineates zones of “Too Much,” “Too Little,” and “Proper” anesthesia. Each cell includes actionable guidance and pharmacologic considerations, allowing clinicians to quickly interpret and respond to dynamic intraoperative changes.

The PAD Matrix differs from the flowchart by Lee et al, which references only undefined “high,” “normal,” and “low” blood pressures. In contrast, the Matrix prescribes a specific target range for the MAP of 70–100 mmHg, providing actionable thresholds for intraoperative management. Although a MAP of 65 mmHg is commonly cited as the minimum to prevent renal and myocardial injury [4,5], we advocate for a threshold of 70 mmHg. Clinically, this higher target provides a safeguard against accidental IOH. Aiming for 65 mmHg often results in undershooting—thereby increasing the risk of IOH and its associated complications.

While Lee, Egan, and Johnson’s flow chart is comprehensive, its tabular format requires additional cognitive effort during time-sensitive decision-making. The PAD Matrix, by contrast, offers immediate visual cues that align with intuitive clinical reasoning. It reinforces the goals of avoiding IOH and maintaining adequate perfusion while avoiding excessive or insufficient anesthetic depth—principles central to patient safety and neurophysiologic integrity.

Funding: None.

Conflicts of Interest: No potential conflict of interest relevant to this article was reported.

Author Contributions: Donald H. Lambert (Conceptualization; Writing – original draft; Writing – review & editing); Laura Lambert (Validation; Writing – review & editing); Hanzhang Zhao (Data curation; Writing – review & editing); Mauricio Gonzalez (Data curation; Investigation; Writing – review & editing)

Fig. 1.

(A) Reproduction of the flow chart from Lee, Egan, and Johnson [1]. (B) The Proper Anesthetic Depth (PAD) Matrix is a visual decision aid that integrates mean arterial pressure (MAP) with the SedLine^TM Patient State Index (PSI^TM) or BIS^TM to guide intraoperative anesthetic management. It delineates zones of excessive, insufficient, and optimal anesthetic depth, each linked to specific clinical actions and pharmacologic considerations. The central green zone (MAP 70–100 mmHg; PSI 25–50; BIS 40–60) represents the target range for maintaining appropriate anesthetic depth and hemodynamic stability. The Matrix highlights the lower‑right yellow cell to indicate low MAP with inadequate anesthesia (elevated PSi or BIS), underscoring that MAP should be corrected before increasing anesthetic depth. Clinicians should first treat the low MAP using vasopressors, fluids, or inotropes, as appropriate, before escalating total intravenous or inhaled agents.

References

1. Lee KH, Egan TD, Johnson KB. Raw and processed electroencephalography in modern anesthesia practice: a brief primer on select clinical applications. Korean J Anesthesiol 2021; 74: 465-77.

2. Yerdon A. Intraoperative hypotension: a public safety announcement for anesthesia professionals. APSF Newsletter 2024; 39: 42-5.

3. Lambert D, Lambert L, Gonzalez M. Response to Yerdon, Sherrer, and Chappell, Intraoperative Hypotension: A Public Safety Announcement for Anesthesia Professionals. APSF Newsletter 2024. Published online November 2, 2024. Available from https://www.apsf.org/article/response-intraoperative-hypotension-a-public-safety-announcement-for-anesthesia-professionals/

4. Maheshwari K, Turan A, Mao G, Yang D, Niazi AK, Agarwal D, et al. The association of hypotension during non-cardiac surgery, before and after skin incision, with postoperative acute kidney injury: a retrospective cohort analysis. Anaesthesia 2018; 73: 1223-8.

5. Salmasi V, Maheshwari K, Yang D, Mascha EJ, Singh A, Sessler DI, et al. Relationship between intraoperative hypotension, defined by either reduction from baseline or absolute thresholds, and acute kidney and myocardial injury after noncardiac surgery: a retrospective cohort analysis. Anesthesiology 2017; 126: 47-65.