Health Data Visualization and Communication
Master in Health Data Science (MHEDAS)
Júlia Arbat, Laia Colomé, Joana Ros

Making the invisible visible:
an anatomy of surgical struggle

A unified metric to uncover hidden tendencies in the surgical landscape

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Chapter 1

The illusion of stability

In the operating room, stability is the ultimate goal. Anesthesiologists monitor a continuous stream of vital signs: heart rate, blood pressure, and oxygen saturation. These numbers tell us what is happening, but not the effort required to maintain it.

Two patients can share an identical heart rate of 70 bpm, yet their physiological realities are worlds apart. While one is self-sustaining, the other requires liters of fluid and continuous vasoactive support. On the monitor, they appear identical; in reality, one is naturally stable while the other is in a state of managed struggle.

How do we quantify this hidden struggle?
Patient A — Heart Rate: 70 bpm
  • Crystalloid fluids: 250–500 mL
  • Vasopressor use: None
  • Blood products: 0 mL
Patient B — Heart Rate: 70 bpm
  • Crystalloid/colloid fluids: 2000–3000 mL
  • Ephedrine: 40–60 mg total
  • Blood products: 500–1000 mL
Chapter 2

The problem of incomparability

To measure the body's hidden struggle, we track three levers of rescue used to maintain stability:

Fluids: To maintain volume

Blood: To restore oxygen capacity

Vasopressors: To drive the failing heart

These signals, however, speak different languages. Fluids and blood are delivered in milliliters, while vasopressors are measured in milligrams; their raw values cannot be directly combined. A small vasopressor dose reflects far greater physiological distress than a routine bag of saline.

Because these interventions operate on different scales, raw units are not comparable.
A standardized metric of physiological stress is therefore required.
Chapter 3

Synthesizing support

To resolve the comparability problem, we translate each patient’s support requirements into a single score.

Physiological Support Score (PSS)
0 — stable, unsupported
1 — unstable, fully supported

Support variables are log-transformed to suppress the dominance of large fluid volumes and then normalized, ensuring that a critical vasopressor dose is weighted comparably to liters of fluid.

This unifies heterogeneous clinical inputs into a single measure of survival effort, revealing the hidden escalation of care that distinguishes routine maintenance from physiological crisis.

Chapter 4

The spectrum of stability

The PSS measures the burden during surgery, but it strongly aligns with established pre-operative risk (ASA levels), with higher ASA classes consistently shifted upward.

This shift reveals a critical disparity in physiological reserve: an ASA 4 patient reaches a high burden at a much lower percentile than an ASA 1 patient. This confirms the score captures graded vulnerability, showing that high-risk bodies exhaust their stability threshold far earlier than their healthy counterparts.

Vulnerability shifts the curve: high levels of support are required at much lower percentiles for at-risk patients.
Chapter 5

Impact of surgical choices

Beyond measuring individual patient risk, the PSS can serve as a flexible tool for comparing the broader surgical context. We examine how the physiological burden shifts across three distinct dimensions: surgical technique, patient position, and the performing specialty.

These applications demonstrate the score's versatility as a comparative lens, allowing us to quantify and observe how support requirements vary not only by patient vulnerability but also by the nature of the intervention itself.

These illustrate the score's potential as a unified metric to objectively compare the physiological impact of diverse surgical choices.
Surgical technique
Patient position
Specialty variation

Quantifying the cost of stability

We return to the scenario of two patients with identical heart rates. With the Physiological Support Score, the difference between natural stability and managed struggle is no longer invisible. By integrating fluids, blood, and vasopressors, we have created a unified metric that tracks the effort required to maintain equilibrium.

Our analysis validates this as a practical tool. It captures differences in patient risk and surgical complexity, proving that measuring the input of care adds critical context to standard monitoring.

Standard monitoring tracks the result of stability; this score quantifies the intervention behind it.