Hypnos MEDICAL
Synapse
Stimulus 0.0

Physiology

Underlying model state — the real variables driving the monitor. Updates live.

Directed influence map. Green = positive drive, red = negative. Edge thickness reflects how active each pathway is right now; dashed edges are baroreflex feedback.

Synapse

An anaesthesia teaching simulator by Dr Kieran Gillick
Version 4.15

Clinical disclaimer

Synapse is a teaching simulator only. It must not be used for clinical decision-making, drug-dose calculation, ventilator setting, or any other aspect of real patient care. Physiology and pharmacology are deliberately simplified for didactic purposes and may not match real human responses. No warranty is provided. Use at your own risk.

Licence

Synapse is released under the Apache License, Version 2.0. You are free to use, modify, and redistribute it (including in commercial settings) provided you retain the copyright notice and this licence.

Copyright 2025–2026 Hypnos Medical / Kieran Gillick. Licensed under the Apache License, Version 2.0 (the "License"). Distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND.

Intended audience

Anaesthetists, trainee anaesthetists, simulation educators, and qualified clinicians using the simulator for self-directed study, teaching, or peer discussion of perioperative physiology and pharmacology.

Feedback

For questions, feedback, or bug reports, please contact the author.

You are running a saved offline copy of Synapse. For the latest scenarios and fixes, use the live version at synapse.hypnos.one.

Start here

A two-minute orientation for your first time in the simulator

You are the anaesthetist

For the next while, you are the anaesthetist looking after a patient through an operation.

This screen is the patient monitor — the same kind that sits beside an anaesthetised patient in theatre. Your job is to keep them asleep, breathing, and stable while the surgery happens. The controls let you give drugs and respond to what the monitor is telling you.

This is a safe place to try things, make mistakes, and watch what happens — none of it can hurt anyone! Note that although the physiology is reasonably high-fidelity it does not capture every nuance, and real patients may behave differently.

The next three steps cover the monitor, the controls, and how to start your first case. You can reopen this any time from Start here in the top bar.

The monitor

This is what you will be watching. You already know the basics like heart rate and blood pressure — the parts worth learning are the ones specific to anaesthesia. Here is what each part means.

ECG
PLETH
ART
PAW
FLOW
CO2
HR72
SpO299
NIBP118/74
ABP120/76
etCO238
RR12
etSEVO2.0
BIS50
TOF4
PIP18
Vt (mL)480

Illustrative values for a stable, anaesthetised patient.

The numbers
HR — heart rate
Under anaesthesia it often runs lower than the awake 60–100, as anaesthetic agents blunt sympathetic tone.
SpO2 — oxygen saturation
Patients get supplemental oxygen, so this usually sits at 98–100%. A sustained fall is an early warning that the patient is not getting enough oxygen.
NIBP — cuff blood pressure
Blood pressure from an arm cuff, in mmHg. It is intermittent — here it cycles automatically every 2.5 minutes — so between readings you cannot see the blood pressure unless an arterial line is in.
ABP — arterial blood pressure
Continuous, beat-to-beat blood pressure from a fine catheter (an "arterial line") placed in an artery, usually at the wrist. You see changes instantly rather than waiting for the next cuff cycle — used when blood pressure needs tight control.
etCO2 — exhaled carbon dioxide
The CO2 at the very end of an exhaled breath (mmHg, normal ~35–45). It confirms the lungs are being ventilated and the breathing circuit is intact, and tracks how effectively. A sudden drop toward zero is a red flag — a disconnection, a blocked tube, or collapsing cardiac output.
RR — respiratory rate
Breaths per minute. When the patient is breathing on their own, this is one of the first things to fall as anaesthetic — especially opioid — doses deepen: a slow rate is an early sign of respiratory depression, and 0 means apnoea (not breathing). When the ventilator is breathing for the patient, it shows the delivered rate.
etSEVO — exhaled anaesthetic vapour
End-tidal sevoflurane (%). Sevoflurane is the anaesthetic vapour the patient breathes; the exhaled percentage closely mirrors the brain concentration keeping them asleep. Around 2% is a typical surgical depth (about 1 MAC). This is your main readout of how much volatile agent is on board.
BIS — depth of anaesthesia
Bispectral index: a processed brain-wave number from 0 (no activity) to 100 (wide awake). Aim for 40–60 during surgery — deep enough to be properly unconscious, not needlessly deeper.
TOF — train-of-four
Tests how much muscle relaxant is still working. A nerve is stimulated four times and the twitches counted — 4 means little or no block, 0 means deep block. You watch it to time relaxant doses and confirm recovery before waking the patient.
PIP — peak inspiratory pressure
The highest pressure (cmH2O) reached in the breathing circuit during each ventilator breath. Rising PIP for the same tidal volume means stiffer or more obstructed lungs — for example bronchospasm, a kinked tube, or a patient coughing on the tube.
Vt — tidal volume
The size of each breath in mL. In volume-controlled ventilation (VCV) this is fixed by the ventilator setting; in pressure-controlled ventilation (PCV) it varies with lung compliance and resistance — a falling Vt in PCV is an early sign of worsening bronchospasm or stiffening lungs.
The waveforms
ECG
The heart's electrical trace. Watch the rate and rhythm.
PLETH
The pulse waveform from the SpO2 probe; each upstroke is a pulse of blood reaching the finger. A strong, regular trace means good perfusion; a damped one can mean poor perfusion or a probe problem.
ART
The arterial pressure waveform that accompanies the arterial line — one upstroke per beat.
PAW
Airway pressure across a single breath: it rises as the ventilator delivers the breath, then falls on exhalation.
FLOW
Gas flowing in and out of the lungs through the breath cycle (in above the line, out below).
CO2 — capnogram
The CO2 waveform across each breath — a near-square shape that climbs as the patient exhales, plateaus, then drops to zero on the next breath in. A flat line means no CO2 is being exhaled: no effective ventilation.

The controls

Everything you do happens through two areas.

The drug deck runs along the bottom of the screen, organised into tabs: hypnotics (to send the patient to sleep), opioids (pain relief), pressors (to raise blood pressure), other cardiovascular drugs, muscle relaxants (NMB), fluids, and emergency drugs. Tap a drug to give a bolus. Some drugs can also run as continuous infusions — switch to the Infusions tab and adjust the rate with a slider.

The side panel opens with the PANEL button at the top-left. There you can change ventilator settings, see the detailed underlying variables, and read the event log — a running record of everything that has happened in the case.

The whole simulator works on one loop: give something, then watch the monitor respond. Let the anaesthetic lighten and BIS climbs; drop the blood pressure and a pressor brings it back. Watching that cause and effect is the point.

Start your first case

The best place to begin is a guided scenario rather than a blank patient.

Tap Scenarios in the top bar and choose the induction walkthrough. It takes you step by step through sending a patient to sleep — the sequence every anaesthetic begins with. Every scenario comes with a brief setting out its setup, objectives, and hints.

When you are ready, press Get started below to jump straight to the scenario picker.

Scenarios

Pick a scenario to start. Sim continues running underneath; loading a scenario applies its setup.

Patient profile
Time compression
PROFILE
Profile--
Weight (kg)--
HR baseline (bpm)--
MAP target (mmHg)--
SVR baseline (x)--
Lung compliance (mL/cmH2O)--
FRC (mL)--
TLC (mL)--
Baro sensitivity--
Time scale--
CIRCULATION
Central Volume (L)--
Volume overload (%)--
Preload (x)--
Fluid Buffer (L)--
Bleed Rate (L/s)--
SVR tone (live / base)--
Contractility (x)--
AUTONOMIC
Alpha tone--
Beta tone--
Beta blockade %--
Parasympathetic Tone--
Nociception (input)--
Analgesia Cover--
Effective Stimulus--
MAP error (norm)--
Baro efficacy--
VENTILATION & GAS
Resp Drive (%)--
Airway Resistance--
Peak Pressure (cmH2O)--
Tidal Vol (mL)--
Minute Vent (L/min)--
Lung Volume (mL)--
Auto-PEEP (cmH2O)--
Dynamic compl. (mL/cmH2O)--
Exp time const (s)--
FiO2--
FRC O2 Reserve (mL)--
Circuit Sevo (%)--
etSevo (%)--
FGF (L/min)--
Bag Pressure--
METABOLISM
Metabolic Rate (x)--
O2 use (mL/s)--
CO2 prod (mmHg*L/min)--
AIRWAY REACTIVITY
Reactivity (x)--
Risk accumulator--
Airway change boost (s)--
Cough timer (s)--
Last reaction--
AWARENESS
Awareness risk (0-1)--
Movement timer (s)--
Breath hold timer (s)--
CNS / NMB / DRUG Ce (mcg/mL)
Consciousness--
BIS (monitor)--
Paralysis (0-1)--
Propofol Ce--
Remifentanil Ce--
Fentanyl Ce--
Alfentanil Ce--
Morphine Ce--
Midazolam Ce--
Dexmed Ce--
Metaraminol Ce--
Ephedrine Ce--
Adrenaline Ce--
Atropine Ce--
Glycopyrrolate Ce--
Ketamine Ce--
Rocuronium Ce--
Sugammadex Ce--
Neostigmine Ce--
Phenylephrine Ce--
Noradrenaline Ce--
Esmolol Ce--
GTN Ce--
Dobutamine Ce--
Vasopressin Ce--
Calcium Ce--
Dantrolene Ce--
Furosemide Ce--
Salbutamol Ce--
Magnesium Ce--
Cum. urine output (L)0.000
SATURATION DIAGNOSTICS
Live pushUp and pushDown drive sums feeding the saturating HR and SVR sigmoids. Larger drives = closer to ceiling/floor with diminishing marginal effect.
HR pushUp--
HR pushDown--
SVR pushUp--
SVR pushDown--
ACTIVE EVENTS
--
PHARMACOKINETIC PARAMETERS
Simplified single-compartment with effect site. Vd = volume of distribution (L/kg). k10 = elimination rate constant (per min). ke0 = plasma-to-effect-site equilibration rate (per min). Shorter ke0 = faster onset/offset.
DrugVd (L/kg)k10 (/min)ke0 (/min)
EVENT LOG
Timestamps are sim-time since session start.
ECG
PLETH
ART
PAW
FLOW
CO2
INIT ECG
INIT PLETH
INIT ART LINE
HR --
SpO2--
NIBP (AUTO 2.5min)--/--
ABP (ART)--/--
etCO2--
RR (/min)--
etSEVO (%)--
BIS --
INIT BIS
TOF4
PIP --
Vt (mL) --

Anaesthetic

Boluses & Fluids

Ventilator

Airway device

Ventilation mode

Settings

FiO20.21
Respiratory rate (bpm)12
Tidal volume (mL)500
Inspiratory pressure (cmH2O)15
PEEP (cmH2O)5
Sevoflurane (dial %)0.0
Fresh Gas Flow (L/min)2.0

Scenario

Learning objectives