Simple approaches to difficult topics Measurement and Monitoring Dr Alan McLintic Middlemore Hospital

Q: How do you measure Cardiac output using thermodilution?

Q: How do you measure Cardiac output using thermodilution? Summary Thermodilution principle is a modification of the Fick principle

Q: How do you measure Cardiac output using thermodilution? Summary Thermodilution principle is a modification of the Fick principle

Q: How do you measure Cardiac output using thermodilution? Summary Pulmonary artery catheter (‘Swan-Ganz’ catheter) Proximal lumen Thermistor Balloon Connection for thermistor Distal lumen

Q: How do you measure Cardiac output using thermodilution? Summary Inserted through large neck vein

Q: How do you measure Cardiac output using thermodilution? Summary Floated through heart until the tip is in the pulmonary artery

Q: How do you measure Cardiac output using thermodilution? 10 ml dextrose (21ºC) Dilution of ‘coldness’ measured here

Q: How do you measure Cardiac output using thermodilution? Recirculation Colder  Body temperature Time 

Q: How do you measure Cardiac output using thermodilution? The greater the cardiac output, faster the dilution, the smaller the Area Under the Curve (AUC) High cardiac output Lower cardiac output Colder  Colder  Time  Time 

Q: How do you measure Cardiac output using thermodilution? Dye dilution: Mass of dye (g) Mean concentration dye (g)

Q: How do you measure Cardiac output using thermodilution? Dyes: Concentration dye (g/l)  Time 

Q: How do you measure Cardiac output using thermodilution? Colder  Body temperature Time 

Q: How do you measure Cardiac output using thermodilution? Colder  Body temperature Time 

Q: How do you measure Cardiac output using thermodilution? Colder  Modified Stewart-Hamilton equation Body temperature Time 

Q: How do you measure Cardiac output using thermodilution? Colder  Body temperature Time 

Q: How do you measure FRC using a Body Plethysmograph?

Q: How do you measure FRC using a Body Plethysmograph? The Body Plethysmograph is a method to measure lung volumes by the application of Boyle’s Law

Q: How do you measure FRC using a Body Plethysmograph? Box pressure Mouth pressure Shutter Calibrating syringe

Q: How do you measure FRC using a Body Plethysmograph? Step1. Calibrate changes in box pressure as changes in volume of air in the box Box volume

Q: How do you measure FRC using a Body Plethysmograph? Step2. Apply Boyle’s Law to lung air…. …while panting against closed shutter Box volume

Q: How do you measure FRC using a Body Plethysmograph? Step2. Apply Boyle’s Law to lung air…. Box volume PBar. VFRC = (PBar- P). (VFRC + V)

Q: How do you measure FRC using a Body Plethysmograph? Step2. Box volume Atmospheric pressure: 100 kPa FRC?  Box volume PBar. VFRC = (PBar- P). (VFRC + V) FRC? Mouth pressure when shutter closed

Q: How do you measure FRC using a Body Plethysmograph? Summary Method of measuring lung volumes by the application of Boyle’s law Briefly explain set up and calibration of box pressure for box air volume Write equation Summary: Atmospheric pressure: 100 kPa FRC?  Box volume PBar. VFRC = (PBar- P). (VFRC + V) FRC? Mouth pressure when shutter closed

Q: What are the important physical principles in the design of an invasive pressure monitoring system?

Q: What are the important physical principles in the design of an invasive pressure monitoring system?

Full answer regarding accuracy Q: What are the important physical principles in the design of an invasive pressure monitoring system? Full answer regarding accuracy Practical aspects Prevention clot, kinking, choice of artery, cannulae Zeroing Static accuracy Dynamic accuracy

Q: What are the important physical principles in the design of an invasive pressure monitoring system? Natural frequency (FN) Frequency at which a system oscillates most freely Tendency for a system to resist oscillation through friction Damping

Q: What are the important physical principles in the design of an invasive pressure monitoring system? Natural frequency (FN) Frequency at which a system oscillates most freely The FN is the same frequency as the upstroke of trace  resonance and overshoot

Q: What are the important physical principles in the design of an invasive pressure monitoring system? Prevents resonance from biological signals Natural frequency High as possible Short, stiff, short, wide tubing Small stiff transducer Low density fluid

Q: What are the important physical principles in the design of an invasive pressure monitoring system? Prevents resonance from biological signals Natural frequency High as possible Damping Optimal 7% overshoot in fast flush test

Q: What are the important physical principles in the design of an invasive pressure monitoring system? Prevents resonance from biological signals Natural frequency High as possible Damping Optimal Short, stiff, short, wide tubing Small stiff transducer High density fluid D = 0.64

Q: What are the important physical principles in the design of an invasive pressure monitoring system? Prevents resonance from biological signals Natural frequency High as possible To produce flat frequency response Prevents amplitude distortion of high frequency waveforms Damping Optimal Prevent phase distortion All elements of the waveform are delayed by the same time interval

To produce flat frequency response Arterial waveforms are made up of several different sine waves of different frequencies Fourier analysis

To produce flat frequency response Very under-damped (0.1) Too big Amplitude relative to correct amplitude 1.0 Ideal Flat frequency response to 2/3 FN Too small Optimal damping (0.64) All but the very fastest waveforms will be reproduced without amplitude distortion FN Frequency of sine waves

Q: What are the important physical principles in the design of an invasive pressure monitoring system?

Q: What are the important physical principles in the design of an invasive pressure monitoring system? Prevents resonance from biological signals Natural frequency High as possible To produce flat frequency response Prevents amplitude distortion of high frequency waveforms Damping Optimal Prevent phase distortion All elements of the waveform are delayed by the same time interval

Q: What are the important physical principles in the design of an invasive pressure monitoring system? Prevent phase distortion All elements of the waveform are delayed by the same time interval

Q: What are the important physical principles in the design of an invasive pressure monitoring system? Prevents resonance from biological signals Natural frequency High as possible To produce flat frequency response Damping Optimal D = 0.64 Prevent phase distortion

Q: How does BIS analyse EEG?

Q: How does BIS analyse EEG? How the algorithm was determined

Q: How does BIS analyse EEG? How the real time analysis works on patients

Q: How does BIS analyse EEG? Bispectral: Degree of EEG synchronisation Bispectral: Phase coupling Power spectral analysis Burst suppression

Q: How does BIS analyse EEG?

Q: How does BIS analyse EEG?

Q: How does BIS analyse EEG?