Invasive Measurement of Blood Pressure

Transcription

1 Invasive Measurement of Blood Pressure Arterial Lines & Pulmonary Artery Lines Key Points Invasive Measurement of Blood Pressure: - understand blood flow through the body - understand Pulmonary Artery catheters and their placement - understand pressure transducers, strain gauge, wheatstone bridge - know the concept of damping in any oscillating system - know the function of the Swan-Ganz (Pulmonary Artery) catheter - know the passage and placement of the Swan-Ganz catheter - understand when and why a Swan-Ganz catheter would be used - is it diagnostic or therapeutic? - know typical pressures for CVP and for wedge pressure - understand impact of air bubbles in a pressure transducer setup - understand importance of leveling the transducer with the heart - are most IBP problems electronic or plumbing? - be familiar with simulators and test devices D. J. McMahon rev cewood Measuring Blood Pressure Invasively Chatterjee FIGURE 9-5 Blood circulation First attempt at direct blood pressure measurement: Dr. Hale ~ 1773

2 An Electronic Analog of the Cardiovascular System More Analogs of the CV System Dennis s Electronic Analog:

3 Pressure Conversions (most useful conversions shown in bold) PSI KiloPascal cm of H 2 O mm of Hg atmosphere millibar 1 PSI = KiloPascal = cm of H 2 O = mm of Hg = atmosphere = millibar = remember: 1 atmosphere = 14.7 psi = 760 mmhg = 1033 cmh 2 O = 101 kpa Hg: 760 mm = inches H 2 O: 1033 cm = 33.9 feet Arteries, meet veins. Veins, meet arteries. How do you do? Blood pressure in systemic circulation Blood Pressure thru the Vascular Tree

4 Options for invading the vascular system for pressure measurement: Invasive Arterial Line Setup ( A-Line ) > Plastic catheter in the artery connects to a transducer > Transducer converts pressure to voltage signal, which is displayed on a monitor > In order to keep the catheter patent, a solution of heparinized saline is made to flow into the catheter at a very slow rate, typically 3mL/hr. The saline is under ~300 mmhg pressure.

5 Inside view: transducer in disposable arterial line kits: Major vessels of the hand Typical current invasive pressure kit a.k.a. an Arterial Line Setup or A-Line Setup

6 Electronic analogs of pressure monitoring lines: Allen s Test for vascular competence hyperaemia: an excess of blood in the vessels Ideal arterial pressure waveform: Dicrotic Notch Damping in any oscillating system: Damping is an effect on any oscillating system that reduces or restricts its oscillations. In a mechanical system, damping is produced by drag in the system. In a fluid system, damping is caused by viscosity. In an electronic system, damping is caused by impedance. Undamped: The system oscillates at its natural resonant frequency. Critically damped: When disturbed, the system returns to equilibrium quickly, without oscillation. Overdamped: When disturbed, the system returns to equilibrium without oscillating. Underdamped: When disturbed, the system oscillates, but the amplitude decreases to zero.

7 Troubleshooting invasive BP lines: Basic circuit for direct pressure monitoring Almost ideal Air bubbles in the line Line is partially occluded 3-position switch to select full-scale reading value Systolic, Diastolic, and Mean separated out for extra precision Detail of Systolic and Diastolic detection sections -

8 Typical pressure channel module The Swan-Ganz (Pulmonary Artery) Catheter Open system to room air, then press and hold ~3 to zero the transducer. Use for changing the pressure range, labels, & alarm settings on the display. Dr Swan Dr Ganz

9 The passage of the Swan- Ganz catheter through the heart. Pressure Waveforms during cardiac catheterization: RA: Right Atrium Pressure Waveforms during cardiac catheterization: Pressure Waveforms during cardiac catheterization: PA: Pulmonary Artery RV: Right Ventricle

10 Pressure Waveforms during cardiac catheterization: Final position of the P-A catheter for monitoring: PCW: Pulmonary Catheter Wedge note: final position can be on either side Pressure waveforms during insertion of the Swan-Ganz catheter: Most used:

11 Importance of zeroing the setup to the patient s heart level: ( the Hydrostatic Issue ) Importance of zeroing the setup to the patient s heart level: The zero point must be at the patient s heart level: OK, even though the transducer is not at the pt s heart level. NOT OK: Zero point here is 6 below the pt s heart level, so the entire pressure waveform will be offset by an increased value. Troubleshooting Direct BP Setups- Vast majority of problems are in the plumbing, not the electronics: > the hydrostatic issue > air bubbles in the system > occlusion of the catheter > set-up problems (zeroing & calibration of transducer) > bad cables or connectors (especially pins) If in doubt, use a simulator with a good cable to rule-out the plumbing as the problem. Connector problems -

12 Pressure line connector for HP / Agilent / Philips monitors Test devices for Direct BP channels: Functional ~click~ 0 mmhg ~click~ 100 mmhg Not very functional Static calibration checker from manufacturer Dynamic simulators for calibration of pressure - Current simulators for pressure verification - Note the selection of transducer sensitivity. ( All disposable transducers now use a sensitivity of 5µV/V/mmHg ).