Blood pressure monitoring Monica Morosan. AAGBI standards of monitoring A - Induction and Maintenance of Anaesthesia 1. Pulse oximeter 2. Non invasive.
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Blood pressure monitoring
Monica Morosan
AAGBI standards of monitoring
A - Induction and Maintenance of Anaesthesia1. Pulse oximeter2. Non invasive blood pressure monitor3. Electrocardiograph4. Airway gases: oxygen, carbon dioxide and vapour5. Airway pressure
The following must also be available6. A nerve stimulator whenever a muscle relaxant is used7. A means of measuring the patient’s temperature
Methods of BP monitoring
• Indirect: Mercury manometer Oscillometry Automatic oscillometric technique (DINAMAP) Radial arterial compression Finapress technique Microphone (Doppler)• Direct (Invasive)
Mercury manometer
• BP determined by palpation or auscultation
• Korotkoff sounds
Oscillometry
• Aneroid gauge (Bourdon gauge)
• Measures high pressures
• Coiled tube connected to a pointer
• Bellows
Oscillotonometry
• Does not use palpation or auscultation
• 2 cuffs (occluding –upper, overlaps the sensing cuff-lower)
• Inflate both and release the occluding
DINAMAP
• Air pump• Bleed valve• Pressure transducer
(measures both pressure and oscillations)
• Microprocessor
Problems
• Cuff too small-over reads• Cuff too large-under
reads• Over reads at low BP,
under reads at high BP• Arrhythmias• External pressure on cuff• Nerve palsy• Petechial haemorrhages
Radial artery compression
• Pressure sensor strapped to wrist
• Sensor driven hydraulically by a control system (applies pressure and senses oscillations)
• Algorithm –BP from table values
Finapress technique
• Cuff on finger –infrared LED and photocell- detects the volume of arterial blood in the finger
• Electronic processor analyses the photoplethysmograph to determine the volume at MAP
Microphone over artery
• Doppler changes
Invasive measurement
Indications for A line insertion
Uses:• Arterial pressure
measurement• Drug delivery
(thrombolysis)• Procedural access
(angio)• Mechanical support
techniques (IABP, ECMO)
Indications:• Cardiovascular
instability• Vasoconstrictors/
Inotropes• BP manipulation• Blood sampling
Transducer
• Transforms one form of energy into another
• Based on Wheatstone bridge
Information from the trace
• BP (systolic, diastolic, MAP)
• Pulse rate• Position of dicrotic
notch reflects peripheral resistance
• Upstroke part reflects miocardial contractility
Resonance and damping
• Resonance
-Measuring system posseses a resonant frequency
-Oscilations occuring at this frequency will produce a sine wave superimposed on the BP waveform
• Damping
-Property of a system to resist mechanical oscillations
-Air bubbles
-Clot
Step response
• Complications:• Medical (AV fistula,
false anaeurysm, thrombosis, ischaemia, infection)
• Equipment (disconnection, loss wire, catheter fracture, inadvertent intra arterial injection of drugs)
Summary
Direct
Indirect
Complications
Sources of error
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