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