This is the gold standard of blood pressure measurement giving accurate beat-to-beat information. In general, systolic pressure will be slightly higher and diastolic pressure slightly lower (510 mm Hg), than non-invasive measurements. It is useful when rapid changes in blood pressure are anticipated (due to cardiovascular instability, large fluid shifts or pharmacological effects) or when non-invasive blood pressure monitoring is not possible or likely to be inaccurate (obesity, arrhythmias such as atrial fibrillation, non-pulsatile blood flow during cardiopulmonary bypass). It is also used when long-term measurement in sick patients is required as it avoids the problem of repeated cuff inflation (causing localized tissue damage) and allows repetitive sampling for blood gases and laboratory analysis.
Continuous invasive BP monitors display the information both numerically and graphically. The basic principle is to provide a solid column of liquid connecting arterial blood to a pressure transducer (hydraulic coupling) and requires the following components:
tubing (incorporating an infusion system);
microprocessor and display screen;
mechanism for zeroing and calibration.
Intra-Arterial Cannula.A short, parallel-sided cannula made of Teflon or polyurethane is inserted into an artery. Normally, a 20G cannula is used although 22G, and 25G are available for children and neonates. Preferably, a non-end artery, such as radial or dorsalis pedis is cannulated. Should thrombosis of the artery occur, arterial sufficiency is maintained via a collateral supply. The collateral supply to the hand can be assessed using Allen's test although this is not 100% reliable. If cannulation of those arteries is not possible, end arteries such as brachial or femoral may be used with due care to distal arterial sufficiency.
|Brand Name||Cables and Sensors|
|Operating Pressure Range||±300 mmHg, 1 mmHg resolution|
|Operating Temperature||15° C to 40° C (60° F to 105° F)|
|Storage Temperature||-20° C to 65° C (-5° F to 150° F)|
|Operating Humidity||80% RH Max., Non-Condensing|
|Accuracy||±1% of reading or ±1 mmHg, whichever is greater|
|Repeatability and Hysteresis||±0.15% full scale output|
|Transducer Simulator Sensitivity||5 µV/V/mmHg, ±1%|
|Excitation Voltage and Frequency||2 to 10 VDC or VAC RMS, up to 5 kHz|
|Output Impedance||< 400 Ohms|
|Input Impedance||350 Ohms ±10%|