Invasive blood pressure monitoring:
Invasive blood pressure monitoring is a commonly used technique in intensive care units and is also frequently used in operating rooms. The technique involves inserting a catheter into the appropriate artery and then displaying the measured pressure waves on a monitor. The most common reason for using intra-arterial blood pressure monitoring is to obtain successive continuous monitoring of the patient's blood pressure, and to display a graph of pressure versus time, as a waveform.
There are a variety of invasive blood pressure monitors for trauma, intensive care, and operating room applications. These include single pressure, dual pressure and multiple parameters (ie pressure/temperature).
The components of an intra-arterial monitoring system can be divided into three main parts:
- measuring equipment
The measurement device consists of an arterial cannula connected to a tube containing a continuous column of saline that conducts pressure waves to the transducer. The arterial line is also connected to an irrigation system consisting of a bag of saline that is pressurized to 300 mmHg through the irrigation device.
There are advantages to IBP monitoring.
• Continuous "sequential" blood pressure monitoring is very beneficial in patients who may experience sudden changes in blood pressure (eg, vascular surgery). These patients may be those who require close blood pressure control or receive medications to maintain blood pressure, such as those receiving cardiotonic agents such as epinephrine.
• This technology can accurately read blood pressure at low pressures.
• Mainly for patients who may require close monitoring of blood pressure for extended periods of time, eg, ICU patients to avoid trauma caused by repeated inflation of the cuff.
• Intravascular volume status can be estimated by observation or device-specific waveform analysis for arterial pressure trajectory shape.
• Invasive blood pressure measurement can accurately assess blood pressure in some patients who are not suitable for non-invasive blood pressure monitoring, such as patients with severe peripheral edema or morbidly obese patients in the ICU.
• Indwelling arterial cannulae facilitate repeated arterial blood sampling.
Disadvantages of IBP Monitoring
• Arterial catheters are a potential focal point of infection, although the frequency of infection in arterial catheters is much lower than in venous catheters, especially central venous catheters.
• Catheter arteriosus may lead to local thrombosis, which may cause emboli to travel down the limb or cause arterial occlusion (rare if the catheter has been flushed with saline and an appropriate vessel has been selected). The radial, femoral, and axillary arteries are commonly used, as well as the podia, posterior tibial, and dorsal pedis arteries. Because the brachial artery is a terminal artery without collateral blood supply, and brachial artery occlusion can result in a loss of blood supply to the arm, the brachial artery should be avoided when possible.
• If the drug is inadvertently injected into the artery, crystals may form and cause catastrophic ischemia of the limb. All arterial lines should be clearly identified and color-coded (usually with a red stripe) to avoid confusion. At the same time we must keep in mind that the drug should never be administered through the artery.
• Implementation of an arterial blood pressure monitoring system can be difficult and time-consuming, especially if the patient is in shock. This can lead to distraction from other, more urgent issues.
• Monitoring equipment, spare parts and cannula are expensive compared to non-invasive blood pressure monitoring methods.
• Arterial monitors require power, which limits their usefulness in certain environments.