Published on 07/02/2015 by admin
Filed under Anesthesiology
Last modified 07/02/2015
This article have been viewed 1530 times
Avishai Ziser, MD
The use of arterial catheters is classically indicated for continuous hemodynamic monitoring and for obtaining blood for laboratory determinations in critically ill patients and those undergoing major operations. The beat-to-beat visual arterial pressure wave and numerical pressure display enable prompt identification of trends or changes in blood pressure that could potentially be missed with noninvasive blood pressure monitoring. The systolic pressure variation (SPV), the pulse pressure variation (PPV), and the stroke volume variation (SVV) based on the arterial waveform may provide an indication of the patient’s volume status and prediction of fluid responsiveness. Accurate measurement of cardiac output (CO) can be performed based on the arterial waveform. Several monitoring instruments apply this technology at the patient’s bedside.
The arterial catheter is placed in a peripheral artery or the femoral artery, with the radial artery being the most commonly used cannulation site. Arterial spasm and thrombosis, local infection and hematoma, distal ischemia, hemorrhage, and air embolism are the main complications. A 20G cannula is appropriate for the cannulation of a small artery, and an 18G for a larger one. Aseptic technique should always be applied. The arterial cannula is connected to a pressure transducer via high-pressure tubing. The pressure transducer should usually be located at the level of the right atrium, or at the level of the external auditory meatus for the sitting patient who is undergoing a neurosurgical procedure. Air should be thoroughly evacuated from the entire system. Zeroing to atmospheric pressure is done before first use and as needed afterward. The continuous flash device is connected to a bag of normal saline under a pressure of 300 mm Hg that brings a continuous flash of 1 to 3 mL/h to prevent clot formation at the tip of the arterial cannula. Heparin (1-2 μ/mL or 10-20 μgr/mL) can be added to the flush solution, but this is not mandatory, and the risk of heparin-induced thrombocytopenia should be kept in mind.
The arterial waveform provides valuable and continuous hemodynamic information. It changes as the measuring catheter is located more distally from the heart. The pulse pressure increases, and the dicrotic notch is delayed and then disappears. The systolic pressure is higher in a peripheral artery, compared with the ascending aorta, but the mean pressure is minimally affected or slightly reduced. The heart rate and rhythm can be determined from the arterial tracing. The effect of ectopic beats on arterial pressure and waveform can be evaluated. The pulse pressure may help to evaluate the patient’s hemodynamic status. High pulse pressure can be seen after exercise and in patients with hyperthyroidism, aortic insufficiency, peripheral vasodilatation, arteriovenous malformation, increased stiffness of the aorta (most common in older patients), and mild hypovolemia. Narrow pulse pressure can be seen in patients with hypovolemia, pericardial tamponade, congestive heart failure, aortic stenosis, and shock states. The area under the arterial curve, from the onset of systole to the dicrotic notch, can estimate the stroke volume (SV), and the systolic rise may reflect myocardial contractility. However, the arterial curve changes as the location of the arterial cannula insertion moves distally from the ascending aorta.
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