A new study entitled “Accuracy of invasive arterial pressure monitoring in cardiovascular patients: an observational study” was published in Critical Care by Dr. Stefano Romagnoli, part of Dr. A Raffaele De Gaudio’s research team from the Department of Anesthesia and Intensive Care at the University of Florence. The study focused on five key parameters, including chronic obstructive pulmonary disease and arterial hypertension.
Intra-arterial blood pressure (IABP) procedure is the most common way to perform blood pressure measurements. However, interferences due to inadequate dynamic response of the fluid-filled monitoring systems may induce important differences between actual and displayed pressure values.
In this study, the research team evaluated the frequency and causes of resonance/underdamping phenomena in patients submitted to major vascular and cardiac surgery. All material has a frequency at which it oscillates freely, named natural frequency. If a force with a similar frequency to the natural frequency is applied to a system, it will begin to oscillate at its maximum amplitude. This process is called resonance. The damping phenomenon happens when something reduces the energy of an oscillating system and consequently the amplitude of the oscillations. In all systems there is always some degree of damping, but if insufficient it is called underdamping, and the result will be adversely affected. In an IABP measuring system, most damping is due to friction in the fluid pathway.
In this study, the research team evaluated the frequency and causes of resonance/underdamping process in patients submitted to important vascular and cardiac surgery. The researchers measured the arterial pressures by an invasive way and each patient was distributed between two groups accordingly to the presence (R-group) or absence (NR-group) of resonance/underdamping signals based on the fast-flush Gardner’s test, which is the test that enables to obtain in vivo the natural frequency and damping coefficient using an invasive blood pressure monitoring system. After these measurements, both values — the invasive blood pressure with the non-invasive — were compared. The researchers analyzed in 300 patients a total of 11,610 pulses and 1,200 measurements of non-invasive blood pressure. They found that 30.7% of the patients (92/300) had arterial underdamping/resonance signals. For patients that had underdamping/resonance signals (R-group), the average of systolic invasive blood pressure (IBP) was overestimated when compared to non-invasive blood pressure (NIBP), 28.5 (15.9) mmHg (P <0.0001), while in the NR-group the overestimation was 4.1(5.3) mmHg (P <0.0001).
A multivariate logistic regression identified five parameters independently associated with underdamping/resonance: polydistrectual arteriopathy (P =0.0023; OR?=?2.82), history of arterial hypertension (P =0.0214), chronic obstructive pulmonary disease (P =0.198; OR?=?2.09), arterial catheter diameter (20 vs. 18 gauge) (P <0.0001; OR?=?0.34) and sedation (P =0.0131; OR?=?0.5)
The authors concluded that IBP can be potentially inaccurate in a constant number of patients due to underdamping/resonance events. While Non-invasive intra-arterial blood pressure (NIBP) measurements can be useful to validate or exclude the presence of this artifact avoiding inappropriate treatments.