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I wonder how much more accurate and reliable indwelling arterial catheters are compared to standard, non-invasive techniques to monitor ICU patients' blood pressure.

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  • Maybe you could elaborate how you would compare accuracy and reliability. Also, did you research this somewhere?
    – Thomas
    Jul 27, 2020 at 0:13

1 Answer 1

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Methods of monitoring blood pressure

Pressure in the blood vessels can be measured by invasive or non-invasive means.

Invasive blood pressure uses an arterial catheter with a pressure transducer.

Non-invasive measurements use a cuff to compress the artery and take measurements as the pressure is reduced. This can be done with either automated oscilliometry or the traditional auscultation for Korotkof sounds while a manometer measures the pressure in the cuff.

In a general sense, NIBP via auscultation is taken to be the gold standard.

However, invasive blood pressure (IBP) and non-invasive blood pressure (NIBP) monitoring are used in different circumstances.

From reference 1:

The most accurate method of obtaining blood pressure measurements is with the use of an invasive probe that is inserted directly into the lumen of an artery. An advantage of invasive monitoring is the ability to display blood pressure variations with each heartbeat. However, given the invasive nature of this method and the associated risks, its use is limited to critical care or operative settings.

IBP is highly accurate as there is a pressure transducer in the artery. It can detect rapid changes in blood pressure and can be used in different parts of the vascular system for different purposes (e.g. pressure measurements in different cardiac chambers during cardiac catheterisation).

NIBP only approximates this intra-arterial pressure, but is of course not invasive and thus does not have the risks of IBP which include thromboembolism, infection and vascular damage.

From reference 2:

Many consider IBP monitoring to be the gold standard, as it directly measures intra-arterial pressures. An arterial line is used in patients who are anticipated to experience extremes of BP, are unstable, would be unable to be monitored accurately by NIBP means, require continuous monitoring, or are expected to have frequent intraoperative blood sampling. Despite that, there are no evidence-based indications for arterial line placement and the decision regarding its use are usually made on a case-by-case basis [23]. Use of IBP requires an invasive procedure that may produce rare but serious complications and requires trained personal for its placement, removal and care.

Non-invasive continuous arterial pressure monitoring

There are non-invasive continuous arterial pressure (NICAP) monitors, but they may not be as reliable. The paper in reference 3 concludes:

NICAP has a poor correlation with the arterial line in elderly patients for the whole surgery or during anesthesia induction. Moreover, it showed poor comparability in the detection of blood pressure change trends with arterial lines. Our findings suggest that NICAP might not be sufficiently accurate to be applied clinically in elderly patients with comorbidities. More accurate calibration and iteration are needed.

Comparison of NIBP and IBP monitoring.

This table is from reference 2: Comparison of NIBP and IBP

Pragmatic approach when BP readings differ

In reference 2, the authors conclude the following (emphasis added):

NIBP monitors are usually sufficient for hemodynamic monitoring in the perioperative period, however IBP may be needed. Advantages, limitations, and complications of both methods must be considered when utilizing them. Using both NIBP and IBP monitors concurrently during the intra- and postoperative periods may result in discordant BP values and pose a management dilemma. When NIBP and IBP measurements differ significantly in the postoperative period despite troubleshooting potential sources of error inherent to each modality, we suggest NIBP should generally be the preferred monitor for clinical decision making. This is our general recommendation because NIBP is the method used outside of the perioperative period to determine BP baseline and guide therapeutic management. It is reasonable to assume that factors affecting NIBP accuracy are unchanged between the preoperative and in the perioperative period, therefore accuracy of the monitor should be consistent in both settings.

Here the authors suggest falling back to NIBP, even though it can be less accurate, as it will be consistent with readings outside the perioperative period and less prone to technical error.

References

  1. Hashmi and Nelson. Blood pressure measurement.
  2. Storozh et al. Postoperative Hypertension: When Blood Pressure Cuff and Arterial Line Disagree.
  3. Zhao et al. Comparison of noninvasive continuous arterial blood pressure measured by NICAP with arterial line in elderly patients.

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