Introduction
Arterial line cannulation has emerged as a widely used procedure in diverse critical care settings for determining blood pressure readings on a real-time and continuous basis, and in blood gas determination, among other laboratory tests (Nutall et al, 2016). In humans, the use of arterial catheters can be traced as far back as 1949, with current widespread use throughout the United States and Europe constituting 8 million and 2.5 million placements, respectively (Hambsch et al., 2015). Nutall et al. (2016) have identified anatomical and surgical considerations as determining factors in the selection of the site for arterial cannulation. Examples of the most ideal sites for cannulation are: axillary, posterior, temporal, ulnar, and radial arteries, among others (Hambsch et al., 2015). In particular, the radial artery is widely used for this procedure, due to its association with a limited number of complications. This low rate of complication is thought to be due to the widespread collateral circulation of palmar arches and ulnar artery, both of which flow to the distal limb (Thai et al., 2015). This low rate of complication is due to extensive collateral circulation comprising the ulnar artery and the palmar arch artery. The two arteries flow to the distal limb. Nutall et al. (2016) have identified various complications linked to arterial cannulation, which include thrombosis, sepsis, ischemia, catheter infections, and temporary vascular occlusion. Other rare complications include severe ischaemia and nerve damage. While vascular complications can be due to various risk factors, Nutall et al. (2016) note that past research has failed to offer reliable data on risk factors linked to arterial cannulation. Most of such previous research provides inconsistent and invalid information, and this has necessitated the need to undertake an extensive examination of the risk factors for arterial line cannulation. In light of the complications that may arise because of the arterial line placement, monitoring of patients with such arterial placement to identify signs of complications to correct them (Clermont & Theodore, 2017). The essay will delve into the available literature on the best practices for monitoring patients to ensure their safety of the patient.
Literature Review
Lavdaniti (2008) reports that while there are numerous methods of monitoring hemodynamic changes in patients, these are broadly categorised into either non-invasive or invasive methods. This review of literature discusses studies that compare the arterial line monitoring technique with other non-invasive techniques. Some studies (for example, Díaz et al. 2015) have sought to demonstrate the potential of consistent assessment of variations in PPV (pulse pressure variation) and blood pressure as a basis for fluid management to retain a patient’s hemodynamic parameters at acceptable levels (Rathole et al, 2017). The risks linked to the use of an arterial line to monitor hemodynamic changes associated with operations have encouraged experts to consider non-invasive techniques for monitoring nuanced changes in arterial blood pressure, stroke volumes, cardiac output, and PPV, among others.
Some non-invasive techniques have been developed to circumvent the complications that can arise from using invasive techniques. The Nexfin device is one such technique that relies on finger cuff technology to monitor the pressure waveform (Truijen et al, 2012). In this regard, some studies have assessed the potential of this technique to substitute invasive arterial lines. Netflix works by computing the mean arterial blood pressure, as well as brachial systolic and diastolic pressure, using an algorithm modeling the characteristics of the vascular tree. It also calculates the pulse contour-derived cardiac output.
Martina et al. (2010) described the finger cuff technology with the reconstruction of finger-to-brachial pressure. The changes in the waveform of arterial blood pressure occur slowly from the brachial artery down the arteries in the fingers, resulting in a fall in the diastolic pressure and a rise in systolic arterial pressure. De Wilde, de Wit, Geerts, and van Vliet (2016) assert that pulse pressure increase begs the question about the consistency of the systolic arterial pressure (SAP ), diastolic arterial pressure (DAP), MAP, and PPV as computed by the Nexfin device compared to the values achieved using the radial artery line. De Wilde et al. (2016) point out that the initial studies comparing the technique revealed inconsistency in the findings. While some studies showed moderate to good concordance in patients after cardiac surgery, other studies underscored the non-invasive pressure monitoring as inadequate to substitute for monitoring of blood pressure using arterial line techniques. Nevertheless, De Wilde and colleagues (2016) found that monitoring PPV with the Nexfin technique was accurate and foretold responders of fluid with an accuracy equivalent to that assessed using a radial artery line. In addition, the computation of PPV was significantly free of systematic errors in measuring arterial blood pressure.
De Wilde et al. (2016) found that the Nexfin device correctly identified patients with an increase in stroke volume greater than 10% on 500 ml fluid loading with considerable sensitivity and specificity for PPVfin values above 9.6% at baseline. However, these researchers found a small variation in the PPV values obtained using the Nexfin technique compared to those obtained by arterial line placement, despite the comparability in the results obtained for the prediction of responders using Nexfin and arterial lines.
Further, de Wilde et al. (2016) findings mimic the results of de Keijzer and van de Hoeven (2011). The former researchers obtained a high sensitivity and specificity of 100% and 94%, respectively, using the Nexfin device to predict fluid responders with PPVfin in patients who underwent surgery of heart surgery. Lanszdorp et al. (2011) reported a cardiac output volume (COV) of 22%. Elsewhere, Fischer et al. (2013) assessed the ability of Nexfin to predict the volume responsiveness via its dynamic indices and concluded that the PPV values obtained with the Nexfin device were inadequate to predict fluid responsiveness. Based on Ribezzo et al. (2014), non-invasive and invasive techniques for monitoring different types of arterial blood pressures must achieve an accuracy and precision lower than 5 mmHg to be suitable for clinical application. Because this criterion for determining the suitability of a technique for use in monitoring the blood pressures has become popular in healthcare, analysis of data obtained using a target technique suffices to establish its potential for use to monitor hemodynamic changes for patients who undergo major surgeries. In light of this, de Wilde, de Wit, Geerts, and van Vliet (2016) found that the data obtained using Nexflin satisfied the mentioned eligibility criteria.
De Wilde and colleagues (2016) emphasized that recent studies comparing the capacity of Nexflin technology with an arterial catheter in monitoring blood pressure in patients who have undergone major operations indicate conflicting results. They showed that Nexfin could achieve between moderate and good accuracy in patients who have undergone a cardiac surgery, although it did not achieve adequate accuracy sufficient to substitute measurement of pressure using intra-arterial techniques. De Wilde et al. (2016) asserted that the results of their study were consistent with the criteria the Association of Medical Instrumentation formulated, as were the findings of Martina et al. (2010).
Meidert, Huber, and Hapfelmeier (2013) compared measurements of different blood pressure parameters using applanation tonometry with those obtained using an arterial line placement in patients in the intensive care unit (ICU) with multiple organ dysfunction syndrome (MODS). Meidert and colleagues (2013) found that applanation tonometry could accurately and precisely measure mean arterial pressure with a mean difference of 1.0 mmHg relative to mean arterial pressure measured using arterial line placement. Moreover, the technique permitted real-time measurement of diastolic arterial pressure with desired accuracy and precision. However, the 95% limits suggest rather lower precision for establishing systolic arterial pressure, although the technique could allow accurate determination of the parameter.
Earlier, Pressman and Newgard (1963) compared applannation tonometry to the sphygmomanometer and were the first to describe the application for continuous monitoring of blood pressure. Stein and Blick (1971) described the principles by which arterial tonometry works to determine blood pressure by placing its transducer in either the dorsalis pedis or radial artery. In this light, Stein and colleagues (1971) indicated that the device was liable to slight movements of the limb of interest or the transducer. Nevertheless, the tonometry system had considerable capability of tracking various blood pressures relative to the arterial line catheter.
According to Meidert, Huber, and Hapfelmeier (2013), various versions of tonometry systems were developed over the past decades to measure continuous percutaneous blood pressure. Some of the systems employ the oscillometric calibration for measuring blood pressure. The researchers employed a version of the tonometry that used the t-line technology to monitor mean arterial pressure and calibrated the blood pressure waveform based on a proprietary scaling algorithm to determine systolic and diastolic arterial pressure measurements.
Continuous monitoring of blood pressure using a noninvasive technique in surgical patients using T-line-based applanation tonometry of the radial artery is achievable with the systolic and diastolic artery pressure, and mean arterial pressure close to arterial line blood pressure measurements. Additionally, the findings of the researchers were promising. This research aimed to assess the accuracy of radial artery applanation tonometry in patients with serious acute conditions, including patients with a major organ dysfunction score of at least 4 and 2 impaired organs at a minimum.
Meidert, Huber, and Hapfelmeier (2013) found that applanation tonometry could measure diastolic arterial pressure and mean arterial pressure with considerable accuracy and precision relative to arterial line placement despite the severity of the conditions of the patients studied. Nevertheless, systolic arterial pressure measurements were less precise, as shown by a broader 95% SD limits of consistency, but a high accuracy, as shown by a low difference between the measurement of blood pressure from arterial catheter and the technique in question.
Previous studies report BP measurement in anesthetized patients using applanation tonometry. These studies investigated predecessor forms of the T-line device in comparison with arterial catheter lines.
In these studies, predecessor versions of the t-line device used in the present analysis were investigated in comparison with invasive blood pressure readings from radial arterial catheters (Meidert, Huber, & Hapfelmeier, 2013). Meidert et al. (2013) compared radial applanatory tonometry with central aortic BP obtained using an arterial line placed in the abdominal aorta via the femoral artery. The past studies used exactly the same approach and sample as that used by Meidert et al (2013).
In this context, one should be aware that systolic arterial pressure and diastolic arterial pressure values are derived from the scaled blood pressure waveform when using the t-line system for applanation tonometry. The t-line system's proprietary scaling algorithm for the assessment of systolic arterial pressure and diastolic arterial pressure values was derived from a database containing invasive blood pressure measurements from radial arterial catheters. Thus, the more pronounced bias between radial artery applanation tonometry–derived and invasively assessed central aortic systolic arterial pressure and diastolic arterial pressure measurements compared with mean arterial pressure measurements was likely affected by the fact that invasive radial artery reference values are used for t-line systolic arterial pressure and diastolic arterial pressure scaling (Meidert et al., 2013). Therefore, one might speculate that in critically ill patients with major organ dysfunction syndrome, a modification of the proprietary blood pressure waveform-scaling algorithm might help improve the accuracy and precision of t-line system–derived systolic arterial pressure measurements.
Another factor that could potentially have had an influence on systolic arterial pressure differences between the central aortic (arterial catheter) and radial (applanation tonometry) site might be respiration-induced systolic arterial pressure variation - the difference between maximum and minimum systolic blood pressure during the respiratory cycle. It has been demonstrated that in patients with spontaneous breathing, there is a decrease in systolic arterial pressure during inspiration, whereas there is an increase in systolic arterial pressure during inspiration in mechanically ventilated patients (Meidert et al., 2013). It has to be emphasized that respiratory cycle effects on blood pressure were not specifically assessed in our study (with about 50% of patients breathing spontaneously and 50% of patients on mechanical ventilation). On the one hand, one could speculate that this respiration-dependent systolic arterial pressure variation might take different forms when comparing central aortic and radial blood pressure. On the other hand, that we analyzed 10-beat averages in our study should minimize the impact of this respiration-associated variation of pulse amplitude on Systolic Arterial Pressure bias.
Furthermore, invasively assessed central aortic pressure might have been increased by high intra-abdominal pressure in some patients in our study because 39% of patients had either liver cirrhosis or acute pancreatitis. In addition to Bland-Altman analysis, we assessed the ability of the applanation tonometry device to track Blood Pressure changes over time by performing concordance analysis derived from 4-quadrant plots. This analysis demonstrated good trending abilities of radial artery applanation tonometry regarding Blood Pressure changes in comparison with invasive measurements (Meidert, Huber, & Hapfelmeier, 2013).
Learning and Development
I have learned that some noninvasive techniques can achieve desirable results concerning monitoring the hemodynamic changes in critical care patients. I think that although measuring blood pressure changes in anesthetized and intensive care unit patients using the invasive technique of arterial catheter appears to be the standard, complications associated with the technique render the use of non-invasive techniques a better option. The studies comparing the results between non-invasive techniques, such as applanation tonometry and nexflin, reveal that they can achieve accurate and precise determination of mean arterial pressure and diastolic arterial pressure. However, the former noninvasive method of measuring these parameters does not yield a precise determination of systolic arterial pressure because the results indicate a wider 95% limit of agreement (Meidert, Huber, & Hapfelmeier, 2013).
Moreover, studies have shown that non-invasive techniques have the potential to replace invasive techniques as the ideal means for measuring hemodynamic changes in critical care patients (for example, Lanszdorp et al., 2011; de Wilde et al., 2016; Stens et al., 2016). Pulse pressure variation (PPV) and stroke volume variation (SVV) measured using the Nexfin technique reflect accurate changes in the fluid state of the patient in critical care settings, as they a more sensitive than MAP and cardiac index. Nexfin can be beneficial in monitoring patients in the operating theatres and ICU who are liable to hemodynamic shifts attributed to loss of blood and subsequent fluid adjustment. Nevertheless, the age-dependent variations in the two parameters inform the selection of the right dynamic indicator for fluid responsiveness.
Conclusion
Noninvasive techniques for monitoring fluid changes in patients can replace arterial line placements in monitoring blood pressure in critical care patients. Nexflin and applanation tonometry have the potential to replace invasive techniques for measuring blood pressure in this population. Despite the limitations in non-invasive techniques for systolic arterial pressure, these techniques are reliable. Therefore, they can replace the arterial line catheter as a technique for monitoring blood pressure changes. The low precision in the measurement of SAP can be compensated for by the measurement of diastolic and mean arterial pressure. All in all, these techniques do not transcend arterial line placement with regard to patient-related characteristics, especially age and severity of disease.
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