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Check out the latest from Medic Mindset with Ginger Locke! Since the inception of hemodynamic monitoring, square wave testing, also known as dynamic response testing, continues to intermittently confuse both new and experienced critical care providers. Square wave testing can have a direct impact on the validity and accuracy of the hemodynamic values which are obtained from the invasive monitoring device.
It is imperative that critical care clinicians be competent in understanding not only the purpose of square wave testing, but how to interpret its results. The primary utilization of the square wave test is with arterial lines — those invasive monitoring cannulations which reside within the lumen of a systemic artery — and can be transduced to reveal a beat by beat graphic of luminal arterial tension.
In order to properly and accurately interpret the values being transduced, it is recommended to perform a square wave test. What comes next is the ability to interpret what is displayed on the monitor! There are two factors to consider when evaluating the square wave test or the dynamic response test.
The first is called the natural resonant frequency, and the second is referred to as the damping coefficient. When the invasive monitoring system is flushed, it exposes the transducer to a pressure signal a very high-pressure signalwhich in turn causes the transducer to vibrate.
How quickly the system vibrates is, essentially, the natural resonant frequency. This phenomenon is rapidly followed by the damping coefficient, which is the speed at which those vibrations stop and return to normal transduction. The vibrations caused by the fast flush should be quickly quelled and the system should return to pressure transduction. In broad terms, there are three responses that are typically seen with a square wave test; adequately-damped, over-damped, and under-damped.
An adequately-damped waveform is when there are only two oscillations that follow the fast-flush wave. The two oscillations should be no more than one-third the height of the previous oscillation.
The subsequent transducing should demonstrate a clear arterial waveform with a discernable dicrotic notch. This result requires no further intervention or evaluation, and the hemodynamic values displayed on the monitoring device, can be interpreted with legitimacy and accuracy. A waveform that is damped will appear small in amplitude and flattened. The dicrotic notch will be hard to visualize and appreciate. Additionally, the systolic pressure will be poorly reflected, causing it to be reported lower than it actually is.
Conversely, the diastolic blood pressure will be over-estimated, and will be reported higher than it actually is. There are a number of causes of an over-damped waveform. Remember that air is easily compressible, and will almost always cause an over-damped waveform. An over-damped waveform is a relatively common occurrence and can be fairly easy to correct. A waveform that is under-damped will appear saltatory in nature causing variations in the systolic and diastolic blood pressure values.
Typically, the systolic blood pressure will be reported higher than it actually is, and the diastolic blood pressure will be reported lower than it truly is. The dicrotic notch will be visible and likely exaggerated in size in an under-damped waveform. The causes of this type of waveform are limited and therefore, it is not as common to see in clinical practice.
Things like excessive tubing length, the use of multiple stopcocks, and patient conditions, such as tachycardia, or a high cardiac output, can all cause under-damping. In the event that the patient condition is causing a under-damped waveform, it is acceptable to treat the underlying condition to ensure a more adequate and accurate waveform interpretation.
In order to ensure that invasive monitoring be used as a reliable resource, critical care providers should be challenged to master the skill of performing a square wave test and competently interpreting the ensuing waveform — whether it is adequately-damped, under-damped or over-damped. The best practitioners know that information such as this is only as good as the technical quality will allow — therefore making it an additional priority when caring for a patient undergoing invasive hemodynamic monitoring.
Peer Review:.Nonetheless, artifacts due to inappropriate dynamic response of the fluid-filled monitoring systems may lead to clinically relevant differences between actual and displayed pressure values.
Invasive pressure values were then compared with the non-invasive ones. A total of 11, pulses and 1, non-invasive blood pressure measurements were analyzed in patients. Ninety-two out of The mean arterial pressure difference was 7. The ROC curve for the maximal pressure—time ratio, showed an optimum selected cut-off point of 1.Fix system error lol
In every clinical condition, arterial pressure monitoring should hence be as accurate as possible [ 23 ]. For this reason, in critically ill patients and in patients undergoing high-risk and major surgery, direct intra-arterial pressure measurement invasive blood pressure, IBP is considered the gold standard, allowing beat-by-beat measures even in patients receiving inotropic or vasoactive drugs, or in cases of abrupt changes in blood volume or arterial tone, or those with arrhythmias [ 3 - 5 ].
However, NIBP measurement is not continuous and, during hemodynamic instability, severe hypotension, in conditions of increased arterial stiffness and in obese patients, this technique is expected to be less accurate than the invasive one [ 24 - 8 ]. These considerations may be disregarded in case of IBP system calibration errors, altered pulse travelling arterial dissection or stenosis and artifacts due to movement or inappropriate dynamic response of the fluid-filled monitoring systems overdamping and underdamping [ 910 ].
Inwe demonstrated that in patients undergoing vascular surgery, the incidence of arterial pressure artifacts due to underdamping of the pressure transducer or resonance artifact was as high as A prospective observational cohort study was conducted. The study was approved by the hospital ethics committee of the Azienda Ospedaliero-Universitaria Careggi - University of Florence, and informed consent was obtained by all participants.
All consecutive patients with indwelling radial arterial catheter as standard practice in vascular surgery and cardiac surgery operating theatres and cardiac surgery ICU were enrolled in the study.
Data acquisition has been performed by the investigators prior to anesthesia induction, during surgery, in the ICU, with or without sedation.Liteboat price list
None of the investigators was involved in the clinical management of the patients. A standard procedure was used for all measurement collection. First, the arterial pressure transducer was leveled and zeroed to the intersection of the anterior axillary line and the fifth intercostal space.Mc cabinda ft xuxu bower
The investigators then purged the system of any air bubble with a dedicated inflated flush system set at mmHg. The fast-flush test is the only one that allows clinicians to evaluate, the appropriateness of the dynamic response of the blood pressure measuring system at the bedside. The test is described elsewhere in details [ 9 ]: briefly, it is performed by flushing saline with high pressure mmHg via the flush system of the transducer. Damping anything that reduces energy in an oscillating system will reduce the amplitude of the oscillations and some degree of damping is required in all systems for example, friction in the fluid pathway.
The analog pressure signals are recorded on a personal computer for fast-flush test registration and analysis. Fast-flush test. The corresponding damping coefficient is 0. N: normal QRS complex. Diagram showing the three areas for underdamped, overdamped, and optimally damped blood pressure signal. Blood pressure values were recorded for thirty seconds each and the average value taken for analysis.Celinski Michael G. Seneff Arterial catheterization is the second most frequent invasive procedure performed in the intensive care unit ICU.
In nearly all institutions, the logistics of setup, maintenance, and troubleshooting of pressure monitoring equipment are now largely relegated to personnel other than physicians [ 1 ]. Unfortunately, this shift away from physician involvement has left many intensivists without an adequate working knowledge of these important systems. While historically the most common indications to place an arterial catheter have been for beat-to-beat monitoring of blood pressure in unstable patients and frequent blood gas sampling, new technologies have arisen that necessitate arterial access.
For example, arterial pulse contour analysis can now be used to determine cardiac output reliably and less invasively in patients compared to the traditional thermodilution method [ 23 ]. Additional technological improvements will undoubtedly follow, and the need for arterial line placement may decrease as technologies such as transcutaneous PCO 2 monitoring and noninvasive systems for measuring arterial waveforms mature [ 45 ].
In this chapter, we review the principles of hemodynamic monitoring and discuss the indications and routes of arterial cannulation. Indications for Arterial Cannulation Arterial catheters should be inserted only when they are specifically required and removed immediately when no longer needed. Too often, they are left in place for convenience to allow easy access to blood sampling.
Many studies have documented that arterial catheters are associated with an increased number of laboratory blood tests, leading to greater costs and excessive diagnostic blood loss [ 67 ]. Protocols incorporating guidelines for arterial catheterization and alternative noninvasive monitoring, such as pulse oximetry and end tidal CO 2 monitoring, have realized significant improvements in resource utilization and cost savings, without impacting the quality of care [ 8 ]. The indications for arterial cannulation can be grouped into four broad categories Table : a hemodynamic monitoring including pulse contour cardiac output monitoring ; b frequent arterial blood gas sampling; c arterial administration of drugs, such as thrombolytics; and d intraaortic balloon pump use.
Noninvasive, indirect blood pressure measurements determined by auscultation of Korotkoff sounds distal to an occluding cuff Riva-Rocci method are generally accurate, although systolic readings are consistently lower compared to a simultaneous direct measurement.
In hemodynamically unstable patients, however, indirect techniques may significantly underestimate blood pressure [ 9 ]. Automated noninvasive blood pressure measurement devices can also be inaccurate, particularly in rapidly changing situations, at the extremes of blood pressure, and in patients with dysrhythmias [ 10 ].Ambarella s2l
For these reasons, direct blood pressure monitoring is usually required for unstable patients. Rapid beat-to-beat changes can easily be monitored and appropriate therapeutic modalities initiated, and variations in individual pressure waveforms may prove diagnostic. Waveform inspection can rapidly diagnose electrocardiogram ECG lead disconnect, indicate the presence of aortic valve disease, help determine the effect of dysrhythmias on perfusion, and reveal the impact of the respiratory cycle on blood pressure pulsus paradoxus.
Additionally, the responsiveness of cardiac output to fluid boluses may be predicted by calculating the systolic pressure variation SPV or pulse pressure variation PPV through the respiratory cycle. Recent advances allow continuous CO monitoring using arterial pulse contour analysis. This method relies on the assumption that the contour of the arterial pressure waveform is proportional to the stroke volume [ 12 ].
This, however, does not take into consideration the differing impedances between the arteries of individuals, and therefore requires calibration with another method of determining cardiac output [ 13 ]. Calibration is usually done with lithium or transpulmonary thermal dilution methods. A new pulse contour analysis instrument has been introduced that does not require an additional method of determining CO for calibration, but instead estimates impedance based on the waveform and patient demographic data [ 3 ].
This method has significant limitations i. Management of patients in critical care units typically requires multiple laboratory determinations.
Unstable patients on mechanical ventilators or in whom intubation is contemplated may need frequent monitoring of arterial blood gases. In these situations, arterial cannulation prevents repeated trauma by frequent arterial punctures and permits routine laboratory tests without multiple needle sticks. In our opinion, an arterial line for blood gas determination should be placed when a patient will require three or more measurements daily.
TABLE It deals with the practical aspects of measuring the performance characteristics of the arterial pressure transducer system. When you squeeze the fast flush valve, you let the transducer taste some of the mmHg in the pressurized saline bag. This produces a waveform that rises sharply, plateaus, and drops off sharply when the flush valve is released again.
Peripheral arterial lines: insertion and care
After the fast flush has ended, the transducer system returns to baseline. It does so as a harmonic oscillator, "bouncing" a couple of times before coming to rest. The accurate, responsive, adequately damped arterial line waveform will have the following features:.
The over-damped trace will lose its dicrotic notch, and there wont be more than one oscillation. This happens when there is clot in the catheter tip, or an air bubble in the tubing. The higher frequency components of the complex wave which forms the pulse are damped to the point where they noi longer contribute to the shape of the pulse waveform. The under-damped trace will overestimate the systolic, and there will be many post-flush oscillations.
For those who like hardcore physics, this excellent resource will be an enormous source of amusement. It appears to be a free online textbook of anaesthesia. Nowhere else was this topic covered with a greater depth, or with a greater attention to mathematical detail. Previous chapter: The arterial line pressure transducer setup Next chapter: Normal arterial line waveforms.
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In summary: Dynamic Response is a function of Natural Resonant Frequency and Damping Coefficient The Natural Resonant Frequency: How fast the system vibrates in response to a pressure signal The Damping coefficient: How quickly those vibrations come to rest in the system The dynamic response of an arterial line system is tested using the "fast flush" test, where the transducer is briefly exposed to pressure straight from the counterpressure bag.
When the fast flush abruptly ends, the transducer system oscillates at its natural frequency. This can be measured and assessed for adequacy. The transducer system needs to have a natural frequency in excess of 24 Hz in order to resolve fine features of the arterial line trace eg.
Email Address. Send Message.Metrics details. Nonetheless, artifacts due to inappropriate dynamic response of the fluid-filled monitoring systems may lead to clinically relevant differences between actual and displayed pressure values. Invasive pressure values were then compared with the non-invasive ones. A total of 11, pulses and 1, non-invasive blood pressure measurements were analyzed in patients.
Ninety-two out of The mean arterial pressure difference was 7. The ROC curve for the maximal pressure—time ratio, showed an optimum selected cut-off point of 1.
In every clinical condition, arterial pressure monitoring should hence be as accurate as possible [ 2 ],[ 3 ]. For this reason, in critically ill patients and in patients undergoing high-risk and major surgery, direct intra-arterial pressure measurement invasive blood pressure, IBP is considered the gold standard, allowing beat-by-beat measures even in patients receiving inotropic or vasoactive drugs, or in cases of abrupt changes in blood volume or arterial tone, or those with arrhythmias [ 3 ]-[ 5 ].Ip_icmp.h
However, NIBP measurement is not continuous and, during hemodynamic instability, severe hypotension, in conditions of increased arterial stiffness and in obese patients, this technique is expected to be less accurate than the invasive one [ 2 ],[ 4 ]-[ 8 ].
These considerations may be disregarded in case of IBP system calibration errors, altered pulse travelling arterial dissection or stenosis and artifacts due to movement or inappropriate dynamic response of the fluid-filled monitoring systems overdamping and underdamping [ 9 ],[ 10 ]. Inwe demonstrated that in patients undergoing vascular surgery, the incidence of arterial pressure artifacts due to underdamping of the pressure transducer or resonance artifact was as high as A prospective observational cohort study was conducted.
The study was approved by the hospital ethics committee of the Azienda Ospedaliero-Universitaria Careggi - University of Florence, and informed consent was obtained by all participants. All consecutive patients with indwelling radial arterial catheter as standard practice in vascular surgery and cardiac surgery operating theatres and cardiac surgery ICU were enrolled in the study.
Data acquisition has been performed by the investigators prior to anesthesia induction, during surgery, in the ICU, with or without sedation. None of the investigators was involved in the clinical management of the patients.
A standard procedure was used for all measurement collection.
First, the arterial pressure transducer was leveled and zeroed to the intersection of the anterior axillary line and the fifth intercostal space. The investigators then purged the system of any air bubble with a dedicated inflated flush system set at mmHg.The accuracy of arterial lines AL using the flush test or stopcock test has not been described in children, nor has the difference between invasive arterial blood pressure IABP versus non-invasive cuff NIBP blood pressure.
There were AL tests in enrolled patients with mean age Optimally damped AL occur in half of critically ill children, and this is not predictable.
In critically ill children, NIBP may not be accurate enough to guide management, and more attention to ensuring the AL is optimally damped is needed. The online version of this article doi Blood pressure is a crucial vital sign in critically ill children. Accurate measurement of blood pressure is assumed in the diagnosis of hypovolemic, cardiogenic, vasodilatory, and obstructive shock, and of hypertension from any cause. Accurate measurement of blood pressure is also assumed in the often urgent management of any of these conditions with volume, vasoactive medication infusions, and even extracorporeal support.
Even triage and resource allocation decisions, such as whether to transport and admit to the pediatric intensive care unit PICUare often based on the assumption of accurate blood pressure measurement. Nevertheless, there is no study we are aware of that determines the accuracy of blood pressure measurement in children in the PICU, whether invasive arterial blood pressure IABP is measured using an invasive arterial line ALor whether non-invasive cuff blood pressure NIBP is measured.
Accurate IABP measurement requires an optimally damped measurement system, and if the pressure is over or under damped the measured IABP is theoretically underestimated or overestimated, respectively [ 12 ]. This test was first described inand has since been used in studies in adults in intensive care, and is suggested in standard anesthesia texts [ 1 — 4 ].
This test can easily be done when AL are set up with an Intraflo continuous flush element. Alternatively, it has been suggested that closing the stopcock to the continuously infusing AL for several seconds followed by quickly opening the stopcock will result in a similar rapid flush to the system [ 1 ]. To our knowledge, the usefulness of this stopcock test has never been reported. Although NIBP is routinely measured in the PICU, the ethics committee required signed informed consent from legal guardians prior to inclusion in the study because it was decided that the extra NIBP measurement may be of discomfort to the patients.
Exclusion criteria were: extracorporeal life support; abnormal aortic arch, including after subclavian flap repair of coarctation; known non-functioning AL e.
A case report form and study instruction manual were created prior to patient recruitment, with standard definitions, calculation instructions, and procedure instructions Additional files 1 and 2. Demographic age, sex, diagnostic categoryseverity of illness inotrope infusion score, vasodilator infusion in use, ventilation in usepotentially confounding factors for NIBP obesity defined as over the 90 th percentile weight for age; severe edema in the limb used for NIBP; chronic hypertension; and obstructive airway diseaseand site of the AL peripheral or femoral variables were recorded.
A stopcock test was then done and the AL waveform printed for later calculations. These procedures were done on the day d of the AL as follows: d1—3, d4—6, and d7—10 as appropriate; on d1—3 a second set of procedures was done 2—3 hours later on the same day if this occurred during working hours. The arterial line was set up as follows. The transducer was connected by the invasive pressure cable into the blood pressure module of the Phillips IntelliVue MP70 bedside monitor.
The pressure monitoring set has an Intraflo continuous flush element pigtail that can be pulled to allow rapid flush of the system, and this is functional when not on the Alaris pump. Pre-specified variables entered in the regression models were: gender, weight, inotrope in use, vasodilator in use, ventilation in use, peripheral site of the AL, day category of AL d1—3, d4—6, or d7—10diagnostic category of the patient postoperative cardiovascular vs otherand optimally damped AL for predicting NIBP—IABP.
Sensitivity analyses were done using results from only the first testing of the AL that were in the d1—3 category.This Guideline is applicable to all Medical and nursing staff working in neonatal units in the West of Scotland. Separate guidance is available for aseptic technique for procedures and for taking blood samples from an indwelling arterial catheter. Staff should also be familiar with the use of equipment to which the arterial catheters will be connected, including: syringe driver; invasive blood pressure monitoring system; and blood sampling circuits.
The use of these is covered in separate guidance. Umbilical arterial lines should be sited in preference to peripheral arterial lines during the immediate newborn period unless contraindicated. The decision to site a peripheral arterial line should be discussed with the attending neonatal consultant. The need for arterial lines should be reviewed on a daily basis on the consultant ward round.
Where time permits explain the procedure to the parents, including what the procedure involves, the reason for the cannula, the potential risks of a cannula. Other sites should be avoided, except by agreement with the attending consultant. All arterial lines must be connected to a pressure monitoring system. This allows invasive blood pressure monitoring and also provides a warning of disconnection or occlusion of the catheter.
The arterial pressure monitoring system and blood sampling line should be primed before use and calibrated.
Avoid Errors in Invasive Blood Pressure Measurement
Patency of the peripheral arterial line is maintained with an infusion of 0. The Heparinised saline should be changed every 24 hours. Choose the most appropriate artery to cannulate. When inserting a peripheral arterial line, a sterile procedure should be adopted in line with the applicable antisepsis guideline.
Once successfully inserted, inspect the cannula site every hour and document findings on the observation chart. As these observations need to be made frequently staff should ensure that the site is easily visible and not covered with blankets or bedding.
If any concerns are identified they should be reported immediately to the medical staff. Accidental displacement of the arterial cannula will require immediate application of pressure to the site for mins or until bleeding has stopped. Peripheral Arterial cannula should be removed when no longer required, or if there are complications or contraindications. Continuous arterial blood pressure monitoring will be carried out on all babies with intra-arterial lines in situ.
Arterial waveform analysis provides valuable information as well as the absolute systolic and diastolic pressures. The normal wave should have a sharp peak systole upstroke and a definite end diastole. Oxford, Wiley-Blackwell. Oxford, Blackwell Science.
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