Welcome, everyone. Thank you all for registering and joining our course series. My name is Sebastian Tuma and it is my pleasure to present to you didactic lecture covering the topic of non-invasive and invasive hemodynamic monitoring in critical care setting. My clinical and academic backgrounds include an assistant professor of pediatrics at Baylor College of Medicine, and I also work as a cardiac intensivist and a medical director of the Pediatric Cardiac Intensive Care Unit at Texas Children's Hospital. My only disclosure is that I'm currently a PI on an advanced hemodynamic monitoring trial which is sponsored by Edwards. There are two primary objectives to this presentation and they're fairly broad. Number one will describe the benefits and challenges of non-invasive hemodynamic monitoring as well as outline the benefits and challenges of invasive hemodynamic monitoring. I hope that the information provided in this course will help you determine how to choose the appropriate mode of monitoring for a given patient as well as develop therapeutic plan based on accurate interpretation of hemodynamic data. Before we continue with this presentation, we must appreciate that the accuracy of monitoring is the key not only for data acquisition but also therapeutic interventions. The user should understand limitations and sources of error for each device deployed in their clinical setting. One must ensure that the measurements are performed only after appropriate calibration of the system is performed. This will minimize the inaccuracy of monitoring. The provider must also have complete understanding of the value of the hemodynamic data and define an accurate hemodynamic profile. Last, once therapeutic interventions are actually deployed, we must evaluate hemodynamic response and its expected behavior to support our assessment and eliminate error in measurement or interpretation. This quote highlights an important concept to consider as we move through the course. It's a quote from Essential Anesthesia by Juliano and colleagues. The quote states, no monitor is therapeutic in itself but requires the skill and vigilance of a trained observer to interpret the information in the context of ever-changing clinical picture. That concept forms the foundation for this presentation. Why use hemodynamic monitoring? What are the overall benefits? We can all appreciate that hemodynamic monitoring provides valuable information to guide clinical decision-making right at the bedside with the end goal of improving patient outcomes. The choice of type of monitoring to use is determined by patient's condition and the anticipated trajectory of illness. Of course, it must be interpreted and applied in conjunction with the clinical assessment findings. My approach to choice of hemodynamic monitoring in critical care setting includes a decision of which component we would like to focus on, pressure, content, or flow. Thus, in this presentation, I will focus on blood pressure monitoring, pulmonary arterial pressure monitoring, as well as central venous pressure monitoring. We'll evaluate venous saturation monitoring, end-tidal CO2 with capnography, near-infrared spectroscopy, as well as focus on newer non-invasive cardiac output monitoring devices. Blood pressure can be defined as the lateral pressure exerted on the walls of the vessels that contain blood within them. In other words, it's a consequence of compliance of the vascular system and volume within it. There are several factors that can impact blood pressure. These include hormonal mechanisms, catecholamines, renin, angiotensin, and antidiuretic hormone, and atrial natriuretic peptide. Other factors include central and otomonomic nervous functions, peripheral vascular resistance, cardiac output, and cardiopulmonary interactions. All of these factors can have a dynamic effect on the patient's blood pressure measurement. Blood pressure can be measured indirectly or directly. The indirect measurement uses a cuff placed around the extremity. Indirect pressure measurements can be achieved by either auscultation or oscillometric methods. During auscultation, the cuff distorts the artery, causing a turbulence in the blood flow that leads to a creation of corticofound. The first corticofound is the systolic blood pressure. The second is the diastolic blood pressure. This method requires extensive training, and results are dependent on the person taking the measurements. The oscillometric method, on the other hand, offers overall good interadherability, but it's less accurate at the measuring extremes of high or low blood pressures. It also uses a standardized inflation point, which is often much higher than needed in our pediatric population. The direct monitoring involves inserting a catheter into an artery and generating a waveform. The most common sites for catheter insertion include radial, posterior tibial, dorsalis pedis, and femoral sites. However, a different site might be called for in patients with trauma, burns, or occluded vessels from prior cannulations. How do we choose between invasive and noninvasive blood pressure monitoring? In part, it will be based on the resources available in your units. It will also be dependent on the patient's condition and the anticipated trajectory of the illness. Many patients will have arterial lines placed without problems, however, we do have to be mindful of the complication that can occur with invasive monitoring. These include vascular damage or compromise, infections, bleeding, and sites hematoma. Invasive blood pressure monitoring does offer some significant advantages for the appropriately selected patients. These include continuous monitoring of the blood pressure, ability to obtain lab samples, as well as the displayed waveform on the monitor, which provides useful clinical information about the patient. That waveform is a consequence of culmination of various harmonic wave frequencies. We have to remember that when using these methods, it is essential to calibrate the system by positioning the transducer at the phlebostatic axis. When the patient is shifted or moved, the system requires recalibration, and if not performed accurately, we are at risk of obtaining inaccurate information. This figure nicely delineates an example of an arterial line tracing. It clearly shows the start of the systole, the systolic peak pressure, the dicrotic notch and aortic valve closure, as well as the end of diastole. We can also deduct the area under the curve, which is representative as the stroke volume. Invasive blood pressure monitoring allows for continuous monitoring of systolic, diastolic, and mean arterial pressures. Following placement of an arc line, we can encounter situations of over-damping or under-damping of our arterial monitoring system. The figure below, on the left, represents a normal appearance of the arterial waveform. The figure in the middle highlights an over-damped system, which can be caused by additional stopcocks or tubing, as well as air in monitoring line. We can appreciate the significant reduction of the systolic pressures. An under-dampened system can be caused by catheter width, artifacts, hypothermia, or dysrhythmia in patients. This often results in falsely elevated blood pressure. The shape of the arterial line tracing from the catheter can provide important clues about the child's clinical state. A rapid ab stroke typically indicates good contractility. A slow rise in ab stroke can indicate reduced cardiac function or increased systemic vascular resistance. The rate of the down stroke is related to peripheral vascular resistance. A narrow pulse pressure may signal low stroke volume. On the other hand, a widened pulse pressure can indicate low systemic vascular resistance, aortic insufficiency, or aortic runoff. Lastly, pulse paradoxes might indicate cardiac tamponade, severe airway obstruction, tension pneumothorax, or other issues. Patients with non-pulsatile flow states will produce a tracing only with no true waveforms. Pulses paradoxes is defined as a fall of systolic blood pressure of greater than 10 millimeters of mercury during inspiratory phase. In the setting of positive pressure ventilation, decrease in atrial transmittal pressure results in impediment to ventricular filling and decreased stroke volume with each inspiration. Some of the causes of pulses paradoxes result from significant limitation in preload and include asthma, exacerbation of COPD, cardiac tamponade, constrictive pericarditis, restrictive cardiomyopathy, hypovolemia, distributive shock, tension pneumothorax, pulmonary embolism, and pericardial effusions. In pediatric patients, asthma, tamponade, hypovolemia, and pneumothorax are probably the most common causes. Arterial line complications are not uncommon. These have been reported in 10 to 33% of those undergoing this type of monitoring. Those complications are listed on the left and range from mild, such as side bleeding, to extreme, such as extremity loss or vascular injury. Patient factors that can increase the risk of these complications include age, medications, and underlying condition. It is important to know that we, as providers, can help reduce these complications by minimizing insertion attempts through use of resources such as ultrasound-guided placement. Pulmonary artery pressure monitoring remains an advanced method for hemodynamic monitoring. Following published adult trials, its use in pediatric critical care has been rare, with exception of some of the cardiac critical care settings. One of the major benefits of PE catheter is its ability to monitor multiple variables, such as central venous pressure, pulmonary artery and capillary wedge pressure, as well as mixed venous oxygen saturation. PE catheters also contain ability to measure cardiac output through their thermodilution capabilities. The ability to directly monitor pulmonary artery pressure may offer benefits for some patients, including children with refractory shock, extensive burns, complex congenital heart disease, pulmonary hypertension, and cardiomyopathy. Important limitations to pulmonary artery catheter use in any patient should be considered. These include severe valvular regurgitation and presence of a cardiac shunt. These two lesions can contribute to inaccurate measurements of cardiac output. There are also risks, which include bleeding, cardiac perforation, inadvertent persistent wedge, thromboembolism, infection, and even knotting of the catheter. It is recommended that extreme caution should be taken in the setting of pulmonary hypertension and use of these catheters minimized in this setting. Central venous pressure is measured using an indwelling central venous catheter that terminates in the superior vena cava or right atrium. These two locations are the preferred monitoring sites providing accurate assessment of venous system. In certain situations, pressure can be measured at other sites such as IVC. It should be noted that the measurement of pressure at these sites might be impacted by external factors such as increased abdominal pressure affecting the accuracy of our measurements. The central venous pressure reading can represent right atrial pressure and right ventricular filling pressure, but does not imply right ventricular filling or fluid responsiveness as these are dependent on ventricular compliance. This table shows some of the factors that can increase central venous pressure. The right column indicates whether the change is due to compliance or volume. So for instance, decreased cardiac output, atrial dilation, or a change in patient position is primarily related to volume. On the other hand, venous constriction or force expiration points to a change in compliance. Muscle contraction can be related to either a compliance change or a volume change. What is the effect of positive pressure ventilation on central venous pressure? As shown in this schematic, as the intrathoracic pressure goes up, the transmural atrial pressure is reduced, which makes it harder for volume to return to the right side of the heart, thus impeding ventricular preload. That leads to decreased ventricular stroke volume and decreased pulmonary artery blood flow. Therefore, a higher end diastolic pressure is required to maintain ventricular filling and stroke volume, and the patient may need more volume to maintain that central venous pressure and sufficient preload. Central venous saturations can be used to evaluate oxygen consumption and delivery in our patients, which can be particularly helpful in children at risk of shock or in states of shock. The acceptable sampling locations include jugular vein, inferior vena cava, superior vena cava, and right atrium, as long as no left-to-right shunting is present. Before sampling takes place, it is very important to locate where the catheter terminates. How can we utilize the central venous saturation in a clinical setting? This chart gives a basic overview of various clinical scenarios where a state of increased or decreased oxygen extraction results in respective changes in venous saturations. If venous saturation is high, that could indicate high cardiac output state, decreased metabolic rate, oxygen transport or utilization disturbance, such as in states of septic shock or supranormal oxygen delivery. On the other hand, a low venous saturation is associated with states such as compromised cardiac output, increased metabolic rate, or states of limited oxygen delivery, such as anemia or hypoxia. Note that the decreased oxygen delivery to the peripheral tissue results in increased arteriovenous oxygen content difference. A critical threshold is defined when the cardiac output or tissue oxygen delivery are significantly reduced, resulting in uncoupling of oxygen delivery from demand, and thus resultant anaerobic metabolism, lactate formation, both of which can be measured and tracked on blood gas sampling. The oxygen extraction ratio helps in determining the adequacy of tissue oxygenation. The equation represented here highlights that this assessment can be performed in hypoxic patients, such as single ventricle physiology, because of its accounting for their desaturated state. In normal states, the extraction ratio is between 25-30%. An increasing extraction ratio indicates that oxygen delivery is inadequate for the demands of the body. Once the extraction ratio reaches more than 50%, anaerobic metabolism occurs, concurrent with a state of shock. Another form of gas content monitoring available in critical care setting is an n-tidal carbon dioxide monitoring. N-tidal carbon dioxide measurement is performed through noninvasive infrared monitoring technique using either sidestream or midstream technology. The sidestream technology uses endotracheal tube adapter, which samples gas and delivers it to the detector distant from the patient. In setting of mainstream technology, the detector is located on the adapter attached to the endotracheal tube. This measurement can also be performed using noninvasive nasocannula devices. Normal n-tidal carbon dioxide values are between 35 and 45 millimeters mercury, but many factors can affect measurement, including circuit leaks. The determinants of the n-tidal carbon dioxide level include tissue perfusion, pulmonary blood flow, and alveolar ventilation. In normal healthy subjects, measured arterial carbon dioxide and n-tidal carbon dioxide values are almost similar with small gradient representing dead space ventilation. When pulmonary blood flow is reduced or when ventilation perfusion mismatching is on the rise, increased ventilation perfusion gradients may be generated, resulting in an accumulation of carbon dioxide and wasted ventilation. That can also lead to the development of a larger arterial n-tidal carbon dioxide gradients. Therapies targeted in improving pulmonary blood flow and ventilation perfusion matching will enhance CO2 clearance. N-tidal CO2 can be a noninvasive surrogate of cardiac output and organ perfusion during cardiac arrest. It can be used to monitor the quality of CPR, where it correlates with return of spontaneous circulation. A study by Sandrani and colleagues, as well as quite a few other studies over the past few years have shown that persistently low n-tidal CO2 values during resuscitation without of hospital cardiac arrest have been associated with poor outcomes. Near-infrared spectroscopy, otherwise known as NIRS, provides us with another form of noninvasive content monitoring. NIRS uses near-infrared light emitted by paths placed on the skin. The light penetrates tissues including bones and muscle and returns data to the sensors in arc-like pattern. This technology, unlike pulse oximetry, is not dependent on pulsatile flow. NIRS has become increasingly popular in recent years for measuring regional oxygen saturations in critically ill patients, especially children after cardiac surgery. Monitoring regional oxygen saturation can provide important data on the oxygen supply and demand state of the underlying organs. Most common locations of monitoring include brain or kidney. Different color has no effect on the measurements except for hyperlipidemia with some devices. However, because different devices use proprietary algorithms, the accuracy of values obtained may vary slightly from one manufacturer to another. The correlation of cerebral measurements with internal jugular saturations has been shown in multiple studies to be very good in both cath lab and critical care setting. How does near-infrared spectroscopy work? Oxygenated hemoglobin and deoxygenated hemoglobin absorb different wavelengths of near-infrared light. Sensors measure the proportion or ratio of light absorbed by oxygenated hemoglobin to that absorbed by total hemoglobin in the region. The regional oxygen saturation reflects both the arterial and venous saturations in the area that is being sampled, but it's weighted towards the venous saturation because most of the systemic blood volume is contained within the venous system. The probes are commonly placed on the forehead to measure cerebral regional oxygen saturation and on the flank to measure somatic or renal regional oxygen saturation. The cerebral measure is typically lower than somatic, reflecting the increased oxygen consumption of the brain relative to other organs such as kidneys. As stated previously, a pulse is not required for measurement. That means this method can provide information on regional oxygen supply and demand in non-pulsatile states such as cardiopulmonary bypass or extracorporeal membrane oxygenation. Recent studies support the use of near-infrared spectroscopy monitoring for postoperative care of children of congenital heart disease. In a study by Hoffman et al., the best predictors of 30-day survival were the difference in somatic and cerebral regional oxygen saturations, the mean arterial pressure, the somatic regional oxygen saturation, as measured at 6 hours of surgery. The latter was also a predictor of the ultimate need for extracorporeal membrane oxygenation in the study population. The authors proposed that these early postoperative measures may be a good target for goal-directed interventions. Other investigators report an association between low postoperative cerebral regional oxygen saturation and neurodevelopmental abnormalities, as well as longer duration of mechanical ventilation and longer hospital intensive care unit stay. Other uses of NEARS monitoring that may be helpful in the broader pediatric intensive care population have also been reported. In a prospective study of infants undergoing cardiopulmonary bypass, a 48-hour average of regional oxygen saturation values was significantly associated with acute kidney injury. In another study, by Gradich et al., found an association between low pre-extubation cerebral and somatic regional oxygen saturation values and failed extubations in neonates following cardiac surgery. This is another study that showed an association between a minimum somatic regional oxygen saturations of less than 70% in the first 4 hours of admission with the need of subsequent life-saving interventions including resuscitation, ECMO, blood transfusions, and other interventions shown here. Further investigation is needed to establish monitoring standards and promote goal-directed interventions to improve patient outcomes. Neurogenic ultrasound can be quite helpful in defining cardiac anatomy and some physiological states of the critically ill patients. This method is non-invasive, doesn't use radiation, and provides excellent anatomical information. Common challenges with these studies, however, is that the findings are not reported in a way that support clinical decision making in ICU setting. For instance, the report typically doesn't indicate volume responsiveness, intravascular state, or cardiac output, making it difficult to define the need for inotropes or vasopressor support. It also requires both a technologist and a cardiologist to interpret the results of the exam, which can lead to delays and limits its full application in an intensive care setting. The drawbacks and limitations of standard ultrasound led to the development and implementation of point-of-care ultrasound in intensive care and emergency medicine. The main benefit of point-of-care ultrasound is that it allows the bedside provider to perform ultrasound exams and evaluate the patient's status in real time. This can facilitate quick decision making. It also supports early diagnosis and treatment strategies without the delays associated with interpreting traditional ultrasound scans. In addition, repeat imaging allows us to track the success of treatments. Common uses of point-of-care ultrasound include quantifying hypovolemia, cardiac function, pericardial effusions, or tamponette physiology, as well as the effects of various valvular abnormalities. This study by Rado and associates evaluated the impact of point-of-care ultrasound in the pediatric intensive care setting. Assessment scans were performed by intensivists on 80 children. New findings were identified in 7% of the total number of patients. In 35 of the patients, the clinical impression changed after completion of the exam. The authors also found that after the exam, plant therapy changed in 36 children, that is almost half of the patients that were enrolled in the study. This rapid echo examination is a hybrid of point-of-care ultrasound, cardiac echo, and anatomic assessment of transthoracic echo. It is designed to specifically address hemodynamic status. To that end, it includes measurements and calculations found on point-of-care ultrasound, as well as stroke volume, cardiac output, cardiac index, IVC diameter, and change in internal jugular diameter with change in position. This provides information of cardiac function, cardiac diastolic dysfunction, and ability of the cardiovascular system to respond to a fluid bolus. In one highlighted study, using a focused rapid echo examination result led to a change in patient management in about 50% of instances. The gold standard for measurement of cardiac output in critical care setting remains a thermodilution performed with swan-gans catheters. Due to their invasive nature, this approach has been recently replaced with less invasive transpulmonary thermodilution method. This method relies on a beat-to-beat pulse-counter cardiac output monitor. Both a central venous catheter and an arterial catheter are required, which are often present in children residing in the ICU or in those who have had prolonged surgical procedures. The central arterial catheter has a thermistor located at the tip, and the central venous catheter has an injection device of injected probe attached to the distal lumen. Measurement of cardiac output using transpulmonary thermodilution requires cold saline injection into the central venous line, which subsequently results in change in blood temperature, which is then monitored on the central artery catheter. This thermodilution component allows for calibration of the system to increase accuracy of the pulse pressure-derived cardiac output. One of the benefits of the transpulmonary thermodilution method is that it provides a quantitative intermittent and continuous hemodynamic measurements to guide goal-directed therapy so that intravascular volume and perfusion can be optimized. The validity and accuracy of this method has been documented in several adult and pediatric studies. The last non-invasive technique that I would like to highlight is the ultrasound cardiac output monitor. It provides for a rapid, non-invasive measurement of central hemodynamic indices, including cardiac output and stroke volume, as well as the ability to calculate systemic vascular resistance if central venous axis is present. It is based on transthoracic measurement of Doppler flow velocity over the aortic and pulmonary outflow tract. Cardiac output is displayed beat by beat. This method has the advantage of being easy to operate. Here are the results of two pediatric studies focusing on ultrasound cardiac output monitoring. The first study looked at the validity of measurements in 78 hemodynamically stable and unstable pediatric patients, comparing results to those of two-dimensional echocardiography. The tests were performed within 30 minutes of each other. The investigators found a good correlation of stroke volume in hemodynamically stable, mechanically ventilated, and unstable patients. However, the agreement for cardiac index was moderate in stable patients and only fair in ventilated patients. The second study looked at the feasibility of ultrasound cardiac output monitoring as an adjunct during hemodynamic assessments by a pediatric medical emergency team. This study included 41 patients from 85 consultations, with a total of 55 ultrasound assessments on 36 patients, or roughly 40%. About 95% of the team members found the equipment was easy to transport and apply, and it was not obstructive to patient care. Roughly three-quarters said ultrasound cardiac output monitoring provided good data quality. In conclusion, the selection of available platforms for hemodynamic monitoring in pediatric patients remains wide and fairly well validated in this population. The final selection should be determined by the patient's clinical status and anticipated trajectory of their illness. Finally, the clinician should ensure that values obtained through the hemodynamic monitoring techniques are accurate and interpreted in conjunction with the clinical exam findings, which will drive optimal care and minimize complication. Thank you very much for your time.

hemodynamic monitoring

non-invasive methods

invasive methods

cardiac output

pulmonary artery catheters

central venous pressure

Sebastian Tuma