Pulse Wave Analysis to Estimate Cardiac Output

Karim Kouz, M.D.; Thomas W. L. Scheeren, M.D.; Daniel de Backer, M.D.; Bernd Saugel, M.D.

Disclosures

Anesthesiology. 2020;134(1):119-126. 

In This Article

Clinical Application of Pulse Wave Analysis

The decision to use—or not use—a certain pulse wave analysis system in an individual patient or clinical setting is influenced by numerous factors. These include patient-centered factors; the invasiveness, measurement performance, clinical applicability, and signal stability of the pulse wave analysis system; institutional factors such as the availability and the costs; and personal experience with monitoring systems of the caregiver.[41] A profound understanding of pulse wave analysis measurement principles and strengths and limitations of pulse wave analysis systems is important for clinicians to choose the appropriate pulse wave analysis system for the individual patient.

All pulse wave analysis systems discussed in this review have been investigated against pulmonary artery or transpulmonary thermodilution in method comparison studies.[10,17,42,43] Those method comparison studies are highly heterogenous regarding their study design, patient population, clinical setting, and results and, therefore, are hardly comparable with respect to the measurement performance of the investigated pulse wave analysis system. Even though there are studies showing clinical interchangeability between pulse wave analysis–derived CO measurements and reference indicator dilution CO measurements, the pooled overall results indicate that CO measurements by either method are not interchangeable.

Pulmonary artery thermodilution remains the clinical reference method for CO monitoring.[3] Pulmonary artery catheterization additionally provides numerous advanced hemodynamic variables that help guiding therapy in patients having cardiac surgery (in combination with transesophageal echocardiography) or liver transplant surgery or in patients with pulmonary hypertension or right ventricular failure.[5] However, pulmonary artery catheterization is an invasive procedure associated with potential complications. This may be one of the reasons for a decrease in the use of the pulmonary artery catheter over the last years.[4] Although the CO measurement performance of pulmonary artery thermodilution is superior to that of pulse wave analysis, pulse wave analysis may be a reasonable choice for CO monitoring in a broad spectrum of surgical and critically ill patients.

Pulse Wave Analysis in Perioperative Medicine

Major surgery under general anesthesia causes marked hemodynamic alterations and impaired tissue oxygenation.[44] Perioperative goal-directed therapy based on advanced hemodynamic monitoring has thus been proposed to optimize CO and global oxygen delivery. Goal-directed therapy refers to protocolized hemodynamic treatment strategies that are used to titrate fluids, vasopressors, and inotropes to predefined target values of hemodynamic variables to optimize global cardiovascular dynamics and maintain adequate organ perfusion pressure and oxygen delivery.[45] There is evidence that goal-directed therapy can improve postoperative outcomes and reduce postoperative mortality in high-risk patients having major surgery.[46,47] Pulse wave analysis is frequently used in studies of goal-directed therapy because it provides CO and dynamic cardiac preload variables that can be used as target variables.[46,48]

Minimally invasive internally calibrated pulse wave analysis (ProAQT/Pulsioflex system) was used in a multicenter randomized controlled trial in patients having major abdominal surgery investigating the impact of goal-directed therapy on postoperative complications compared with routine care.[49] In goal-directed therapy group patients, the individual optimal CO was determined after anesthetic induction by giving fluids until pulse pressure variation was less than 10%. During surgery, fluids, vasopressors, and inotropes were titrated according to pulse pressure variation, the individual CO, and a mean arterial blood pressure of more than 65 mmHg. Patients treated with goal-directed therapy had significantly less postoperative complications compared with routine care patients.[49]

In the Optimisation of Perioperative Cardiovascular Management to Improve Surgical Outcome (OPTIMISE) trial,[47] the to-date largest randomized controlled trial on goal-directed therapy, minimally invasive internally calibrated pulse wave analysis (LiDCOrapid system), was used to optimize blood flow by maximizing stroke volume with repetitive colloidal fluid boluses and the inotrope dopexamine in high-risk patients having major abdominal surgery. The primary endpoint—a composite of moderate or severe postoperative complications—occurred less frequently in goal-directed therapy group patients compared with routine care group patients. However, the clinically important difference in the incidence of postoperative complications was not statistically significant.

Based on the OPTIMISE trial, the OPTIMISE II trial—an international multicenter pragmatic randomized controlled trial in high-risk patients having major surgery—is currently being carried out.[50] Minimally invasive internally calibrated (FloTrac system) or noninvasive (ClearSight system) pulse wave analysis is used to maximize stroke volume with fluid challenges and low-dose dobutamine or dopexamine. Stroke volume variation less than 5% or an absence of a sustained rise in stroke volume after a fluid challenge are considered indicators of fluid nonresponsiveness. The primary endpoint of the study is the incidence of postoperative infection within 30 days of randomization.

For goal-directed therapy to be even more effective, personalized target values based on patients' preoperative baseline cardiovascular dynamics may be promising.[51] In this regard, noninvasive pulse wave analysis systems enable clinicians to determine baseline CO before surgery (e.g., the day before surgery on the ward). In the Targeting Preoperatively Assessed Personal Cardiac Index in Major Abdominal Surgery Patients (TAPIR) trial,[52] noninvasive pulse wave analysis (CNAP system) was used to determine the individual patient's baseline cardiac index the day before surgery. In patients assigned to personalized management, clinicians strove to maintain this baseline cardiac index during surgery—where cardiac index was measured using minimally invasive internally calibrated pulse wave analysis (ProAQT/Pulsioflex system)—by using fluids and dobutamine based on a goal-directed therapy algorithm. The primary outcome, a composite of major postoperative complications or death within 30 days of surgery, occurred less frequently in patients in the personalized management group compared with patients in the routine management group.

In addition to the use of pulse wave analysis for goal-directed therapy in high-risk patients having major surgery, noninvasive pulse wave analysis may be useful for continuous arterial blood pressure monitoring in low- or intermediate-risk patients that would otherwise have only intermittent arterial blood pressure monitoring. Recent randomized controlled trials in patients having moderate-risk noncardiac surgery revealed that continuous noninvasive arterial blood pressure monitoring reduces the amount of intraoperative hypotension compared with intermittent blood pressure monitoring using upper-arm cuff oscillometry.[53,54]

Pulse Wave Analysis in Intensive Care Medicine

In critically ill patients with complex circulatory shock, CO monitoring is recommended to diagnose the type of shock and to evaluate the response to fluids or inotropes.[2] For the diagnosis of the type of shock, pulmonary artery thermodilution or transpulmonary thermodilution are recommended[2] because the diagnosis depends on accurate and precise absolute CO measurements and additional hemodynamic variables.[55]

Because pulse wave analysis provides CO continuously and in real time, it is recommended to monitor CO during tests of fluid responsiveness (fluid challenges[56] or passive leg raising test[57]).[2] Circulatory shock—especially septic shock—is characterized by marked alterations in systematic vascular resistance.[55] Invasive externally calibrated pulse wave analysis systems offer the opportunity to frequently recalibrate pulse wave analysis–derived CO estimations and thereby improve the measurement performance regarding absolute CO values. In patients with circulatory shock, absolute CO measurement by minimally invasive internally calibrated or uncalibrated pulse wave analysis systems may become unreliable because of marked alterations in vasomotor tone.[17] Noninvasive pulse wave analysis systems are not recommended in critically ill patients with shock because these patients will be equipped with an arterial catheter anyway.[9]

Conclusions

Pulse wave analysis is the mathematical analysis of the arterial blood pressure waveform and enables CO to be estimated continuously and in real time. In addition to CO, pulse wave analysis allows assessing dynamic cardiac preload variables, i.e., pulse pressure variation and stroke volume variation that can be used to predict fluid responsiveness in patients with sinus rhythm and controlled mechanical ventilation. Pulse wave analysis methods are classified into invasive, minimally invasive, and noninvasive methods. Pulse wave analysis methods are further classified into externally calibrated, internally calibrated, and uncalibrated methods depending on the type of calibration they use to calibrate pulse wave analysis–derived CO values. In high-risk patients having major surgery, pulse wave analysis–derived CO and dynamic cardiac preload variables can be used for perioperative goal-directed therapy. In critically ill patients, pulse wave analysis–derived continuous real-time CO estimations can be used to monitor CO during tests of fluid responsiveness (fluid challenges or passive leg raising test).

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