The role of pulse wave analysis indexes for critically ill patients: a narrative review.

Objective.Arterial pulse wave analysis (PWA) is now established as a powerful tool to investigate the cardiovascular system, and several clinical studies have shown how PWA can provide valuable prognostic information over and beyond traditional cardiovascular risk factors. Typically these techniques are applied to chronic conditions, such as hypertension or aging, to monitor the slow structural changes of the vascular system which lead to important alterations of the arterial PW. However, their application to acute critical illness is not currently widespread, probably because of the high hemodynamic instability and acute dynamic alterations affecting the cardiovascular system of these patients.Approach.In this work we propose a review of the physiological and methodological basis of PWA, describing how it can be used to provide insights into arterial structure and function, cardiovascular biomechanical properties, and to derive information on wave propagation and reflection.Main results.The applicability of these techniques to acute critical illness, especially septic shock, is extensively discussed, highlighting the feasibility of their use in acute critical patients and their role in optimizing therapy administration and hemodynamic monitoring.Significance.The potential for the clinical use of these techniques lies in the ease of computation and availability of arterial blood pressure signals, as invasive arterial lines are commonly used in these patients. We hope that the concepts illustrated in the present review will soon be translated into clinical practice.

Impact of respiratory cycle during mechanical ventilation on beat-to-beat right ventricle stroke volume estimation by pulmonary artery pulse wave analysis.

BACKGROUND: The same principle behind pulse wave analysis can be applied on the pulmonary artery (PA) pressure waveform to estimate right ventricle stroke volume (RVSV). However, the PA pressure waveform might be influenced by the direct transmission of the intrathoracic pressure changes throughout the respiratory cycle caused by mechanical ventilation (MV), potentially impacting the reliability of PA pulse wave analysis (PAPWA). We assessed a new method that minimizes the direct effect of the MV on continuous PA pressure measurements and enhances the reliability of PAPWA in tracking beat-to-beat RVSV. METHODS: Continuous PA pressure and flow were simultaneously measured for 2-3 min in 5 pigs using a high-fidelity micro-tip catheter and a transonic flow sensor around the PA trunk, both pre and post an experimental ARDS model. RVSV was estimated by PAPWA indexes such as pulse pressure (SVPP), systolic area (SVSystAUC) and standard deviation (SVSD) beat-to-beat from both corrected and non-corrected PA signals. The reference RVSV was derived from the PA flow signal (SVref). RESULTS: The reliability of PAPWA in tracking RVSV on a beat-to-beat basis was enhanced after accounting for the direct impact of intrathoracic pressure changes induced by MV throughout the respiratory cycle. This was evidenced by an increase in the correlation between SVref and RVSV estimated by PAPWA under healthy conditions: rho between SVref and non-corrected SVSD - 0.111 (0.342), corrected SVSD 0.876 (0.130), non-corrected SVSystAUC 0.543 (0.141) and corrected SVSystAUC 0.923 (0.050). Following ARDS, correlations were SVref and non-corrected SVSD - 0.033 (0.262), corrected SVSD 0.839 (0.077), non-corrected SVSystAUC 0.483 (0.114) and corrected SVSystAUC 0.928 (0.026). Correction also led to reduced limits of agreement between SVref and SVSD and SVSystAUC in the two evaluated conditions. CONCLUSIONS: In our experimental model, we confirmed that correcting for mechanical ventilation induced changes during the respiratory cycle improves the performance of PAPWA for beat-to-beat estimation of RVSV compared to uncorrected measurements. This was demonstrated by a better correlation and agreement between the actual SV and the obtained from PAPWA.

Variability in the Hemodynamic Response to Fluid Bolus in Pediatric Septic Shock.

OBJECTIVES: Fluid boluses are commonly administered to improve the cardiac output and tissue oxygen delivery in pediatric septic shock. The objective of this study is to evaluate the effect of an early fluid bolus administered to children with septic shock on the cardiac index and mean arterial pressure, as well as on the hemodynamic response and its relationship with outcome. DESIGN, SETTING, PATIENTS, AND INTERVENTIONS: We prospectively collected hemodynamic data from children with septic shock presenting to the emergency department or the PICU who received a fluid bolus (10 mL/kg of Ringers Lactate over 30 min). A clinically significant response in cardiac index-responder and mean arterial pressure-responder was both defined as an increase of greater than or equal to 10% 10 minutes after fluid bolus. MEASUREMENTS AND MAIN RESULTS: Forty-two children with septic shock, 1 month to 16 years old, median Pediatric Risk of Mortality-III of 13 (interquartile range, 9-19), of whom 66% were hypotensive and received fluid bolus within the first hour of shock recognition. Cardiac index- and mean arterial pressure-responsiveness rates were 31% and 38%, respectively. We failed to identify any association between cardiac index and mean arterial pressure changes (r = 0.203; p = 0.196). Cardiac function was similar in mean arterial pressure- and cardiac index-responders and nonresponders. Mean arterial pressure-responders increased systolic, diastolic, and perfusion pressures (mean arterial pressure - central venous pressure) after fluid bolus due to higher indexed systemic vascular resistance and arterial elastance index. Mean arterial pressure-nonresponders required greater vasoactive-inotrope support and had higher mortality. CONCLUSIONS: The hemodynamic response to fluid bolus in pediatric septic shock was variable and unpredictable. We failed to find a relationship between mean arterial pressure and cardiac index changes. The adverse effects of fluid bolus extended beyond fluid overload and, in some cases, was associated with reduced mean arterial pressure, perfusion pressures and higher vasoactive support. Mean arterial pressure-nonresponders had increased mortality. The response to the initial fluid bolus may be helpful to understand each patient's individualized physiologic response and guide continued hemodynamic management.

Assessment of central hemodynamic effects of phenylephrine: an animal experiment.

Phenylephrine is an α1-adrenergic receptor agonist widely used to treat perioperative hypotension. Its other hemodynamic effects, in particular on preload and contractility, remain controversial. We, therefore, investigated the effect of continuously applied phenylephrine on central hemodynamics in eight mechanically ventilated domestic pigs. Mean arterial pressure (MAP) was increased in steps by 50%, and 100% using phenylephrine. Besides stroke volume (SV), cardiac output (CO), and MAP, mean systemic vascular resistance (SVR) and dynamic arterial elastance (Eadyn) were assessed for characterization of afterload. Changes in preload were assessed by central venous pressure (CVP), global end-diastolic volume (GEDV), mean systemic filling pressure analog (Pmsfa), pulse pressure variation (PPV), and stroke volume variation (SVV). Further, cardiac function index (CFI), global ejection fraction and dPmax were measured as markers of preload dependent contractility. MAP, SV, and CO significantly increased following both interventions, as did SVR. In contrast, Eadyn did not show significant changes. Although the volumetric preload variable GEDV increased after the first step of phenylephrine, this was not reflected by significant changes in CVP or Pmsfa. CFI and dPmax significantly increased after both steps. Phenylephrine does not only affect cardiac afterload, but also increases effective preload. In contrast to CVP and Pmsfa, this effect can be monitored by GEDV. Further, phenylephrine affects contractility.

Fluid administration for acute circulatory dysfunction using basic monitoring: narrative review and expert panel recommendations from an ESICM task force.

An international team of experts in the field of fluid resuscitation was invited by the ESICM to form a task force to systematically review the evidence concerning fluid administration using basic monitoring. The work included a particular emphasis on pre-ICU hospital settings and resource-limited settings. The work focused on four main questions: (1) What is the role of clinical assessment to guide fluid resuscitation in shock? (2) What basic monitoring is required to perform and interpret a fluid challenge? (3) What defines a fluid challenge in terms of fluid type, ranges of volume, and rate of administration? (4) What are the safety endpoints during a fluid challenge? The expert panel found insufficient evidence to provide recommendations according to the GRADE system, and was only able to make recommendations for basic interventions, based on the available evidence and expert opinion. The panel identified significant gaps in the scientific evidence on fluid administration outside the ICU (excluding the operating theater). Globally, scientific communities and health care systems should address these critical gaps in evidence through research on how basic fluid administration in resource-rich and resource-limited settings can be improved for the benefit of patients and societies worldwide.

Correction to: Fluid administration for acute circulatory dysfunction using basic monitoring: narrative review and expert panel recommendations from an ESICM task force.

The original article can be found online.

Effects on Pulmonary Vascular Mechanics of Two Different Lung-Protective Ventilation Strategies in an Experimental Model of Acute Respiratory Distress Syndrome.

OBJECTIVES: To compare the effects of two lung-protective ventilation strategies on pulmonary vascular mechanics in early acute respiratory distress syndrome. DESIGN: Experimental study. SETTING: University animal research laboratory. SUBJECTS: Twelve pigs (30.8 ± 2.5 kg). INTERVENTIONS: Acute respiratory distress syndrome was induced by repeated lung lavages and injurious mechanical ventilation. Thereafter, animals were randomized to 4 hours ventilation according to the Acute Respiratory Distress Syndrome Network protocol or to an open lung approach strategy. Pressure and flow sensors placed at the pulmonary artery trunk allowed continuous assessment of pulmonary artery resistance, effective elastance, compliance, and reflected pressure waves. Respiratory mechanics and gas exchange data were collected. MEASUREMENTS AND MAIN RESULTS: Acute respiratory distress syndrome led to pulmonary vascular mechanics deterioration. Four hours after randomization, pulmonary vascular mechanics was similar in Acute Respiratory Distress Syndrome Network and open lung approach: resistance (578 ± 252 vs 626 ± 153 dyn.s/cm; p = 0.714), effective elastance, (0.63 ± 0.22 vs 0.58 ± 0.17 mm Hg/mL; p = 0.710), compliance (1.19 ± 0.8 vs 1.50 ± 0.27 mL/mm Hg; p = 0.437), and reflection index (0.36 ± 0.04 vs 0.34 ± 0.09; p = 0.680). Open lung approach as compared to Acute Respiratory Distress Syndrome Network was associated with improved dynamic respiratory compliance (17.3 ± 2.6 vs 10.5 ± 1.3 mL/cm H2O; p < 0.001), driving pressure (9.6 ± 1.3 vs 19.3 ± 2.7 cm H2O; p < 0.001), and venous admixture (0.05 ± 0.01 vs 0.22 ± 0.03, p < 0.001) and lower mean pulmonary artery pressure (26 ± 3 vs 34 ± 7 mm Hg; p = 0.045) despite of using a higher positive end-expiratory pressure (17.4 ± 0.7 vs 9.5 ± 2.4 cm H2O; p < 0.001). Cardiac index, however, was lower in open lung approach (1.42 ± 0.16 vs 2.27 ± 0.48 L/min; p = 0.005). CONCLUSIONS: In this experimental model, Acute Respiratory Distress Syndrome Network and open lung approach affected pulmonary vascular mechanics similarly. The use of higher positive end-expiratory pressures in the open lung approach strategy did not worsen pulmonary vascular mechanics, improved lung mechanics, and gas exchange but at the expense of a lower cardiac index.

The Open Lung Approach Improves Pulmonary Vascular Mechanics in an Experimental Model of Acute Respiratory Distress Syndrome.

OBJECTIVE: To test whether positive end-expiratory pressure consistent with an open lung approach improves pulmonary vascular mechanics compared with higher or lower positive end-expiratory pressures in experimental acute respiratory distress syndrome. DESIGN: Experimental study. SETTING: Animal research laboratory. SUBJECTS: Ten pigs, 35 ± 5.2 kg. INTERVENTIONS: Acute respiratory distress syndrome was induced combining saline lung lavages with injurious mechanical ventilation. The positive end-expiratory pressure level resulting in highest compliance during a decremental positive end-expiratory pressure trial after lung recruitment was determined. Thereafter, three positive end-expiratory pressure levels were applied in a random order: hyperinflation, 6 cm H2O above; open lung approach, 2 cm H2O above; and collapse, 6 cm H2O below the highest compliance level. High fidelity pressure and flow sensors were placed at the main pulmonary artery for measuring pulmonary artery resistance (Z0), effective arterial elastance, compliance, and reflected pressure waves. MEASUREMENTS AND MAIN RESULTS: After inducing acute respiratory distress syndrome, Z0 and effective arterial elastance increased (from 218 ± 94 to 444 ± 115 dyn.s.cm and from 0.27 ± 0.14 to 0.62 ± 0.22 mm Hg/mL, respectively; p < 0.001), vascular compliance decreased (from 2.76 ± 0.86 to 1.48 ± 0.32 mL/mm Hg; p = 0.003), and reflected waves arrived earlier (0.23 ± 0.07 vs 0.14 ± 0.05, arbitrary unit; p = 0.002) compared with baseline. Comparing the three positive end-expiratory pressure levels, open lung approach resulted in the lowest: 1) Z0 (297 ± 83 vs 378 ± 79 dyn.s.cm, p = 0.033, and vs 450 ± 119 dyn.s.cm, p = 0.002); 2) effective arterial elastance (0.37 ± 0.08 vs 0.50 ± 0.15 mm Hg/mL, p = 0.04, and vs 0.61 ± 0.12 mm Hg/mL, p < 0.001), and 3) reflection coefficient (0.35 ± 0.17 vs 0.48 ± 0.10, p = 0.024, and vs 0.53 ± 0.19, p = 0.005), comparisons with hyperinflation and collapse, respectively. CONCLUSIONS: In this experimental setting, positive end-expiratory pressure consistent with the open lung approach resulted in the best pulmonary vascular mechanics compared with higher or lower positive end-expiratory pressure settings.

The use of pulse pressure variation and stroke volume variation in spontaneously breathing patients to assess dynamic arterial elastance and to predict arterial pressure response to fluid administration.

BACKGROUND: Dynamic arterial elastance (Eadyn), defined as the pulse pressure variation (PPV) to stroke volume variation (SVV) ratio, has been suggested as a predictor of the arterial pressure response to fluid administration. In this study, we assessed the effectiveness of Eadyn to predict the arterial blood pressure response to a fluid challenge (FC) in preload-dependent, spontaneously breathing patients. METHODS: Patients admitted postoperatively and monitored with the Nexfin monitor (BMEYE, Amsterdam, The Netherlands) were enrolled in the study. Patients were included in the analysis if they were spontaneously breathing and had an increase in cardiac output ≥10% during an FC. Patients were classified according to the increase in mean arterial blood pressure (MAP) after FC into MAP-responders (MAP increase ≥10%) and MAP-nonresponders (MAP increase <10%). Eadyn was continuously calculated from the PPV and SVV values obtained from the monitor. RESULTS: Thirty-four FCs from 26 patients were studied. Seventeen FCs (50%) induced a positive MAP response. Preinfusion Eadyn was significantly higher in MAP-responders (1.39 ± 0.41 vs 0.85 ± 0.23; P = 0.0001). Preinfusion Eadyn predicted a positive MAP response to FC with an area under the receiver-operating characteristic curve of 0.92 ± 0.04 of standard error (95% confidence interval, 0.78-0.99; P < 0.0001). A preinfusion Eadyn value ≥1.06 (gray zone: 0.9-1.15) discriminated MAP-responders with a sensitivity and specificity of 88.2% (approximate 95% confidence interval, 64%-99%), respectively. CONCLUSIONS: Noninvasive Eadyn, defined as the PPV to SVV ratio, predicted the arterial blood pressure increase to fluid administration in spontaneously breathing, preload-dependent patients.