Contribution of arterial stiffness and stroke volume to peripheral pulse pressure in ICU patients: an arterial tonometry study

Rethinking Fluid Responsiveness during Septic Shock: Ameliorate Accuracy of Noninvasive Cardiac Output Measurements through Evaluation of Arterial Biomechanical Properties

Beat-to-beat estimates of cardiac output from the direct measure of peripheral arterial blood pressure rely on the assumption that changes in the waveform morphology are related to changes in blood flow and vasomotor tone. However, in septic shock patients, profound changes in vascular tone occur that are not uniform across the entire arterial bed. In such cases, cardiac output estimates might be inaccurate, leading to unreliable evaluation of fluid responsiveness. Pulse wave velocity is the gold-standard method for assessing different arterial biomechanical properties. Such methods might be able to guide, personalize and optimize the management of septic patients.

The Eight Unanswered and Answered Questions about the Use of Vasopressors in Septic Shock

Septic shock is mainly characterized-in addition to hypovolemia-by vasoplegia as a consequence of a release of inflammatory mediators. Systemic vasodilatation due to depressed vascular tone results in arterial hypotension, which induces or worsens organ hypoperfusion. Accordingly, vasopressor therapy is mandatory to correct hypotension and to reverse organ perfusion due to hypotension. Currently, two vasopressors are recommended to be used, norepinephrine and vasopressin. Norepinephrine, an α₁-agonist agent, is the first-line vasopressor. Vasopressin is suggested to be added to norepinephrine in cases of inadequate mean arterial pressure instead of escalating the doses of norepinephrine. However, some questions about the bedside use of these vasopressors remain. Some of these questions have been well answered, some of them not clearly addressed, and some others not yet answered. Regarding norepinephrine, we firstly reviewed the arguments in favor of the choice of norepinephrine as a first-line vasopressor. Secondly, we detailed the arguments found in the recent literature in favor of an early introduction of norepinephrine. Thirdly, we reviewed the literature referring to the issue of titrating the doses of norepinephrine using an individualized resuscitation target, and finally, we addressed the issue of escalation of doses in case of refractory shock, a remaining unanswered question. For vasopressin, we reviewed the rationale for adding vasopressin to norepinephrine. Then, we discussed the optimal time for vasopressin administration. Subsequently, we addressed the issue of the optimal vasopressin dose, and finally we discussed the best strategy to wean these two vasopressors when combined.

How to integrate hemodynamic variables during resuscitation of septic shock?

Resuscitation of septic shock is a complex issue because the cardiovascular disturbances that characterize septic shock vary from one patient to another and can also change over time in the same patient. Therefore, different therapies (fluids, vasopressors, and inotropes) should be individually and carefully adapted to provide personalized and adequate treatment. Implementation of this scenario requires the collection and collation of all feasible information, including multiple hemodynamic variables. In this review article, we propose a logical stepwise approach to integrate relevant hemodynamic variables and provide the most appropriate treatment for septic shock.

Prediction of stroke using an algorithm to estimate arterial stiffness

Background

Arterial stiffness is important because it is associated with adverse cardiovascular events including stroke. Methods that are based on pulse wave velocity have significant limitations in estimating arterial stiffness. The purpose of this paper is to present a novel easy to apply non-invasive method to estimate arterial stiffness that is based on pulse pressure.

Methods

Two indices to estimate arterial stiffness, (1) arterial stiffness 1 (AS1) and (2) arterial stiffness 2 (AS2) were developed and applied in two National Institutes of Health funded clinical trials, the Systolic Hypertension in the Elderly Program and the Systolic Blood Pressure Intervention Trial. These indices were developed by fitting individual survival models for selected predictor variables to the response, i.e. time to stroke, by selecting the coefficients that were statistically significant at the 0.05 α level after adjusting the variable weights. The indices were derived as the weighted linear combination of the coefficients.

Results

AS1 and AS2 performed well in two goodness of fit criteria i.e. overall model p-value and concordance correlation. Comparison of Cox models using indices AS1 and AS2 and chronological age indicated that AS1 and AS2 independently predicted the occurrence of stroke at five years better than chronological age. Nearly identical effects were observed when the analyses were limited to Black participants in SPRINT with a concordance correlation of 0.80 and log rank test p-value of 0.007.

Conclusion

These indices that are derived from pulse pressure predict the occurrence of stroke better than either pulse pressure or chronological age alone and may be used in designing new randomized clinical trials, and possibly incorporated in hypertension and stroke guidelines.

Feasibility of non-invasive measurement of central blood pressure and arterial stiffness in shock

BACKGROUND

Patients in haemodynamic shock are in need for an intensive care treatment. Invasive haemodynamic monitoring is state of the art for these patients. However, evolved, non-invasive blood pressure monitoring devices offer advanced functions like the assessment of central blood pressure and arterial stiffness. We analysed the feasibility of two oscillometric blood pressure devices in patients with shock.

METHODS

We performed a monocentre prospective study, enrolling 57 patients admitted to the intensive care unit (ICU), due to septic and/or cardiogenic shock. We assessed invasive and non-invasive peripheral and central blood pressure <24 hours and 48 hours after admission on the ICU. Additional haemodynamic parameters such as pulse wave velocity (PWV), augmentation pressure and augmentation index were obtained through Mobil-o-Graph PWA (IEM) and SphygmoCor XCEL (AtCor Medical).

RESULTS

A complete haemodynamic assessment was successful in all patients (48) with the Mobil-o-Graph 24 hours PWA and in 29 patients with the SphygmoCor XCEL (P = .001), when cases of death or device malfunction were excluded. Reasons for failure were severe peripheral artery disease, haemodynamic instability, oedema and agitation. Invasive blood pressure showed a sufficient correlation with both devices; however, large differences between invasive and non-invasive techniques were recorded in Bland-Altmann analysis (P < .05 for all parameters). PWV differed between the two devices.

CONCLUSION

Non-invasive peripheral blood pressure measurement remains a rescue technique. However, non-invasive assessment of arterial stiffness and central blood pressure is possible in patients with septic or cardiogenic shock. Further studies are required to assess their clinical significance for patients in shock.

Hemodynamic Monitoring in Sepsis-A Conceptual Framework of Macro- and Microcirculatory Alterations

Circulatory failure in sepsis is common and places a considerable burden on healthcare systems. It is associated with an increased likelihood of mortality, and timely recognition is a prerequisite to ensure optimum results. While there is consensus that aggressive source control, adequate antimicrobial therapy and hemodynamic management constitute crucial determinants of outcome, discussion remains about the best way to achieve each of these core principles. Sound cardiovascular support rests on tailored fluid resuscitation and vasopressor therapy. To this end, an overarching framework to improve cardiovascular dynamics has been a recurring theme in modern critical care. The object of this review is to examine the nature of one such framework that acknowledges the growing importance of adaptive hemodynamic support combining macro- and microhemodynamic variables to produce adequate tissue perfusion.

Increased aortic stiffness and elevated blood pressure in response to exercise in adult survivors of prematurity

Objectives

Adults born prematurely have an increased risk of early heart failure. The impact of prematurity on left and right ventricular function has been well documented, but little is known about the impact on the systemic vasculature. The goals of this study were to measure aortic stiffness and the blood pressure response to physiological stressors; in particular, normoxic and hypoxic exercise.

Methods

Preterm participants (n = 10) were recruited from the Newborn Lung Project Cohort and matched with term‐born, age‐matched subjects (n = 12). Aortic pulse wave velocity was derived from the brachial arterial waveform and the heart rate and blood pressure responses to incremental exercise in normoxia (21% O₂) or hypoxia (12% O₂) were evaluated.

Results

Aortic pulse wave velocity was higher in the preterm groups. Additionally, heart rate, systolic blood pressure, and pulse pressure were higher throughout the normoxic exercise bout, consistent with higher conduit artery stiffness. Hypoxic exercise caused a decline in diastolic pressure in this group, but not in term‐born controls.

Conclusions

In this first report of the blood pressure response to exercise in adults born prematurely, we found exercise‐induced hypertension relative to a term‐born control group that is associated with increased large artery stiffness. These experiments performed in hypoxia reveal abnormalities in vascular function in adult survivors of prematurity that may further deteriorate as this population ages.

Comparison of exercise intensity during four early rehabilitation techniques in sedated and ventilated patients in ICU: a randomised cross-over trial

BACKGROUND

In the ICU, out-of-bed rehabilitation is often delayed and in-bed exercises are generally low-intensity. Since the majority of rehabilitation is carried out in bed, it is essential to carry out the exercises that have the highest intensity. The aim of this study was to compare the physiological effects of four common types of bed exercise in intubated, sedated patients confined to bed in the ICU, in order to determine which was the most intensive.

METHODS

A randomised, single-blind, placebo-controlled crossover trial was carried out to evaluate the effects of four bed exercises (passive range of movements (PROM), passive cycle-ergometry, quadriceps electrical stimulation and functional electrical stimulation (FES) cycling) on cardiac output. Each exercise was carried out for ten minutes in ventilated, sedated patients. Cardiac output was recorded using cardiac Doppler ultrasound. The secondary aims were to evaluate right heart function and pulmonary and systemic artery pressures during the exercises, and the microcirculation of the vastus lateralis muscle.

RESULTS

The results were analysed in 19 patients. FES cycling was the only exercise that increased cardiac output, with a mean increase of 1 L/min (15%). There was a concomitant increase in muscle oxygen uptake, suggesting that muscle work occurred. FES cycling thus constitutes an effective early rehabilitation intervention. No muscle or systemic effects were induced by the passive techniques.

CONCLUSION

Most bed exercises were low-intensity and induced low levels of muscle work. FES cycling was the only exercise that increased cardiac output and produced sufficient intensity of muscle work. Longer-term studies of the effect of FES cycling on functional outcomes should be carried out.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT02920684 . Registered on 30 September 2016. Prospectively registered.

Norepinephrine reduces arterial compliance less than phenylephrine when treating general anesthesia-induced arterial hypotension

INTRODUCTION

During general anesthesia, arterial hypotension is frequent and may be an important contributor to perioperative morbidity. We assessed the effect of a 5 μg bolus of Norepinephrine (NA) when compared with 50 μg bolus of Phenylephrine (PE) administered to treat hypotension during maintenance anesthesia, on MAP, derived cardiac output and arterial stiffness parameters.

METHODS

Patients scheduled for a neurosurgical procedure under general anesthesia were prospectively included. Monitoring included invasive blood pressure, esophageal Doppler, and arterial tonometer used to estimate central aortic pressure with arterial stiffness parameters, such as augmentation index (Aix). After initial resuscitation, hypotensive episodes were corrected by a bolus administration of NA or PE in a peripheral venous line.

RESULTS

There were 269 bolus administrations of vasopressors (149 NA, 120 PE) in 47 patients with no adverse effects detected. A decrease in stroke volume (SV) was observed with PE compared with NA (-18 ± 9% vs. -14 ± 7%, P < 0.001). This decrease was associated with an increase in Aix, which was greater for PE than for NA (+10 ± 8% vs. +6 ± 6%, P < 0.0001), and a decrease in total arterial compliance greater for PE compared to NA (Ctot = SV/Central Pulse Pressure) (-35 ± 9% vs. -29 ± 10%, P < 0.001).

DISCUSSION

This study suggests that 5 μg of NA administered as a bolus in a peripheral venous line could treat general anesthesia-induced arterial hypotension with a smaller decrease in SV and arterial compliance when compared to PE.

Hemodynamic monitoring in the intensive care unit

Patients in the intensive care unit are often critically ill with inadequate tissue perfusion and oxygenation. This inadequate delivery of substrates at the cellular level is a common definition of shock. Hemodynamic monitoring is the observation of cardiovascular physiology. The purpose of hemodynamic monitoring is to identify abnormal physiology and intervene before complications, including organ failure and death, occur. The most common types of invasive hemodynamic monitors are central venous catheters, pulmonary artery catheters, and arterial pulse-wave analysis. Ultrasonography is a noninvasive alternative being used in intensive care units for hemodynamic measurements and assessments.

Pulse pressure variation predicts fluid responsiveness in elderly patients after coronary artery bypass graft surgery

OBJECTIVE

To assess the ability of pulse pressure variation to predict fluid responsiveness in mechanically ventilated elderly patients after coronary artery bypass graft surgery.

DESIGN

A prospective, interventional study.

SETTING

An academic, tertiary referral hospital.

PARTICIPANTS

Sixty patients >70 years old and mechanically ventilated after coronary artery bypass graft surgery.

INTERVENTIONS

Intravascular volume expansion using 6% hydroxyethyl starch solution, 7 mL/kg over 20 minutes.

MEASUREMENTS AND MAIN RESULTS

Heart rate, arterial blood pressure, pulse pressure variation, central venous pressure, pulmonary artery occlusion pressure, and stroke volume index were measured immediately before and after volume expansion. Fluid responsiveness was defined as an increase in stroke volume index ≥ 15% after volume expansion. Forty-one patients were fluid responders and 19 patients were nonresponders. In contrast to central venous pressure or pulmonary artery occlusion pressure, pulse pressure variation was higher in the responders than in the nonresponders (22 ± 6% v 9.3 ± 3%, p = 0.001) and correlated with the percent changes in the stroke volume index after volume expansion (r = 0.47, p = 0.001). The area under the receiver operating characteristic curve for pulse pressure variation was 0.85 (95% confidence interval 0.75-0.94). The threshold value of 11.5% allowed the discrimination between responders and nonresponders with a sensitivity of 80% and a specificity of 74%.

CONCLUSIONS

Pulse pressure variation is a reliable predictor of fluid responsiveness in mechanically ventilated elderly patients after coronary artery bypass graft surgery.

Noninvasive evaluation of coronary distensibility in older adults: a feasibility study with MR angiography

PURPOSE

To assess the feasibility of using magnetic resonance (MR) angiography to noninvasively measure the coronary distensibility index (CDI) in older adults.

MATERIALS AND METHODS

This study was approved by the institutional review board and was compliant with HIPAA. Informed consent was obtained from all participants. Three-dimensional MR angiography was performed in 23 patients with type 2 diabetes mellitus (DM) (mean age, 72.9 years ± 5.8 [standard deviation]; age range, 65-84 years; 12 men, 11 women) and 50 healthy aging control subjects (mean age, 73.1 years ± 5.6; age range, 64-84 years; 28 men, 22 women). Imaging data were acquired in the rest periods of cardiac motion identified during end systole and middiastole. For imaging data with different acquisition windows, cross-sectional coronary planes were reconstructed and matched for the same anatomy according to coronary landmarks. The CDI, defined as [(lumen area at systole--lumen area at diastole)/(lumen area at diastole × pulse pressure)] × 1000, was compared between patients with DM and control subjects by using the Student t test. With the same protocol, CDIs were calculated in 10 randomly selected subjects by two independent readers. In addition, MR angiography (in systole and diastole) was repeated in those 10 subjects after repositioning.

RESULTS

CDIs were measured in 43 coronary segments of patients with DM and in 124 coronary segments of control subjects. The mean CDI in patients with DM was significantly lower than that in control subjects (2.79 mm Hg(-1) ± 2.12 vs 9.14 mm Hg(-1) ± 5.87, respectively; P < .001). CDI measurements showed good intraobserver (r = 0.914), interobserver (r = 0.820), and imaging-repeat imaging agreements (r = 0.811).

CONCLUSION

Coronary MR angiography is a reproducible and repeatable noninvasive method for detecting significant differences in coronary distensibility between patients with DM and healthy aging control subjects.

Changes in pulse pressure following fluid loading: a comparison between aortic root (non-invasive tonometry) and femoral artery (invasive recordings)

PURPOSE

To document the relationship between stroke volume (SV) and pulse pressure (PP) recorded at the femoral and aortic sites during volume expansion (VE) in patients in shock. We hypothesized that non-invasively estimated aortic PP would exhibit the same ability as PP recorded invasively at the femoral level to track SV changes.

METHODS

Included in this prospective study were 56 ICU patients needing VE. Femoral PP (indwelling catheter), aortic PP (tonometry) and cardiac output (thermodilution) were recorded before and after VE. Responders were defined as patients who showed an increase in SV of ≥15% after VE.

RESULTS

Of the 56 included patients in shock, 39 (age 57 ± 14 years, SAPS II 46 ± 18) completed the study. At both sites, PP increased after VE in responders (n=17, mean SV increase 30 ± 15%) but not in non-responders. In the overall population, there was a positive relationship between VE-induced changes in SV and in PP at the femoral (r=0.60, p<0.001) and aortic (r=0.52, p<0.001) sites. Increases in femoral PP of ≥9% indicated SV increases of ≥15% with 82% sensitivity and 95% specificity. Increases in aortic PP of ≥4.5% indicated SV increases of ≥15% with 76% sensitivity and 82% specificity. Areas under the ROC curves indicated that aortic PP was not different from femoral PP for tracking changes in SV.

CONCLUSION

The ability of non-invasively estimated aortic PP to track fluid response was the same as that of invasively recorded femoral PP. This may have implications for non-invasive haemodynamic monitoring.

Dynamic arterial elastance to predict arterial pressure response to volume loading in preload-dependent patients

Introduction

Hemodynamic resuscitation should be aimed at achieving not only adequate cardiac output but also sufficient mean arterial pressure (MAP) to guarantee adequate tissue perfusion pressure. Since the arterial pressure response to volume expansion (VE) depends on arterial tone, knowing whether a patient is preload-dependent provides only a partial solution to the problem. The objective of this study was to assess the ability of a functional evaluation of arterial tone by dynamic arterial elastance (Ea_dyn), defined as the pulse pressure variation (PPV) to stroke volume variation (SVV) ratio, to predict the hemodynamic response in MAP to fluid administration in hypotensive, preload-dependent patients with acute circulatory failure.

Methods

We performed a prospective clinical study in an adult medical/surgical intensive care unit in a tertiary care teaching hospital, including 25 patients with controlled mechanical ventilation who were monitored with the Vigileo^® monitor, for whom the decision to give fluids was made because of the presence of acute circulatory failure, including arterial hypotension (MAP ≤65 mmHg or systolic arterial pressure <90 mmHg) and preserved preload responsiveness condition, defined as a SVV value ≥10%.

Results

Before fluid infusion, Ea_dyn was significantly different between MAP responders (MAP increase ≥15% after VE) and MAP nonresponders. VE-induced increases in MAP were strongly correlated with baseline Ea_dyn (r² = 0.83; P < 0.0001). The only predictor of MAP increase was Ea_dyn (area under the curve, 0.986 ± 0.02; 95% confidence interval (CI), 0.84-1). A baseline Ea_dyn value >0.89 predicted a MAP increase after fluid administration with a sensitivity of 93.75% (95% CI, 69.8%-99.8%) and a specificity of 100% (95% CI, 66.4%-100%).

Conclusions

Functional assessment of arterial tone by Ea_dyn, measured as the PVV to SVV ratio, predicted arterial pressure response after volume loading in hypotensive, preload-dependent patients under controlled mechanical ventilation.

Determinants of arterial and central venous blood pressure variation in ventilated critically ill children

PURPOSE

Ventilation-induced arterial pressure variation predicts volume responsiveness in adults. Several factors are known to influence the interpretability of these variations. We analysed ventilation-induced variations in critically ill children with reference to ventilatory and circulatory parameters.

METHODS

We prospectively included 20 paediatric patients. Variation of systolic pressure (SPV), pulse pressure (PPV) and central venous pressure (CVP) were assessed during pressure-controlled ventilation with inspiratory pressures (P(insp)) of 20 and 28 cmH(2)O. Blood gases were analysed and echocardiography was performed.

RESULTS

SPV, PPV and CVP variation significantly increased with elevated P(insp) (p < 0.001, p = 0.008 and p = 0.003). Baseline CVP and shortening fraction were significant negative predictors of PPV and SPV.

CONCLUSION

This preliminary study identified P(insp) as a determinant of SPV, PPV and CVP variation in children. Further independent determinants of SPV and PPV were baseline CVP and ventricular performance, both of which must be considered when interpreting pressure variations.

Noninvasive assessment of arterial pressure

PURPOSE OF REVIEW

To briefly review recent advances in the noninvasive assessment of arterial pressure (indirect methods) in the field of critical care.

RECENT FINDINGS

Automated oscillometric measurements underestimate intraarterial systolic blood pressure. Digital photoplethysmography has led to conflicting results, although the obtained respiratory pulse pressure variation correlates with the fluid-challenge-induced changes in stroke volume. The pulse oximetry photoplethysmographic signal recorded at the digital or ear level may be useful in monitoring respiratory arterial pressure variations, although technical improvements and clarifications are needed. Arterial tonometry is increasingly used in the cardiovascular field to reconstruct central aortic pressure. A recent study has shown that radial artery tonometry is feasible in hemodynamically stable patients and that peripheral pulse pressure reflects the combined influences of arterial stiffness and stroke volume, especially in elderly patients. The limitations of this technique include the potential bias related to the use of a generalized transfer function and the difficulty in obtaining reliable recordings in hemodynamically unstable patients.

SUMMARY

Intraarterial blood pressure must be preferred over noninvasive blood pressure recordings when critical decisions are required. In hemodynamically stable patients, valuable information may be obtained by using noninvasive techniques, amongst which arterial tonometry seems especially promising.