Pulse pressure variation, stroke volume variation and dynamic arterial elastance

A norepinephrine weaning strategy using dynamic arterial elastance is associated with reduction of acute kidney injury in patients with vasoplegia after cardiac surgery: A post-hoc analysis of the randomized SNEAD study

STUDY OBJECTIVE

To evaluate the impact of a dynamic arterial elastance guided norepinephrine weaning strategy on the occurrence of acute kidney injury (AKI) in patients with vasoplegia after cardiac surgery.

DESIGN

A post-hoc analysis of a monocentric randomized controlled trial.

SETTING

A tertiary care hospital in France.

PARTICIPANTS

Vasoplegic cardiac surgical patients treated with norepinephrine.

INTERVENTION

Patients were randomized to an algorithm-based norepinephrine weaning intervention (dynamic arterial elastance) group or a control group.

MEASUREMENTS

The primary endpoint was the number of patients with AKI defined according to Kidney Disease Improving Global Outcomes (KDIGO) criteria. The secondary endpoint were major adverse cardiac post-operative events (new onset of atrial fibrillation or flutter, low cardiac output syndrome, and in-hospital death). End points were evaluated during the first seven post-operative days.

RESULTS

118 patients were analyzed. In the overall study population, the mean age was 70 (62-76) years, 65% were male and the median EuroSCORE was 7 (5-10). Overall, 46 (39%) patients developed AKI (30 KDIGO 1, 8 KDIGO 2, 8 KDIGO 3), and 6 patients required renal replacement therapy. The incidence of AKI was significantly lower in the intervention group than in the control group (16 patients (27%) vs 30 patients (51%), p = 0.12). Higher dose and longer duration of norepinephrine were associated with AKI severity.

CONCLUSION

Decreasing norepinephrine exposure by using a dynamic arterial elastance guided norepinephrine weaning strategy was associated with a reduced incidence of acute kidney injury in patients with vasoplegia after cardiac surgery. Further prospective multicentric studies are needed to confirm these results.

Dynamic Arterial Elastance to Predict Mean Arterial Pressure Decrease after Reduction of Vasopressor in Septic Shock Patients

After fluid status optimization, norepinephrine infusion represents the cornerstone of septic shock treatment. De-escalation of vasopressors should be considered with caution, as hypotension increases the risk of mortality. In this prospective observational study including 42 patients, we assess the role of dynamic elastance (EaDyn), i.e., the ratio between pulse pressure variation and stroke volume variation, which can be measured noninvasively by the MostCare monitoring system, to predict a mean arterial pressure (MAP) drop > 10% 30 min after norepinephrine reduction. Patients were divided into responders (MAP falling > 10%) and non-responders (MAP falling < 10%). The receiver-operating-characteristic curve identified an area under the curve of the EaDyn value to predict a MAP decrease > 10% of 0.84. An EaDyn cut-off of 0.84 predicted a MAP drop > 10% with a sensitivity of 0.71 and a specificity of 0.89. In a multivariate logistic regression, EaDyn was significantly and independently associated with MAP decrease (OR 0.001, 95% confidence interval 0.00001−0.081, p < 0.001). The nomogram model for the probability of MAP decrease > 10% showed a C-index of 0.90. In conclusion, in a septic shock cohort, EaDyn correlates well with the risk of decrease of MAP > 10% after norepinephrine reduction.

Is dynamic arterial elastance a predictor of an increase in blood pressure after fluid administration in pediatric patients with hypotension? Reanalysis of prospective observational studies

BACKGROUND

Dynamic arterial elastance (Ea_dyn ) has been proposed to predict an increase in mean arterial pressure (MAP) after volume expansion in hypotensive adults. We aimed to evaluate the clinical usefulness of Ea_dyn as a predictor of arterial pressure response after fluid loading in pediatric patients with hypotension.

METHODS

We re-analyzed data of 63 hypotensive children (age, ≤5 years), collected from three previous prospective observational studies about fluid responsiveness. Pulse pressure variation (PPV), stroke volume variation (SVV), and respiratory variation in aortic blood flow velocity (ΔVpeak) were used to calculate Ea_dyn (PPV/SVV) and modified Ea_dyn (PPV/ΔVpeak). Preload-dependent patients were defined as those with ΔVpeak ≥12% before fluid loading. Patients were classified as pressure responders, if their MAP increased ≥15% after fluid administration.

RESULTS

Mean Ea_dyn (SD) was 1.06 (0.47) in pressure responders (n=39) and 0.99 (0.48) in nonresponders (n = 24) (mean difference, 0.08; 95% confidence interval [CI], -0.19-0.34; P = .567). Additionally, mean modified Ea_dyn was 1.27 (0.64) in responders and 1.11 (0.43) in nonresponders (mean difference, 0.17; 95% CI, -0.13-0.46; P = 0.269). Both Ea_dyn (AUC 0.506; 95% confidence interval [CI], 0.337 to 0.675; P = 0.948) and modified Ea_dyn (AUC 0.498; 95% CI, 0.328-0.669; P = 0.983), as well as other dynamic variables, could not predict pressure responsiveness in children. Sub-group analysis revealed similar findings in both in 39 preload-dependent and hypotensive patients (26 pressure responders and 13 nonpressure responders).

CONCLUSION

Both Ea_dyn and modified Ea_dyn cannot predict whether blood pressure increases with fluid administration in pediatric patients with hypotension.

Respiratory Variations in Electrocardiographic R-Wave Amplitude during Acute Hypovolemia Induced by Inferior Vena Cava Clamping in Patients Undergoing Liver Transplantation

The aim of this study was to analyze whether the respiratory variation in electrocardiogram (ECG) standard lead II R-wave amplitude (ΔRDII) could be used to assess intravascular volume status following inferior vena cava (IVC) clamping. This clamping causes an acute decrease in cardiac output during liver transplantation (LT). We retrospectively compared ΔRDII and related variables before and after IVC clamping in 34 recipients. Receiver operating characteristic (ROC) curve and area under the curve (AUC) analyses were used to derive a cutoff value of ΔRDII for predicting pulse pressure variation (PPV). After IVC clamping, cardiac output significantly decreased while ΔRDII significantly increased (p = 0.002). The cutoff value of ΔRDII for predicting a PPV >13% was 16.9% (AUC: 0.685) with a sensitivity of 57.9% and specificity of 77.6% (95% confidence interval 0.561 – 0.793, p = 0.015). Frequency analysis of ECG also significantly increased in the respiratory frequency band (p = 0.016). Although significant changes in ΔRDII during vena cava clamping were found at norepinephrine doses <0.1 µg/kg/min (p = 0.032), such changes were not significant at norepinephrine doses >0.1 µg/kg/min (p = 0.093). ΔRDII could be a noninvasive dynamic parameter in LT recipients presenting with hemodynamic fluctuation. Based on our data, we recommended cautious interpretation of ΔRDII may be requisite according to vasopressor administration status.

Dynamic arterial elastance measured by uncalibrated pulse contour analysis predicts arterial-pressure response to a decrease in norepinephrine

BACKGROUND

Dynamic arterial elastance (Ea_dyn) has been proposed as an indicator of vascular tone that predicts the decrease in arterial pressure in response to changes in norepinephrine (NE). The purpose of this study was to determine whether Ea_dyn measured by uncalibrated pulse contour analysis (UPCA) can predict a decrease in arterial pressure when the NE dosage is decreased.

METHODS

We conducted a prospective study in a university hospital intensive care unit. Patients with vasoplegic syndrome for whom the intensive care physician planned to decrease the NE dosage were included. Haemodynamic and UPCA (VolumeView and FloTrac; Edwards Lifesciences, Irvine, CA, USA) values were obtained before and after decreasing the NE dosage. Responders were defined by a >10% decrease in mean arterial pressure (MAP).

RESULTS

Of 35 patients included, 11 (31%) were pressure responders with a median decrease of 13%. Ea_dyn was correlated to systolic arterial pressure (SAP) (r=0.255; P=0.033), diastolic arterial pressure (r=0.271; P=0.024), MAP (r=0.310; P=0.009), heart rate (r=0.543; P=0.0001), and transthoracic echography cardiac output (r=0.264; P=0.024). Baseline Ea_dyn was correlated with MAP changes (r=0.394; P=0.019) and SAP changes (r=0.431; P=0.009). Ea_dyn predicted the decrease in arterial pressure with an area under the receiver-operating-characteristic curve of 0.84 (95% confidence interval: 0.70-0.97). The best cut-off was 0.90.

CONCLUSIONS

The present study confirms the ability of Ea_dyn measured by UPCA to predict an arterial pressure response to a decrease in NE. Ea_dyn may constitute an easy-to-use functional approach to arterial tone assessment regardless of the monitor used to measure its determinant.

CLINICAL TRIAL REGISTRATION

DRCIT95.

Influence of intra-abdominal pressure on the specificity of pulse pressure variations to predict fluid responsiveness

BACKGROUND

The positive predictive value of pulse pressure variations (ΔPP) to discriminate patients who should respond to volume expansion (VE) may be altered in mechanically ventilated patients. Our goal was to determine whether intra-abdominal pressure (IAP) measurements could discriminate patients with true-positive ΔPP values versus patients with false-positive ΔPP values.

METHODS

We designed a prospective pathophysiologic study in a mixed intensive care unit of a university hospital. Sixteen mechanically ventilated patients with hypotension (SAP, <90 mm Hg) and with ΔPP of 13% or more were included. Cardiac output was assessed using Doppler echocardiography before and after VE; IAP was measured using the bladder pressure method. Patients were classified into two groups according to their response to a standardized VE (500 mL of NaCl 0.9%): responders (≥15% increase in cardiac output) and nonresponders.

RESULTS

Nine patients (57%) were responders, and seven patients (43%) were nonresponders. Before VE, IAP was statistically higher in nonresponders (15 [11-22] mm Hg vs. 9 [6.5-11] mm Hg; p = 0.008). The area under the curve of the receiver operating characteristic curve was 0.9 ± 0.08. In patients with ΔPP of 13% or more, an IAP cutoff value of 10.5 mm Hg discriminated between responders and nonresponders with a sensitivity of 100% (59-100%) and a specificity of 78% (40-97%).

CONCLUSION

An increase in IAP of more than 10.5 mm Hg can decrease the positive predictive value of ΔPP. Hence, in patients prone to present abnormal IAP values, IAP should be measured before performing VE directed by the ΔPP marker.

LEVEL OF EVIDENCE

Diagnostic study, level II.

Optimizing oxygen delivery in the critically ill: assessment of volume responsiveness in the septic patient

BACKGROUND

Assessing volume responsiveness, defined as an increase in cardiac index after infusion of fluids, is important when caring for critically ill patients in septic shock, as both under- and over-resuscitation can worsen outcomes. This review article describes the currently available methods of assessing volume responsiveness for critically ill patients in the emergency department, with a focus on patients in septic shock.

OBJECTIVE

The single-pump model of the circulation utilizing cardiac-filling pressures is reviewed in detail. Additionally, the dual-pump model evaluating cardiopulmonary interactions both invasively and noninvasively will be described.

DISCUSSION

Cardiac filling pressures (central venous pressure and pulmonary artery occlusion pressure) have poor performance characteristics when used to predict volume responsiveness. Cardiopulmonary interaction assessments (inferior vena cava distensibility/collapsibility, systolic pressure variation, pulse pressure variation, stroke volume variation, and aortic flow velocities) have superior test characteristics when measured either invasively or noninvasively.

CONCLUSION

Cardiac filling pressures may be misleading if used to determine volume responsiveness. Assessment of cardiopulmonary interactions has superior performance characteristics, and should be preferentially used for septic shock patients in the emergency department.

Dynamic variables and fluid responsiveness in patients for aortic stenosis surgery

BACKGROUND

Aortic stenosis is the most common valvular disease in developed countries, but it carries an increased mortality during non-cardiac surgery underscoring the importance of adequate hemodynamic management. Further, haemodynamic management of patients immediately after surgery for aortic stenosis can be challenging. Prediction of fluid responsiveness using dynamic variables has not been sufficiently studied in patients for aortic stenosis surgery.

METHODS

Observational study evaluating fluid responsiveness on 32 (31 analysed) patients scheduled for aortic valve replacement due to aortic stenosis on mechanical ventilation before and after valve replacement. Increase in stroke volume (oesophagus Doppler) ≥ 15% to a fluid challenge defined fluid responders.

RESULTS

Before surgery (31 fluid loads performed in 31 patients), areas under receiver operating characteristics curves (95% confidence intervals) were stroke volume variation (from arterial pulse contour analysis) 0.77 (0.58-0.90), pulse pressure variation 0.75 (0.54-0.90) and Pleth variability index 0.51 (0.31-0.69). After aortic valve replacement (31 fluid loads performed in 23 patients) the values were stroke volume variation 0.90 (0.74-0.98), pulse pressure variation 0.95 (0.80-1.0) and Pleth variability index 0.72 (0.52-0.87).

CONCLUSIONS

The arterial pressure-based variables had moderate predictive values before valve replacement, but it predicted fluid responsiveness well postoperatively. Pleth variability index did not predict fluid responsiveness preoperatively, and it had a moderate predictive value postoperatively. These results indicate that arterial pressure-based dynamic variables have limited potential to guide fluid therapy in patients with aortic stenosis. Their ability to guide fluid therapy after aortic valve replacement seems better.

Functional haemodynamic monitoring

PURPOSE OF REVIEW

Functional haemodynamic monitoring is the assessment of the dynamic interactions of haemodynamic variables in response to a defined perturbation.

RECENT FINDINGS

Fluid responsiveness can be predicted during positive pressure breathing by variations in venous return or left ventricular output using numerous surrogate markers, such as arterial pulse pressure variation (PPV), left ventricular stroke volume variation (SVV), aortic velocity variation, inferior and superior vena cavae diameter changes and pulse oximeter pleth signal variability. Similarly, dynamic changes in cardiac output to a passive leg raising manoeuvre can be used in any patient and measured invasively or noninvasively. However, volume responsiveness, though important, reflects only part of the overall spectrum of functional physiological variables that can be measured to define physiologic state and monitor response to therapy. The ratio of PPV to SVV defines central arterial elastance and can be used to identify those hypotensive patients who will not increase their blood pressure in response to a fluid challenge despite increasing cardiac output. Dynamic tissue O2 saturation (StO2) responses to complete stop flow conditions, as can be created by measuring hand StO2 and occluding flow with a blood pressure cuff, assesses cardiovascular sufficiency and micro-circulatory blood flow distribution. They can be used to identify those ventilator-dependent individuals who will fail a spontaneous breathing trial or trauma patients in need of life-saving interventions.

SUMMARY

Functional haemodynamic monitoring approaches are increasing in numbers, conditions in which they are useful and resuscitation protocol applications. This is a rapidly evolving field whose pluripotential is just now being realized.

Respiratory change in ECG-wave amplitude is a reliable parameter to estimate intravascular volume status

Electrocardiogram (ECG) is a standard type of monitoring in intensive care medicine. Several studies suggest that changes in ECG morphology may reflect changes in volume status. The "Brody effect", a theoretical analysis of left ventricular (LV) chamber size influence on QRS-wave amplitude, is the key element of this phenomenon. It is characterised by an increase in QRS-wave amplitude that is induced by an increase in ventricular preload. This study investigated the influence of changes in intravascular volume status on respiratory variations of QRS-wave amplitudes (ΔECG) compared with respiratory pulse pressure variations (ΔPP), considered as a reference standard. In 17 pigs, ECG and arterial pressure were recorded. QRS-wave amplitude was measured from the Biopac recording to ensure that in all animals ECG electrodes were always at the same location. Maximal QRS amplitude (ECGmax) and minimal QRS amplitude (ECGmin) were determined over one respiratory cycle. ΔECG was calculated as 100 × [(ECGmax - ECGmin)/(ECGmax + ECGmin)/2]. ΔECG and ΔPP were simultaneously recorded. Measurements were performed at different time points: during normovolemic conditions, after haemorrhage (25 mL/kg), and following re-transfusion (25 mL/kg) with constant tidal volume (10 mL/kg) and respiration rate (15 breath/min). At baseline, ΔPP and ΔECG were both <12 %. ΔPP were significantly correlated with ΔECG (r(2) = 0.89, p < 0.001). Volume loss induced by haemorrhage increased significantly ΔPP and ΔECG. Moreover, during this state, ΔPP were significantly correlated with ΔECG (r(2) = 0.86, p < 0.001). Re-transfusion significantly decreased ΔPP and ΔECG, and ΔPP were significantly correlated with ΔECG (r(2) = 0.90, p < 0.001). The observed correlations between ΔPP and ΔECG at each time point of the study suggest that ΔECG is a reliable parameter to estimate the changes in intravascular volume status and provide experimental confirmation of the "Brody effect."