Indicator Of Fluid Responsiveness Research Articles

Plethysmography Variation Index versus Pulse Pressure Variation as an Indicator of Fluid Responsiveness in Colorectal Surgeries during Immediate Postoperative Period

Abstract Objective Goal directed fluid therapy during major abdominal surgery may reduce postoperative morbidity. The Plethysmography Variability Index (PVI), derived from the pulse oximeter waveform, has been shown to be able to predict fluid responsiveness in a number of surgical circumstances. In this study, we will compare the effectiveness and re liability of Plethysmography variation index (PPV) and Pulse pressure variation (PPV) in prediction of fluid responsiveness in all sedated intubated mechanically ventilated patients admitted for postoperative resuscitation in our surgical ICU. Method 100 patients were placed in two different groups equally where heart rate, PPV, CI, and PVI were recorded on admission. Immediately after volume expansion is performed by infusing saline 500 ml over 30 mins and at the end of volume expansion PPV, CI, PVI will be recorded every 2 hours for the first 24 hours. Results Hundred patients aged from 18 to 64 years who were scheduled for colorectal surgery and were to be transferred to the intensive care unit for postoperative care for the f irst 24 hours post operatively who didn’t have any of the exclusion criteria were included in this prospective randomized comparative single blinded research. 100 patients were divided in to “responders” and “non responders”. Both groups received a volume 500 ml saline over 30 minutes immedietly postoperatively. Fluid responsiveness was tested in both groups using PVI (Plethysmography variability index) and PPV ( pulse pressure variation) using cardiac index as a reference parameter. PVI showed accurate fluid responsiveness in comparison with PPV in responders with mean ranging from ( (-6.66 ± 0.90) and (-5.89 ± 1.93) respectively, with a P-value<0.01 Conclusion This study revealed that after giving a fluid challenge of 500 ml of saline over 30 minutes, a rise in PVI and PPV was demonstrated using cardiac index as a reference for reliability for comparing the effectiveness and accuracy between PVI and PPV.comparing the effectiveness and accuracy between PVI and PPV.PVI and PVI and PPV PPV can be used can be used in assessment of fluid responsiveness of the intubated ventilated sedated patients in assessment of fluid responsiveness of the intubated ventilated sedated patients with sinus rhythm in ICU, and both methods can be performed at the bedside, but with sinus rhythm in ICU, and both methods can be performed at the bedside, but PVI has advantage of being continuousPVI has advantage of being continuous, operator independent, and more reliable, operator independent, and more reliable thanthan PPVPPV.

Visual Evaluation of Plethysmographic Waveforms: Introducing the Simple Systolic Ratio as an Indicator of Fluid Responsiveness.

For patient safety, maintaining hemodynamic stability during surgical procedures is critical. Dynamic indices [such as systolic pressure variation (SPV) and pulse pressure variation (PPV)], have recently seen an increase in use. Given the risks associated with such invasive techniques, there is growing interest in non-invasive monitoring methods-and plethysmographic waveform analysis. However, many such non-invasive methods involve intricate calculations or brand-specific monitors. This study introduces the simple systolic ratio (SSR), derived from pulse oximetry tracings, as a non-invasive method to assess fluid responsiveness. This prospective observational study included 25 adult patients whose SPV, PPV, and SSR values were collected at 30-min intervals during open abdominal surgery. The SSR was defined as the ratio of the tallest waveform to the shortest waveform within pulse tracings. The correlations among SSR, SPV, and PPV were analyzed. Additionally, anaesthesia specialists visually assessed pulse oximetry tracings to determine fluid responsiveness using the SSR method. Strong correlations were observed between SSR and both SPV (r = 0.715, P < 0.001) and PPV (r = 0.702, P < 0.001). Receiver operator curve analysis identified optimal SSR thresholds for predicting fluid responsiveness at 1.47 for SPV and 1.50 for PPV. A survey of anaesthesia specialists using the SSR method to visually assess fluid responsiveness produced an accuracy rate of 83%. Based on the strong correlations it exhibits with traditional markers, SSR has great potential as a clinical tool, especially in resource-limited settings. However, further research is needed to establish its role, especially as it pertains to its universal applicability across monitoring devices.

The Ability ofMilitary Critical Care Air Transport Members to Visually Estimate Percent Systolic Pressure Variation.

Inappropriate fluid management during patient transport may lead to casualty morbidity. Percent systolic pressure variation (%SPV) is one of several technologies that perform a dynamic assessment of fluid responsiveness (FT-DYN). Trained anesthesia providers can visually estimate and use %SPV to limit the incidence of erroneous volume management decisions to 1-4%. However, the accuracy of visually estimated %SPV by other specialties is unknown. The aim of this article is to determine the accuracy of estimated %SPV and the incidence of erroneous volume management decisions for Critical Care Air Transport (CCAT) team members before and after training to visually estimate and utilize %SPV. In one sitting, CCAT team providers received didactics defining %SPV and indicators of fluid responsiveness and treatment with %SPV ≤7 and ≥14.5 defining a fluid nonresponsive and responsive patient, respectively; they were then shown ten 45-second training arterial waveforms on a simulated Propaq M portable monitor's screen. Study subjects were asked to visually estimate %SPV for each arterial waveform and queried whether they would treat with a fluid bolus. After each training simulation, they were told the true %SPV. Seven days post-training, the subjects were shown a different set of ten 45-second testing simulations and asked to estimate %SPV and choose to treat, or not. Nonparametric limits of agreement for differences between true and estimated %SPV were analyzed using Bland-Altman graphs. In addition, three errors were defined: (1) %SPV visual estimate errors that would label a volume responsive patient as nonresponsive, or vice versa; (2) incorrect treatment decisions based on estimated %SPV (algorithm application errors); and (3) incorrect treatment decisions based on true %SPV (clinically significant treatment errors). For the training and testing simulations, these error rates were compared between, and within, provider groups. Sixty-one physicians (MDs), 64 registered nurses (RNs), and 53 respiratory technicians (RTs) participated in the study. For testing simulations, the incidence and 95% CI for %SPV estimate errors with sufficient magnitude to result in a treatment error were 1.4% (0.5%, 3.2%), 1.6% (0.6%, 3.4%), and 4.1% (2.2%, 6.9%) for MDs, RNs, and RTs, respectively. However, clinically significant treatment errors were statistically more common for all provider types, occurring at a rate of 7%, 10%, and 23% (all P < .05). Finally, students did not show clinically relevant reductions in their errors between training and testing simulations. Although most practitioners correctly visually estimated %SPV and all students completed the training in interpreting and applying %SPV, all groups persisted in making clinically significant treatment errors with moderate to high frequency. This suggests that the treatment errors were more often driven by misapplying FT-DYN algorithms rather than by inaccurate visual estimation of %SPV. Furthermore, these errors were not responsive to training, suggesting that a decision-making cognitive aid may improve CCAT teams' ability to apply FT-DYN technologies.

97 Arterial Waveform Variations as Measures of Resuscitation Adequacy in a Porcine Model of Burn Injury

IntroductionOptimized fluid resuscitation of burn patients is a clinical care challenge as both under- and over- resuscitation have deleterious consequences. The gold-standard endpoint guiding burn resuscitation is urinary output (UO), which is known to have limited efficacy. We investigated the potential of the dynamic indices of fluid responsiveness derived from arterial blood pressure (BP) waveforms in conveying information about burn resuscitation. In particular, we investigated pulse pressure variation (PPV) and systolic pressure variation (SPV), which have been shown to be valuable in a number of other indications.MethodsWe conducted a retrospective analysis of arterial BP waveform data acquired from six anesthetized and mechanically-ventilated pigs (33±5 kg weight and 40% total burned surface area) which were instrumented for hemodynamic monitoring for 24 hours. The animals were either under-, over-, or adequately-resuscitated (guided by a burn resuscitation decision support system), with two animals in each group. PPV and SPV were calculated on an hourly basis. Fluid responsiveness thresholds of 15% and 6% were used respectively for PPV and SPV, as per literature.ResultsAll of the animals experienced an immediate rise in PPV and SPV following the injury (PPV and SPV start from large values as seen in Fig. 1 and Fig. 2). In the under-resuscitated group, PPV and SPV increased above the threshold, reaching maximum values in the last eight hours (PPV: 49.8±20%, SPV: 24.7±3.6%), indicating severe hypovolemia. In the over-resuscitated group, PPV and SPV decreased below the threshold, reaching their minimum in the last eight hours (PPV: 8.7±3.6%, SPV: 4.1±1.9%), indicating major hypervolemia. In the adequately-resuscitated group, PPV and SPV maintained closer to the threshold throughout the duration of the experiment, and at the end, PPV was 15.6±4.2% and SPV was 6.2±2.6%.ConclusionsOur initial results suggest that PPV and SPV may help distinguish under-, adequately-, and over-resuscitated burn patients, and potentially complement UO in the hemodynamic assessment of the burn injury patients.

Prediction of fluid responsiveness in spontaneously breathing patients.

In patients with acute circulatory failure, the primary goal of volume expansion is to increase cardiac output. However, this expected effect is inconstant, so that in many instances, fluid administration does not result in any haemodynamic benefit. In such cases, fluid could only exert some deleterious effects. It is now well demonstrated that excessive fluid administration is harmful, especially during acute respiratory distress syndrome and in sepsis or septic shock. This is the reason why some tests and indices have been developed in order to assess “fluid responsiveness” before deciding to perform volume expansion. While preload markers have been used for many years for this purpose, they have been repeatedly shown to be unreliable, which is mainly related to physiological issues. As alternatives, “dynamic” indices have been introduced. These indices are based upon the changes in cardiac output or stroke volume resulting from various changes in preload conditions, induced by heart-lung interactions, postural manoeuvres or by the infusion of small amounts of fluids. The haemodynamic effects and the reliability of these “dynamic” indices of fluid responsiveness are now well described. From their respective advantages and limitations, it is also possible to describe their clinical interest and the clinical setting in which they are applicable.

Comparison of pulse pressure variation versus echocardiography-derived stroke volume variation for prediction of fluid responsiveness in mechanically ventilated anesthetized dogs

ObjectiveTo evaluate the ability and accuracy of aortic flow velocity–time integral variation (ΔVTI) and peak aortic velocity variation (ΔVpeak) compared with pulse pressure variation (PPV) to predict fluid responsiveness in mechanically ventilated dogs. Study designProspective clinical study. AnimalsA group of 50 mechanically ventilated dogs with spontaneous hypotension during orthopedic or oncologic surgery. MethodsInvestigations were performed in the surgery room. When mean arterial pressure (MAP) decreased to <65 mmHg, measurements were performed before and after a fluid challenge (lactated Ringer’s solution 5 mL kg−1 over 15 minutes). Responders were defined as a change in stroke volume (SV; transesophageal Doppler) ≥15%. Data were analyzed using paired/unpaired t test or Mann–Whitney/Wilcoxon test when appropriate and receiver operating characteristics (ROC) curves; a p value <0.05 was considered statistically significant. ResultsAfter the fluid challenge, 35 (70%) of 50 dogs were responders with significant increases in SV and decreases in PPV; 15 dogs were nonresponders. ΔVTI and ΔVpeak correlated with a 15% increase in SV. The optimum cut-off value for PPV was 15.6% (sensitivity, 88%; specificity, 100%), for ΔVTI was 10.65% (sensitivity, 65%; specificity, 100%) and for ΔVpeak was 10.15% (sensitivity, 80%; specificity, 100%). The area under the ROC curve for PPV was (0.93 ± 0.08) and for ΔVpeak was (0.89 ± 0.09), before fluid challenge. The gray zone area spread from 6.15% to 15.6% for PPV (18 dogs), 2.45% to 10.65% for ΔVTI (22 dogs) and 0.6% to 10.15% for ΔVpeak (25 dogs). ConclusionsWhen using mechanical ventilation, ΔVTI and ΔVpeak predicted fluid responsiveness with the same ability as PPV, based on the area under the ROC curve analysis. However, PPV showed great accuracy demonstrated by a narrower gray zone that included fewer individuals. Clinical relevanceΔVTI and ΔVpeak can be used as indices of fluid responsiveness in anesthetized dogs.

Changes in Stroke Volume Variation Induced by Passive Leg Raising to Predict Fluid Responsiveness in Cardiac Surgical Patients With Protective Ventilation

Stroke volume variation (SVV) has been used to predict fluid responsiveness. The authors hypothesized the changes in SVV induced by passive leg raising (PLR) might be an indicator of fluid responsiveness in patients with protective ventilation after cardiac surgery. A prospective single-center observational study. A single cardiac surgery intensive care unit at a tertiary hospital. A total of 123 patients undergoing cardiac surgery with hemodynamic instability. Tidal volume was set between 6 and 8 mL/kg of ideal body weight. PLR maneuver, fluid challenge. SVV was continuously recorded using pulse contour analysis before and immediately after a PLR test and after fluid challenge (500 mL of colloid given over 30 min). Sixty-three (51.22%) patients responded to fluid challenge, in which PLR and fluid challenge significantly increased the SV and decreased the SVV. The decrease in SVV induced by PLR was correlated with the SV changes induced by fluid challenge. A 4% decrease in the SVV induced by PLR-discriminated responders to fluid challenge with an area under the curve of 0.90. The gray zone identified a range of SVV changes induced by PLR (between -3.94% and -2.91%) for which fluid responsiveness could not be predicted reliably. The gray zone included 15.45% of the patients. The SVV at baseline predicted fluid responsiveness with an area under the curve of 0.72. Changes in the SVV induced by PLR predicted fluid responsiveness in cardiac surgical patients with protective ventilation.

N-terminal pro-B-type natriuretic peptide for predicting fluid challenge in patients with septic shock.

The aim of this study is to examine whether plasma N-terminal pro-B-type natriuretic peptide (NT-proBNP) concentration could predict fluid responsiveness in septic shock patients following fluid challenge (FC). We reviewed prospectively collected data from 79 septic shock patients who received invasive cardiac output (CO) monitoring following a 500 mL FC. Haemodynamics were recorded, and blood sampling for NT-proBNP values was performed. Patients were divided into responders and non-responders according to fluid responsiveness, which was defined as cardiac index (CI) increase ≥10% induced by FC. The NT-proBNP and the CI changes were analysed using Pearson correlation. The area under the curve (AUC) for NT-proBNP was used to test its ability to distinguish responders and non-responders. Subgroup analyses were also explored. Among 79 patients, there were 55 responders. High NT-proBNP values were common in the study cohort. Baseline NT-proBNP values were comparable between responders and non-responders. In general, NT-proBNP values were not significantly correlated with CI changes after FC (r=-0.104, P=0.361). Similarly, the NT-proBNP baseline values could not identify responders to FC with an AUC of 0.508 (95% confidence interval, 0.369-0.647). This result was further confirmed in the subgroup analyses. Baseline NT-proBNP concentration value may not serve as an indicator of fluid responsiveness in patients with septic shock and should not be an indicator to withhold fluid loading.

Diastolic Function and Peripheral Venous Pressure as Indices for Fluid Responsiveness in Cardiac Surgical Patients

Identifying fluid responsiveness is critical to optimizing perfusion while preventing fluid overload. An experimental study of hypovolemic shock resuscitation showed the importance of ventricular compliance and peripheral venous pressure (PVP) on fluid responsiveness. The authors tested the hypothesis that reduced ventricular compliance measured using transesophageal echocardiography results in decreased fluid responsiveness after a fluid bolus. Prospective observational study. Two-center, university hospital study. The study comprised 29 patients undergoing elective coronary revascularization. Albumin 5%, 7 mL/kg, was infused over 10 minutes to characterize fluid responders (>15% increase in stroke volume) from nonresponders. Invasive hemodynamics and the ratio of mitral inflow velocity (E-wave)/annular relaxation (e'), or E/e' ratio, were measured using transesophageal echocardiography to assess left ventricular (LV) compliance at baseline and after albumin infusion. Fifteen patients were classified as responders and 14 as nonresponders. The E/e' ratio in responders was 7.4 ± 1.9 at baseline and 7.1 ± 1.8 after bolus. In contrast, E/e' was significantly higher in nonresponders at baseline (10.7 ± 4.6; p = 0.04) and further increased after bolus (12.6 ± 5.5; p = 0.002). PVP was significantly greater in the nonresponders at baseline (14 ± 4 mmHg v 11 ± 3 mmHg; p = 0.02) and increased in both groups after albumin infusion. Fluid responsiveness was tested using the area under the receiver operating characteristic curve and was 0.74 for the E/e' ratio (95% confidence interval 0.55-0.93; p = 0.029) and 0.72 for the PVP (95% confidence interval 0.52-0.92; p = 0.058). Fluid responders had normal LV compliance and lower PVP at baseline. In contrast, nonresponders had reduced LV compliance, which worsened after fluid bolus. E/e,' more than PVP, may be a useful clinical index to predict fluid responsiveness.

Internal jugular vein variability predicts fluid responsiveness in cardiac surgical patients with mechanical ventilation

BackgroundTo evaluate the efficacy of using internal jugular vein variability (IJVV) as an index of fluid responsiveness in mechanically ventilated patients after cardiac surgery.MethodsSeventy patients were assessed after cardiac surgery. Hemodynamic data coupled with ultrasound evaluation of IJVV and inferior vena cava variability (IVCV) were collected and calculated at baseline, after a passive leg raising (PLR) test and after a 500-ml fluid challenge. Patients were divided into volume responders (increase in stroke volume ≥ 15%) and non-responders (increase in stroke volume < 15%). We compared the differences in measured variables between responders and non-responders and tested the ability of the indices to predict fluid responsiveness.ResultsThirty-five (50%) patients were fluid responders. Responders presented higher IJVV, IVCV and stroke volume variation (SVV) compared with non-responders at baseline (P < 0.05). The relationship between IJVV and SVV was moderately correlated (r = 0.51, P < 0.01). The areas under the receiver operating characteristic (ROC) curves for predicting fluid responsiveness were 0.88 (CI 0.78–0.94) for IJVV compared with 0.83 (CI 0.72–0.91), 0.97 (CI 0.89–0.99), 0.91 (CI 0.82–0.97) for IVCV, SVV, and the increase in stroke volume in response to a PLR test, respectively.ConclusionsUltrasound-derived IJVV is an accurate, easily acquired noninvasive parameter of fluid responsiveness in mechanically ventilated postoperative cardiac surgery patients, with a performance similar to that of IVCV.

Early goal directed therapy: where do we stand after the individual patient’s meta-analysis?

In the recent years, the issue of early goal directed therapy (EGDT) has led to many debate. EGDT became popular after the Rivers’ trial (1). In that single center trial including 263 patients with septic shock, EGDT application in the emergency department (ED) resulted in an important decrease in 28-day mortality from 46.5% to 30.5% (P<0.01). Even though the main difference in hemodynamic goal was the target of central venous oxygen saturation (ScvO2) that has to be maintained above 70%, the entire package, including maintenance of mean arterial pressure (MAP) ≥65 mmHg, central venous pressure (CVP) between 8-12 mmHg and urine output ≥0.5 mL/kg.h, was adopted in resuscitation guidelines (2). The trial was heavily criticized. Many of the criticisms were directed to the targets, and especially CVP as CVP is not an excellent indicator of fluid responsiveness, as well as to some of the interventions used to increase ScvO2 and in particular to the frequent use of red blood cell transfusions. Also the incidence of low ScvO2 at baseline was higher than in subsequent observational trials. All these factors raised the issue of the external validity of the trial.

Respiratory Variation in Femoral Vein Diameter Has Moderate Accuracy as a Marker of Fluid Responsivity in Mechanically Ventilated Septic Shock Patients

Ultrasound (US) is considered the first step in evaluation of patients with shock; respiratory variation of the inferior vena cava (inferior vena cava collapsibility [IVCc]) is an important measurement in this scenario that can be impaired by patient condition or technical skills. The main objective of this study was to evaluate if respiratory variation of the femoral vein (femoral vein collapsibility [FVc]), which is easier to visualize, can adequately predict fluid responsiveness in septic shock patients. Forty-five mechanically ventilated septic shock patients in a mixed clinical–surgical, 30-bed intensive care unit were enrolled in this study. All patients underwent assessments of FVc, IVCc and cardiac output using a portable US device. The passive leg raising test was used to evaluate fluid responsiveness. FVc presented an area under the receiver operating characteristic curve of 0.678 (95% confidence interval: 0.519–0.837, p = 0.044) with a cutoff point of 17%, yielding a sensitivity of 62% and specificity of 65% in predicting fluid responsiveness. IVCc had greater diagnostic accuracy compared with FVc, with an area under the receiver operating characteristic curve of 0.733 (95% confidence interval: 0.563–0.903, p = 0.024) and a cutoff point of 29%, yielding a sensitivity of 47% and specificity of 86%. In conclusion, FVc has moderate accuracy when employed as an indicator of fluid responsiveness in spontaneously mechanically ventilated septic shock patients.

Measurement of brachial artery velocity variation and inferior vena cava variability to estimate fluid responsiveness

To investigate the accuracy and feasibility of brachial artery peak velocity variation (ΔVpeakbrach) and inferior vena cava variability (VIVC) as indicators of fluid responsiveness in critically ill patients. A single-center prospective observation was conducted. The patients on mechanical ventilation with spontaneously breathing admitted to Department of Critical Care Medicine of the Second Affiliated Hospital of Kunming Medical University from June 2013 to August 2015 were enrolled. The patients were diagnosed as severe sepsis or sepsis shock. The peak velocity in brachial artery and diameter of the inferior vena cava at the end of inspiration and expiration was measured by bedside portable ultrasonic machine, and then ΔVpeakbrach and VIVC were calculated. The hemodynamic parameters were collected at baseline and after volume expansion (VE). The stroke volume (SV) was measured by pulse-indicated continuous cardiac output (PiCCO). Patients were classified as responders or non-responders according to the variation of SV (ΔSV) increased ≥ 15% or not after VE. Receiver operating characteristic curve (ROC) was plotted to evaluate the sensitivity and specificity of ΔVpeakbrach and VIVC in predicting volume responsiveness. Among 58 patients after VE, 32 patients were defined as responders and the rest 26 were defined as non-responders.There were no differences in gender, age, acute physiology and chronic health evaluation II (APACHE II) score, dose of vasoactive agent, ventilator parameters and infection site. Compared with baseline hemodynamic parameters, heart rate (HR) was decreased (bpm: 95±18 vs. 103±21), and systolic blood pressure (SBP) was increased [mmHg (1 mmHg = 0.133 kPa): 92±8 vs. 80±7] after VE in responders; central venous pressure (CVP) was increased after VE in non-responders (mmHg: 11±4 vs. 8±3, all P < 0.05). The ΔVpeakbrach [(15.4±4.3)% vs. (11.2±3.5)%] and VIVC [(18.6±4.1)% vs. (14.3±3.6)%] in responders were significantly increased as compared with those of non-responders (both P < 0.05). The area under ROC curve (AUC) of ΔVpeakbrach for predicting volume responsiveness was 0.816. When the cut-off value of ΔVpeakbrach was ≥ 13.3%, the sensitivity was 71.9%, and the specificity was 80.8%. AUC of VIVC for predicting volume responsiveness was 0.733. When the cut-off value of VIVC was ≥ 19.25%, the sensitivity was 53.1%, and the specificity was 88.5%. ΔVpeakbrach and VIVC are reliable indicators for predicting volume responsiveness in critical patients.

Is internal jugular vein extensibility associated with indices of fluid responsiveness in ventilated patients?

Ultrasound of the inferior vena cava provides rapid and non-invasive assessment of fluid responsiveness. We hypothesized that the extensibility of the internal jugular vein (IJV) as well reflects intravascular volume state. We assessed IJV dimensions together with pulse pressure variation (PPV) as dynamic index for fluid responsiveness in mechanically ventilated patients. Of 50 patients after cardiac surgery were assessed. Ultrasound of IJV dimensions as well as collection of hemodynamic data were performed in 30° and horizontal (0°) position, and the ventilator- and position-induced IJV extensibilities (E-IJV) were calculated. Mean ventilator-induced E-IJV in 30° position was 56%, and mean PPV in 30° position was 13.7%. Changing the patient's position from 30° to 0° significantly reduced ventilator-induced E-IJV as well as PPV. Pearson's correlation test revealed significant association between ventilator-induced E-IJV and fluid responsiveness deduced from PPV in 0° position (r = 0.43, P < 0.005). An E-IJV threshold >5% identified patients with significantly elevated PPV values. Ultrasound of the IJV and PPV as a dynamic index for fluid responsiveness can be associated under certain defined conditions. Whether or not ultrasound of the IJV can be useful to predict patient intravascular volume state should be further studied using invasive cardiac output monitoring.

Passive leg raising: five rules, not a drop of fluid!

Passive leg raising: five rules, not a drop of fluid!

Passive leg raising and compression stockings: a note of caution

In a recent editorial in Critical Care, Monnet and Teboul emphasize the value of passive leg raising (PLR) as a reliable bedside indicator of fluid responsiveness in critically ill patients [1]. This is because PLR induces changes in venous return, regardless of the mode of ventilation or the underlying cardiac arrhythmias. In their eloquently written editorial, they provide five practical rules for performing a PLR maneuver. The authors state that during PLR about 300 mL of blood is auto-transfused from the lower limbs and splanchnic circulation into the central compartment, resulting in an increased cardiac output. This maneuver has been validated in cohorts of patients with either hypovolaemic or septic shock [2, 3]. It is a prerequisite of the test that the volume of blood that is auto-transfused be sufficient to increase mean circulatory pressure which drives venous return [3]. We hypothesize that this may not be the situation in all patients and that, if there is no change in cardiac output, blood pressure, or right atrial pressure [4], an inadequate volume of blood will be returned to the right heart. This may be relevant in patients with elastic compression stockings, which are widely used to prevent venous thromboembolism in critically ill patients. The effectiveness of PLR as a measure of fluid responsiveness can be compromised by elastic compression stockings [5]. Consequently, we would recommend that elastic compression stockings be routinely removed prior to the PLR maneuver.

ROLES OF SO2 INDEX FOR PREDICTING OF FLUID RESPONSIVENESS IN HIGH RISK CARDIAC SURGICAL PATIENTS

Purpose: (1) Study the change in SO2 value in fluid therapy in patients after cardiac surgery; (2) Evaluate the role of SO2 monitoring in serving as an indicator of fluid responsiveness in patients after cardiac surgery. Methods: This was a prospective study reported earlier on critically ill patients with clinical hypovolemia after cardiac surgery. Fluid therapy was guided by changes in pulmonary artery wedge pressure or central venous pressure. Fluid responsiveness was defined as ≥15% increase in cardiac index. Hemodynamics, including left ventricular ejection fraction, cardiac index, and oxygen delivery were measured when SO2 blood samples taken. Results: There was 110 patients receiving fluid therapy in postoperative period. The SO2 increased in 104 patients responding to fluid loading (≥15% in cardiac index in n=107) versus those not responding (n=6). The increase in ejection fraction, cardiac index and oxygen delivery was also greater in responders (p=0.005). The area under the receiver operating characteristic curve for fluid responsiveness of changes in SO2 was 0.78 (p=0.05), with an optimal cutoff of 2%. The value of SO2 increased to reflect cardiac index increases with fluid loading was in 66.7% of patients. Conclusions: An increase in SO2 ≥ 2% can thus be used as an indicator of fluid responsiveness in clinically hypovolemic patients after cardiac surgery, particularly in those with systolic cardiac dysfunction. Fluid responsiveness concurs with increased tissue oxygen delivery. Key words: mixed venous oxygen saturation (SO2); oxygen delivery (DO2); oxygen consumption (VO2); central venous pressure (CVP), pulmonary artery wedge pressure (PAWP); cardiac index (CI); hypovolemia; fluid therapy.

Central venous pressure in combination with visual left ventricular ejection fraction as an indicator of fluid responsiveness in patients with septic shock

Objective To investigate the value of central venous pressure(CVP) combined with visual left ventricular ejection fraction(LVEF)as an indicator of fluid responsiveness in patients with septic shock. Methods A retrospective analysis of 83 patients with septic shock receiving fluid challenge was conducted. The hemodynamic changes were evaluated with the pulse indicator continuous cardiac output (PiCCO) monitor, and all the patients were divided into two groups: the responded group(△CI% ≥ 15%)and the unresponded group(△CI < 15%), according to the change in CI(△CI%). Those patients were divided into several subgroups, including low CVP group(CVP < 8 mmHg) and high CVP group(CVP ≥ 8 mmHg), low LVEF group(LVEF < 50%) and high LVEF group(LVEF ≥ 50%), according to the initial value of CVP and LVEF. The changes in hemodynamic variables were compared before and after fluid challenge in each subgroup. The ability of CVP and visual LVEF was evaluated to predict fluid responsiveness with receiver operating characteristic curves. Results Fifty three (63.9%)patients responded to the fluid challenge, and lower CVP and higher LVEF patients were more frequency in responded group. The threshold value of 8 mmHg CVP for prediction of fluid responsiveness revealed the area under the curve (AUC) of 0.646(P=0.219), and 50% visual LVEF revealed AUC of 0.729(P=0.023). CVP in combination with visual LVEF for prediction of fluid responsiveness showed an AUC of 0.817 (P=0.001) with a sensitivity of 76.3% and a specificity of 88.2%. Conclusions Visual LVEF alone and combined with CVP can be used as an indicator of fluid responsiveness in patients with septic shock. Key words: Central venous pressure; Heart ventricles/US; Ventricular function, left; Stroke volume; Shock/DI/PP; Hemodynamics

Does Inferior Vena Cava variability predict fluid responsiveness in critically ill patients with atrial fibrillation

To assess the reliability of the variability of the inferior vena cava diameter as an indicator of fluid responsiveness in critically ill patients with atrial fibrillation. Adult critically ill patients with atrial fibrillation requiring mechanical ventilation were enrolled. The variability of the inferior vena cava diameter (V(IVC)) was measured during a breath and then calculated as the maximum diameter (Dmax) minus minimum diameter (Dmin) divided by Dmin. All the hemodynamic parameters were collected at baseline and after a manoeuvre of passive leg raising (PLR). A 15% of VTI increase after the PLR was the criterion to identify the patients with or without fluid responsiveness. ROC curve was used to assess the sensitivity and specificity of V(IVC) as an indicator of fluid responsiveness for critically ill patients with atrial fibrillation. There were 34 patients enrolled in our study, with 14 of them responsed to PLR and the rest 20 did not. For patients with fluid responsiveness V(IVC) was significantly higher than patients without fluid responsiveness. The sensitivity and specificity of V(IVC) ≥ 16% to predict fluid responsiveness in patients with atrial fibrillation were 57.1% and 89.9% respectively. V(IVC) proved to be a reliable predictor of fluid responsiveness in critical ill patients with atrial fibrillation.

Model-Based Stressed Blood Volume is an Index of Fluid Responsiveness

Fluid therapy is frequently used to manage acute circulatory failure. This therapy aims to restore cardiac output by fluid administration, which increases the quantity of fluid in the circulation. However, it has been shown to be effective only in certain cases, leading to the need for indices of fluid responsiveness. Total stressed blood volume has recently been shown to be such an index of fluid responsiveness. However, the current methods to determine this parameter require specific procedures. In this work, a more straightforward method is developed using data available in the intensive care unit. A simple three-chamber cardiovascular system model is used, of which total stressed blood volume is a parameter. All model parameters (including total stressed blood volume) are adjusted to pig experimental data during fluid administrations. The resulting value of total stressed blood volume is always negatively associated with the relative change in cardiac output after fluid administration. This finding confirms that total stressed blood volume is an index of fluid responsiveness. Another finding of this study is that the response curves are subject-specific. The method developed in this work can be applied to humans, since the data required is typically available in an intensive care unit.