Right Atrial Pressure

Do ScvO2 variations induced by passive leg raising predict fluid responsiveness? A prospective study

OBJECTIVE

The present study investigates whether ScvO2 variations induced by passive leg raising (PLR) are able to predict fluid responsiveness (FR) in mechanically ventilated patients.

DESIGN

A monocentric prospective clinical study.

SETTING

An intensive care division in a tertiary hospital.

PATIENTS

The inclusion criteria were elective postoperative cardiac surgery patients who were over 18 years old, deeply sedated, mechanically ventilated and needed volume expansion (VE). Fluid responders (R) were defined as patients who increased their left ventricular outflow tract velocity time integral (VTI) ≥15% after VE.

INTERVENTION

In patients included in this study, continuous ScvO2  monitoring (CeVOX device, Pulsion Medical Systems) and VTI (transthoracic echocardiography) were measured simultaneously before and during a PLR test and before and after VE (with 500 ml of saline).

MEASUREMENTS AND MAIN RESULTS

Thirty-three consecutive patients were included in this study. In 15 patients with a positive PLR test (increase in VTI ≥15%), ScvO2 increased during PLR by 9 ± 4%. In the 18 patients with a negative PLR test, ScvO2 did not significantly change during PLR. VE increased ScvO2 by 9 ± 6% and 2 ± 4% in responders and nonresponders, respectively. If ScvO2 increased by >4% during the PLR test, then a positive VTI response (≥15%) was diagnosed with a sensitivity of 93% (68-99%) and a specificity of 94% (63-99%) (Area under the receiver operating characteristic curve 0.92 ± 0.58, p < 0.05). Moreover, ScvO2 variations were able to distinguish responders to VE from nonresponders to VE with a sensitivity of 87% (68-99%) and a specificity of 89% (63-99%) (Area under the receiver operating characteristic curve 0.89 ± 0.07, p < 0.05).

CONCLUSIONS

ScvO2 variation induced by PLR is a reliable, minimally invasive parameter for predicting FR at the postoperative cardiac surgery bedside of mechanically ventilated, critically ill patients.

Can VA-ECMO Be Used as an Adequate Treatment in Massive Pulmonary Embolism?

Introduction: Massive acute pulmonary embolism (MAPE) with obstructive cardiogenic shock is associated with a mortality rate of more than 50%. Venoarterial extracorporeal membrane oxygenation (VA-ECMO) has been increasingly used in refractory cardiogenic shock with very good results. In MAPE, although it is currently recommended as part of initial resuscitation, it is not yet considered a stand-alone therapy. Material and Methods: All patients with MAPE requiring the establishment of VA-ECMO and admitted to our tertiary intensive care unit were analysed over a period of 10 years. The characteristics of these patients, before, during and after ECMO were extracted and analysed. Results: A total of 36 patients were included in the present retrospective study. Overall survival was 64%. In the majority of cases, the haemodynamic and respiratory status of the patient improved significantly within the first 24 h on ECMO. The 30-day survival significantly increased when ECMO was used as stand-alone therapy (odds ratio (OR) 15.58, 95% confidence interval (CI) 2.65–91.57, p = 0.002). Nevertheless, when ECMO was implanted following the failure of thrombolysis, the bleeding complications were major (17 (100%) vs. 1 (5.3%) patients, p < 0.001) and the 30-day mortality increased significantly (OR 0.11, 95% CI 0.022–0.520, p = 0.006). Conclusions: The present retrospective study is certainly one of the most important in terms of the number of patients with MAPE and shock treated with VA-ECMO. This short-term mechanical circulatory support, used as a stand-alone therapy in MAPE, allows for the optimal stabilisation of patients.

Journal of clinical monitoring and computing end of year summary 2018: hemodynamic monitoring and management

Hemodynamic management is a mainstay of patient care in the operating room and intensive care unit (ICU). In order to optimize patient treatment, researchers investigate monitoring technologies, cardiovascular (patho-) physiology, and hemodynamic treatment strategies. The Journal of Clinical Monitoring and Computing (JCMC) is a well-established and recognized platform for publishing research in this field. In this review, we highlight recent advancements and summarize selected papers published in the JCMC in 2018 related to hemodynamic monitoring and management.

Cardiovascular Autonomic Response to Orthostatic Stress Under Hypoxia in Patients with Spinal Cord Injury

Huang, Shu-Chun, Kuo-Cheng Liu, Alice M.K. Wong, Shih-Chieh Chang, and Jong-Shyan Wang. Cardiovascular autonomic response to orthostatic stress under hypoxia in patients with spinal cord injury. High Alt Med Biol. 19:201-207, 2018.

AIMS

Determining whether systemic hypoxia aggravates the severity of autonomic cardiovascular dysfunction in orthostatic stress among patients with spinal cord injuries (SCIs).

METHODS

Twenty-four male patients with chronic SCI whose neurological levels were above T6 were recruited. Twenty-five healthy men were enrolled in the control group. Five-minute supine rest (SR) and head-up tilt (HUT) at 60° were performed in normoxia and after 1 hour, 13.5% fraction of inspired O₂ exposure. A noninvasive cardiac output (CO) monitor was used to measure stroke volume (SV), CO, total peripheral resistance (TPR), and blood pressure (BP), whereas heart rate variability (HRV) was performed to determine cardiac autonomic activity. Digital volume pulse analysis was applied to measure arteriolar tone.

RESULTS

In normoxia from SR to HUT, systolic and diastolic BPs declined, SV decreased, and heart rate increased, whereas CO and TPR showed a declining trend in the SCI group. Sympathetic activation and vagal withdrawal were also disclosed in the HRV analysis. In hypoxia, the change of these cardiovascular responses from SR to HUT exhibited no difference to normoxia in the SCI group. No significant difference in arterial desaturation was observed between the two groups (82.9% vs. 80.4%).

CONCLUSIONS

Cardiovascular adaptation to orthostatic stress is not affected by subacute steady-state hypoxia in chronic SCI patients with neurological levels higher than T6.

Journal of Clinical Monitoring and Computing 2017 end of year summary: cardiovascular and hemodynamic monitoring

Hemodynamic monitoring provides the basis for the optimization of cardiovascular dynamics in intensive care medicine and anesthesiology. The Journal of Clinical Monitoring and Computing (JCMC) is an ideal platform to publish research related to hemodynamic monitoring technologies, cardiovascular (patho)physiology, and hemodynamic treatment strategies. In this review, we discuss selected papers published on cardiovascular and hemodynamic monitoring in the JCMC in 2017.

Effects of cardiac output on the initial distribution volume of glucose in the absence of fluid gain or loss in pigs

The initial distribution volume of glucose (IDVG) has been reported to be a surrogate marker of cardiac preload. However, the relationship between cardiac output and IDVG is not fully understood. We investigated the effects of cardiac output on IDVG in the absence of fluid gain or loss in pigs.

MATERIALS AND METHODS

Thirteen pigs were anesthetized and allocated to either the modified cardiac output group (m-CO group, n = 10) or the control group (control group, n = 3). In the m-CO group, CO was sequentially modulated from high CO (high CO) to two grades of low CO (low CO-1 and low CO-2) with dobutamine and propranolol with lidocaine, respectively, in the absence of any apparent change in basal fluid volume status. Thermodilutional CO and IDVG were measured at each CO condition. The IDVG was measured according to a one-compartment model with 2 g glucose. The same parameters were measured in the control group using the same time schedule as for the m-CO group but without inotropes and at a stable CO state. Thereafter, 250 ml of 10% dextran were infused over 15 min to compare the effects of a preload-dependent increase in CO on IDVG measurements to the effects of the pharmacological modification of CO. Data were expressed as the mean ± SD. Statistical analysis was performed with repeated measures ANOVA followed by Dunnett's test. Pearson's correlation test was also used. A P value of <0.05 was considered to indicate statistical significance.

RESULTS

In the m-CO group, where CO increased to 147.2 ± 26.7% of the baseline CO value in the high CO state and decreased to 65.9 ± 11.0 and 37.3 ± 14.4% of the baseline CO value in the low CO-1 state and the low CO-2 state, respectively, the IDVG did not change as CO was modified. IDVG significantly increased in response to volume loading of dextran in the control group. There was no correlation between the IDVG and CO in the m-CO group when there was no fluid gain or loss (r = 0.097, n = 40, P = 0.554), but the IDVG was well correlated with CO in the control group with volume loading (r = 0.764, n = 18, P = 0.0002).

CONCLUSION

This study suggests that the IDVG is dependent on the central extracellular fluid volume and not on cardiac output.

Surviving Sepsis Campaign: international guidelines for management of severe sepsis and septic shock, 2012

OBJECTIVE

To provide an update to the "Surviving Sepsis Campaign Guidelines for Management of Severe Sepsis and Septic Shock," last published in 2008.

DESIGN

A consensus committee of 68 international experts representing 30 international organizations was convened. Nominal groups were assembled at key international meetings (for those committee members attending the conference). A formal conflict of interest policy was developed at the onset of the process and enforced throughout. The entire guidelines process was conducted independent of any industry funding. A stand-alone meeting was held for all subgroup heads, co- and vice-chairs, and selected individuals. Teleconferences and electronic-based discussion among subgroups and among the entire committee served as an integral part of the development.

METHODS

The authors were advised to follow the principles of the Grading of Recommendations Assessment, Development and Evaluation (GRADE) system to guide assessment of quality of evidence from high (A) to very low (D) and to determine the strength of recommendations as strong (1) or weak (2). The potential drawbacks of making strong recommendations in the presence of low-quality evidence were emphasized. Recommendations were classified into three groups: (1) those directly targeting severe sepsis; (2) those targeting general care of the critically ill patient and considered high priority in severe sepsis; and (3) pediatric considerations.

RESULTS

Key recommendations and suggestions, listed by category, include: early quantitative resuscitation of the septic patient during the first 6 h after recognition (1C); blood cultures before antibiotic therapy (1C); imaging studies performed promptly to confirm a potential source of infection (UG); administration of broad-spectrum antimicrobials therapy within 1 h of the recognition of septic shock (1B) and severe sepsis without septic shock (1C) as the goal of therapy; reassessment of antimicrobial therapy daily for de-escalation, when appropriate (1B); infection source control with attention to the balance of risks and benefits of the chosen method within 12 h of diagnosis (1C); initial fluid resuscitation with crystalloid (1B) and consideration of the addition of albumin in patients who continue to require substantial amounts of crystalloid to maintain adequate mean arterial pressure (2C) and the avoidance of hetastarch formulations (1B); initial fluid challenge in patients with sepsis-induced tissue hypoperfusion and suspicion of hypovolemia to achieve a minimum of 30 mL/kg of crystalloids (more rapid administration and greater amounts of fluid may be needed in some patients (1C); fluid challenge technique continued as long as hemodynamic improvement is based on either dynamic or static variables (UG); norepinephrine as the first-choice vasopressor to maintain mean arterial pressure ≥65 mmHg (1B); epinephrine when an additional agent is needed to maintain adequate blood pressure (2B); vasopressin (0.03 U/min) can be added to norepinephrine to either raise mean arterial pressure to target or to decrease norepinephrine dose but should not be used as the initial vasopressor (UG); dopamine is not recommended except in highly selected circumstances (2C); dobutamine infusion administered or added to vasopressor in the presence of (a) myocardial dysfunction as suggested by elevated cardiac filling pressures and low cardiac output, or (b) ongoing signs of hypoperfusion despite achieving adequate intravascular volume and adequate mean arterial pressure (1C); avoiding use of intravenous hydrocortisone in adult septic shock patients if adequate fluid resuscitation and vasopressor therapy are able to restore hemodynamic stability (2C); hemoglobin target of 7-9 g/dL in the absence of tissue hypoperfusion, ischemic coronary artery disease, or acute hemorrhage (1B); low tidal volume (1A) and limitation of inspiratory plateau pressure (1B) for acute respiratory distress syndrome (ARDS); application of at least a minimal amount of positive end-expiratory pressure (PEEP) in ARDS (1B); higher rather than lower level of PEEP for patients with sepsis-induced moderate or severe ARDS (2C); recruitment maneuvers in sepsis patients with severe refractory hypoxemia due to ARDS (2C); prone positioning in sepsis-induced ARDS patients with a PaO (2)/FiO (2) ratio of ≤100 mm Hg in facilities that have experience with such practices (2C); head-of-bed elevation in mechanically ventilated patients unless contraindicated (1B); a conservative fluid strategy for patients with established ARDS who do not have evidence of tissue hypoperfusion (1C); protocols for weaning and sedation (1A); minimizing use of either intermittent bolus sedation or continuous infusion sedation targeting specific titration endpoints (1B); avoidance of neuromuscular blockers if possible in the septic patient without ARDS (1C); a short course of neuromuscular blocker (no longer than 48 h) for patients with early ARDS and a PaO (2)/FI O (2) <150 mm Hg (2C); a protocolized approach to blood glucose management commencing insulin dosing when two consecutive blood glucose levels are >180 mg/dL, targeting an upper blood glucose ≤180 mg/dL (1A); equivalency of continuous veno-venous hemofiltration or intermittent hemodialysis (2B); prophylaxis for deep vein thrombosis (1B); use of stress ulcer prophylaxis to prevent upper gastrointestinal bleeding in patients with bleeding risk factors (1B); oral or enteral (if necessary) feedings, as tolerated, rather than either complete fasting or provision of only intravenous glucose within the first 48 h after a diagnosis of severe sepsis/septic shock (2C); and addressing goals of care, including treatment plans and end-of-life planning (as appropriate) (1B), as early as feasible, but within 72 h of intensive care unit admission (2C). Recommendations specific to pediatric severe sepsis include: therapy with face mask oxygen, high flow nasal cannula oxygen, or nasopharyngeal continuous PEEP in the presence of respiratory distress and hypoxemia (2C), use of physical examination therapeutic endpoints such as capillary refill (2C); for septic shock associated with hypovolemia, the use of crystalloids or albumin to deliver a bolus of 20 mL/kg of crystalloids (or albumin equivalent) over 5-10 min (2C); more common use of inotropes and vasodilators for low cardiac output septic shock associated with elevated systemic vascular resistance (2C); and use of hydrocortisone only in children with suspected or proven "absolute"' adrenal insufficiency (2C).

CONCLUSIONS

Strong agreement existed among a large cohort of international experts regarding many level 1 recommendations for the best care of patients with severe sepsis. Although a significant number of aspects of care have relatively weak support, evidence-based recommendations regarding the acute management of sepsis and septic shock are the foundation of improved outcomes for this important group of critically ill patients.

Demonstration of inferior vena cava compression by probe pressure during subxiphoid echocardiography

We sought to compare the inferior vena cava diameter measured by transthoracic echocardiography and by transesophageal echocardiography in human and animals. Transthoracic echocardiography yielded lower inferior vena cava diameter values than transesophageal echocardiography. Adult and pediatric intensivists should pay attention to the risk of false measurement of the inferior vena cava anterior-posterior diameter that may be due to compression of the inferior vena cava by the sonographic probe when the subxiphoid view is used.

[Microcirculatory alterations in critically ill patients: pathophysiology, monitoring and treatments]

Microcirculation represents a complex system devoted to provide optimal tissue substrates and oxygen. Therefore, pathophysiological and technological knowledge developments tailored for capillary circulation analysis should generate major advances for critically ill patients' management. In the future, microcirculatory monitoring in several critical care situations will allow recognition of macro-microcirculatory decoupling, and, hopefully, it will promote the use of treatments aimed at preserving tissue oxygenation and substrate delivery.

Adverse hemodynamic effects of lateral rotation during mechanical ventilation

Turning critically ill, mechanically ventilated patients every 2 hours is a fundamental nursing intervention to reduce the negative impact of prolonged immobility from preventable pulmonary complications such as ventilator-associated pneumonia and atelectasis. Unfortunately, when coupled with positive pressure ventilation, the benefits of turning may come at the expense of cardiovascular function. Clinicians should closely monitor the hemodynamic response to turning mechanically ventilated patients, and if compromise is observed, the degree and duration of compromise may provide guidance to the appropriate intervention.

Surviving Sepsis Campaign: international guidelines for management of severe sepsis and septic shock: 2008

OBJECTIVE

To provide an update to the original Surviving Sepsis Campaign clinical management guidelines, "Surviving Sepsis Campaign Guidelines for Management of Severe Sepsis and Septic Shock," published in 2004.

DESIGN

Modified Delphi method with a consensus conference of 55 international experts, several subsequent meetings of subgroups and key individuals, teleconferences, and electronic-based discussion among subgroups and among the entire committee. This process was conducted independently of any industry funding.

METHODS

We used the Grades of Recommendation, Assessment, Development and Evaluation (GRADE) system to guide assessment of quality of evidence from high (A) to very low (D) and to determine the strength of recommendations. A strong recommendation (1) indicates that an intervention's desirable effects clearly outweigh its undesirable effects (risk, burden, cost) or clearly do not. Weak recommendations (2) indicate that the tradeoff between desirable and undesirable effects is less clear. The grade of strong or weak is considered of greater clinical importance than a difference in letter level of quality of evidence. In areas without complete agreement, a formal process of resolution was developed and applied. Recommendations are grouped into those directly targeting severe sepsis, recommendations targeting general care of the critically ill patient that are considered high priority in severe sepsis, and pediatric considerations.

RESULTS

Key recommendations, listed by category, include early goal-directed resuscitation of the septic patient during the first 6 hrs after recognition (1C); blood cultures before antibiotic therapy (1C); imaging studies performed promptly to confirm potential source of infection (1C); administration of broad-spectrum antibiotic therapy within 1 hr of diagnosis of septic shock (1B) and severe sepsis without septic shock (1D); reassessment of antibiotic therapy with microbiology and clinical data to narrow coverage, when appropriate (1C); a usual 7-10 days of antibiotic therapy guided by clinical response (1D); source control with attention to the balance of risks and benefits of the chosen method (1C); administration of either crystalloid or colloid fluid resuscitation (1B); fluid challenge to restore mean circulating filling pressure (1C); reduction in rate of fluid administration with rising filing pressures and no improvement in tissue perfusion (1D); vasopressor preference for norepinephrine or dopamine to maintain an initial target of mean arterial pressure > or = 65 mm Hg (1C); dobutamine inotropic therapy when cardiac output remains low despite fluid resuscitation and combined inotropic/vasopressor therapy (1C); stress-dose steroid therapy given only in septic shock after blood pressure is identified to be poorly responsive to fluid and vasopressor therapy (2C); recombinant activated protein C in patients with severe sepsis and clinical assessment of high risk for death (2B except 2C for postoperative patients). In the absence of tissue hypoperfusion, coronary artery disease, or acute hemorrhage, target a hemoglobin of 7-9 g/dL (1B); a low tidal volume (1B) and limitation of inspiratory plateau pressure strategy (1C) for acute lung injury (ALI)/acute respiratory distress syndrome (ARDS); application of at least a minimal amount of positive end-expiratory pressure in acute lung injury (1C); head of bed elevation in mechanically ventilated patients unless contraindicated (1B); avoiding routine use of pulmonary artery catheters in ALI/ARDS (1A); to decrease days of mechanical ventilation and ICU length of stay, a conservative fluid strategy for patients with established ALI/ARDS who are not in shock (1C); protocols for weaning and sedation/analgesia (1B); using either intermittent bolus sedation or continuous infusion sedation with daily interruptions or lightening (1B); avoidance of neuromuscular blockers, if at all possible (1B); institution of glycemic control (1B), targeting a blood glucose < 150 mg/dL after initial stabilization (2C); equivalency of continuous veno-veno hemofiltration or intermittent hemodialysis (2B); prophylaxis for deep vein thrombosis (1A); use of stress ulcer prophylaxis to prevent upper gastrointestinal bleeding using H2 blockers (1A) or proton pump inhibitors (1B); and consideration of limitation of support where appropriate (1D). Recommendations specific to pediatric severe sepsis include greater use of physical examination therapeutic end points (2C); dopamine as the first drug of choice for hypotension (2C); steroids only in children with suspected or proven adrenal insufficiency (2C); and a recommendation against the use of recombinant activated protein C in children (1B).

CONCLUSIONS

There was strong agreement among a large cohort of international experts regarding many level 1 recommendations for the best current care of patients with severe sepsis. Evidenced-based recommendations regarding the acute management of sepsis and septic shock are the first step toward improved outcomes for this important group of critically ill patients.

Surviving Sepsis Campaign: international guidelines for management of severe sepsis and septic shock: 2008

OBJECTIVE

To provide an update to the original Surviving Sepsis Campaign clinical management guidelines, "Surviving Sepsis Campaign guidelines for management of severe sepsis and septic shock," published in 2004.

DESIGN

Modified Delphi method with a consensus conference of 55 international experts, several subsequent meetings of subgroups and key individuals, teleconferences, and electronic-based discussion among subgroups and among the entire committee. This process was conducted independently of any industry funding.

METHODS

We used the GRADE system to guide assessment of quality of evidence from high (A) to very low (D) and to determine the strength of recommendations. A strong recommendation indicates that an intervention's desirable effects clearly outweigh its undesirable effects (risk, burden, cost), or clearly do not. Weak recommendations indicate that the tradeoff between desirable and undesirable effects is less clear. The grade of strong or weak is considered of greater clinical importance than a difference in letter level of quality of evidence. In areas without complete agreement, a formal process of resolution was developed and applied. Recommendations are grouped into those directly targeting severe sepsis, recommendations targeting general care of the critically ill patient that are considered high priority in severe sepsis, and pediatric considerations.

RESULTS

Key recommendations, listed by category, include: early goal-directed resuscitation of the septic patient during the first 6 hrs after recognition (1C); blood cultures prior to antibiotic therapy (1C); imaging studies performed promptly to confirm potential source of infection (1C); administration of broad-spectrum antibiotic therapy within 1 hr of diagnosis of septic shock (1B) and severe sepsis without septic shock (1D); reassessment of antibiotic therapy with microbiology and clinical data to narrow coverage, when appropriate (1C); a usual 7-10 days of antibiotic therapy guided by clinical response (1D); source control with attention to the balance of risks and benefits of the chosen method (1C); administration of either crystalloid or colloid fluid resuscitation (1B); fluid challenge to restore mean circulating filling pressure (1C); reduction in rate of fluid administration with rising filing pressures and no improvement in tissue perfusion (1D); vasopressor preference for norepinephrine or dopamine to maintain an initial target of mean arterial pressure > or = 65 mm Hg (1C); dobutamine inotropic therapy when cardiac output remains low despite fluid resuscitation and combined inotropic/vasopressor therapy (1C); stress-dose steroid therapy given only in septic shock after blood pressure is identified to be poorly responsive to fluid and vasopressor therapy (2C); recombinant activated protein C in patients with severe sepsis and clinical assessment of high risk for death (2B except 2C for post-operative patients). In the absence of tissue hypoperfusion, coronary artery disease, or acute hemorrhage, target a hemoglobin of 7-9 g/dL (1B); a low tidal volume (1B) and limitation of inspiratory plateau pressure strategy (1C) for acute lung injury (ALI)/acute respiratory distress syndrome (ARDS); application of at least a minimal amount of positive end-expiratory pressure in acute lung injury (1C); head of bed elevation in mechanically ventilated patients unless contraindicated (1B); avoiding routine use of pulmonary artery catheters in ALI/ARDS (1A); to decrease days of mechanical ventilation and ICU length of stay, a conservative fluid strategy for patients with established ALI/ARDS who are not in shock (1C); protocols for weaning and sedation/analgesia (1B); using either intermittent bolus sedation or continuous infusion sedation with daily interruptions or lightening (1B); avoidance of neuromuscular blockers, if at all possible (1B); institution of glycemic control (1B) targeting a blood glucose < 150 mg/dL after initial stabilization ( 2C ); equivalency of continuous veno-veno hemofiltration or intermittent hemodialysis (2B); prophylaxis for deep vein thrombosis (1A); use of stress ulcer prophylaxis to prevent upper GI bleeding using H2 blockers (1A) or proton pump inhibitors (1B); and consideration of limitation of support where appropriate (1D). Recommendations specific to pediatric severe sepsis include: greater use of physical examination therapeutic end points (2C); dopamine as the first drug of choice for hypotension (2C); steroids only in children with suspected or proven adrenal insufficiency (2C); a recommendation against the use of recombinant activated protein C in children (1B).

CONCLUSION

There was strong agreement among a large cohort of international experts regarding many level 1 recommendations for the best current care of patients with severe sepsis. Evidenced-based recommendations regarding the acute management of sepsis and septic shock are the first step toward improved outcomes for this important group of critically ill patients.

Assessing fluid responsiveness: the role of dynamic haemodynamic indices

Intravenous fluid infusion is a simple way of improving cardiac output and oxygen delivery in shock. However, the consequences of fluid overload can be serious. Direct measurement of cardiac output after fluid administration may not always be feasible and simple measures of arterial or central venous pressure are poor indicators of hypovolaemia and fluid responsiveness. Measures based on the change in these parameters with variation in preload such as occurs during the respiratory cycle are more powerful predictors of the cardiovascular response to filling as they relate to the shape of the cardiac output performance curve. In this article, we describe the origin, interpretation and limitations of such dynamic indices.