Respiratory changes in aortic blood velocity as an indicator of fluid responsiveness in ventilated patients with septic shock

Ability of pulse power, esophageal Doppler, and arterial pulse pressure to estimate rapid changes in stroke volume in humans

INTRODUCTION

Measures of arterial pulse pressure variation and left ventricular stroke volume variation induced by positive-pressure breathing vary in proportion to preload responsiveness. However, the accuracy of commercially available devices to report dynamic left ventricular stroke volume variation has never been validated.

METHODS

We compared the accuracy of measured arterial pulse pressure and estimated left ventricular stroke volume reported from two Food and Drug Administration-approved aortic flow monitoring devices, one using arterial pulse power (LiDCOplus) and the other esophageal Doppler monitor (HemoSonic). We compared estimated left ventricular stroke volume and their changes during a venous occlusion and release maneuver to a calibrated aortic flow probe placed around the aortic root on a beat-to-beat basis in seven anesthetized open-chested cardiac surgery patients.

RESULTS

Dynamic changes in arterial pulse pressure closely tracked left ventricular stroke volume changes (mean r .96). Both devices showed good agreement with steady-state apneic left ventricular stroke volume values and moderate agreement with dynamic changes in left ventricular stroke volume (esophageal Doppler monitor -1 +/- 22 mL, and pulse power -7 +/- 12 mL, bias +/- 2 sd). In general, the pulse power signals tended to underestimate left ventricular stroke volume at higher left ventricular stroke volume values.

CONCLUSION

Arterial pulse pressure, as well as, left ventricular stroke volume estimated from esophageal Doppler monitor and pulse power reflects short-term steady-state left ventricular stroke volume values and tract dynamic changes in left ventricular stroke volume moderately well in humans.

Uncalibrated pulse contour-derived stroke volume variation predicts fluid responsiveness in mechanically ventilated patients undergoing liver transplantation

BACKGROUND

Stroke volume variation (SVV) is able to predict adequately the individual response to fluid loading. Our objective was to assess whether the SVV measured by a new algorithm (Vigileo; Flotrac) can predict fluid responsiveness.

METHODS

Forty mechanically ventilated patients undergoing liver transplantation, who needed volume expansion (VE), were included. VE was done with albumin (4%) 20 mlxBMI over 20 min. SVV, pulse pressure variation (PPV), central venous pressure (CVP), and pulmonary artery occlusion pressure (PAOP) were measured immediately before and after VE. Cardiac output (CO) measured by transthoracic echocardiography (CO-TTE) was used to define responder patients if CO increased by 15% or more after VE, or non-responder otherwise. CO obtained with the pulmonary artery catheter (CO-PAC) and with Vigileo (CO-Vigileo) were also recorded.

RESULTS

Five patients were excluded. Seventeen patients were responders (Rs) and 18 were non-responders (NRs). Before VE (i) SVV and PPV were higher in Rs and (ii) CVP and PAOP were lower in Rs. Baseline SVV and PPV correlated with change in CO induced by VE (respectively, r(2)=0.72, P<0.0001; r(2)=0.84, P<0.0001). An SVV threshold of >10% discriminated Rs with a sensitivity of 94% and a specificity of 94%. After VE, the decrease in SVV was significantly correlated with the increase in CO (r(2)=0.51; P<0.0001). There was no difference between the area under the ROC curves of SVV and PPV. After VE, the change in CO-Vigileo was closely correlated with change in CO-TTE (r(2)=0.74, P<0.0001) and with change in CO-PAC (r(2)=0.77, P<0.0001).

CONCLUSIONS

The SVV obtained by the Vigileo system may be used as a predictor of fluid responsiveness in patients with circulatory failure after liver transplantation. CO-Vigileo is able to track the change in CO induced by VE.

Echocardiography practice, training and accreditation in the intensive care: document for the World Interactive Network Focused on Critical Ultrasound (WINFOCUS)

Echocardiography is increasingly used in the management of the critically ill patient as a non-invasive diagnostic and monitoring tool. Whilst in few countries specialized national training schemes for intensive care unit (ICU) echocardiography have been developed, specific guidelines for ICU physicians wishing to incorporate echocardiography into their clinical practice are lacking. Further, existing echocardiography accreditation does not reflect the requirements of the ICU practitioner. The WINFOCUS (World Interactive Network Focused On Critical UltraSound) ECHO-ICU Group drew up a document aimed at providing guidance to individual physicians, trainers and the relevant societies of the requirements for the development of skills in echocardiography in the ICU setting. The document is based on recommendations published by the Royal College of Radiologists, British Society of Echocardiography, European Association of Echocardiography and American Society of Echocardiography, together with international input from established practitioners of ICU echocardiography. The recommendations contained in this document are concerned with theoretical basis of ultrasonography, the practical aspects of building an ICU-based echocardiography service as well as the key components of standard adult TTE and TEE studies to be performed on the ICU. Specific issues regarding echocardiography in different ICU clinical scenarios are then described. Obtaining competence in ICU echocardiography may be achieved in different ways - either through completion of an appropriate fellowship/training scheme, or, where not available, via a staged approach designed to train the practitioner to a level at which they can achieve accreditation. Here, peri-resuscitation focused echocardiography represents the entry level--obtainable through established courses followed by mentored practice. Next, a competence-based modular training programme is proposed: theoretical elements delivered through blended-learning and practical elements acquired in parallel through proctored practice. These all linked with existing national/international echocardiography courses. When completed, it is anticipated that the practitioner will have performed the prerequisite number of studies, and achieved the competency to undertake accreditation (leading to Level 2 competence) via a recognized National or European examination and provide the appropriate required evidence of competency (logbook). Thus, even where appropriate fellowships are not available, with support from the relevant echocardiography bodies, training and subsequently accreditation in ICU echocardiography becomes achievable within the existing framework of current critical care and cardiological practice, and is adaptable to each countrie's needs.

Passive leg raising for predicting fluid responsiveness: importance of the postural change

OBJECTIVE

For predicting fluid responsiveness by passive leg raising (PLR), the lower limbs can be elevated at 45 degrees either from the 45 degrees semi-recumbent position (PLR(SEMIREC)) or from the supine position (PLR(SUPINE)). PLR(SUPINE) could have a lower hemodynamic impact than PLR(SEMIREC) since it should not recruit the splanchnic venous reservoir.

DESIGN

Prospective study

SETTING

A 24-bed medical intensive care unit.

PATIENTS AND PARTICIPANTS

A total of 35 patients with circulatory failure who responded to an initial PLR(SEMIREC) by an increase in cardiac index >/= 10%.

INTERVENTIONS

PLR(SEMIREC), a transfer from the semi-recumbent to the supine position and PLR(SUPINE) were performed in all patients in a random order before fluid expansion (500 mL saline).

MEASUREMENTS AND RESULTS

PLR(SEMIREC), supine transfer and PLR(SUPINE) significantly increased the pulse-contour derived cardiac index (PiCCOplus) by 22 (17-28)%, 9 (5-15)% and 10 (7-14)% (P < 0.05 vs. PLR(SEMIREC) for the latter two), respectively. These maneuvers significantly increased the right ventricular end-diastolic area (echocardiography) by 20 (14-29)%, 9 (5-16)% and 10 (5-16)% (P < 0.05 vs. PLR(SEMIREC) for the latter two) and the central venous pressure by 33 (22-50)%, 15 (10-20)% and 20 (15-29)% (P < 0.05 vs. PLR(SEMIREC) for the latter two), respectively. Volume expansion significantly increased cardiac index by 27 (21-38)% and all patients were responders to volume expansion. If an increase in cardiac index >/= 10% is considered as a positive response to PLR(SUPINE), 15 (43%) patients would have been unduly predicted as non-responders to fluid administration by PLR(SUPINE).

CONCLUSIONS

PLR(SEMIREC) induces larger increase in cardiac preload than PLR(SUPINE) and may be preferred for predicting fluid responsiveness.

Functional hemodynamic monitoring

PURPOSE OF REVIEW

To assess the recent literature on effective use of information received from hemodynamic monitoring.

RECENT FINDINGS

Dynamic hemodynamic measures are more effective in assessing cardiovascular status than static measures. In this review, we will focus on the application of hemodynamic monitoring to evaluate the effect of therapy.

SUMMARY

A systematic approach to an effective resuscitation effort can be incorporated into a protocolized cardiovascular management algorithm, which, in turn, can improve patient-centered outcomes and the cost of healthcare systems, by faster and more effective response in order to diagnose and treat hemodynamically unstable patients both inside and outside of intensive care units.

Online monitoring of pulse pressure variation to guide fluid therapy after cardiac surgery

BACKGROUND

The arterial pulse pressure variation induced by mechanical ventilation (deltaPP) has been shown to be a predictor of fluid responsiveness. Until now, deltaPP has had to be calculated offline (from a computer recording or a paper printing of the arterial pressure curve), or to be derived from specific cardiac output monitors, limiting the widespread use of this parameter. Recently, a method has been developed for the automatic calculation and real-time monitoring of deltaPP using standard bedside monitors. Whether this method is to predict reliable predictor of fluid responsiveness remains to be determined.

METHODS

We conducted a prospective clinical study in 59 mechanically ventilated patients in the postoperative period of cardiac surgery. Patients studied were considered at low risk for complications related to fluid administration (pulmonary artery occlusion pressure < 20 mm Hg, left ventricular ejection fraction > or = 40%). All patients were instrumented with an arterial line and a pulmonary artery catheter. Cardiac filling pressures and cardiac output were measured before and after intravascular fluid administration (20 mL/kg of lactated Ringer's solution over 20 min), whereas deltaPP was automatically calculated and continuously monitored.

RESULTS

Fluid administration increased cardiac output by at least 15% in 39 patients (66% = responders). Before fluid administration, responders and nonresponders were comparable with regard to right atrial and pulmonary artery occlusion pressures. In contrast, deltaPP was significantly greater in responders than in nonresponders (17% +/- 3% vs 9% +/- 2%, P < 0.001). The deltaPP cut-off value of 12% allowed identification of responders with a sensitivity of 97% and a specificity of 95%.

CONCLUSION

Automatic real-time monitoring of deltaPP is possible using a standard bedside monitor and was found to be a reliable method to predict fluid responsiveness after cardiac surgery. Additional studies are needed to determine if this technique can be used to avoid the complications of fluid administration in high-risk patients.

The ability of a novel algorithm for automatic estimation of the respiratory variations in arterial pulse pressure to monitor fluid responsiveness in the operating room

BACKGROUND

Respiratory variations in arterial pulse pressure (deltaPP(man)) are accurate predictors of fluid responsiveness in mechanically ventilated patients. However, they cannot be continuously monitored. In our study, we assessed the clinical utility of a novel algorithm for automatic estimation of deltaPP (deltaPP(auto)).

METHODS

We studied 25 patients referred for coronary artery bypass grafting. DeltaPP(auto) was continuously displayed using a method based on automatic detection algorithms, kernel smoothing, and rank-order filters. All patients were under general anesthesia, mechanical ventilation, and were also monitored with a pulmonary artery catheter. DeltaPP(man) and deltaPP(auto) were recorded simultaneously at eight steps during surgery including before and after intravascular volume expansion (500 mL hetastarch). Responders to volume expansion were defined as patients whose cardiac index increased by more than 15% after volume expansion.

RESULTS

Agreement between deltaPP(man) and deltaPP(auto) over the 200 pairs of collected data was 0.7% +/- 3.4% (mean bias +/- SD). Seventeen patients were responders to volume expansion. A threshold deltaPP(man) value of 12% allowed discrimination of responders to volume expansion with a sensitivity of 88% and a specificity of 100%. A threshold deltaPP(auto) value of 10% allowed discrimination of responders to volume expansion with a sensitivity of 82% and a specificity of 88%.

CONCLUSION

DeltaPP(auto) is strongly correlated to deltaPP(man) is an accurate predictor of fluid responsiveness, and allows continuous monitoring of deltaPP. This novel algorithm has potential clinical applications.

Ability of pleth variability index to detect hemodynamic changes induced by passive leg raising in spontaneously breathing volunteers

INTRODUCTION

Pleth Variability Index (PVI) is a new algorithm that allows continuous and automatic estimation of respiratory variations in the pulse oximeter waveform amplitude. Our aim was to test its ability to detect changes in preload induced by passive leg raising (PLR) in spontaneously breathing volunteers.

METHODS

We conducted a prospective observational study. Twenty-five spontaneously breathing volunteers were enrolled. PVI, heart rate and noninvasive arterial pressure were recorded. Cardiac output was assessed using transthoracic echocardiography. Volunteers were studied in three successive positions: baseline (semirecumbent position); after PLR of 45 degrees with the trunk lowered in the supine position; and back in the semirecubent position.

RESULTS

We observed significant changes in cardiac output and PVI during changes in body position. In particular, PVI decreased significantly from baseline to PLR (from 21.5 +/- 8.0% to 18.3 +/- 9.4%; P < 0.05) and increased significantly from PLR to the semirecumbent position (from 18.3 +/- 9.4% to 25.4 +/- 10.6 %; P < 0.05). A threshold PVI value above 19% was a weak but significant predictor of response to PLR (sensitivity 82%, specificity 57%, area under the receiver operating characteristic curve 0.734 +/- 0.101).

CONCLUSION

PVI can detect haemodynamic changes induced by PLR in spontaneously breathing volunteers. However, we found that PVI was a weak predictor of fluid responsiveness in this setting.

Fluid therapy in resuscitated sepsis: less is more

Fluid infusion may be lifesaving in patients with severe sepsis, especially in the earliest phases of treatment. Following initial resuscitation, however, fluid boluses often fail to augment perfusion and may be harmful. In this review, we seek to compare and contrast the impact of fluids in early and later sepsis; show that much fluid therapy is clinically ineffective in patients with severe sepsis; explore the detrimental aspects of excessive volume infusion; examine how clinicians assess the intravascular volume state; appraise the potential for dynamic indexes to predict fluid responsiveness; and recommend a clinical approach.

Hemodynamic evaluation and monitoring in the ICU

Hemodynamic monitoring, a cornerstone in the management of the critically ill patient, is used to identify cardiovascular insufficiency, its probable cause, and response to therapy. Still it is difficult to document the efficacy of monitoring because no device improves outcome unless coupled to a treatment that improves outcome. Several clinical trials have consistently documented that preoptimization for high-risk surgery patients treated in the operating room and early (< 12 h) goal-directed resuscitation in septic patients treated in the emergency department reduce morbidity, mortality, and resource use (costs) when the end points of resuscitation were focused on surrogate measures of adequacy of global oxygen delivery (Do2). The closer the resuscitation is to the insult, the greater the benefit. When resuscitation was started after ICU admission in high-risk surgical patients, reduced length of stay was also seen. The focus of these monitoring protocols is to establish a mean arterial pressure > 65 mm Hg and then to increase Do2 to 600 mL/min/m2 within the first few minutes to hours of presentation. To accomplish these goals, hemodynamic monitoring focuses more on measures of cardiac output and mixed venous oxygen saturation to access adequacy of resuscitation efforts than on filling pressures. Although these protocols reduce mortality and morbidity is selected high-risk patient groups, the widespread use of monitoring-driven treatment protocols has not yet happened, presumably because all studies have been single-center trials using a single, proprietary blood flow-monitoring device. Multicenter trials are needed of early goal-directed therapies for all patients presenting in shock of various etiologies and when the protocol and not the monitoring device is the primary variable.

Respiratory variations in aortic blood flow predict fluid responsiveness in ventilated children

OBJECTIVE

To investigate whether respiratory variations in aortic blood flow velocity (DeltaVpeak ao), systolic arterial pressure (DeltaPS) and pulse pressure (DeltaPP) could accurately predict fluid responsiveness in ventilated children.

DESIGN AND SETTING

Prospective study in a 18-bed pediatric intensive care unit.

PATIENTS

Twenty-six children [median age 28.5 (16-44) months] with preserved left ventricular (LV) function.

INTERVENTION

Standardized volume expansion (VE).

MEASUREMENTS AND MAIN RESULTS

Analysis of aortic blood flow by transthoracic pulsed-Doppler allowed LV stroke volume measurement and on-line DeltaVpeak ao calculation. The VE-induced increase in LV stroke volume was >15% in 18 patients (responders) and <15% in 8 (non-responders). Before VE, the DeltaVpeak ao in responders was higher than that in non-responders [19% (12.1-26.3) vs. 9% (7.3-11.8), p=0.001], whereas DeltaPP and DeltaPS did not significantly differ between groups. The prediction of fluid responsiveness was higher with DeltaVpeak ao [ROC curve area 0.85 (95% IC 0.99-1.8), p=0.001] than with DeltaPS (0.64) or DeltaPP (0.59). The best cut-off for DeltaVpeak ao was 12%, with sensitivity, specificity, and positive and negative predictive values of 81.2%, 85.7%, 93% and 66.6%, respectively. A positive linear correlation was found between baseline DeltaVpeak ao and VE-induced gain in stroke volume (rho=0.68, p=0.001).

CONCLUSIONS

While respiratory variations in aortic blood flow velocity measured by pulsed Doppler before VE accurately predict the effects of VE, DeltaPS and DeltaPP are of little value in ventilated children.

Advances in critical care for the nephrologist: hemodynamic monitoring and volume management

The monitoring of physiologic variables is an integral part of the diagnosis and management of the critically ill patient. Restoration of tissue perfusion and oxygen delivery is the ultimate goal for any state of circulatory collapse. Insight into a patient's intravascular volume status and cardiac performance, particularly in the early stages of shock, can help guide management and potentially change outcome. In the past 30 years, various bedside monitoring techniques and indices have been developed in an effort to determine and optimize a patient's cardiac performance. This article reviews the physiologic parameters that best predict intravascular volume status and volume responsiveness. We examine the controversies surrounding the pulmonary arterial catheter and describe the less invasive methods of measuring cardiac performance.

Passive leg raising

OBJECTIVE

To assess whether the passive leg raising test can help in predicting fluid responsiveness.

DESIGN

Nonsystematic review of the literature.

RESULTS

Passive leg raising has been used as an endogenous fluid challenge and tested for predicting the hemodynamic response to fluid in patients with acute circulatory failure. This is now easy to perform at the bedside using methods that allow a real time measurement of systolic blood flow. A passive leg raising induced increase in descending aortic blood flow of at least 10% or in echocardiographic subaortic flow of at least 12% has been shown to predict fluid responsiveness. Importantly, this prediction remains very valuable in patients with cardiac arrhythmias or spontaneous breathing activity.

CONCLUSIONS

Passive leg raising allows reliable prediction of fluid responsiveness even in patients with spontaneous breathing activity or arrhythmias. This test may come to be used increasingly at the bedside since it is easy to perform and effective, provided that its effects are assessed by a real-time measurement of cardiac output.

A clinician's guide to predicting fluid responsiveness in critical illness: applied physiology and research methodology

Intravenous fluid administration is often used in critical care with the goal of improving haemodynamics and consequently tissue perfusion and oxygen delivery. While inotropic and vasoactive drugs are often necessary to correct haemodynamic instability, resuscitation usually begins with fluid therapy. As fluid challenge can result in clinical deterioration, the ability to predict haemodynamic response is desirable. In this way it might be possible to avoid unnecessary volume replacement in critically ill patients. Cardiac preload is a concept that accounts for the relationship between ventricular filling and stroke volume. It has been challenging to apply this concept to clinical practice. For this reason, the study of fluid responsiveness is of increasing research and clinical interest. The clinical application of predicting fluid responsiveness requires an understanding of relevant physiological principles. Furthermore, an improved understanding of these principles should assist the clinician in appraising published data, which has been characterised by significant methodological differences. This review aims to assist the clinician by detailing the physiological principles that underlie the prediction of fluid responsiveness in the critically ill. In addition, the potential importance of methodological differences in the cutrent literature will be considered.

Cardiac morphological and functional changes during early septic shock: a transesophageal echocardiographic study

OBJECTIVE

The objective was to prospectively evaluate cardiac morphological and functional changes using transesophageal echocardiography (TEE) during early septic shock.

DESIGN

Prospective, observational study.

SETTING

Medical-surgical intensive care unit of a teaching hospital.

PATIENTS AND PARTICIPANTS

Ventilated patients with septic shock, sinus rhythm and no cardiac disease underwent TEE within 12h of admission (Day0), after stabilization of hemodynamics by fluid loading (median volume: 4.9l [lower and upper quartiles: 3.7-9.6l]) and vasopressor therapy, and after vasopressors were stopped (Dayn).

MEASUREMENTS AND RESULTS

Thirty-five patients were studied (median age: 60 years [range 44-68]; SAPS II: 53 [46-62]; SOFA score: 9 [8-11]) and 9 of them (26%) died while on vasopressors. None of the patients exhibited TEE findings of cardiac preload dependence. Between Day0 and Dayn (7 days [range 6-9]), mean left ventricular (LV) ejection fraction (EF) increased (47 +/- 20 vs. 57 +/- 14%: p < 0.05), whereas mean LV end-diastolic volume decreased (97 +/- 25 vs. 75 +/- 20ml: p < 0.0001). Out of 16 patients (46%) with LV systolic dysfunction on Day0, 12 had normal LVEF on Dayn and 4 patients fully recovered by Day28. Only 4 women had LV dilatation (range, LV end-diastolic volume: 110-148ml) on Day0, but none on Dayn. Doppler tissue imaging identified an LV diastolic dysfunction in 7 patients (20%) on Day0 (3 with normal LVEF), which resolved on Dayn.

CONCLUSIONS

This study confirms that LV systolic and diastolic dysfunctions are frequent, but LV dilatation is uncommon in fluid-loaded septic patients on vasopressors. All abnormalities regressed in survivors, regardless of their severity.

DESCRIPTORS

Shock: clinical studies (38), Cardiovascular monitoring (34).

Assessment of fluid-responsiveness parameters for off-pump coronary artery bypass surgery: a comparison among LiDCO, transesophageal echochardiography, and pulmonary artery catheter

OBJECTIVE

To verify the reliability of different markers of fluid-responsiveness during off-pump cardiac surgery (OPCAB).

DESIGN

A clinical prospective, nonblinded, nonrandomized study.

SETTING

A community hospital.

PARTICIPANTS

Nineteen patients.

INTERVENTIONS

Pulmonary artery catheter (PAC), LiDCO (LiDCO, London, UK), and transesophageal echocardiography (TEE) parameters were measured before (t0) and after (t1) a fluid challenge was performed 20 minutes after induction of anesthesia, but before sternotomy and without inotropic infusion. A Student t test and Spearman test were performed for statistical analysis.

MEASUREMENTS AND MAIN RESULTS

According to the variation of cardiac index after the fluid challenge (DeltaCI%), 2 groups of patients were identified: the responders (Re, DeltaCI% > 15%) and the nonresponders (nRe). Mean pulse pressure variation (PPV) and mean stroke volume variation (SVV) before the fluid challenge (t0) were significantly different between the 2 groups. No significant differences were shown in systolic pressure variation (SPV), left ventricular end-diastolic area, left ventricular end-diastolic volume, and peak changes of aortic flow (DeltaVAo). A statistically significant correlation was observed between DeltaCI% and PPV (R = 0.793), DeltaCI% and SVV (R = 0.809), and DeltaCI% and SPV (R = 0.766). No correlation with central venous pressure and pulmonary capillary wedge pressure was found.

CONCLUSIONS

Dynamic parameters of fluid responsiveness by LiDCO are highly sensitive for assessment of intravascular volume status during OPCAB surgery. In contrast, even if static parameters by TEE reflect changes in ventricular diastolic volume, they are poor indicators of fluid responsiveness. Surprisingly, no significant correlation between DeltaVAo (TEE) and DeltaCI% was found.

Volume responsiveness

PURPOSE OF REVIEW

In the ICU only half of the patients are volume responsive - that is, they respond to fluid administration by increasing their cardiac output. We aim to summarize the methods available for predicting volume responsiveness, focusing on recent findings in patients with spontaneous breathing activity.

RECENT FINDINGS

New information mainly comes from studies that have attempted to find accurate predictors of volume responsiveness in cases of spontaneous breathing activity when heart-lung interaction indices cannot be reliably used. Passive leg raising has emerged as a reliable test for this purpose. The hemodynamic response to this maneuver, which induces a transient increase in cardiac preload, has been shown to provide a robust prediction of volume responsiveness. Assessment of the effects of passive leg raising requires real-time measurement of cardiac output/stroke volume or their surrogates.

SUMMARY

Predicting the hemodynamic response to fluid administration in patients with acute circulatory failure is of major importance and numerous methods are now available. While the respiratory variations of stroke volume (or its surrogates) can be used in patients fully adapted to their ventilator, the passive leg-raising test has become a reliable predictive method in patients with spontaneous breathing activity.

Global end-diastolic volume as a variable of fluid responsiveness during acute changing loading conditions

OBJECTIVE

Dynamic variables of preload such as stroke volume variation (SVV) have been shown to be good predictors of fluid responsiveness. They are, however, not applicable during spontaneous breathing and cardiac arrhythmias. Volumetric variables of preload, such as global end-diastolic volume (GEDV) and left ventricular end-diastolic area (LVEDA), might be alternative variables of preload to guide fluid administration. Therefore, the present study was designed to evaluate whether GEDV and LVEDA are suitable parameters of preload and fluid responsiveness during rapidly changing loading conditions.

DESIGN

Prospective animal study.

SETTING

Animal laboratory of a university hospital.

PARTICIPANTS

Fourteen pigs.

INTERVENTIONS

The pigs were studied during changing loading conditions as follows: normovolemia, after removal of 500 mL of blood, and after retransfusion plus an additional 500 mL of 6% hydroxyethyl starch. Cardiac output (CO), stroke volume index (SVI), and GEDV were obtained by transpulmonary thermodilution. Additionally, CO, SVI, and SVV were monitored continuously by pulse-contour analysis.

MEASUREMENTS AND MAIN RESULTS

Measurements of hemodynamic variables at each experimental stage were obtained after a period of stabilization. GEDV and LVEDA but not SVV, central venous pressure, and pulmonary capillary wedge pressure accurately reflected rapid changes in preload. When analyzing the correlation of percentage change of preload variables with the percentage change of SVI after fluid resuscitation, only SVV and GEDV showed a significant correlation with fluid responsiveness.

CONCLUSIONS

In this animal model, GEDV and LVEDA were superior to SVV in accurately reflecting hemorrhage. However, GEDV and SVV but not LVEDA were suitable to predict fluid responsiveness.

Which cardiac surgical patients can benefit from placement of a pulmonary artery catheter?

The use of pulmonary artery catheters (PACs) during cardiac surgery varies considerably depending on local policy, ranging from use in 5–10% of the patient population to routine application. However, as in other clinical fields, recent years have witnessed a progressive decline in PAC use. One of the reasons for this is probably the increasing use of transoesophageal echocardiograpy, even though careful analysis of the information provided by PAC and transoesophageal echocardiograpy indicates that the two tools should be considered subsidiary rather than alternatives. The principal categories of cardiac patients who can benefit from PAC monitoring are those with present and those with possible haemodynamic instability. On this basis we can identify five groups: patients with impaired left ventricular systolic function; those with impaired right ventricular systolic function; those with left ventricular diastolic dysfunction; those with an acute ventricular septal defect; and those with a left ventricular assist device. This review highlights the specific role of PAC-derived haemodynamic data for each category.

Variations in pulse oximetry plethysmographic waveform amplitude induced by passive leg raising in spontaneously breathing volunteers

PURPOSE

Noninvasive methods that could predict preload responsiveness are lacking. Our objective was to evaluate variations in pulse oximetry plethysmographic (POP) waveform amplitude (deltaPOP) induced by passive leg raising (PLR).

METHODS

We attached a pulse oximeter to the middle finger of 25 spontaneously breathing volunteers at several time points: baseline (ie, semirecumbent position), during PLR at 60 degrees while each subject's trunk was lowered in a supine position at 1 minute, and after putting the patient back in the semirecumbent position (5-minute rest). Heart rate, noninvasive arterial pressures (mean arterial pressure and pulse pressure), maximal POP (POPmax), minimal POP (POPmin), and deltaPOP defined as [POPmax - POPmin]/[(POPmax + POPmin)/2] were recorded using a monitor.

RESULTS

Heart rate, mean arterial pressure, pulse pressure, POPmax, and POPmin values were not different at baseline, during PLR at 1 minute, and after the 5-minute rest (repeated-measures analysis of variance). The median deltaPOP significantly decreased from 16% (95% confidence interval = 11%-23%) to 11% (95% confidence interval = 8%-14%) (P < .05) and then increased to 13% (95% confidence interval = 10%-21%) after the 5-minute rest (P = nonsignificant).

CONCLUSION

Passive leg raising induces a significant decrease in deltaPOP among spontaneously breathing volunteers.

Noninvasive Hemodynamic Monitoring in the Intensive Care Unit

This article reviews the clinically available devices that have been approved for noninvasive hemodynamic monitoring in critically ill patients. In addition this article reviews some of the surrogate markers that can be used to assess adequacy of cardiac output.

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

OBJECTIVE

Peripheral arterial pulse pressure is increasingly used to assess hemodynamic status. Our aim was to test the respective influence of arterial stiffness, stroke volume, peripheral resistance, and various hemodynamic and demographic variables on peripheral pulse pressure in critically ill patients.

DESIGN

Prospective study.

SETTING

Medical intensive care unit of a university hospital.

INTERVENTIONS

None.

PATIENTS

67 sinus rhythm patients (mean age 57+/-17 years) of whom 17 received vasoactive agents.

MEASUREMENTS AND RESULTS

The stroke volume was calculated by Doppler echocardiography. Radial pressures were calibrated from systolic and diastolic brachial cuff pressures. Central aortic pressure was estimated by radial applanation tonometry. The arterial compliance was estimated from the aortic pressure curve using the area method and the arterial stiffness was calculated as 1/compliance. The influences of age, body surface area, arterial stiffness, stroke volume, peripheral resistance, and time intervals on peripheral pulse pressure were tested using univariate and multivariate analyses. The mean arterial pressure ranged from 42 to 113 mmHg. Peripheral pulse pressure (59+/-17 mmHg) was higher than aortic pulse pressure (40+/-14 mmHg, p<0.001). In patients aged >or= 60 years whose mean arterial pressure was >or= 80 mmHg, peripheral pulse pressure was related to arterial stiffness (r2=0.41) and to stroke volume (multiple r2 =0.90). A similar but weaker relationship was observed in the overall population (multiple r2=0.52).

CONCLUSIONS

In critically ill patients, and especially in aged subjects with hemodynamic stability, peripheral pulse pressure mainly reflected the combined influences of arterial stiffness and stroke volume.

Bedside echocardiography in the assessment of the critically ill

Advances in ultrasound technology continue to enhance its diagnostic applications in daily medical practice. Bedside echocardiographic examination has become useful to properly trained cardiologists, anesthesiologists, intensivists, surgeons, and emergency room physicians. Cardiac ultrasound can permit rapid, accurate, and noninvasive diagnosis of a broad range of acute cardiovascular pathologies. Although transesophageal echocardiography was once the principal diagnostic approach using ultrasound to evaluate intensive care unit patients, advances in ultrasound imaging, including harmonic imaging, digital acquisition, and contrast for endocardial enhancement, has improved the diagnostic yield of transthoracic echocardiography. Ultrasound devices continue to become more portable, and hand-carried devices are now readily available for bedside applications. This article discusses the application of bedside echocardiography in the intensive care unit. The emphasis is on echocardiography and cardiovascular diagnostics, specifically on goal-directed bedside cardiac ultrasonography.

The pulmonary artery catheter in critical care

Pulmonary artery catheterization has been a routine part of care for critically ill patients over the past 25 years. Primary hemodynamic data regarding cardiac output and pulmonary pressures can be utilized to make diagnoses and guide therapy. Tissue oxygen delivery and utilization allow inferences about the efficiency of the cardiopulmonary system and the impact of disease and medical therapies on tissue metabolism. Goals of high level invasive monitoring of cardiopulmonary function with pulmonary artery catheterization are organ salvage and minimizing complications associated with critical illness. Optimizing renal perfusion and minimizing pulmonary congestion with precise volume titration are common reasons for performing pulmonary artery catheterization in the intensive care unit. Despite being reassuring to clinicians that hemodynamic therapy is optimal, multiple data from well conducted clinical studies have not demonstrated outcome benefits to patients related to pulmonary artery catheterization. Less invasive techniques to obtain data regarding hemodynamic function are now entering the clinical arena and are being actively investigated.

Can dynamic indicators help the prediction of fluid responsiveness in spontaneously breathing critically ill patients?

OBJECTIVE

To investigate whether the respiratory changes in arterial pulse (DeltaPP) and in systolic pressure (DeltaSP) could predict fluid responsiveness in spontaneously breathing (SB) patients. Because changes in intrathoracic pressure during spontaneous breathing (SB) might be insufficient to modify loading conditions of the ventricles, performances of indicators were also assessed during a forced respiratory maneuver.

DESIGN

Prospective interventional study.

SETTING

A 34-bed university hospital medico-surgical ICU.

PATIENTS AND PARTICIPANTS

Thirty-two SB patients with clinical signs of hemodynamic instability.

INTERVENTION

A 500-ml volume expansion (VE).

MEASUREMENTS AND RESULTS

Cardiac index, assessed using transthoracic echocardiography, increased by at least 15% after VE in 19 patients (responders). At baseline, only dynamic indicators were higher in responders than in nonresponders (13+/-5% vs. 7+/-3%, p=0.003 for DeltaPP and 10+/-4% vs. 6+/-2%, p=0.002 for DeltaSP). Moreover, they significantly decreased after VE (11+/-5% to 6+/-4%, p<0.001 for DeltaPP and 8+/-4% to 6+/-3%, p<0.001 for DeltaSP). DeltaPP and DeltaSP areas under the ROC curve were high (0.81+/-0.08 and 0.82+/-0.08; p=0.888, respectively). A DeltaPP>or=12% predicted fluid responsiveness with high specificity (92%) but poor sensitivity (63%). The forced respiratory maneuver reproducing a dyspneic state decreased the predictive power.

CONCLUSIONS

Due to their lack of sensitivity and their dependence to respiratory status, DeltaPP and DeltaSP are clearly less reliable to predict fluid responsiveness during SB than in mechanically ventilated patients. However, when their baseline value is high without acute right ventricular dysfunction in a participating patient, a positive response to fluid is likely.

Echocardiographic prediction of volume responsiveness in critically ill patients with spontaneously breathing activity

OBJECTIVE

In hemodynamically unstable patients with spontaneous breathing activity, predicting volume responsiveness is a difficult challenge since the respiratory variation in arterial pressure cannot be used. Our objective was to test whether volume responsiveness can be predicted by the response of stroke volume measured with transthoracic echocardiography to passive leg raising in patients with spontaneous breathing activity. We also examined whether common echocardiographic indices of cardiac filling status are valuable to predict volume responsiveness in this category of patients.

DESIGN AND SETTING

Prospective study in the medical intensive care unit of a university hospital.

PATIENTS

24 patients with spontaneously breathing activity considered for volume expansion.

MEASUREMENTS

We measured the response of the echocardiographic stroke volume to passive leg raising and to saline infusion (500 ml over 15 min). The left ventricular end-diastolic area and the ratio of mitral inflow E wave velocity to early diastolic mitral annulus velocity (E/Ea) were also measured before and after saline infusion.

RESULTS

A passive leg raising induced increase in stroke volume of 12.5% or more predicted an increase in stroke volume of 15% or more after volume expansion with a sensitivity of 77% and a specificity of 100%. Neither left ventricular end-diastolic area nor E/Ea predicted volume responsiveness.

CONCLUSIONS

In our critically ill patients with spontaneous breathing activity the response of echocardiographic stroke volume to passive leg raising was a good predictor of volume responsiveness. On the other hand, the common echocardiographic markers of cardiac filling status were not valuable for this purpose.

Radial Artery Pulse Pressure Variation Correlates With Brachial Artery Peak Velocity Variation in Ventilated Subjects When Measured by Internal Medicine Residents Using Hand-Carried Ultrasound Devices

BACKGROUND

Rapid prediction of the effect of volume expansion is crucial in unstable patients receiving mechanical ventilation. Both radial artery pulse pressure variation (DeltaPP) and change of aortic blood flow peak velocity are accurate predictors but may be impractical point-of-care tools.

PURPOSES

We sought to determine whether respiratory changes in the brachial artery blood flow velocity (DeltaVpeak-BA) as measured by internal medicine residents using a hand-carried ultrasound (HCU) device could provide an accurate corollary to DeltaPP in patients receiving mechanical ventilation.

METHODS

Thirty patients passively receiving volume-control ventilation with preexisting radial artery catheters were enrolled. The brachial artery Doppler signal was recorded and analyzed by blinded internal medicine residents using a HCU device. Simultaneous radial artery pulse wave and central venous pressure recordings (when available) were analyzed by a blinded critical care physician.

RESULTS

A Doppler signal was obtained in all 30 subjects. The DeltaVpeak-BA correlated well with DeltaPP (r = 0.84) with excellent agreement (weighted kappa, 0.82) and limited intraobserver variability (2.8 +/- 2.8%) [mean +/- SD]. A DeltaVpeak-BA cutoff of 16% was highly predictive of DeltaPP > or = 13% (sensitivity, 91%; specificity, 95%). A poor correlation existed between the CVP and both DeltaVpeak-BA (r = - 0.21) and DeltaPP (r = - 0.16).

CONCLUSIONS

The HCU Doppler assessment of the DeltaVpeak-BA as performed by internal medicine residents is a rapid, noninvasive bedside correlate to DeltaPP, and a DeltaVpeak-BA cutoff of 16% may prove useful as a point-of-care tool for the prediction of volume responsiveness in patients receiving mechanical ventilation.

Pulse Pressure Respiratory Variation as an Early Marker of Cardiac Output Fall in Experimental Hemorrhagic Shock

Pulse pressure (DeltaPp) and systolic pressure (DeltaPs) variations have been recommended as predictors of fluid responsiveness in critically ill patients. We hypothesized that changes in DeltaPp and DeltaPs parallel alterations in stroke volume (SV) and cardiac output (CO) during hemorrhage, shock, and resuscitation. In anesthetized and mechanically ventilated mongrel dogs, a graded hemorrhage (20 mL/min) was induced to a target mean arterial pressure (MAP) of 40 mm Hg, which was maintained for additional 30 min. Total shed-blood volume was then retransfused at a 40 mL/min rate. CO, SV, right atrial pressure (RAP), pulmonary artery occlusion pressure (PAOP), and continuous mixed venous oxygen saturation (SvO(2)) were assessed. Both DeltaPp and DeltaPs were calculated from direct arterial pressure waveform. Removal of about 9% of estimated blood volume promoted a reduction in SV (14.8 +/- 2.2 to 10.6 +/- 1.3 mL, P < 0.05). At approximately 18% blood volume removal, significant changes in CO (2.4 +/- 0.2 to 1.5 +/- 0.2 mL/min, P < 0.05), DeltaPp (12.6 +/- 1.4 to 15.8 +/- 2.0%, P < 0.05), and SvO(2) (82 +/- 1.4 to 73 +/- 1.7%, P < 0.05) were observed. Alterations in MAP, RAP, PAOP, and DeltaPs could be detected only after each animal had lost over 36% of estimated initial blood volume. There was correlation between blood volume loss and SV, CO, and SvO(2), as well as between blood loss and MAP, DeltaPp, and DeltaPs. Blood volume loss showed no correlation with cardiac filling pressures. DeltaPp is a useful, early marker of SV and CO for the assessment of cardiac preload changes in hemorrhagic shock, while cardiac filling pressures are not.

Does a positive end-expiratory pressure-induced reduction in stroke volume indicate preload responsiveness? An experimental study

BACKGROUND

Increases in positive end-expiratory pressure (PEEP) are often associated with cardiovascular depression, responding to fluid loading. Therefore, we hypothesized that if stroke volume (SV) is reduced by an increase in PEEP this reduction is an indicator of hypovolemia or preload responsiveness, i.e. that SV would increase by fluid administration at zero end-expiratory pressure (ZEEP). The relationship between the cardiovascular response to different PEEP levels and fluid load as well as the relation between change in SV as a result of change in preload (Frank-Starling relationship) were evaluated in a porcine model. In addition, other measures of fluid status were assessed.

METHODS

Eight, 20-22 kg, anesthetized, mechanically ventilated pigs were subjected to 0, 10, and 20 cm H(2)O PEEP at 10% (of estimated blood volume) hypovolemia, normo- and 10% hypervolemia, and to ZEEP at 20% hypervolemia. SV, cardiac output, intrathoracic blood volume and airway, esophageal, vascular pressures, stroke volume variations, left ventricular end-diastolic and end-systolic areas and respiratory variations in the diameter of the inferior vena cava were obtained.

RESULTS

At hypovolemia and normovolemia, 10 cm H(2)O PEEP induced a significant decrease in SV, while no change occurred at 10% hypervolemia. SV measured at ZEEP increased from hypovolemia to normovolemia and 10% hypervolemia, while no change was found between 10% and 20% hypervolemia. The sensitivity and specificity decrease in SV by PEEP indicating an increase in SV by fluids was 60-88% and 67%, respectively, depending on the volemic (preload) levels.

CONCLUSION

Although the overall results suggest that a change in SV by PEEP might predict preload responsiveness, the individual response of SV by 10 cm H(2)O PEEP and of the successive fluid administration seemed to be dependent on where on the Frank-Starling curve the heart function was located.

Plethysmographic dynamic indices predict fluid responsiveness in septic ventilated patients

OBJECTIVES

In septic patients, reliable non-invasive predictors of fluid responsiveness are needed. We hypothesised that the respiratory changes in the amplitude of the plethysmographic pulse wave (DeltaP(PLET)) would allow the prediction of changes in cardiac index following volume administration in mechanically ventilated septic patients.

DESIGN

Prospective clinical investigation.

SETTING

An 11-bed hospital medical intensive care unit.

PATIENTS

Twenty-three deeply sedated septic patients mechanically ventilated with tidal volume >or=8 ml/kg and equipped with an arterial catheter and a pulse oximetry plethysmographic sensor.

INTERVENTIONS

Respiratory changes in pulse pressure (DeltaPP), DeltaP(PLET) and cardiac index (transthoracic Doppler echocardiography) were determined before and after volume infusion of colloids (8 ml/kg).

MEASUREMENTS AND MAIN RESULTS

Twenty-eight volume challenges were performed in 23 patients. Before volume expansion, DeltaPP correlated with DeltaP(PLET) (r2 = 0.71, p<0.001). Changes in cardiac index after volume expansion significantly (p<0.001) correlated with baseline DeltaPP (r2 = 0.76) and DeltaP(PLET) (r2 = 0.50). The patients were defined as responders to fluid challenge when cardiac index increased by at least 15% after the fluid challenge. Such an event occurred 18 times. Before volume challenge, a DeltaPP value of 12% and a DeltaP(PLET) value of 14% allowed discrimination between responders and non-responders with sensitivity of 100% and 94% respectively and specificity of 70% and 80% respectively. Comparison of areas under the receiver operator characteristic curves showed that DeltaPP and DeltaP(PLET) predicted similarly fluid responsiveness.

CONCLUSION

The present study found DeltaP(PLET) to be as accurate as DeltaPP for predicting fluid responsiveness in mechanically ventilated septic patients.

Prediction of fluid responsiveness using respiratory variations in left ventricular stroke area by transoesophageal echocardiographic automated border detection in mechanically ventilated patients

Background

Left ventricular stroke area by transoesophageal echocardiographic automated border detection has been shown to be strongly correlated to left ventricular stroke volume. Respiratory variations in left ventricular stroke volume or its surrogates are good predictors of fluid responsiveness in mechanically ventilated patients. We hypothesised that respiratory variations in left ventricular stroke area (ΔSA) can predict fluid responsiveness.

Methods

Eighteen mechanically ventilated patients undergoing coronary artery bypass grafting were studied immediately after induction of anaesthesia. Stroke area was measured on a beat-to-beat basis using transoesophageal echocardiographic automated border detection. Haemodynamic and echocardiographic data were measured at baseline and after volume expansion induced by a passive leg raising manoeuvre. Responders to passive leg raising manoeuvre were defined as patients presenting a more than 15% increase in cardiac output.

Results

Cardiac output increased significantly in response to volume expansion induced by passive leg raising (from 2.16 ± 0.79 litres per minute to 2.78 ± 1.08 litres per minute; p < 0.01). ΔSA decreased significantly in response to volume expansion (from 17% ± 7% to 8% ± 6%; p < 0.01). ΔSA was higher in responders than in non-responders (20% ± 5% versus 10% ± 5%; p < 0.01). A cutoff ΔSA value of 16% allowed fluid responsiveness prediction with a sensitivity of 92% and a specificity of 83%. ΔSA at baseline was related to the percentage increase in cardiac output in response to volume expansion (r = 0.53, p < 0.01).

Conclusion

ΔSA by transoesophageal echocardiographic automated border detection is sensitive to changes in preload, can predict fluid responsiveness, and can quantify the effects of volume expansion on cardiac output. It has potential clinical applications.

Interdépendance cœur–poumons chez le patient ventilé par pression positive

Heart-lung interactions during positive-pressure ventilation are characterized by an extreme sensibility to the patient's intravascular volume status. Indeed, a fall in cardiac output due to decreased ventricular preload can be observed when initiating positive-pressure ventilation. This phenomenon is due to the close anatomic-functional association between heart and lungs, and to the fact that pulmonary volume and intrathoracic pressure variations cyclically modify heart-lung interactions. The present review address the questions of the physiological and physiopathological effects of positive-pressure ventilation on the right and left venous returns, and on pulmonary and systemic vascular resistances.

Respiratory variations in pulse oximeter waveform amplitude are influenced by venous return in mechanically ventilated patients under general anaesthesia

BACKGROUND AND OBJECTIVES

Respiratory variations in pulse oximetry plethysmographic waveform amplitude (DeltaPOP) are related to respiratory variations in arterial pulse pressure (DeltaPP) in the critical care setting. The aims of this study were to test the hypothesis that in mechanically ventilated patients undergoing general anaesthesia, DeltaPOP calculation is feasible and can detect changes in preload.

METHODS

Twenty-five mechanically ventilated patients were studied immediately after induction of general anaesthesia. Haemodynamic data (mean arterial pressure [MAP], central venous pressure [CVP], DeltaPP and DeltaPOP) were recorded at baseline, before and after tilting the patient from anti-Trendelenburg to Trendelenburg position in order to induce preload changes.

RESULTS

Change from anti-Trendelenburg to Trendelenburg position induced changes in MAP (58 +/- 9 to 67 +/- 10 mmHg, P < 0.05), CVP (4 +/- 4 to 13 +/- 5 mmHg, P < 0.05), DeltaPP (14 +/- 8 to 7 +/- 5%, P < 0.05) and DeltaPOP (17 +/- 12 to 9 +/- 5%, P < 0.05). There was a significant relationship between DeltaPOP in anti-Trendelenburg position and percent change in MAP after volume expansion (r = 0.82; P < 0.05).

CONCLUSIONS

DeltaPOP can be determined in the operating room and is influenced by changes in preload. This new index has potential clinical applications for the prediction of fluid responsiveness.

Practical issues of hemodynamic monitoring at the bedside

The hemodynamic monitoring of a surgical patient acquires a major relevance in high-risk patients and those suffering from surgical diseases associated with hemodynamic instability, such as hemorrhagic or septic shock. This article reviews the fundamental physiologic principles needed to understand hemodynamic monitoring at the bedside. Monitoring defines stability, instability, and response to therapy. The major hemodynamic parameters measured and derived from invasive hemodynamic monitoring, such as arterial, central venous, and pulmonary catheterization, are discussed, as are its clinical indications, benefits, and complications. The current clinical data relevant to hemodynamic monitoring are reviewed and discussed.

Measuring aortic diameter improves accuracy of esophageal Doppler in assessing fluid responsiveness

OBJECTIVE

Fluid responsiveness requires the accurate measurement of cardiac output that can be approached by aortic blood flow (ABF) as measured by esophageal Doppler monitoring (EDM). EDM devices may either include an echo-determination of aortic diameter or estimate aortic diameter from nomograms and thus consider it as constant. However, it is unclear if measuring aortic diameter increases the accuracy of EDM to identify fluid responsiveness. Aortic diameter varies with arterial pressure such that its measure could be essential for assessing the changes in ABF during acute circulatory failure. We attempted to demonstrate that measuring aortic diameter improved the accuracy of EDM to assess fluid responsiveness.

DESIGN

Prospective study.

SETTING

University hospital intensive care unit.

PATIENTS

Seventy-six patients with acute circulatory failure in whom a fluid challenge was given.

INTERVENTIONS

Rapid volume expansion (500 mL of NaCl 0.9%).

MEASUREMENTS AND MAIN RESULTS

We measured aortic velocity and area by EDM before and after fluid loading and evaluated the effects of fluid challenge on ABF, either measured after fluid infusion (measured ABFafter) or estimated assuming an unchanging aortic area (estimated ABFafter). If measured ABFafter was used for assessing fluid response, it was increased above 15% compared with ABF at baseline in 41 patients (responders). Conversely, estimated ABFafter increased above 15% from ABF at baseline in 27 patients only; that is, the effects of the challenge were underestimated in 14 patients. In these 14 patients, the relative change in mean arterial pressure during volume expansion was of greater magnitude than in patients who were classified as nonresponders by considering measured ABFafter.

CONCLUSIONS

Monitoring the changes in aortic diameter improves the accuracy of EDM in assessing the hemodynamic effects of a fluid challenge, especially if it induces a large increase in arterial pressure. Estimating rather than measuring the aortic diameter may lead to underestimation of fluid responsiveness.

Cardiopulmonary interactions in patients with heart failure

PURPOSE OF REVIEW

The purpose of this review was to summarize recent findings concerning the consequences of cardiopulmonary interactions in acute cardiogenic pulmonary edema, weaning from mechanical ventilation and fluid-responsiveness assessment by respiratory variations of stroke volume.

RECENT FINDINGS

The efficacy of continuous or bilevel positive airway pressure in patients with acute cardiogenic pulmonary edema was strongly suggested by two recent meta-analyses. There is growing evidence to suggest that weaning-induced cardiac dysfunction and acute cardiogenic pulmonary edema could explain a large amount of liberation failure from mechanical ventilation. Despite a potential role for echocardiography and plasma measurements of B-type natriuretic peptide in demonstrating a cardiac origin to weaning failure, the demonstration of a significant increase in pulmonary-artery occlusion pressure during the weaning trial remains the gold standard for this purpose. In patients with heart failure there is no evidence for revisiting the reliability of the respiratory variation of stroke-volume surrogates to predict fluid responsiveness.

SUMMARY

For clinical practice, the knowledge of cardiopulmonary interactions is of paramount importance in understanding the crucial role of mechanical ventilation for treating patients with heart failure and, by contrast, the deleterious cardiovascular effects of weaning in patients with overt or hidden cardiac failure.

Cardiac filling pressures are not appropriate to predict hemodynamic response to volume challenge

OBJECTIVE

Values of central venous pressure of 8-12 mm Hg and of pulmonary artery occlusion pressure of 12-15 mm Hg have been proposed as volume resuscitation targets in recent international guidelines on management of severe sepsis. By analyzing a large number of volume challenges, our aim was to test the significance of the recommended target values in terms of prediction of volume responsiveness.

DESIGN

Retrospective study.

SETTING

A 24-bed medical intensive care unit.

PATIENTS

All consecutive septic patients monitored with a pulmonary artery catheter who underwent a volume challenge between 2001 and 2004.

INTERVENTION

None.

MEASUREMENTS AND MAIN RESULTS

A total of 150 volume challenges in 96 patients were reviewed. In 65 instances, the volume challenge resulted in an increase in cardiac index of > or =15% (responders). The pre-infusion central venous pressure was similar in responders and nonresponders (8 +/- 4 vs. 9 +/- 4 mm Hg). The pre-infusion pulmonary artery occlusion pressure was slightly lower in responders (10 +/- 4 vs. 11 +/- 4 mm Hg, p < .05). However, the significance of pulmonary artery occlusion pressure to predict fluid responsiveness was poor and similar to that of central venous pressure, as indicated by low values of areas under the receiver operating characteristic curves (0.58 and 0.63, respectively). A central venous pressure of <8 mm Hg and a pulmonary artery occlusion pressure of <12 mm Hg predicted volume responsiveness with a positive predictive value of only 47% and 54%, respectively. With the knowledge of a low stroke volume index (<30 mL.m), their positive predictive values were still unsatisfactory: 61% and 69%, respectively. When the combination of central venous pressure and pulmonary artery occlusion pressure was considered instead of either pressure alone, the degree of prediction of volume responsiveness was not improved.

CONCLUSION

Our study demonstrates that cardiac filling pressures are poor predictors of fluid responsiveness in septic patients. Therefore, their use as targets for volume resuscitation must be discouraged, at least after the early phase of sepsis has concluded.

Increased intra-abdominal pressure affects respiratory variations in arterial pressure in normovolaemic and hypovolaemic mechanically ventilated healthy pigs

OBJECTIVE

To evaluate the effect of increased intra-abdominal pressure (IAP) on the systolic and pulse pressure variations induced by positive pressure ventilation in a porcine model.

DESIGN AND SETTING

Experimental study in a research laboratory.

SUBJECTS

Seven mechanically ventilated and instrumented pigs prone to normovolaemia and hypovolaemia by blood withdrawal.

INTERVENTION

Abdominal banding gradually increased IAP in 5-mmHg steps up to 30 mmHg.

MEASUREMENTS AND MAIN RESULTS

Variations in systolic pressure, pulse pressure, inferior vena cava flow, and pleural and transmural (LVEDPtm) left-ventricular end-diastolic pressure were recorded at each step. Systolic pressure variations were 6.1+/-3.1%, 8.5+/-3.6% and 16.0+/-5.0% at 0, 10, and 30 mmHg IAP in normovolaemic animals (mean+/-SD; p<0.01 for IAP effect). They were 12.7+/-4.6%, 13.4+/-6.7%, and 23.4+/-6.3% in hypovolaemic animals (p<0.01 vs normovolaemic group) for the same IAP. Fluctuations of the inferior vena cava flow disappeared as the IAP increased. Breath cycle did not induce any variations of LVEDPtm for 0 and 30 mmHg IAP.

CONCLUSIONS

In this model, the systolic pressure and pulse pressure variations, and inferior vena cava flow fluctuations were dependent on IAP values which caused changes in pleural pressure swing, and this dependency was more marked during hypovolaemia. The present study suggests that dynamic indices are not exclusively related to volaemia in the presence of increased IAP. However, their fluid responsiveness predictive value could not be ascertained as no fluid challenge was performed.

How can the response to volume expansion in patients with spontaneous respiratory movements be predicted?

INTRODUCTION

The aim of the study was to evaluate the ability of different static and dynamic measurements of preload to predict fluid responsiveness in patients with spontaneous respiratory movements.

METHODS

The subjects were 21 critically ill patients with spontaneous breathing movements receiving mechanical ventilation with pressure support mode (n = 9) or breathing through a face mask (n = 12), and who required a fluid challenge. Complete hemodynamic measurements, including pulmonary artery occluded pressure (PAOP), right atrial pressure (RAP), pulse pressure variation (DeltaPP) and inspiratory variation in RAP were obtained before and after fluid challenge. Fluid challenge consisted of boluses of either crystalloid or colloid until cardiac output reached a plateau. Receiver operating characteristics (ROC) curve analysis was used to evaluate the predictive value of the indices to the response to fluids, as defined by an increase in cardiac index of 15% or more.

RESULTS

Cardiac index increased from 3.0 (2.3 to 3.5) to 3.5 (3.0 to 3.9) l minute-1 m-2 (medians and 25th and 75th centiles), p < 0.05. At baseline, DeltaPP varied between 0% and 49%. There were no significant differences in DeltaPP, PAOP, RAP and inspiratory variation in RAP between fluid responders and non-responders. Fluid responsiveness was predicted better with static indices (ROC curve area +/- SD: 0.73 +/- 0.13 for PAOP, p < 0.05 vs DeltaPP and 0.69 +/- 0.12 for RAP, p = 0.054 compared with DeltaPP) than with dynamic indices of preload (0.40 +/- 0.13 for DeltaPP and 0.53 +/- 0.13 for inspiratory changes in RAP, p not significant compared with DeltaPP).

CONCLUSION

In patients with spontaneous respiratory movements, DeltaPP and inspiratory changes in RAP failed to predict the response to volume expansion.

Comparison of stroke volume (SV) and stroke volume respiratory variation (SVV) measured by the axillary artery pulse-contour method and by aortic Doppler echocardiography in patients undergoing aortic surgery

BACKGROUND

The goal of the study was to compare stroke volume (SV) and respiratory stroke volume variation (SVV) measured by pulse-contour analysis and aortic Doppler.

METHODS

These were measured by pulse-contour analysis and thermodilution (PiCCO) and by aortic pulsed wave Doppler with transoesophageal echocardiography in patients undergoing abdominal aortic surgery. Simultaneous measurements were done at different times of surgery. All data were recorded on PiCCOwin software and videotape and analysed off-line by a blinded investigator.

RESULTS

A total of 114 measurements were achieved in 20 patients. There was a good correlation and small bias between the PiCCO and the echo-Doppler values of the mean SV [r=0.885; bias=0.2 (8) ml], and between the minimum [r=0.842; bias=1 (9) ml] and maximum SV [r=0.840; bias=2 (10) ml] values.

CONCLUSIONS

There is a fair correlation between pulse-contour analysis and aortic Doppler for beat-by-beat measurement of SV but not for calculation of SV respiratory ventilation.

Ability of pulse contour and esophageal Doppler to estimate rapid changes in stroke volume

OBJECTIVE

Two technologies to acquire beat-to-beat stroke volume values exist, pulse contour analysis and esophageal Doppler monitoring. Pulse contour analysis assumes fixed aortic impedance. Esophageal Doppler assumes a constant proportional descending aortic flow and diameter. These assumptions may not be correct as arterial tone or myocardial contractility vary. We tested these relationships in the setting of rapidly changing stroke volumes and different cardiovascular states over a period of 10-15 cardiac cycles.

DESIGN AND SETTING

In a university research facility we compared beat-to-beat changes in stroke volume as measure by aortic root flow probe or conductance catheter to pulse contour analysis and stroke distance as measured by esophageal Doppler.

SUBJECTS

Five purpose-bred research hounds.

INTERVENTIONS

To obtain a wide range of rapidly changing stroke volumes measurements were made during transient inferior vena cava occlusion. Data were gathered under baseline conditions and during norepinephrine, nitroprusside, and dobutamine infusions.

MEASUREMENTS AND RESULTS

The pulse contour stroke volumes and esophageal Doppler stroke distance paralleled flow probe stroke volumes under all conditions (R(2)=0.89 for all measures). However, the absolute changes and proportional changes and the absolute values for both surrogate measures differed from absolute stroke volumes. Bland-Altman analysis showed no consistent bias or degree of precision across all animals under any given cardiovascular state.

CONCLUSIONS

Both pulse contour stroke volumes and esophageal Doppler derived stroke distance estimates yield significant correlations with aortic root flow probe. However, the absolute values, absolute changes, or proportional changes may not reflect actual stroke volumes as cardiovascular state varies, making their use in estimating absolute changes in stroke volume potentially inaccurate.