Cyclic changes in arterial pulse during respiratory support revisited by Doppler echocardiography

Pulse oximetry and photoplethysmographic waveform analysis of the esophagus and bowel

PURPOSE OF REVIEW

This article reviews the development of novel reflectance pulse oximetry sensors for the esophagus and bowel, and presents some of the techniques used to analyze the waveforms acquired with such devices.

RECENT FINDINGS

There has been much research in recent years to expand the utility of pulse oximetry beyond the simple measurement of arterial oxygen saturation from the finger or earlobe. Experimental sensors based on reflectance pulse oximetry have been developed for use in internal sites such as the esophagus and bowel. Analysis of the photoplethysmographic waveforms produced by these sensors is beginning to shed light on some of the potentially useful information hidden in these signals.

SUMMARY

The use of novel reflectance pulse oximetry sensors has been successfully demonstrated. Such sensors, combined with the application of more advanced signal processing, will hopefully open new avenues of research leading to the development of new types of pulse oximetry-based monitoring techniques.

Fluid therapy in acute myocardial infarction: evaluation of predictors of volume responsiveness

BACKGROUND

Static vascular filling pressures suffer from poor predictive power in identifying the volume-responsive heart. The use of dynamic arterial pressure variables, including pulse pressure variation (PPV) has instead been suggested to guide volume therapy. The aim of the present study was to evaluate the performance of several clinically applicable haemodynamic parameters to predict volume responsiveness in a pig closed chest model of acute left ventricular myocardial infarction.

METHODS

Fifteen anaesthetized, mechanically ventilated pigs were studied following acute left myocardial infarction by temporary coronary occlusion. Animals were instrumented to monitor central venous (CVP) and pulmonary artery occlusion (PAOP) pressures and arterial systolic variations (SPV) and PPV. Cardiac output (CO) was measured using the pulmonary artery catheter and by using the PiCCO monitor also giving stroke volume variation (SVV). Variations in the velocity time integral by pulsed-wave Doppler echocardiography were determined in the left (DeltaVTI(LV)) and right (DeltaVTI(RV)) ventricular outflow tracts. Consecutive boluses of 4 ml/kg hydroxyethyl starch were administered and volume responsiveness was defined as a 10% increase in CO.

RESULTS

Receiver-operator characteristics (ROC) demonstrated the largest area under the curve for DeltaVTI(RV) [0.81 (0.70-0.93)] followed by PPV [0.76 (0.64-0.88)] [mean (and 95% CI)]. SPV, DeltaVTI(LV) and SVV did not change significantly during volume loading. CVP and PAOP increased but did not demonstrate significant ROC.

CONCLUSION

PPV may be used to predict the response to volume administration in the setting of acute left ventricular myocardial infarction.

Hemodynamic effects of passive leg raising: an echocardiographic study in patients with shock

OBJECTIVES

To determine the effects of passive leg raising (PLR) on hemodynamics and on cardiac function according to the preload dependency defined by the superior vena cava collapsibility index (DeltaSVC).

RESULTS

Forty patients with shock, sedated and mechanically ventilated, were included. Transesophageal echocardiography was performed. At baseline (T1), two groups were defined according to DeltaSVC. Eighteen patients presenting a DeltaSVC > 36%, an indicator of preload dependency, formed group 1, whereas 22 patients (group 2) exhibited a DeltaSVC < 30% (not preload-dependent). Measurements were then performed during PLR (T2), back to baseline (T3), and after volume expansion (T4) in group 1 only. At T1, DeltaSVC was significantly higher in group 1 than in group 2, 50 +/- 9% and 7 +/- 6%, respectively. In group 1, we found a decrease in DeltaSVC at T2 (24 +/- 9%) and T4 (17 +/- 7%), associated with increased systolic, diastolic and arterial pulse pressures. Cardiac index also increased, from 1.92 +/- 0.74 (T1) to 2.35 +/- 0.92 (T2) and 2.85 +/- 1.2 l/min/m(2) (T4) and left ventricular end-diastolic volume from 51 +/- 41 to 61 +/- 51 and 73 +/- 51 ml/m(2). None of these variations was found in group 2. No change in heart rate was observed.

CONCLUSION

Hemodynamic changes related to PLR were only induced by increased cardiac preload.

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.

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.

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.

Efficacy of therapeutic hypothermia after out-of-hospital cardiac arrest due to ventricular fibrillation

AIM OF THE STUDY

We investigated implementation and efficacy of mild therapeutic hypothermia in the treatment of out-of-hospital cardiac arrest due to ventricular fibrillation.

MATERIALS AND METHODS

Two periods were compared, an historical one (36 patients) between 2000 and 2002 where therapeutic hypothermia was never used, and a recent period (32 patients) between 2003 and 2005 where therapeutic hypothermia (32-34 degrees C) was implemented prospectively in our unit. Cooling was obtained by simply using wet cloths and ice packs. Survival in the two groups and factors associated with survival were analysed, together with the neurological prognosis in discharged patients.

RESULTS

Survival was significantly higher in the hypothermia group (56% versus 36%), whereas no significant difference was observed in severity between the two periods. Only age, time from return to spontaneous circulation <20min, and therapeutic hypothermia were independently associated with survival. Therapeutic hypothermia was well tolerated and was associated with a significant improvement in neurological outcome. Whereas only 23% of patients actually reached the target temperature in 2003, 100% did in 2005.

CONCLUSION

Therapeutic hypothermia is efficient in significantly improving survival and neurological outcome of out-of-hospital cardiac arrest with ventricular fibrillation. By using a simple method, it can be implemented easily and quickly, without side effects.

Pulse pressure variation as a tool to detect hypovolaemia during pneumoperitoneum

BACKGROUND

Pulse pressure variation (DeltaPP) and systolic pressure variation (SPV) induced by mechanical ventilation have been proposed to detect hypovolaemia and guide fluid therapy. During laparoscopic surgery, chest compliance is decreased by pneumoperitoneum. This may affect the value of SPV and DeltaPP as indicators of intravascular volume status. Thereby, we investigated the effects of pneumoperitoneum and hypovolaemia on SPV and DeltaPP.

METHODS

We measured DeltaPP, SPV and the inspiratory (Deltaup) and expiratory (Deltadown) components of SPV, at baseline, during pneumoperitoneum, during pneumoperitoneum and hypovolaemia and after the return to baseline conditions, in 11 mechanically ventilated rabbits. Pneumoperitoneum was induced by inflating the abdomen with carbon dioxide, and hypovolaemia was induced by controlled haemorrhage.

RESULTS

Pneumoperitoneum induced an increase in SPV from 8.5 +/- 1.6 to 13.3 +/- 2.6 mmHg (+56%, P < 0.05) as a result of an increase in Deltaup from 2.0 +/- 1.0 to 6.7 +/- 2.1 mmHg (+236%, P < 0.05), but no significant change in Deltadown, nor in DeltaPP. Haemorrhage induced a significant (P < 0.05) increase in SPV from 13.3 +/- 2.6 to 19.9 +/- 3.7 mmHg (+50%), in Deltadown from 6.6 +/- 3.3 to 14.0 +/- 4.9 mmHg (+112%) and in DeltaPP from 11.1 +/- 4.8 to 24.9 +/- 9.8% (+124%) but no change in Deltaup. All parameters returned to baseline values after blood re-infusion and abdominal deflation.

CONCLUSIONS

SPV is modified by haemorrhage but it is also influenced by pneumoperitoneum. In contrast, DeltaPP is modified by haemorrhage but not by pneumoperitoneum. These findings suggest that DeltaPP should be used preferentially instead of SPV to detect hypovolaemia and guide fluid therapy during laparoscopic surgery.

[Cardiopulmonary interactions in patients under positive pressure ventilation]

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.

Stroke volume estimation by thoracocardiography is better when glottis is closed

Thoracocardiography approach pretends to non-invasively monitor stroke volume by inductive plethysmographic recording of ventricular volume curves by a transducer placed on the chest. The purpose of this study was to investigate the potential of thoracocardiography to estimate stroke volumes while apnea with open glottis. We hypothesized that, when glottis is open, stroke volumes would be better estimated if airways flow curves were taken into account.

Changes in pulse pressure variability during cardiac resynchronization therapy in mechanically ventilated patients

INTRODUCTION

The respiratory variation in pulse pressure (PP) has been established as a dynamic variable of cardiac preload which indicates fluid responsiveness in mechanically ventilated patients. The impact of acute changes in cardiac performance on respiratory fluctuations in PP has not been evaluated until now. We used cardiac resynchronization therapy as a model to assess the acute effects of changes in left ventricular performance on respiratory PP variability without the need of pharmacological intervention.

METHODS

In 19 patients undergoing the implantation of a biventricular pacing/defibrillator device under general anesthesia, dynamic blood pressure regulation was assessed during right ventricular and biventricular pacing in the frequency domain (power spectral analysis) and in the time domain (PP variation: difference between the maximal and minimal PP values, normalized by the mean value).

RESULTS

PP increased slightly during biventricular pacing but without statistical significance (right ventricular pacing, 33 +/- 10 mm Hg; biventricular pacing, 35 +/- 11 mm Hg). Respiratory PP fluctuations increased significantly (logarithmically transformed PP variability -1.27 +/- 1.74 ln mm Hg2 versus -0.66 +/- 1.48 ln mm Hg2; p < 0.01); the geometric mean of respiratory PP variability increased 1.8-fold during cardiac resynchronization. PP variation, assessed in the time domain and expressed as a percentage, showed comparable changes, increasing from 5.3% (3.1%; 12.3%) during right ventricular pacing to 6.9% (4.7%; 16.4%) during biventricular pacing (median [25th percentile; 75th percentile]; p < 0.01).

CONCLUSION

Changes in cardiac performance have a significant impact on respiratory hemodynamic fluctuations in ventilated patients. This influence should be taken into consideration when interpreting PP variation.

Variation in amplitude of central venous pressure curve induced by respiration is a useful tool to reveal fluid responsiveness in postcardiac surgery patients

We tested the hypothesis that the dynamic evaluation of central venous pressure (CVP) amplitude could be a reliable predictor of fluid responsiveness in patients under mechanical ventilation, similar to the variation of arterial pulse pressure (DeltaPp). Thirty postcardiac surgery patients, under mechanical ventilation, were evaluated. The percentual difference between inspiratory (Ppins) and expiratory pulse pressure (Ppins) was so calculated: DeltaPp (%) = 100 x (Ppins - Ppexp)/[(Ppins + Ppexp)/2]. The respiratory variation of CVP curves amplitude were calculated by determining the percentual difference between inspiratory (CVPpins) and expiratory (CVPpexp) variation using vena cava "pressure" collapsibility index according the following formula: Cvci (%) = [(CVPpexp - CVPpins)/CVPpexp] x 100. There was a correlation between DeltaPp and Cvci (Pearson correlation coefficient, r = 0.45). Receiver operating characteristic curves showed that the Cvci value more than or equal to 5% predicted DeltaPp more than or equal to 13% with 91% specificity, 89% sensitivity, and AUC of 0.90. Therefore, Cvci presented a good agreement with DeltaPp (kappa = 0.76) to identify potential fluid responders (patients with DeltaPp > or =13%). In 9 potential fluid responders, both DeltaPp and Cvci significantly decreased from 18% +/- 8% to 8% +/- 6% (P < 0.004) and 23% +/- 15% to 7% +/- 6% (P < 0.004), respectively, after fluid replacement. Our findings suggest that vena cava "pressure" collapsibility index can be used as a marker of fluid responsiveness in postcardiac surgery patients under mechanical ventilation, such as arterial pulse pressure respiratory variation.

Open lung ventilation does not increase right ventricular outflow impedance: An echo-Doppler study

OBJECTIVE

Ventilation according to the open lung concept (OLC) consists of recruitment maneuvers, followed by low tidal volume and elevated positive end-expiratory pressure (PEEP). Elevated PEEP is associated with an increased right ventricular afterload. We investigated the effect of OLC ventilation on right ventricular outflow impedance during inspiration and expiration in patients after cardiac surgery using transesophageal echo-Doppler.

DESIGN

A prospective, single-center, crossover, randomized, controlled clinical study.

SETTING

Cardiothoracic intensive care unit of a university hospital.

PATIENTS

Twenty-eight patients scheduled for elective cardiac surgery with cardiopulmonary bypass.

INTERVENTIONS

In the intensive care unit, each patient was ventilated for approximately 30 mins according to both OLC and conventional ventilation. During OLC ventilation, recruitment maneuvers were applied until PaO2/FiO2 was >375 torr (50 kPa); during conventional ventilation no recruitment maneuvers were performed.

MEASUREMENTS AND MAIN RESULTS

Transesophageal echo-Doppler measurements were performed at end-inspiration and end-expiration in a steady-state condition, 20 mins after initiation of a ventilation strategy. Mean acceleration of flow was determined in the long axis of the pulmonary artery in a transverse axis view. During OLC ventilation, a total PEEP of 14 +/- 4 cm H2O was applied vs. 5 cm H2O during conventional ventilation. Mean acceleration during expiration was comparable between groups. During inspiration, OLC ventilation did not cause a decrease of mean acceleration compared with expiration, whereas this did occur during conventional ventilation.

CONCLUSIONS

Despite the use of elevated PEEP levels, ventilation according to OLC does not change right ventricular outflow impedance during expiration and decreases right ventricular outflow impedance during inspiration.

Echocardiographic measurement of fluid responsiveness

PURPOSE OF REVIEW

Fluid responsiveness is a relatively new concept. It enables the efficacy of volume expansion to be predicted before use, rather than assessed afterwards, thus avoiding inappropriate fluid infusion. Echocardiography is a fantastic noninvasive tool which can directly visualize the heart and assess cardiac function. Its use was long limited by the absence of accurate indices to diagnose hypovolemia and predict the effect of volume expansion. In the last few years, several French teams have used echocardiography to develop new parameters of fluid responsiveness, taking advantage of its ability to monitor cardiac function beat by beat during the respiratory cycle.

RECENT FINDINGS

In mechanically ventilated patients perfectly adapted to the respirator, respiratory variations in superior and inferior vena cava diameters and in left ventricular stroke volume have been validated as parameters of fluid responsiveness. In our opinion, the collapsibility index of the superior vena cava is the most reliable of these parameters, but does require transesophageal echocardiography.

SUMMARY

Echocardiography has been widely demonstrated to predict fluid responsiveness accurately. This is now a complete and noninvasive tool able to accurately determine hemodynamic status in circulatory failure.

Myocardial Systolic Function Increases During Positive Pressure Lung Inflation

Lung inflation with positive airway pressure may have rapid and dynamic effects on myocardial contractile function. We designed this study to assess the magnitude and time to onset of myocardial function changes during the initiation of single positive pressure lung inflation at clinically relevant inflation pressures. In 8 anesthetized 40-kg pigs, left ventricular pressures and volumes were measured directly (conductance volumetry). A 15 cm H2O airway pressure plateau with lung inflation (PPLI-15) was performed, and 2 single beats from that sequence, one from resting apnea at zero airway pressure and the second from the point when the lungs were first maximally inflated, were selected for analysis. Systolic function variables for zero airway pressure and PPLI-15 were analyzed. Systolic elastance, derived from bilinear time-varying elastance curves, increased approximately 15% during PPLI-15 from zero airway pressure. This agreed with other systolic function variables that identified an increase in left ventricular contractile function for the lung inflation beat. Serial measurements of myocardial function should be conducted with constant airway pressure and lung inflation conditions.

Pre-ejection period variations predict the fluid responsiveness of septic ventilated patients

OBJECTIVES

In septic patients with acute circulatory failure, reliable predictors of fluid responsiveness are needed at the bedside. We hypothesized that the respiratory change in pre-ejection period (DeltaPEP) would allow the prediction of changes in cardiac index following volume administration in mechanically ventilated septic patients.

DESIGN

Prospective clinical investigation.

SETTING

A ten-bed hospital intensive care unit.

PATIENTS

Patients admitted after septic shock equipped with an arterial catheter.

INTERVENTIONS

Pre-ejection period (PEP)--defined as the time interval between the beginning of the R wave on the electrocardiogram and the upstroke of the radial arterial pressure curve (PEPKT) or the pulse plethysmographic waveforms (PEPPLET)--and cardiac index (transthoracic echocardiography-Doppler) were determined before and after volume infusion of colloid (8 mL x kg). DeltaPEP (%) was defined as the difference between expiratory and inspiratory PEP divided by the mean of expiratory and inspiratory values. Respiratory changes in pulse pressure (DeltaPP) was also measured.

MEASUREMENTS AND MAIN RESULTS

: Twenty-two volume challenges were done in 20 deeply sedated patients. DeltaPEPKT, DeltaPEPPLET, and DeltaPP (measured in all patients) before volume expansion were correlated with cardiac index change after fluid challenge (r = .73, r = .67, and r = .70, respectively, p < .0001). Patients with a cardiac index increase induced by volume expansion > or = 15% and <15% were classified as responders and nonresponders, respectively. Receiver operating characteristic curves showed that the threshold DeltaPP value of 17% allowed discrimination between responder/nonresponder patients with a sensitivity of 85% and a specificity of 100%. For both DeltaPEPKT and DeltaPEPPLET, the best threshold value was 4% with a sensitivity-specificity of 92%-89% and 100%-67%, respectively.

CONCLUSIONS

The present study found DeltaPEPKT and DeltaPEPPLET to be as accurate as DeltaPP in the prediction of fluid responsiveness in mechanically ventilated septic patients.

Myocardial perfusion monitoring during coronary artery bypass using an electrocardiogram-triggered laser Doppler technique

Electrocardiogram (ECG)-triggered laser Doppler perfusion monitoring (LDPM) was used to assess myocardial perfusion, with minimum myocardial tissue motion influence, during coronary artery bypass grafting (CABG). Thirteen subjects were investigated at six phases: pre- and post-CABG; post aorta cross-clamping; pre and post left internal mammary artery (LIMA) graft declamping; and post aorta declamping. The perfusion signal was calculated in late systole and late diastole, with expected minimum tissue motion, and compared with arrested heart measurements. Patient conditions or artifacts caused by surgical activity made it impossible to perform and analyse data in all six phases for some patients. No significant (n = 5) difference between perfusion signals pre- and post-CABG was found. Diastolic perfusion signal levels were significantly (p < 0.02) lower compared with systolic levels. After aorta cross-clamping, the signal level was almost zero. A distinct perfusion signal increase after LIMA and aorta declamping, compared with pre-LIMA declamping, was found in ten cases out of 13. A significantly (p < 0.04) lower perfusion signal in the arrested heart compared with in the beating heart was registered. Influence from mechanical ventilation was observed in 14 measurements out of 17. In conclusion, ECG-triggered LDPM can be used to assess myocardial perfusion during CABG. Perfusion signals were lower in the arrested heart compared with in the beating heart and in late diastole compared with late systole. No significant difference between pre- and post-CABG was found.

Let us use the pulmonary artery catheter correctly and only when we need it

OBJECTIVE

To clarify the issues related to the use of the pulmonary artery catheter within a rational clinical perspective.

RESULTS

Barriers include a) increased patient risk of pulmonary artery catheter placement; b) ability to measure similar variables via central venous catheterization, echocardiography, or other less invasive techniques; c) increased cost; d) inaccurate measurements; e) incorrect interpretation and application of pulmonary artery catheter-derived variables; and f) lack of proven benefit of pulmonary artery catheter use in the overall management of patients.

INTERPRETATION

a) The risks are mainly due to insertion of a central catheter, not a pulmonary artery catheter; b) continuous monitoring of left ventricular filling pressures, pulmonary vascular pressures, and mixed venous oxygen saturation is a unique feature; c) additional costs are minimal relative to the cost of intensive care; d) measurement errors require ongoing programmatic educational efforts; e) pulmonary artery catheter-derived data need to be used within the context of a defined treatment protocol; and f) no monitoring device, no matter how simple or sophisticated, will improve patient-centered outcomes unless coupled with a treatment that, itself, improves outcome.

CONCLUSION

A treatment protocol for the use of pulmonary artery catheter-derived variables is proposed that could serve as a basis for a prospective clinical trial.

Assessing Fluid-Responsiveness by a Standardized Ventilatory Maneuver: The Respiratory Systolic Variation Test

Respiratory-induced changes in arterial blood pressure predict fluid responsiveness. However, the accuracy of these variables is affected by the preset tidal volume and by the early inspiratory increase in arterial blood pressure. We have therefore calculated the slope produced by the minimal systolic blood pressures (plotted against the respective airway pressures) during a ventilatory maneuver consisting of four incremental, successive, pressure-controlled breaths, termed the Respiratory Systolic Variation Test (RSVT). In 14 ventilated patients, after major vascular surgery, the slope of the RSVT decreased significantly after intravascular fluid administration and correlated with the end-diastolic area and with changes in cardiac output better than filling pressures. This preliminary study suggests that a standardized ventilatory maneuver may be useful in guiding fluid therapy in ventilated patients.

Pulse pressure variations to predict fluid responsiveness: influence of tidal volume

OBJECTIVE

To evaluate the influence of tidal volume on the capacity of pulse pressure variation (DeltaPP) to predict fluid responsiveness.

DESIGN

Prospective interventional study.

SETTING

A 31-bed university hospital medico-surgical ICU.

PATIENTS AND PARTICIPANTS

Sixty mechanically ventilated critically ill patients requiring fluid challenge, separated according to their tidal volume.

INTERVENTION

Fluid challenge with either 1,000 ml crystalloids or 500 ml colloids.

MEASUREMENTS AND RESULTS

Complete hemodynamic measurements including DeltaPP were obtained before and after fluid challenge. Tidal volume was lower than 7 ml/kg in 26 patients, between 7-8 ml/kg in 9 patients, and greater than 8 ml/kg in 27 patients. ROC curve analysis was used to evaluate the predictive value of DeltaPP at different tidal volume thresholds, and 8 ml/kg best identified different behaviors. Overall, the cardiac index increased from 2.66 (2.00-3.47) to 3.04 (2.44-3.96) l/min m(2) ( P <0.001). It increased by more than 15% in 33 patients (fluid responders). Pulmonary artery occluded pressure was lower and DeltaPP higher in responders than in non-responders, but fluid responsiveness was better predicted with DeltaPP (ROC curve area 0.76+/-0.06) than with pulmonary artery occluded pressure (0.71+/-0.07) and right atrial (0.56+/-0.08) pressures. Despite similar response to fluid challenge in low (<8 ml/kg) and high tidal volume groups, the percent of correct classification of a 12% DeltaPP was 51% in the low tidal volume group and 88% in the high tidal volume group.

CONCLUSIONS

DeltaPP is a reliable predictor of fluid responsiveness in mechanically ventilated patients only when tidal volume is at least 8 ml/kg.

Management of severe sepsis and septic shock

PURPOSE OF REVIEW

Severe sepsis and septic shock are common and deadly conditions for which the epidemiology, pathogenesis, and management continue to evolve. Recent publications (2003 and early 2004) have been systematically reviewed for important new original research and scholarly reviews, with an emphasis on clinical advances in adults.

RECENT FINDINGS

Important new epidemiologic studies establish the increasing frequency (nearly 9% per year) and falling mortality rates associated with sepsis. Sepsis definitions were reviewed by a group of experts, and the principal features of the 1991 consensus conference definitions were supported, with a new framework for evaluation of sepsis proposed. New research and thoughtful reviews continue to elucidate the pathogenesis of sepsis, with emphasis on innate immunity and time-based changes in immune status, varying from hyperreactive immunity and inflammation to immune depression with enhanced risk for nosocomial infections. A comprehensive evidence-based approach to the management of severe sepsis is presented in an important document developed by representatives from many critical care and infectious disease societies. Management includes early targeted resuscitation, broad empiric antibiotic coverage and source control, effective shock evaluation and treatment, adjuvant therapy with recombinant human activated protein C and moderate-dose hydrocortisone in selected patients, and comprehensive supportive care. Recently published multicenter clinical trials for novel agents have been disappointing, particularly for a nitric oxide synthase inhibitor that effectively supported blood pressure but increased mortality.

SUMMARY

The works reviewed reflect the advances in the care of patients with sepsis.

Comparison of Cardiac Output Determined by Bioimpedance, Thermodilution, and the Fick Method

• Background Cardiac output can be determined by using a variety of methods.

• Objectives To determine the precision and bias between 3 methods for determining cardiac output: bioimpedance, thermodilution, and the Fick method.

• Methods Cardiac output was determined by using bioimpedance via neck and thorax patches and thermodilution via pulmonary artery catheter in 46 patients in the intensive care unit. A subset of 15 patients also had cardiac output determined by using the Fick method.

• Results Mean (SD) cardiac output in all patients was 6.3 (2.2) L/min by thermodilution and 5.6 (2.0) L/min by bioimpedance. In the 15 patients in whom all 3 methods were used, mean cardiac output was 6.0 (1.7) L/min by thermodilution, 5.3 (1.7) L/min by bioimpedance, and 8.6 (4.5) L/min by the Fick method. Bias and precision (mean difference ± 2 SDs) were 0.7 ± 2.9 L/min between thermodilution and bioimpedance, 1.7 ± 3.8 L/min between the Fick method and thermodilution, and 2.4 ± 4.7 L/min between the Fick method and bioimpedance.

• Conclusion Bioimpedance, thermodilution, and Fick determinations of cardiac outputs are not interchangeable in a heterogenous population of critically ill patients.

Pulse Pressure Variation Predicts Fluid Responsiveness Following Coronary Artery Bypass Surgery

STUDY OBJECTIVE

To determine whether the degree of pulse pressure variation (PPV) and systolic pressure variation (SPV) predict an increase in cardiac output (CO) in response to volume challenge in postoperative patients who have undergone coronary artery bypass grafting (CABG), and to determine whether PPV is superior to SPV in this setting.

DESIGN AND SETTING

This was a prospective clinical study conducted in the cardiovascular ICU of a university hospital.

PATIENTS

Twenty-one patients were studied immediately after arrival in the ICU following CABG.

INTERVENTION

A fluid bolus was administered to all patients.

MEASUREMENTS

Hemodynamic measurements, including central venous pressure (CVP), pulmonary artery occlusion pressure (PAOP), CO (thermodilution), percentage of SPV (%SPV), and percentage of PPV (%PPV), were performed shortly after patient arrival in the ICU. Patients were given a rapid 500-mL fluid challenge, after which hemodynamic measurements were repeated. Patients whose CO increased by >/= 12% were considered to be fluid responders. The ability of different parameters to distinguish between responders and nonresponders was compared.

RESULTS

In response to the volume challenge, 6 patients were responders and 15 were nonresponders. Baseline CVP and PAOP were no different between these two groups. In contrast, the %SPV and the %PPV were significantly higher in responders than in nonresponders. Receiver operating characteristic curve analysis suggested that the %PPV was the best predictor of fluid responsiveness. The ideal %PPV threshold for distinguishing responders from nonresponders was found to be 11. A PPV value of >/= 11% predicted an increase in CO with 100% sensitivity and 93% specificity.

CONCLUSION

PPV and SPV can be used to predict whether or not volume expansion will increase CO in postoperative CABG patients. PPV was superior to SPV at predicting fluid responsiveness. Both of these measures were far superior to CVP and PAOP.

Superior vena caval collapsibility as a gauge of volume status in ventilated septic patients

OBJECTIVE

In mechanically ventilated patients inspiratory increase in pleural pressure during lung inflation may produce complete or partial collapse of the superior vena cava. Occurrence of this collapse suggests that at this time external pressure exerted by the thoracic cavity on the superior vena cava is greater than the venous pressure required to maintain the vessel fully open. We tested the hypothesis that measurement of superior vena caval collapsibility would reveal the need for volume expansion in a given septic patient.

DESIGN AND SETTING

Prospective data collection for 66 successive patients in septic shock admitted in a medical intensive care unit and mechanically ventilated for an associated acute lung injury.

MEASUREMENTS AND RESULTS

We simultaneously measured superior vena caval collapsibility by echocardiography and cardiac index by the Doppler technique at baseline and after a 10 ml/kg volume expansion by 6% hydroxyethyl starch in 30 min. The threshold superior vena caval collapsibility of 36%, calculated as (maximum diameter on expiration-minimum diameter on inspiration)/maximum diameter on expiration, allowed discrimination between responders (defined by an increase in cardiac index of at least 11% induced by volume expansion) and nonresponders, with a sensitivity of 90% and a specificity of 100%.

CONCLUSIONS

Superior vena cava measurement should be systematically performed during routine echocardiography in septic shock as it gives an accurate index of fluid responsiveness.

The respiratory variation in inferior vena cava diameter as a guide to fluid therapy

OBJECTIVE

To investigate whether the respiratory variation in inferior vena cava diameter (DeltaD(IVC)) could be related to fluid responsiveness in mechanically ventilated patients.

DESIGN

Prospective clinical study.

SETTING

Medical ICU of a non-university hospital.

PATIENTS

Mechanically ventilated patients with septic shock (n=39).

INTERVENTIONS

Volume loading with 8 mL/kg of 6% hydroxyethylstarch over 20 min.

MEASUREMENTS AND RESULTS

Cardiac output and DeltaD(IVC) were assessed by echography before and immediately after the standardized volume load. Volume loading induced an increase in cardiac output from 5.7+/-2.0 to 6.4+/-1.9 L/min (P<0.001) and a decrease in DeltaD(IVC) from 13.8+/-13.6 vs 5.2+/-5.8% (P<0.001). Sixteen patients responded to volume loading by an increase in cardiac output > or =15% (responders). Before volume loading, the DeltaD(IVC) was greater in responders than in non-responders (25+/-15 vs 6+/-4%, P<0.001), closely correlated with the increase in cardiac output (r=0.82, P<0.001), and a 12% DeltaD(IVC) cut-off value allowed identification of responders with positive and negative predictive values of 93% and 92%, respectively.

CONCLUSION

Analysis of DeltaD(IVC) is a simple and non-invasive method to detect fluid responsiveness in mechanically ventilated patients with septic shock.