Understanding central venous pressure: not a preload index? Curr Opin Crit Care. 2015;21:369-375. [PMID: 26348416 DOI: 10.1097/mcc.0000000000000238]

What is cardiogenic shock? New clinical criteria urgently needed

PURPOSE OF REVIEW

Cardiogenic shock is a clinical syndrome with different causes and a complex pathophysiology. Recent evidence from clinical trials evokes the urgent need for redefining clinical diagnostic criteria to be compliant with the definition of cardiogenic shock and current diagnostic methods.

RECENT FINDINGS

Conflicting results from randomized clinical trials investigating mechanical circulatory support in patients with cardiogenic shock have elicited several extremely important questions. At minimum, it is questionable whether survivors of cardiac arrest should be included in trials focused on cardiogenic shock. Moreover, considering the wide availability of ultrasound and hemodynamic monitors capable of arterial pressure analysis, the current clinical diagnostic criteria based on the presence of hypotension and hypoperfusion have become insufficient. As such, new clinical criteria for the diagnosis of cardiogenic shock should include evidence of low cardiac output and appropriate ventricular filling pressure.

SUMMARY

Clinical diagnostic criteria for cardiogenic shock should be revised to better define cardiac pump failure as a primary cause of hemodynamic compromise.

Haemodynamic monitoring during noncardiac surgery: past, present, and future

During surgery, various haemodynamic variables are monitored and optimised to maintain organ perfusion pressure and oxygen delivery - and to eventually improve outcomes. Important haemodynamic variables that provide an understanding of most pathophysiologic haemodynamic conditions during surgery include heart rate, arterial pressure, central venous pressure, pulse pressure variation/stroke volume variation, stroke volume, and cardiac output. A basic physiologic and pathophysiologic understanding of these haemodynamic variables and the corresponding monitoring methods is essential. We therefore revisit the pathophysiologic rationale for intraoperative monitoring of haemodynamic variables, describe the history, current use, and future technological developments of monitoring methods, and finally briefly summarise the evidence that haemodynamic management can improve patient-centred outcomes.

Incidence and Determinants of Acute Kidney Injury after Prone Positioning in Severe COVID-19 Acute Respiratory Distress Syndrome

(1) Background: Acute kidney injury (AKI) is common among critically ill COVID-19 patients, but its temporal association with prone positioning (PP) is still unknown, and no data exist on the possibility of predicting PP-associated AKI from bedside clinical variables. (2) Methods: We analyzed data from 93 COVID-19-related ARDS patients who underwent invasive mechanical ventilation (IMV) and at least one PP cycle. We collected hemodynamic variables, respiratory mechanics, and circulating biomarkers before, during, and after the first PP cycle. PP-associated AKI (PP-AKI) was defined as AKI diagnosed any time from the start of PP to 48 h after returning to the supine position. A t-test for independent samples was used to test for the differences between groups, while binomial logistical regression was performed to assess variables independently associated with PP-associated AKI. (3) Results: A total of 48/93 (52%) patients developed PP-AKI, with a median onset at 24 [13.5-44.5] hours after starting PP. No significant differences in demographic characteristics between groups were found. Before starting the first PP cycle, patients who developed PP-AKI had a significantly lower cumulative fluid balance (CFB), even when normalized for body weight (p = 0.006). Central venous pressure (CVP) values, measured before the first PP (OR 0.803, 95% CI [0.684-0.942], p = 0.007), as well as BMI (OR 1.153, 95% CI = [1.013-1.313], p = 0.031), were independently associated with the development of PP-AKI. In the multivariable regression analysis, a lower CVP before the first PP cycle was independently associated with ventilator-free days (OR 0.271, 95% CI [0.123-0.936], p = 0.011) and with ICU mortality (OR:0.831, 95% CI [0.699-0.989], p = 0.037). (4) Conclusions: Acute kidney injury occurs frequently in invasively ventilated severe COVID-19 ARDS patients undergoing their first prone positioning cycle. Higher BMI and lower CVP before PP are independently associated with the occurrence of AKI during prone positioning.

RESPIRATION-RELATED VARIATIONS IN CENTRAL VENOUS PRESSURE AS PREDICTORS OF FLUID RESPONSIVENESS IN SPONTANEOUSLY BREATHING PATIENTS

ABSTRACT

Objective : The hemodynamic parameters used to accurately predict fluid responsiveness (FR) in spontaneously breathing patients (SB) require specific material and expertise. Measurements of the central venous pressure (CVP) are relatively simple and, importantly, are feasible in many critically ill patients. We analyzed the accuracy of respiration-related variations in CVP (vCVP) to predict FR in SB patients and examined the optimization of its measurement using a standardized, deep inspiratory maneuver. Patients and Methods : We performed a monocentric, prospective, diagnostic evaluation. Spontaneously breathing patients in intensive care units with a central venous catheter were prospectively included. The vCVP was measured while the patient was spontaneously breathing, both with (vCVP-st) and without (vCVP-ns) a standardized inspiratory maneuver, and calculated as: Minimum inspiratory v-wave peak pressure - Maximum expiratory v-wave peak pressure. A passive leg raising-induced increase in the left ventricular outflow tract velocity-time integral ≥10% defined FR. Results : Among 63 patients, 38 (60.3%) presented FR. The vCVP-ns was not significantly different between responders and nonresponders (-4.9 mm Hg [-7.5 to -3.1] vs. -4.1 mm Hg [-5.4 to 2.8], respectively; P = 0.15). The vCVP-st was lower in responders than nonresponders (-9.7 mm Hg [-13.9 to -6.2] vs. -3.6 mm Hg [-10.6 to -1.6], respectively; P = 0.004). A vCVP-st < -4.7 mm Hg predicted FR with 89.5% sensitivity, a specificity of 56.0%, and an area under the receiver operating characteristic curve of 0.72 (95% CI, 0.58 to 0.86) ( P = 0.004). Conclusion : When a central venous catheter is present, elevated values for vCVP-st may be useful to identify spontaneously breathing patients unresponsive to volume expansion. Nevertheless, the necessity of performing a standardized, deep-inspiration maneuver may limit its clinical application.

Effect of positive end expiratory pressure on central venous pressure in closed and open thorax

OBJECTIVE

The magnitude and mechanism of the rise of central venous pressure (CVP) after positive end-expiratory pressure (PEEP) among patients with cardiac disease is poorly understood. Therefore, the study aimed to compare the magnitude of change in CVP after PEEP in patients with TR (tricuspid regurgitation), high CVP and high PCWP (pulmonary capillary wedge pressure) with no TR, low CVP and low PCWP. Additionally, we hypothesized that PEEP in the open thorax would also lead to a rise in CVP.

APPROACH

This prospective, quasi-experimental study was conducted in patients undergoing cardiac surgery. Three consecutive readings of variables were obtained at 1-minute intervals after PEEP (5 and 10 cm H2O) application in the closed and open thorax. Patients were stratified a priori into low CVP (<10 cm H2O) and high CVP (≥10 cm H2O), no TR and TR and low PCWP (<15 mm Hg) and high PCWP (≥15 mm Hg) in the closed and open thorax.

MAIN RESULTS

Sixty-two patients were eligible for final analysis. The mean difference (MD) in ∆CVP (CVP10 cm H2O of PEEP - CVP zero end-expiratory pressure) was 2.33±1.13 (95% CI, 2.04-2.62, P=0.000) and 1.02±0.77 (95% CI, 0.82-1.22, P=0.000) in the closed and open thorax, respectively. The increase in CVP was higher among patients who had a lower CVP (2.64 ± 0.9 mm Hg vs 1.45± 1.17 mm Hg; p=0.000), without TR (2.64 ± 0.97 mm Hg vs 2.14 ± 1.2 mm Hg, p=0.09) and lower PCWP (2.4 ± 0.9 mm Hg vs 2.3 ± 1.4 mm Hg, p=0.67) at 10 cm H2O PEEP in the closed thorax.

SIGNIFICANCE

The rise in CVP was higher among patients without TR, low CVP and low PCWP. Zero intrathoracic pressure in the open thorax did not abolish the effect of PEEP on CVP rise altogether.

Correlation Between Ultrasound-Measured Diameter and Blood Flow Velocity of the Internal Jugular Veins with the Preoperative Blood Volume in Elderly Patients

The study aimed to explore the correlation of the diameter and blood flow velocity of the internal jugular vein with the preoperative blood volume in elderly patients and to providence for rapid evaluation of preoperative blood volume with ultrasound in elderly patients. Thirty patients over 65 years old were recruited in the study. Patient’s central venous pressure (CVP) was recorded before anesthesia. The maximum diameter (Dmax) and the minimum diameter (Dmin) of the left internal jugular vein were measured by M type ultrasound and the respiratory variation index (RVI), defined as (Dmax − Dmin) / Dmax × 100%, was calculated. The maximum blood flow velocity (BVmax) and the minimum blood flow velocity (BVmin) were measured by Doppler ultrasound, and the blood flow variation index (BVI), defined as (BVmax − BVmin) / BVmax × 100%, was calculated. Then, each of the patients was given with 5 ml/kg crystalloid solution, and the relevant data were measured again and compared to that before infusion. The correlation between each measurement index and CVP, and their efficiency in predicting CVP > 6 mmHg were statistically evaluated. No matter before or after infusion, Dmax, Dmin, BVmax, and BVmin were positively correlated with CVP (Correlation is significant at the 0.01 level (2-tailed)); and RVI was negatively correlated with CVP (Correlation is significant at the 0.01 level (2-tailed)); however, BVI is negatively correlated with the CVP with no statistically significant difference. Through the analysis of ROC curve, Dmax, Dmin, RVI, BVmax, and BVmin could be used to predict the CVP > 6 mmHg in these patients, and the best index was BVmax; BVI diagnosis was not effective. Ultrasonic measurements of internal jugular vein diameter, respiratory variability, and blood flow velocity were correlated with preoperative CVP in elderly patients, indicating that these indexes could potentially be used to evaluate the preoperative blood volume in elderly patients.

Central venous pressure and acute kidney injury in critically ill patients with multiple comorbidities: a large retrospective cohort study

Background

Given the traditional acceptance of higher central venous pressure (CVP) levels, clinicians ignore the incidence of acute kidney injury (AKI). The objective of this study was to assess whether elevated CVP is associated with increased AKI in critically ill patients with multiple comorbidities.

Methods

This was a retrospective observational cohort study using data collected from the Medical Information Mart for Intensive Care (MIMIC)-III open-source clinical database (version 1.4). Critically ill adult patients with CVP and serum creatinine measurement records were included. Linear and multivariable logistic regression were performed to determine the association between elevated CVP and AKI.

Results

A total of 11,135 patients were enrolled in our study. Critically ill patients in higher quartiles of mean CVP presented greater KDIGO AKI severity stages at 2 and 7 days. Linear regression showed that the CVP quartile was positively correlated with the incidence of AKI within 2 (R² = 0.991, P = 0.004) and 7 days (R² = 0.990, P = 0.005). Furthermore, patients in the highest quartile of mean CVP exhibited an increased risk of AKI at 7 days than those in the lowest quartile of mean CVP with an odds ratio of 2.80 (95% confidence interval: 2.32–3.37) after adjusting for demographics, treatments and comorbidities. The adjusted odds of AKI were 1.10 (95% confidence interval: 1.08–1.12) per 1 mmHg increase in mean CVP.

Conclusions

Elevated CVP is associated with an increased risk of AKI in critically ill patients with multiple comorbidities. The optimal CVP should be personalized and maintained at a low level to avoid AKI in critical care settings.

PPV May Be a Starting Point to Achieve Circulatory Protective Mechanical Ventilation

Pulse pressure variation (PPV) is a mandatory index for hemodynamic monitoring during mechanical ventilation. The changes in pleural pressure (Ppl) and transpulmonary pressure (PL) caused by mechanical ventilation are the basis for PPV and lead to the effect of blood flow. If the state of hypovolemia exists, the effect of the increased Ppl during mechanical ventilation on the right ventricular preload will mainly affect the cardiac output, resulting in a positive PPV. However, PL is more influenced by the change in alveolar pressure, which produces an increase in right heart overload, resulting in high PPV. In particular, if spontaneous breathing is strong, the transvascular pressure will be extremely high, which may lead to the promotion of alveolar flooding and increased RV flow. Asynchronous breathing and mediastinal swing may damage the pulmonary circulation and right heart function. Therefore, according to the principle of PPV, a high PPV can be incorporated into the whole respiratory treatment process to monitor the mechanical ventilation cycle damage/protection regardless of the controlled ventilation or spontaneous breathing. Through the monitoring of PPV, the circulation-protective ventilation can be guided at bedside in real time by PPV.

Fluid Responsiveness Predictability in Immediate Postoperative Pediatric Cardiac Surgery. Is the Old Slandered Central Venous Pressure Back Again?

OBJECTIVE

Acute low cardiac output (CO) is a frequent scenario in pediatric cardiac intensive care units (PCICU). While fluid responsiveness has been studied extensively, literature is scarce for the immediate postoperative congenital heart surgery population admitted to PCICUs. This study analyzed the utility of hemodynamic, bedside ultrasound, and Doppler parameters for prediction of fluid responsiveness in infants and neonates in the immediate postoperative cardiac surgery period.

DESIGN

A prospective observational study.

SETTING

University affiliated, tertiary care hospital, PCICU.

PARTICIPANTS

Immediate postoperative pediatric patients displaying a presumed hypovolemic low CO state were included. A clinical, arterial derived, hemodynamic, sonographic, Doppler-based, and echocardiographic parameter assessment was performed, followed by a fluid bolus therapy.

INTERVENTIONS

Fifteen to 20 cc/kg crystalloid fluid bolus.

MAIN OUTCOME MEASURES

Fluid responsiveness was defined as an increase in cardiac index >10% by echocardiography.

RESULTS

Of 52 patients, 34 (65%) were fluid responsive. Arterial systolic pressure variation, continuous-Doppler preload parameters, and inferior vena-cava distensibility index (IVCDI) by bedside ultrasound all failed to predict fluid responsiveness. Dynamic central venous pressure (CVP) change yielded a significant but modest fluid responsiveness predictability of area under the curve 0.654 (P = 0.0375).

CONCLUSIONS

In a distinct population of mechanically ventilated, young, pediatric cardiac patients in the immediate postoperative period, SPV, USCOM preload parameters, as well as IVC-based parameters by bedside ultrasound failed to predict fluid responsiveness. Dynamic CVP change over several hours was the only parameter that yielded significant but modest fluid responsiveness predictability.

Dyspnea in Chronic Low Ventricular Preload States

Dyspnea in low-preload states is an underrecognized but growing diagnosis in patients with unexplained dyspnea. Patients can often experience debilitating symptoms at rest and with exertion, as low measured preload often leads to decreased cardiac output and ultimately dyspnea. In the present article, we performed a review of the literature and a multidisciplinary evaluation to understand the pathophysiology, diagnosis, and treatment of dyspnea in low-preload states. We explored selected etiologies and suggested an algorithm to approach unexplained dyspnea. The mainstay of diagnosis remains as invasive cardiopulmonary exercise testing. We concluded with a variety of nonpharmacological and pharmacological therapies, highlighting that a multifactorial approach may lead to the best results.

Assessment of Fluid Status by Bioimpedance Analysis and Central Venous Pressure Measurement and Their Association with the Outcomes of Severe Acute Kidney Injury

Background and Objectives: Fluid disbalance is associated with adverse outcomes in critically ill patients with acute kidney injury (AKI). In this study, we intended to assess fluid status using bioimpedance analysis (BIA) and central venous pressure (CVP) measurement and to evaluate the association between hyperhydration and hypervolemia with the outcomes of severe AKI. Materials and Methods: A prospective study was conducted in the Hospital of the Lithuanian University of Health Sciences Kauno Klinikos. Forty-seven patients treated at the Intensive Care Unit (ICU) with severe AKI and a need for renal replacement therapy (RRT) were examined. The hydration level was evaluated according to the ratio of extracellular water to total body water (ECW/TBW) of bioimpedance analysis and volemia was measured according to CVP. All of the patients were tested before the first hemodialysis (HD) procedure. Hyperhydration was defined as ECW/TBW > 0.39 and hypervolemia as CVP > 12 cm H₂O. Results: According to bioimpedance analysis, 72.3% (n = 34) of patients were hyperhydrated. According to CVP, only 51.1% (n = 24) of the patients were hypervolemic. Interestingly, 69.6% of hypovolemic/normovolemic patients were also hyperhydrated. Of all study patients, 57.4% (n = 27) died, in 29.8% (n = 14) the kidney function improved, and in 12.8% (n = 6) the demand for RRT remained after in-patient treatment. A tendency of higher mortality in hyperhydrated patients was observed, but no association between hypervolemia and outcomes of severe AKI was established. Conclusions: Three-fourths of the patients with severe AKI were hyperhydrated based on bioimpedance analysis. However, according to CVP, only half of these patients were hypervolemic. A tendency of higher mortality in hyperhydrated patients was observed.

Assessing volume responsiveness using right ventricular dynamic indicators of preload

PURPOSE

Dynamic indicators of preload currently only do reflect preload requirements of the left ventricle. To date, no dynamic indicators of right ventricular preload have been established. The aim of this study was to calculate dynamic indicators of right ventricular preload and assess their ability to predict ventricular volume responsiveness.

MATERIALS AND METHODS

The study was designed as experimental trial in 20 anaesthetized pigs. Micro-tip catheters and ultrasonic flow probes were used as experimental reference to enable measurement of right ventricular stroke volume and pulse pressure. Hypovolemia was induced (withdrawal of blood 20 ml/kg) and thereafter three volume-loading steps were performed. ROC analysis was performed to assess the ability of dynamic right ventricular parameters to predict volume response.

RESULTS

ROC analysis revealed an area under the curve (AUC) of 0.82 (CI 95% 0.73-0.89; p < 0.001) for right ventricular stroke volume variation (SVV_RV), an AUC of 0.72 (CI 95% 0.53-0.85; p = 0.02) for pulmonary artery pulse pressure variation (PPV_PA) and an AUC of 0.66 (CI 95% 0.51-0.79; p = 0.04) for pulmonary artery systolic pressure variation (SPV_PA).

CONCLUSIONS

In our experimental animal setting, calculating dynamic indicators of right ventricular preload is possible and appears promising in predicting volume responsiveness.

Central Venous Pressure Estimation by Ultrasound Measurement of Inferior Vena Cava and Aorta Diameters in Pediatric Critical Patients: An Observational Study

OBJECTIVES

To evaluate the ability to predict central venous pressure by ultrasound measured inferior vena cava and aortic diameters in a PICU population and to assess interoperator concordance.

DESIGN

Noninterventional observational study.

SETTING

PICU of a tertiary-care academic center.

PATIENTS

Eighty-eight pediatric patients (0-16 yr old) with a central venous catheter in place were studied. Sixty-nine percent of the patients received positive-pressure ventilation.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

An experienced and a nonexperienced operator used ultrasound to measure the maximal diameter of inferior vena cava and minimal diameter of the inferior vena cava and the maximum diameter of the abdominal aorta from the subxiphoid window. The inferior vena cava collapsibility index and the ratio of maximal diameter of inferior vena cava/maximum diameter of the abdominal aorta were then derived. The central venous pressure was measured using a central venous catheter and recorded. Twenty-three patients had low central venous pressure values (≤ 4 mm Hg), 35 patients a value in the range of 5-9 mm Hg, and 30 patients high values (≥ 10 mm Hg). Both inferior vena cava collapsibility index and ratio of maximal diameter of inferior vena cava/maximum diameter of the abdominal aorta were predictive of high (≥ 10 mm Hg) or low (≤ 4 mm Hg) central venous pressure. The test accuracy showed the best results in predicting low central venous pressure with an inferior vena cava collapsibility index greater than or equal to 35% and ratio of maximal diameter of inferior vena cava/maximum diameter of the abdominal aorta less than or equal to 0.8, and in predicting high central venous pressure with an inferior vena cava collapsibility index less than or equal to 20% and ratio of maximal diameter of inferior vena cava/maximum diameter of the abdominal aorta greater than or equal to 1.3. Inferior vena cava collapsibility index returned generally higher accuracy values than ratio of maximal diameter of inferior vena cava/maximum diameter of the abdominal aorta. Lin's coefficient of concordance between the operators was 0.78 for inferior vena cava collapsibility index and 0.86 for ratio of maximal diameter of inferior vena cava/maximum diameter of the abdominal aorta.

CONCLUSIONS

Inferior vena cava collapsibility index and ratio of maximal diameter of inferior vena cava/maximum diameter of the abdominal aorta correlate well with central venous pressure measurements in this PICU population, and specific inferior vena cava collapsibility index or ratio of maximal diameter of inferior vena cava/maximum diameter of the abdominal aorta thresholds appear to be able to differentiate children with high or low central venous pressure. However, the actual clinical application of these statistically significant results remains limited, especially by the intrinsic flaws of the procedure.

This is your toolkit in hemodynamic monitoring

PURPOSE OF REVIEW

To appraise the basic and more advanced methods available for hemodynamic monitoring, and describe the definitions and criteria for the use of hemodynamic variables.

RECENT FINDINGS

The hemodynamic assessment in critically ill patients suspected of circulatory shock follows a step-by-step algorithm to help determine diagnosis and prognosis. Determination of accurate diagnosis and prognosis in turn is crucial for clinical decision-making. Basic monitoring involving clinical examination in combination with hemodynamic variables obtained with an arterial catheter and a central venous catheter may be sufficient for the majority of patients with circulatory shock. In case of uncertainty of the underlying cause or to guide treatment in severe shock may require additional advanced hemodynamic technologies, and each is utilized for different indications and has specific limitations. Future developments include refining the clinical examination and performing studies that demonstrate better patient outcomes by targeting hemodynamic variables using advanced hemodynamic monitoring.

SUMMARY

Determination of accurate diagnosis and prognosis for patients suspected of circulatory shock is essential for optimal decision-making. Numerous techniques are available, and each has its specific indications and value.

B-Lines Scores Derived From Lung Ultrasound Provide Accurate Prediction of Extravascular Lung Water Index: An Observational Study in Critically Ill Patients

Introduction:

Visualization of B-lines via lung ultrasound provides a non-invasive estimation of pulmonary hydration. Extravascular lung water index (EVLWI) and pulmonary vascular permeability index (PVPI) assessed by transpulmonary thermodilution (TPTD) represent the most validated parameters of lung water and alveolocapillary permeability, but measurement is invasive and expensive. This study aimed to compare the correlations of B-lines scores from extensive 28-sector and simplified 4-sector chest scan with EVLWI and PVPI derived from TPTD in the setting of intensive care unit (primary endpoint).

Methods:

We performed scoring of 28-sector and 4-sector B-Lines in 50 critically ill patients. TPTD was carried out with the PiCCO-2-device (Pulsion Medical Systems SE, Maquet Getinge Group). Median time exposure for ultrasound procedure was 12 minutes for 28-sector and 4 minutes for 4-sector scan.

Results:

Primarily, we found close correlations of 28-sector as well as 4-sector B-Lines scores with EVLWI (R² = 0.895 vs. R² = 0.880) and PVPI (R² = 0.760 vs. R² = 0.742). Both B-lines scores showed high accuracy to identify patients with specific levels of EVLWI and PVPI. The extensive 28-sector B-lines score revealed a moderate advantage compared to simplified 4-sector scan in detecting a normal EVLWI ≤ 7 (28-sector scan: sensitivity = 81.8%, specificity = 94.9%, AUC = 0.939 versus 4-sector scan: sensitivity = 81.8%, specificity = 82.1%, AUC = 0.902). Both protocols were approximately equivalent in prediction of lung edema with EVLWI ≥ 10 (28-sector scan: sensitivity = 88.9%, specificity = 95.7%, AUC = 0.977 versus 4-sector scan: sensitivity = 81.5%, specificity = 91.3%, AUC = 0.958) or severe pulmonary edema with EVLWI ≥ 15 (28-sector scan: sensitivity = 91.7%, specificity = 97.4%, AUC = 0.995 versus 4-sector scan: sensitivity = 91.7%, specificity = 92.1%, AUC = 0.978). As secondary endpoints, our evaluations resulted in significant associations of 28-sector as well as simplified 4-sector B-Lines score with parameters of respiratory function.

Conclusion:

Both B-line protocols provide accurate non-invasive evaluation of lung water in critically ill patients. The 28-sector scan offers a marginal advantage in prediction of pulmonary edema, but needs substantially more time than 4-sector scan.

Understanding preload and preload reserve within the conceptual framework of a limited range of possible left ventricular end-diastolic volumes

Preload has been variously defined, but if there is to be a direct relationship with activity of the Frank-Starling mechanism in its action to increase the force and extent of contraction, preload must directly reflect myocardial stretch. The Frank-Starling mechanism is activated during any stretch of a cardiac chamber beyond its resting size, which is present immediately before contraction. Every left ventricle has an intrinsic and limited range of possible volumes at end diastole. There is a curvilinear relationship between left ventricular (LV) end-diastolic pressure (LVEDP) and LV end-diastolic volume (LVEDV), and, at maximal or near maximal LVEDV, there will be a high LVEDP. Within the possible range, the LVEDV will be determined by the extent of filling, any change in LVEDV will result in changed activity of the Frank-Starling mechanism, and change in LVEDV might, therefore, be considered to represent change in preload. On the other hand, it is the difference between the current and the maximal possible LVEDV (or the preload reserve) that may be of the most clinical relevance. There is a reciprocal relationship between preload and preload reserve, with minor or absent LV preload reserve indicating that there will be either minimal or no increase in stroke volume following intravenous fluid administration. As left atrial pressure can remain within the normal range when the LVEDP is elevated, it is LVEDP, and not left atrial pressure, that provides the most reliable guide to preload reserve in an individual at a specific period in time.

Contraction of atrial smooth muscle reduces cardiac output in perfused turtle hearts

Unusual undulations in resting tension (tonus waves) were described in isolated atria from freshwater turtles more than a century ago. These tonus waves were soon after married with the histological demonstration of a rich layer of smooth muscle on the luminal side of the atrial wall. Research thereafter waned and the functional significance of this smooth muscle has remained obscure. Here, we provide evidence that contraction of the smooth muscle in the atria may be able to change cardiac output in turtle hearts. In in situ perfused hearts of the red-eared slider turtle (Trachemys scripta elegans), we demonstrated that activation of smooth muscle contraction with histamine (100 nmol kg^-1 bolus injected into perfusate) reduced cardiac output by decreasing stroke volume (>50% decrease in both parameters). Conversely, inhibition of smooth muscle contraction with wortmannin (10 µmol l^-1 perfusion) approximately doubled baseline stroke volume and cardiac output. We suggest that atrial smooth muscle provides a unique mechanism to control cardiac filling that could be involved in the regulation of stroke volume during diving.

Renal failure in critically ill patients, beware of applying (central venous) pressure on the kidney

The central venous pressure (CVP) is traditionally used as a surrogate of intravascular volume. CVP measurements therefore are often applied at the bedside to guide fluid administration in postoperative and critically ill patients. Pursuing high CVP levels has recently been challenged. A high CVP might impede venous return to the heart and disturb microcirculatory blood flow which may cause tissue congestion and organ failure. By imposing an increased "afterload" on the kidney, an elevated CVP will particularly harm kidney hemodynamics and promote acute kidney injury (AKI) even in the absence of volume overload. Maintaining the lowest possible CVP should become routine to prevent and treat AKI, especially when associated with septic shock, cardiac surgery, mechanical ventilation, and intra-abdominal hypertension.

A Quality Control Study of the Adherence to Recommended Physiological Targets for the Management of Brain-Dead Organ Donors in South Australian Intensive Care Units

BACKGROUND

The Australian and New Zealand Intensive Care Society and the Australasian Transplant Coordinators Association provide recommendations on the physiological management of brain-dead donors.

PROBLEM STATEMENT

How often physiological targets are prescribed for brain-dead donors in Australian intensive care units (ICUs), and how well these compare to recommended targets is unknown. It is also unknown how often recommended targets are achieved, irrespective of prescribed targets.

METHODS

We performed a retrospective, observational quality control study in 81 adult (>18 years) brain-dead donors to describe how often physiological targets were prescribed, comparing these to current guidelines. We determined the proportion of observations within the recommended target range, irrespective of any prescribed target. We aimed to identify poor adherence to recommended targets to guide future quality improvement initiatives.

OUTCOMES

Seventy-four (91%) donors had at least 1 prescribed physiological target written on the ICU chart, with a median of 2 (range 2-5), and a maximum of 13 targets. Prescribed targets appeared to adhere well with recommended targets. Most recommended physiological targets were met irrespective of any prescribed target. However, one-quarter of serum sodium observations and one-third of blood glucose levels were above the recommended target.

IMPLICATIONS FOR PRACTICE

Quality improvement initiatives are required to improve the prescription of physiological targets in brain-dead donors in South Australia. Serum sodium and serum glucose targets were not met. However, this most likely reflects the need for current guidelines to be updated in line with current evidence.

Tricuspid annular plane systolic excursion and central venous pressure in mechanically ventilated critically ill patients

Background

The tricuspid annular plane systolic excursion (TAPSE) is commonly recommended for estimating the right ventricular systolic function. The central venous pressure (CVP), which is determined by venous return and right heart function, was found to be associated with right ventricular outflow fractional shortening. This study thus aimed to investigate the relationship between the TAPSE and CVP in mechanically ventilated critically ill patients.

Methods

This is a prospective observational study. From October 1 to December 31, 2017, patients admitted to the intensive care unit with CVP monitoring and controlled mechanical ventilation were screened for enrolment. Echocardiographic parameters, including the TAPSE, mitral annular plane systolic excursion (MAPSE), left ventricular ejection fraction (LVEF), and internal diameter of inferior vena cava (dIVC), and haemodynamic parameters, including the CVP, were collected.

Results

Seventy-four patients were included. Thirty-one were included in the low LVEF (< 55%) group, and 43 were included in the high LVEF (≥55%) group. In the high LVEF group, the TAPSE and CVP were not correlated (r = − 0.234, P = 0.151). In the low LVEF group, partial correlation analysis indicated that the TAPSE and CVP were correlated (r = − 0.516, P = 0.006), and multivariable linear regression analysis indicated that the TAPSE was independently associated with the CVP (standard coefficient: − 0.601, p < 0.001). Additionally, in the low LVEF group, a ROC analysis showed that the area under the curve of the TAPSE for the detection of CVP greater than 8 mmHg was 0.860 (95% confidence interval: 0.730–0.991; P = 0.001). The optimum cut-off value was 1.52 cm, which resulted in a sensitivity of 75.0%, a specificity of 86.7%, a positive predictive value of 84.6% and a negative predictive value of 77.8%.

Conclusions

The TAPSE is inversely correlated with the CVP in mechanically ventilated critically ill patients who have a LVEF less than 55%.

Fluid therapy in the emergency department: an expert practice review

Intravenous fluid therapy is one of the most common therapeutic interventions performed in the ED and is a long-established treatment. The potential benefits of fluid therapy were initially described by Dr W B O’Shaughnessy in 1831 and first administered to an elderly woman with cholera by Dr Thomas Latta in 1832, with a marked initial clinical response. However, it was not until the end of the 19th century that medicine had gained understanding of infection risk that practice became safer and that the practice gained acceptance. The majority of fluid research has been performed on patients with critical illness, most commonly sepsis as this accounts for around two-thirds of shocked patients treated in the ED. However, there are few data to guide clinicians on fluid therapy choices in the non-critically unwell, by far our largest patient group. In this paper, we will discuss the best evidence and controversies for fluid therapy in medically ill patients.

Impact of large volume paracentesis on respiratory parameters including transpulmonary pressure and on transpulmonary thermodilution derived hemodynamics: A prospective study

Introduction

Appropriate mechanical ventilation and prevention of alveolar collaps is mainly dependent on transpulmonary pressure TPP. TPP is assessed by measurement of esophageal pressure EP, largely influenced by pleural and intraabdominal pressure IAP. Consecutively, TPP-guided ventilation might be particularly useful in patients with high IAP.

This study investigates the impact of large volume paracentesis LVP on TPP, EP, IAP as well as on hemodynamic and respiratory function in patients with liver cirrhosis and tense ascites.

Material and methods

We analysed 23 LVP-procedures in 11 cirrhotic patients ventilated with the AVEA Viasys respirator (CareFusion, USA) which is capable to measure EP via an esophageal tube.

Results

LVP of a mean volume of 4826±1276 mL of ascites resulted in marked increases in inspiratory (17.9±8.9 vs. 5.4±13.3 cmH₂O; p<0.001) as well as expiratory TPP (-3.0±4.7 vs. -15.9±10.9 cmH₂O; p<0.001; primary endpoint). In parallel, the inspiratory (2.4±8.7 vs. 14.1±14.5 cmH₂O; p<0.001) and expiratory EP (12.4±6.0 vs. 24.9±11.3 cmH₂O; p<0.001) significantly decreased. The effects were most pronounced for the release of the first 500 mL of ascites. LVP evoked substantial decreases in IAP and central venous pressure CVP. By contrast, mean arterial pressure, cardiac index, global end-diastolic volume index, extravascular lung water index and systemic vascular resistance index did not change.

Among the respiratory parameters we observed an increase in p_aO₂/F_iO₂ (247.7±60.9 vs. 208.3±46.8 mmHg; p<0.001) and a decrease in Oxygenation Index OI (4.8±2.0 vs. 5.8±3.1 cmH₂O/mmHg; p = 0.002). Tidal volume (510±100 vs. 452±113 mL; p = 0.008) and dynamic respiratory system compliance C_dyn (46.8±15.9 vs. 35.1±14.6 mL/cmH₂0; p<0.001) increased, whereas p_aCO₂ (47.3±10.7 vs. 51.2±12.3mmHg; p = 0.046) and the respiratory rate decreased (17.1±7.3 vs. 19.6±7.8 min^-1; p = 0.010).

Conclusions

In mechanically ventilated patients with decompensated cirrhosis, intraabdominal hypertension resulted in a substantially decreased TPP despite PEEP-setting according to the ARDSNet.

In these patients LVP markedly increased TPP and improved respiratory function in parallel with a decline of EP. Furthermore, LVP induced a decrease in IAP and CVP, while other hemodynamic parameters did not change.

Next-generation, personalised, model-based critical care medicine: a state-of-the art review of in silico virtual patient models, methods, and cohorts, and how to validation them

Critical care, like many healthcare areas, is under a dual assault from significantly increasing demographic and economic pressures. Intensive care unit (ICU) patients are highly variable in response to treatment, and increasingly aging populations mean ICUs are under increasing demand and their cohorts are increasingly ill. Equally, patient expectations are growing, while the economic ability to deliver care to all is declining. Better, more productive care is thus the big challenge. One means to that end is personalised care designed to manage the significant inter- and intra-patient variability that makes the ICU patient difficult. Thus, moving from current "one size fits all" protocolised care to adaptive, model-based "one method fits all" personalised care could deliver the required step change in the quality, and simultaneously the productivity and cost, of care. Computer models of human physiology are a unique tool to personalise care, as they can couple clinical data with mathematical methods to create subject-specific models and virtual patients to design new, personalised and more optimal protocols, as well as to guide care in real-time. They rely on identifying time varying patient-specific parameters in the model that capture inter- and intra-patient variability, the difference between patients and the evolution of patient condition. Properly validated, virtual patients represent the real patients, and can be used in silico to test different protocols or interventions, or in real-time to guide care. Hence, the underlying models and methods create the foundation for next generation care, as well as a tool for safely and rapidly developing personalised treatment protocols over large virtual cohorts using virtual trials. This review examines the models and methods used to create virtual patients. Specifically, it presents the models types and structures used and the data required. It then covers how to validate the resulting virtual patients and trials, and how these virtual trials can help design and optimise clinical trial. Links between these models and higher order, more complex physiome models are also discussed. In each section, it explores the progress reported up to date, especially on core ICU therapies in glycemic, circulatory and mechanical ventilation management, where high cost and frequency of occurrence provide a significant opportunity for model-based methods to have measurable clinical and economic impact. The outcomes are readily generalised to other areas of medical care.

Role of central venous pressure monitoring in critical care settings

Central venous pressure (CVP) monitoring is used to assess the fluid status of patients in critical care settings. This article explains CVP monitoring, discussing the rationale for its use, the ways CVP can be measured, and the physiological factors that can affect the reliability and validity of CVP measurement. It also discusses the complications associated with CVP monitoring and the nursing responsibilities in relation to this activity.

Stroke volume variation (SVV) and pulse pressure variation (PPV) as indicators of fluid responsiveness in sevoflurane anesthetized mechanically ventilated euvolemic dogs

Changes in stroke volume variation (SVV) and pulse pressure variation (PPV) in response to fluid infusion were experimentally evaluated during vecuronium infusion and sevoflurane anesthesia in 5 adult, mechanically ventilated, euvolemic, beagle dogs. Sequential increases in central venous pressure (CVP; 3-7[baseline], 8-12, 13-17, 18-22 and 23-27 mmHg) were produced by infusing lactated Ringer's solution and 6% hydroxyethyl starch solution. Heart rate (beats/min), right atrial pressure (RAP, mmHg), pulmonary arterial pressure (PAP, mmHg), pulmonary capillary wedge pressure (PCWP, mmHg), transpulmonary thermodilution cardiac output (TPTDCO, l/min), stroke volume (SV, ml/beat), arterial blood pressure (ABP, mmHg), extravascular lung water (EVLW, ml), pulmonary vascular permeability index (PVPI, calculated), SVV (%), PPV (%) and systemic vascular resistance (SVR, dynes/sec/cm⁵) were determined at each predetermined CVP range. Heart rate (P=0.019), RAP (P<0.001), PAP (P<0.001), PCWP (P<0.001), TPTDCO (P=0.009) and SV (P=0.04) increased and SVR (P<0.001), SVV (P<0.001) and PPV (P<0.001) decreased associated with each stepwise increase in CVP. Arterial blood pressure, EVLW, PVPI and the arterial partial pressures of oxygen and carbon dioxide did not change. The changes in SVV and PPV directly reflected the fluid load and the minimum threshold values for detecting fluid responsiveness were SVV ≥11% and PPV ≥7% in dogs.

Right Atrial Pressure in the Critically Ill: How to Measure, What Is the Value, What Are the Limitations?

Right atrial pressure (P_ra) is determined by the interaction of the function of the heart as a pump, which is called cardiac function, and the factors that determine the return of blood to the heart, which is called return function. Thus, monitoring P_ra or its surrogate, central venous pressure (CVP), can give important insights into mechanisms behind changes in hemodynamic status, responses to interventions, and the likelihood of diagnoses. Examination of the components of the P_ra tracing, especially during the ventilator cycle, can also give information about right-sided cardiac diastolic function, the status of the tricuspid valve, volume responsiveness, and the cardiac rhythm. Importantly, the pressure difference from the large venous reservoir to the heart is small, and thus great care must be taken with technical factors that affect the measurement.

Systemic hemodynamics in advanced cirrhosis: Concerns during perioperative period of liver transplantation

Advanced liver cirrhosis is usually accompanied by portal hypertension. Long-term portal hypertension results in various vascular alterations. The systemic hemodynamic state in patients with cirrhosis is termed a hyperdynamic state. This peculiar hemodynamic state is characterized by an expanded blood volume, high cardiac output, and low total peripheral resistance. Vascular alterations do not disappear even long after liver transplantation (LT), and recipients with cirrhosis exhibit a persistent systemic hyperdynamic state even after LT. Stability of optimal systemic hemodynamics is indispensable for adequate portal venous flow (PVF) and successful LT, and reliable parameters for optimal systemic hemodynamics and adequate PVF are required. Even a subtle disorder in systemic hemodynamics is precisely indicated by the balance between cardiac output and blood volume. The indocyanine green (ICG) kinetics reflect the patient’s functional hepatocytes and effective PVF, and PVF is a major determinant of the ICG elimination constant (kICG) in the well-preserved allograft. The kICG value is useful to set the optimal PVF during living-donor LT and to evaluate adequate PVF after LT. Perioperative management has a large influence on the postoperative course and outcome; therefore, key points and unexpected pitfalls for intensive management are herein summarized. Transplant physicians should fully understand the peculiar systemic hemodynamic behavior in LT recipients with cirrhosis and recognize the critical importance of PVF after LT.

Hypotension and hypovolemia during hemodialysis: is the usual suspect innocent?

Hypotension during intermittent hemodialysis is common, and has been attributed to acute volume shifts, shifts in osmolarity, electrolyte imbalance, temperature changes, altered vasoregulation, and sheer hypovolemia. Although hypovolemia may intuitively seem a likely cause for hypotension in intensive care patients, its role in the pathogenesis of intradialytic hypotension may be overestimated.