Volume status and volume responsiveness in postoperative cardiac surgical patients: An observational, multicentre cohort study.

BACKGROUND: The best strategy to identify patients in whom fluid loading increases cardiac output (CO) following cardiac surgery remains debated. This study examined the utility of a calculated mean systemic filling pressure analogue (Pmsa ) and derived variables to explain the response to a fluid bolus. METHODS: The Pmsa was calculated using retrospective, observational cohort data in the early postoperative period between admission to the intensive care unit and extubation within 6 hours. The venous return pressure gradient (VRdP) was calculated as Pmsa  - central venous pressure. Concurrent changes induced by a fluid bolus in the ratio of the VRdP over Pmsa , the volume efficiency (Evol ), were studied to assess fluid responsiveness. Changes between Pmsa and derived variables and CO were analysed by Wilcoxon rank-sum test, hierarchial clustering and multiple linear regression. RESULTS: Data were analysed for 235 patients who received 489 fluid boluses. The Pmsa increased with consecutive fluid boluses (median difference [range] 1.3 [0.5-2.4] mm Hg, P = .03) with a corresponding increase in VRdP (median difference 0.4 [0.2-0.6] mm Hg, P = .04). Hierarchical cluster analysis only identified Evol and the change in CO within one cluster. The multiple linear regression between Pmsa and its derived variables and the change in CO (overall r2  = .48, P < .001) demonstrated the best partial regression between the continuous change in CO and the concurrent Evol (r = .55, P < .001). CONCLUSION: The mean systemic filling Pmsa enabled a comprehensive interpretation of fluid responsiveness with volume efficiency useful to explain the change in CO as a continuous phenomenon.

Assessment of volume status and volume responsiveness in the ICU: Protocol for an observational, multicentre cohort study.

BACKGROUND: Expansion of the intravascular compartment is common to treat haemodynamic instability in ICU patients. The most useful and accurate variables to guide and evaluate a fluid challenge remain debated and incompletely investigated resulting in significant variability in practice. The analogue mean systemic pressure has been reported as a measure of the intravascular volume state. METHODS: This is a protocol and statistical analysis plan for a review of the application of an analogue of the mean systemic pressure and the use of derived variables to assess the volume state and volume responsiveness. A pulmonary artery catheter was used in 286 postoperative cardiac surgical patients to monitor cardiac output before and after a fluid bolus in addition to arterial and central venous pressures. With otherwise similar monitoring, echocardiography was used in 540 general ICU patients to determine cardiac outputs and indices related to intravascular filling. The responses to a fluid bolus or the passive leg raising manoeuvre will be investigated using continuous and dichotomous definitions of volume responsiveness. The results will be stratified according to the method of monitoring cardiac output. CONCLUSIONS: This study investigating 2 cohorts that encompass a wide variety of reasons for haemodynamic instability will illustrate the applicability of the analogue mean systemic pressure and derived variables to assess the volume state and responsiveness. The results may guide the rationale and design of interventional studies.

Central venous pressure: soon an outcome-associated matter.

PURPOSE OF REVIEW: Central venous pressure (CVP) alone has so far not found a place in outcome prediction or prediction of fluid responsiveness. Improved understanding of the interaction between mean systemic pressure (Pms) and CVP has major implications for evaluating volume responsiveness, heart performance and potentially patient outcomes. RECENT FINDINGS: The literature review substantiates that CVP plays a decisive role in causation of operative haemorrhage and renal failure. The review details CVP as a variable integral to cardiovascular control in its dual role of distending the diastolic right ventricle and opposing venous return. SUMMARY: The implication for practice is in the regulation of the circulation. It is demonstrated that control of the blood pressure and cardiac output/venous return calls upon regulation of the volume state (Pms), the heart performance (Eh) and the systemic vascular resistance. Knowledge of the CVP is required to calculate all three.

Comparison of echocardiographic and invasive measures of volaemia and cardiac performance in critically ill patients.

Echocardiographic measurements are used in critical care to evaluate volume status and cardiac performance. Mean systemic filling pressure and global heart efficiency measures intravascular volume and global heart function. This prospective study conducted in fifty haemodynamically stabilized, mechanically ventilated patients investigated relationships between static echocardiographic variables and estimates of global heart efficiency and mean systemic filling pressure. Results of univariate analysis demonstrated weak correlations between left ventricular end-diastolic volume index (r = 0.27, p = 0.04), right atrial volume index (rho = 0.31, p = 0.03) and analogue mean systemic filling pressure; moderate correlations between left ventricular ejection fraction (r = 0.31, p = 0.03), left ventricular global longitudinal strain (r = 0.36, p = 0.04), tricuspid annular plane systolic excursion (rho = 0.37, p = 0.01) and global heart efficiency. No significant correlations were demonstrated by multiple regression. Mean systemic filling pressure calculated with cardiac output measured by echocardiography demonstrated good agreement and correlation with invasive techniques (bias 0.52 ± 1.7 mmHg, limits of agreement -2.9 to 3.9 mmHg, r = 0.9, p < 0.001). Static echocardiographic variables did not reliably reflect the volume state as defined by estimates of mean systemic filling pressure. The agreement between static echocardiographic variables of cardiac performance and global heart efficiency lacked robustness. Echocardiographic measurements of cardiac output can be reliably used in calculation of mean systemic filling pressure.

"Likely overassistance" during invasive pressure support ventilation in patients in the intensive care unit: a multicentre prospective observational study.

OBJECTIVE: To evaluate the prevalence of "likely overassistance" (categorised by respiratory rate [RR] ≤ 17 breaths/min or rapid shallow breathing index [RSBI] ≤ 37 breaths/min/L) during invasive pressure support ventilation (PSV), and the additional prevalence of fixed ventilator settings. DESIGN: Multicentre prospective observational study of invasive PSV practice in six general Victorian intensive care units with blinding of staff members to data collection. PATIENTS: At each hospital, investigators collected data between 11 am and 2 pm on all invasive PSV-treated patients on 60 sequential days, excluding weekends and public holidays, between 22 February and 30 August 2017. Each patient was included for maximum of 3 days. MAIN RESULTS: We studied 231 patients, with a total of 379 observations episodes over the study period. There were 131 patients (56.7%) with at least one episode of RR ≤ 17 breaths/min; 146 patients (63.2%) with at least one episode of RSBI ≤ 37 breaths/min/L, and 85 patients (36.8%) with at least one episode of combined RR ≤ 17 breaths/min and RSBI ≤ 37 breaths/min/L. Moreover, the total number of observations with "likely overassistance" (RR ≤ 17 or RSBI ≤ 37 breaths/min/L) was 178 (47%) and 204 (53.8%), respectively; while for both combined criteria, it was 154 (40.6%). We also found that 10 cmH2O pressure support was delivered on 210 of the observations (55.4%) and adjusted in less than 25% of observations. Finally, less than half (179 observations) of all PSV-delivered tidal volumes (VT) were at the recommended value of 6-8 mL/kg predicted body weight (PBW) and more than 20% (79 observations) were at ≥ 10 mL/kg PBW. CONCLUSION: In a cohort of Victorian hospitals in Australia, during invasive PSV, "likely overassistance" was common, and the pressure support level was delivered in a standardised and unadjusted manner at 10 cmH2O, resulting in the frequent delivery of potentially injurious VT.

Applying mean systemic filling pressure to assess the response to fluid boluses in cardiac post-surgical patients.

PURPOSE: To evaluate an analogue of mean systemic filling pressure (P(msa)) and derived variables to quantitatively assess the effectiveness of volume expansion in increasing cardiac output. METHODS: Sixty-one cardiac post-surgical patients were studied and 107 fluid boluses were captured. Cardiac output, mean arterial pressure and right atrial pressure were recorded with P msa before and after a bolus fluid. An increase in cardiac output greater than 10 % following a fluid bolus defined a patient as a responder. Cardiac power (i.e. the product of arterial pressure and cardiac output) and P(msa) to right atrial pressure gradient (i.e. the driving pressure for venous return and hence cardiac output) were evaluated to assess the efficiency of volume expansion to increase cardiac output. Cardiac power relative to P(msa) (CP(vol)), its dynamic changes and the dynamic changes in P msa-right atrial pressure gradient relative to the P(msa) change (E(vol)) were investigated. RESULTS: CP(vol) was lower and E(vol) was higher in responders vs. non-responders. Furthermore, in patients receiving a second fluid bolus, E(vol) correlated with the degree of increase in cardiac output. Multivariate regression analysis identified both CP(vol) and E(vol) as independent variables associated with volume responsiveness. CONCLUSIONS: Using an algorithm to derive a mean systemic filling pressure analogue, cardiac power and dynamic measures of the venous return pressure gradient relative to the mean systemic filling pressure provided an assessment of the efficiency of volume expansion in post-surgical cardiac patients.

Geriatric critical care.

Demographic compulsions are inescapable. There has been a 50% increase in life expectancy at birth for persons born in 1980 compared to those born in 1900. Not only do critical care units utilize up to a third of hospital expenditures and about 1% of GNP, the critically ill elderly consume a disproportionate amount of ICU resources. Outcome prediction models for very elderly critically ill patients have been proposed with age as one of numerous model variables; but such models have not been widely validated. Despite the burgeoning emphasis on evidence-based population approach to health care, there is insufficient research to guide the critical care clinician. There remains a modicum of subjectivity in crucial decisions that affect the elderly patient receiving intensive care. Older age is also one of the factors that lead to a physician bias in refusing ICU admission; this has recently been borne out in a multivariate analysis. Physicians generally consider their older patients' quality of life to be worse than do the patients, although other studies that have assessed the quality of live show no age-related differences among ICU survivors. Furthermore, physicians' estimations of patient quality of life significantly influence physicians' attitudes to futility of care issues, in contrast to patients' perceptions. Threshold for life-sustaining treatment in the elderly will continue to be different among the ICUs. In critical care of the elderly, geography may well be destiny. Clinical decisions will be subjected to many ethical, legal, and socioeconomic pressures. Personal and religious beliefs will inevitably influence societal expectations and clinician practices. Severity of illness has the biggest influence on outcome in a critical illness. Age alone is not a predictor of short-term or long-term outcome in the older patient who is critically ill. Critical illness in the elderly remains a fertile area for future research.