Normovolemia defined according to cardiac stroke volume in healthy supine humans

Prediction of fluid responsiveness in spontaneously breathing patients with hemodynamic stability: a prospective repeated-measures study

Evaluating fluid responsiveness with dynamic parameters is recommended for fluid management. However, in hemodynamically stable patients who are breathing spontaneously, accurately measuring stroke volume variation via echocardiography and passive leg raising is challenging due to subtle SV changes. This study aimed to identify normal SV changes in healthy volunteers and evaluate the precision of hemodynamic parameters in screening mild hypovolemia in patients. This prospective, repeated-measures, cross-sectional study screened 269 subjects via echocardiography. Initially, 45 healthy volunteers underwent a fluid challenge test, the outcomes of which served as criteria to screen 215 ICU patients. Among these patients, 53 underwent additional fluid challenge testing. Hemodynamic parameters, including medians of maximum velocity time integrals (VTImaxs), peak velocity of VTImax (PV), internal jugular vein diameters (IJVD), and area (IJVA) were repeatedly measured first at a 60° upper body elevation (UBE), second in a supine position, third at UBE, fourth in a supine position, and lastly in a supine position after fluid loading. The hemodynamic responses to the position changes were compared between 83 fluid non-responders and 15 fluid responders. Fluid responsiveness was defined as fluid-induced medians' change of VTImaxs (fluid-induced median VTImax change) ≥ 10%. None of the healthy volunteers showed the mean value of repeatedly measured medians of VTImaxs ≥ 7%, following either UBE position (UBE-induced median VTImax change) or fluid loading (fluid-induced median VTImax change). UBE-induced median VTImax and PV changes were significantly correlated with fluid responsiveness (p < 0.001, AUC 0.959; p < 0.001, AUC 0.804). The significant correlations were demonstrated via multivariable analysis using binary logistic regression (p = 0.001, OR 90.1) and the correlation coefficient (R2 = 0.793) using linear regression analysis. UBE-induced median VTImax changes (≥ 11.8% and 7.98%) predicted fluid-induced median VTImax changes ≥ 10% and 7% (AUC 0.959 and 0.939). The collapsibility and variation of IJVD and IJVA showed no significant correlation. An increase in the mean value of medians of repeatedly measured VTImaxs transitioning from an UBE to a supine position, effectively screened mild hypovolemia and demonstrated a significant correlation with fluid responsiveness in spontaneously breathing patients maintaining hemodynamic stability.

Mid‐regional plasma pro‐atrial natriuretic peptide and stroke volume responsiveness for detecting deviations in central blood volume following major abdominal surgery

Background

A reduced central blood volume is reflected by a decrease in mid‐regional plasma pro‐atrial natriuretic peptide (MR‐proANP), a stable precursor of ANP, and a volume deficit may also be assessed by the stroke volume (SV) response to head‐down tilt (HDT). We determined plasma MR‐proANP during major abdominal procedures and evaluated whether the patients were volume responsive by the end of the surgery, taking the fluid balance and the crystalloid/colloid ratio into account.

Methods

Patients undergoing pancreatic (n = 25), liver (n = 25), or gastroesophageal (n = 38) surgery were included prospectively. Plasma MR‐proANP was determined before and after surgery, and the fluid response was assessed by the SV response to 10^° HDT after the procedure. The fluid strategy was based mainly on lactated Ringer's solution for gastroesophageal procedures, while for pancreas and liver surgery, more human albumin 5% was administered.

Results

Plasma MR‐proANP decreased for patients undergoing gastroesophageal surgery (−9% [95% CI −3.2 to −15.3], p = .004) and 10 patients were fluid responsive by the end of surgery (∆SV > 10% during HDT) with an administered crystalloid/colloid ratio of 3.3 (fluid balance +1389 ± 452 ml). Furthermore, plasma MR‐proANP and fluid balance were correlated (r = .352 [95% CI 0.031–0.674], p < .001). In contrast, plasma MR‐proANP did not change significantly during pancreatic and liver surgery during which the crystalloid/colloid ratio was 1.0 (fluid balance +385 ± 478 ml) and 1.9 (fluid balance +513 ± 381 ml), respectively. For these patients, there was no correlation between plasma MR‐proANP and fluid balance, and no patient was fluid responsive.

Conclusion

Plasma MR‐proANP was reduced in fluid responsive patients by the end of surgery for the patients for whom the fluid strategy was based on more lactated Ringer's solution than human albumin 5%.

To identify normovolemia in humans: The stroke volume response to passive leg raising vs. head-down tilt

Volume responsiveness can be evaluated by tilting maneuvers such as head-down tilt (HDT) and passive leg raising (PLR), but the two procedures use different references (HDT the supine position; PLR the semi-recumbent position). We tested whether the two procedures identify "normovolemia" by evaluating the stroke volume (SV) and cardiac output (CO) responses and whether the peripheral perfusion index (PPI) derived from pulse oximetry provides similar information. In randomized order, 10 healthy men were exposed to both HDT and PLR, and evaluations were made also when the subjects fasted. Central cardiovascular variables were derived by pulse contour analysis and changes in central blood volume assessed by thoracic electrical admittance (TEA). During HDT, SV remained stable (fasted 110 ± 16 vs. 109 ± 16 ml; control 113 ± 16 vs. 111 ± 16 ml, p > 0.05) with no change in CO, TEA, PPI, or SV variation (SVV). In contrast during PLR, SV increased (fasted 108 ± 17 vs. 117 ± 17 ml; control 108 ± 18 vs. 117 ± 18 ml, p < 0.05) followed by an increase in TEA (p < 0.05) and CO increased when subjects fasted (6.7 ± 1.5 vs. 7.1 ± 1.5, p = 0.007) with no change in PPI or SVV. In conclusion, SV has a maximal value for rest in supine men, while PLR restores SV as CBV is reduced in a semi-recumbent position and the procedure thereby makes healthy volunteers seem fluid responsive.

The haemodynamic effects of crystalloid and colloid volume resuscitation on primary, derived and efficiency variables in post-CABG patients

Background

Recent studies in haemodynamic management have focused on fluid management and assessed its effects in terms of increase in cardiac output based on fluid challenges or variations in pulse pressure caused by cyclical positive pressure ventilation. The theoretical scope may be characterised as Starling-oriented. This approach ignores the actual events of right-sided excitation and left-sided response which is consistently described in a Guyton-oriented model of the cardiovascular system.

Aim

Based on data from a previous study, we aim to elucidate the primary response to crystalloid and colloid fluids in terms of cardiac output, mean blood pressure and right atrial pressure as well as derived and efficiency variables defined in terms of Guyton venous return physiology.

Method

Re-analyses of previously published data.

Results

Cardiac output invariably increased on infusion of crystalloid and colloid solutions, whereas static and dynamic efficiency measures declined in spite of increasing pressure gradient for venous return.

Discussion

We argue that primary as well as derived and efficiency measures should be reported and discussed when haemodynamic studies are reported involving fluid administrations.

The haemodynamic dilemma in emergency care: Is fluid responsiveness the answer? A systematic review

BACKGROUND

Fluid therapy is a common and crucial treatment in the emergency department (ED). While fluid responsiveness seems to be a promising method to titrate fluid therapy, the evidence for its value in ED is unclear. We aim to synthesise the existing literature investigating fluid responsiveness in ED.

METHODS

MEDLINE, Embase and the Cochrane library were searched for relevant peer-reviewed studies published from 1946 to present.

RESULTS

A total of 249 publications were retrieved of which 22 studies underwent full-text review and eight relevant studies were identified. Only 3 studies addressed clinical outcomes - including 2 randomised controlled trials and one feasibility study. Five articles evaluated the diagnostic accuracy of fluid responsiveness techniques in ED. Due to marked heterogeneity, it was not possible to combine results in a meta-analysis.

CONCLUSION

High quality, adequately powered outcome studies are still lacking, so the place of fluid responsiveness in ED remains undefined. Future studies should have standardisation of patient groups, the target response and the underpinning theoretic concept of fluid responsiveness. The value of a fluid responsiveness based fluid resuscitation protocol needs to be established in a clinical trial.

Postoperative volume balance: does stroke volume increase in Trendelenburg's position?

In healthy humans, stroke volume (SV) and cardiac output (CO) do not increase with expansion of the central blood volume by head-down tilt or administration of fluid. Here, we exposed 85 patients to Trendelenburg's position about one hour after surgery while cardiovascular variables were determined non-invasively by Modelflow. In Trendelenburg's position, SV (83 ± 19 versus 89 ± 20 ml) and CO (6·2 ± 1·8 versus 6·8 ± 1·8 l/min; both P<0·05) increased, while heart rate (75 ± 15 versus 76 ± 14 b min^-1 ) and mean arterial pressure were unaffected (84 ± 15 versus 84 ± 16 mmHg). For the 33 patients (39%) with a > 10% increase in SV (from 78 ± 16 to 90 ± 17 ml) corresponding to an increase in CO from 5·9 ± 1·5 to 6·9 ± 1·6 l min^-1 (P<0·05) when tilted head-down, administration of 250 ml Ringer's lactate solution increased SV (to 88 ± 18 ml) and CO (to 6·8 ± 1·7 l min^-1 ). In conclusion, determination of SV and/or CO in Trendelenburg's position can be used to evaluate whether a patient is in need of IV fluid as here exemplified after surgery.

A prospective observational study of stroke volume responsiveness to a passive leg raise manoeuvre in healthy non-starved volunteers as assessed by transthoracic echocardiography

Current guidelines for intra-operative fluid management recommend the use of increments in stroke volume following intravenous fluid bolus administration as a guide to subsequent fluid therapy. To study the physiological premise of this paradigm, we tested the hypothesis that healthy, non-starved volunteers would develop an increment in their stroke volume following a passive leg raise manoeuvre. Subjects were positioned supine and stroke volume was measured by transthoracic echocardiography at baseline, 30 s, 1 min, 3 min and 5 min after passive leg raise manoeuvre to 45°. Stroke volume was measured at end-expiration during quiet breathing, as the mean of three sequential measurements. Seventeen healthy volunteers were recruited; one volunteer in whom it was not possible to obtain Doppler measurements and a further five for reasons of poor Doppler image quality were not included in the study. Mean (SD) percentage difference from baseline to the largest change in stroke volume was 5.7 (9.6)% (p = 0.16). Of the 11 volunteers evaluated, five (45%) had stroke volume increases of greater than 10%. Mean (SD) maximum percentage change in cardiac index was 14.8 (9.7)% (p = 0.004). A wide variation in baseline stroke volume and response to the passive leg raise manoeuvre was seen, suggesting greater heterogeneity in the normal population than current clinical guidelines recognise.

O2 supplementation to secure the near-infrared spectroscopy determined brain and muscle oxygenation in vascular surgical patients: a presentation of 100 cases

This study addresses three questions for securing tissue oxygenation in brain (rScO2) and muscle (SmO2) for 100 patients (age 71 ± 6 years; mean ± SD) undergoing vascular surgery: (i) Does preoxygenation (inhaling 100% oxygen before anesthesia) increase tissue oxygenation, (ii) Does inhalation of 70% oxygen during surgery prevent a critical reduction in rScO2 (<50%), and (iii) is a decrease in rScO2 and/or SmO2 related to reduced blood pressure and/or cardiac output?Intravenous anesthesia was provided to all patients and the intraoperative inspired oxygen fraction was set to 0.70 while tissue oxygenation was determined by INVOS 5100C. Preoxygenation increased rScO2 (from 65 ± 8 to 72 ± 9%; P < 0.05) and SmO2 (from 75 ± 9 to 78 ± 9%; P < 0.05) and during surgery rScO2 and SmO2 were maintained at the baseline level in most patients. Following anesthesia and tracheal intubation an eventual change in rScO2 correlated to cardiac output and cardiac stroke volume (coefficient of contingence = 0.36; P = 0.0003) rather to a change in mean arterial pressure and for five patients rScO2 was reduced to below 50%. We conclude that (i) increased oxygen delivery enhances tissue oxygenation, (ii) oxygen supports tissue oxygenation but does not prevent a critical reduction in cerebral oxygenation sufficiently, and (iii) an eventual decrease in tissue oxygenation seems related to a reduction in cardiac output rather than to hypotension.