Morten Bundgaard-Nielsen

‘Liberal’ vs. ‘restrictive’ perioperative fluid therapy – a critical assessment of the evidence

Background: Several studies have assessed the effect of a ‘liberal’ vs. a ‘restrictive’ perioperative fluid regimen on post‐operative outcome. The literature was reviewed in order to provide recommendations regarding perioperative fluid regimens.

Monitoring of peri‐operative fluid administration by individualized goal‐directed therapy

Background:  In order to avoid peri‐operative hypovolaemia or fluid overload, goal‐directed therapy with individual maximization of flow‐related haemodynamic parameters has been introduced. The objectives of this review are to update research in the area, evaluate the effects on outcome and assess the use of strategies, parameters and monitors for goal‐directed therapy.

Goal-directed perioperative fluid management: why, when, and how?

PRINCIPLES of perioperative fluid management have received increased interest in recent years within type and amount of crystalloid and colloid, the concept of individualized goal-directed cardiovascular optimization (GDT), and finally assessed on a procedure-specific basis. In this issue, Kimberger et al., investigated the underlying tissue mechanisms during GDT management with crystalloids or colloids for abdominal surgery with a colonic anastomosis. This elegant experimental study in pigs included detailed techniques of postsurgical assessments of conventional cardiovascular variables (blood pressure, heart rate, urinary output) and microcirculatory blood flow and tissue oxygen tension in healthy and perianastomotic colonic tissue. Three types of fluid management were instituted at the end of surgery: restricted Ringer lactate (RL) versus GDT RL or GDT colloid to achieve a mixed venous oxygen saturation (SvO2) greater than 60%. The results show no significant differences between the groups in conventional cardiovascular functional parameters or urinary output, but an increased oxygen tension in healthy colonic tissue compared with RL and a further increase with GDT colloid compared with GDT RL. Of special interest, oxygen tension in perianastomotic tissue increased to 245% with GDT colloid versus 147% in the GDT RL group versus 116% in the restricted RL group. Furthermore, microcirculatory flow was higher with GDT colloid. Interestingly, anastomotic tissue edema was not different between groups. The study by Kimberger et al. may add important new knowledge to the understanding of the apparent beneficial effects of GDT in surgical patients, where the 11 randomized clinical studies have mostly shown outcome benefits within postoperative nausea and vomiting, ileus, morbidity, and hospital stay. Until now, however, only limited pathophysiological data are available to explain this benefit. Thus, Mythen and Webb showed GDT to improve morbidity and hospital stay after cardiac surgery related to the demonstrated increased gut mucosal perfusion (gastric intramucosal pH), but this could not be confirmed by a less well-designed study in abdominal surgery. In the colorectal surgery study by Noblett et al., the reduced morbidity and hospital stay by GDT was associated with a reduced interleukin-6 response. These findings together suggest that GDT may attenuate stress-induced organ dysfunctions and thereby have a pivotal role on outcome, including anastomotic complications. The recent studies on perioperative changes of the vascular barrier suggest that the endothelial glycocalyx plays a key role, which needs to be studied within the context of GDT and use of colloid. In the discussion of GDT, it is essential that the present individualized GDT approach includes optimization of flow-related parameters, such as cardiac stroke volume, within the limit of the individual patient’s cardiac capacity. The concept is therefore different from the original Shoemaker concept for optimization, which used predetermined supraphysiologic values of cardiac index and DO2 as therapeutic goals. 12 Interestingly, the study by Kimberger et al. also used fixed goals for GDT optimization (SvO2 60%) and not the individualized approach. Most of the 11 clinical GDT outcome studies are positive and may have widespread implications for clinical practice; therefore, there is an urgent need to evaluate the pathophysiological mechanisms, such as done by Kimberger et al. and others. In addition, when to institute GDT needs to be clarified. The studies predominantly perform GDT in the intraoperative period, and there have been only 2 studies within the very early postoperative period and no studies in the later postoperative period, where major fluid shifts and requirements may occur. Interestingly, the GDT optimization by Kimberger et al. was done postabdominal closure. However, the studies provide little or no detailed data of GDT in relation to type of anesthesia, including epidural anesthesia and its well-known effects on cardiovascular function; therefore, the practicing anesthesiologist is left with several unanswered questions for the interpretation of the GDT approach during the entire anesthetic-surgical period. In this context, precision of GDT requires averaging of stroke volume over at least 10 heartbeats when using the esophageal Doppler technology. Also, it has been suggested that the timing of GDT may be important because the total perioperative administration of crystalloid and colloid was not different between the GDT and control groups, despite major differences in outcome in favor of GDT. These results again call for confirmative studies, as well as pathophysiological explanations. Colloids for GDT have been used in the clinical studies and are supported by the study by Kimberger et al. as well as by a previous study demonstrating that GDT-administered crystalloid This Editorial View accompanies the following article: Kimberger O, Arnberger M, Brandt S, Plock J, Sigurdsson GH, Kurz A, Hiltebrand L: Goal-directed colloid administration improves the microcirculation of healthy and perianastomotic colon. ANESTHESIOLOGY 2009; 110:496 –504.

Functional intravascular volume deficit in patients before surgery

Background: Stroke volume (SV) maximization with a colloid infusion, referred to as individualized goal‐directed therapy, improves outcome in high‐risk surgery. The fraction of patients who need intravascular volume to establish a maximal SV has, however, not been evaluated, and there are only limited data on the volume required to establish a maximal SV before the start of surgery. Therefore, we estimated the occurrence and size of the potential functional intravascular volume deficit in surgical patients.

Modelflow underestimates cardiac output in heat stressed individuals

An estimation of cardiac output can be obtained from arterial pressure waveforms using the Modelflow method. However, whether the assumptions associated with Modelflow calculations are accurate during whole body heating is unknown. This project tested the hypothesis that cardiac output obtained via Modelflow accurately tracks thermodilution-derived cardiac outputs during whole body heat stress. Acute changes of cardiac output were accomplished via lower-body negative pressure (LBNP) during normothermic and heat-stressed conditions. In nine healthy normotensive subjects, arterial pressure was measured via brachial artery cannulation and the volume-clamp method of the Finometer. Cardiac output was estimated from both pressure waveforms using the Modeflow method. In normothermic conditions, cardiac outputs estimated via Modelflow (arterial cannulation: 6.1 ± 1.0 l/min; Finometer 6.3 ± 1.3 l/min) were similar with cardiac outputs measured by thermodilution (6.4 ± 0.8 l/min). The subsequent reduction in cardiac output during LBNP was also similar among these methods. Whole body heat stress elevated internal temperature from 36.6 ± 0.3 to 37.8 ± 0.4°C and increased cardiac output from 6.4 ± 0.8 to 10.9 ± 2.0 l/min when evaluated with thermodilution (P < 0.001). However, the increase in cardiac output estimated from the Modelflow method for both arterial cannulation (2.3 ± 1.1 l/min) and Finometer (1.5 ± 1.2 l/min) was attenuated compared with thermodilution (4.5 ± 1.4 l/min, both P < 0.01). Finally, the reduction in cardiac output during LBNP while heat stressed was significantly attenuated for both Modelflow methods (cannulation: -1.8 ± 1.2 l/min, Finometer: -1.5 ± 0.9 l/min) compared with thermodilution (-3.8 ± 1.19 l/min). These results demonstrate that the Modelflow method, regardless of Finometer or direct arterial waveforms, underestimates cardiac output during heat stress and during subsequent reductions in cardiac output via LBNP.

Techniques of cardiac output measurement during liver transplantation: Arterial pulse wave versus thermodilution

In this study, we compared continuous cardiac output (CO) obtained from the femoral arterial pressure by simulation of an aortic input impedance model [model‐simulated cardiac output (MCO)] to thermodilution cardiac output (TDCO) determined by bolus injection during liver transplantation. Both variables were measured in 39 adult patients (13 females) every 10th minute during liver transplant surgery. Paired measurements were compared during the 4 phases of surgery—dissection, anhepatic phase, early reperfusion (the first 15 minutes after reperfusion), and late reperfusion (15‐60 minutes after reperfusion)—without the detection of any significant difference between the 2 estimates of CO. TDCO ranged from 2.3 to 17.2 L/minute, and the bias (the mean difference between MCO and TDCO) prior to calibration was −0.4 ± 1.6 L/minute (mean ± standard deviation; 1309 paired measurements; 95% limits of agreement: −3.4 to 2.6 L/minute). After calibration of the first determined MCO by the simultaneously determined TDCO, the bias was 0.1 ± 1.5 L/minute, with 57% (n = 744) of the comparisons being less than 1 L/minute and 35% (n = 453) being less than 0.5 L/minute; this was independent of the level of CO, and the mutual correlation coefficient was 0.812 (P < 0.001). This study indicates that during liver transplantation surgery, MCO reflects TDCO throughout the operation. Thus, for CO, this less invasive method appears to provide a reliable uninterrupted measurement during orthotopic liver transplantation. Liver Transpl 15:287–291, 2009.

Relationship between stroke volume, cardiac output and filling of the heart during tilt

Background: Cardiac function curves are widely accepted to apply to humans but are not established for the entire range of filling of the heart that can be elicited during head‐up (HUT) and head‐down tilt (HDT), taken to represent minimal and maximal physiological filling of the heart, respectively. With the supine resting position as a reference, we assessed stroke volume (SV), cardiac output (CO) and filling of the heart during graded tilt to evaluate whether SV and CO are maintained during an assumed maximal physiological filling of the heart elicited by 90° HDT in healthy resting humans.

Effect of volume loading on the Frank-Starling relation during reductions in central blood volume in heat-stressed humans.

During reductions in central blood volume while heat stressed, a greater decrease in stroke volume (SV) for a similar decrease in ventricular filling pressure, compared to normothermia, suggests that the heart is operating on a steeper portion of a Frank–Starling curve. If so, volume loading of heat‐stressed individuals would shift the operating point to a flatter portion of the heat stress Frank–Starling curve thereby attenuating the reduction in SV during subsequent decreases in central blood volume. To investigate this hypothesis, right heart catheterization was performed in eight males from whom pulmonary capillary wedge pressure (PCWP), central venous pressure and SV (via thermodilution) were obtained while central blood volume was reduced via lower‐body negative pressure (LBNP) during normothermia, whole‐body heating (increase in blood temperature ∼1°C), and during whole‐body heating after intravascular volume expansion. Volume expansion was accomplished by administration of a combination of a synthetic colloid (HES 130/0.4, Voluven) and saline. Before LBNP, SV was not affected by heating (122 ± 30 ml; mean ±s.d.) compared to normothermia (110 ± 20 ml; P= 0.06). However, subsequent volume loading increased SV to 143 ± 29 ml (P= 0.003). LBNP provoked a larger decrease in SV relative to the decrease in PCWP during heating (8.6 ± 1.9 ml mmHg−1) compared to normothermia (4.5 ± 3.0 ml mmHg−1, P= 0.02). After volume loading while heat stressed, the reduction in the SV to PCWP ratio during LBNP was comparable to that observed during normothermia (4.8 ± 2.3 ml mmHg−1; P= 0.78). These data support the hypothesis that a Frank–Starling mechanism contributes to compromised blood pressure control during simulated haemorrhage in heat‐stressed individuals, and extend those findings by showing that volume infusion corrects this deficit by shifting the operating point to a flatter portion of the heat stress Frank–Starling curve.

A definition of normovolaemia and consequences for cardiovascular control during orthostatic and environmental stress

The Frank–Starling mechanism describes the relationship between stroke volume and preload to the heart, or the volume of blood that is available to the heart—the central blood volume. Understanding the role of the central blood volume for cardiovascular control has been complicated by the fact that a given central blood volume may be associated with markedly different central vascular pressures. The central blood volume varies with posture and, consequently, stroke volume and cardiac output (