Direct markers of organ perfusion to guide fluid therapy: When to start, when to stop

Hypervolemia suppresses dilutional anaemic injury in a rat model of haemodilution

Background and Objectives

Haemodilution leads to complications in clinical practice. It is exactly unknown whether this damage is caused by the fluid or by the stretching of the vascular bed. We aimed to compare two different haemodilution techniques at the same anaemic level.

Methods

Normovolemic or hypervolemic haemodilution was performed on twelve adult male Wistar rats. In the normovolemic procedure, blood was withdrawn and instantaneously administered with similar amounts of 6% hydroxyethyl starch (HES 130/0.4). Fluid was administered without withdrawing blood in the hypervolemic procedure. In both models, a 25% haematocrit level was targeted and kept at this level for 90 min to deepen the anaemia effect. Besides haemodynamics measurement, renal function (creatinine, blood urea nitrogen) and injury (tissue norepinephrine, malondialdehyde) were evaluated. Also, systemic hypoxia (lactate), oxidative stress (malondialdehyde, ischaemia-modified albumin), inflammation (tumour necrosis factor-alpha [TNF-α]), osmotic stress, adrenal stress (norepinephrine, epinephrine), and vascular stretching (atrial natriuretic peptide [ANP]) were assessed.

Results

Arterial pressure in the normovolemic group was lower than in the hypervolemic group. Serum creatinine, blood urea nitrogen, and lactate levels were higher in the normovolemic group. Tissue norepinephrine and malondialdehyde levels were higher in the normovolemic group. Serum ANP, malondialdehyde, ischaemia-modified albumin, free haemoglobin, syndecan-1, and TNF-α were higher in both groups compared to respective baseline.

Conclusions

Normovolemic haemodilution may lead to hypoxic kidney injury. The hypervolemic state may be advantageous if fluid is to be administered. Thus, the effect of the fluid itself can be relatively masked.

The Relation of Calculated Plasma Volume Status to Sublingual Microcirculatory Blood Flow and Organ Injury

BACKGROUND

The calculated plasma volume status (cPVS) was validated as a surrogate of intravascular filling. The aim of this study is to assess the cPVS in relation to sublingual perfusion and organ injury.

METHODS

Pre- and postoperative cPVS were obtained by determining the actual and ideal plasma volume levels in surgical patients. The sublingual microcirculation was assessed using SDF imaging, and we determined the De Backer score, the Consensus Proportion of Perfused Vessels (Consensus PPV), and the Consensus PPV (small). Our primary outcome was the assessment of the distribution of cPVS and its association with intraoperative sublingual microcirculation and postoperative complications.

RESULTS

The median pre- and postoperative cPVS were -7.25% (IQR -14.29--1.88) and -0.4% (IQR -5.43-6.06), respectively (p < 0.001). The mean intraoperative administered fluid volume was 2.5 ± 2.5 L (1.14 L h^-1). No statistically significant correlation was observed between the pre- or postoperative cPVS and sublingual microcirculation variables. Higher preoperative (OR = 1.04, p = 0.098) and postoperative cPVS (OR = 1.057, p = 0.029) were associated with postoperative organ injury and complications (sepsis (30%), anemia (24%), respiratory failure (13%), acute kidney injury (6%), hypotension (6%), stroke (3%)).

CONCLUSIONS

The calculated PVS was associated with an increased risk of organ injury and complications in this cohort.

Investigating spectroscopic measurement of sublingual veins and tissue to estimate central venous oxygen saturation

BACKGROUND

Venous oxygen saturation reflects venous oxygenation status and can be used to assess treatment and prognosis in critically ill patients. A novel method that can measure central venous oxygen saturation (ScvO2) non-invasively may be beneficial and has the potential to change the management routine of critically ill patients.

OBJECTIVE

The study aims to evaluate the potential of sublingual venous oxygen saturation (SsvO2) to be used in the estimation of ScvO2.

METHODS

We have developed two different approaches to calculate SsvO2. In the first one, near-infrared spectroscopy (NIRS) measurements were performed directly on the sublingual veins. In the second approach, NIRS spectra were acquired from the sublingual tissue apart from the sublingual veins, and arterial oxygen saturation was measured using a pulse oximeter on the fingertip.

RESULTS

Twenty-six healthy subjects were included in the study. In the first and second approaches, average SsvO2 values were 75.0% ± 1.8 and 75.8% ± 2.1, respectively. The results of the two different approaches were close to each other and similar to ScvO2 of healthy persons (> 70%).

CONCLUSION

Oxygen saturation of sublingual veins has the potential to be used in intensive care units, non-invasively and in real-time, to estimate ScvO2.

Automated quantification of tissue red blood cell perfusion as a new resuscitation target

PURPOSE OF REVIEW

Identification of insufficient tissue perfusion is fundamental to recognizing circulatory shock in critically ill patients, and the primary target to restore adequate oxygen delivery. However, the concept of tissue perfusion remains ill-defined and out-of-reach for clinicians as point-of-care resuscitation target. Even though handheld vital microscopy (HVM) provides the technical prerequisites to collect information on tissue perfusion in the sublingual microcirculation, challenges in image analysis prevent quantification of tissue perfusion and manual analysis steps prohibit point-of-care application. The present review aims to discuss recent advances in algorithm-based HVM analysis and the physiological basis of tissue perfusion-based resuscitation parameters.

RECENT FINDINGS

Advanced computer vision algorithm such as MicroTools independently quantify microcirculatory diffusion and convection capacity by HVM and provide direct insight into tissue perfusion, leading to our formulation a functional parameter, tissue red blood cell (RBC) perfusion (tRBCp). Its definition is discussed in terms of the physiology of oxygen transport to the tissue and its expected effect as a point-of-care resuscitation target. Further refinements to microcirculatory monitoring include multiwavelength HVM techniques and maximal recruitable microcirculatory diffusion and convection capacity.

SUMMARY

tRBCp as measured using algorithm-based HVM analysis with an automated software called MicroTools, represents a promising candidate to assess microcirculatory delivery of oxygen for microcirculation-based resuscitation in critically ill patients at the point-of-care.

Differences in capillary recruitment between cardiac surgery and septic patients after fluid resuscitation

BACKGROUND

Clinical evaluation of the effects of fluid therapy remains cumbersome and strategies are based on the assumption that normalization of macrohemodynamic variables will result in parallel improvement in organ perfusion. Recently, we and others suggested the use of direct in-vivo observation of the microcirculation to evaluate the effects of fluid therapy.

METHODS

A single-centre observational study, using in-vivo microscopy to assess total vessel density (TVD) in two subsets of ICU patients.

RESULTS

After fluid resuscitation TVD showed no difference between sepsis patients (N = 47) and cardiac surgery patients (N = 52): 18.4[16.8-20.8] vs 18.7[16.8-20.9] mm/mm², p = 0.59. In cardiac surgery patients there was a significant correlation between the amount of fluids administered and TVD, with an optimum in the third quartile. However, such correlation was absent in septic patients.

CONCLUSIONS

TVD after fluid administration is not different between 2 subtypes of intensive care patients. However, only in septic patients we observed a lack of coherence between the amount of fluids administered and TVD. Further research is needed to determine if TVD may serve as potential endpoint for fluid administration.

Assessment of endothelial cell function and physiological microcirculatory reserve by video microscopy using a topical acetylcholine and nitroglycerin challenge

BACKGROUND

Assessment of the microcirculation is a promising target for the hemodynamic management of critically ill patients. However, just as the sole reliance on macrocirculatory parameters, single static parameters of the microcirculation may not represent a sufficient guide. Our hypothesis was that by serial topical application of acetylcholine (ACH) and nitroglycerin (NG), the sublingual microcirculation can be challenged to determine its endothelial cell-dependent and smooth muscle-dependent physiological reserve capacity.

METHODS

In 41 healthy subjects, sublingual capillary microscopy was performed before and after topical application of ACH and NG. Total vessel density (TVD) was assessed in parallel using manual computer-assisted image analysis as well as a fully automated analysis pathway utilizing a newly developed computer algorithm. Flow velocity was assessed using space-time diagrams of the venules as well as the algorithm-based calculation of an average perfused speed indicator (APSI).

RESULTS

No change in all measured parameters was detected after sublingual topical application of ACH. Sublingual topical application of NG however led to an increase in TVD, space-time diagram-derived venular flow velocity and APSI. No difference was detected in heart rate, blood pressure, and cardiac output as measured by echocardiography, as well as in plasma nitric oxide metabolite content before and after the topical application of ACH and NG.

CONCLUSIONS

In healthy subjects, the sublingual microcirculatory physiological reserve can be assessed non-invasively by topical application of nitroglycerin without affecting systemic circulation.

Intravenous Fluids and Acute Kidney Injury

Over 50% of the human body is comprised of fluids that are distributed in defined compartments. Although compartmentalized, these fluids are dynamically connected. Fluids, electrolytes, and acid-base balance in each compartment are tightly regulated, mostly in an energy-dependent manner to achieve their designed functions. For over a century, our understanding of the microvascular fluid homeostasis has evolved from hypothesized Ernest Starling principle to evidence-based and the revised Starling principle, incorporating the functional endothelial surface layer. The kidney is a highly vascular and encapsulated organ that is exquisitely sensitive to inadequate (insufficient or excess) blood flow. The kidney is particularly sensitive to venous congestion, and studies show that reduced venous return triggers a greater degree of kidney damage than that from lacking arterial flow. Thus, fluid overload can induce severe and sustained kidney injury. In the setting of established acute kidney injury, fluid management can be challenging. Impaired capacity of urine output and urine concentration and dilution should be taken into consideration when designing fluid therapy. Video Journal Club 'Cappuccino with Claudio Ronco' at http://www.karger.com/?doi=452702.

A mini volume loading test (mVLT) using 2.5-mLkg-1 boluses of crystalloid for indication of perioperative changes in hydration status

BACKGROUND AND OBJECTIVE

A mini volume loading test (mVLT) evaluating hemodilution during step-wise crystalloid infusion has established that the arterio-capillary plasma dilution difference is inversely correlated to the body hydration level of subjects. This observational study aimed to test whether this can be replicated in a perioperative setting using a 2.5-mLkg^-1 boluses.

MATERIALS AND METHODS

The mVLT was performed before induction of regional anesthesia and 24h later. Step-wise infusion implied six mini fluid challenges. These consisted of 2.5-mLkg^-1 boluses of Ringer's acetate infused during 2-3min and followed by 5-min periods with no fluids. Invasive (arterial) and noninvasive (capillary) measurements of hemoglobin were performed before and after each mini fluid challenge, as well as after a 20-min period without fluid following the last bolus. Hemoglobins were used to calculate the arterio-capillary plasma dilution difference which is used as an indication of changes in body hydration level. The 24-h fluid balance was calculated.

RESULTS

Subjects were 69.5 (6.0) years old, their height was 1.62m (1.56-1.65), weight was 87.0kg (75.5-97.5) and body mass index (BMI) was 33.5kg/m² (31.0-35.1). Preoperative arterio-capillary plasma dilution difference was significantly higher than postoperative (0.085 [0.012-0.141] vs. 0.006 [-0.059 to 0.101], P=0.000). The perioperative 24-h fluid balance was 1976mL (870-2545).

CONCLUSIONS

The mVLT using 2.5-mLkg^-1 boluses of crystalloid was able to detect the higher postoperative body hydration level in total knee arthroplasty patients.

Anesthesia for colorectal surgery

Anesthesiologists play a pivotal role in facilitating recovery of patients undergoing colorectal surgery, as many Enhanced Recovery After Surgery (ERAS) elements are under their direct control. Successful implementation of ERAS programs requires that anesthesiologists become more involved in perioperative care and more aware of the impact of anesthetic techniques on surgical outcomes and recovery. Key to achieving success is strict adherence to the principle of aggregation of marginal gains. This article reviews anesthetic and analgesic care of patients undergoing elective colorectal surgery in the context of an ERAS program, and also discusses anesthesia considerations for emergency colorectal surgery.