Gastric intramucosal pH changes after volume replacement with hydroxyethyl starch or crystalloid in patients undergoing elective abdominal aortic aneurysm repair

Intravenous Fluid of Choice in Major Abdominal Surgery: A Systematic Review

Background

Intravenous fluid therapy plays a role in maintaining the hemodynamic status for tissue perfusion and electrolyte hemostasis during surgery. Recent trials in critically ill patients reported serious side effects of some types of fluids. Since the most suitable type of fluid is debatable, a consensus in perioperative patients has not been reached.

Method

We performed a systematic review of randomized control trials (RCTs) that compared two or more types of fluids in major abdominal surgery. The outcomes were related to bleeding, hemodynamic status, length of hospital stay, and complications, such as kidney injury, electrolyte abnormality, major cardiac adverse event, nausea, vomiting, and mortality. A literature search was performed using Medline and EMBASE up to December 2019. The data were pooled to investigate the effect of fluid on macrocirculation and intravascular volume effect.

Results

Forty-three RCTs were included. Eighteen fluids were compared: nine were crystalloids and nine were colloids. The results were categorized into macrocirculation and intravascular volume effect, microcirculation, anti-inflammatory parameters, vascular permeability, renal function (colloids), renal function and electrolytes (crystalloids), coagulation and bleeding, return of bowel function, and postoperative nausea vomiting (PONV). We found that no specific type of fluid led to mortality and every type of colloid was equivalent in volume expansion and did not cause kidney injury. However, hydroxyethyl starch and dextran may lead to increased bleeding. Normal saline can cause kidney injury which can lead to renal replacement therapy, and dextrose fluid can decrease PONV.

Conclusion

In our opinion, it is safe to give a balanced crystalloid as the maintenance fluid and give a colloid, such as HES130/0.4, 4% gelatin, or human albumin, as a volume expander.

Albumin: friend or foe?

In the absence of red blood cells or any other colloid, human albumin has saved thousands of lives since its first use in 1941. However, for general volume expansion purposes including trauma resuscitation, published evidence suggests that albumin has now been superseded by synthetic colloids, which are more effective volume expanders, have vascular protective effects and are cheaper.

Effect of Hydroxyethyl Starch on Outcomes in High-Risk Vascular Surgery Patients: A Retrospective Analysis

OBJECTIVE

To assess the effect of using hydroxyethyl starch (HES) for intraoperative fluid therapy on outcomes in high-risk vascular surgery patients.

DESIGN

Retrospective case series.

SETTING

Single-center academic hospital.

PARTICIPANTS

The study included 1,395 adult vascular surgery patients with peripheral vascular disease.

INTERVENTIONS

Retrospective review of hospital databases.

MEASUREMENTS AND MAIN RESULTS

Outcomes were compared between patients who were intraoperatively administered HES (Voluven [Fresenius Kabi, Bad Homburg, Germany] or Pentaspan [Bristol-Myers Squibb Canada, Montreal, Quebec, Canada]) versus patients who received only crystalloids during their procedure. Logistic regression was used to assess for association between these groups and mortality (in-hospital, 30-day), intensive care unit admission, hemodialysis requirement, vasopressor requirement, and ventilator requirement. Overall, 796 patients had complete fluid records and were included in the analysis. After adjustment for potential confounders, receiving an HES solution was associated with increased likelihood of 30-day mortality (odds ratio [OR] 2.11, 95% confidence interval [CI] 1.05-3.80), postoperative requirement for hemodialysis (OR 6.17, 95% CI 1.09-35.10), intensive care unit admission (OR 3.52, 95% CI 2.15-5.74), and mechanical ventilation (OR 3.16, 95% CI 1.84-5.41).

CONCLUSIONS

Intraoperative administration of HES was associated with an increased likelihood of adverse outcomes compared with use of crystalloids alone.

The physiologic perspective in fluid management in vascular anesthesiology

Vascular surgery patients frequently suffer from atherosclerosis and peripheral arterial occlusive disease generating endothelial dysfunction. Furthermore, ischemia and reperfusion during surgery damage endothelial cells and, especially, the endothelial glycocalix. The damage of the glycocalix promotes an increase in permeability. Not only crystalloids, which freely diffuse between the intravascular and the interstitial compartment, but also colloidal fluids cross from the intravascular space in the interstitial space with the consequence of edema formation. Possible tissue edema may result in an impairment of tissue oxygenation, leading to wound healing disturbances and initiation of inflammatory responses up to tissue apoptosis. Particularly in vascular anesthesia, this possibly means that colloids only should be administered in acute volume resuscitation immediately after unclamping a big vessel for immediate volume restoration. Which colloidal fluid should be administered is still under intense discussion. From a theoretical physiologic point of view, iso-osmolar albumin is the best choice regarding volume effect, antioxidative properties, and protection against destruction of the glycocalix. Nonetheless, albumin experimentally has not lived up to its promise in the clinical setting. Thus, further well-conducted large randomized clinical trials are necessary to ascertain the optimal fluid therapy in vascular surgery patients.

Transfusion practices in trauma

Resuscitation of a severely traumatised patient with the administration of crystalloids, or colloids along with blood products is a common transfusion practice in trauma patients. The determination of this review article is to update on current transfusion practices in trauma. A search of PubMed, Google Scholar, and bibliographies of published studies were conducted using a combination of key-words. Recent articles addressing the transfusion practises in trauma from 2000 to 2014 were identified and reviewed. Trauma induced consumption and dilution of clotting factors, acidosis and hypothermia in a severely injured patient commonly causes trauma-induced coagulopathy. Early infusion of blood products and early control of bleeding decreases trauma-induced coagulopathy. Hypothermia and dilutional coagulopathy are associated with infusion of large volumes of crystalloids. Hence, the predominant focus is on damage control resuscitation, which is a combination of permissive hypotension, haemorrhage control and haemostatic resuscitation. Massive transfusion protocols improve survival in severely injured patients. Early recognition that the patient will need massive blood transfusion will limit the use of crystalloids. Initially during resuscitation, fresh frozen plasma, packed red blood cells (PRBCs) and platelets should be transfused in the ratio of 1:1:1 in severely injured patients. Fresh whole blood can be an alternative in patients who need a transfusion of 1:1:1 thawed plasma, PRBCs and platelets. Close monitoring of bleeding and point of care coagulation tests are employed, to allow goal-directed plasma, PRBCs and platelets transfusions, in order to decrease the risk of transfusion-related acute lung injury.

Incidence of postoperative death and acute kidney injury associated with i.v. 6% hydroxyethyl starch use: systematic review and meta-analysis

BACKGROUND

Trials suggest that the use of i.v. hydroxyethyl starch (HES) solutions is associ-ated with increased risk of death and acute kidney injury (AKI) in critically ill patients. It is uncertain whether similar adverse effects occur in surgical patients.

METHODS

Systematic review and meta-analysis of trials in which patients were randomly allocated to 6% HES solutions or alternative i.v. fluids in patients undergoing surgery. Ovid Medline, Embase, Cinhal, and Cochrane Database of Systematic Reviews were searched for trials comparing 6% HES with clinically relevant non-starch comparator. The primary end-point was hospital mortality. Secondary endpoints were requirement for renal replacement therapy (RRT) and author-defined AKI. Pre-defined subgroups were cardiac and non-cardiac surgery.

RESULTS

Four hundred and fifty-six papers were identified; of which 19 met the inclusion criteria. In total, 1567 patients were included in the analysis. Dichotomous outcomes were expressed as a difference of proportions [risk difference (RD)]. There was no difference in hospital mortality [RD 0.00, 95% confidence interval (CI) -0.02, 0.02], requirement for RRT (RD -0.01, 95% CI -0.04, 0.02), or AKI (RD 0.02, 95% CI -0.02 to 0.06) between compared arms overall or in predefined subgroups.

CONCLUSIONS

We did not identify any differences in the incidence of death or AKI in surgical patients receiving 6% HES. Included studies were small with low event rates and low risk of heterogeneity. Narrow CIs suggest that these findings are valid. Given the absence of demonstrable benefit, we are unable to recommend the use of 6% HES solution in surgical patients.

Glycocalyx degradation causes microvascular perfusion failure in the ex vivo perfused mouse lung: hydroxyethyl starch 130/0.4 pretreatment attenuates this response

The endothelial glycocalyx (GLX) is pivotal to vascular barrier function. We investigated the consequences of GLX degradation on pulmonary microvascular perfusion and, prompted by evidence that hydroxyethyl starch (HES) improves microcirculation, studied the effects of two HES preparations during GLX diminution. C57 BL/6 black mice lungs were explanted and perfused with 1-mL/min buffer solution containing autologous erythrocytes (red blood cells) at a hematocrit of 5%. Microvessel perfusion was quantified by video fluorescence microscopy at 0 and 90 min. To register interstitial edema, alveolar septal width was quantified. Pulmonary artery pressure (PAP), airway pressure, and left atrial pressure were recorded continuously. Lungs were randomly assigned to four groups (each n = 5): (i) control: no treatment, (ii) HEP1: heparinase I (1 mU/mL) was injected for GLX degradation, (iii) HES 130, and (iv) HES 200: one third of perfusion fluid was exchanged for 6% HES 130/0.4 or 10% HES 200/0.5 before GLX degradation. Analysis of variance on ranks and pairwise multiple comparisons were used for statistics, P < 0.05. Compared with control, GLX degradation effected perfusion failure in microvessels, increased PAP, and facilitated interstitial edema formation after a 90-min period of perfusion. In contrast to HES 200/0.5, pretreatment with HES 130/0.4 attenuated all of these consequences. Sequelae of GLX degradation in lung include perfusion failure in microvessels, interstitial edema formation, and increase in PAP. We assume that these effects are a consequence of vascular barrier dysfunction. Beneficial effects of HES 130/0.4 are presumably a result of its lower red blood cell bridging capacity compared with HES 200/0.5.

Descending aortic blood flow during aortic cross-clamp indicates postoperative splanchnic perfusion and gastrointestinal function in patients undergoing aortic reconstruction

BACKGROUND

The purpose of this observational study was to investigate the relationship between splanchnic and renal blood flow during infrarenal aortic cross-clamp (XC) and postoperative gastrointestinal perfusion and function.

METHODS

Descending aortic blood flow (DABF) was continuously monitored with an oesophageal Doppler monitor (Cardio-Q, Deltex Ltd, Chichester, UK) in 31 patients undergoing elective abdominal aortic aneurysm repair. Cardiac output (CO) was determined by indocyanine green dilution before, during, and after XC. Perioperative gastrointestinal perfusion was assessed by gastric intramucosal pH (pHi, Tonocap, GE Healthcare, Helsinki, Finland). Postoperative gastrointestinal recovery was assessed by the number of postoperative days until the patient successfully resumed solid food intake. The relationship between the mean DABF during XC and gastric pHi after XC release and postoperative gastrointestinal recovery was analysed with Spearman's correlation coefficient.

RESULTS

accounted for ∼ 55% of CO during XC and significantly decreased during XC, despite arterial pressure remaining within an optimal range. There were two distinct relationships between DABF during XC and gastric pHi after XC release. Gastric pHi steeply and linearly declined when indexed DABF was below 0.82 litre min(-1) m(-2). Above this critical value, there was no linear relationship between them. The duration of postoperative gastrointestinal dysfunction was inversely correlated with the mean DABF during XC. The best cut-off value of the mean indexed DABF during XC to prevent prolonged gastrointestinal dysfunction was 1.2 litre min(-1) m(-2).

CONCLUSIONS

Decreased DABF during XC associates splanchnic hypoperfusion after XC release and delayed recovery of gastrointestinal function.

The impact of fluid therapy on microcirculation and tissue oxygenation in hypovolemic patients: a review

PURPOSE

An optimal volume replacement strategy aims to restore systemic hemodynamics with the ultimate goals of improving organ perfusion and microcirculation for sustaining adequate tissue oxygenation. This review presents the (patho)physiological basis of hypovolemia, microcirculation, and tissue oxygenation and presents a literature review on the effects of plasma substitutes on microperfusion and oxygenation in the clinical setting.

METHODS

Literature review of the effects of fluid therapy on microcirculation and tissue oxygenation using PubMed search including original papers in English from 1988 to 2009.

RESULTS

We identified a total of 14 articles dealing with the effects of different crystalloids and colloids on organ perfusion, microcirculation, and tissue oxygenation in patients. The results are divergent, but there is a general trend that colloids are superior to crystalloids in improving organ perfusion, microcirculation, and tissue oxygenation. Due to the limited number of studies and different study conditions, a meta-analysis on the effects of the volume replacement strategies on microcirculation is not possible.

CONCLUSIONS

Improving the microcirculation by volume replacement appears to be a promising issue when treating the critically ill. The growing insights from animal experiments have to be translated into the clinical setting to identify the optimal fluid regimen for correcting hypovolemia. New techniques for monitoring microcirculation at the bedside might provide such endpoints, although these have to be validated also in the clinical setting. Whether improved microperfusion and tissue oxygenation by fluid therapy will also improve patient outcomes will have to be proven by future studies.

Intravenous fluids for abdominal aortic surgery

BACKGROUND

Surgery on the abdominal aorta to treat aneurysms or occlusive disease is a major undertaking which requires intensive physiological support and fluid management. Blood products are often used but the main fluid replacement is with crystalloids or colloids. For years there has been controversy over which fluid is optimal and a number of studies have examined the subject. This is an update of a Cochrane review first published in 2000 and previously updated in 2002.

OBJECTIVES

To determine the effectiveness of different non-blood replacement fluids used in abdominal aorta procedures with a view to identifying the optimal fluid for use.

SEARCH STRATEGY

The Cochrane Peripheral Vascular Diseases Group searched their Specialised Register (August 2009) and the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2009, Issue 3) for publications describing randomised controlled trials of non-blood replacement fluids in abdominal aortic surgery. In addition, the reference lists from retrieved trials were screened for further information about trials.

SELECTION CRITERIA

Randomised controlled trials assessing the effects of at least one specific non-blood fluid used for replacement therapy in operations on, and confined to, the abdominal aorta.

DATA COLLECTION AND ANALYSIS

Data were extracted and then entered into the Review Manager software where statistical analyses were performed.

MAIN RESULTS

Thirty-eight trials involving 1589 patients were included. Patients undergoing aortic surgery had various physiological parameters measured before and after their operation (these were cardiac, respiratory, haematological, and biochemical). Patients were randomised to a fluid type. This review demonstrated that no single fluid affects any outcome measure significantly more than another fluid across a range of outcomes. The death rate in these studies was 2.45% (39 patients).

AUTHORS' CONCLUSIONS

Despite the confirmed beneficial effects of colloids in this review, further studies are still required. There are no studies examining the effects of combination fluid therapy. The primary research outcome was death, for which results were limited; therefore, future studies should pay more attention to short-term outcomes such as minimising the need for allogenic blood transfusion, complications (organ failure), and length of stay in both the intensive care unit and hospital.

Clinical consequences of red cell storage in the critically ill

Red cell (RBC) transfusions are a potentially life-saving therapy employed during the care of many critically ill patients to replace losses in hemoglobin to maintain oxygen delivery to vital organs. During storage, RBCs undergo a series of biochemical and biomechanical changes that reduce their survival and function. Additionally, accumulation of other biologic by-products of RBC preservation may be detrimental to recipients of blood transfusions. Laboratory studies and an increasing number of observational studies have raised the possibility that prolonged RBC storage adversely affects clinical outcomes. In this article, the laboratory and animal experiments evaluating changes to RBCs during prolonged storage are reviewed. Subsequently, the clinical studies that have evaluated the clinical consequences of prolonged RBC storage are reviewed. These data suggest a possible detrimental clinical effect associated with the transfusion of stored RBCs; randomized clinical trials further evaluating the clinical consequences of transfusing older stored RBCs are required.

Comparison of lactated Ringer's, gelatine and blood resuscitation on intestinal oxygen supply and mucosal tissue oxygen tension in haemorrhagic shock

OBJECTIVES

To evaluate the effects on intestinal oxygen supply, and mucosal tissue oxygen tension during haemorrhage and after fluid resuscitation with either blood (B; n=7), gelatine (G; n=8), or lactated Ringer's solution (R; n=8) in an autoperfused, innervated jejunal segment in anaesthetized pigs.

METHODS

To induce haemorrhagic shock, 50% of calculated blood volume was withdrawn. Systemic haemodynamics, mesenteric venous and systemic acid-base and blood gas variables, and lactate measurements were recorded. A flowmeter was used for measuring mesenteric arterial blood flow. Mucosal tissue oxygen tension (PO(2)muc), jejunal microvascular haemoglobin oxygen saturation (HbO(2)) and microvascular blood flow were measured. Measurements were performed at baseline, after haemorrhage and at four 20 min intervals after fluid resuscitation. After haemorrhage, animals were retransfused with blood, gelatine or lactated Ringer's solution until baseline pulmonary capillary wedge pressure was reached.

RESULTS

After resuscitation, no significant differences in macrohaemodynamic parameters were observed between groups. Systemic and intestinal lactate concentration was significantly increased in animals receiving lactated Ringer's solution [5.6 (1.1) vs 3.3 (1.1) mmol litre(-1); 5.6 (1.1) vs 3.3 (1.2) mmol litre(-1)]. Oxygen supply to the intestine was impaired in animals receiving lactated Ringer's solution when compared with animals receiving blood. Blood and gelatine resuscitation resulted in higher HbO(2) than with lactated Ringer's resuscitation after haemorrhagic shock [B, 43.8 (10.4)%; G, 34.6 (9.4)%; R, 28.0 (9.3)%]. PO(2)muc was better preserved with gelatine resuscitation when compared with lactated Ringer's or blood resuscitation [20.0 (8.8) vs 13.8 (7.1) mm Hg, 15.2 (7.2) mm Hg, respectively].

CONCLUSION

Blood or gelatine infusion improves mucosal tissue oxygenation of the porcine jejunum after severe haemorrhage when compared with lactated Ringer's solution.

Cardiac response is greater for colloid than saline fluid loading after cardiac or vascular surgery

OBJECTIVE

To study the effects on volume expansion and myocardial function of colloids or crystalloids in the treatment of hypovolaemic hypotension after cardiac and major vascular surgery.

DESIGN AND SETTING

A single-centre, single-blinded, randomized clinical trial at the intensive care unit of a university hospital.

PATIENTS AND METHODS

Patients (n=67) were subjected to a 90-min filling pressure-guided fluid challenge with saline 0.9% or the colloids gelatin 4%, hydroxyethyl starch 6% or albumin 5%. Biochemical variables and haemodynamics (transpulmonary thermodilution) were measured.

RESULTS

An amount of 1800 (1300-1800) ml of saline or 1600 (750-1800) ml of colloid solution (P< 0.005) was infused. Colloid osmotic pressure (COP) decreased in the saline group and increased in the colloid groups (P< 0.001). Plasma volume increased by 3.0% (-18 to 24) in the saline versus 19% (-11 to 50) in the colloid groups (P< 0.001). Cardiac index increased by median 13% (ns) in the saline group and by 22% in the colloid groups (P<0.005). The rise in left ventricular stroke work index was greater in the colloid than in the saline groups. The different colloids were equally effective. The rise in cardiac index related to the rise in plasma volume and global end-diastolic volume, confirming plasma volume and preload augmentation by the fluid loading.

CONCLUSION

After cardiac or major vascular surgery, the pressure- and time-guided fluid response is dependent on the type of fluid used. Colloid fluid loading leads to a greater increase in preload-recruitable cardiac and left ventricular stroke work indices than that with saline, because of greater plasma volume expansion following an increase in plasma COP.

DO PLASMA SUBSTITUTES HAVE ADDITIONAL PROPERTIES BEYOND CORRECTING VOLUME DEFICITS?

The best strategy for volume therapy has been the focus of debate and there are still no unique accepted guidelines. There is increasing evidence that some plasma substitutes possess additional effects on organ perfusion, microcirculation, tissue oxygenation, inflammation, endothelial activation, capillary leakage, and tissue edema that are beyond their volume replacing properties. Whether the different plasma substitutes differ with regard this additional effects was reviewed. The additional effects of plasma substitutes have mostly been studied experimentally or in animals, much less results are available in humans. The results are not uniform ranging from beneficial to even detrimental effects of a certain volume replacement strategy. Some important results from the literature are not reflected in the actual recommendations for treating volume deficits in the critically ill: although crystalloids have been shown to have considerable negative effects on microcirculation, organ perfusion, tissue oxygenation, and endothelial integrity, they are still often recommended as first choice volume replacement strategy. In several experimental studies hypertonic solutions have been shown to have various beneficial effects, they have not been, however, translated into humans. In future, the choice of the ideal volume replacement regimen should not only be focused on its volume restoring properties, but additional effects (e.g. on organ perfusion on, tissue oxygenation, inflammation, endothelial activation, capillary leakage) should also be taken into account when treating hypovolemia in the critically ill.

Inhibition of Platelet Function by Hydroxyethyl Starch Solutions in Chronic Pain Patients Undergoing Peridural Anesthesia

The use of hydroxyethyl starch (HES) solutions as a fluid replacement before peridural blockade may compromise blood coagulation, thus increasing the risk of neuraxial bleeding. In this prospective, double-blind, placebo-controlled, crossover study, we compared the influence of HES 130 (molecular weight in kilodalton), HES 200, and lactated Ringer's solution on platelet function and hemodynamics in chronic low back pain patients scheduled for peridural blockades. Patients received 3 test infusions of 10 mL/kg each administered IV for 30 min. Collagen/epinephrine and collagen/adenosine diphosphate were used as agonists for assessment of platelet function analyzer-closure times. Arterial blood pressure, heart rate, platelet counts, and hemoglobin levels were documented. Platelet function analyzer-closure times remained stable after lactated Ringer's solution but were significantly prolonged after HES. The platelet-inhibiting effect of HES 200 was more than that of HES 130. Hemodynamic stability was sufficiently maintained by all test infusions. In contrast to previous observations, a relevant antiplatelet effect of both low and medium molecular weight HES solutions was found in this study in chronic pain patients undergoing peridural anesthesia. Because hemostasiological competence is a prerequisite for safe neuraxial blockade, the decision of HES for intravascular fluid administration before blockade should be critically made.

The Early Systemic and Gastrointestinal Oxygenation Effects of Hemorrhagic Shock Resuscitation with Hypertonic Saline and Hypertonic Saline 6% Dextran-70: A Comparative Study in Dogs

The smaller volemic state from hypertonic (7.5%) saline (HS) solution administration in hemorrhagic shock can determine lesser systemic oxygen delivery and tissue oxygenation than conventional plasma expanders. In a model of hemorrhagic shock in dogs, we studied the systemic and gastrointestinal oxygenation effects of HS and hyperoncotic (6%) dextran-70 in combination with HS (HSD) solutions in comparison with lactated Ringer's (LR) and (6%) hydroxyethyl starch (HES) solutions. Forty-eight mongrel dogs were anesthetized, mechanically ventilated, and subjected to splenectomy. A gastric air tonometer was placed in the stomach for intramucosal gastric CO(2) (Pgco(2)) determination and for the calculation of intramucosal pH (pHi): The dogs were hemorrhaged (42% of blood volume) to hold mean arterial blood pressure at 40-50 mm Hg over 30 min and were then resuscitated with LR (n = 12) in a 3:1 relation to removed blood volume; HS (n = 12), 6 mL/kg; HSD (n = 12), 6 mL/kg; and HES (mean molecular weight, 200 kDa; degree of substitution, 0.5) (n = 12) in a 1:1 relation to the removed blood volume. Hemodynamic, systemic, and gastric oxygenation variables were measured at baseline, after 30 min of hemorrhage, and 5, 60, and 120 min after intravascular fluid resuscitation. After fluid resuscitation, HS showed significantly lower arterial pH and mixed venous Po(2) and higher systemic oxygen uptake index and systemic oxygenation extraction than LR and HES (P < 0.05), whereas HSD showed significantly lower arterial pH than LR and HES (P < 0.05). Only HS and HSD did not return arterial pH and pHi to control levels (P < 0.05). In conclusion, all solutions improved systemic and gastrointestinal oxygenation after hemorrhagic shock in dogs. However, the HS solution showed the worst response in comparison to LR and HES solutions in relation to systemic oxygenation, whereas HSD showed intermediate values. HS and HSD solutions did not return regional oxygenation to control values.

Salt of the earth or a drop in the ocean? A pathophysiological approach to fluid resuscitation

The evolved endocrine response after injury leads to sodium, chloride, and water retention at a time when large volumes of sodium containing fluids are given to maintain the circulation and preserve tissue oxygenation. Sodium, chloride, and water are also retained because of increased systemic vascular permeability to plasma proteins, especially albumin, which sequesters fluid in the interstitial space and causes oedema. Excessive fluid and electrolyte retention and interstitial oedema are associated with the systemic inflammatory response syndrome and multiple organ dysfunction, and failure. This review attempts an overview of these processes and addresses the question, "Can manipulation of fluid resuscitation influence the inflammatory response to injury and organ function". Results of randomised controlled prospective clinical studies suggest that limiting the sodium and chloride input and optimal use of synthetic colloids, which are well retained in the vascular space, can reduce the inflammatory response to injury and improve organ function.

Influence of two different volume replacement regimens on renal function in elderly patients undergoing cardiac surgery: comparison of a new starch preparation with gelatin

OBJECTIVE

There is continuing concern on the influence of hydroxethyl starch (HES) on renal function.

DESIGN

Prospective, randomized study.

SETTING

University-affiliated medical center.

PATIENTS

Forty consecutive patients aged >70 years undergoing cardiac surgery using cardiopulmonary bypass.

INTERVENTIONS

Either low-molecular HES (mean molecular weight: 130 kD) with low degree of substitution (0.4) (6% HES 130/0.4) (n=20) or gelatin ( n=20) was given after induction of anesthesia until the 2nd postoperative day (POD) to keep central venous pressure between 12-14 mmHg.

MEASUREMENTS AND RESULTS

Creatinine clearance (CC) and fractional sodium clearance (FSC) were measured. N-acetyl-beta-D-glucosamidase, alpha-1-microglobulin, glutathione transferase-pi, and glutathione transferase-alpha were measured from urine specimens. Measurements were made after induction of anesthesia, at the end of surgery, and at the first and the second POD. More gelatin (total: 4150+/-490 ml) than HES 130/0.4 (total: 3450+/-450 ml) was infused within the study. CC and FSC were without differences between the two groups. All measured kidney-specific proteins were almost within normal range at baseline. They increased significantly after surgery, however, without significant group differences. At the 2nd POD, kidney-specific proteins had returned almost to normal values. None of the patients developed acute renal failure.

CONCLUSIONS

Sensitive markers of kidney dysfunction increased in our elderly patients indicating moderate alterations in kidney integrity during cardiac surgery. The two volume replacement regimens did not differ with regard to kidney integrity in elderly patients undergoing cardiac surgery.

Clinical review: hemodynamic monitoring in the intensive care unit

Since the beginning of modern anesthesia, in 1846, the anesthetist has relied on his natural senses to monitor the patient, aided more recently by simple technical devices such as the stethoscope. There has been a tremendous increase in the availability of monitoring devices in the past 30 years. Modern technology has provided a large number of sophisticated monitors and therapeutic instruments, particularly in the past decade. Most of these techniques have enhanced our understanding of the mechanism of the patients' decompensation and have helped to guide appropriate therapeutic interventions. As surgery and critical care medicine have developed rapidly, patient monitoring capability has become increasingly complex. The most important aspect in monitoring the critically ill patient is the detection of life-threatening derangements of vital functions. Aggressive marketing strategies have been promoted to monitor almost every aspect of the patient's status. However, these strategies are only telling us what is possible; they do not tell us whether they enhance patient safety, improve our therapy, or even improve patient outcome.

The Effects of Hydroxyethyl Starches of Varying Molecular Weights on Platelet Function

We evaluated the effect of various hydroxyethyl starch (HES) solutions on platelet function. Blood was obtained before and after the IV infusion (10 mL/kg) of saline (n = 10), HES 70/0.5--0.55 (molecular weight in kD/degree of substitution; n = 10), HES 130/0.38--0.45 (n = 10), HES 200/0.6--0.66 (n = 10), or HES 450/0.7--0.8 (n = 10) in otherwise healthy patients scheduled for elective surgery. Collagen and epinephrine were used as agonists for assessment of platelet function analyzer closure times. Flow cytometry was used to assess agonist-induced expression of activated glycoprotein IIb/IIIa complex and P-selectin. Infusion of HES 450/0.7--0.8, HES 200/0.6--0.66, and HES 70/0.5--0.55 prolonged closure times and reduced glycoprotein IIb/IIIa expression, whereas saline and HES 130/0.38--0.45 had no significant effect on platelet variables. P selectin expression was not affected by any solution tested. In vitro experiments demonstrated a less inhibiting effect of HES 130/0.38--0.45 on closure times when compared with other HES solutions. This study shows that HES 450/0.7--0.8, HES 200/0.6--0.66, and HES 70/0.5--0.55 inhibit platelet function by reducing the availability of the functional receptor for fibrinogen on the platelet surface. Our data indicate that fluid resuscitation with HES 130/0.38--0.45 may reduce the risk of bleeding associated with synthetic colloids of higher molecular weight and degree of substitution.

Effect of hydroxyethyl starch infusion on colloid oncotic pressure in hypoproteinemic horses

OBJECTIVE

To determine the effect of hydroxyethyl starch (HES) on colloid oncotic pressure (pi) during fluid resuscitation of hypoproteinemic horses and to evaluate the clinical usefulness of direct and indirect methods for determination of pi before and after infusion of a synthetic colloid.

DESIGN

Prospective clinical study.

ANIMALS

11 hypoproteinemic horses.

PROCEDURE

Horses received IV infusions of 8 to 10 ml of a 6% solution of HES/kg (3.6 to 4.5 ml/lb) of body weight during fluid resuscitation. Blood samples were obtained for determination of plasma measured colloid oncotic pressure (pi meas) and plasma total protein and albumin (A) concentrations. Plasma globulin concentration (G) was calculated as the difference between plasma total protein and albumin concentrations. Calculated values for colloid oncotic pressure (piA + G) were determined by use of a predictive nomogram previously developed for horses.

RESULTS

There was no significant difference between the means of pi meas and piA + G at the beginning of HES infusion. After HES infusion, the mean of pi meas was increased significantly from baseline for 6 hours. Mean plasma total protein and albumin concentrations and piA + G were decreased significantly from baseline for 24 hours. Differences between mean pi meas and piA + G after HES infusion were significant for 24 hours.

CONCLUSIONS AND CLINICAL RELEVANCE

There was good agreement between plasma pi meas and piA + G in blood samples obtained from hypoproteinemic horses immediately before infusion of HES. Use of a predictive nomogram did not, however, account for the oncotic effect of HES. Results of comparison of pi meas to piA + G after HES infusion suggest that a significant oncotic effect was maintained for 24 hours in the study horses.

Intraoperative and Early Postoperative Gastric Intramucosal pH Predicts Morbidity and Mortality after Major Abdominal Surgery

The present study was undertaken to investigate the correlation between the intraoperative and postoperative gastric intramucosal pH (pHi) with important perioperative variables and to explore any potential relationship of the measured pHi with the patients’ postoperative course. A prospective study was carried out in a group of 48 patients who underwent major abdominal operations over an 8-month period at St. John Hospital and Medical Center. An automated air tonometer was used for gastric pHi monitoring. Twenty-eight elective and 20 emergency abdominal operations were performed in 23 men and 25 women. Twenty-six patients (54%) required postoperative hospitalization in the Intensive Care Unit (ICU). Seventeen patients (35%) developed early postoperative complications. The non-ICU and ICU mortality rates were 4.5 and 19.2 per cent respectively. The mean intraoperative pHi (pHiOR) and postoperative pHi (pHiPO) ranged between 7.03 and 7.58 (7.38 ± 0.12) and 6.89 and 7.56 (7.35 ± 0.12) respectively (mean ± standard deviation). There was a significant decrease of the gastric pHi at the first hour intraoperatively compared with the pHi after induction to anesthesia (7.44 vs 7.38 ± 0.14, P < 0.001). Patients who underwent emergent abdominal procedures were characterized by lower pHiOR and pHiPO values (7.43 ± 0.08 vs 7.30 ± 0.13 and 7.39 ± 0.84 vs 7.30 ± 0.15, P < 0.001 and P < 0.05). Similarly patients who required surgical ICU admission had significantly lower pHiOR and pHiPO measurements (7.3 ± 0.12 and 7.28 ± 0.12) compared with the rest (7.46 ± 0.06 and 7.43 ± 0.06; P < 0.001). Overall, lower pHiOR and pHiPO values were associated with the occurrence of postoperative complications ( P < 0.001), the postoperative mortality ( P < 0.001), the requirement for postoperative mechanical ventilator ( P < 0.001) and its duration ( P < 0.001), longer ICU stay ( P < 0.001), and prolonged hospitalization ( P < 0.05). Evidence of intraoperative and early postoperative gastric mucosal ischemia (pHiOR and pHiPO ≤ 7.32) was observed in 12 (25%) and 15 (31%) patients respectively. The incidence of postoperative complications and the mortality rate were higher in this group of patients ( P < 0.001). At a cutoff point of 7.32 gastric pHiOR gave a sensitivity of 69 per cent and specificity of 97 per cent for predicting postoperative complications as well as a sensitivity and specificity of 67 per cent and 81 per cent for predicting death. Intraoperative and early postoperative gastric pHi is a reliable predictor of patient outcome after major abdominal operations. Splanchnic ischemia may play an important role in determining early complications and survival; therapy guided by the gastric pHi might improve outcome.

Intravenous fluids for abdominal aortic surgery

BACKGROUND

Surgery on the abdominal aorta, for aneurysmal and occlusive disease is a major undertaking which requires intensive support and fluid management. Blood products are often used, but the major fluid replacement is with crystalloids or colloids. There has been controversy for many years over which fluid is optimal and a number of studies have examined this subject, without any systematic review.

OBJECTIVES

The objective of this review was to determine the effectiveness of different non-blood replacement fluids used in surgery on the abdominal aorta with a view to identifying the optimal fluid for use in such surgery.

SEARCH STRATEGY

All publications describing (or which might describe) randomised controlled trials of non-blood replacement fluids in abdominal aortic surgery were sought using the search strategy described by the Cochrane Review Group on Peripheral Vascular Diseases. This strategy includes hand searching of relevant medical journals and extensive MEDLINE and EMBASE searches. In addition, trials have been identified from searches of references included in those trials already retrieved.

SELECTION CRITERIA

Randomised controlled trials assessing the effects of one or more specific non-blood fluids used for replacement therapy in operations on, and confined to, the abdominal aorta.

DATA COLLECTION AND ANALYSIS

Data were extracted to pre-prepared tables and then entered into the Review Manager software where statistical analysis and descriptive subjective analysis were performed.

MAIN RESULTS

Nine trials, involving 412 patients were included. Patients undergoing aortic surgery had various physiological parameters measured before and after their operation (cardiac, respiratory, biochemical, haematological and protein). Ten fluids were studied: Ringer lactate, 5% dextrose in Ringer lactate, 5% dextrose in 0.45% saline, 5% dextrose in water, 1.8% saline, human albumin solution in Ringer lactate, human albumin solution in water, 5% dextrose with human albumin solution, Dextran 60, Hetastarch. Patients were randomised to fluid type. This review demonstrates that no single fluid has been shown to affect any outcome measure significantly more than any other across a range of outcome measures. However, each trial compared different fluids, and each fluid has not been compared against all others. The death rate in these studies was 2.9% (12 patients).

REVIEWER'S CONCLUSIONS

Further studies are required, with sufficient sample size and power, to draw any further conclusions. There are no studies examining the effects of combination fluid therapy.

Neither dopamine nor dobutamine corrects mesenteric blood flow depression caused by positive end-expiratory pressure in a rat model of acute lung injury

OBJECTIVE

To determine if either dopamine or dobutamine would counteract the deleterious effect that positive end-expiratory pressure (PEEP) has on cardiac output and mesenteric blood flow in a rat model of acute lung injury.

DESIGN

Prospective, randomized, controlled trial in a clinically relevant model of acute lung injury.

SETTING

Microcirculation research laboratory.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

The animals were anesthetized with pentobarbital (30 mg/kg) by intraperitoneal injection. They underwent tracheostomy, jugular and femoral vein cannulation, femoral artery cannulation, carotid artery thermistor placement, and bowel preparation for in vivo video microscopy. Acute lung injury was created by administering 0.1 N hydrochloric acid (1 mL/kg) via the tracheostomy. Dopamine or dobutamine (2.5 or 12.5 microg/kg/min), followed by two intravenous fluid boluses, was administered to rats ventilated with 5, 10, 15, and 20 cm H2O of PEEP.

MEASUREMENTS AND MAIN RESULTS

Mean arterial pressure, thermodilution cardiac output, mesenteric arteriolar diameter, and red blood cell velocity were measured and mesenteric blood flow was calculated. Cardiac output was depressed in rats exposed to 20 cm H2O of PEEP by 32+/-2%. The corresponding values for cardiac output depression at 20 cm H2O of PEEP in rats receiving 2.5 and 12.5 microg/kg/min of dopamine and 2.5 and 12.5 microg/kg/min of dobutamine were 31+/-1%, 21+/-1%, 29+/-0%, and 24+/-2%, respectively. Mesenteric blood flow was depressed in rats ventilated with 20 cm H2O of PEEP by 74+/-3%, while the corresponding values in rats exposed to 20 cm H2O of PEEP and receiving 2.5 or 12.5 microg/kg/min of dopamine or 2.5 or 12.5 microg/kg/min of dobutamine were 86+/-3%, 77+/-3%, 73+/-3%, and 66+/-3%, respectively. Fluid boluses did not correct the deficits in cardiac output or mesenteric blood flow caused by the combination of acute lung injury and PEEP.

CONCLUSIONS

The higher doses of dopamine and dobutamine partially, but insignificantly, corrected the cardiac output depression caused by PEEP in a model of acute lung injury. Neither dose of dopamine nor dobutamine was able to improve PEEP-induced mesenteric blood flow depression.