Tissue Oxygen Delivery

Heterogeneous impact of hypotension on organ perfusion and outcomes: a narrative review

Arterial blood pressure is the driving force for organ perfusion. Although hypotension is common in acute care, there is a lack of accepted criteria for its definition. Most practitioners regard hypotension as undesirable even in situations that pose no immediate threat to life, but hypotension does not always lead to unfavourable outcomes based on experience and evidence. Thus efforts are needed to better understand the causes, consequences, and treatments of hypotension. This narrative review focuses on the heterogeneous underlying pathophysiological bases of hypotension and their impact on organ perfusion and patient outcomes. We propose the iso-pressure curve with hypotension and hypertension zones as a way to visualize changes in blood pressure. We also propose a haemodynamic pyramid and a pressure-output-resistance triangle to facilitate understanding of why hypotension can have different pathophysiological mechanisms and end-organ effects. We emphasise that hypotension does not always lead to organ hypoperfusion; to the contrary, hypotension may preserve or even increase organ perfusion depending on the relative changes in perfusion pressure and regional vascular resistance and the status of blood pressure autoregulation. Evidence from RCTs does not support the notion that a higher arterial blood pressure target always leads to improved outcomes. Management of blood pressure is not about maintaining a prespecified value, but rather involves ensuring organ perfusion without undue stress on the cardiovascular system.

LA TRASFUSIONE DI SANGUE NELLA CHIRURGIA ONCOLOGICA: RUOLO DELLA ERITROPOIETINA RICOMBINANTE UMANA (rHuEPO)

Anemia is common in cancer patients. The pathophysiology is multifactorial, however the most common cause is the anemia of chronic diseases (ACD). In 20-50% of cancer patients, anemia restricts physical activity and quality of life and requires transfusion support. The percentage of patients necessitating transfusion dramatically increases when patients require surgery.

The traditional belief that blood transfusion is an effective and safe therapy has been challenged by a heightened awareness of the infectious and immunologic risks associated with allogeneic blood administration. In cancer patients transfusion-induced immunomodulation may have the potential to significantly increase postoperative infections and cancer recurrence so that it seems reasonable to minimize allogeneic blood exposure.

Several strategies have been adopted to reduce allogeneic transfusion in surgical patients, however to properly select the appropriate blood conservation strategies the blood transfusion requirements for each patient should be defined.

Allogeneic blood transfusion in surgery can be reduced by the introduction of autologous blood (AB) programmes and by the use of rHuEPO, alone or in association with AB techniques. AB donation is currently a standard of care for elective surgical patients but its efficacy is limited by anemia that prevents the donation of the optimal number of AB units. rHuEPO has been shown to significantly increase the volume of AB that anemic patients can predeposit or, used perisurgically, to expand the circulating RBCs mass before surgery. Moreover clinical trials employed rHuEPO in anemic cancer patients with various solid tumors both on and off chemotherapy reporting a significantly increase in Hct in more than 50% of the treated patients. Recently different studies have shown the efficacy of rHuEPO in increasing the volume of AB also in patients with ACD and cancer, thus proving to be a useful addition to existing strategies of blood conservation to minimize exposure to allogeneic blood in surgical cancer patients.

Management of the Jehovah's Witness in Obstetrics and Gynecology: A Comprehensive Medical, Ethical, and Legal Approach

IMPORTANCE

Obstetricians and gynecologists frequently deal with hemorrhage so they should be familiar with management of patients who refuse blood transfusion. Although there are some reports in the literature about management of Jehovah's Witness patients in obstetrics and gynecology, most of them are case reports, and a comprehensive review about these patients including ethicolegal perspective is lacking.

OBJECTIVE

This review outlines the medical, ethical, and legal implications of management of Jehovah's Witness patients in obstetrical and gynecological settings.

EVIDENCE ACQUISITION

A search of published literature using PubMed, Ovid Medline, EMBASE, and Cochrane databases was conducted about physiology of oxygen delivery and response to tissue hypoxia, mortality rates at certain hemoglobin levels, medical management options for anemic patients who refuse blood transfusion, and ethical/legal considerations in Jehovah's Witness patients.

RESULTS

Early diagnosis of anemia and immediate initiation of therapy are essential in patients who refuse blood transfusion. Medical management options include iron supplementation and erythropoietin. There are also some promising therapies that are in development such as antihepcidin antibodies and hemoglobin-based oxygen carriers. Options to decrease blood loss include antifibrinolytics, desmopressin, recombinant factor VII, and factor concentrates. When surgery is the only option, every effort should be made to pursue minimally invasive approaches.

CONCLUSION AND RELEVANCE

All obstetricians and gynecologists should be familiar with alternatives and "less invasive" options for patients who refuse blood transfusions.

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.

Physiologic aspects of anemia

The most important adaptive responses from a physiological stance involved the cardiovascular system, consisting in particular of elevation of the cardiac output and its redistribution to favor the coronary and cerebral circulations, at the expense of the splanchnic vascular beds. The evidence regarding these physiological responses, especially in experimental studies that permit the control of many variables, is particularly powerful and convincing. On the other hand, there is a remarkable lack, in quality and quantity, of clinical studies addressing how normal physiological adaptive responses may be affected by a variety of diseases and conditions that often accompany and may complicate anemia, and interactions with other such compounding variables as age and different patient populations. For these reasons, it is not possible to offer guidelines on how to increase, maintain, or even to determine optimal DO2 in high-risk patients and how best transfusion strategies might be used under these conditions. From the brief review of physiological principles and the strong consensus in the literature, it is evident that cardiac function must be a central consideration in decisions regarding transfusion in anemia, because of the critical role it plays in assuring adequate oxygen supply of all vital tissues. Particular attention should be paid to the possible presence of CAD or incipient or cardiac failure, as these conditions may require careful transfusions to improve DO2 at levels that may not necessitate such interventions when cardiac disease is absent. Although the cerebral circulation also serves an obligate aerobic organ unable to tolerate significant hypoxia, there is little convincing evidence to support the notion that cerebral ischemia is aggravated by anemia and that this can be prevented by improved DO2 through rapid correction of anemia. Consequently, the arguments favoring transfusions in the presence of ischemic heart disease do not appear to apply to occlusive cerebrovascular disease. Because firm evidence is lacking on the interactions of concurrent diseases and anemia in various patient populations, understanding of the physiological consequences of anemia, and of the diseases concerned, is useful but not fully sufficient to provide firm and rational guidance to transfusion practice in specific complex clinical instances. A good deal of clinical and experimental investigation is required to support fully rational and comprehensive guidelines. In the meantime, prudent and conservative management, based on awareness of risks and sound understanding of the normal and pathological physiology, must remain the guiding principle.

Anemia in cancer: therapeutic implications and interventions

Significant progress has been made in the prevention and management of many symptoms associated with cancer and its therapy. Anemia in cancer may be secondary to blood loss, displacement of normal bone marrow cells by malignant cells, myelotoxic therapy, or the tumor itself. Practitioners may not always adequately assess anemia unless it represents a source of significant symptoms or patient distress. Risk factors include platinum-based treatment regimens, specific tumor types, and low baseline hemoglobin levels. Anemia may have an impact on patient performance status, quality of life, clinical symptoms, and possibly therapeutic efficacy and survival. Treatment interventions, directed toward the underlying etiology of the anemia, involve iron supplementation, blood transfusion, and administration of recombinant human erythropoietin. Future advances may include new tools to assess physical or functional symptoms and predict therapeutic response more accurately, and more cost-effective, convenient agents to prevent or treat anemia in cancer. Novel approaches that may add to the armamentarium of strategies designed to address anemia in patients with cancer currently are being developed.

The Concept of Hemoglobin Equivalency of Perfluorochemical Emulsions

Perfluorochemical (PFC) emulsions have been in development as intravenous oxygen carriers for a number of years and many publications have dealt with their oxygen transport characteristics in both experimental models and in clinical trials. Though it has been stressed on numerous occasions that PFCs deliver oxygen to the tissues in very different ways to those by which Hemoglobin (Hb) releases oxygen (O2), no serious attempts have been made to correlate the oxygen delivery capacity of PFCs to those of Hb. This paper presents theoretical ways in which this can be done and demonstrates that a 2.7 g/kg dose of PFC is approximately equivalent to 4 g/dL [Hb]. Clinical trial planning is discussed.

Perioperative blood transfusion therapy in pediatric patients

In general, transfusion guidelines for non-neonatal pediatric patients are similar to those for adults. However, some differences do exist and certain precautions may be necessary particularly in the setting of massive transfusions. We review these differences as they apply to general pediatric surgery outside of the neonatal period, with respect to the transfusion of red blood cells (RBCs), platelets, fresh-frozen plasma (FFP), and cryoprecipitate. We include a discussion of the indications for transfusion and practical considerations such as dosing and administration. Finally, we briefly review the use of directed donations and specialized (irradiated, CMV seronegative) blood components.

Perioperative autologous blood donation in children

Autologous blood donation in children has become a standard of care. Children have to live with the life-time complications associated with allogeneic blood including the transmission of known and unknown pathogens, and the impact of alloimmunization on future blood transfusions, organ transplants and pregnancies. Donor reaction, allogeneic exposure and utilization rates in pediatric preoperative autologous donation (PAD) programs are as good if not better than reported in adult literature. Children are very resilient when undergoing extreme isovolemic hemodilution (IHD). PAD, IHD and intraoperative blood recovery appear to be useful components of a pediatric blood conservation program. Prospective, randomized studies addressing the specific needs of children are required to properly define their perioperative role.

Anemia in the patient undergoing surgery and the transfusion decision. A review

The heightened awareness of the problems of transfusion reactions, disease transmission, and potential immunosuppression has led surgeons to reevaluate their reasons for transfusion. Current practice policies recommend that elective transfusion of allogeneic blood be avoided whenever possible in patients having surgery. If patients are to have appropriate transfusion, the basic pathophysiology and clinical response of the patient to anemia must be understood. This article reviews the physiologic response to anemia in the patient having surgery and explores the components of the decision to use transfusion.

Acute dilutional anemia and critical left anterior descending coronary artery stenosis impairs end organ oxygen delivery

OBJECTIVE

Limited cardiac reserve, secondary to coronary disease, may be associated with end organ morbidity. In this study, we investigate the significance of anemia in the pathogenesis of this phenomenon.

DESIGN

Nonrandomized controlled animal trial.

SETTINGS

Animal laboratory in a university hospital.

SUBJECT

Anesthetized dogs. INTERVENTIONS/MEASUREMENTS: Fourteen anesthetized dogs underwent isovolemic hemodilution with 6% hetastarch from a baseline hematocrit of 40 to 20%. Radioactive microspheres were used to evaluate regional blood flow and cardiac index. Systemic oxygen delivery, consumption, serum lactate, and systemic vascular resistance were recorded during each experiment. Arterial venous oxygen difference was determined from arterial and mixed venous blood. Seven dogs had an iatrogenic critical stenosis of their left anterior descending coronary artery (experimental group); seven dogs did not (control).

MAIN RESULTS

Only in the control animals, the cardiac index increased by 35% with hemodilution to 20%. Systemic oxygen delivery decreased in both the control and the experimental animals. Systemic oxygen consumption and lactate levels were unchanged in both groups. In the renal cortex, spleen, distal colon, ileum, gallbladder, and stomach body, regional O2 delivery was significantly decreased with hemodilution to 20% in both groups. This finding was also observed in the left ventricle and cervical spinal cord in the experimental group. In addition, regional O2 delivery was reduced in the spleen, distal colon, and gallbladder with hemodilution to only 30%. Regional blood flow in the stomach body, gallbladder, ileum, renal cortex, and distal colon, in both groups, and the spleen in the control group was unchanged from baseline with hemodilution to 20%. However, regional blood flow under all other circumstances (control or experimental) was significantly increased with hemodilution to 20% with the exception of the spleen, which showed significant regional blood flow decrease in the experimental group only.

CONCLUSIONS

These data suggest that with limited cardiac reserve, anemia may compromise aerobic splanchnic circulation. These observations may further our understanding of the pathogenesis of cholecystitis, gastric stress ulcers, ileal endotoxin translocation, and ischemic colitis in critically ill patients with coronary artery disease.

Cardiovascular effects of moderate normovolaemic haemodilution during enflurane-nitrous oxide anaesthesia in man

The cardiovascular effects of mild normovolaemic haemodilution during enflurane-nitrous oxide anaesthesia were studied in 20 patients with normal cardiac function before, during and after total hip replacement. After induction of anaesthesia, patients were randomly allocated to one control group (C), or one haemodiluted group (H) where Hct was decreased to 30% by replacement of blood volume by an identical volume of hydroxyethyl starch 200/05. Each patient was monitored with a pulmonary artery catheter allowing the measurement of right ventricular ejection fraction. During haemodilution, stroke index and right ventricular end-diastolic volume index increased from 33.1 +/- 7.9 to 39.3 +/- 7.1 ml.M-2 and from 73.8 +/- 20.3 to 94.9 +/- 18.5 ml.M-2 respectively (mean +/- s.d., both P < 0.05). However, heart rate decreased so that cardiac index did not change. O2 delivery decreased significantly (from 389 +/- 70 to 311 +/- 63 ml.min-1.m-2; P < 0.05), but was not different to the control group. O2 consumption was maintained by an increase in O2 extraction. During the surgical procedure, cardiac index was higher in the haemodiluted group than in the control group, so that O2 delivery was similar in the two groups. O2 consumption tended to be greater in the haemodiluted group. In patients with normal cardiac function, enflurane-nitrous oxide anesthesia could alter the normal physiologic response to mild normovolaemic haemodilution.

Perioperative haemotherapy: I. Indications for blood component transfusion

The practice of transfusion medicine has undergone substantial change over the last decade. Much of the impetus for the change has come from the isolation of human immunodeficiency virus (HIV) and the linkage of HIV transmission to blood transfusion. The purpose of this paper is to collate and review the literature relating to the indications for blood transfusion and provide recommendations for the appropriate utilization of blood products. Peer-reviewed and published studies and reviews relating to aspects of clinical blood transfusion were identified through computer searches and searching of the bibliographies of identified articles. Emphasis was placed on the literature published within the last decade and particularly in the years 1985-91. Material was chosen which was of proved clinical importance and in which findings were consistent among different investigators or different centres. Less emphasis was placed on material reporting new findings of uncertain clinical relevance or findings that were not consistent with majority reports. It is concluded that the only indication for red cell transfusion is to increase the oxygen carrying capacity of the blood and that an adjustment downwards in the haemoglobin concentration at which blood is transfused (transfusion trigger) from the traditional level of 100 g.L-1 is supported by the physiological and clinical data. Perioperative haemoglobin concentrations of 80 g.L-1 are acceptable in otherwise healthy young patients. The transfusion trigger should be adjusted upwards from this in medically compromised patients and in the elderly (greater than 60 yr). Fresh frozen plasma (FFP) is only indicated when there are documented deficiencies of coagulation factors. Platelet concentrates (PC) are indicated for the treatment of clinical coagulopathy resulting from thrombocytopaenia or platelet dysfunction. Routine or prophylactic administration of either FFP or PC after cardiopulmonary bypass or during resuscitation from haemorrhage is not indicated.