Maternal body weight and estimated circulating blood volume: a review and practical nonlinear approach.

Postpartum haemorrhage continues to be a leading cause of morbidity and mortality in the obstetric population worldwide, especially in patients at extremes of body weight. Quantification of blood loss has been considered extensively in the literature. However, these volumes must be contextualised to appreciate the consequences of blood loss for individual parturients. Knowledge of a patient's peripartum circulating blood volume is essential to allow accurate interpretation of the significance of haemorrhage and appropriate resuscitation. Greater body weight in obesity can lead to overestimation of blood volume, resulting in inappropriately high thresholds for blood product transfusion and delays in treatment. The most recent Mothers and Babies: Reducing Risk through Audits and Confidential Enquiries across the UK (MBRRACE-UK) surveillance report demonstrated the risk to this population, with more than half of all maternal mortality recorded in parturients who were either overweight or obese. Current linear calculations used to estimate circulating blood volumes based on patients' weights could be contributing to this phenomenon, as blood volume increases at a disproportional rate to body composition. In this review, we summarise the relevant physiology and explore the existing literature on the estimation of circulating blood volume, both during pregnancy and in obesity. Building on key works and principal findings, we present a practical, nonlinear approach to the adjustment of estimated blood volume with increasing body mass. This clinical tool aims to reduce the clinical bias influencing the management of obstetric haemorrhage in a population already at increased risk of morbidity and mortality. Discussion of the limitations of this approach and the call for further research within this field completes this review.

The role of hospital transfusion committees in blood product conservation.

Transfusion committees have been created in different countries to oversee all aspects of blood product transfusion within individual institutions. A fundamental role of hospital transfusion committees is to ensure appropriate blood product use by developing local policies, educating clinicians, and auditing blood use. Unfortunately, this task is hampered by the lack of universally accepted criteria for blood product transfusion. Several examples of specific interventions directed toward improving blood use have been described in the literature. Despite some limitations of these reports, largely because of shortfalls in study design, such interventions appear to be generally effective, but there is not enough evidence to recommend a specific course of action to ensure appropriate blood use. Notwithstanding such problems, a functional hospital transfusion committee can have a major impact on local rates of inappropriate transfusion.

Cerebral and peripheral oxygen saturation during red cell transfusion.

BACKGROUND: Changes in regional hemoglobin oxygen saturation occur in response to blood transfusion and can be measured by near infrared spectroscopy. PATIENTS AND METHODS: Cerebral (CsO2) and peripheral (PsO2) oxygen saturation were monitored with an INVOS 4100 near infrared spectroscopy oximeter in 29 patients undergoing 84 intraoperative blood transfusions during aortic or spinal surgery. Hemoglobin concentration was measured before and after transfusion. Mean arterial pressure, end tidal carbon dioxide tension, and arterial oxygen saturation were also monitored. RESULTS: Mean arterial pressure, arterial oxygen saturation and end tidal carbon dioxide tension remained stable during transfusion, while CsO2 rose by a mean (95% CI) of 4.2 (3.2-5.2%; P = 0.001) and PsO2 rose by a mean (95% CI) of 1.6 (0.3-2.8%; P = 0.016). The rise in CsO2 correlated well with the rise in hemoglobin (r = 0.59, P < 0.001) and with the volume transfused (r = 0.58, P < 0.001). PsO2 correlated with the volume transfused (r = 0.35, P = 0.019) but not with hemoglobin concentration (r = 0.08, P = 0.47). CONCLUSIONS: Near infrared spectroscopy detected significant rises in tissue oxygenation in response to blood transfusion, particularly in the cerebral cortex. CsO2 may be developed into a blood loss monitor if further research confirms our findings.

Can hospital transfusion committees change transfusion practice?

Blood and blood products are commonly over-used in hospital practice. We investigated whether the introduction of a red-cell transfusion trigger (haemoglobin <8 g dL(-1)) influenced transfusion practice in surgery. Coronary artery bypass grafts (CABGs, n=400), total hip replacements (n=107), colectomies (n=85) and transurethral prostatectomies (TURPs, n=158) were reviewed over two periods of six months, before and after the introduction of the policy by the local hospital transfusion committee. After introduction of the policy, the proportion of patients transfused fell from 57% to 45% with CABGs (P=0.02) and from 52% to 26% with hip replacements (P=0.006); for colectomies and TURPs there was no change. Hospital stay did not increase in any of the groups. In the second period, haemoglobin concentration on discharge was lower after total hip replacement, by a mean (95% CI) of 0.7 (0.3-1.2) g dL(-1) (P=0.002) and after colectomy, by a mean of 0.6 (0.1-1.1) g dL(-1) (P=0.03). Although other factors cannot be excluded, we suggest that the reductions in red-cell transfusion were in large part attributable to the new transfusion policy.

Acute normovolemic hemodilution and intraoperative cell salvage in aortic surgery.

OBJECTIVE: The objective of this study was to report current transfusion requirements and outcomes in patients undergoing elective aortic surgery with autologous transfusion. METHODS: This was a retrospective review of transfusion practice in infrarenal aortic surgery in a tertiary vascular unit with a longstanding interest in autologous transfusion. One hundred and ten consecutive patients underwent infrarenal aortic surgery with a combination of acute normovolemic hemodilution (ANH) and intraoperative cell salvage (ICS). All patients underwent hemodilution to a target hemoglobin concentration of 11 g/dL and underwent ICS with a centrifugal device. RESULTS: Median blood loss was 1140 mL (interquartile range [IQR], 683 to 1609 mL) in 78 aneurysm repairs and 775 mL (IQR, 400 to 1225 mL) in 32 aortobifemoral bypasses for occlusive disease (P =.02), resulting in a median salvaged red cell volume of 403 mL (IQR, 256 to 563 mL) for aneurysm repairs and 250 mL (IQR, 200 to 290 mL) in bypass surgery (P =.001). Thirty-six patients (33%) needed transfusion of stored blood, for a total of 115 units, with just four patients needing more than five units. The mortality rate was 8% (9/110). With multivariate analysis, low hemoglobin level (P =.006) and low platelet count (P =.023) were associated with stored blood transfusion. CONCLUSION: Blood loss is too small to justify ICS in surgery for occlusive disease; ANH alone may be a suitable strategy. With appropriate experience, the combination of ANH and ICS may render crossmatching unnecessary, even in aortic aneurysm surgery.

Autologous versus allogeneic transfusion in aortic surgery: a multicenter randomized clinical trial.

OBJECTIVE: To evaluate the efficacy of acute normovolemic hemodilution (ANH) and intraoperative cell salvage (ICS) in blood-conservation strategies for infrarenal aortic surgery. SUMMARY BACKGROUND DATA: Recent concerns over the risks of transfusion-related infection have resulted in sharp rises in the cost of blood preparations. Autologous transfusion may be a safe alternative to allogeneic transfusion, which has been associated with immune modulation and postoperative infection. METHODS: This multicenter prospective randomized trial compared standard transfusion practice with autologous transfusion combining ANH with ICS in 145 patients undergoing elective aortic surgery. The primary outcome measures were the proportion of patients requiring allogeneic blood and the volume of allogeneic transfusion. The secondary outcome measures were the frequency of complications, including postoperative infection, and postoperative hospital stay. RESULTS: The combination of ANH and ICS reduced the volume of allogeneic blood transfused from a median of two units to zero units. The proportion of patients transfused was 56% in allogeneic and 43% in autologous. There were no significant differences in complications or length of hospital stay. CONCLUSIONS: Both ANH and ICS were safe and reduced the allogeneic blood requirement in patients undergoing elective infrarenal aortic surgery.