Cardiovascular response to acute normovolemic hemodilution in patients with coronary artery diseases: Assessment with transesophageal echocardiography

Hypotensive anesthesia versus normotensive anesthesia during major maxillofacial surgery: a review of the literature

Steady blood pressure within normal limits during surgery is one of the markers of the ideal and skillful anesthesia. Yet, reduced blood pressure is advantageous in some settings because it can contribute to a reduction in overall blood loss and improve the surgical field conditions. Controlled hypotension during anesthesia or hypotensive anesthesia is often used in major maxillofacial operations. Since hypotensive anesthesia carries the risk of hypoperfusion to important organs and tissues, mainly the brain, heart, and kidneys, it cannot be applied safely in all patients. In this paper we review the medical literature regarding hypotensive anesthesia during major maxillofacial surgery, the means to achieve it, and the risks and benefits of this technique, in comparison to normotensive anesthesia.

Cardiac function assessed by exercise echocardiography on the first morning after coronary artery bypass grafting

Cardiac surgery patients are urged to resume light physical activity on the first postoperative day, even if cardiac function may not have recovered fully after the operation. To elucidate the postoperative recovery process, we examined cardiac surgery patients with exercise echocardiography before and on the first day after the operation. Patients undergoing on-pump coronary artery bypass grafting were examined with echocardiography during semirecumbent cycle exercise. Patients exercised for five minutes at 10 W intensity and five minutes at 30 W intensity in bed with the upper body supported to approximately 30°. Fourteen patients were studied. Mitral annulus excursion and pulsed wave Doppler from the left ventricular outflow tract indicated postoperatively reduced cardiac stroke volume. Early diastolic tissue velocities of the mitral annulus were reduced, and early trans-mitral flow velocity was increased. The ratio between early mitral flow velocity and early diastolic mitral tissue velocity was increased postoperatively, indicating impaired left ventricular relaxation and increased left atrial pressure. Postoperative systolic mitral annulus tissue velocities were similar to preoperative velocities, indicating maintained systolic function. Postoperative exercise was associated with improvements in myocardial function indices and cardiac stroke volume similar to preoperative improvements. There were no signs of further deterioration in myocardial function during 30 W exercise. In summary, reduced left ventricular diastolic function after surgery resulted in reduced cardiac stroke volume, increased left atrial pressure and a higher rate of perceived exertion on the first postoperative day.

Acute normovolemic hemodilution can aggravate neurological injury after spinal cord ischemia in rats

BACKGROUND

Acute normovolemic hemodilution (ANH) is currently performed during thoracoabdominal aortic surgery. However, the effects of ANH on spinal cord ischemic injury are currently unknown. Because hemodilution below a certain level of hematocrit (Hct) aggravates the neurological damage after cerebral ischemia, we hypothesized that ANH may increase neurological damage after spinal cord ischemia. The aim of these experiments was to determine the effects of ANH on spinal cord ischemic injury.

METHODS

Thirty male Sprague-Dawley rats were randomly assigned to 1 of the following 3 groups: no hemodilution (group C), target Hct level of 30% (group HD30), and target Hct level of 25% (group HD25). ANH was performed upon withdrawal of blood and simultaneous replacement with the same volume with hydroxyethyl starch. Spinal cord ischemia and reperfusion were induced by using a balloon-tipped catheter placed in the descending thoracic aorta, and changes in mean arterial blood pressure were recorded. Neurological function of the hindlimbs was evaluated for 7 days and recorded using a motor deficit score (MDS) (0 = normal; 5 = complete paraplegia). The number of motor neurons within the spinal cord was counted after final MDS evaluation.

RESULTS

Group HD25 developed hypotension during the latter part of the ANH procedure. Group C and group HD30 experienced 3 minutes of reperfusion hypotension, whereas 6 minutes of hypotension was observed in group HD25. Two rats in group HD25 died during the experimental period. Seven days after reperfusion, the MDS of group C, group HD30, and group HD25 was 1.0 (0.5-2.0), 1.0 (0.5-2.0), and 4.0 (2.8-4.2) (median [95% confidence interval]), respectively. Group HD25 showed significantly higher MDS compared with group C (corrected P = 0.0018; 95% CI for median difference = 1.0-3.5). Motor neuron numbers in the anterior horns of group C, group HD30, and group HD25 were 26.5 (25.0-27.5), 23.5 (22.0-26.5), and 12.5 (8.4-16.6) (median [95% CI]), respectively. Motor neuron numbers of group HD25 were significantly lower than those of group C (corrected P < 0.0001; 95% CI for median difference = 9.0-18.0).

CONCLUSION

The results of the present study indicate that intraoperative ANH to an Hct of 25%, combined with coincident hypotension, caused a delayed recovery of baseline mean arterial blood pressure during the reperfusion period and aggravated neurological outcome after spinal cord ischemia.

Controversies related to red blood cell transfusion in critically ill patients

OBJECTIVE

To review the evolution of and controversies associated with allogenic blood transfusion in critically ill patients.

DATA SOURCES

Veterinary and human literature review.

HUMAN DATA SYNTHESIS

RBC transfusion practices for ICU patients have come under scrutiny in the last 2 decades. Human trials have demonstrated relative tolerance to severe, euvolemic anemia and a significant outcome advantage following implementation of more restricted transfusion therapy. Investigators question the ability of RBCs stored longer than 2 weeks to improve tissue oxygenation, and theorize that both age and proinflammatory or immunomodulating effects of transfused cells may limit efficacy and contribute to increased patient morbidity and mortality. Also controversial is the ability of pre- and post-storage leukoreduction of RBCs to mitigate adverse transfusion-related events.

VETERINARY DATA SYNTHESIS

While there are several studies evaluating the transfusion trigger, the RBC storage lesion and transfusion-related immunomodulation in experimental animal models, there is little research pertaining to clinical veterinary patients.

CONCLUSIONS

RBC transfusion is unequivocally indicated for treatment of anemic hypoxia. However, critical hemoglobin or Hct below which all critically ill patients require transfusion has not been established and there are inherent risks associated with allogenic blood transfusion. Clinical trials designed to evaluate the effects of RBC age and leukoreduction on veterinary patient outcome are warranted. Implementation of evidence-based transfusion guidelines and consideration of alternatives to allogenic blood transfusion are advisable.

Factors affecting blood loss during percutaneous nephrolithotomy using balloon dilation in a large contemporary series

OBJECTIVE

Renal hemorrhage is a common and worrisome complication of percutaneous nephrolithotomy (PNL). We review factors affecting blood loss and transfusion requirements in a large contemporary series of patients undergoing PNL utilizing balloon dilation.

METHODS

We retrospectively reviewed all patients undergoing PNL at one institution from July 2000 to January 2008. Demographics, stone parameters, perioperative factors, complications, and stone-free rates were evaluated. Hemorrhage was estimated using hematocrit and blood transfusion requirement. Various factors were assessed for their association with blood loss using univariate models.

RESULTS

The 225 patients reviewed had a mean stone size of 3.5 +/- 1.8 cm (range, 0.6-9.0 cm), with 54 (23.4%) staghorn and 93 (40.3%) partial staghorn calculi. One hundred and seventy-five (75.8%), 173 (74.9%), and 80 (34.6%) had pelvic, lower pole, and upper pole calculi, respectively. Multiple access tracts were used in 12 (5.2%) patients, with overall stone-free and complication rates of 80.4% and 14.1%. Complications included postoperative fever in 15 patients (6.4%), clinically insignificant pleural effusion in 8 patients (3.4%), 2 (0.8%) renal artery pseudoaneurysms requiring angioembolization, and 1 (0.4%) urinoma requiring stent placement. Mean hematocrit decrease was 6.1 +/- 4.3%, with three (1.3%) patients receiving blood transfusions. On univariate analysis no other statistically significant differences were found between hematocrit decrease and stone size or location, presence of partial or complete staghorn calculi, diabetes, or number of access tracts.

CONCLUSIONS

We report a comparable stone-free rate and a lower incidence of blood transfusion among patients undergoing PNL using balloon dilation.

Red blood cell transfusion in the treatment and management of anaemia: the search for the elusive transfusion trigger

Therapeutic red blood cell (RBC) transfusion is widely utilized in the management of anaemia. Critically ill intensive care unit (ICU) patients in particular, as well as medical and haematology-oncology patients, are among the largest groups of users of RBC products. While anaemia is common in these patients, its treatment and management, including appropriate thresholds for RBC transfusion, remain controversial. We review here the function of RBCs in oxygen transport and physiology, with a view to their role in supporting and maintaining systemic tissue oxygenation. Adaptive and physiological compensatory mechanisms in the setting of anaemia are discussed, along with the limits of compensation. Finally, data from clinical studies will be examined in search of evidence for, or against, a clinically relevant transfusion trigger.

The effect of hemodilution during normothermic cardiac surgery on renal physiology and function: a review

Although the definitions of renal dysfunction vary, loss of renal function is a common complication following cardiac surgery using cardiopulmonary bypass (CPB). When postoperative dialysis is required, mortality is approximately 50%. CPB-accompanied hemodilution is a major contributing factor to renal damage as it notably reduces oxygen delivery by reducing the oxygen transport capacity of the blood as well as disturbing the microcirculation. To minimize hypoxemic damage during CPB, lowering of body temperature is applied to reduce the patient’s metabolic rate. At present, however, temperature management during elective adult cardiac surgery is shifting from moderate hypothermia to normothermia. To determine whether the currently accepted levels of hemodilution during CPB can suffice the normothermic patient’s high oxygen demand, we focused this study on renal physiology and postoperative renal function. Hemodilution reduces the capillary density through a diminished capillary viscosity, thereby, redistributing blood from the renal medulla to the renal cortex. As the physiology of the renal medulla makes it a hypoxic environment, this part of the kidney appears to be especially at risk for hypoxic damage caused by a hemodilution-induced lowered oxygen transport and oxygen delivery. In addition, hemodilution is also likely to disturb the hormonal systems regulating renal blood distribution. Clinical studies, mostly of retrospective or observational nature, show that perioperative nadir hematocrit levels lower than approximately 24% are associated with an increased risk to develop postoperative renal failure. A better comprehension of the cause-and-effect relation between low perioperative hematocrits and loss of postoperative renal function may enable more effective renal protective strategies.

Red blood cell transfusion in clinical practice

Every year, about 75 million units of blood are collected worldwide. Red blood cell (RBC) transfusion is one of the few treatments that adequately restore tissue oxygenation when oxygen demand exceeds supply. Although the respiratory function of blood has been studied intensively, the trigger for RBC transfusion remains controversial, and doctors rely primarily on clinical experience. Laboratory assays that indicate failing tissue oxygenation would be ideal to guide the need for transfusion, but none has proved easy, reproducible, and sensitive to regional tissue hypoxia. The clinical importance of the RBCs storage lesion (ie, the time-dependent metabolic, biochemical, and molecular changes that stored blood cells undergo) is poorly understood. RBCs can be filtered, washed, frozen, or irradiated for specific indications. Donor screening and testing have dramatically reduced infectious risks in the developed world, but infection remains a major hazard in developing countries, where 13 million units of blood are not tested for HIV or hepatitis viruses. Pathogen inactivation techniques are in clinical trials for RBCs, but none is available for use. Despite serious immunological and non-immunological complications, RBC transfusion holds a therapeutic index that exceeds that of many common medications.

Allogeneic red blood cell transfusion: Physiology of oxygen transport

Allogeneic red blood cell (RBC) transfusions have been shown to be associated with considerable risks. While their efficiency in many clinical situations has not been proven, the number of studies finding adverse outcomes in terms of morbidity (e.g. postoperative infections) and mortality continues to rise. In view of these facts, physicians involved in transfusion medicine have to be as restrictive as possible with RBC transfusions. Only a thorough knowledge of the physiology and pathophysiology of oxygen transport can be a solid base for meaningful transfusion decisions. Therefore, the goal of this article is to review the basics of oxygen transport and normovolaemic anaemia.

Percutaneous nephrolithotomy: variables that influence hemorrhage

OBJECTIVES

Renal hemorrhage is one of the most common and worrisome complications of percutaneous nephrolithotomy (PCNL). This study attempted to identify variables that might influence hemorrhage during PCNL to help urologists establish preventative and treatment strategies for bleeding during PCNL procedures.

METHODS

The data of 193 patients (193 PCNL procedures) were retrospectively analyzed. Hemorrhage was estimated by the postoperative decrease in hematocrit factored by the quantity of any blood transfusion. Various preoperative and operative factors were assessed for their association with blood loss using univariate, forward multivariate regression and correlation analysis.

RESULTS

The mean patient age was 45.7 +/- 14.4 years (range 5 to 74). The overall stone-free rate was 85.4%. The average hematocrit decrease was 8.7% +/- 5.39% (range 0.3 to 24.7). Forward multivariate regression analysis identified five significant variables that influenced PCNL-related hemorrhage: stone type (P = 0.003), number of tracts (P = 0.010), method of dilation (P = 0.010), diabetes (P = 0.022), and stone surface area (P = 0.049). A statistically significant difference was found in relation to the occurrence of hemorrhage between patients with caliceal stones and partial staghorn stones (P = 0.008) and complete staghorn stones (P = 0.006), single tracts and multiple tracts (P = 0.038), balloon dilators and Amplatz dilators (P = 0.007), patients with small stones (1000 mm2 or smaller) and large stones (greater than 1000 mm2; P = 0.018) on univariate analysis. Also, the stone surface area (P = 0.019) and number of tracts (P = 0.024) showed a positive correlation with the mean hematocrit decrease.

CONCLUSIONS

Staghorn stones, multiple tracts, the presence of diabetes, and large stones were associated with increased renal hemorrhage during PCNL on multivariate analysis. However, balloon dilation was associated with decreased hemorrhage.

[Tolerance to perioperative anemia. Mechanisms, influencing factors and limits]

The expected cost explosion in transfusion medicine increases the socio-economic significance of specific institutional transfusion programs. In this context the estimated use of the patient's physiologic tolerance represents an integral part of any blood conservation concept. The present article summarizes the mechanisms, influencing factors and limits of this natural tolerance to anemia and deduces the indication for perioperative red blood cell transfusion. The current recommendations coincide to the effect that perioperative transfusion is unnecessary up to a Hb concentration of 10 g/dl (6.21 mmol/l) even in older patients with cardiopulmonary comorbidity and is only recommended in cases of Hb <6 g/dl (<3.72 mmol/l) in otherwise healthy subjects including pregnant women and children. Critically ill patients with multiple trauma and sepsis do not seem to benefit from transfusions up to Hb concentrations >9 g/dl (>5.59 mmol/l). In cases of massive hemorrhaging and diffuse bleeding disorders the maintenance of a Hb concentration of 10 g/dl (6.21 mmol/l) seems to contribute to stabilization of coagulation.

Indications for Blood Transfusion in Cardiac Surgery

In addition to its life-saving effect in hemorrhagic shock, transfusion of allogenic packed red blood cells can be beneficial in situations where a critically low hematocrit is contributing to a state of oxygen-supply dependency. These benefits are countered by the risks of transfusion-associated lung injury, transfusion-associated immunomodulation, and cellular hypoxia after RBC transfusion. The critical hematocrit is patient and organ specific, and varies intraoperatively according to the duration and temperature of bypass, as well as for a variable postoperative period. Future randomized studies must prospectively evaluate regional indicators of tissue oxygenation in transfusion algorithms.

[Tolerance to perioperative anemia. Mechanisms, influencing factors and limits]

The expected cost explosion in transfusion medicine (increasing imbalance between donors and potential recipients, treatment of transfusion-associated complications) increases the socio-economic significance of specific institutional transfusion programs. In this context the estimated use of the patient's physiologic tolerance to anemia enables 1) the tolerance of larger blood losses (loss of "diluted blood"), 2) the onset of transfusion to the time after surgical control of bleeding to be delayed and 3) the perioperative collection of autologous red blood cells. The present review article summarizes the mechanisms, influencing factors and limits of this natural tolerance to anemia and deduces the indication for perioperative red blood cell transfusion. Under strictly controlled conditions (anesthesia, normovolemia, complete muscular relaxation, hyperoxemia, mild hypothermia) extremely low hemoglobin concentrations [Hb <3 g/dl (<1.86 mmol/l)] are tolerated without transfusion by individuals with no cardiopulmonary disease. In the clinical routine these situations are limited to borderline situations e.g. unexpected massive blood losses in Jehovah's Witnesses or unexpected shortcomings in blood supply. The current recommendations coincide to the effect that perioperative red blood cell transfusion 1) is unnecessary up to a Hb concentration of 10 g/dl (6.21 mmol/l) even in older patients with cardiopulmonary comorbidity and 2) is only recommended in cases of Hb <6 g/dl (<3.72 mmol/l) in otherwise healthy subjects including pregnant women and children. Critically ill patients with multiple trauma and sepsis do not seem to benefit from transfusions up to Hb concentrations >9 g/dl (>5.59 mmol/l). In cases of massive hemorrhaging and diffuse bleeding disorders the maintenance of a Hb concentration of 10 g/dl (6.21 mmol/l) seems to contribute to stabilization of coagulation.

The Effect of Gain in Total Body Water on Haemoglobin Concentration and Body Weight Following Cardiac Surgery

BACKGROUND

Haemodilution contributes to a low post-operative haemoglobin concentration in cardiac surgery patients. An assessment of the degree of haemodilution could contribute to the avoidance of red cell transfusion when such an act is based simply on a haemoglobin "transfusion trigger". We have recorded post-operative change in total body water along with body weight to assess the impact of haemodilution on haemoglobin concentration.

METHODS

Total body water, measured by bio-electrical impedance analysis, haemoglobin and body weight were measured pre-operatively and on the 1st, 3rd, 5th and 10th post-operative days. The percentage peri-operative change in all three variables was used to examine the paired associations.

RESULTS

Total body water and body weight underwent a fall from day 1, with both variables significantly associated up until day 10. Haemoglobin rose steadily from day 1 to 10. This rise was associated with falling total body water and body weight until day 5, but not from day 5 to 10.

CONCLUSION

Following cardiac surgery, an individual's fluid state should be considered in determining a patient's need for red cell transfusion. Monitoring body weight provides a simple estimate. Such an approach may reduce the incidence of unnecessary, and potentially counterproductive, transfusion in cardiac surgery patients.

The Marked Reduction in Mixed Venous Oxygen Saturation During Early Mobilization After Cardiac Surgery: The Effect of Posture or Exercise?

Early mobilization after cardiac surgery induces a marked reduction in mixed venous oxygen saturation (Svo2). Using pulmonary artery catheters and indirect calorimetry, we investigated the effects of exercise and postural change on cardiac index (CI) and Svo2 before and on the first morning after coronary artery bypass surgery. Sixteen patients with an ejection fraction >0.50 were studied at rest, during supine bicycle exercise, and during passive standing. Supine cycling at 30 W increased CI by 1.5 +/- 0.8 L x min(-1) x m(-2) before and 0.9 +/- 0.7 L x min(-1) x m(-2) after surgery (P < 0.05), whereas Svo2 was reduced from 80% +/- 4% at rest to 63 +/- 6% preoperatively (P < 0.05) and from 71% +/- 5% to 46% +/- 11% postoperatively (P < 0.05). Passive standing reduced CI by 0.8 +/- 0.5 L x min(-1) x m(-2) before and 0.3 +/- 0.4 L x min(-1) x m(-2) after surgery (P < 0.05). Svo2 was reduced from 79% +/- 5% to 64% +/- 7% preoperatively (P < 0.05) and from 72% +/- 6% to 60% +/- 6% postoperatively (P < 0.05). The exercise challenge revealed an altered cardiovascular response after surgery, causing a larger reduction in Svo2 for the same workload. Passive standing significantly reduced Svo2 both days, but this effect was less pronounced after surgery. The response to postural change and exercise was altered after surgery and may both contribute to the reduction in Svo2 during postoperative mobilization.

Anemia and perioperative red blood cell transfusion: a matter of tolerance

In the past, anemia in the perioperative period has been treated by red blood cell (RBC) transfusions relatively uncritically. RBC transfusions were believed to increase oxygen delivery by increasing hemoglobin concentration. Arbitrary transfusion triggers such as the "10/30 rule" (i.e., RBC transfusion indicated below a hemoglobin concentration of 10 g/dL or a hematocrit of 30%) were applied. However, there is now increasing evidence that RBC transfusions are associated with adverse outcomes and should be avoided whenever possible. Restraining from RBC transfusions and maintaining normovolemia in patients suffering from surgical blood loss results in acute anemia. Therefore, knowing the compensatory mechanisms during acute anemia is crucial. This review focuses on acute anemia tolerance, its limits, and physiologic transfusion triggers in the perioperative period.

Cardioprotective effects of acute isovolemic hemodilution in a rat model of transient coronary occlusion*

OBJECTIVES

Following isovolemic hemodilution (AIH), lowering blood viscosity induces acceleration of erythrocyte velocity resulting in improved tissue oxygen delivery. Using a rat model of myocardial infarct, we tested the hypothesis that AIH would attenuate myocardial damage due to transient coronary occlusion.

DESIGN

Prospective, randomized, and controlled animal study.

SETTING

Animal research laboratory in a university hospital.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

All rats were subjected to 30 mins of left coronary artery occlusion followed by 48 hrs of reperfusion. Before the ischemic period, the anesthetized rats were randomly allocated to undergo either 15 mins of waiting (controls) or AIH to achieve a hematocrit of 30% (AIH-CO) by stepwise blood withdrawal and isovolemic compensation with 6% hydroxyethylstarch 200-0.5.

MEASUREMENTS AND MAIN RESULTS

Hemodynamic variables were comparable in the two groups, except for higher indexes of stroke volume in the AIH-CO group. During coronary occlusion and the reperfusion period, AIH resulted in a lower incidence of fatal ventricular tachyarrhythmia (17% vs. 50% in control group, p < .05) and higher survival at 48 hrs of postreperfusion (83% vs. 42%, p < .05).Preischemic hemodilution significantly attenuated myocardial damage as shown by lower release of cardiac troponin I and reduction in myocardial infarct size as measured by tetrazolin staining. Histologic examination revealed no difference regarding peri-ischemic infiltration with neutrophil granulocytes.

CONCLUSIONS

Our data provide the first experimental demonstration that preischemic moderate AIH confers cardioprotection and improves survival in a rat model of myocardial infarct.