A simple method for calculating component dilution during fluid resuscitation: the Leuven approach

Hemostasis and hemodilution: a quantitative mathematical guide for clinical practice

Quantitative changes of hemostasis during hemodilution remain unclear. With the increasing popularity of artificial blood substitutes (ABS), which solely provide oxygen-transport capacity, this issue becomes even more complex. We developed a mathematical model to quantitatively analyze hemostasis during hemodilution and validated it by recalculating patient data. We calculated and compared maximal allowable blood losses (MABL) related to minimal acceptable hematocrit, platelet concentration, and plasma fibrinogen concentration. MABL is the maximal blood loss that can be tolerated without any additional blood products. The variable with the smallest MABL thus limits hemodilution foremost. Hemodilution included isovolemic replacement of blood loss with colloid or acute normovolemic hemodilution (ANH) followed by isovolemic replacement of blood loss with colloid and ABS. We also related our findings to preoperative patient data (n = 204). The decline in platelet concentrations rarely (<2% of all patients) limits hemodilution. By contrast, critical plasma fibrinogen (< or =100 mg/dL) concentrations can often (< or =20% of all patients) limit hemodilution if their initial concentrations are within the lower normal range (<300 mg/dL). These findings become more frequent if ANH is combined with ABS. Under those circumstances ANH blood products are solely required for stabilization of hemostasis, thereby defeating the original purpose of combining ANH with ABS.

IMPLICATIONS

The causes of quantitative changes of hemostasis during hemodilution, as well as their clinical effect and relevance, remain unclear. Using a validated, realistic mathematical model, we demonstrate that hemostasis, especially plasma fibrinogen, can limit the extent of hemodilution. This phenomenon is particularly prominent when acute normovolemic hemodilution is combined with artificial blood substitutes.

A cohort study of coagulation parameters and the use of blood products in surgery of the thoracic and thoracoabdominal aorta

OBJECTIVES

We sought to study the hemostatic profile and the use of blood products in patients undergoing thoracic and thoracoabdominal aortic aneurysm repair.

METHODS

This is a cohort study comparing three groups of patients: 7 undergoing elective acute normovolemic hemodilution (ANH); 15 undergoing elective procedures without ANH (non-ANH); and 8 undergoing repair of ruptured thoracoabdominal aneurysms. A control group of 10 patients was used for comparison of preoperative hemostasis. The parameters studied were platelet concentration, partial thromboplastin time (PTT), and international normalized ratio (before and after surgery), packed red blood cells, fresh frozen plasma, platelets, cryoprecipitates, donor exposure, and use of desmopressin and epsilon-aminocaproic acid. Analysis of variance and multiple stepwise regression analysis were used.

RESULTS

Before operation the patients with aneurysms had PTTs prolonged compared with control subjects (P <.05). After operation the ANH group had higher platelet counts than the ruptured group (P =.001) and higher platelet counts (P =.05) and lower PTTs (P =.001) than the non-ANH group. The ANH group was transfused fewer platelets than the non-ANH group (P =.001) and less of every blood product than the ruptured group (P =.05); statistically significant differences were not observed for packed red blood cells, fresh frozen plasma, or platelets. The ANH group was exposed to an average of 65 donors fewer than the ruptured group (P <.001) and 34 fewer than the non-ANH group (P <.05). These differences could not be explained by baseline coagulation status or by the intraoperative use of desmopressin or epsilon-aminocaproic acid.

CONCLUSIONS

The coagulation abnormality identified before surgery is that of higher PTT values, suggesting a disturbance of the extrinsic coagulation pathway. Blood losses, donor exposure, and platelet use were highest in the ruptured group and lowest in the ANH group. After surgery the ruptured group exhibited the worst coagulation parameters, and the ANH group exhibited the best with higher platelet count and lower PTT values than the other groups. The ANH technique appears to be an useful adjunct in the anesthetic management of these patients.

Effects of 6% hydroxyethyl starch and 3% modified fluid gelatin on intravascular volume and coagulation during intraoperative hemodilution

In the perioperative period, artificial colloids are most often infused in doses of 500-1000 mL intravenously. This randomized study compared the effects on intravascular volume and coagulation of approximately 2000 mL of two isooncotic artificial colloids: 6% hydroxyethyl starch (HES; MW 200,000; substitution ratio 0.40-0.55) and 3% modified fluid gelatin (GEL). We hypothesized more pronounced hypocoagulation with HES and a weaker intravascular volume effect of GEL. Forty-two patients, scheduled for primary total hip replacement, were allocated randomly to receive HES or GEL during acute normovolemic hemodilution and subsequent further intraoperative hemodilution. Blood samples were taken before and after 500 mL and 1000 mL of acute normovolemic hemodilution; intraoperatively after 20 mL/kg of artificial colloid and at the end of colloid infusion; on arrival in the recovery room; and 3 h later. We quantified: 1) coagulation variables; 2) blood loss; 3) hemodynamic stability; 4) necessary infusion volume; 5) interstitial extravasation, calculated from plasma volunteers measured using albumin marked with technetium-99m and iodine-125, respectively; 6) percentage volume effect at the end of the study as well as hematocrit, total serum protein, and colloid osmotic pressure. Intraoperative volume therapy was guided by radial systolic pressure and systolic pressure variation, mixed venous hemoglobin saturation in the pulmonary artery, and pulmonary capillary occlusion pressure.(ABSTRACT TRUNCATED AT 250 WORDS)