Relationship between antithrombin and thrombin levels in plasma and serum

The haemodilution enhanced onset of coagulation as measured by the thrombelastogram is transient

BACKGROUND AND OBJECTIVE

Crystalloid haemodilution has been widely found to enhance coagulation onset, but the duration of this effect has never been documented.

METHODS

Twelve healthy, consenting volunteers had a rapid infusion of 14 mL kg-1 of normal (0.9%) saline. Blood samples were taken, prior to (control), and immediately after (30 min) the rapid saline infusion was completed (30 min). They were then repeated at regular intervals up to 120 min. Haematocrit/platelet counts were taken to determine the degree of dilution and thrombelastograms, with and without platelet antagonists (ReoPro, Abciximab), were measured in all samples. Antithrombin levels were selectively measured.

RESULTS

The haematocrit and platelet count showed a rapid dilutional decrease at 30 min (mean of -12.2% and -14.4%, respectively), with values returning towards baseline within 15 min after finishing the infusion. There was a significantly faster onset of coagulation (decrease in r-time) in the post-infusion sample (30 min) compared to control (P<0.05), again returning towards normal as the dilution effect was reversed. Similar thrombelastograms findings were evident in the plasma factor only group (platelets inhibited by ReoPro). Antithrombin levels changed in keeping with the haemodilution effect (P<0.0001). There was a linear relationship between antithrombin and thrombelastograms r-time (P=0.012).

CONCLUSION

The faster onset of coagulation brought on by haemodilution return towards normal as the dilutional effect is reversed. This effect is mediated through plasma clotting factors. Of interest is the significant inverse correlation of the onset of coagulation increasing as the antithrombin levels decreased with dilution.

Are lactated Ringer's solution and normal saline solution equal with regard to coagulation?

Crystalloids represent an attractive strategy to alleviate intravascular volume deficits. Crystalloid hemodilution was associated with hypercoagulability in in vitro and in vivo studies. The influence of different crystalloids on coagulation in the surgical patient is not well studied. In a prospective, randomized study in patients undergoing major abdominal surgery, we used either lactated Ringer's solution (RL) (n = 21) or 0.9% saline solution (SS) (n = 21) exclusively for intravascular volume replacement over 48 h to maintain central venous pressure between 8 and 12 mm Hg. Activated thrombelastography (TEG) using different activators (intrinsic TEG, extrinsic TEG, heparinase TEG, aprotinin TEG) was used to measure coagulation time, clot formation time, and maximum clot firmness. Measurements were performed after induction of anesthesia (T0), immediately after surgery (T1), 5 h after surgery (T2), and on the morning of the first (T3) and second (T4) postoperative days. RL 18,750 +/- 1890 mL and 17,990 +/- 1790 mL of SS were infused during the study period. Acidosis was seen only in the SS-treated group. Blood loss was not different between the groups. Fibrinogen and antithrombin III decreased similarly at T1 and T2 in both groups, most likely because of hemodilution. Differences in TEG data from normal baseline were seen only immediately after surgery and 5 h thereafter, indicating mild hypercoagulability in the intrinsic TEG (RL, from 147 +/- 130 s to 130 +/- 11 s; SS, from 146 +/- 12 s to 131 +/- 12 s). There were no differences in coagulation between RL- and SS-treated patients. We conclude that in major abdominal surgery intravascular volume replacement with crystalloids resulted in only moderate and abbreviated changes in coagulation. No differences in activated TEG and blood loss were seen between an RL- and an SS-based intravascular volume replacement regimen.

IMPLICATIONS

In 42 patients undergoing major abdominal surgery, either lactated Ringer's solution or 0.9% saline solution were exclusively used for volume therapy for 48 h. Activated thrombelastography revealed some mild hypercoagulability after surgery. No differences in coagulation were seen between the two intravascular volume replacement strategies.

Haemodilution-induced enhancement of coagulation is attenuated in vitro by restoring antithrombin III to pre-dilution concentrations

Moderate haemodilution enhances coagulability in vitro and in vivo as measured by thrombelastography (TEG). The mechanism has never been established. We have conducted an in vitro study to determine whether the effect can be moderated or prevented when the reduction in antithrombin III caused by dilution is prevented by supplementation. Blood from 20 volunteers was divided into four samples. One sample was not diluted and served as control (C). Another was diluted (by 20%) with saline (S). The third was diluted by 20% with saline plus two units of antithrombin (AT III) (SA). The fourth remained undiluted, with two units of added AT III (CA). Coagulation was measured in all four samples using the TEG. In a separate laboratory study, the levels of AT III were measured in control samples and compared with levels after 20% dilution, and 20% dilution with two units of AT III added to the diluent. Enhanced coagulation was demonstrated in saline-diluted samples (S) by shortening of r- and k-times, and increased alpha angle. In the SA samples, r-time shortening was prevented; k-time shortening and alpha-angle increase persisted, but to a reduced degree (difference from saline-only dilution P<0.051). There were no differences between samples C and CA. A predictable drop of AT III (24.2%) occurred with saline dilution, while AT III levels in the AT III/Saline group were similar to the undiluted control. Haemodilution-induced coagulation enhancement is attenuated, but not prevented, if AT III levels are maintained in the normal range. This is in keeping with the established concept of an antithrombin threshold preventing positive coagulation feedback into the intrinsic pathway.

THROMBIN GENERATION IN NORMAL SUBJECTS AND CARDIAC PATIENTS

A refined, reliable thrombin generation test with good sensitivity for both hypo- and hypercoagulability is described. When serial thrombin generation curves were obtained in cardiac patients subjected to standardized treadmill stress, fluctuations of the clotting system were observed in some and a marked tendency to hypercoagulability in others. The relationship of in vitro hypercoagulability as reflected by thrombin generation to an increased tendency to thrombosis remains to be determined.

Early oral hydration: a novel regimen for management after elective cesarean section

OBJECTIVE

To compare early oral hydration versus the conventional intravenous fluid replacement after elective cesarean section.

METHODS

Two hundred women performed elective cesarean section were selected and randomized to: Regimen I (n = 100): early oral hydration (sips of fruit juices sweetened with honey once the women felt thirst immediately after the operation, then solid food 24 hours later, the amounts of juice or food were determined by the patient herself, i.e. she would regulate her physiological needs) versus regimen II (n = 100): conventional intravenous hydration (2-3 L of dextrose saline/24 hours and solid food thereafter). Biochemical, metabolic values, postoperative nausea and vomiting, propulsive bowel movements, tolerance of solid food, hospital stay and successful continuation of breast feeding were compared in both groups.

RESULTS

The two regimens were equally effective in maintaining fluid balance and normal plasma and urinary electrolytes without any observed differences in biochemical or metabolic values. The return of bowel sounds, first occurrence of flatus and tolerance of solid food were achieved in regimen I at time periods significantly shorter than those attained with regimen II (p < 0.0001). The incidence of nausea and vomiting, ileus and deep vein thrombosis was higher in regimen II than in regimen I but the difference is statistically insignificant (p > 0.05). Patients in regimen II were hospitalized for significantly longer times than those on regimen I (p < 0.0001). Successful continuation of breast feeding was significantly more in regimen I than in regimen II (p < 0.01).

CONCLUSION

Early oral hydration after elective cesarean section effectively maintained fluid balance and it was associated with rapid return of propulsive bowel movements, successful breast feeding, less side effects and shorter hospital stay than the conventional intravenous hydration. So, it should be used in most cases after elective cesarean section.

The end of the crystalloid era? A new approach to peri-operative fluid administration

The metabolic response to surgery causes sodium and water retention. It does not seem logical to pour crystalloid solutions into patients in the peri-operative period, particularly when these solutions can cause deterioration in lung function. Plasma volume must be maintained to prevent a decreased blood flow to vital organs such as the kidneys. Blood or colloid solutions, not crystalloid solutions, should be used for this purpose, since the latter are distributed throughout the whole extracellular space and are less effective in maintaining plasma volume. Water given as 5% dextrose should be given in minimal quantities to maintain intracellular hydration. Patients undergoing minor to moderate surgery when they are likely to be drinking within 24 hours do not usually require any intravenous infusion. Moreover, to administer intravenous fluids to these patients may cause harm. No fluid regimens should be inflexible and the patient's size, age and fluid losses should be taken into account.

Postoperative deep vein thrombosis caused by intravenous fluids during surgery

Using a new method of measuring whole blood clotting time, we have confirmed the findings of others, that blood clots faster when diluted with saline. A prospective trial was designed to test the hypothesis that intravenous saline peroperatively causes hypercoagulation and increases the risk of venous thrombosis. Sixty patients admitted for routine laparotomy were randomly allocated to either a group receiving intravenous fluids during or after operation (Wet), or a group receiving no intravenous fluids (Dry). The Wet patients became significantly more haemodilute and hypercoagulable than the Dry (P < 0.001), and these changes correlated. A postoperative deep vein thrombosis occurred in 30 per cent of the Wet patients, but in only 7 per cent of the Dry (P < 0.05). The need for intravenous fluids during uncomplicated surgery is probably unproved, and their greater use may have contributed to the increasing prevalence of venous thromboembolism.

CHANGES IN THROMBIN GENERATION AND ANTITHROMBIN TITER FOLLOWING MASSIVE BLEEDING AND TRANSFUSION IN DOGS

Thrombin generation, plasma antithrombin levels, and plasma protein levels were measured in dogs following rapid massive bleeding and transfusion. Three groups of four dogs per group were used. One group was transfused with saline, one with dextran, and one with a plasma fraction. The plasma fraction was prepared from mixed dog plasma by a procedure designed to remove most of the known clotting factors with a minimum of damage to other proteins. The in vivo dilution of blood by transfusion with two volumes of saline or one of plasma fraction increased the rate of thrombin generation. Dilution by transfusion with dextran decreased both rate and amount of thrombin generation. For the first few hours following transfusion with saline, plasma antithrombin increased more rapidly than total plasma protein. This was probably a result of increased lymph flow. Fluctuations in the coagulability of the blood were observed up to 72 hours following bleeding and transfusion. The fluctuations following saline transfusion were less prolonged than when dextran or plasma fraction was used.