Cardiac response is greater for colloid than saline fluid loading after cardiac or vascular surgery

OBJECTIVE

To study the effects on volume expansion and myocardial function of colloids or crystalloids in the treatment of hypovolaemic hypotension after cardiac and major vascular surgery.

DESIGN AND SETTING

A single-centre, single-blinded, randomized clinical trial at the intensive care unit of a university hospital.

PATIENTS AND METHODS

Patients (n=67) were subjected to a 90-min filling pressure-guided fluid challenge with saline 0.9% or the colloids gelatin 4%, hydroxyethyl starch 6% or albumin 5%. Biochemical variables and haemodynamics (transpulmonary thermodilution) were measured.

RESULTS

An amount of 1800 (1300-1800) ml of saline or 1600 (750-1800) ml of colloid solution (P< 0.005) was infused. Colloid osmotic pressure (COP) decreased in the saline group and increased in the colloid groups (P< 0.001). Plasma volume increased by 3.0% (-18 to 24) in the saline versus 19% (-11 to 50) in the colloid groups (P< 0.001). Cardiac index increased by median 13% (ns) in the saline group and by 22% in the colloid groups (P<0.005). The rise in left ventricular stroke work index was greater in the colloid than in the saline groups. The different colloids were equally effective. The rise in cardiac index related to the rise in plasma volume and global end-diastolic volume, confirming plasma volume and preload augmentation by the fluid loading.

CONCLUSION

After cardiac or major vascular surgery, the pressure- and time-guided fluid response is dependent on the type of fluid used. Colloid fluid loading leads to a greater increase in preload-recruitable cardiac and left ventricular stroke work indices than that with saline, because of greater plasma volume expansion following an increase in plasma COP.

Registered Replication Report: Schooler and Engstler-Schooler (1990)

Trying to remember something now typically improves your ability to remember it later. However, after watching a video of a simulated bank robbery, participants who verbally described the robber were 25% worse at identifying the robber in a lineup than were participants who instead listed U.S. states and capitals-this has been termed the "verbal overshadowing" effect (Schooler & Engstler-Schooler, 1990). More recent studies suggested that this effect might be substantially smaller than first reported. Given uncertainty about the effect size, the influence of this finding in the memory literature, and its practical importance for police procedures, we conducted two collections of preregistered direct replications (RRR1 and RRR2) that differed only in the order of the description task and a filler task. In RRR1, when the description task immediately followed the robbery, participants who provided a description were 4% less likely to select the robber than were those in the control condition. In RRR2, when the description was delayed by 20 min, they were 16% less likely to select the robber. These findings reveal a robust verbal overshadowing effect that is strongly influenced by the relative timing of the tasks. The discussion considers further implications of these replications for our understanding of verbal overshadowing.

Thiols protect the inhibition of myocardial aconitase by peroxynitrite

Peroxynitrite (ONOO-) is a potent inhibitor of myocardial aconitase. Because ONOO- reacts with sulfhydryl moieties, we investigated whether thiols protect against ONOO(-)-mediated inhibition of aconitase. Aconitase activity was examined in ventricular homogenates prepared from freshly isolated rat hearts. Peroxynitrite, but not the nitric oxide donor S-nitroso-N-acetyl-d,l-penicillamine (0.03-300 microM), inhibited aconitase activity (IC50 = 47 +/- 6 microM). L-Cysteine (0.03-3 mM), glutathione (0.03-3 mM), and N-(2-mercaptoproprionyl)-glycine (MPG, 0.1-3 mM) protected against the inhibitory effect of ONOO- (100 microM) with the rank order of potency of MPG > glutathione > L-cysteine. D-Cysteine (3 mM) had a protective effect similar to L-cysteine, but L-cystine, the oxidized form of L-cysteine, offered no protection. Ferrous ammonium sulfate (1 mM) markedly enhanced the protection provided by L-cysteine, but not by glutathione or MPG. Thiols protect myocardial aconitase against inhibition by ONOO- in a manner which is sulfhydryl group dependent and not stereospecific. The protection is related to the maintenance of the redox state of the iron-sulfur cubane cluster and cysteine residues at the active site of the enzyme. Both naturally occurring thiols and thiol-based drugs may be useful to protect the heart during ischemia-reperfusion injury where there is an excessive production of ONOO-.

Effect of high or low protamine dosing on postoperative bleeding following heparin anticoagulation in cardiac surgery

While experimental data state that protamine exerts intrinsic anticoagulation effects, protamine is still frequently overdosed for heparin neutralisation during cardiac surgery with cardiopulmonary bypass (CPB). Since comparative studies are lacking, we assessed the influence of two protamine-to-heparin dosing ratios on perioperative haemostasis and bleeding, and hypothesised that protamine overdosing impairs the coagulation status following cardiac surgery. In this open-label, multicentre, single-blinded, randomised controlled trial, patients undergoing on-pump coronary artery bypass graft surgery were assigned to a low (0.8; n=49) or high (1.3; n=47) protamine-to-heparin dosing group. The primary outcome was 24-hour blood loss. Patient haemostasis was monitored using rotational thromboelastometry and a thrombin generation assay. The low protamine-to-heparin dosing ratio group received less protamine (329 ± 95 vs 539 ± 117 mg; p<0.001), while post-protamine activated clotting times were similar among groups. The high dosing group revealed increased intrinsic clotting times (236 ± 74 vs 196 ± 64 s; p=0.006) and the maximum post-protamine thrombin generation was less suppressed in the low dosing group (38 ± 40% vs 6 ± 9%; p=0.001). Postoperative blood loss was increased in the high dosing ratio group (615 ml; 95% CI 500–830 ml vs 470 ml; 95% CI 420–530 ml; p=0.021) when compared to the low dosing group, respectively. More patients in the high dosing group received fresh frozen plasma (11% vs 0%; p=0.02) and platelet concentrate (21% vs 6%; p=0.04) compared to the low dosing group. Our study confirms in vitro data that abundant protamine dosing is associated with increased postoperative blood loss and higher transfusion rates in cardiac surgery.

A Pharmacokinetic Model for Protamine Dosing After Cardiopulmonary Bypass

OBJECTIVE

This study investigated postoperative hemostasis of patients subjected to conventional protamine dosing compared with protamine dosing based on a pharmacokinetic (PK) model following cardiopulmonary bypass.

DESIGN

Retrospective case-control study.

SETTING

Tertiary university hospital.

PARTICIPANTS

Patients undergoing elective cardiac surgery with cardiopulmonary bypass.

INTERVENTIONS

In 56 patients, protamine was dosed in a fixed ratio (CD), while 62 patients received protamine based on the PK model.

MEASUREMENTS AND MAIN RESULTS

There was no difference in heparin administration (414±107 mg (CD) v 403±90 mg (PK); p = 0.54), whereas protamine dosing was considerably different with a protamine-to-heparin dosing ratio of 1.1±0.3 for the CD group and 0.5±0.1 for the PK group (p<0.001). The changes in activated coagulation time (ΔACT) values (ACT after protamine minus preoperative ACT;+17±77 s v+6±15 s; p = 0.31) were equal between groups. Yet, the thromboelastometric intrinsically activated coagulation test clotting time (CT; 250±76 s v 203±44 s; p<0.001) and intrinsically activated coagulation test without the heparin effect CT (275±105 v 198±32 s; p<0.001) were prolonged in the CD group. Median packed red blood cell transfusion (0 [0-2] v 0 [0-0]), fresh frozen plasma transfusion (1 [0-2] v 0 [0-0]), and platelet concentrate transfusion (0 [0-1] v 0 [0-0]) were different between the fixed ratio and PK group, respectively (all p<0.001).

CONCLUSIONS

This study showed that patient-tailored protamine dosing based on a PK model was associated with a reduction in protamine dosing, with better hemostatic test results when compared with fixed-ratio protamine dosing.

Thickness matching in planar multilayer waveguides

A theoretical method is described from which the thickness of an arbitrary layer in a dielectric multilayer stack is determined if all other thicknesses and all refractive indices are given, such that a prescribed effective index for a given mode of the stack is obtained. The same theory can determine the optimal cover thickness of such a stack for prism coupling. Experimental verification shows effective indices that are in agreement with the designed values.

Ac-225 radiochemistry through the lens of [225Ac]Ac-DOTA-TATE

BACKGROUND

Targeted alpha therapy with Ac-225 showed to be effective in treating metastatic cancers. However, the complex decay chain requires optimized radiolabeling and quality control. This study aims to determine critical parameters and establish optimal labeling and accurate measuring techniques for radiochemical yield and purity with DOTA-TATE as a model molecule. Ac-225 sources were analyzed for metals (ΣFe, Zn, Cu) and quantified by UPLC. Optimization of radiolabeling kinetics for clinical conditions was performed in regards to temperature (20-90 °C), heating time (5-60 min), pH (2.5-10, with/without excess of metal ions), buffers, quenchers, volume (0.1-10 mL) and molar activity (90-540 kBq/nmol). The quality control was investigated using radio-TLC/HPLC by changing gradient to evaluate peak separation, radiolysed peptide and impurity separation.

RESULTS

Metal ingrowth was observed in Ac-225 stocks (n = 3), (time of arrival: 17.9, 36.8 and 101.4 nmol per 10 MBq). Optimal radiochemical yields were achieved with > 80 °C (20 min) at pH 8.5 (15 mM TRIS) up to 270 kBq. Labeling at a high pH showed a higher RCY, even in presence of an excess of metals. High stability (RCP > 90%) was achieved after addition of quenchers (cysteine, methionine, ascorbate, histidine, or gentisic acid (35 mM)) up to 24 h. For optimal determination of the radiochemical purity (indirect HPLC) fifty fractions are required.

CONCLUSION

The quality of Ac-225 labeled DOTA-radiopharmaceuticals is highly dependent on the pH and stabilization (buffer/quencher). Within this research it is demonstrated that optimized quality control methods and accurate measurement of the radiolabeling kinetics are crucial to ensure safe implementation for patient treatment.