Variations in blood platelet-activating-factor levels after protamine reversal of heparin in humans

Thrombocytosis and neutrophilia associated with oxygenator failure and protamine reaction after cardiopulmonary bypass: a case report and literature review

Thrombocytosis has been feared as a source of thrombotic complications during the conduct of cardiopulmonary bypass (CPB) for patients undergoing cardiac procedures. We present a patient urgently requiring repair/replacement of three heart valves that had preexisting myelofibrosis with thrombocytosis (platelet count of 800,000 per µl) and neutrophilia (40,000 per µl). Despite achieving an activated clotting time > 500 s with heparin and antithrombin concentrate administration prior to CPB, the pump oxygenator and reservoir demonstrated significant clot just prior to restoration of the patient's circulation. The patient subsequently suffered a severe protamine reaction that was successfully managed. A review of the literature of similar patients and the relevant cellular and biochemical mechanisms in this setting are presented, with potential therapeutic approaches to prevent such complications noted.

Effects of a platelet-activating factor antagonist on lung injury and ventilation after cardiac operation

BACKGROUND

Platelet-activating factor is a mediator of lung injury during cardiac operation. Platelet-activating factor antagonists reduce lung injury in animal models of cardiopulmonary bypass but there is no confirmatory evidence in clinical practice.

METHODS

The effect of a low or high dose of a platelet-activating factor antagonist (Lexipafant) was assessed in a single center, double-blind, placebo-controlled, parallel group study. One hundred fifty patients undergoing coronary artery bypass grafting were randomized by minimization into three groups to receive placebo infusion, 10 or 100 mg of lexipafant for over 24 hours. Serial arterial oxygen and carbon dioxide tension, alveolar arterial oxygen gradient, and percent saturation were measured before operation and at 1, 6, 24, 48 hours, and 5 days after operation.

RESULTS

Patient groups were similar with respect to age, sex, body surface area, and urgency of operation. Likewise, the groups were similar with respect to duration of cardiopulmonary bypass and the number and type of grafts. Maximum lung injury occurred at 48 hours when the arterial oxygen tension and percent saturation reached a nadir (both p < 0.001) accompanied by the maximum increase in the alveolar arterial gradient (p < 0.001). All measurements demonstrated partial recovery by 5 days but remained significantly (p < 0.001) impaired in comparison to baseline values. Duration of ventilation was similar in all groups. Lexipafant, at low or high dose, did not moderate lung injury after cardiopulmonary bypass and did not influence the duration of postoperative ventilation.

CONCLUSIONS

Despite experimental and clinical evidence implicating platelet-activating factor in the pathophysiology of lung injury after cardiopulmonary bypass, no beneficial effect of a platelet-activating factor antagonist on lung function or ventilation could be demonstrated in this clinical trial.

Presence and metabolism of lyso platelet-activating factor in human bone marrow

Lyso platelet-activating factor (PAF) is the precursor of PAF, an inflammatory phospholipid molecule present in human bone marrow. The present study shows that in healthy volunteers lyso PAF concentrations are significantly lower (P = 0.0001, Mann-Whitney U-test) in bone marrow plasma (594 +/- 67 ng/ml, n = 47) than in blood plasma (1448 +/- 99 ng/ml, n = 31). Marrow plasma lyso PAF concentrations are similar in patients with lymphoid and nonlymphoid malignancies as compared with controls. Freshly isolated mononuclear marrow cells and cultures of marrow stromal cells contain lyso PAF. Experiments with [3H]lyso PAF indicate that human mononuclear bone marrow cells and marrow stromal cells actively acylate lyso PAF into a 1-alkyl analogue of phosphatidylcholine. Results of this investigation indicate: (1) that lyso PAF is present in human marrow cells and plasma; and (2) that marrow cells and stromal cells metabolize it, thus suggesting their role in the regulation of lyso PAF amounts in human bone marrow.

Biochemical and cellular effects of heparin-protamine injection in rabbits are partially inhibited by a PAF-acether receptor antagonist

The origin of the thrombocytopenia and leucopenia induced by protamine-heparin complexes is unknown. We studied the biochemical and cellular effects of protamine (6 mg x kg-1, i.v.) injected after heparin (5 mg x kg-1, i.v.) in New Zealand rabbits. After protamine injection (0.5 min) increases in blood platelet-activating factor (PAF-acether, PAF) (27.6 +/- 27.6 to 148.2 +/- 48.9 pg x ml-1, P < 0.05), thrombocytopenia (403 +/- 64 to 166 +/- 13 cells x 10(-3) x mm-3, P < 0.05) and leucopenia (7650 +/- 930 to 4300 +/- 668 cells x mm-3, P < 0.05) were noted. Plasma thromboxane B2 increased at 1 min (125.6 +/- 24.4 to 879.7 +/- 141.0 pg x ml-1, P < 0.01). Protamine alone induced no change. Indomethacin (3 mg x kg-1, i.v.) did not counteract the effects of heparin-protamine. Pretreatment with the PAF receptor antagonist BN 52021 [9H1, 7a-(epoxymethano)-1 H,6aH-cyclopenta[c]furo[2,3-b]furo-[3',2',3,4]cyclopenta[1,2-d]fur an-5,9, 12(4H)trione,3-tert-butylhexahydro-4,7b,11 hydroxy-8 methyl] alone (3 mg x kg-1, i.v.) delayed thrombocytopenia and reduced plasma thromboxane B2 concentration but did not modify leucopenia. Thus thrombocytopenia and thromboxane B2 release triggered by heparin-protamine may be potentiated by the release of PAF.

Effects of a paf-receptor antagonist on hemodynamics during and after cardiopulmonary bypass

OBJECTIVES

To assess after cardiopulmonary bypass (CPB) the role of paf-acether (paf), a phospholipid mediator whose injection in animal mimics the hemodynamics observed after CPB.

DESIGN

Prospective double-blind randomized study.

SETTING

Single institutional university hospital.

PARTICIPANTS

18 patients scheduled to undergo coronary artery bypass graft.

INTERVENTIONS

18 patients randomly received a placebo (n = 8) or 120 mg BN52021 (n = 10), a paf-receptor antagonist injected twice just before vascular cannulation and before cross-clamp release.

MEASUREMENTS AND MAIN RESULTS

Hemodynamic measurements were performed with a pulmonary artery and a radial artery catheter before and after the first injection of BN52021 or placebo, at the end of CPB, 1, 15, and 30 minutes after protamine infusion, then 6 hours and 24 hours postoperatively. BN52021 infusion, did not affect hemodynamic parameters. After CPB, the pulmonary artery pressures, the cardiac index, and the pulmonary artery occlusion pressures were statistically the same between groups. By contrast, the pulmonary vascular resistances (1.5 +/- 0.5 IU v 4.5 +/- 0.6 IU, p < 0.05), the right ventricular systolic work index (5.3 +/- 0.91 g m m-2 v 9.37 +/- 1.02 g m m-2, p < 0.05) and the transpulmonary gradient (4.7 +/- 1.1 mmHg v 12.0 +/- 1.2 mmHg, p < 0.05) were lower in the BN52021 group as compared with the placebo group. After protamine infusion, these differences between groups disappeared.

CONCLUSION

Because the inotropic and vasodilator therapy and the volume loading were the same between groups, this study suggests that pretreatment with a paf-receptor antagonist improves post-CPB pulmonary resistance. Nevertheless, this beneficial effect is transient without consequences on left ventricular function indices.