The features of thrombus in a microvessel injury model and the antithrombotic efficacy of heparin, urokinase, and prostaglandin E1

Clinical effectiveness of postoperative prostaglandin E1 administration in reducing flap necrosis following microsurgical reconstruction

BACKGROUND

Extensive experimental evidence has suggested the potential efficacy of prostaglandin E1 (PGE1) in enhancing flap survival, leading to its widespread empirical use following free flap operation. However, the translation of these experimental findings into clinical benefits remains uncertain. This study aimed to assess the clinical effectiveness of postoperative PGE1 administration on the outcomes of microsurgical reconstruction.

METHODS

A retrospective review was conducted for patients who underwent free flap-based reconstruction between September 2020 and November 2022, dividing into two cohorts. For all consecutive cases conducted during the formal half, PGE1 was administered for postoperative 7 days (PGE1 cohort), and for those during the latter, PGE1 was not given (non-PGE1 cohort). The profiles of perfusion-related complications (PRC) were compared between the two cohorts. Further analyses after propensity-score matching were performed.

RESULTS

In total, 274 cases were analyzed, consisting of 142 in PGE1 and 132 in non-PGE1 cohort. Baseline characteristics were similar between the two cohorts, except for higher rates of comorbidities and chronic wound-related defects in the PGE1 cohort. Overall PRC developed in 37 cases (13.5%), including 6 (2.1%) total loss and 38 (10.2%) partial necrosis. Compared to the control, the PGE1 cohort exhibited significantly lower rates of overall PRC and partial flap necrosis. This difference remained significant on multivariable analyses. The rate of total flap loss did not differ between the cohorts. Consistent associations were observed in the propensity-score matching analysis.

CONCLUSION

Postoperative administration of PGE1 appears to be associated with reduced risks for the development of partial flap necrosis.

Effects of microneedle length and duration of preconditioning on random pattern skin flaps in rats

To date, the surgical delay of skin flaps is the most common and reliable method that increases skin flap survival. In this study, we aimed to increase skin flap viability using preconditioning by microneedling. Seventy-two Sprague Dawley rats were randomly divided into control, surgical flap delay (SFD), and four microneedling groups (7 or 14 days of preconditioning with 0.5 mm or 1 mm needles). Modified McFarlane flaps were raised on the back of rats. In Group I, a caudal pedicled skin flap was raised and the flap survival rate was assessed on postoperative day 14. In the SFD group, a bipedicled flap was created and after 14 days of surgical delay, all skin flaps were raised. In the microneedling groups, 0.5 mm or 1 mm needles were used for 7 or 14 days. The flap survival rates of all microneedling and SFD groups were significantly higher than the control group. The plasma levels of vascular endothelial growth factor (VEGF) did not significantly differ between groups, but the VEGF level of skin samples in the SFD group was higher than the control group. The vessel counts of all microneedling and SFD groups were statistically higher than the control group in all skin samples taken before raising the flaps, but skin samples taken 14 days after raising the skin flap did not show any difference between groups. We showed that preconditioning by microneedling can be used to improve the viability of critical ischemic skin flaps at a level similar to surgical delay.

Impact of different antithrombotics on the microcirculation and viability of perforator-based ischaemic skin flaps in a small animal model

The effects of antithrombotic drugs on random and free flap survival have been investigated in the past, but the experimental and clinical results are not in agreement. A perforator-based critical ischaemia model was used to evaluate the effects of different perioperatively administered pharmaceutical agents on tissue ischaemia and to assess the potential additional haemorheological or vasodilative effects of antithrombotics on flap microcirculation. Combined laser Doppler flowmetry and remission spectroscopy revealed an increase in certain microcirculation parameters in most groups in comparison with saline controls, and these changes correlated with flap survival. Clopidogrel and hirudin significantly improved the amount of viable flap tissue in comparison with controls, while unfractioned heparin had a negative effect on flap survival. Low molecular weight heparin, aspirin, pentoxifylline, and hydroxyethyl starch had no impact on the amount of viable flap tissue. A higher complication rate was observed in all experimental groups, but only clopidogrel had a negative impact on the flap viability. Our results add to the body of evidence supporting the conclusion that perioperative antithrombotic treatment improves flap survival. Clopidogrel and hirudin are effective pharmacological agents that significantly increased the viability of perforator-based skin flaps in rats, but at a higher risk of postoperative bleeding.

The outcome of prostaglandin-E1 and dextran-40 compared to no antithrombotic therapy in head and neck free tissue transfer: analysis of 1,351 cases in a single center

Free tissue transfer has become a popular technique for soft tissue defect reconstruction in head and neck cancer ablation. Although high success rates and good reliability of free flaps are proven, microvascular thrombosis is still the most critical issue for microsurgeons. Pharmacological antithrombotic agents are widely used but their efficacy is still debated. In this study, we analyzed whether prostaglandin-E1 (PGE1) and dextran-40 can improve the outcomes compared to no antithrombotic therapy at all. We retrospectively reviewed 1,351 free flaps performed for head and neck reconstruction after cancer ablation. Three groups defined were 232 flaps received PGE1, 283 flaps received dextran-40, and 836 received no antithrombotic therapy. The demographics of these three groups indicated no statistical differences. The results showed that flap survival revealed no significant difference among PGE1, dextran-40, and control group (P = 0.734). There was a tendency to hematomas in PGE1 group (P = 0.056) when compared with other two groups. Dextran-40 significantly increased flap failure rate in high-risk patients with diabetes mellitus (P = 0.006) or hypertension (P = 0.003), when compared with PGE1 and control group. These results revealed antithrombotic therapy with PGE1 and dextran-40 do not determine a significant improvement in flap survival.

Effect of heparin following cervical spinal cord injuries in rats

BACKGROUND

Risks of neurological deterioration after heparin administration following cervical spinal cord injury (SCI) in humans are unknown.

OBJECTIVE

To elucidate the safety of heparin following cervical SCI and investigate its potential neuroprotectant role.

METHODS

Sixty-two Sprague Dawley adult rats were subjected to mild (0.6 mm), moderate (0.9 mm), or severe (1.2 mm) C7-SCI. At each injury severity, intravenous heparin or saline was administered for 72 hours following SCI. Behavioral tests (Basso, Beattie, Bresnahan scores, Hargreave's) were performed before killing the rats at week 7. Half of the rats were killed at day 3, and the remainder at week 7 after SCI. Immunohistochemistry, Western blot analysis, and axonal retrograde tracing were conducted at both times.

RESULTS

Subpial hemorrhage was greater in heparin-treated animals compared with controls at all severities of SCI day 3 after injury. Counterintuitively, intraparencyhmal hemorrhage was minimal in the lesion epicenter following mild SCI in the heparin-treated animals compared with controls. India ink perfusion revealed greater preservation of microcirculation in heparin-treated animals compared with a reduction in control animals. A decrease in spinal cord perfusion correlated directly with an increase in hypoxia-inducible factor-1α expression. There was significant gray matter sparing, but no change in white matter volume after heparin treatment at week 7 in the mild SCI group. Beneficial effects on hemorrhagic volume, axon sparing, and functional recovery following heparin treatment were not observed in the moderate or severe SCI group.

CONCLUSION

Heparin treatment following SCI is safe at all degrees of injury. Heparin decreases platelet aggregation and microvascular occlusion, providing a potential neuroprotective effect following mild SCI.

In vivo real-time two-photon microscopic imaging of platelet aggregation induced by selective laser irradiation to the endothelium created in the beta-actin-green fluorescent protein transgenic mice

Although thrombus formation in vivo has recently been reported, all previous laser induced thrombus models have been associated with vessel wall disruption. This study aimed to evaluate in vivo real-time platelet aggregation after selective endothelial injury, and to visualize thrombus formation without disruption and swelling of the arterial intima induced by two-photon laser irradiation. Cecal arteriole thrombi were created in beta-actin-green fluorescent protein transgenic mice by selective endothelial injury using two-photon laser-scanning microscopy (TPLSM). The in vivo real-time process of thrombus formation was assessed. Anticoagulant drug efficiency for thrombi was also analyzed in detail. TPLSM allowed visualization of microvessel components from the arterial smooth muscle to the intimal layer. Immediately after selective laser irradiation of the intimal layer, platelet adhesion and aggregation were seen only at the area of injury of the intimal layer after forming linear adhesions downstream of the injured area. When shear stress was overcome, thrombus formation began at the downstream edge of the injured area. Thrombus volume plateaued approximately 60 min after laser irradiation. The thrombolytic effects of anticoagulant drugs were precisely assessed; therefore, our model appears the most advanced model in point of real-time imaging of pathophysiological processes in vivo currently reported. In vivo real-time imaging of thrombus formation can be achieved using TPLSM in combination with an organ stabilizing system. The high magnification and resolution of TPLSM allows investigation of the mechanisms of thrombus formation along with assessment of antithrombotic drug efficacy with little interexperimental variation.

Erythropoietin protects critically perfused flap tissue

OBJECTIVE

The objective of this study was to analyze whether erythropoietin (EPO) protects from necrosis of critically perfused musculocutaneous tissue and the mechanisms by which this protection is achieved.

BACKGROUND

EPO is the regulator of erythropoiesis and is used to treat patients with anemia of different causes. Recent studies suggest that EPO has also other tissue-protective effects, irrespective of its erythropoietic properties.

MATERIAL AND METHODS

C57BL/6-mice were treated with 3 doses of EPO at 500 IU/kg intraperitoneally. EPO was given either before (preconditioning, n = 7), before and after (overlapping treatment, n = 7), or after (treatment, n = 7) surgery. Animals receiving only saline served as controls (CON). Acute persistent ischemia was induced by elevating a randomly perfused flap in the back of the animals. This critically perfused tissue demonstrates an initial microvascular failure of approximately 40%, resulting in approximately 50% tissue necrosis if kept untreated. Repetitive fluorescence microscopy was performed over 10 days, assessing angiogenesis, functional capillary density, inflammatory leukocyte-endothelial cell interaction, apoptotic cell death, and tissue necrosis. Additional molecular tissue analyses included the determination of inducible nitric oxide synthase, erythropoietin receptor (EPO-R), and vascular endothelial growth factor (VEGF).

RESULTS

EPO preconditioning did not affect hematocrit and EPO-R expression, but increased inducible nitric oxide synthase in the critically perfused tissue. This correlated with a significant arteriolar dilation, which resulted in a maintained functional capillary density (CON: 0 +/- 0 cm/cm(2); preconditioning: 37 +/- 21 cm/cm(2); overlapping treatment: 72 +/- 26 cm/cm(2); P < 0.05). EPO pretreatment further significantly reduced microvascular leukocyte adhesion and apoptotic cell death. Moreover, EPO pretreatment induced an early VEGF upregulation, which resulted in new capillary network formation (CON: 0 +/- 0 cm/cm(2); preconditioning: 40 +/- 3 cm/cm(2); overlapping treatment: 33 +/- 3 cm/cm(2); P < 0.05). Accordingly, EPO pretreatment significantly reduced tissue necrosis (CON: 48% +/- 2%; preconditioning: 26% +/- 3%; overlapping treatment: 20% +/- 3%; P < 0.05). Of interest, EPO treatment was only able to alleviate ischemia-induced inflammation but could not improve microvascular perfusion and tissue survival.

CONCLUSIONS

EPO pretreatment improves survival of critically perfused tissue by nitric oxide -mediated arteriolar dilation, protection of capillary perfusion, and VEGF-initiated new blood vessel formation.