Perioperative transcranial Doppler US to evaluate intracranial compliance in young children undergoing craniosynostosis repair surgery.

PURPOSE: To determine whether measurements with transcranial Doppler ultrasonography (US) of resistive indexes (RIs) of basal cerebral arteries with pressure provocation can be used to identify infants and children with craniosynostosis who have abnormal intracranial compliance and to study the effects of surgery on compliance. MATERIALS AND METHODS: Transcranial Doppler US was performed through the temporal squama, fontanels, and existing skull defects prior to and immediately following cranioplasty. Twenty-four studies were performed in six patients with multisuture synostosis, and 61 studies were performed in 26 patients with single-suture synostosis. Study findings were compared with those of 23 control subjects and were characterized as normal or abnormal on the basis of age-specific normal criteria for RI. RESULTS: In multisuture synostosis, results of six of the nine preoperative transcranial Doppler US studies were abnormal. During postoperative follow-up, three recurrences requiring reoperation occurred, one of which was detected with abnormal transcranial Doppler US findings. In single-suture synostosis, results of seven of the 26 preoperative transcranial Doppler US studies were abnormal, and all occurred in young infants with sagittal and unicoronal synostosis. Immediate effects of surgery were variable. All patients with sagittal synostosis had a significant immediate postoperative increase in RI, which normalized during postoperative follow-up. There was no significant difference in RI between patients with successfully treated craniosynostosis and control subjects. CONCLUSION: Transcranial Doppler US can be used to identify patients with craniosynostosis with decreased intracranial compliance, and it is a suitable noninvasive test to monitor the effects of surgery on compliance.

Kinetics of E-selectin expression in surgical flaps.

During the ischemia/reperfusion phenomenon, adhesion molecules seem to play a critical role in the recruitment of neutrophils to sites of eventual tissue injury. E-selectin is an endothelium-derived molecule that mediates adhesion of neutrophils to activated endothelial cells. In vitro expression of E-selectin, after exposure to stimuli such as endotoxin, interleukin 1, or tumor necrosis factor alpha is maximal at 4 to 6 h, followed by a decline toward basal levels at 24 to 48 h. Characterizing the temporal expression of E-selectin in an in vivo model of skin flap ischemia-reperfusion would help to determine the optimal approach to eventual pharmacologic blockade. This intervention may prove therapeutically beneficial in attenuating flap injury. This study, using the standard porcine buttock skin flap model, was designed to evaluate immunohistochemically the expression of E-selectin in flaps subjected to (1) arterial ischemia (8 h)-reperfusion (18 h), (2) venous ischemia (8 h)-reperfusion (18 h), and (3) distal ischemia (26 h). Four flaps were examined per group, with 8 biopsies being collected sequentially over the 26-h study period from each flap. Blinded, semi-quantitative histologic scoring revealed the following results: (1) E-selectin is absent in normal porcine skin; (2) with arterial ischemia/reperfusion, E-selectin expression in flaps was maximal at 1 h of reperfusion, declining thereafter; (3) with venous ischemia/reperfusion, E-selectin expression peaked during the first hour of ischemia, with subsequent decline; and (4) within a flap designed to sustain distal ischemia, E-selectin expression is relatively more intense in regions of the flap distant from the vascular pedicle, and maximal at 6 h after flap elevation. Our conclusion, therefore, is that the kinetics of E-selectin expression within the tissues of porcine skin flaps differs depending on the type of ischemic insult sustained. Interpretation of these findings, correlating possible pathophysiologic differences in the different models of ischemia, is offered.

E- and L-selectin adhesion molecules in musculocutaneous flap reperfusion injury.

Definition of the elements governing leukocyte adhesion to the microvascular endothelium may lead to new forms of treatment for reperfusion injury. The objectives of this study, employing a porcine latissimus dorsi flap reperfusion model, were (1) to characterize the expression of E- and L-selectin adhesion molecules and (2) to test for a possible benefit of E- and L-selectin blockade in the preceding experimental setting. In experiment 1, full-thickness biopsies were collected sequentially over an 8-hour ischemia and subsequent 6-hour reperfusion period. Immunocytochemistry was performed with monoclonal antibody EL-246, an antibody that crossreacts with both E- and L-selectin. In experiment 2, the binding of EL-246 to L-selectin on circulating porcine neutrophils was determined by flow cytometric analysis. In experiment 3, in situ hybridization was performed using complementary RNA probes for detection of endothelial E-selectin mRNA. In experiment 4, bilateral flaps were elevated in six pigs and subjected to 8 hours of arterial ischemia followed by 20 hours of reperfusion. Flaps on each animal were randomly assigned to receive either treatment with a continuous local intraarterial infusion of EL-246 (1 mg per flap) or solvent vehicle. Muscle and skin survivals were assessed by nitroblue tetrazolium and intravenous fluorescein staining techniques, respectively. Computer digitization permitted quantitation of relative tissue survival. In experiment 1, specific immunostaining of microvascular endothelium was achieved using EL-246. Greater-intensity staining was detected in reperfusion than in baseline or ischemic sections. In experiment 2, flow cytometric analysis indicated specific recognition by EL-246 of isolated peripheral porcine neutrophils (> 45 percent staining) as compared with an isotype-matched control antibody (< 3 percent staining). In experiment 3, in situ hybridization studies demonstrated an early ischemic up-regulation and later reperfusion downregulation of E-selectin mRNA during the reperfusion period. In experiment 4, administration of monoclonal antibody EL-246 afforded a significant augmentation in mean percentage survival of muscle (37.6 versus 18.7 percent, p = 0.015) and skin (48.6 versus 29.3 percent, p = 0.046). In conclusion, it was determined that E-selectin is expressed along the microvascular surface and is upregulated and subsequently downregulated during ischemia-reperfusion conditions. The monoclonal antibody EL-246 appears to recognize porcine L-selectin as well as E-selectin. Blockade of E/L-selectin-mediated leukocyte adhesion significantly reduces musculocutaneous flap reperfusion injury.

The role of platelet-activating factor in musculocutaneous flap reperfusion injury.

UNLABELLED: Platelet-activating factor is an extremely potent lipid-inflammatory mediator implicated in the pathophysiologic mechanism of reperfusion injury in a variety of organs. The purpose of this study, employing a porcine latissimus dorsi flap model, was to (1) examine the expression of platelet-activating factor and (2) evaluate the possible benefit and mechanism of action of platelet-activating factor antagonism in musculocutaneous flap reperfusion injury. Experiment 1: In 6 pigs, bilateral flaps underwent 8 hours of arterial ischemia followed by 12 hours of reperfusion. Biopsies were collected sequentially and analyzed immunohistochemically for platelet-activating factor expression. Different processing techniques, however, were unable to detect specific tissue expression of platelet-activating factor. Experiment 2: In 11 pigs, bilateral flaps underwent 8 hours of arterial ischemia followed by 20 hours of reperfusion. A lipophilic platelet-activating factor receptor antagonist (L-659,989) was administered as a single dose to treated flaps by a local intraarterial route prior to reperfusion. This treatment augmented the survival of both muscle (48.3 versus 19.7 percent) and skin (49.8 versus 42.0 percent) components of the flaps in a statistically significant fashion (p = 0.001). Experiment 3: In 3 pigs, a radiolabeled structural analogue of L-659,989 (14C-L-680,573) was administered to flaps in a fashion similar to experiment 2. After 8 hours of ischemia, sequential full-thickness flap biopsies were collected over the initial 6 hours of reperfusion. The radio-labeled platelet-activating factor receptor antagonist was found to be highly concentrated within treated flaps, with gradual decay over the initial 6 hours of reperfusion. Experiment 4: Thirty minutes prior to completion of 8 hours of arterial ischemia, autologous neutrophils labeled with indium-111 were reintroduced into the systemic-circulation of 5 pigs. Prior to reperfusion, treated flaps received L-659,989 as in experiment 2. Over the initial 4 hours of reperfusion, the flaps were imaged in situ by a gamma camera at 3-minute intervals. The platelet-activating factor receptor antagonist was found to significantly attenuate the accumulation of radioactivity within treated flaps. CONCLUSION: Platelet-activating factor expression within musculocutaneous flaps subjected to ischemia and reperfusion was non directly demonstrated in this study. Still, we have shown that (1) the specific platelet-activating factor receptor antagonist L-659,989 is beneficial to the survival of both muscle and skin flap components, (2) a single, prereperfusion local dose of this lipophilic drug remains concentrated within the flap during the early inflammatory phase of reperfusion, and (3) during reperfusion, platelet-activating factor antagonism is able to directly or indirectly diminish the accumulation of acute inflammatory cells in musculocutaneous flaps.

Ischemia reperfusion injury: a review.

Ischemia reperfusion injury is reviewed in the context of the evolution of flap research over the past decade. A description of the clinical relevance of this field is presented and the possible etiologies are reviewed. The pathophysiology of this injury is then explored in some detail. Both skin and myocutaneous flaps, in a variety of animal models, are discussed. Research performed in vitro, as well as in other organ systems similarly affected by ischemia and reperfusion, is also examined. Particular attention is placed on the function of several newly described inflammatory mediators where it appears relevant to future research and treatment in the field of reconstructive microsurgery.

Characteristics of secondary hyperparathyroidism in vitamin D-deficient dogs.

Characteristics of secondary hyperparathyroidism were evaluated in dogs with mild vitamin D deficiency. The animals were normocalcemic with reduced concentrations of 1,25-dihydroxy vitamin D3 [1,25(OH)2D3] and elevations in parathyroid hormone (PTH) concentrations, parathyroid mass, and prepro PTH mRNA levels. Dynamic testing revealed a sigmoidal relationship between plasma calcium and PTH, although PTH concentrations were increased relative to values in vitamin D-sufficient dogs. Infusions of chelator elicited lower plasma calcium levels and greater augmentations in biologically active PTH in vitamin D-deficient than in D-sufficient animals. Induced hypercalcemia lowered both immunoreactive and bioactive hormone to stable but detectable levels. The results demonstrate the decreased capacity of vitamin D-deficient animals to defend against acute hypocalcemia, despite the presence of abundant PTH, and indicate that increased circulating PTH levels in early vitamin D deficiency is due predominantly to an augmentation in the quantity of releasable hormone. The latter appears secondary to an increase in parathyroid mass and synthetic activity regulated by 1,25(OH)2D3 per se.