Role of circulating fibrocytes in the diagnosis of acute appendicitis.

BACKGROUND: Improved diagnostic biomarkers are required for acute appendicitis. The circulating fibrocyte percentage (CFP) is increased in inflammatory states, but has not been studied in acute appendicitis. This study aimed to determine CFP in acute appendicitis and compare diagnostic accuracy with standard serological biomarkers. METHODS: A prospective cohort study was carried out between June 2015 and February 2016 at University Hospital Limerick. The CFP was determined by dual-staining peripheral venous samples for CD45 and collagen I using fluorescence-activated cell sorting, and correlated with histopathological diagnoses. The accuracy of CFP in determining histological acute appendicitis was characterized and compared with the white cell count, C-reactive protein concentration, neutrophil count, lymphocyte count and neutrophil : lymphocyte ratio. RESULTS: Of 95 adults recruited, 15 were healthy individuals and 80 had suspected appendicitis at presentation. Forty-six of these 80 patients had an appendicectomy, of whom 34 had histologically confirmed appendicitis. The CFP was statistically higher in patients with pathologically proven acute appendicitis than in healthy controls (median 6·1 (i.q.r. 1·6-11·6) versus 2·3 (0·9-3·4) per cent respectively; P = 0·008). The diagnostic accuracy of CFP, as determined using the area under the receiver operating characteristic (ROC) curve, was similar to that of standard biomarkers. In multinomial regression analysis, only raised CFP was retained as an independent prognostic determinant of acute appendicitis (odds ratio 1·57, 95 per cent c.i. 1·05 to 2·33; P = 0·027). CONCLUSION: The CFP is increased in histologically confirmed acute appendicitis and is as accurate as standard serological biomarkers in terms of diagnosis.

Adrenocortical sensitivity to adrenocorticotropin (ACTH) in awake dogs changes as a function of the time of observation and after hemorrhage independently of changes in ACTH.

Adrenocortical sensitivity to ACTH, defined as the slope of the log dose-response curve, was determined in awake dogs by measuring cortisol secretory rates after graded doses of ACTH. Adrenocortical sensitivity varied as a function of the time of observation. The AM sensitivity was greater than the PM sensitivity in the absence of an AM-PM difference in basal plasma ACTH. Additionally, sensitivity was increased in the PM 6--8 h after moderate hemorrhage in the AM. However, exogenous ACTH given in the AM did not augment adrenal sensitivity to ACTH in the PM. These data show that adrenocortical sensitivity to ACTH varies in awake dogs and that the changes in sensitivity cannot be completely accounted for by changes in ACTH.

The pituitary-adrenocortical response to hemorrhage depends on the time of day.

The response of plasma ACTH and the secretory response of cortisol to moderate hemorrhage were determined in awake dogs in the morning (AM) and evening (PM). Whereas the magnitudes of the response of ACTH were similar in the AM and PM, the magnitude of the secretory response of cortisol was significantly greater in the AM compared to that in the PM. At both times of day, heart rate, mean arterial pressure, and secretory rates of epinephrine after hemorrhage were similar. These findings suggest that AM-PM differences in stimuli produced by moderate hemorrhage cannot explain the differences in the secretion of cortisol. Instead, AM-PM changes in adrenocortical sensitivity to endogenous ACTH after hemorrhage determine the AM-PM differences in the secretion of cortisol.

Restitution of blood volume after hemorrhage: inhibition by somatostatin.

To determine whether glucagon plays a significant role in the restitution of blood volume after hemorrhage, pentobarbital-anesthetized dogs were treated with somatostatin (SRIF). The administration of SRIF (14 micrograms/kg.h) prevented the increase in osmolality and the complete restitution of plasma protein and blood volume that normally occur after 10% hemorrhage. The intraportal addition of glucagon (20 ng/kg.min) during the initial 4 h after hemorrhage reversed the SRIF-induced block in hyperosmolality and was followed by complete restitution of plasma protein and blood volume. These data suggest that increases in glucagon may be a part of the multi-hormonal response to hemorrhage, and this may be a part of a reflex that mediates the homeostasis of blood volume.

The adrenal medullary response to graded hemorrhage in awake dogs.

The adrenal medullary catecholamine response to graded hemorrhage has not been characterized in awake animals. Using high performance liquid chromatography with electrochemical detection, secretion rates of epinephrine and norepinephrine were measured in trained awake dogs with chronic adrenal venous cannulas. The results indicate that the adrenal medulla responds to small and moderate hemorrhages, and the magnitude of the response is directly related to the magnitude of the hemorrhage. The epinephrine secretory response is greater than the norepinephrine secretory response. The response pattern is biphasic, with an early response by 10 min and a late response by 30 min after the onset of hemorrhage. Finally, the adrenal medullary system appears to have the potential to produce a memory of earlier stimuli, since the response to a small hemorrhage is potentiated if the hemorrhage is preceded by 24 h by a moderate hemorrhage.

Role of solute in the early restitution of blood volume after hemorrhage.

We examined the putative roles of decreased capillary pressure and increased transcapillary osmolar gradient in mediation of the early restitution of blood volume after hemorrhage by comparing the degree of restitution of plasma volume and protein and comparing changes in capillary pressure and osmolality in awake dogs with those in dogs anesthetized with pentobarbital. Decreases in estimated capillary pressure and increases in plasma osmolality were greater in anesthetized than in awake dogs. However, early restitution of plasma volume and of protein was greater in awake animals. Analysis of the Starling forces indicated that interstitial hydrostatic pressure was greater in awake animals than in anesthetized animals, suggesting that interstitial volume increases more rapidly in awake animals. Selective venous sampling in anesthetized dogs indicated that the splanchnic and renal vascular beds release solute to the circulation following hemorrhage. However, rather than promoting the restitution of blood volume by production of a transcapillary osmolar gradient, the data suggest that the solute is delivered to the peripheral tissues, where it mediates the movement of water from cells to the interstitium more rapidly in awake than in anesthetized dogs. It thus appears that the early metabolic changes after hemorrhage, resulting in increased solute production, are important for the early restitution of blood volume and plasma protein.

Cardiovascular stabilization after hemorrhage depends upon restitution of blood volume.

The role of late restitution of blood volume after hemorrhage in cardiovascular stabilization was examined in awake, splenectomized dogs. Cardiovascular variables were measured: at 2 hours after hemorrhage, changes were noted in cardiac output, mean arterial pressure, heart rate, stroke volume, arterial pressure, and CVP in three hemorrhage groups (p less than 0.05), and in total peripheral resistance for 15 ml/kg and 22.5 ml/kg hemorrhage groups (p less than 0.05). At 24 hours after hemorrhage, the degree of restitution of blood volume was correlated with cardiac output (p less than 0.01), stroke volume (p less than 0.02), and total peripheral resistance (p less than 0.01). No correlation was noted with heart rate, CVP, or mean arterial pressure. Blood volume restitution was correlated with degree of hemorrhage throughout the 24-hour period of investigation. Plasma protein content restitution and blood volume restitution were correlated with changes in osmolality. The results suggest thatcardiovascular stabilization after hemorrhage is a function of the degree of restitution of blood volume mediated through a shift of fluids to the interstitutium, mediated in turn by extracellular hyperosmolality.

Impaired restitution of blood volume after large hemorrhage.

Previous studies have suggested that increases in extracellular osmolality mediate a shift of intracellular fluid into the interstitium following 10% hemorrhage. This unidirectional fluid movement is required for full restitution of blood volume (BV) and for cardiovascular stabilization. The extent to which this mechanisms acts in larger hemorrhages was examined in these studies. Forty-two dogs were studies 3 weeks after splenectomy. Twenty were anesthetized with pentobarbital, the others were studied awake. Hemorrhages of 10% (7.5 ml/kg, 15 dogs), 20% (15 ml/kg, 13 dogs), and 30% (22.5 ml/kg, 15 dogs) were carried out over 3 minutes. Patterns of changes in osmolality, total plasma protein content, and blood volume were identical in the two groups, although osmolality was significantly greater during the first 2 hours in anesthetized dogs. Osmolality increased with increasing degrees of hemorrhage, providing an increasing driving force for fluid shifts. Restitution of BV was significantly greater after 20% hemorrhage than after 10% hemorrhage. However, restitution of BV after 30% hemorrhage was no greater than after 10% hemorrhage. Patterns of protein restitution paralleled changes in BV. Cunningham, Shires, and Wagner (7) reported fluid shifts into cells after a 30% hemorrhage associated with a fall in membrane potential. It thus appears likely that a fluid shift out of cells in response to increased osmolality is offset by shifts into cells as the magnitude of hemorrhage becomes large. This failure of homeostatic restoration of BV with consequent failure of cardiovascular stabilization may represent an early event in the development of hemorrhagic shock.