Peripheral tissue oxygenation and the number of organs transplanted per donor

Current donor management practices target macrohaemodynamic parameters, but it is unclear if this leads to improvements in microvascular perfusion and tissue oxygenation; the latter may have more impact on organ status. In a recent preclinical study we determined that brain death impaired tissue perfusion and oxygen utilisation in swine while pharmacologic correction of these deficits improved organ function and reduced markers of tissue injury. As a first step in translating the preclinical findings, we conducted a prospective observational study to determine if there was an association between peripheral tissue oxygenation (measured by near-infrared spectroscopy) in deceased by neurological criteria human donors and the number of organs transplanted. In 60 donors, the mean time-weighted average of tissue oxygenation was 87.5% (standard deviation, SD, 5.2%) and the average number of organs transplanted was 3.5 (SD 2); there was a positive linear relationship between these two parameters. A 5% rise in tissue oxygenation was associated with an increase of 0.47 organs transplanted (95% confidence intervals 0.16 to 0.78) after adjusting for age (<i>P</i>=0.004). No such correlations were observed for the macrohaemodynamic or macro-oxygenation parameters (including arterial blood oxygenation). The results of this clinical trial are consistent with our preclinical work and support the postulate that targeting the microvasculature to improve tissue perfusion and tissue oxygen delivery in human donors has the potential to increase the quantity of organs suitable for transplant.

Recent advances in perioperative anesthetic management update on the role of vasopressin and its effects on outcomes

The vasoconstrictive and antidiuretic physiologic properties of vasopressin (antidiuretic hormone) have long been known. Until recently however, vasopressin was mostly used for diabetes insipidus and noctournal enuresis. This review summarizes the growing body of evidence regarding the perioperative use of vasopressin and its analogues in the management of certain forms of cardiovascular collapse. Physiologically, vasopressin is involved in regulating osmotic, volemic, and cardiovascular homeostasis. It acts via several specific vasopressin receptors that are variably distributed in the heart, kidneys and vasculature etc. Under normal conditions, its antidiuretic effect predominates and vasopressin only induces vasoconstriction at high concentrations. Regarding catecholamine-resistant vasodilatory shock, current evidence suggests that with adequate volume resuscitation, exogenous vasopressin in low "physiologic" doses (0.01-0.04 units/min) safely supports mean arterial pressure without adversely affecting myocardial function and splanchnic circulation. One possible explanation is that metabolic acidosis impairs the function of alpha-adrenergic (but not vasopressin) receptors, thus diminishing the response to catecholamines. Although there is yet no clear cut mortality benefit, vasopressin is now recommended as a second-line agent in septic shock for its catecholamine-sparing effect and as an alternative to epinephrine in cardiopulmonary resuscitation. It has also demonstrated efficacy in ameliorating vasoplegia after cardiopulmonary bypass as well as perioperative hypotension in patients on renin-angiotensin system antagionists preoperatively. In summary, accumulating clinical experience and formal studies indicate that vasopressin has a role in restoring vascular tone in refractory vasodilatory shock states with minimal adverse effects provided that euvolemia is assured.

Impact of transesophageal echocardiography on the anticoagulation management of patients admitted with focal cerebral ischemia

Transesophageal echocardiography (TEE) improves the diagnostic accuracy of transthoracic echocardiography in the identification of potential cardiac sources of embolus. However, there are few studies of the impact of TEE on the medical management of patients with focal cerebral ischemia. The records of 52 consecutive, hospitalized patients undergoing both TEE and transthoracic echocardiography for suspected cardiac source of embolus were reviewed to determine the influence of TEE on the decision to anticoagulate patients. Of 52 patients, 39 had focal cerebral ischemia (transient ischemic attack, n = 9; acute cerebral infarction, n = 30). In 4 of these 39 patients (10%), the TEE results changed the management of anticoagulation. In 19 of 39 patients (49%), the TEE results helped confirm anticoagulation decisions, and in 16 (41%), the results had no effect on anticoagulation decisions, because of overriding clinical information. Ten of the latter 16 patients had TEE evidence for a possible source of an embolus, but were not anticoagulated; 5 of these were poor candidates for long-term anticoagulation, and the others had right-to-left shunting across a patent foramen ovale or an interatrial septal aneurysm. Clinical variables (atrial fibrillation, TEE findings and pre-TEE anticoagulation status) were considered as possible predictors of post-TEE anticoagulation status using logistic regression analysis; the strongest predictor of post-TEE anticoagulation status was pre-TEE anticoagulation status (p < 0.0005). Despite the selection of patients presumed to receive maximal benefit from TEE, this study suggests that TEE findings are not predictive of subsequent anticoagulation management. However, TEE is at least confirmatory of anticoagulation decisions in most cases.

Airway adherence of Pseudomonas aeruginosa: mucoexopolysaccharide binding to human and bovine airway proteins

The ability of Pseudomonas aeruginosa (PA) to adhere to cells of the upper and lower airways is considered the initial step in its colonization and subsequent infection. Many potential adhesins exist, but few eukaryote receptors have been reported. This study evaluates the adherence of PA and the well-recognized adhesin mucoexopolysaccharide, of the mucoid variant, to tracheal epithelial cells and airway secretions. A number of tools were used to systematically examine this process, each in increasing detail. Scanning electron microscopy of infected tracheal cell monolayers showed that although nonmucoid PA adhered most often as individual organisms, mucoid strains frequently were adherent in the form of clusters of microcolonies. Partially purified mucoexopolysaccharide was itself adherent to the tracheal cell monolayers. More quantitative studies of carbon 14-labeled PA adherence to tracheal cell monolayers demonstrated that (1) bacterial adherence was temperature dependent; (2) mucoid PA was more adherent than nonmucoid PA (p less than 0.005); (3) proteinase treatment of the intact monolayers increased adherence of mucoid PA; and (4) adherence of nonmucoid PA was partially inhibited by pretreatment with N-acetylglucosamine, a normal constituent of airway mucus (control, 9.5 +/- 2.0 bacteria/cell; N-acetylglucosamine, 5.8 +/- 1.5 bacteria/cell; p = 0.05). These observations suggest that N-acetylglucosamine may play a role in the epithelial cell receptor for ligands on the surface of nonmucoid strains of PA. Pretreatment of mucoid PA with N-acetylglucosamine, D-arabinose, D-mannose, or N-acetylneuraminic acid did not affect adherence. Partially purified proteins isolated from the apical plasma membrane of bovine tracheal epithelial cells probed in a Western analysis with the iodine 125-labeled PA mucoexopolysaccharide revealed two binding proteins of 45,000 mol wt and 104,000 mol wt. Human airway secretions of patients with chronic PA infection were screened by the dot blot technique and demonstrated selective binding of mucoexopolysaccharide ligand. Western analysis of these biologically important secretions revealed that PA mucoexopolysaccharide bound to a 65,000 mol wt protein in airway secretions of infected individuals. This glycoprotein is similar to a previously described cell receptor for bacterial type 1 fimbriae.

Pseudomonas aeruginosa and the airways disease of cystic fibrosis

The gram-negative organism Pseudomonas aeruginosa plays a major role in the morbidity and mortality of patients with cystic fibrosis (CF). Inherent properties of this organism, together with alterations in the CF airway, lead to colonization of the CF patient and, ultimately, contribute to the destructive lung lesion of CF. Innovative antibiotic therapies for the CF patient are discussed, including new potent oral and parenteral pseudomonicidal antibiotics, the re-emergence of nebulized delivery systems, and the validation of home intravenous therapy.