Propofol depressed neutrophil hydrogen peroxide production more than midazolam, whereas adhesion molecule expression was minimally affected by both anesthetics in rats with abdominal sepsis

Concerns of the anesthesiologist: anesthetic induction in severe sepsis or septic shock patients

Septic patients portray instable hemodynamic states because of hypotension or cardiomyopathy, caused by vasodilation, thus, impairing global tissue perfusion and oxygenation threatening functions of critical organs. Therefore, it has become the primary concern of anesthesiologists in conducting anesthesia (induction, maintenance, recovery, and postoperative care), especially in the induction of those who are prone to fall into hemodynamic crisis, due to hemodynamic instability. The anesthesiologist must have a precise anesthetic plan based on a thorough preanesthetic evaluation because many cases are emergent. Primary circulatory status of patients, including mental status, blood pressure, urine output, and skin perfusion, are necessary, as well as more active assessment methods on intravascular volume status and cardiovascular function. Because it is difficult to accurately evaluate the intravascular volume, only by central venous pressure (CVP) measurements, the additional use of transthoracic echocardiography is recommended for the evaluation of myocardial performance and hemodynamic state. In order to hemodynamically stabilize septic patients, adequate fluid resuscitation must be given before induction. Most anesthetic induction agents cause blood pressure decline, however, it may be useful to use drugs, such as ketamine or etomidate, which carry less cardiovascular instability effects than propofol, thiopental and midazolam. However, if blood pressure is unstable, despite these efforts, vasopressors and inotropic agents must be administered to maintain adequate perfusion of organs and cellular oxygen uptake.

Sedative drug modulates T-cell and lymphocyte function-associated antigen-1 function

BACKGROUND

Sedative drugs modify immune cell functions via several mechanisms. However, the effects of sedatives on immune function have been primarily investigated in neutrophils and macrophages, and to the lesser extent lymphocytes. Lymphocyte function-associated antigen-1 (LFA-1) is an adhesion molecule that has a central role in regulating immune function of lymphocytes including interleukin-2 (IL-2) production and lymphocyte proliferation. Previous clinical studies reported that propofol and isoflurane reduced IL-2 level in patients, but midazolam did not. We previously demonstrated that isoflurane inhibited LFA-1 binding to its counter ligand, intercellular adhesion molecule-1 (ICAM-1), which might contribute to the reduction of IL-2 levels. In the current study, we examined the effect of propofol, midazolam, and dexmedetomidine on LFA-1/ICAM-1 binding, and the subsequent biological effects.

METHODS

The effect of sedative drugs on T-cell proliferation and IL-2 production was measured by calorimetric assays on human peripheral blood mononuclear cells. Because LFA-1/ICAM-1 binding has an important role in T-cell proliferation and IL-2 production, we measured the effect of sedative drugs on ICAM-1 binding to LFA-1 protein (cell-free assay). This analysis was followed by flow cytometric analysis of LFA-1 expressing T-cell binding to ICAM-1 (cell-based assay). To determine whether the drug/LFA-1 interaction is caused by competitive or allosteric inhibition, we analyzed the sedative drug effect on wild-type and high-affinity LFA-1 and a panel of monoclonal antibodies that bind to different regions of LFA-1.

RESULTS

Propofol at 10 to 100 μM inhibited ICAM-1 binding to LFA-1 in cell-free assays and cell-based assays (P < 0.05). However, dexmedetomidine and midazolam did not affect LFA-1/ICAM-1 binding. Propofol directly inhibits LFA-1 binding to ICAM-1 by binding near the ICAM-1 contact area in a competitive manner. At clinically relevant concentrations, propofol, but not dexmedetomidine or midazolam, inhibited IL-2 production (P < 0.05). Additionally, propofol inhibited lymphocyte proliferation (P < 0.05).

CONCLUSIONS

Our study suggests that propofol competitively inhibits LFA-1 binding to ICAM-1 on T-cells and suppresses T-cell proliferation and IL-2 production, whereas dexmedetomidine and midazolam do not significantly influence these immunological assays.

Intensive Care Unit-acquired infection as a side effect of sedation

Introduction

Sedative and analgesic medications are routinely used in mechanically ventilated patients. The aim of this review is to discus epidemiologic data that suggest a relationship between infection and sedation, to review available data for the potential causes and pathophysiology of this relationship, and to identify potential preventive measures.

Methods

Data for this review were identified through searches of PubMed, and from bibliographies of relevant articles.

Results

Several epidemiologic studies suggested a link between sedation and ICU-acquired infection. Prolongation of exposure to risk factors for infection, microaspiration, gastrointestinal motility disturbances, microcirculatory effects are main mechanisms by which sedation may favour infection in critically ill patients. Furthermore, experimental evidence coming from studies both in humans and animals suggest that sedatives and analgesics present immunomodulatory properties that might alter the immunologic response to exogenous stimuli. Clinical studies comparing different sedative agents do not provide evidence to recommend the use of a particular agent to reduce ICU-acquired infection rate. However, sedation strategies aiming to reduce the duration of mechanical ventilation, such as daily interruption of sedatives or nursing-implementing sedation protocol, should be promoted. In addition, the use of short acting opioids, propofol, and dexmedetomidine is associated with shorter duration of mechanical ventilation and ICU stay, and might be helpful in reducing ICU-acquired infection rates.

Conclusions

Prolongation of exposure to risk factors for infection, microaspiration, gastrointestinal motility disturbances, microcirculatory effects, and immunomodulatory effects are main mechanisms by which sedation may favour infection in critically ill patients. Future studies should compare the effect of different sedative agents, and the impact of progressive opioid discontinuation compared with abrupt discontinuation on ICU-acquired infection rates.

Anesthetic modulation of immune reactions mediated by nitric oxide

Nitric oxide (NO), when produced via inducible NO synthase (iNOS) in excess under pathological conditions (e.g., inflammation, endotoxemia, and septic shock), may lead to tissue injury and organ dysfunction. The bioavailability of NO and the activity and expression of iNOS are regulated by anesthetic agents. Volatile anesthetics mostly suppress, but in some instances may upregulate, the lipopolysaccharide-and cytokine-induced expression of iNOS in blood vessels and macrophages. Intravenous anesthetics inhibit iNOS expression in macrophages and the liver. Local anesthetics decrease the production of NO by inhibiting iNOS expression in macrophages and increase NO production in glial cells. Based on the literature reported so far, the effects of anesthetics on iNOS expression and activity under conditions of inflammation are controversial, with the observed effects depending on the experimental methods and animal species used. On the other hand, it has been shown that volatile and intravenous anesthetics consistently prevent the development of multiple organ failure elicited by endotoxemia or septic shock. Information, although still insufficient, regarding the interactions between anesthetic agents and the detrimental effects of NO formed during inflammatory processes may help us to construct advanced strategies for anesthetizing and sedating patients with inflammation and sepsis and for anesthetic preconditioning against ischemic injury.

Endotoxin-induced acute lung injury and organ dysfunction are attenuated by pentobarbital anaesthesia

1. Acute lung injury (ALI) as a result of sepsis is a major cause of mortality. Certain anaesthetic agents have been reported to suppress pro-inflammatory cytokines and inducible nitric oxide (NO) synthase (iNOS) activities. We investigated the effects of pentobarbital on ALI and organ functions after the administration of endotoxin. 2. Intravenous (i.v.) pentobarbital (20 or 40 mg/kg) was administered 5 min after lipopolysaccharide (LPS; 10 or 30 mg/kg via i.v. infusion). To avoid hypoxia and/or hypercapnia following anaesthesia, we installed a special chamber connected to a rodent ventilator to provide ventilation with 95% oxygen content and 5% nitrogen. The animal was kept at eucapnic conditions (arterial PCO2 at an average of 38 +/- 2 mmHg). 3. We monitored the arterial pressure (AP) and heart rate (HR). Acute lung injury was evaluated by lung weight changes, protein concentration in bronchoalveolar lavage, and Evans blue leakage. Plasma nitrate/nitrite, methyl guanidine and biochemical factors were determined. Pathological and immunofluorescent examinations were performed to observe the lung changes and to determine the activities of pro-inflammatory cytokines, nitrotyrosine and iNOS. 4. Lipopolysaccharide caused dose-dependent systemic hypotension with an increase in the extent of ALI. The lung pathology included oedema and inflammatory cell infiltration. Accompanying the ALI, LPS elevated plasma nitrate/nitrite, methyl guanidine, blood urea nitrogen, lactic dehydrogenase, creatinine phosphokinase, glutamic transaminase and amylase. The lung tissue content of tumour necrosis factor-alpha, interleukin-lbeta, iNOS and nitrotyrosine was increased following LPS administration. These changes were abrogated by pentobarbital anaesthesia. 5. Our results indicated that pentobarbital anaesthesia significantly augmented the LPS-induced systemic hypotension. However, it attenuated the LPS-induced ALI and organ dysfunctions. This agent also improved the survival rate following LPS at high and low doses. This mechanism may be related to the inhibitory effects on the increases in the production or activity of NO, free radicals, pro-inflammatory cytokines, nitrotyrosine and iNOS.

Anaesthetics and immune function

Surgical trauma and anaesthetics may cause immune suppression, predisposing patients to postoperative infections. Furthermore, stress such as surgery and pain per se is associated with immune suppression which, in animal models, leads to an increased susceptibility to infection and tumour spread. Thus, by modulating the neurohumoral stress response, anaesthesia may indirectly affect the immune system of surgical patients. In particular, regional anaesthesia attenuates this stress response and the associated effects on cellular and humoral immunity. Additionally, anaesthetics may directly affect the functions of immune-competent cells. However, the reported effects of commercial preparations of, for example, propofol, etomidate and midazolam are highly dependent on the applied solvent. Immunosuppressive effects may be particularly relevant in the intensive care unit when anaesthetics are used as long-term sedatives. There is a striking body of evidence that long-term exposure to certain sedatives is paralleled by infectious complications. On the other hand, anti-inflammatory effects of anaesthetics may be therapeutically beneficial in distinct situations such as those involving ischaemia/reperfusion injury or the systemic inflammatory response syndrome. Consequently, sedatives should be administered with careful regard to their respective potential immunomodulatory properties, the clinical situation, and the immunity status of the critically ill patient.

Effects of propofol vs methohexital on neutrophil function and immune status in critically ill patients

PURPOSE

Patients with severe brain injury often require long-term sedation and have a high incidence of nosocomial infections, causing an increased mortality rate. However, whether anesthetic drugs might contribute to immunosuppressive effects remains unclear.

METHODS

In this prospective study, we investigated the effects of propofol (4-6 mg x kg(-1) x h(-1)) and methohexital (1-3 mg x kg(-1) x h(-1)) on neutrophil leukocyte function and immune status in 21 patients with brain injury who either received propofol (n = 12; 9 male, 3 female; mean age, 51 +/- 15 years) or methohexital (n = 9; 8 male, 1 female; mean age, 48 +/- 17 years) after admission to the intensive care unit (ICU). Both sedatives were administered over 7 days and individual dosage was adapted according to clinical requirements. Neutrophil leukocyte function was assessed as phagocytosis and respiratory oxidative burst activity. Furthermore, leukocyte subpopulations, and surface markers of lymphocytes and monocytes (CD3; CD4; CD45RO; CD4/CD45RO; CD25; CD4 and CD25; CD54; CD69; CD14/HLA-DR; CD8; CD3/HLA-DR; CD4 : CD8 ratio) were assessed. Blood samples were drawn on ICU admission, and on days 3, 7, and 14. Patients' demographics were compared by Wilcoxon test and laboratory results were compared by analysis of variance (ANOVA) for repeated measurements, with an all pairwise multiple comparison procedure.

RESULTS

There were no significant differences in neutrophil oxidative burst and phagocytosis within or between the two groups at the different time points. With respect to cellular markers of lymphocytes and monocytes, all values throughout remained in the normal range.

CONCLUSION

Methohexital and propofol exhibited no significant effects on neutrophil function and immune status in patients with severe brain injury requiring long-term sedation.

Effects of propofol on endotoxin-induced acute lung injury in rabbit

This study was undertaken to clarify the effects of propofol on endotoxin-induced acute lung injury. Rabbits were randomly assigned to one of four groups. Each group received intravenous infusion of saline only, saline and Escherichia coli endotoxin, propofol (1 mg/kg bolus, then 5 mg/kg/hr) and endotoxin, or propofol (4 mg/kg bolus, then 20 mg/kg/hr) and endotoxin respectively. Infusion of saline or propofol was started 0.5 hr before the infusion of saline or endotoxin, and continued for 6 hr thereafter. The lungs of rabbits were ventilated with 40% oxygen. Mean blood pressure, heart rate, arterial oxygen tension (PaO2), and peripheral blood leukocyte and platelet count were recorded. The wet/dry (W/D) weight ratio of lung and lung injury score were measured, and analysis of bronchoalveolar lavage fluid (BALF) was done. Endotoxin decreased PaO2, and peripheral blood leukocyte and platelet count. And it increased W/D ratio of lung, lung injury score and leukocyte count, percentage of PMN cells, concentration of albumin, thromboxane B2 and IL-8 in BALF. Propofol attenuated all these changes except the leukocyte count in peripheral blood. In conclusion, propofol attenuated endotoxin-induced acute lung injury in rabbits mainly by inhibiting neutrophil and IL-8 responses, which may play a central role in sepsis-related lung injury.