Different effects of propofol and dexmedetomidine on preload dependency in endotoxemic shock with norepinephrine infusion

Cardiopulmonary function and intestinal blood flow in anaesthetised, experimentally endotoxaemic horses given a constant rate infusion of dexmedetomidine

BACKGROUND

Endotoxaemia causes untoward inflammatory-mediated effects that might be attenuated by dexmedetomidine.

OBJECTIVES

To evaluate the effects of a dexmedetomidine intravenous (IV) infusion on systemic and intestinal haemodynamics and arterial blood gas values in sevoflurane-anaesthetised horses administered Escherichia coli O55:B5 lipopolysaccharides (LPS).

STUDY DESIGN

Randomised controlled in vivo experiment.

METHODS

A total of 13 horses weighing 456 ± 86 kg (mean ± standard deviation) and aged 13.9 ± 9.0 years donated for euthanasia underwent ventral midline celiotomy using sevoflurane anaesthesia. Baseline physiological variables were recorded after a 90-minute equilibration period. All horses were given 0.1 mcg/kg bwt LPS IV. Horses were randomly assigned to no further treatment (group LPS; seven horses) or IV administration of dexmedetomidine (loading dose 1.75 mcg/kg bwt followed by 1.75 mcg/kg bwt/h; group LPS-Dex; six horses) with concurrent target sevoflurane dose reduction of 50%. Cardiac index (CI; thermodilution), intestinal blood flow, arterial blood parameters and plasma dexmedetomidine concentration measurements were recorded every 30 minutes until euthanasia at 390 minutes. Data were compared between and within groups to baseline using a mixed model analysis (significance P < .05).

RESULTS

In LPS-Dex horses, intestinal blood flow and CI were transiently decreased after the dexmedetomidine loading dose, but no significant differences were found compared with baseline during the infusion. Sevoflurane dose was reliably reduced by approximately 40%. Significant differences were identified in creatinine (115  umol/L LPS-Dex; 195 umol/L LPS), bicarbonate (29.7 mmol/L LPS-Dex; 23 mmol/L LPS) and base excess (2.0 mmol/L LPS-Dex; -5.3 mmol/L LPS). Dexmedetomidine plasma concentrations were highest after the loading dose and stable during infusion dosing.

MAIN LIMITATIONS

Experimental conditions are not reflective of clinical colic management.

CONCLUSIONS

A dexmedetomidine infusion with sevoflurane dose reduction attenuated some deleterious changes in anaesthetised horses administered LPS without sustained negative cardiovascular effects and may be beneficial during colic surgery.

Dexmedetomidine effects in different experimental sepsis in vivo models

Sepsis is a major cause of death and the most common cause of death among critically ill, non-ICU patients. Dexmedetomidine (DEX), an <alpha>₂ adrenergic receptor agonist, presents sympatholytic action in certain parts of the brain with anxiolytic, sedative, and pain killing effects. Additionally, through the activation of <alpha>₇ nicotinic acetylcholine receptor receptors, DEX reduces cytokine transcription and inhibits inflammation, rendering it beneficial during septic conditions. Moreover, there is a lot of interest in designing experimental sepsis models, where the administration of DEX is evaluated for its impact on multiple systems. This review focuses on experimental studies published between 1999 to March 2019 that were using DEX administration in sepsis in vivo models. From these, 36 articles were selected and summarized. Overall results show evidence that DEX may decrease mortality and inhibit inflammation, as it enhances the activity of the immune system while reducing its systemic reaction and lowering cytokine concentrations. Moreover DEX succeeds to alleviate heart injury during sepsis, acting beneficially for microcirculation and shows a neuroprotective role by inhibiting apoptotic pathways. In addition, DEX appears to have a protective role for liver and spleen as well as a beneficial role for the function of lungs and kidneys as it reduces sepsis-induced injuries and apoptosis in intra-abdominal experimental sepsis models.

Midazolam increases preload dependency during endotoxic shock in rabbits by affecting venous vascular tone

Background

Septic patients often require sedation in intensive care unit, and midazolam is one of the most frequently used sedatives among them. But the interaction between midazolam and septic shock is not known. The aim of this study is to investigate the effects of midazolam on preload dependency in an endotoxic shock model by evaluating systemic vascular tone and cardiac function.

Methods

Eighteen rabbits were randomly divided into three groups: Control group, MID1 group and MID2 group. Rabbits underwent ketamine anaesthesia and mechanical ventilation, and haemodynamic assessments were recorded in three groups (T0). Endotoxic shock was induced by lipopolysaccharide intravenously, and fluid resuscitation and norepinephrine were administered to obtain the baseline mean arterial pressure (MAP) (T1). Rabbits received equivalent normal saline (Control) and two consecutive dosages of midazolam: 0.3 mg kg⁻¹ h⁻¹ (MID1) and 3 mg kg⁻¹ h⁻¹ (MID2) (T2). Rabbits received another round of fluid challenge and norepinephrine infusion to return the MAP to normal (T3).

Results

No significant differences in haemodynamic parameters were observed in three groups at T0, T1 or T3. Midazolam infusion significantly increased pulse pressure variation (PPV) and stroke volume variation (SVV) compared to the values in Control group, and MAP, central venous pressure (CVP), mean systemic filling pressure (Pmsf) and cardiac output (CO) decreased at T2. Same effects were observed with increasing doses of midazolam, and resistance for venous return (Rvr) decreased (MID1 vs. MID2) at T2. PPV and SVV increased significantly at T2 compared to the values at T1. MAP, CVP, Pmsf and CO decreased in MID1 and MID2 groups. Rvr also decreased in MID2 group (T2 vs. T1). Midazolam did not affect cardiac function index, systemic vascular resistance or artery resistance (T2 vs. T1).

Conclusions

Midazolam administration promoted preload dependency in septic shock models via decreased venous vascular tone without affecting cardiac function.

Misdirected Sympathy: The Role of Sympatholysis in Sepsis and Septic Shock

The spectrum of sepsis and septic shock remains a highly prevalent disease state, carrying a high risk of morbidity and mortality. The sympathetic nervous system (SNS) plays an important role in this initial cascade, enabling the host to respond to invading pathogens; however, prolonged activation can become pathological. The potential for unregulated sympathetic tone to become of detriment in patients with sepsis has fueled interest in the role and impact of sympatholysis, the selective inhibition of sympathetic tone. The cornerstone of septic shock therapy for decades has been the supplementation of catecholamines and thus potential further perpetuation of this sympathetic dysregulation. Although the theory of sympatholysis circulates around cardiovascular effects and stroke volume optimization, the impact of augmenting the SNS may extend well beyond this, including the impacts on the immune system, inflammatory cascade, and even gene transcription. Presently, the most robust clinical evidence involves the use of the cardioselective β-blocker esmolol in patients with septic shock with persistent tachycardia secondary to catecholamine use. Evidence is isolated only to animal models with α-agonists. Future evidence stands to elucidate the balance of sympathetic and autonomic tone as well as the potential role of redirecting and maximizing sympathetic activity.