The Effects of Clonidine on Sensitivity to Phenylephrine and Nitroprusside in Patients with Essential Hypertension Recovering from Surgery

The effect of dexmedetomidine on vasopressor requirements in patients with septic shock: a subgroup analysis of the Sedation Practice in Intensive Care Evaluation [SPICE III] Trial

BACKGROUND

Septic shock is associated with decreased vasopressor responsiveness. Experimental data suggest that central alpha2-agonists like dexmedetomidine (DEX) increase vasopressor responsiveness and reduce catecholamine requirements in septic shock. However, DEX may also cause hypotension and bradycardia. Thus, it remains unclear whether DEX is hemodynamically safe or helpful in this setting.

METHODS

In this post hoc subgroup analysis of the Sedation Practice in Intensive Care Evaluation (SPICE III) trial, an international randomized trial comparing early sedation with dexmedetomidine to usual care in critically patients receiving mechanical ventilation, we studied patients with septic shock admitted to two tertiary ICUs in Australia and Switzerland. The primary outcome was vasopressor requirements in the first 48 h after randomization, expressed as noradrenaline equivalent dose (NEq [μg/kg/min] = noradrenaline + adrenaline + vasopressin/0.4).

RESULTS

Between November 2013 and February 2018, 417 patients were recruited into the SPICE III trial at both sites. Eighty-three patients with septic shock were included in this subgroup analysis. Of these, 44 (53%) received DEX and 39 (47%) usual care. Vasopressor requirements in the first 48 h were similar between the two groups. Median NEq dose was 0.03 [0.01, 0.07] μg/kg/min in the DEX group and 0.04 [0.01, 0.16] μg/kg/min in the usual care group (p = 0.17). However, patients in the DEX group had a lower NEq/MAP ratio, indicating lower vasopressor requirements to maintain the target MAP. Moreover, on adjusted multivariable analysis, higher dexmedetomidine dose was associated with a lower NEq/MAP ratio.

CONCLUSIONS

In critically ill patients with septic shock, patients in the DEX group received similar vasopressor doses in the first 48 h compared to the usual care group. On multivariable adjusted analysis, dexmedetomidine appeared to be associated with lower vasopressor requirements to maintain the target MAP.

TRIAL REGISTRATION

The SPICE III trial was registered at ClinicalTrials.gov ( NCT01728558 ).

Hypothesis: Fever control, a niche for alpha-2 agonists in the setting of septic shock and severe acute respiratory distress syndrome?

During severe septic shock and/or severe acute respiratory distress syndrome (ARDS) patients present with a limited cardio-ventilatory reserve (low cardiac output and blood pressure, low mixed venous saturation, increased lactate, low PaO2/FiO2 ratio, etc.), especially when elderly patients or co-morbidities are considered. Rescue therapies (low dose steroids, adding vasopressin to noradrenaline, proning, almitrine, NO, extracorporeal membrane oxygenation, etc.) are complex. Fever, above 38.5-39.5°C, increases both the ventilatory (high respiratory drive: large tidal volume, high respiratory rate) and the metabolic (increased O2 consumption) demands, further limiting the cardio-ventilatory reserve. Some data (case reports, uncontrolled trial, small randomized prospective trials) suggest that control of elevated body temperature ("fever control") leading to normothermia (35.5-37°C) will lower both the ventilatory and metabolic demands: fever control should simplify critical care management when limited cardio-ventilatory reserve is at stake. Usually fever control is generated by a combination of general anesthesia ("analgo-sedation", light total intravenous anesthesia), antipyretics and cooling. However general anesthesia suppresses spontaneous ventilation, making the management more complex. At variance, alpha-2 agonists (clonidine, dexmedetomidine) administered immediately following tracheal intubation and controlled mandatory ventilation, with prior optimization of volemia and atrio-ventricular conduction, will reduce metabolic demand and facilitate normothermia. Furthermore, after a rigorous control of systemic acidosis, alpha-2 agonists will allow for accelerated emergence without delirium, early spontaneous ventilation, improved cardiac output and micro-circulation, lowered vasopressor requirements and inflammation. Rigorous prospective randomized trials are needed in subsets of patients with a high fever and spiraling toward refractory septic shock and/or presenting with severe ARDS.

Pharmacological Review of Postoperative Hypertension

Postoperative hypertension is an acute, transient increase in blood pressure that develops within 30 to 90 minutes following a surgical procedure and typically lasts for 4 to 8 hours after surgery. It is defined as a systolic blood pressure greater than 160 mm Hg or a diastolic blood pressure greater than 90 mm Hg. The increase in blood pressure is primarily due to increased systemic vascular resistance brought about by reflex changes in humoral factors, including increased levels of catecholamines, renin, and serotonin as well as alterations in baroreceptor function and carotid reflexes. Potential complications of untreated postoperative hypertension include depressed left ventricular performance, increased myocardial oxygen demand resulting in ischemic episodes, cerebrovascular accidents, arrhythmias, and suture line disruption and bleeding. Despite longstanding recognition that high blood pressure is a frequent complication after surgery, formal guidelines for the treatment of postoperative hypertension have not been developed. Postoperative hypertension is a pathophysiological state that requires rapid assessment and appropriate treatment. Several pharmacologic agents are available to achieve and maintain normotension after surgery, including nitrovasodilators (nitroglycerin and sodium nitroprusside), adrenergic blocking agents, and dihydroperidine calcium channel antagonists. Angiotensin-converting enzyme inhibitors and fenoldopam also have been used. Each has its own distinct mechanism of action and adverse effect profile. In cardiac surgery, nicardipine is as effective as nitrovasodilators and offers coronary selectivity. In patients who are hypertensive after neurosurgical procedures, avoid direct-acting vasodilators, which may exacerbate increased intracranial pressure; β-adrenergic receptor antagonists and ACEIs are the preferred agents in these patients. More data are needed to define roles and benefits of fenoldopam in managing postoperative hypertension.

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

BACKGROUND

To clarify whether propofol (PROP) and dexmedetomidine (DEX) differentially affect preload dependency in an endotoxemic model based on evaluations of the systemic vascular system and cardiac function.

METHODS

Animals were prepared under PiCCO monitoring (BL), and endotoxemic shock was induced using an intravenous bolus of lipopolysaccharide (055:B5) in 16 New Zealand ketamine-anesthetized rabbits. After fluid resuscitation and norepinephrine infusion (SD0), the animals were randomized to PROP (n = 8) or DEX (n = 8) sedation at two incremental doses (SD1 and SD2). The mean arterial pressure and the central venous pressure were monitored. Pulse pressure variation (PPV) was assessed to evaluate preload dependency. Global end-diastolic volume, vascular resistance, mean systemic filling pressure, and cardiac function index were assessed at each time point.

RESULTS

PPV progressively and significantly increased with increasing infusion rates of PROP (SD1 versus SD0, P < 0.01; SD2 versus SD0, P < 0.001; and SD2 versus SD1, P = 0.024) but not DEX. PPV was higher at SD1 and SD2 in the PROP group than in the DEX group (P < 0.001). PROP increased the heart rate without affecting cardiac contractility or vascular resistance. In contrast, DEX decreased heart contractility and increased vascular resistance at the highest dose. However, neither drug affected mean arterial pressure, central venous pressure, mean systemic filling pressure, global end-diastolic volume, or venous return.

CONCLUSIONS

PROP more effectively increased PPV than DEX in an endotoxemic shock model after fluid resuscitation during norepinephrine infusion. DEX, but not PROP, at the highest dose influenced vascular resistance and heart contractility.

Is there a place for pressure-support ventilation and high positive end-expiratory pressure combined to alpha-2 agonists early in severe diffuse acute respiratory distress syndrome?

Acute respiratory distress syndrome (ARDS) is associated with a high mortality linked primarily to co-morbidities (sepsis, cardiac failure, multiple organ failure, etc.). When the lung is the single failing organ, quick resolution of ARDS should skip some complications arising from a prolonged stay in the critical care unit. In severe ARDS (PaO2/FIO2=P/F<100 with positive end-expiratory pressure (PEEP) ≥ 5 cm H2O), current recommendations are to intubate the trachea of the patient and use mechanical ventilation, low tidal volume, high PEEP, prone positioning and possibly neuromuscular blockade in association with intravenous sedation. Another strategy is possible. Firstly, spontaneous ventilation (SV) coupled with pressure support (PS) ventilation and high PEEP is possible from tracheal intubation onwards, with the possible exception of the short period following immediately tracheal intubation. Secondly, using alpha-2 adrenergic agonists (e.g. clonidine, dexmedetomidine) can provide first-line sedation from the beginning of mechanical ventilation, as they preserve respiratory drive, lower oxygen consumption and pulmonary hypertension and increase diuresis. Alpha-2 agonists are to be supplemented, if appropriate, by drugs devoid of effect on respiratory drive (neuroleptics, etc.). The expected benefits would be to prevent acquired diaphragmatic weakness, accumulation of sedation, cognitive dysfunction, and presumably improved outcome. This hypothesis should be tested in a double blind randomized controlled trial.

[Dexmedetomidine and clonidine: a review of their pharmacodynamy to define their role for sedation in intensive care patients]

Alpha-2 adrenergic agonists ("alpha-2 agonists") present multiple pharmacodynamic effects: rousable sedation, decreased incidence of delirium in the setting of critical care, preservation of respiratory drive, decreased whole body oxygen consumption, decreased systemic and pulmonary arterial impedance, improved left ventricular systolic and diastolic function, preserved vascular reactivity to exogenous catecholamines, preserved vasomotor baroreflex with lowered set point, preserved kidney function, decreased protein catabolism. These pharmacodynamic effects explain the interest for these drugs in the critical care setting. However, their exact role for sedation in critically ill-patients remains open for further studies. Given the few double-blind randomized multicentric trials available, the present non exhaustive analysis of the literature aims at presenting the utilization of alpha-2 agonists as potential first-line sedative agents, in the critical care setting. Suggestions regarding the use of alpha-2 agonists as sedatives are detailed.

Alpha-2 agonists to reduce vasopressor requirements in septic shock?

One of the unsolved problems of septic shock is the poor responsiveness, or reduced vascular reactivity, to vasopressors used to increase blood pressure (BP). Attempts to restore vascular reactivity with NO inhibitors or low dose steroids have met with little success. Low vascular reactivity, which may lead to refractory shock and death, is linked to desensitization or down-regulation of alpha-1 adrenergic receptors. Our working hypothesis is that the use of alpha-2 agonists (e.g. clonidine or dexmedetomidine) in septic shock, in addition to the state-of-the-art treatment (including volume load and vasopressors), will reduce the vasopressor requirements needed to restore adequate BP. This counter-intuitive proposal is based on the fact that alpha-2 agonists will reduce the massive release of endogenous catecholamines. A decrease in plasma endogenous catecholamine concentrations will be followed by reduced down-regulation of alpha-1 receptors and/or a gradual re-sensitization of alpha-1 adrenergic receptors. In turn, this will lead to lowered vasopressor requirement, with respect to dose and duration. Our hypothesis, based on a reverse "denervation hypersensitivity", is at variance with accepted treatments, which rest only on volume load and vasopressors and emphasizes restoration of blood pressure per se. Several observations in the cardiology and anesthesia setting have shown increased vascular reactivity following alpha-2 agonist administration. Our preliminary observations in the setting of septic shock again suggest such increased vascular reactivity. Improved outcome was also observed. Rigorous work is warranted to verify reduced vasopressor requirement and improved outcome, when an alpha-2 agonist is combined with state-of -the-art treatment of septic shock.

Normal Aging Impairs Upregulation of the Beta-adrenergic but not the Alpha-Adrenergic Response: Aging and Adrenergic Upregulation

OBJECTIVES

To determine if centrally reducing sympathetic tone with clonidine will reverse the downregulation in the alpha-adrenergic (alphaAR) and beta-adrenergic (betaAR) responses seen with normal aging.

METHODS

Twelve rigorously screened young adult (mean age, 26 years) and 15 older adult (mean age, 69 years) subjects were studied before and after using the clonidine patch (TTS-2) for 2 weeks. betaAR (isoproterenol at 35 ng/kg/min) and alphaAR (phenylephrine at 1.0 microg/kg/min) were assessed using radionuclide measures of end diastolic, end systolic, and stroke volume indices, cardiac index, and ejection fraction.

RESULTS

Clonidine reduced resting plasma norepinephrine and this reduction was greater in older subjects (-47 +/- 3 versus -26 +/- 6%, P = 0.001). After 2 weeks of clonidine patch, upregulation of the betaAR was significantly higher in young subjects for heart rate (+10.7 +/- 1.5 versus +4.6 +/- 1.5 bpm; P = 0.01). There was no significant age-associated difference in the upregulation of the alphaAR with clonidine for systolic, diastolic, and mean blood pressure or systemic vascular resistance.

CONCLUSIONS

With aging, there is an impaired resensitization of the chronotropic betaAR response with central sympathetic downregulation that is not seen with the alphaAR.

Conduite à tenir concernant le traitement médicamenteux des patients adressés pour chirurgie programmée

This review focuses on potential drug interactions between anaesthetic drugs or techniques and chronic medications in patients scheduled for surgery. The vast majority of therapeutics can be continued until the morning of surgery. However, for some drugs such as ACE inhibitors, there is strong evidence to recommend their discontinuation prior to surgery. When juged necessary, interruption of chronic therapeutic needs to be anticipated and planned. In the other hand, for other drugs such as beta-blockers or L-Dopa, acute withdrawal is associated with documented adverse outcome. As a result, such drugs have to be continuing throughout the operative period. Although a general consensus exists for many medications, there are still controverses as to the management of antithrombotic drugs and some central nervous system agents. Advances in anaesthesia include knowledge on the mechanisms involved in drug interactions, which allows us to improve the preoperative management of chronic therapeutics.

Gaining control: can we reduce perioperative cardiovascular complications?

Cardiovascular complications are common in patients at risk for coronary disease undergoing surgery. The role of hyperactivity of the sympathetic nervous system and impaired parasympathetic control mechanisms in the genesis and consequences of perioperative myocardial ischemia has been discussed. Sympathetic blocking drugs of the beta blocker and alpha₂ agonist classes have been used extensively in the perioperative setting to control hemodynamic responses and reduce episodes of myocardial ischemia. To date, perioperative beta blockade is the only strategy shown to improve long-term outcome after surgery in this population.