The effects of milrinone on hemodynamics in an experimental septic shock model

Left Ventricular Outflow Tract Obstruction in Patients Treated With Milrinone for Cerebral Vasospasm: Case Report and Literature Review

Subarachnoid hemorrhage is associated with high morbidity and mortality, and cerebral arterial vasospasm is one of its main complications that determines neurological prognosis. The use of intravenous milrinone is becoming more common in the treatment of vasospasm. This molecule has positive inotropic and vasodilating properties by inhibiting phosphodiesterase-3. Its most described side effects are cardiac arrhythmias and arterial hypotension. In this paper, we raise a new issue concerning milrinone and discuss an undescribed side effect of this treatment, left ventricular outflow tract obstruction (LVOTO). Dynamic LVOTO is a clinical situation favored by hypovolemia, decreased left ventricular afterload, and excessive inotropism that can lead to severe hemodynamic failure and pulmonary edema. To our knowledge, this is the first study describing milrinone-induced LVOTO. This could compromise cerebral perfusion and therefore the neurological prognosis of patients. While it is known that catecholamines may induce LVOTO, milrinone-induced LVOTO appears to be a new pathophysiological entity of which neurosurgical intensivists should be aware.

Inodilators in septic shock: should these be used?

Septic shock involves a complex interaction between abnormal vasodilation, relative and/or absolute hypovolemia, myocardial dysfunction, and altered blood flow distribution to the tissues. Fluid administration, vasopressor support and inotropes, represent fundamental pieces of quantitative resuscitation protocols directed to assist the restoration of impaired tissue perfusion during septic shock. Indeed, current recommendations on sepsis management include the use of inotropes in the case of myocardial dysfunction, as suggested by a low cardiac output, increased filling pressures, or persisting signals of tissue hypoperfusion despite an adequate correction of intravascular volume and mean arterial pressure by fluid administration and vasopressor support. Evidence supporting the use of inotropes in sepsis and septic shock is mainly based on physiological studies. Most of them suggest a beneficial effect of inotropes on macro hemodynamics especially when sepsis coexists with myocardial dysfunction; others, however, have demonstrated variable results on regional splanchnic circulation, while others suggest favorable effects on microvascular distribution independently of its impact on cardiac output. Conversely, impact of inodilators on clinical outcomes in this context has been more controversial. Use of dobutamine has not been consistently related with more favorable clinical results, while systematic administration of levosimendan in sepsis do not prevent the development of multiorgan dysfunction, even in patients with evidence of myocardial dysfunction. Nevertheless, a recent metanalysis of clinical studies suggests that cardiovascular support regimens based on inodilators in sepsis and septic shock could provide some beneficial effect on mortality, while other one corroborated such effect on mortality specially in patients with proved lower cardiac output. Thus, using or not inotropes during sepsis and septic shock remains as controversy matter that deserves more research efforts.

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.

Endotoxemia accelerates diaphragm dysfunction in ventilated rabbits

BACKGROUND

Ventilators may induce diaphragm dysfunction, and most of the septic population who are admitted to the intensive care unit require mechanical ventilation. However, there is no evidence that sepsis accelerates the onset of ventilator-induced diaphragm dysfunction or affects the microcirculation. Our study investigated whether lipopolysaccharide (LPS)-induced endotoxemia accelerated diaphragm dysfunction in ventilated rabbits by evaluating microcirculation, lipid accumulation, and diaphragm contractility.

METHODS

After anesthesia and tracheostomy, 25 invasively monitored and mechanically ventilated New Zealand white rabbits were randomized to control (n = 5), controlled mechanical ventilation (CMV) (n = 5), pressure support ventilation (PSV; n = 5), CMV or PSV with LPS-induced endotoxemia (CMV-LPS and PSV-LPS, respectively; n = 5 for each). Rabbits were anesthetized and ventilated for 24 h, except the control rabbits (30 min). Diaphragmatic contractility was evaluated using neuromechanical and neuroventilatory efficiency. We evaluated the following at the end of the protocol: (1) diaphragm microcirculation; (2) lipid accumulation; and (3) diaphragm muscular fibers structure.

RESULTS

Diaphragm contractility, microcirculation, lipid accumulation, and fiber structures were severely compromised in endotoxemic animals after 24 h compared to nonendotoxemic rabbits. Moreover, a slight but significant increase in lipid accumulation was observed in CMV and PSV groups compared with controls (P < 0.05).

CONCLUSIONS

Endotoxemia accelerates the diaphragm dysfunction process in ventilated rabbits, affects the microcirculation, and results in diaphragmatic lipid accumulation and contractility impairment.

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.

Milrinone attenuates arteriolar vasoconstriction and capillary perfusion deficits on endotoxemic hamsters

Background and Objective

Apart from its inotropic property, milrinone has vasodilator, anti-inflammatory and antithrombotic effects that could assist in the reversal of septic microcirculatory changes. This paper investigates the effects of milrinone on endotoxemia-related microcirculatory changes and compares them to those observed with the use of norepinephrine.

Materials and Methods

After skinfold chamber implantation procedures and endotoxemia induction by intravenous Escherichia coli lipopolysaccharide administration (2 mg.kg-1), male golden Syrian hamsters were treated with two regimens of intravenous milrinone (0.25 or 0.5 μg.kg-1.min-1). Intravital microscopy of skinfold chamber preparations allowed quantitative analysis of microvascular variables. Macro-hemodynamic, biochemical, and hematological parameters and survival rate were also analyzed. Endotoxemic non-treated animals, endotoxemic animals treated with norepinephrine (0.2 μg.kg-1.min-1), and non-endotoxemic hamsters served as controls.

Results

Milrinone (0.5 μg.kg-1.min-1) was effective in reducing lipopolysaccharide-induced arteriolar vasoconstriction, capillary perfusion deficits, and inflammatory response, and in increasing survival. Norepinephrine treated animals showed the best mean arterial pressure levels but the worst functional capillary density values among all endotoxemic groups.

Conclusion

Our data suggests that milrinone yielded protective effects on endotoxemic animals’ microcirculation, showed anti-inflammatory properties, and improved survival. Norepinephrine did not recruit the microcirculation nor demonstrated anti-inflammatory effects.

An enhanced automatic algorithm for estimation of respiratory variations in arterial pulse pressure during regions of abrupt hemodynamic changes

We describe an improved automatic algorithm to estimate the pulse-pressure-variation (PPV) index from arterial blood pressure (ABP) signals. This enhanced algorithm enables for PPV estimation during periods of abrupt hemodynamic changes. Numerous studies have shown PPV to be one of most specific and sensitive predictors of fluid responsiveness in mechanically ventilated patients. The algorithm uses a beat detection algorithm to perform beat segmentation, kernel smoothers for envelope detection, and a suboptimal Kalman filter for PPV estimation and artifact removal. In this paper, we provide a detailed description of the algorithm and assess its performance on over 40 h of ABP signals obtained from 18 mechanically ventilated crossbred Yorkshire swine. The subjects underwent grade V liver injury after splenectomy, while receiving mechanical ventilation, and general anesthesia with isoflurane. All subjects in the database underwent a period of abrupt hemodynamic change after an induced grade V liver injury involving severe blood loss resulting in hemorrhagic shock, followed by fluid resuscitation with either 0.9% normal saline or lactated ringers solutions. Trained experts manually calculated PPV at five time instances during the period of abrupt hemodynamic changes. We report validation results comparing the proposed algorithm against a commercial system (pulse contour cardiac output, PICCO) with continuous PPV monitoring capabilities. Both systems were assessed during periods of abrupt hemodynamic changes against the "gold-standard" PPV, calculated and manually annotated by experts. Our results indicate that the proposed algorithm performs considerably better than the PICCO system during regions of abrupt hemodynamic changes.

Cardiopulmonary resuscitation: special considerations for infants and children with cardiac disease

Pulseless cardiac arrest, defined as the cessation of cardiac mechanical activity, determined by unresponsiveness, apneoa, and the absence of a palpable central pulse, accounts for around one-twentieth of admissions to paediatric intensive care units, be they medical or exclusively cardiac. Such cardiac arrest is higher in children admitted to a cardiac as opposed to a paediatric intensive care unit, but the outcome of these patients is better, with just over two-fifths surviving when treated in the cardiac intensive care unit, versus between one-sixth and one-quarter of those admitted to paediatric intensive care units. Children who receive chest compressions for bradycardia with pulses have a significantly higher rate of survival to discharge, at 60%, than do those presenting with pulseless cardiac arrest, with only 27% surviving to discharge. This suggests that early resuscitation before the patient becomes pulseless, along with early recognition and intervention, are likely to improve outcomes. Recently published reports of in-hospital cardiac arrests in children can be derived from the multi-centric National Registry of Cardiopulmonary Resuscitation provided by the American Heart Association. The population is heterogeneous, but most arrests occurred in children with progressive respiratory insufficiency, and/or progressive circulatory shock. During the past 4 years at the Children's Hospital of Philadelphia, 3.1% of the average 1000 annual admissions to the cardiac intensive care unit have received cardiopulmonary resuscitation. Overall survival of those receiving cardiopulmonary resuscitation was 46%. Survival was better for those receiving cardiopulmonary resuscitation after cardiac surgery, at 53%, compared with survival of 33% for pre-operative or non-surgical patients undergoing resuscitation. Clearly there is room for improvement in outcomes from cardiac resuscitation in children with cardiac disease. In this review, therefore, we summarize the newest developments in paediatric resuscitation, with an expanded focus upon the unique challenges and importance of anticipatory care in infants and children with cardiac disease.