Haemodynamic Effects of Pimobendan during General Anaesthesia in Healthy Senior Dogs: A Prospective, Randomised, Triple-Blinded, Placebo-Controlled Clinical Study

Pimobendan is an inotropic and vasodilator drug with no sympathomimetic effects. This study aimed to evaluate the haemodynamic effects of pimobendan during anaesthesia in healthy senior dogs. A prospective, randomised, triple-blinded, placebo-controlled clinical study was conducted. Thirty-three dogs (median [range]: 9 [7, 12] years) were anaesthetised for surgical procedures. The dogs were randomly allocated into two groups: eighteen dogs received intravenous pimobendan at a dose of 0.15 mg/kg (PIMOBENDAN), and fifteen dogs received intravenous saline solutions at a dose of 0.2 mL/kg (PLACEBO). Data were recorded before, 1 min, 10 min, and 20 min after injection. Velocity-time integral (VTI), peak-velocity (PV), and mean-acceleration (MA) were measured using an oesophageal Doppler monitor (ODM). Heart rate and mean arterial pressure were also registered. The data were analysed using a two-way ANOVA for trimmed means. Statistical differences were considered if p < 0.05. Twenty minutes after injection, the VTI (13.0 cm [10.4, 22.3]), PV (95.0 [83.0, 160] m/s), and MA (12.6 [9.40, 17.0] m/s²) were significantly higher in the PIMOBENDAN group compared to the PLACEBO group (VTI: 10.5 [6.50, 17.4] cm, PV: 80.0 [62.0, 103] m/s and MA: 10.2 [7.00, 16.0] ms²). No significant differences were observed in the rest of the variables. Using pimobendan during anaesthesia increases VTI, PV, and MA, as measured by an ODM.

How to detect a positive response to a fluid bolus when cardiac output is not measured?

Background

Volume expansion is aimed at increasing cardiac output (CO), but this variable is not always directly measured. We assessed the ability of changes in arterial pressure, pulse pressure variation (PPV) and heart rate (HR) or of a combination of them to detect a positive response of cardiac output (CO) to fluid administration.

Methods

We retrospectively included 491 patients with circulatory failure. Before and after a 500-mL normal saline infusion, we measured CO (PiCCO device), HR, systolic (SAP), diastolic (DAP), mean (MAP) and pulse (PP) arterial pressure, PPV, shock index (HR/SAP) and the PP/HR ratio.

Results

The fluid-induced changes in HR were not correlated with the fluid-induced changes in CO. The area under the receiver operating characteristic curve (AUROC) for changes in HR as detectors of a positive fluid response (CO increase ≥ 15%) was not different from 0.5. The fluid-induced changes in SAP, MAP, PP, PPV, shock index (HR/SAP) and the PP/HR ratio were correlated with the fluid-induced changes in CO, but with r < 0.4. The best detection was provided by increases in PP, but it was rough (AUROC = 0.719 ± 0.023, best threshold: increase ≥ 10%, sensitivity = 72 [66–77]%, specificity = 64 [57–70]%). Neither the decrease in shock index nor the changes in other indices combining changes in HR, shock index, PPV and PP provided a better detection of a positive fluid response than changes in PP.

Conclusion

A positive response to fluid was roughly detected by changes in PP and not detected by changes in HR. Changes in combined indices including the shock index and the PP/HR ratio did not provide a better diagnostic accuracy.

Less or more hemodynamic monitoring in critically ill patients

PURPOSE OF REVIEW

Hemodynamic investigations are required in patients with shock to identify the type of shock, to select the most appropriate treatments and to assess the patient's response to the selected therapy. We discuss how to select the most appropriate hemodynamic monitoring techniques in patients with shock as well as the future of hemodynamic monitoring.

RECENT FINDINGS

Over the last decades, the hemodynamic monitoring techniques have evolved from intermittent toward continuous and real-time measurements and from invasive toward less-invasive approaches. In patients with shock, current guidelines recommend the echocardiography as the preferred modality for the initial hemodynamic evaluation. In patients with shock nonresponsive to initial therapy and/or in the most complex patients, it is recommended to monitor the cardiac output and to use advanced hemodynamic monitoring techniques. They also provide other useful variables that are useful for managing the most complex cases. Uncalibrated and noninvasive cardiac output monitors are not reliable enough in the intensive care setting.

SUMMARY

The use of echocardiography should be initially encouraged in patients with shock to identify the type of shock and to select the most appropriate therapy. The use of more invasive hemodynamic monitoring techniques should be discussed on an individualized basis.

The use of the oesophageal Doppler in perioperative medicine: new opportunities in research and clinical practice

The oesophageal Doppler (OD) is a minimally invasive haemodynamic monitor used in the surgical theatre and the ICU. Using the OD, goal-directed therapy (GDT) has been shown to reduce perioperative complications in high-risk surgical patients. However, most GDT protocols currently in use are limited to stroke volume optimisation. In the present manuscript, we examine the conceptual models behind new OD-based measurements. These would provide the clinician with a comprehensive view of haemodynamic pathophysiology; including pre-load, contractility, and afterload. Specifically, volume status could be estimated using mean systemic filling pressure (MSFP), the pressure to which all intravascular pressures equilibrate during asystole. Using the OD, MSFP could be readily estimated by simultaneous measurements of aortic blood flow and arterial pressure with sequential manoeuvres of increasing airway pressure. This would result in subsequent reductions in cardiac output and arterial pressure and would allow for a linear extrapolation of a static MSFP value to a "zero flow" state. In addition, we also demonstrate that EF is proportional to mean blood flow velocity measured in the descending thoracic aorta with the OD. Furthermore, OD-derived indexes of blood flow velocity and acceleration, as well as force and kinetic energy, can be derived and used for continuous assessment of cardiac contractility at the bedside. Using OD-derived parameters, the different components of afterload: inertia, resistance and elastance, could also be individually determined. The integration of these additional haemodynamic parameters could assist the clinician in optimising and individualising haemodynamic performance in unstable patients.

Monitoring: from cardiac output monitoring to echocardiography

PURPOSE OF REVIEW

Hemodynamic exploration is mandatory in patients with shock to identify the type of shock, to select the best therapeutic strategy, and to assess the efficacy of the selected therapy. In this review, we summarize the characteristics of the main available hemodynamic monitoring systems and emphasize on how to select the most appropriate ones in patients with circulatory shock.

RECENT FINDINGS

Over the past decade, hemodynamic monitoring techniques have progressively evolved from intermittent toward real-time measurements and from invasive toward less invasive approaches. Nowadays, echocardiography is recommended as the first-line modality of hemodynamic evaluation in patients with shock. Current guidelines recommend reserving advanced hemodynamic monitoring systems for patients not responding to the initial therapy and/or for complex conditions such as combination of shock with acute respiratory distress syndrome. Invasive and noninvasive uncalibrated cardiac output monitors, as well as esophageal Doppler, could find their place in the perioperative context rather than in patients with shock.

SUMMARY

The use of echocardiography should be encouraged at the initial period of shock to identify main involved mechanisms and to select the appropriate therapy. The use of more invasive monitoring systems should be discussed on an individualized basis.

End-tidal carbon dioxide variation after a 100- and a 500-ml fluid challenge to assess fluid responsiveness

Background

EtCO₂ variation has been advocated replacing cardiac output measurements to evaluate fluid responsiveness (FR) during sepsis. The ability of EtCO₂ variation after a fluid challenge to detect FR in the context of general anaesthesia has not been investigated. Forty patients were prospectively studied. They underwent general anaesthesia for major surgeries. CO was measured by transoesophageal Doppler, and EtCO₂ was recorded as well as other haemodynamic parameters [heart rate (HR), mean arterial pressure (MAP), pulse pressure (PP)] at baseline, after 100-ml fluid load over 1 min, and at the end of the 500-ml fluid load. We measured the variation of EtCO₂ at 100 (ΔEtCO₂100) and 500 ml (ΔEtCO₂500), and ROC curves were generated. A threshold for ΔEtCO₂ to predict FR was determined with receiver operating curves (ROC) analysis. The primary end point was the ability of EtCO₂ variation after a 500-ml fluid load to diagnose FR.

Results

Fifteen patients (38 %) were fluid responders. ROC analysis showed that for a threshold of 5.8 % (ΔEtCO₂500), sensitivity was 0.6 IC 95 % [0.33; 0.86] and specificity was 1.0 IC 95 % [1.0; 1.0]. An absolute increase of more than 2 mmHg of EtCO₂ is specific to diagnose fluid responsiveness (spe = 96 [88–100] %, sens = 60 [33–88] %, AUC = 0.80 [0.96–0.65]). HR, MAP, and PP variations and ΔEtCO₂100 did not bring information to predict or diagnose FR. During fluid challenge, the correlation between CI variation and EtCO₂ variation was r = 0.566, p < 0.001.

Conclusions

During surgery, when alveolar ventilation and CO₂ production are constant, ΔEtCO₂500 is fairly reliable to assess FR. When the variation of EtCO₂ is >5.8 %, all patients were responders, but no conclusion could be done when this variation was <5.8 %. ΔEtCO₂100 failed to predict FR.

Trial registration CPP Lyon Sud Est III ref: 2013-027 B, Number ID RCB: 2013-A00729-36 delivered by the ANSM).

Evolving concepts of hemodynamic monitoring for critically ill patients

The last decades have been characterized by a continuous evolution of hemodynamic monitoring techniques from intermittent toward continuous and real-time measurements and from an invasive towards a less invasive approach. The latter approach uses ultrasounds and pulse contour analysis techniques that have been developed over the last 15 years. During the same period, the concept of prediction of fluid responsiveness has also been developed and dynamic indices such as pulse pressure variation, stroke volume variation, and the real-time response of cardiac output to passive leg raising or to end-expiration occlusion, can be easily obtained and displayed with the minimally invasive techniques. In this article, we review the main hemodynamic monitoring devices currently available with their respective advantages and drawbacks. We also present the current viewpoint on how to choose a hemodynamic monitoring device in the most severely ill patients and especially in patients with circulatory shock.

Comparison of cardiac output measured by oesophageal Doppler ultrasonography or pulse pressure contour wave analysis

BACKGROUND

Maintaining adequate organ perfusion during high-risk surgery requires continuous monitoring of cardiac output to optimise haemodynamics. Oesophageal Doppler Cardiac Output monitoring (DCO) is commonly used in this context, but has some limitations. Recently, the cardiac output estimated by pulse pressure analysis- (PPCO) was developed. This study evaluated the agreement of cardiac output variations estimated with 9 non-commercial algorithms of PPCO compared with those obtained with DCO.

METHODS

High-risk patients undergoing neurosurgery were monitored with invasive blood pressure and DCO. For each patient, 9 PPCO algorithms and DCO were recorded before and at the peak effect for every haemodynamic challenge.

RESULTS

Sixty-two subjects were enrolled; 284 events were recorded, including 134 volume expansions and 150 vasopressor boluses. Among the 9 algorithms tested, the Liljestrand-Zander model led to the smallest bias (0.03 litre min(-1) [-1.31, +1.38] (0.21 litre min(-1) [-1.13; 1.54] after volume expansion and -0.13 litre min(-1) [-1.41, 1.15] after vasopressor use). The corresponding percentage of the concordance was 91% (86% after volume expansion and 94% after vasopressor use). The other algorithms, especially those using the Winkessel concept and the area under the pressure wave, were profoundly affected by the vasopressor.

CONCLUSIONS

Among the 9 PPCO algorithms examined, the Liljestrand-Zander model demonstrated the least bias and best limits of agreement, especially after vasopressor use. Using this particular algorithm in association with DCO calibration could represent a valuable option for continuous cardiac output monitoring of high risk patients.

CLINICAL TRIAL REGISTRATION

Comité d'éthique de la Société de Réanimation de Langue Française No. 11-356.

Low predictability of three different noninvasive methods to determine fluid responsiveness in critically ill children

OBJECTIVE

To predict fluid responsiveness by noninvasive methods in a pediatric critical care population.

DESIGN

Prospective observational clinical trial.

SETTING

PICU in a tertiary care academic hospital.

PATIENTS

Thirty-one pediatric patients aged from 1 day to 13 years under mechanical ventilation and on catecholamine support.

INTERVENTIONS

We tested three noninvasive methods to predict fluid responsiveness: an esophageal Doppler system (CardioQ), a pulse contour analysis algorithm system (LiDCOrapid), and respiratory variations in vena cava inferior diameter. Stroke volume index was measured by transthoracic echocardiography before and after fluid challenge to determine fluid responders. Infusion of 10 mL/kg hydroxyethylstarch 130/0.4.

MEASUREMENTS AND MAIN RESULTS

Predictability of fluid responsiveness was only found in Doppler peak velocity of descending aortal blood flow. Increased peak velocity with reduction after fluid bolus was predictive for nonresponding to IV fluid challenge. Sensitivity and specificity of peak velocity were 69% and 73%, respectively. The cut point was set at 135.5 cm/s. The lower the Doppler peak velocity, the higher was the probability for a fluid response. Neither stroke volume variations nor respiratory variations in vena cava inferior diameter during mechanical ventilation were useful in predicting fluid responsiveness in this pediatric patient population. None of the children had abdominal hypertension measured by bladder pressure.

CONCLUSIONS

Dynamic preload variables such as stroke volume variation or respiratory variations in vena cava inferior diameter may not be useful for predicting fluid responsiveness in certain pediatric patient populations. Esophageal Doppler peak velocity was predictive of fluid responsiveness where a target value of more than 135,5 cm/s may be a signal to terminate further fluid challenges. This target value may be different in different age groups, as esophageal Doppler peak velocity varies with age.