Research PaperEvaluation of the ability of haemodynamic variables obtained with minimally invasive techniques to assess fluid responsiveness in endotoxaemic Beagles
Introduction
Sepsis is a systemic, maladaptive and harmful immune response to infection linked to high mortality. Septic shock is associated with profound hypotension caused by vasoplegia (Rhodes et al. 2017). The recommended first-line therapy of septic shock consists of a rapid goal-directed fluid resuscitation (Kelm et al. 2015), although septic shock does not represent a typical volume-depleted state with fluids often being redistributed only and not lost. Approximately 50% of all septic human patients respond positively to fluid expansion (Marik & Weinmann 2019) and septic patients are therefore at a high risk of developing fluid overload. A deranged cardiac function and increased vascular permeability complicates the assessment of a patient’s need for fluid resuscitation. A prospective observational study involving 173 human patients with sepsis showed that a positive fluid balance was independently associated with an increased risk of death (Acheampong & Vincent 2015). Administration of fluids will improve the cardiovascular state when the cardiac output (CO) is preload-dependent. To avoid unnecessary fluid administration, the concept of fluid responsiveness (FR) has been introduced. To assess if a patient reacts positively to a fluid bolus, the stroke volume (SV) is measured before and after fluid administration. Currently, an increase in SV of 10–15% after a so-called fluid challenge is defined as a positive FR (Marik & Bellomo 2016; Bednarczyk et al. 2017). However, invasive, time-consuming and expensive measurements of SV are necessary to assess FR accurately. Because SV measurement is often not feasible under clinical conditions, especially in veterinary medicine, less invasive tools and techniques to assess FR have been introduced.
Conventional cardiovascular variables like changes (Δ) in heart rate (HR) and systemic arterial blood pressure are clinically still used to assess FR, although several authors discourage their use in humans (Marik 2009) and in dogs (Muir et al. 2014). The static preload variables right atrial pressure and pulmonary capillary wedge pressure are no longer recommended for the assessment of FR in humans (Marik & Cavallazzi 2013) or in dogs (Fantoni et al. 2017).
More recently, Δ pulse wave transit time detected ΔSV and reliably assessed FR in healthy anaesthetized Beagles (Sano & Chambers 2017; Sano et al. 2019). The pulse wave transit time is defined as the time between the rise point of the SpO2 plethysmogram and the peak of the R-wave in the ECG and can be measured with a multiparameter monitor. This time interval is inversely proportional to SV (Sugo et al. 2010).
Another minimally invasive monitoring technique, oesophageal Doppler monitoring (ODM) measures the velocity of blood flow in the descending aorta using a Doppler probe placed in the patient’s oesophagus. The velocity time integral equals the stroke distance and is a measure of the distance that blood travels within the aorta in one heartbeat. The stroke distance is a surrogate for SV and it was able to trend ΔSV in adult humans (Dépret et al. 2019) and paediatric human patients (Tibby et al. 2001). Flow time corrected (FTc), another variable measured with ODM, is defined as the duration of blood flow in the aorta during systole, normalized to a HR of 60 beats minute–1. This time is positively correlated to SV and negatively to vascular resistance.
The objective of this study was to evaluate the ability of different haemodynamic variables recorded by minimally invasive monitoring techniques to assess FR in endotoxaemic Beagles. The hypothesis was that minimally invasively measured haemodynamic variables can be used to predict FR during experimentally induced endotoxaemia in dogs.
Section snippets
Animals
Ethical approval (ZH057/17) was obtained from the Cantonal Veterinary Office of Zurich, Switzerland. A total of six purpose-bred Beagle dogs (three intact females and three males) with an age of 7.4 (5–9.8) years [median (range)] and a body weight of 13.7 (11.4–17.9) kg were included in this study. On the study days the dogs were transported to the study site in a travel cage. They were fasted for 12 hours but water was available ad libitum.
The dogs had been scheduled for euthanasia owing to
Results
A total of 35 measurements were obtained. During measurements, the blood temperature of the dogs was maintained between 37.2 °C and 38.9 °C. Of the 33 measurements obtained with the ODM, five were excluded from analysis because of incorrect HR, waveforms or marker placement. The recorded cardiovascular variables before and after 35 boluses are shown for positive and negative FR in Table 1. A total of 19 fluid boluses (54%) resulted in a ΔSV ≥15% and were considered positive FR. The remaining 16
Discussion
This study examined the ability of different minimally invasive cardiovascular monitoring techniques to predict FR in mechanically ventilated anaesthetized endotoxaemic dogs. The results of this study demonstrate that the haemodynamic variables we assessed did not provide good predictive values of FR. However, assessing FTc, Δ pulse pressure, Δ shock index or ΔROPE may offer fair FR predictive abilities. To our knowledge, this is the first study to assess the ability of a range of minimally
Conclusion
In anaesthetized Beagles during endotoxaemic shock after IV LPS, none of the minimally invasively measured haemodynamic variables could predict FR with high sensitivity and specificity.
Acknowledgements
We would like to thank Professor Dr. Zeki Yilmaz and PD Dr. Martin Schläpfer and his team for their professional advice.
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