The paper which changed my practice

The paper which changed my practice

  • issue 81

From the deputy editor

With this article, we open up a new rubric presenting various publications that influenced anaesthesia and intensive care specialists and lead to a change for better in their clinical practice. We hope that these articles, old or new, will entice and help you in your daily practice.

Systolic blood pressure variation is a sensitive indicator of hypovolemia in ventilated dogs subjected to graded haemorrhage

Perel A,  Pizov R, Cotev S Anesthesiology 67: 498-502, 1987

Liana Valeanu
ESA Newsletter Deputy Editor
liana.valeanu@yahoo.com

Serban- Ion Bubenek-Turconi
Professor of Anaesthesiology and Intensive Care
Chair of NASC
bubenek@alsys.ro

 

Optimising tissue perfusion and restoring systemic haemodynamics are key cornerstones in managing critically ill patients. Although intravenous fluids remain the most frequently used therapy in anaesthesia and intensive care settings, there is no “one-size fits it all” recipe for fluid administration. The assessment of fluid responsiveness is essential in determining the optimal fluid loading and also avoiding the deleterious effects of fluid overload.

Fluid therapy increases the stressed volume and venous return. Volume responsiveness is defined as a significant increase in stroke volume / cardiac output due to a fluid bolus, while volume unresponsiveness is an abnormal state in which both ventricles are on the flat part of the Frank-Starling curve: fluid administration will result in increased filling pressures and a modest increased or even a decreased cardiac output.

There is no simple answer to the question “Should I give fluids to my patients?”. Rather than following a predefined protocol, the answer should provoke clinical reasoning aiming to assess fluid responsiveness, the need for higher cardiac output and microcirculatory perfusion improvement.

Old static parameters such as central venous pressure or pulmonary artery occlusion pressure have been historically used to assess fluid status. However, static measures of preload depend on many variables and their use in practice usually ends in poor clinical decisions as many randomised control trials demonstrated. Their limits and inability to differentiate between various pathological conditions resulted in the need to find other parameters to assess fluid responsiveness.

One of the very first studies in which dynamic parameters were suggested to be accurate indicators of fluid responsiveness and hypovolaemia in the controlled mechanically ventilated subject was performed by Perel, Pizov and Cotev in dogs. The study proved that systolic pressure variation and its delta down component correlated well with changes in cardiac output. In consequence, simple dynamic parameters (but still surrogates of the stroke volume variations) that could be determined using an invasive arterial waveform and were able to predict fluid responsiveness were proposed to be used in anaesthesia and intensive care environment.

The impact of mechanical ventilation on the cardiovascular system has been known for decades. However, the above study which demonstrated that mechanical ventilation mimics a reversible fluid loading strong enough to be used for further identification of new dynamic predictors of fluid responsiveness has changed the paradigms in anaesthesia and intensive care.  Since that moment, new invasive or non-invasive technologies based on arterial blood pressure curve analysis and offering a wide range of dynamic parameters have emerged.

Simple dynamic parameters that can be calculated using almost any intensive care monitor are of great use in taking the right decision for fluid therapy. Moreover, echocardiography offers today both dynamic parameters and direct visual estimation of cardiac function. However, we should also remember the limits of every method. On the other hand, not all patients that are fluid responders need more fluid. Avoiding under-resuscitation and overtreatment are equally important since both conditions can lead to poor outcomes.

Nowadays, anaesthesiologists and intensivists frequently benefit from easy-to-obtain comprehensive data (dynamic parameters included) and simplified algorithms are proposed by manufacturers. Although an attractive option, the use of these algorithms should not replace the continuous curiosity for clinical reasoning, as each patient is different.