In this issue of the Journal of Clinical Monitoring and Computing, Dr. Vistisen and colleagues emphasise the inadequacy of the variation in the pre-ejection period (PEP) following deep breathing to predict the hemodynamic response to controlled haemorrhage 1. The present clinical report may lead to the implication that this marker of hypovolemia should be disregarded in cases of spontaneous ventilation.The PEP includes excitation-contraction coupling and isovolumic contraction. Accordingly, the normovolemic left ventricle has a short PEP, whereas a hypovolemic ventricle has a long PEP. In this regard, mechanistically, searching the preload prediction from the pre-ejection period measurement makes sense. Indeed, there have been numerous published studies, both in human patients and in various animal models supporting the use of the pre-ejection period to characterise the preload 2. These findings are based on direct observations and are independent of the type of respiration, as studies have been performed under conditions of spontaneous 3 and mechanical ventilation 4, 5.
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