Monitoring non-invasive cardiac output and stroke volume during experimental human hypovolaemia and resuscitation

† Controlled application oflower body negativepressure simulatedhypovolaemia andresuscitation in humansubjects.† Thoracic electricalbioimpedance, andarterial blood pressure(ABP) analysis by the LongTime Interval method,were the mostdiscriminatorymeasurements.† The Modelﬂow method ofABP analysis effectivelytracked hypovolaemia, butunderestimatedresuscitation.† Pulse pressure trackedhypovolemia andresuscitation, butunderestimated changesin stroke volume.Background. Multiple methods for non-invasive measurement of cardiac output (CO) andstroke volume (SV) exist. Their comparative capabilities are not clearly established.Methods. Healthy human subjects (n¼21) underwent central hypovolaemia throughprogressive lower body negative pressure (LBNP) until the onset of presyncope, followedby termination of LBNP, to simulate complete resuscitation. Measurement methods wereelectrical bioimpedance (EBI) of the thorax and three measurements of CO and SVderived from the arterial blood pressure (ABP) waveform: the Modelﬂow (MF) method, thelong-time interval (LTI) method, and pulse pressure (PP). We computed areas underreceiver-operating characteristic curves (ROC AUCs) for the investigational metrics, todetermine how well they discriminated between every combination of LBNP levels.Results. LTI and EBI yielded similar reductions in SV during progressive hypovolaemia andresuscitation (correlation coefﬁcient 0.83) with ROC AUCs for distinguishing major LBNP(260 mm Hg) vs resuscitation (0 mm Hg) of 0.98 and 0.99, respectively. MF yielded verysimilar reductions and ROC AUCs during progressive hypovolaemia, but afterresuscitation, MF-CO did not return to baseline, yielding lower ROC AUCs (DROC AUCrange, 20.18 to 20.26, P,0.01). PP declined during hypovolaemia but tended to be aninferior indicator of speciﬁc LBNP levels, and PP did not recover during resuscitation,yielding lower ROC curves (P,0.01).Conclusions. LTI, EBI, and MF were able to track progressive hypovolaemia. PP decreasedduring hypovolaemia but its magnitude of reduction underestimated reductions in SV. PPand MF were inferior for the identiﬁcation of resuscitation.Keywords: arterial pressure, measurement; blood, loss; cardiovascular system, responses;equipment, ﬁnapres; monitoring, cardiopulmonaryAccepted for publication: 5 September 2010Progressive haemorrhage is a serious cause of hypotensionand shock, causing morbidity and mortality in diversepatient populations, including trauma casualties, surgicalpatients, and patients treated with anticoagulation. Ofcourse, the earlier haemorrhage is detected, the greaterthe opportunity exists for caregivers to administer volumereplacement or perform a haemostatic intervention. More-over, it is important to assess the efﬁcacy of volume resusci-tation, for example, to discriminate between patients inwhom aggressive volume therapy is failing so operative man-agement may be necessary, vs patients who are being suc-cessfully treated with volume therapy and may even be atrisk for over-resuscitation. However, conventional vitalsigns, such as arterial blood pressure (ABP)