Oesophageal Doppler monitoring overestimates cardiac output during lumbar epidural anaesthesia

Oesophageal Doppler monitoring (ODM) has been advocated as anon-invasive means of measuring cardiac output (CO). However,its reliance upon blood flow measurement in the descending aortato estimate CO is susceptible to error if blood flow is redistributedbetween the upper and lower body. We hypothesize that lumbarepidural anesthesia (LEA), which causes blood flow redistribution,causes errors in CO estimates. We compared ODM with thermodilution(TD) measurements in fourteen patients under general anaesthesiafor radical prostatectomy, who had received an epidural catheterat the intervertebral level L2–L3. Coupled measurementsof CO by means of the TD and ODM techniques were performed atbaseline (general anaesthetic only) and after epidural administrationof 10 ml of 0.25% bupivacaine. The two methods were comparedusing Bland-Altman analysis: before LEA there was a bias of–0.89 litre min^–1 with limits of agreement rangingbetween –2.67 and +0.88 litre min^–1. Following lumbarsympathetic block, bias became positive (+0.55 litre min^–1)and limits of agreement increased to –3.21 and +4.30 litremin^–1. ODM measured a greater increase in CO after LEA(