['The COstatus monitor measures cardiac output via the transpulmonary ultrasound dilution method (COTPUD ) after injection of normal saline, and can calculate continuous cardiac output (CCO) from the arterial pressure waveform. The relationship between arterial waveform and COTPUD however, might be degraded during vasoconstriction/vasodilation.', 'To examine if recalibration of arterial waveform-derived CCO is required during mild vasoconstriction/vasodilation.', 'In 10 anesthetized piglets (6.6-10.1\xa0kg), two COstatus monitors calculated the CCO from the same femoral arterial waveform before and during infusions of phenylephrine (PE; 1 or 3\xa0mg·kg(-1) ·min(-1) ) and sodium nitroprusside (SNP; 1 or 5\xa0mg·kg(-1) ·min(-1) ), administered in random order. One monitor was recalibrated (CCORecal ) after each intervention, while the other monitor was not (CCONon-Recal ). Recalibration was performed with COTPUD with 1\xa0ml·kg(-1) normal saline as indicator. The effects of each infusion on hemodynamic parameters were compared with baseline using paired t-tests. The bias, limits of agreement (LOA), and percentage error between simultaneous measurements (CCORecal and CCONon-Recal ) were examined with Bland-Altman plots.', 'Infusion of PE significantly increased COTPUD , heart rate (HR), and arterial pressures but not systemic vascular resistance (SVR). Infusion of SNP decreased arterial pressures without affecting COTPUD , HR, and SVR. There was no bias between CCORecal and CCONon-Recal at the baseline, but a small bias was observed during PE and SNP infusions. The LOA increased approximately 10 fold during vasoconstriction and vasodilation. The\xa0percentage error increased from ≤ 5% to 32% and 27% during PE and SNP infusions, respectively.'] Is continuous minimally invasive cardiac output monitoring with the COstatus in a neonatal swine model : recalibration necessary during vasoconstriction and vasodilation?