One of not those clinical circumstances is the presence of raised intra-abdominal hypertension (IAH).Using nine haemodynamically stable, fluid-responsive pigs and bolus transcardiopulmonary thermodilution cardiac output (COTCP) as the reference method, Gruenewald and colleagues [26] studied the ability of continuous cardiac output (CCO) methods based on arterial pressure waveform (pulse contour-derived cardiac output [PCCO] and PulseCO) and pulmonary artery catheter thermodilution (CCOPAC) to detect a change in CO following a fluid challenge. CO was measured and compared during four steps of the experimental protocol: (a) at baseline, (b) after a fluid challenge, (c) after induction of IAH by pneumoperitoneum and (d) after a fluid challenge in the presence of IAH.
At baseline, all CO methods showed acceptable agreement in the increase in CO following volume loading. However, PulseCO and pre-calibration PCCO (PCCOpre) grossly under-estimated CCO following volume challenge in the presence of IAH when CO response to fluid was seen in only CCOPAC and COTCP. After recalibration, PCCO was comparable to COTCP. There was also a progressive increase in bias (COTCP-PulseCO versus COTCP-PCCOpre) during the experimental protocol in the presence of IAH.The induction of IAH caused increases in CVP, PAOP and chest wall elastance. Arterial blood pressure increased after fluid challenge only in the absence of IAH. This finding and the mechanical effects of IAH on the arterial elastance could account for the inability of waveform-based CCO algorithms to accurately track changes in CO after fluid loading during IAH.
Two recent papers by the same investigators assessed the performance of a later FloTrac/Vigileo? system algorithm (software version 1.07; Edwards Lifesciences, LLC, Irvine, CA, USA). In both papers, the system was assessed in haemodynamically stable patients with a stable regular heart rate maintained between 80 to 90 beats per minute by fixed external pacing after elective off-pump coronary artery bypass grafting.In the first paper, Hofer and colleagues [27] compared stroke volume variation (SVV) calculated using the new algorithm (SVVFloTrac) with SVV calculated using the PiCCOPlus? system (SVVPiCCO) during a blood volume shift manoeuvre, instigated by changing body positioning from a 30�� head-up position to a 30�� head-down position.
The manoeuvre resulted in significant increases in SV, global end diastolic Brefeldin_A volume and CVP and significant decreases in SVVFloTrac, SVVPiCCO and PPV. Among the patients with an increase in SV of greater than 25% (58% of the population), SVVFloTrac and SVVPiCCO were 16% �� 4% and 19% �� 5%, respectively. In patients with an increase in SV of less than 10%, baseline SVVFloTrac and SVVPiCCO were 9% �� 2% and 11% �� 3%, respectively.