The LiDCOrapid uses the PulseCO algorithm to derive stroke volume (SV) and heart rate from the blood pressure waveform. The key step in the algorithm is the conversion of the blood pressure to volume to account for both aortic compliance and capacitance. The PulseCO algorithm uses a patient specific factor to adjust the aortic capacitance individually for each patient. The factor can be precisely determined by comparing a known cardiac output with the PulseCO estimate. This factor does not change for a patient over the short term.
Because the factor does not change, it was possible to develop a nomogram, or mathematical relationship, using the patient’s characteristics to estimate it. The nomogram used in the LiDCOrapid was developed from carefully controlled studies of the PulseCO algorithm with precise determinations of cardiac output using Lithium indicator dilution. The result is a robust method for estimation of the factor.