Clinical Investigations Lithium dilution cardiac output measurement: A clinical assessment of central venous and peripheral venous indicator injection* Charles Garcia-Rodriguez, MBBS, FRCA; James Pittman, MBBS, FRCA; Cynthia H. Cassell, MA; John Sum-Ping, MBChB, FRCA; Habib El-Moalem, PhD; Christopher Young, MD; Jonathan B. Mark, MD L ithium dilution cardiac output measurement (LiDCO, Lon- don, UK) is a new clinical tech- nique for measuring blood flow (1). Lithium chloride is injected as an intravenous bolus into a vein, and its concentration in arterial blood is then measured over time by a lithium-sensi- tive electrode attached to a peripheral arterial catheter. Cardiac output (CO) can be calculated by using an analytic algo- rithm that calculates CO from the area under the lithium dilution curve. Lith- ium is an appropriate indicator because its plasma concentration is normally neg- ligible, and as it does not bind to plasma or tissue proteins, there is minimal loss of indicator as it passes from the injection catheter through the heart and lungs (2). Furthermore, lithium has no significant toxicity in the doses used to make the measurements. Plasma concentrations of lithium achieved during CO measure- ment are 1% of the desired and thera- peutic levels maintained during clinical therapy for treatment of mania with lith- ium carbonate (3). Several studies have demonstrated that the lithium dilution method using central venous injection provides CO val- ues that are in close agreement with si- multaneously measured CO values ob- tained using other techniques of CO measurement (4, 5). If the lithium dilu- tion technique could be performed accu- rately by using a peripheral vein, then CO could be measured without the risks of central venous catheterization, thereby enhancing the clinical applicability of this measurement technique. Because minimally invasive CO measurement for intravascular volume optimization has been shown to be valuable even for pa- tients who do not have central pressure monitoring (6), it seems important to determine whether lithium dilution CO can be measured without central venous catheterization. In this study, we investigated whether the accuracy of the original lithium dilu- tion CO method was influenced by the site of intravenous lithium injection. In a con- trolled clinical environment in postopera- tive patients, we compared CO measure- ment by peripheral vein administration of lithium (Li-PCO) to CO measurements by central venous administration of lithium (Li-CCO). In a subset of patients who had a pulmonary artery catheter in place, ther- *See also p. 2380. From Duke University Medical Center (CGR, JP, CHC, JSP, HEM, CY, JBM) and Durham Veterans Affairs Med- ical Center (CGR, JP, CHC, JSP, CY, JBM), Durham, NC. Supported, in part, by LiDCO Ltd., London, United Kingdom, and Duke University Medical Center, Durham, NC. Presented, in part, at the American Society of Critical Care Anesthesiologists meeting, San Francisco, CA, October 13, 2000; at the American Society of Anesthesiologists meeting, San Francisco, CA, October 18, 2000; and at the Association of University Anes- thesiologists meeting, May 5, 2000, Salt Lake City, UT. Copyright © 2002 by Lippincott Williams & Wilkins Objective: The lithium indicator dilution technique has been shown to measure cardiac output (CO) accurately by using central venous injection of lithium chloride (Li-CCO). This study aimed to compare the measurement of CO by using peripheral venous administration of lithium chloride (Li-PCO) with Li-CCO. Design: Prospective, observational human study. Setting: Surgical intensive care unit. Patients: Thirty-one patients were studied after major surgery. All patients had arterial, central, and peripheral venous catheters. A total of 24 patients had pulmonary artery catheters. Measurements: Serial measurements of Li-CCO and Li-PCO were made during hemodynamically stable conditions. CO was also measured using thermodilution (TDCO) when a pulmonary artery catheter was present. Data were analyzed by linear regres- sion, the generalized estimating equation, and the comparison method described by Bland and Altman. Main Results: There were 93 Li-CCOs, 93 Li-PCOs, and 216 TDCOs recorded. The ranges of COs were similar: Li-CCO, 2.36 – 11.52 L/min (mean, 5.22 L/min; n  31); Li-PCO, 1.63–9.99 L/min (mean, 5.22 L/min; n  31), and TDCO, 3.28 –10.4 L/min (mean, 5.75 L/min; n  24). There was good linear correlation between Li-CCO and Li-PCO (R 2  .845). The mean difference for Li-CCO– Li-PCO was very small and insignificant (p  .97), and the limits of agreement were acceptable (mean difference  SD, 0.0005  0.64 L/min). The mean difference for Li-CCO–Li-PCO was smaller if the peripheral injection site was proximal rather than distal to the wrist (p  .053). Li-PCO and Li-CCO values were lower than simultaneously obtained TDCO measurements (Li-PCO–TDCO, 0.538  0.95 L/min, p  .003; Li-CCO–TDCO, 0.526  0.67 L/min, p  .0001). Conclusions: Li-PCO gives a measurement that agrees well with Li-CCO. Accuracy of Li-PCO is probably improved if a prox- imal arm vein is used. Li-PCO provides accurate measurements of CO without the risks of pulmonary artery or central venous cath- eterization. (Crit Care Med 2002; 30:2199 –2204) KEY WORDS: cardiac output; measurement techniques; lithium dilution 2199 Crit Care Med 2002 Vol. 30, No. 10