CLAUDE P. TOUSIGNANT, FERGUS WALSH AND C. DAVID MAZER
Department of Anaesthesia, St Michael’s Hospital, University of Toronto, Toronto, Ontario, Canada
Anesth. Analg., 90: 351–355, 2000
Intravenous volume is often given to patients in the intensive care unit (ICU) to improve cardiovascular function. The relationship between stroke volume (SV) and left ventricular (LV) size was investigated using transesophageal echocardiography (TEE) in a population of 20 ICU patients and 21 postoperative cardiac surgical patients. Whether LV end diastolic area (EDA) by TEE could identify patients who increased SV by 20% or more (responders) after administration of 500 mL of pentastarch was examined. Only a modest relationship (r = 0.60) existed between the EDA and the SV in all patients, and none could be established between the pulmonary capillary wedge pressure (PCWP) and the EDA in all patients. Both responder and nonresponder PCWP markedly increased after volume administration. Only responder EDA greatly increased after volume administration. Responders had a much lower EDA (15.3 ± 5.4 cm2) and PCWP (12.2 ± 2.2 mm Hg) when compared with nonresponders (20.2 ± 4.8 cm2 and 15.9 ± 3.1 mm Hg, respectively). Few ICU patients and only those with a small EDA responded to volume administration. An overall optimal LV EDA below which most patients show volume-recruitable increases in SV could not be identified.
Whenever a new diagnostic modality is identified, it is important to specify the parameters of its use. When simple applications can be discovered the tool becomes that much more valuable. Unfortunately, most tools never turn out to be as simple as hoped for. The authors had hypothesized that using transesophageal echocardiography (TEE) to obtain a simple measurement of end diastolic volume (EDV) would help predict whether a volume load would improve cardiac performance in a variety of intensive care patients. Not surprisingly, this did not occur.
Intensive care patients have a wide array of lesions that cause poor myocardial performance. Besides patient differences, TEE is technically difficult to perform. The measurement of EDV requires that the image is truly a cross-section of the ventricle. If the image is obtuse, then the results will be spurious. After acquiring an image, defining the outline of the myocardium is a subjective endeavor. Even within this study, the authors were suspicious that they may have encountered acquisition difficulties. Despite the failure of this study to demonstrate a simple use for TEE in an ICU setting, it is a tool which may well prove to contribute to the care of these most critically ill patients.
Stephen T. Robinson M.D.