DOI: 10.1097/AIA.0b013e3181bff887
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PMID: 20065724
Issn Print: 0020-5907
Publication Date: 2010/01/01
Current Status of Dynamic Parameters of Fluid Loading
Amit Asopa; Swaminathan Karthik; Balachundhar Subramaniam
Excerpt
Perioperative fluid management plays a critical role in the outcomes of surgical patients. There is an ongoing controversy between advocates of a liberal fluid management regimen and a more restrictive fluid replacement strategy. Traditional fluid management emphasizes the replacement of fluid deficits from fasting, insensible, and evaporative losses as well as estimating maintenance fluid and blood loss.1 Such calculations are thought to overestimate fluid requirements and lead to interstitial fluid accumulation and weight gain.2 Another approach uses the measurement of central venous pressures and pulmonary artery diastolic or wedge pressures as measures of cardiac preload. But these parameters have been shown to be completely unrelated to cardiac preload both in healthy volunteers as well as the critically ill.3–5 Recently a more restrictive fluid management regimen has been proposed, which involves replacing only definite fluid losses. This fluid strategy was shown to improve outcomes in certain critically ill surgical populations.6 Brandstrup et al6 demonstrated in a randomized trial that postoperative complications were fewer in the fluid restricted group of patients undergoing colon surgery. McArdle et al showed that positive fluid balance is predictive of major adverse events and increased high dependency unit, intensive care unit (ICU), and overall hospital stay.7 Appropriate fluid therapy in critically ill patients may result in early extubation, less incidence of pulmonary edema, and renal failure. Thus, it is clear that current fluid management strategies have significant deficiencies and adversely influence outcomes in a variety of patient populations. A new paradigm to guide fluid management is essential. A growing body of evidence support the usage of underused dynamic parameters for assessing fluid responsiveness.8 These parameters are based on the cardiopulmonary interaction during positive pressure ventilation. The resulting transpulmonary pressure changes cause variations in venous return, blood pressure (BP), and stroke volume. The amplitude of this variation is inversely proportional to volume status. Thus, hypovolemia is characterized by larger swings in BP and stroke volume.9 Clinicians have subjectively used these for a long time by observing swings in the arterial or plethysmographic waveform. Pulsus paradoxus seen in pericardial tamponade, is an exaggerated example of the same variation. However, the physiologic variation during spontaneous ventilation was not objectively quantified to be a meaningful measure of intravascular volume status for a long period of time.
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