| JOURNAL HOME | CME HOME | THIS MONTH | PAST ISSUES | ETOC | COLLECTIONS |
| AUTHORS | REVIEWERS | EDITORIAL BOARD | FEEDBACK | RSS | HELP |
| ||||||||||||||
| ||||||||||||||
|
|
|
|
||||||||||||
|
||||||||||||||
Department of Anesthesiology and Pain Management, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, girish.joshi{at}utsouthwestern.edu
In Response:
Thank you for the opportunity to reply to Hamilton et al.'s letter. It is interesting that, despite the numerous studies discussed in the review article (1), Hamilton et al. insist that there is no support for intraoperative fluid restriction (or avoidance of fluid overload). Unfortunately, they have overlooked the review's emphasis that "the major reason for the observed benefits may not be solely due to crystalloid restriction but also related to use of colloids instead" and that the review recommends a balanced approach. Furthermore, the review recognizes the limitations of the current literature and calls for further research. This review also highlights that it is not uncommon to administer relatively large amounts of fluids (particularly crystalloids) in the intraoperative period either as a part of routine practice (resulting from the use of algorithms) and/or to maintain hemodynamic stability and urinary output. Such a practice is not necessarily benign because excessive fluid therapy can influence perioperative morbidity and mortality.
There is no question that the variables that are currently used to guide intraoperative fluid therapy (e.g., heart rate, arterial blood pressure, central venous pressures, and urine output) are not reliable indicators of intravascular volume status. Unless it is significant, hypovolemia is difficult to detect based on these routinely used criteria. Importantly, these hemodynamic variables are pressure oriented and may not correlate with organ blood flow. Currently, we do not have any clinical criteria that can be completely relied on. Thus, while we wait for more reliable variables to guide intraoperative fluid therapy, clinicians have no option but to continue to use these criteria. Nevertheless, it is important that practitioners accept these limitations and do not guide therapy solely based on these criteria.
Interestingly, Hamilton et al. claim that "robust" hemodynamic variables derived from the esophageal Doppler device are superior to the currently used variables. Although I agree that the use of flow-based criteria such as those derived from esophageal Doppler (or echo-Doppler) devices is a move in the right direction, the claim that they provide us with "robust" variables is premature.
Hamilton et al. fail to mention the potential limitations of esophageal Doppler monitoring and thus the problems associated with fluid administration based in the values derived. The esophageal Doppler device estimates the aortic cross-sectional area used to calculate stroke volume from nomograms, which may introduce calibration errors, particularly as the aortic diameter can change with each cardiac cycle. Alteration in the diameter of the descending aorta may change the angle of the Doppler transducer, which may affect the validity of measurements. Of note, errors in aortic diameter are magnified, as the square of the diameter is integrated to calculate cardiac output (2). In addition, its use has been limited to patients without known cardiovascular disease or in whom preoperative noninvasive testing was unremarkable and thus may not be applicable in patients with severe aortic atherosclerosis (2). Another source of error stems from the fact that cardiac output is estimated from measured aortic blood flow values with the assumption that lower body blood flow constitutes 70% of the total cardiac output. Numerous intraoperative situations may affect the relative ratio of upper and lower body blood flow, which may invalidate the estimates of cardiac output. Thus, the variables derived using this device remain controversial and cannot be claimed as "robust."
In addition, the benefits of the esophageal Doppler device are based on a few small studies performed by a select group of investigators (3) and there is a need for further validation by larger trials. Other concerns with this approach are that the physiologic end-points may not always be achieved despite aggressive fluid therapy. Of note, a review concluded that intraoperative fluid optimization regimens using minimally invasive monitoring might not be completely benign (4).
References
This article has been cited by other articles:
|
|
 |
|
  S. Peter, P. Subash, and J. Paul Airway Management During Second-Stage Tongue Flap Procedure Anesth. Analg., January 1, 2007; 104(1): 217 - 217. [Full Text] [PDF]
|
|
|
|
|
|
J. V. Roth Cricoid Pressure is for Full Stomachs, Thyroid Pressure is for Assisting Intubations Anesth. Analg., January 1, 2007; 104(1): 219 - 219. [Full Text] [PDF]
|
|
|
|
|
|
N. Eipe, A. D. Pillai, A. Choudhrie, and R. Choudhrie Airway Management During Second-Stage Tongue Flap Procedure Anesth. Analg., January 1, 2007; 104(1): 217 - 218. [Full Text] [PDF]
|
|
|
|
|
|
M. Parish and A. Mahmoudpoor Cricoid Pressure is for Full Stomachs, Thyroid Pressure is for Assisting Intubations Anesth. Analg., January 1, 2007; 104(1): 219 - 219. [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
