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EDITORIAL

Introduction of New Monitors into Clinical Anesthesia

Marcos F. Vidal Melo, MD, PhD^*, and Bruce J. Leone, MD

From the *Cardiac Anesthesia Group, Department of Anesthesia and Critical Care, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts; and Department of Anesthesiology, Mayo Clinic, Jacksonville, Florida.

Address correspondence and reprint requests to Marcos F. Vidal Melo, MD, PhD, Department of Anesthesia and Critical Care, Massachusetts General Hospital, 55 Fruit St., Boston, MA 02114. Address e-mail to mvidalmelo{at}partners.org.

	Introduction

Top Introduction REFERENCES

 
Anesthesiologists are enthusiastic about technological innovation. In general, our field has been at the forefront of technology and safety, often combining technological progress with increases in patient safety. Examples range from currently established methods, such as pulse oximetry and capnometry, to more recent attempts at processing of brain electrical activity to monitor anesthetic depth. Advances in electronics and computer methods continue to occur at a dizzying rate, such that we can be assured that new technologies will be rapidly available to our practice.

In the current issue of Anesthesia & Analgesia, Schober et al.1 advocate the value of one such technological advance. The use of real-time, beat-to-beat assessment of aortic flow, together with indices of intravascular volume, were instrumental in the early detection of hypervolemia from translocation of cystoscopy irrigation solution into the circulation during transurethral resection of the prostate (TURP). The authors report Doppler signal changes as the harbinger of what ultimately became TURP syndrome (neurological findings associated with hyponatremia). This case report would suggest that routine transesophageal Doppler monitoring of cardiac function during TURP could be used successfully in the early diagnosis of TURP syndrome.

Transesophageal ultrasound measurement of cardiac output was first described in 19712 and underwent further refinement and development in 1989.3 This monitor provides a more reliable method of detecting changes in cardiac output than of accurately determining absolute values.4,5 Despite being available clinically for several years, a niche for routine use of esophageal Doppler cardiac output devices has not yet been established; this prompts the question of why so many devices have been Food and Drug Administration (FDA)-approved, since only a small fraction of them have reached widespread clinical use.

Introduction of a new device in the market involves its evaluation by the Center for Devices and Radiological Health (CDRH) at the FDA. Devices are grouped in three classes of ascending risk, which determine the level of control exerted to assure their safety and effectiveness. If the device is classified as Class II or III, i.e., higher risk, it may undergo a process of pre-market approval. Most monitoring devices in anesthesia are Class II, and are actually "cleared" under the 510(k) process, not "approved," by the FDA based on substantial equivalence to other devices already present in the market. FDA does not test new medical devices to determine whether they are safe and effective before they are sold in the United States. Instead, FDA gives guidance to manufacturers on what tests to perform. The CDRH evaluates the scientific test data submitted by manufacturers and authorizes device commercialization.

FDA approval (or clearance) of a device is significantly different from FDA approval of a drug.6 Whereas drug approval involves large randomized clinical trials, in the case of devices, "reasonable assurance of safety and effectiveness" is the essential requirement. Consequently, FDA clearing of a device for clinical use does not imply accurate and precise functioning of that device in all clinical conditions, nor does it imply that there is solid clinical data to support the use of the device in specific clinical settings. The FDA does not regulate the practice of medicine.

There are advantages to this process, since it expedites availability of devices for clinical use, allowing patients to benefit from new or improved technologies, and the FDA to focus resources on areas of highest patient risk. However, if generalization of device use precedes availability of strong clinical data, an unfounded increase in costs of patient care may result. Even worse, if the device’s performance in the clinical setting is not systematically evaluated, and indiscriminate or uncritical application to noninvestigated clinical situations occurs, misleading information could lead to patient harm. The public FDA website (http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/psn/index.cfm) provides many valuable examples of approved device use in clinical situations that result in unintended consequences.

The continuous monitoring of aortic flow and thus cardiac output would appear safe and clinically valuable. Intuitively, the correlation between TURP syndrome and increased aortic flow would appear obvious. An increase in intravascular volume would result in a reflex increase in stroke volume, thus increasing cardiac output and aortic flow, measured by Doppler changes. However, as is the case for any new monitor, extrapolation of success in a given case to use of the monitor as de rigueur in similar situations is hasty and fraught with missteps and unproven assumptions. For instance, what if the requirements for accurate assessment of cardiac output with a Doppler technique changed during the TURP procedure or with medications? We must harness our specialty’s almost innate draw to new technologies with a goodly dose of critical assessment. Definitive determination of the value of monitoring devices in clinical practice, even of noninvasive monitors, must take into account their reliability in different conditions, contribution to patient safety and outcome, and cost-effectiveness in specific clinical situations.

Medical decision-making depends on many variables. Thus, it is not evident that there will ever be a single prescription to the optimal set of monitors for each specific anesthetic case. The creation of networks among clinicians and institutions to facilitate testing of new devices could provide a more objective approach to expedite evaluation and exchange of information and experiences pertaining to new technology. Systematic studies in a large number of cases and in specific physiologic conditions could provide optimal information on effectiveness, and generate sound data to establish new standards of care. Such studies would be highly desirable as new technologies are introduced. For now, we need to be well aware that the responsibility for the indication of a new monitor, and for the clinical decisions derived from the interpretation of obtained measurements, ultimately rest with the clinician.

	ACKNOWLEDGMENTS

 
The authors thank Mr. Michael Husband, Chief of the Anesthesiology and Respiratory Branch, CDRH, FDA, for his valuable insights and suggestions.

	Footnotes

 
Accepted for publication March 16, 2008.

	REFERENCES

Top Introduction REFERENCES

 

1. Schober P, Meuleman EJH, Boer C, Loer SA, Schwarte LA. Transurethral resection of the prostate syndrome detected and managed using transesophageal Doppler. Anesth Analg 2008;107:921–5[Abstract/Free Full Text]
2. Side CD, Gosling RG. Non-surgical assessment of cardiac function. Nature 1971;232:335–6[Web of Science][Medline]
3. Singer M, Clarke J, Bennett ED. Continuous hemodynamic monitoring by esophageal Doppler. Crit Care Med 1989;17:447–52[Web of Science][Medline]
4. Penny JA, Anthony J, Shennan AH, De Swiet M, Singer M. A comparison of hemodynamic data derived by pulmonary artery flotation catheter and the esophageal Doppler monitor in preeclampsia. Am J Obstet Gynecol 2000;183:658–61[Web of Science][Medline]
5. Kim K, Kwok I, Chang H, Han T. Comparison of cardiac outputs of major burn patients undergoing extensive early escharectomy: esophageal Doppler monitor versus thermodilution pulmonary artery catheter. J Trauma 2004;57:1013–7[Web of Science][Medline]
6. Ramsey SD, Luce BR, Deyo R, Franklin G. The limited state of technology assessment for medical devices: facing the issues. Am J Manag Care 1998;4 Spec No:SP188–99

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