To the Editor:—
Dr. Norris et al.
are to be congratulated for their well-designed clinical trial examining influence of epidural anesthesia and analgesia on outcomes after abdominal aortic surgery. 1
A few points of interest deserve more discussion. The authors based their power analysis from a review of 234 previous patients undergoing the same surgery at their institution who required an average postoperative length of stay of 13 days. Although the clinical trial did not observe differences between epidural and nonepidural groups, all study patients experienced a dramatic reduction in length of stay (from 13 to 7 days) for the same surgery at the same institution. This dramatic reduction in length of stay across all groups could easily obscure any potential clinical differences between groups and limits conclusions on effects of epidural anesthesia and analgesia for this patient population undergoing routine clinical care.
Several factors may be involved in this dramatic clinical improvement in all study patients. The study protocol used a defined postoperative clinical pathway, and similar pathways have been shown in other surgical populations to decrease length of stay by 1 to 2 days. 2–4
Just as important a factor in this very intensive clinical trial is the high probability of a Hawthorne effect. This is the undesired effect of an intrusive experiment simply by itself. The inherent process of being in a clinical trial or under observation can lead to enhanced efforts and cooperation in the medical staff and can motivate the patient to increased mental and physical well being. 5,6
Historically, this effect is named after studies performed at the Western Electric Hawthorne Works in Chicago, where Harvard Business School professor Elton Mayo examined productivity and work conditions. Within the context of intrusive observation, productivity increased (approximately 25%) regardless of manipulation of variables such as rest breaks, work hours, temperature, humidity, and even after return of variables back to prestudy conditions. These improvements have generally been interpreted as being caused by the sheer presence of observation and experimentation regardless of variables being studied. The Hawthorne effect is a potential limitation of all prospective clinical trials where the subjects and caregivers are aware of the presence of a study. The intrusive effect of Norris et al.’
s well-designed clinical trial and the use of a clinical pathway could have easily been responsible for the dramatic reduction in length of hospital stay pre- and post-study, and these factors may have overshadowed any effects of epidural anesthesia and analgesia that may exist in the context of ordinary clinical care. Perhaps the most reasonable conclusion from this study is that an intensive, structured, clinical trial can markedly reduce length of stay after abdominal aortic surgery.
Spencer S. Liu, M.D.
1. Norris EJ, Beattie C, Perler BA, Martinez EA, Meinert CL, Anderson GF: Double-masked randomized trial comparing alternate combinations of intraoperative anesthesia and postoperative analgesia in abdominal aortic surgery. A nesthesiology 2001; 95: 1054–67
2. Bradshaw BG, Liu SS, Thirlby RC: Standardized perioperative care protocols and reduced length of stay after colon surgery. J Am Coll Surg 1998; 186: 501–6
3. Bardram L, Funch-Jensen P, Kehlet H: Rapid rehabilitation in elderly patients after laparoscopic colonic resection. Br J Surg 2000; 87: 1540–5
4. Basse L, Hjort Jakobsen D, Billesbolle P, Werner M, Kehlet H: A clinical pathway to accelerate recovery after colonic resection. Ann Surg 2000; 232: 51–7
5. De Amici D, Klersy C, Ramajoli F, Brustia L, Politi P: Impact of the Hawthorne effect in a longitudinal clinical study: the case of anesthesia. Control Clin Trials 2000; 21: 103–14
6. De Amici D, Klersy C, Ramajoli F, Brustia L: The awareness of being observed changes the patient's psychological well-being in anesthesia. Anesth Analg 2000; 90: 739–41
© 2002 American Society of Anesthesiologists, Inc.