Model building, effect modification, and outcomes after sinus surgery

Letters to the editor 3) From group 5 of the rearranged Table 1: E(Y) ⫽ ␤0 ⫹ ␤1 ⫻ 1 ⫹ ␤2 ⫻ 1 ⫹ ␤3(1 ⫻ 1) ⫽ 13.9 4) From group 6 of the rearranged Table 1: E(Y) ⫽ ␤0 ⫹ ␤1 ⫻ 1 ⫹ ␤2 ⫻ 0 ⫹ ␤3(1 ⫻ 0) ⫽ 6.6 Therefore, the final multivariate regression model should be: Y ⫽ ⫺0.33 ⫹ 6.93X1 ⫹ 0.98X2 ⫹ 6.32(X1 · X2) ⫹ ␧. doi:10.1016/j.otohns.2009.05.009

Model building, effect modification, and outcomes after sinus surgery We appreciate the thoughtful and analytical approach taken by Dr Chao in response to our article.1 He correctly points out that if olfactory function (X1) was binary, then the model would need the modifications set forth in the appendix. However, multiple model building approaches exist.2 In our analysis, we accounted for olfactory function as a categorical variable and our original conclusions hold true. Interestingly, in both models, there was a significant interaction between nasal polyposis and olfaction with regard to olfactory outcomes: anosmic patients with nasal polyposis improved to a greater extent than anosmic patients without nasal polyposis. We have also observed an interaction, or effect modification, with nasal polyposis and other clinical variables in the measurement of post– endoscopic sinus surgery (ESS) improvement.3 For example, patients with nasal polyposis and a history of prior sinus surgery are as likely to improve on endoscopy scores after ESS as patients undergoing primary surgery. Patients without nasal polyposis and a history of prior ESS are 3.9 times as likely to improve on endoscopic exam after ESS as primary patients. The differences observed in patients with nasal polyposis illustrate the heterogeneity of patients with chronic rhinosinusitis undergoing ESS. Some findings are likely related to the underlying constructs of the instruments used to measure the outcomes of ESS. However, it is also evident that patients with nasal polyposis behave differently than patients without nasal polyposis. As we learn more about the underlying nature of nasal polyposis and continue to study the clinical behavior of these patients, we will also better understand how this dynamic impacts the outcomes of ESS. Jamie R. Litvack, MD, MS Jess Mace, MPH Timothy L. Smith, MD, MPH Division of Rhinology and Sinus Surgery, Oregon Sinus Center Department of Otolaryngology–Head and Neck Surgery Oregon Health & Science University, Portland, OR

303 REFERENCES 1. Litvack JR, Mace J, Smith TL. Does olfactory function improve after endoscopic sinus surgery? Otolaryngol Head Neck Surg 2009;140: 312–9. 2. Kutner MH, Nachtsheim CJ, Neter J, Li W, editors. Applied linear statistical models. 5th ed. New York: McGraw-Hill Irwin; 2005. 3. Litvack JR, Griest S, James KE, et al. Endoscopic and quality-of-life outcomes after revision endoscopic sinus surgery. Laryngoscope 2007; 117:2233– 8.

doi:10.1016/j.otohns.2009.05.011 Potential hazards of the harmonic scalpel We are writing in reference to the recent article “Modified lateral neck lymphadenectomy: Prospective randomized study comparing harmonic scalpel with clamp-and-tie technique” by Miccoli and colleagues.1 We would like to describe our own experience with the Ethicon Endo-Surgery Harmonic ACE in endocrine surgery of the head and neck. More specifically, we have encountered potential pitfalls with the ACE23E model that were not addressed by Miccoli and colleagues. To date, we have used the ACE23E device in conjunction with surgical clips over conventional clamp-and-tie technique for over 250 consecutive thyroidectomies. Similar to results by Miccoli and colleagues, we previously reported improved hemostasis and reduced operating time with the Harmonic CS-14C model.2 The benefits we have found are similar with the ACE23E, namely, a decrease in surgical time, avoidance of drain placement in all cases, and no cases of postoperative hemorrhage requiring intervention. However, the ACE23E has added advantages of control of larger vessels up to 5 mm in diameter and a handactivated control. Despite this, we would like to mention potential pitfalls in using this device not mentioned in previous publications. With prolonged activation, the ACE23E generates a considerable amount of residual heat. In our initial experience, this has led to unintended burning of adjacent tissue, skin, and drapes, as well as minor burn injury to the surgical assistant and operating room staff. In one instance, prolonged contact with a surgical hemostat caused fracture of the instrument. Our method for avoiding these complications involves using a moist sterile towel fastened to the surgical field, with placement of the device tip into the towel immediately following each use. This has improved the safety of the device considerably. It is possible that other groups are describing their experiences with previous models, in which case these problems may not be reported. We would like other head and neck surgeons to be aware of the benefits and drawbacks of the Harmonic ACE23E model in particular. This is especially crucial for those switching from conventional hemostatic techniques. Pavan S. Mallur, MD Daniel Jethanamest, MD Department of Otolaryngology, New York University Langone Medical Center