Letters to the Editor

The righting response used in our study might be impacted by dynamic behavior and pain threshold. Although we did not evaluate the behavior of vestibular lesion (VL) rats, the righting response latency in VL rats raised in 1 g (1G-VL) did not differ from that of sham rats (1G-sham),6 suggesting that VL itself did not cause the prolonged recovery of righting response. Furthermore, pain sensitivity was assessed using the hot plate test in the additional experiments. Following placement of each subject on a 55°C plate, no difference in latency of pain-related behavior was detected between 1 g raised rats (14.8 ± 3.8 seconds [mean ± SD]) and 3 g raised rats (12.8 ± 1.8 seconds). Thus, chronic hypergravity exposure (2 weeks) did not alter pain sensitivity, whereas acute hypergravity exposure (10 minutes) might alter pain sensitivity.7 Although Petrenko et al. comments that arterial pressure decreases in proportion to anesthetic depth,8 other factors such as autonomic disorders can augment anesthetic-induced hypotension. We have demonstrated that hypergravity exposure suppressed vestibular-mediated pressor response (vestibulo-cardiovascular reflex); however, nonvestibular-mediated pressor response was not affected by hypergravity.9 The possibility that the suppressed vestibulo-cardiovascular reflex affects propofol-induced hypotension is unlikely since hypotension measured in 1G-VL was comparable to that measured in 1G-sham.6 Sensitivity of baroreflex is the most important other factor when determining propofol-induced hypotension. To examine this, the sensitivity of baroreflex control over heart rate was assessed in rats raised in 1 g or 3 g for 2 weeks in the additional experiments, in which heart rate responses to phenylephrine- and nitroprusside-related changes in arterial pressure were plotted and fitted to the logistic function curve. There was no difference in the maximal gain between 1 g raised rats (6.9 ± 1.4 [mean ± SD]) and 3 g raised rats (6.2 ± 1.0). The notable point of our study was that the augmenting effect of propofol was induced via the vestibular-mediated pathway because it was eliminated by the VL. As the peripheral vestibular organs are used as the gravitational sensor, it is reasonable to assume that all vestibular-mediated responses are caused by gravitational change, whether or not they are “stress responses.” Finally, the reply to Petrenko et al.’s last question1 was discussed in the introduction of our original article.6 Chihiro Iwata, MD, PhD Hironobu Morita, MD, PhD Department of Physiology Gifu University Graduate School of Medicine Gifu, Japan [email protected] REFERENCES 1. Petrenko AB, Furutani K, Baba H. More solid evidence is required to validate a hypergravity-induced increase in sensitivity to propofol. Anesth Analg 2014;119:1220 2. Antunes LM, Roughan JV, Flecknell PA. Effects of different propofol infusion rates on EEG activity and AEP responses in rats. J Vet Pharmacol Ther 2003;26:369–76 3. Doyle PW, Matta BF. Burst suppression or isoelectric encephalogram for cerebral protection: evidence from metabolic suppression studies. Br J Anaesth 1999;83:580–4

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4. Michenfelder JD. The interdependency of cerebral functional and metabolic effects following massive doses of thiopental in the dog. Anesthesiology 1971; 41:231–6 5. Brown EN, Lydic R, Schiff ND. General anesthesia, sleep, and coma. N Engl J Med 2010;363:2638–50 6. Iwata C, Abe C, Nakamura M, Morita H. Hypergravity exposure for 14 days increases the effects of propofol in rats. Anesth Analg 2014;118:125–31 7. Kumei Y, Shimokawa R, Terasawa M, Shimokawa H, Kawauchi Y, Makita K, Ohya K, Toda K. Hypergravity and opioid-mediated pain suppression in rats. J Gravit Physiol 2001;8:P111–2 8. Kanaya N, Hirata N, Kurosawa S, Nakayama M, Namiki A. Differential effects of propofol and sevoflurane on heart rate variability. Anesthesiology 2003;98:34–40 9. Abe C, Tanaka K, Awazu C, Morita H. Impairment of vestibular-mediated cardiovascular response and motor coordination in rats born and reared under hypergravity. Am J Physiol Regul Integr Comp Physiol 2008;295:R173–80 DOI: 10.1213/ANE.0000000000000393

Automated Data Transmission for the Society of Thoracic Surgeons’ Adult Cardiac Anesthesia Module To the Editor

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recent article by Aronson et al.1 describes the development of an adult cardiac anesthesia module  to supplement the Society of Thoracic Surgeons’ national database. The development of national databases is a key component of understanding practice patterns in medicine and performing meaningful outcomes research, and the collaborative integration of surgical and anesthesia datasets is critical in advancing perioperative care. However, we are concerned about the Society of Thoracic Surgeons’ decision to only allow data entry via a web module. Although this is a reasonable option for small participating hospitals and does not require special software, it requires increasingly more work for hospitals with high surgical volume and is impractical for a large institution. At Vanderbilt University Medical Center, our adult cardiac service performed approximately 1300 procedures last year. Given that the anesthesia module contains 84 discrete elements, this would require the manual entry of more than 100,000 items per year. Manual data entry has been demonstrated to be less accurate compared to automated methods in creating clinical data repositories.2 In addition, it requires substantial staff time and is thus out of step with the current health care environment, which is focusing on improving value by increasing quality while decreasing cost. Six commercial anesthesia information management systems vendors now control 78% of the market.3 Development of a standardized data transmission format, validation, and field mapping to these vendors would obviate the need for redundant data entry, improve the quality of data capture, and reduce the cost of participation. We know this is both technically possible and feasible, given the success of the Multicenter Perioperative Outcomes Group.4 We urge the Society for Thoracic Surgery to develop the functionality necessary to support automated data transmission.

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E LETTERS TO THE EDITOR Jonathan P. Wanderer, MD, MPhil Andrew D. Shaw, MB, FRCA, FCCM, FFICM Jesse M. Ehrenfeld, MD, MPH Department of Anesthesiology Vanderbilt University Nashville, Tennessee [email protected] REFERENCES 1. Aronson S, Mathew JP, Cheung AT, Shore-Lesserson L, Troianos CA, Reeves S. The rationale and development of an adult cardiac anesthesia module to supplement the Society of Thoracic Surgeons national database: using data to drive quality. Anesth Analg 2014;118:925–32 2. Hong MK, Yao HH, Pedersen JS, Peters JS, Costello AJ, Murphy DG, Hovens CM, Corcoran NM. Error rates in a clinical data repository: lessons from the transition to electronic data transfer–a descriptive study. BMJ Open 2013;3:e002406 3. Provider behavior indicates significant shifts in AIMS market trends. Available at: http://www.klasresearch.com/news/ pressroom/2012/Anesthesia. Accessed May 30, 2014 4. Kheterpal S. Clinical research using an information system: the multicenter perioperative outcomes group. Anesthesiol Clin 2011;29:377–88 DOI: 10.1213/ANE.0000000000000395

The Influence of Positive End-Expiratory Pressure After a Recruitment Maneuver To the Editor

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hile the recent article by Ferrando et al.1 focusing on lung-protective ventilation strategies for patients undergoing 1-lung ventilation did show increased oxygen arterial pressure (PaO2) in patients in whom the positive end-expiratory pressure (PEEP) was increased during 1-lung ventilation, the authors failed to assess outcomes, including underlying safety of the recruitment maneuver. A recruitment maneuver plus PEEP could open the collapsed alveoli and prevent recollapse.2 However, static compliance may not be the best indication for ventilation because alveolar heterogeneity,3 including lung collapse and overdistention, often occur at the same time, especially in patients with bullae. The higher PaCO2 in the study group might be caused by further distention of already opened lung regions and thus the improvement of compliance does not necessarily indicate the optimal PEEP. Also, while in the study group, the PaCO2 was significantly higher (306 vs 231 mm Hg, P = 0.007) for most patients without impaired diffusion. When the PaO2 is >150 mm Hg, hemoglobin is nearly fully saturated and the pulse oximetry is nearly 100%, and thus the higher PaO2 is clinically not very important. In addition, previous studies in patients undergoing pneumonectomy, higher airway pressure during 1-lung ventilation has been shown to be a risk factor for developing acute lung injury/acute respiratory distress syndrome.4 It would therefore be of greater clinical interest if Ferrando et al.1 had data describing postoperative complications between the 2 groups including barotrauma, postoperative

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atelectasis, pneumonia, and 1-month mortality. In the final analysis, the maneuvers performed during surgery should be directed at improving the outcomes of patients. Yabing Zhang, MD Deshui Yu, MD Bin Liu, MD Department of Anesthesiology West China Hospital of Sichuan University Chengdu, Sichuan, China [email protected] REFERENCES 1. Ferrando C, Mugarra A, Gutierrez A, Carbonell JA, García M, Soro M, Tusman G, Belda FJ. Setting individualized positive end-expiratory pressure level with a positive end-expiratory pressure decrement trial after a recruitment maneuver improves oxygenation and lung mechanics during one-lung ventilation. Anesth Analg 2014;118:657–65 2. Futier E, Constantin JM, Paugam-Burtz C, Pascal J, Eurin M, Neuschwander A, Marret E, Beaussier M, Gutton C, Lefrant JY, Allaouchiche B, Verzilli D, Leone M, De Jong A, Bazin JE, Pereira B, Jaber S; IMPROVE Study Group. A trial of intraoperative low-tidal-volume ventilation in abdominal surgery. N Engl J Med 2013;369:428–37 3. Gattinoni L, D’Andrea L, Pelosi P, Vitale G, Pesenti A, Fumagalli R. Regional effects and mechanism of positive end-expiratory pressure in early adult respiratory distress syndrome. JAMA 1993;269:2122–7 4. Jeon K, Yoon JW, Suh GY, Kim J, Kim K, Yang M, Kim H, Kwon OJ, Shim YM. Risk factors for post-pneumonectomy acute lung injury/acute respiratory distress syndrome in primary lung cancer patients. Anaesth Intensive Care 2009;37:14–9 DOI: 10.1213/ANE.0000000000000406

In Response In response to Zhang et al.1 that we failed to assess outcomes, including safety of the recruitment maneuver (RM) and postoperative outcomes,2 while we agree that in the final analysis any maneuver performed during surgery should be directed at improving patient outcomes and is a sound suggestion for future research, the safety and beneficial effects of the RM have already been demonstrated in numerous studies in humans with healthy3 and injured lungs,4 including during thoracic surgery.5 The aim of the current study was simply to describe the physiologic effects of setting an optimal positive end-expiratory pressure (PEEP) compared with standardized PEEP on gas exchange and lung mechanics. Zhang et al.1 also comment that static compliance may not be the best option for setting the PEEP because of alveolar heterogeneity. We agree and as we described in the Methods section, we used dynamic compliance, not static compliance, to set the optimal PEEP. The best dynamic compliance identifies the optimal PEEP in patients with healthy6 and injured lungs7,8 using the PEEP level after an RM that prevents alveolar collapse while minimizing overdistention as the definition of optimal PEEP. In addition, Zhang et al.1 suggest that the higher arterial carbon dioxide tension in the optimal PEEP group may be caused by alveolar overdistention. This is correct when comparing patients with identical carbon dioxide

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