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Eur J Cardiothorac Surg 2008;34:155-158. doi:10.1016/j.ejcts.2007.12.056
Copyright © 2008, European Association for Cardio-thoracic Surgery. Published by Elsevier. All rights reserved.
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Learning curve in videothoracoscopic thymectomy: how many operations and in which situations?

Alper Toker*, Serhan Tanju, Sedat Ziyade, Serkan Kaya, Sukru Dilege

Istanbul University, Istanbul Medical School, Department of Thoracic Surgery, Istanbul, Turkey

Received 29 May 2007; received in revised form 27 November 2007; accepted 10 December 2007.

* Corresponding author. Address: Inonu Cad. Yildiz Sok. STFA Bloklari, B/6 No. 13, Kozyatagi, 81090 Istanbul, Turkey. Tel.: +90 532 422 38 02; fax: +90 216 338 43 80. (Email: atoker{at}istanbul.edu.tr; aetoker{at}superonline.com).


   Abstract
Top
 Abstract
1. Introduction
 2. Patients and methods
 3. Results
 4. Discussion
 References
 
Objective: Videothoracoscopic learning curve is known to vary among different surgeons, and may be influenced by patients and various situations. We aimed to analyze the learning curve of a surgeon in videothoracoscopic thymic surgery for myasthenia gravis. Methods: This is a descriptive single-center study using collected clinical data from 90 patients undergoing videothoracoscopic thymic surgery between June 2002 and September 2006. Cumulative summation (CUSUM) model was used to evaluate the learning curve for videothoracoscopic thymectomy operations. Unsuccessful situations were accepted as longer operation time, surgeon-related open conversions, readmissions and postoperative complications. Factors affecting longer operation time (patients with operation time longer than the average) and longer postoperative stay (patients with postoperative hospital stay longer than average) were analyzed. Results: Body mass index (BMI) was the only predictor of longer operation time (23.04 ± 2.93 vs 25.61 ± 2.70 (p = 0.001) independent samples test). The amount of prescribed pyridostigmine was the only factor for longer hospital stay (213.3 ± 101.5 mg vs 270. 0 ± 122.6 mg (p = 0.044) Mann–Whitney U-test). CUSUM analysis demonstrated a learning curve with success rates of 80%, 90% and 98%, respectively in the first 30 patients, the next 31–60 patients and after 60 patients. Median operative time declined with surgeons’ experience (p < 0.001). Conclusions: A chest surgeon can have a high success rate in videothoracoscopic thymectomy (98%) after 60 operations.

Key Words: Myasthenia gravis • Videothoracoscopy • Learning curve


   1. Introduction
Top
 Abstract
 1. Introduction
2. Patients and methods
 3. Results
 4. Discussion
 References
 
The traditional approach to nonthymomatous thymus (NTT) in myasthenia gravis (MG) has been by partial upper sternotomy. With recent advances in endoscopic instrumentation and video capabilities, video-assisted thoracic surgery (VATS) has become a viable surgical approach to thymus. Previous studies examining thymectomy through VATS have shown to be associated with lesser pain, shorter hospital stay, shorter drainage time, and improved cosmoses when compared to upper sternotomies [1–3]. Yet, despite these superiorities, most surgeons have continued to manage patients with NTT MG with a standard open operative approach called upper sternotomy or partial splitting. Upper sternotomy, having now been performed in a similar fashion for more than half a century, has been an effective method of treating NTT MG and has been demonstrated to have acceptably low morbidity and no mortality rates [4]. Since the surgeons are satisfied with their current approach, the role of VATS thymectomy is still investigational and many surgeons remain skeptical of the value of this recent option.

The evaluation of technical proficiency in a specific operation is a difficult and complex task. Cumulative summation (CUSUM) is a type of control chart that recently gained acceptance in the medical field [5]. The basic point of the analysis is to plot the sequential difference of a set of measured values and to define a target level for those values [6]. With the establishment of the learning curve, surgeons can be objectively evaluated for this approach.

We aimed to define the learning curve of VATS thymectomy and difficult videothoracoscopic thymic operations and difficult situations in patients with MG.


   2. Patients and methods
Top
 Abstract
 1. Introduction
 2. Patients and methods
3. Results
 4. Discussion
 References
 
2.1 Patient characteristics
The perioperative and long-term results of the two thymectomy techniques, videothoracoscopic thymectomy and thymectomy through partial upper sternal splitting, were explained to all patients undergoing videothoracoscopic thymectomy at the Istanbul Medical Faculty between June 2002 and September 2006. Ninety patients who chose videothoracoscopic thymectomy were included in this study. All patients had a chest CT but the quality and the date of CTs varied. We did not have another chest CT if the patient had an old CT. We preferred to have a chest X-ray in case of the presence of an old CT. Patient's age, gender, duration of disease, body mass index (BMI), prescribed medication, length of the operation, chest tube duration time, duration of hospital stay, the amount of drainage, pain score (visual analogue scale (VAS)) and complications were recorded prospectively. Patient's myasthenic condition was graded according to a modified Osserman classification as 0: asymptomatic, 1: ocular sign and symptoms, 2: mild generalized weakness, 3: moderate generalized weakness, bulbar dysfunction or both and 4: severe generalized weakness, respiratory dysfunction or both. Reasons for conversion to open surgery were noted. Conversion to open surgery occurred due to two main factors: surgeon-related conversions which is hemorrhage (two patients) and patient-related conversions (nine patients). Patient-related conversions were excluded from the study.

2.2 Exclusion criteria
Nine patients who had patient-related conversions and seven patients who were operated with VATS but had thymomas were excluded from the study. Patient-related conversions included an unexpected thymoma with invasion to surrounding structures (three patients), inability to have single lung ventilation (one patient), patient's intolerance for single lung ventilation (four patients) and natural pleurodesis (one patient). Ninety patients free of abovementioned criteria were included in the study.

2.3 Operative technique
Right sided operation is preferred because of the landmarks of the right hemithoracic cavity, such as superior vena cava, and phrenic nerve and also the right cavity is larger than the left one. The patient is positioned supine with the table rotated 30° to the surgeon's side. Three thoracoports of 5 mm, 10 mm and 11 or 15 mm are used above and middle around the mammary gland. We prefer to place the ports according to the size and shape of the mammary gland. Dissection with electrocautery and endoscissor is used to dissect out the gland from the pericardium and sternum without violating the capsule. The right side of the mediastinal pleura is incised totally from up to down and the plane between the anterior of the gland and the posterior of the sternum is fully developed. The contralateral pleura into the left hemithorax is then opened both from above and under the left half of the thymus. At the time the left pleural space is entered, the endotracheal tube is temporarily disconnected to allow the left lung to collapse. This manuever helped to have a safe incision along the left mediastinal pleura under the left side of the sternum and the left mediastinal pleura is taken into the specimen.

Dissection of the venous tributaries to the brachiocephalic vein is the most important and accident inviting part. The superior vena cava is mobilized away from the gland to expose the left brachiocephalic vein. Small thymic veins from the superior vena cave are dissected and clipped. These venous tributaries can be avulsed easily and can lead to troublesome bleeding. The superior pole is retracted using a moderate amount of tension. The left upper pole is also dissected in a similar fashion. After these maneuvers, mediastinum is examined carefully and frozen section analyses should be used in case of the presence of suspicious tissue. The brachiocephalic vein, superior vena cava, aorta and pulmonary arteries should be clearly visualized.

Fatty tissue in the right cardiophrenic angle is dissected completely and left cardiophrenic angle partially. Pain management is standardized as intraoperative intercostal blockage with 5 ml of bupivacaine 0.5% (Marcaine, AstraZeneca, Istanbul) to all port sides and additional non-steroid anti-inflammatory agents.

2.4 Statistics
2.4.1 CUSUM analyses
CUSUM model was used for the evaluation of the learning curve for thymectomy operations. The data from all operations can help develop a learning curve for the average of the surgeon. In this study a single surgeon (A.T.) performed all of the operations. We defined the unsuccessful situations as: (1) longer operation time, (2) surgeon-related open conversions, (3) readmissions and (4) postoperative complications.

2.5 Other analyses
Factors effecting longer operation time (patients with operation time longer than the average) and longer postoperative stay (patients with postoperative hospital stay longer than average) were analyzed.

Groups 1, 2 and 3 included patients representing the first 30 patients, the second 30 patients and third 30 patients consecutively of a single surgeon's experience. Using three serial groups of 30 cases patients’ characteristics such as age, gender, BMI, amount of pyridostigmine prescribed, amount of corticosteroid prescribed, modified Ossermann Genkins (M.O.G.) classification have been calculated. Outcome measures were calculated for the surgeon's median operation time, length of chest tube drainage, length of hospital stay, VAS, and complications. To define the statistical differences between groups, we used one-way ANOVA for parametric data and Kruskal–Wallis variance analysis for nonparametric data. In statistically significant parameters, we further compared the groups’ mean values. We found statistically significant differences in nonparametric data. We preferred Mann–Whitney U-test in these situations. In parametric data, we compared the groups with independent samples test.


   3. Results
Top
 Abstract
 1. Introduction
 2. Patients and methods
 3. Results
4. Discussion
 References
 
Videothoracoscopic thymectomy was performed by a single surgeon, excluding the abovementioned cases but keeping even the initial experience. The starting period for the surgeon consisted of the fifth year after completion of the residency program. Using three serial groups of 30 cases, patients characteristics such as age, gender, BMI, amount of pyridostigmine prescribed, amount of corticosteroid prescribed, Ossermann Genkins classification have been calculated (Table 1 ). Patients’ characteristics did not show any statistically significant difference. Outcome of the surgeon's experience such as median operation time, length of chest tube drainage, length of hospital stay, VAS and complications as outcome measures were calculated (Table 2 ). Median operation time in the third group was statistically significantly shorter than the first two groups (p = 0.004) (Mann–Whitney U-test). Pain score was noticed to be statistically significantly higher when compared to the groups 2 and 3 (p = 0.001) (Mann–Whitney U-test).


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  		Table 1 Baseline characteristics of 90 patients who underwent VATS thymectomy
 

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  		Table 2 Outcomes for groups 1, 2 and 3 patients
 
Surgeon-related open conversion rate was 2.2% (n = 2). Body mass index was the only predictor of longer operation time (23.04 ± 2.93 vs 25.61 ± 2.70 (p = 0.001) independent samples test). The amount of pyridostigmine was the only factor for longer hospital stay (213.3 ± 101.5 mg vs 270. 0 ± 122.6 mg (p 0.044) Mann–Whitney U-test).

CUSUM analysis demonstrated a learning curve with success rates of 80%, 90% and 98%, respectively in the first 30 patients, the next 30–60 patients and after 60 patients (Fig. 1 ).


Figure 1
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  		Fig. 1. Learning curve of the surgeon.

 
Median operative time declined with surgeon's experience (p < 0.001).


   4. Discussion
Top
 Abstract
 1. Introduction
 2. Patients and methods
 3. Results
 4. Discussion
References
 
It is a fundamental human characteristic that a person engaged in a repetitive task will improve his performance over time. CUSUM analysis is a statistical and graphical tool that can be used to track the success and failure at a technical skill and examines trends over time [7]. It can be used to demonstrate proficiency in a newly learned technical skill or as a measure of quality assurance once a technical skill has been mastered such as determining whether or not a resident has achieved competency in a particular skill [8,9]. CUSUM has been reported to be a quality control measurement [10]. Recently, it has been used as a measure of competence for technical purposes learned by postgraduate anesthesia trainees [11]. We therefore sought to explore the learning curve associated with VATS thymectomy at a single tertiary care where this operation is carried out largely for MG.

In our study we clearly demonstrated that similar groups of patients had a different outcome at the time. The first 30 patients experienced more pain probably because they had conventional chest tube drainage. After the 31st patient we changed to J.P. drains which were softer. But there were also some patients with conventional chest drains. We also think that changing the type of equipment is related to learning. Our last group had a definitely shorter operation time (51.83 min) when compared to first 60 patients’ average. Length of hospital stay (2.19 days) and length of chest tube drainage (26.47 h) did not change significantly. CUSUM analysis showed an acceptable learning curve of 80% within the first 30 patients, 90% within the second 30 patients and 98% within the final 30 patients. Also statistical analysis showed that some operations lasted longer. By univariate analysis, the factor responsible from this situation was demonstrated to be BMI. Patients having an operation time shorter than the average had a BMI of 23.04 ± 2.93 while patients whose operations lasted longer than the average had a BMI of 25.61 ± 2.70 (p = 0.001). The amount of pyridostigmin which is the predictor of myasthenic condition, was the only factor for longer hospital stay (213.3 ± 101.5 mg vs 270. 0 ± 122.6 mg (p = 0.044)).

With the experience we gained, our neurologists developed changing attitudes which could be recognized easily from Tables 1 and 2. Table 1 demonstrates that (although not statistically significant) prescribed pyridostigmine doses and stages of modified O.G. classification are increasing. This means that patients with more myasthenic problems are being operated on. Prescribed doses of corticosteroids are decreasing, which shows an earlier and positive attitude of our neurologists to the VATS thymectomy.

Learning curve had been studied extensively in surgical fields and advanced technical skills in anesthesia. Technical proficiency of a single endoscopist in performing ERCP was studied and a success rate of 90% was achieved for selective cannulation after 100 procedures and 120 interventions [12]. Seventeen surgical residents were evaluated in an other study [13]. They documented that 25 operations were needed to achieve an acceptable speed in performing appendectomies, open cholecystectomies and inguinal hernia repairs [13]. Proficiency at intraoperative cholangiography was evaluated during laparoscopic cholecystectomies [14]. A 95% success rate was achieved after 46 cases. Twenty-four and 16 cases were required to attain success rates of 90% and 85%, respectively [14]. Surgical residents during their first month of anesthesia rotation were put in CUSUM analysis on intubation. An average intern required 19 intubation attempts to complete the learning curve experience [15].

Learning can be analyzed with other statistical interventions. The first experiences of a surgeon could be compared with the last experiences; as it was studied in pancreaticoduodenectomy. Pancreaticoduodenectomy is a technically complex procedure and it has been shown to have an inherent learning curve. The first 60 cases of three surgeons (a total of 180 cases) were compared in terms of patient data and outcome measures with the second 60 cases of three surgeons (a total of 180 cases). After 60 cases surgeons achieved significantly decreased blood loss, operative time and length of hospital stay. Also they carried out more margin negative resections [16].

In VATS thymectomy experience, even though it was reported to have excellent surgical view and allowed thymectomy to be performed with absolute safety [17], many surgeons still do not accept it as equal to conventional approaches [18,19]. Learning curve was shown to exist in our series; similar and even better outcomes have been presented by Savcenko et al. [20]. In this study [20], authors presented their experience such as changing to the right side of the thoracic cavity after 15 left procedures. They reported no mortality and no long-term morbidity in 36 patients. A similar rate of conversion to open surgery for bleeding (2.6%), reintubation (two patients) and mechanical support (for 24 and 72 h) was noticed in this study. This group stopped intensive care unit admission and even began considering the thymectomy operation as an outpatient basis. They had a mean length of hospital stay of 1.64 days. This study clearly demonstrated that there is a learning curve for the thymectomy operation. Another group in their early experience on 25 patients presented conversion to open surgery for hemorrhage in two patients, average intervention time 110 min, (they indicated that the final eight patients took less than 100 min and the last case lasted only 60 min), complications in seven patients, chest tube removal time of 3–4 days and length of hospital stay as 4.2 days [17]. This experience also shows a learning curve.

In conclusion VATS thymectomy operation has a learning curve. Surgeon gets faster and safer as he or she practices. Outcomes could be better in terms of pain management and cosmosis but it did not reflect a decrease in the length of hospital stay. Length of hospital stay is related to the myasthenic condition of the patient. Patients with lower BMI are advised for surgeons learning this procedure before deciding that this operation is unsafe, not practical and difficult.


   Footnotes
 
{star} Presented at the 15th European Conference on General Thoracic Surgery, Leuven, Belgium, June 3–6, 2007.


   References
Top
 Abstract
 1. Introduction
 2. Patients and methods
 3. Results
 4. Discussion
 References
 

  1. Toker A, Eroglu O, Ziyade S, Tanju S, Senturk M, Dilege S, Kalayci G. Comparison of early postoperative results of thymectomy: partial sternotomy vs videothoracoscopy. Thorac Cardiovasc Surg 2005;53(2):110-113.[CrossRef][Medline]
  2. Mineo TC, Pompeo E, Lerut TE, Barnardi G, Coosemans W, Nofroni I. Thoracoscopic thymectomy in autoimmune myasthenia: results of left sided approach. Ann Thorac Surg 2000;69:1537-1541.[Abstract/Free Full Text]
  3. Savcenko M, Wendt GK, Prince SL, Mack MJ. Video assisted thymectomy for myasthenia gravis: an update of a single institution experience. Eur J Cardiothorac Surg 2002;22:978-983.[Abstract/Free Full Text]
  4. Detterbeck FC, Scott WW, Howard JF, Eagen TM, Keagy BA, Starek JK, Mill MR, Wilcox BR. One hundred consecutive thymectomies for myasthenia gravis. Ann Thorac Surg 1996;62:242-245.[Abstract/Free Full Text]
  5. Ravin L. The CUSUM score. A tool for evaluation of clinical competence. Ugeskrift For Laeger 2001;163:3644-3648.[Medline]
  6. Goldsmith ODaP. Statistical methods in research and production. London: Longman; 1976.
  7. Altman DG, Royston JP. The hidden effect of time. Stat Med 1988;7:629-637.[Medline]
  8. Berwick DM. Continuous improvement as an ideal in the health care. N Engl J Med 1989;320:53-56.[Medline]
  9. Williams SM, Parry RP, Schlup MMT. Quality control: an application of the CUSUM. Br Med J 1992;304:1359-1361.[Free Full Text]
  10. Kestin IG. A statistical approach to measuring the competence of anaesthetic trainees at practical procedures. Br J Anaesth 1995;75:805-809.[Abstract/Free Full Text]
  11. Stewart J, O’Halloran C, Harrigan P, Spencer JA, Barton JR, Singleton SJ. Identifying appropriate task for the preregistration year: modified Delphi technique. BMJ 1999;319:224-229.[Abstract/Free Full Text]
  12. Schlup MM, Williams SM, Barbezat GO. ERCP: a review of technical competency and workload in a small unit. Gastrointest Endosc 1997;46:48-52.[CrossRef][Medline]
  13. Van Rij AM, McDonald JR, Pettigrew R, Petterill M, Reddy C, Wright J. CUSUM as an aid to early assessment of the surgical trainee. Br J Surg 1995;82:1500-1503.[Medline]
  14. Molloy M, Bower RH, Hasselgren P, Dalton B. Cholangiography during laparoscopic cholecystectomy. Cumulative summation analysis of an institutional learning curve. J Gastrointest Surg 1999;3:185-188.[CrossRef][Medline]
  15. Yang A, Miller JP, Azaraov K. Establishing learning curves for surgical residents using cumulative summation analysis. Curr Surg 2005;62:330-334.[CrossRef][Medline]
  16. Tseng JF, Pister PWT, Lee JF, Wang H, Gomez HF, Sun CC, Evans DB. The learning curve in pancreatic surgery. Surgery 2007;141:694-701.[CrossRef][Medline]
  17. Loscarteles J, Arne JA, Congragado M, Tristan AA, Merchan RJ, Arjona JCG, Linares CA. Video-assisted thoracoscopic thymectomy for the treatment of myasthenia gravis. Arch Bronchoneumol 2004;40:409-413.
  18. Jaretzki III A. Thymectomy for myasthenia gravis: analysis of the controversies regarding the technique and results. Neurology 1997;48:S52-S63.[Free Full Text]
  19. Jartezki III A, Barohn RJ, Ernstoff RM, Kaminski HJ, Keesey JC, Penn AS, Sanders B. Myasthenia gravis: recommendation for clinical research and standards. Task Force of the Medical Scientific Advisory Board of the Myasthenia Gravis Foundation of the America. Ann Thorac Surg 2000;69:327-334.
  20. Savcenko M, Wendt GK, Prince SL, Mack MJ. Video-assisted thymectomy for myasthenia gravis: an update of a single institution experience. Eur J Cardiothorac Surg 2002;22:978-983.[Abstract/Free Full Text]



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