Ann Thorac Surg 2005;80:631-635
© 2005 The Society of Thoracic Surgeons
Original article: Cardiovascular
Short Operation Time: An Important Element to Reduce Operative Invasiveness in Pediatric Cardiac Surgery
Makoto Ando, MD
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,
Yukihiro Takahashi, MD,
Toshio Kikuchi, MD
Department of Pediatric Cardiac Surgery, Sakakibara Heart Institute, Tokyo, Japan
Accepted for publication February 28, 2005.
* Address reprint requests to Dr Ando, Department of Cardiac Surgery, Sakakibara Heart Institute, 3-16-1 Asahi-cho, Fuchu-shi, Tokyo 183-0003, Japan (Email: maando{at}shi.heart.or.jp).
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Abstract
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BACKGROUND: The mini skin incision procedure is considered an important element of minimally invasive cardiac surgery because of its definitive cosmetic advantage. However, the operative hazard of limited exposure may be associated with prolonged operation time and increased surgical insult.
METHODS: A total of 357 consecutive patients undergoing repair of an isolated atrial or ventricular septal defect, in whom the mini skin procedure was applied, were investigated. Patients were grouped by diagnosis and body weight. Univariate and multivariate risk analyses were conducted in the specific patient group undergoing ventricular septal defect repair weighing less than 5 kg.
RESULTS: The operation time was reduced by 21.0% (93.4 to 73.8 minutes) during this time period. Univariate risk analysis revealed that the operation time had a significant correlation with time to extubation (p < 0.0001), catecholamine duration (p = 0.0003), intensive care unit stay (p < 0.0001), hospital stay (p = 0.016), arterio-alveolar oxygen tension difference at the time of extubation (p = 0.0253), and furosemide dose required in the first 24 hours (p = 0.0332). Multiple linear regression analysis revealed that the operation time had an impact on time to extubation, arterio-alveolar oxygen tension difference at the time of extubation, and intensive care unit stay. The length of skin incision was not correlated with any outcome measure.
CONCLUSIONS: The mini skin incision, if associated with prolonged operation time, may increase the overall insult in pediatric cardiac surgery. In order to reduce operative invasiveness, simultaneous effort to reduce, or at least not to increase, the operation time are mandatory.
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Introduction
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Agrowing number of centers have been performing open heart surgery for children through a minimal access incision [1, 2]. This is because the operative scar can be an important psychological burden to growing children. Therefore, the mini skin incision procedure is considered an important element of minimally invasive surgery. Besides its definitive cosmetic advantage, it is believed that the smaller area of skeletal trauma is associated with enhanced postoperative recovery [3–5]. However, the operative hazard due to the limited exposure may substantially prolong the operation time [2], especially when it is performed by a resident. In this context, the overall tissue-air exposure may be increased, resulting in increased operative insult. In this article, we discuss this important paradox.
It also has been our practice to perform midline sternotomy through a mini skin incision for patients with simple congenital heart defects. While developing this practice, the operation was serially modified to reduce the overall operation time, because it has been our belief that operative insult parallels operating time. The present study was conducted to assess the legitimacy of our hypothesis, through the review of patients undergoing simple septal defect repair.
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Patients and Methods
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Consecutive patients undergoing repair of an isolated atrial septal defect (ASD) or ventricular septal defect (VSD) from September 2000 to August 2003 were enrolled. During this period, the length of the skin incision was reduced from approximately 7%–8% to 5%–6% of the body height. Those who had a patent ductus arteriosus, or mild right ventricular outflow obstruction that could be tailored through the same cardiotomy incision, were included. Those having other cardiac anomalies that required an extra incision (eg, pulmonary valvotomy combined with ASD closure) were excluded. A total of 357 patients were selected from our database. These patients were stratified into seven groups according to the following diagnoses and patient size: ASD with body weight less than 10 kg (group A, n = 21); ASD from 10 to 30 kg (group B, n = 29); ASD over 30 kg (group C, n = 64); VSD under 5 kg (group D, n = 90); VSD from 5 to 10 kg (group E, n = 95); VSD from 10 to 30 kg (group F, n = 44); and VSD over 30 kg (group G, n = 14). This patient grouping was undertaken to assess alteration of the operation time in each homogeneous group.
The surgeons included two consultant surgeons and residents. The operation was basically achieved by a modification of conventional sternotomy and cannulation techniques. Partial sternotomy was applied in small children (under 15 kg) and full sternotomy in older children.
Technical modifications to reduce the operation time during this study period are summarized as follows. The skin was incised from slightly above the level of the nipple line down towards the xiphoid. The target length of incision was 5% to 6% of the body height of the patient. After subxiphoid dissection, the lower half of the sternum was cut with an oscillating saw. Then the remaining part of the sternum was cut with scissors. The thymus was left in place. While the pericardium was being opened, heparin was infused. Immediately after retraction of the pericardium, an aortic cannula was inserted. Then a cannula was inserted into the superior vena cava through the atrial appendage using a straight cannula (Medtronic, Parker, CO). This was followed by inferior vena caval cannulation and snaring of the vena cavae. Then an Argyle cannula (Tyco Health-Care, Mansfield, MA) was inserted through the right upper pulmonary vein for left ventricular venting (essentially, this procedure was obviated with ASD closure). In general, perimembranous VSDs and ASDs were closed through a right atriotomy. Subarterial VSDs were closed through a pulmonary arteriotomy. Interrupted sutures were used for VSD closure. High flow (150 mL/kg/min) normothermic to mild hypothermic (> 33°C) cardiopulmonary bypass (CPB) was employed. Rewarming was started while closing the ASD-VSD. The core temperature often reached 35°C when the cardiotomy incision was closed and the patient was immediately weaned off CPB. Whenever there was a waiting period during CPB for rewarming or recovery of myocardial contraction, a single chest tube was inserted and sternal wires were placed.
Risk analysis was performed specifically in group D for two major reasons: (1) because this was a relatively homogeneous patient group with similar size and the operation was performed exclusively by a consultant surgeon, and (2) because this was the only group in which outcome measures significantly varied between individuals. In other groups, catecholamines were seldom used and the length of stay in the intensive care unit rarely exceeded one day, which made risk analysis difficult.
Preoperative and intraoperative variables investigated included chronologic order of operation, sex, age, and body weight at operation, length of skin incision (percentage of body height), operation time, CPB time, and aortic cross-clamp time.
Outcome variables analyzed included the length of stay in the intensive care unit, maximal indexed catecholamine dose, time to cessation of catecholamines, time to extubation, arterio-alveolar oxygen tension difference (A-a DO2) at the time of extubation, serum lactate level at the end of operation, urine output during the first 24 hours, total dose of furosemide infused during the first 24 hours, total chest tube output, time to removal of the chest tube, and length of hospital stay. The A-a DO2 was calculated as FiO2 x (PB–PH2O) – PaCO2/R – PaO2, where FiO2 = fraction of inspired oxygen, PB = barometric pressure (= 760), PH2O = water vapor pressure (= 47), R = respiratory quotient (= 0.8), and PO2 = arterial partial oxygen tension. The indexed catecholamine dose was calculated as dopamine (x 1) + epinephrine (x 100) [6].
The SPSS statistical software for Windows (version 11.0; SPSS Inc, Chicago, IL) was used for data analysis. Values were expressed as mean ± standard deviation. Univariate analysis was performed using Pearson’s correlation coefficient or Student’s t test. The linear regression equation was calculated to assess chronologic transition of intraoperative time factors. Multiple linear regression analysis was used to assess the influence of independent valuables on outcome measures. Variables identified as having a p value of less than 0.05 on univariate analyses were considered for inclusion in the multivariate model. All probability values were two-tailed.
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Results
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There were no deaths. Demographics of all patients, together with the operation profiles, are listed in Table 1. Transition of the operation time in each subgroup is shown in Figure 1. Overall operation time was reduced by 21.0% (93.4 to 73.8 minutes) by simple linear regression equation. The CPB time (49.2 to 34.2 minutes) and the time taken for sternal opening and closure (calculated as operation time minus CPB time; 44.2 to 39.5 minutes) were both reduced. The number of operations performed by residents was 31 (8.7% of all cases). By groups, it was 1 (4.8%) case in group A, 17 (26.6%) in group B, 5 (17.2%) in group C, 0 (0%) in group D, 4 (4.2%) in group E, 4 (9.1%) in group F, and 0 (0%) in group G. These cases were concentrated before the year 2001. Virtually, operations were performed by consultant surgeons in the latter half of this study period.
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Fig 1. Operation time in each patient subgroup. Each bar shows the simple linear regression line. Numbers indicate the intercept point of the line at each end of the study period. The regression equation for each subgroup was as follows: Y = 66.4–0.28X (ASD < 10 kg), Y = 105.5–0.14X (ASD 10–30 kg), Y = 146.3–0.182X (ASD > 30 kg), Y = 85.7–0.035X (VSD < 5 kg), Y = 92.8–0.059X (VSD 5–10 kg), Y = 98.7–0.059X (VSD 10–30 kg), Y = 104.0–0.005X (VSD > 30 kg), where Y = operation time (minutes) and X = chronological number of operation. (ASD = atrial septal defect: VSD = ventricular septal defect.)
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Among the patients in group D, 3 had significant depression of ventricular function on echocardiography and required prolonged (> 5 days) catecholamine infusion. Two patients required drainage for pericardial tamponade. One patient developed Serratia pneumonia and required reinstitution of mechanical ventilation.
Univariate risk analysis in the same group revealed that the operation time had a significant correlation with time to extubation (p < 0.0001), time to cessation of catecholamines (p = 0.0003), length of stay in the intensive care unit (p < 0.0001), length of hospital stay (p = 0.016) (Fig 2), A-a DO2 at the time of extubation (p = 0.0253), and dose of furosemide required in the first 24 hours after operation (p = 0.0332).
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Fig 2. Parameters of postoperative recovery plotted against operation time. Linear regression equation, correlation coefficient, and p values are shown in the right upper portion of each graph. Each bar shows the regression line. (A) Time to extubation. (B) ICU stay. (C) Catecholamine duration. (D) Hospital stay. (ICU = intensive care unit; R = Pearson’s product-moment correlation coefficient; Y = values of the response variables to be predicted.)
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After examination by multiple linear regression analysis, operation time still had an impact on time to extubation, A-a DO2 at the time of extubation, and the length of stay in the intensive care unit. Generally, the dominant influential factor on postoperative outcome was the size of patients (Table 2). The length of the skin incision was not correlated with any postoperative outcome.
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Comment
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In the current era, when mortality and morbidity related to simple cardiac repair in children have become minimal, the subsequent goal is to enhance the postoperative recovery of these patients by further reducing the operative insult. The concept of "minimally invasive surgery" has thus been introduced into the field of congenital heart surgery. Physiologically speaking, factors such as avoiding the use of CPB, or more recently, robotic surgery [7] or endoscopic surgery [8], should be the main strategies to reduce operative invasion. Indeed, off-pump coronary artery bypass surgery is mainstream in minimally invasive surgery in adult cardiac surgery [9]. Even in the field of congenital heart surgery, off-pump cardiac procedures are possible in limited circumstances such as off-pump bidirectional cavopulmonary shunt-Fontan procedure [10], and other hybrid surgical procedures [11]. However, the majority of repair procedures for congenital heart defects mandate the use of CPB if not amenable to catheterization intervention. Therefore, reducing the size of the skin incision is considered an important element of minimally invasive surgery in pediatrics, because the surgical scar can be a significant psychological burden on growing children.
Technical modifications to limit the sternotomy skin incision have been promoted in many centers, and this technique has been extended to more complex diseases in the field of congenital heart surgery [12, 13]. Besides the definite cosmetic advantage [1], some argue that less skeletal trauma may result in improved postoperative outcome [3–5]. However, there has been no scientifically sound evidence for this hypothesis [14]. Since this technique is more challenging than conventional full sternotomy with a large skin incision, the operation can be significantly prolonged [2]. Tissue-air exposure should be proportional to the exposed tissue surface multiplied by the exposure time. The term "minimally invasive surgery" may not be adequate in this context, and this technique may merely result in cosmetic surgery associated with an increased operative insult and delayed patient recovery.
Considering this fact, significant effort has been directed to reducing the operation time in our department. The overall operation time was reduced considerably in each subgroup, with the greatest reduction seen in the large ASD patients group. This might, in part, reflect the fact that fewer cases had become available for residents’ training because of the technical difficulty of a mini skin incision.
The operation time, rather than the length of the skin incision or CPB time, had more impact on postoperative outcomes in our cohort. The prolonged operation time due to the operative hazard with limited exposure may compromise the postoperative recovery of patients. This is an especially important consideration when letting residents perform this surgery. It may have to be considered an operation only for surgeons having additional training beyond residency.
Some centers prefer other approaches including lateral thoracotomy [15], subxiphoid approach [16], and limited sternotomy [17]. No physiological benefit of these approaches compared with full sternotomy procedure has been proven [18]. We found that full sternotomy, which provides better exposure of the heart, is feasible with a small skin incision down to 5% of body height in the majority of cases. In children, partial sternotomy leaving a continuation at the top of the sternum is possible without causing fracture. However, full sternotomy or L-shaped sternotomy may be required to avoid fracture in older children and adults. Bone fracture causes significant pain, and probably a local inflammatory response, which compromise postoperative recovery.
Besides the retrospective nature of this study, this study had the following major limitations. (1) The operation time shortened with time during this study period. Generally, the postoperative outcome also improves with time in a single center study. Therefore, the improved outcome might be attributable to accumulated center experience rather than the shortened operation time. We attempted to neutralize this potential problem by incorporating the chronologic number of operations into the analyses. (2) A long operation time might be due to a long CPB time caused by the complexity of the operation (eg, a large VSD requiring a large patch placement, cardiac dysfunction requiring prolonged CPB support). Complex anatomies or ventricular dysfunction is usually associated with delayed postoperative recovery. This was another potential confounding factor, which could skew the analyses.
In summary, a prolonged operation time due to the hazard of a limited skin incision may increase the insult of surgery. In order to reduce operative invasiveness, simultaneous efforts to reduce or at least not to increase the operation time are mandatory. When a resident performs this procedure, he or she must receive additional training compared with that in the era of conventional sternotomy.
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References
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Abstract
Introduction
