Perioperative complications after parotidectomy using a standardized grading scale classification system. Impact on hospitalization stay

Background: Perioperative complications after parotidectomy are poorly studied and have a potential impact on hospitalization stay. The Clavien-Dindo classification of postoperative complications used in visceral surgery allows a recording of all complications, including a grading scale related to the severity of complication. Methods: The cohort analyzed for perioperative complications is composed of 436 parotidectomies. classified into three types, four groups and three classes depending on extent of parotid resection, inclusion of additional procedures and pathology, respectively. Results: Using the Clavien-Dindo classification, complications were reported in 77 % of the interventions. In 438 complications, 430 (98.2%) were classified as minor (332 grade I and 98 grade II) and 8 (1.8%) were classified as major (grade III). Independent variables affecting the risk of perioperative complications were duration of surgery (odds ratio = 1.007, p-value = 0.029) and extent of parotidectomy (odds ratio = 4.043, p-value = 0.007). Total/subtotal parotidectomy was associated with an increased risk of grade II-III complications [odds ratio = 2.866 (95% CI: 1.3076.283), p-value = 0.009]. Hospital stay increased in patients with complications (p= 0.0064). Conclusions: Use of Clavien-Dindo classification shows that parotidectomy is followed by a high rate of perioperative complications. Longer hospital stay is observed in patients with perioperative complications. Almost all complications are minor and have limited consequence on hospital stay.

Parotidectomy is a surgical procedure typically performed in the surgical treatment of primary parotid gland tumors and cutaneous cancers of the head and neck with intraparotid lymph node metastases. The goal of surgery is to perform a complete tumor resection allowing local control with minimal morbidity mainly to the facial nerve. [1] While there is an abundant literature on long term complications of parotidectomy, little is known about the prevalence and the severity of early postoperative complications occurring during the perioperative period. The aim of this study is to retrospectively review perioperative complications in a consecutive series of patients who underwent parotidectomy in our department, using the Clavien-Dindo classification, a standardized grading scale classification system widely used in visceral surgery. [2]

Materials and Methods
The study was approved by the local ethical committee and followed the general recommendations of discretion to personal data as well as the Helsinki declaration.

Patients
The files of all patients who underwent parotidectomy in the department from January 2002 to March 2017 retrospectively reviewed. Four hundred thirty-eight surgical procedures were performed in 430 patients. Eight patients underwent two surgical procedures; three of them had a second intervention for tumor recurrence and five patients had bilateral interventions for: Whartin's tumors in three, Mikulicz syndrome in one and parotid lymph node metastasis from a skin carcinoma in one patient where the first parotidectomy was performed for a pleomorphic adenoma. Two patients were excluded from the analysis of complications for lack of data. Therefore, the cohort analyzed for postoperative complications is composed of 436 parotidectomies performed in 428 patients.
Regarding the facial nerve function assessment specifically, eight patients with preoperative facial nerve paralysis were excluded from the analysis. Facial nerve paralysis was consecutive to previous parotidectomy performed elsewhere in three, primary carcinoma in four and previous stroke in one.
The American Society of Anesthesiologists (ASA) physical status classification is a grading system based on subjective assessment of patient's overall health to determine the physical status of preoperative patients for an anesthetic risk assessment. In 1963, the American Society of Anesthesiologists (ASA) adopted a five-category physical status classification system. The ASA score, routinely used during the preoperative anesthesiology consultation, was initially based on five classes (I to V): 1. Healthy person, 2. Mild systemic disease, 3. Severe systemic disease, 4. Severe systemic disease that is a constant threat to life, 5. Moribund person who is not expected to survive without the operation. Later, a sixth category was included for declared brain-dead organ donors. [3] The Body Mass Index (BMI) was recorded preoperatively according to the correlation of BMI with postoperative complications frequently reported in surgical procedures. [4][5][6][7] Parotidectomies were classified into three types depending on extent of parotid resection. Type 1 included partial resection of the superficial parotid where the main trunk but not all branches of the facial nerve were identified; type 2 included complete resection of the superficial parotid, identifying all branches of the facial nerve; type 3 included resection of the superficial parotid and the deep lobe, partly or totally (subtotal and total parotidectomy), requiring complete release and elevation of the main trunk and branches of the facial nerve.
Surgical procedures were classified in 4 groups based on the inclusion of additional procedures to parotidectomy. Group I included parotidectomy alone, group II included parotidectomy combined with neck dissection, group III included parotidectomy combined with resection of a non-parotid tumor and group IV included parotidectomy combined with neck dissection and resection of a nonparotid primary tumor. Finally, after definitive pathological analysis, three classes were identified. Class 1 included benign tumors and inflammatory diseases, class 2 included primary parotid malignant tumors and intraparotid lymph node metastases from non-parotid cancers, class 3 included non-parotid primary tumors for which parotidectomy has been performed to facilitate tumor access or to achieve clear margins (table 1) As the distinction between seroma and sialocele was often difficult to establish retrospectively, both have been gathered under a single name.

Grade I
Any deviation from the normal postoperative course without the need for pharmacological treatment or surgical, endoscopic, and radiological interventions.
This grade also includes wound infections opened at the bedside.

Grade III
Requiring pharmacological treatment with drugs other than those allowed for grade I complications.
Blood transfusions and total parenteral nutrition are also included.

IIIa
Intervention not under general anesthesia.

IIIb
Intervention under general anesthesia.

Grade V
Death of a patient.  Frequency of missing data were reported and no imputation was done.
In order to identify potential risk factors associated with short-term complications, logistic regression analysis was used based on the proportional odds model. [ Due to the non-normality distribution of the duration of hospital stay distribution, the impact of perioperative complications on the duration of hospital stay was analyzed with a non-parametric test (Mann Whitney U test) comparing the number of days of hospital stay between patients with complications and patients without complication respectively. The lenghts of hospital stays were ranked according to their position when classified in ascending order. The average score was the sum of the ranks of hospital stays divided by the number of interventions. A p-value < 0.05 was considered to be statistically significant.

Patient and surgical procedure characteristics
The cohort under analysis included 428 patients with a median age of 55 Regarding the extent of parotidectomy, type 1 was performed in 88/436 (20.2%) procedures, type 2 in 229 (52.5%) procedures and type 3 parotidectomy in 106 (24.3%) procedures. Thirteen interventions (3.0%) were not classified for lack information.
Twenty interventions (4.6%) were defined as re-interventions because performed in patients with local recurrence after previous surgery performed for pleomorphic adenoma in 14 patients and malignant tumor in six.
Regarding the extent of surgical procedures, group I were performed in 347 (79.6%) interventions, group II in 27 interventions (6.2%), group III in 32 (7.3%) and group IV in 30 interventions (6.9%) of surgical interventions. Overall, in addition to parotidectomy, neck dissections including at least two levels were performed in 57/436 (13.1%) interventions. Selective neck dissections II-III were performed in 28 cases (6.4%), II-IV in 7 (1.6%), II -V in 19 (4.3%) when modified radical neck dissections I-V were performed in only 3 cases (0.1%). In addition to parotidectomy, resections of a non-parotid tumors were performed in 62 cases (14.2%), consisting in resection of primary nonparotid tumors in 59/62 (95.2%) when these combined procedures were not directly related to parotidectomy (e.g., benign skin tumor) in the remaining three (4.8%). At the end of the procedure, a SMAS flap was performed in 311/436 procedures (71.3%). Drainage of the surgical site was provided by vacuum suction drains in 314 procedures (75.5%) and non-suction open drains in 102 (24.5%) when the information was missing in 20 (4.6%). Cheek adenocarcinoma (parotid invaded) 1 Plexiform neurofibroma (parotid invaded) 1 Heterotopic central nervous tissue (parotid invaded) 1     A same analysis was performed on the occurrence of postoperative seromas specifically. In univariate analysis, none of the variables analyzed was significantly associated with a higher rate of seromas (table S3). After selection of variables with a p-value <0.2 for multivariate analysis, use of active suction drains was found as an independent prognostic factor associated with a higher risk of seroma [odds ratio = 3.797 (95% CI: 1.117 -12.901), p-value = 0.033] (table S4).
Next, the relation between selected variables and the severity of complications, pooling together grade II and grade III complications, was analyzed. In univariate analysis, older age was significantly associated with a little lower risk of > grade I complications [odds ratio = 0.981 (95% CI: 0.968-0.994), p-value = 0.004]. The extent of parotidectomy was significantly associated with a higher risk of > grade I complications [odds ratio = 2.963 (95% CI: 1.362-6.444), p-value = 0.006] (table S5). In multivariate analysis, the extent of parotidectomy was an independent prognostic factor significantly associated with a higher risk of grade II-III complications. Type 3 parotidectomy increased the risk of grade II-III complications by almost 3 times than type 1 parotidectomy [odds ratio = 2.866 (95% CI: 1.307-6.283), p-value = 0.009]. Older age was confirmed as independent prognostic factor for a slightly lower risk of > grade I complications [odds ratio = 0.981 (95% CI: 0.968-0.994), p-value = 0.006]. (table S6).

Hospital stay
Finally, the correlation between occurrence of complications and duration of hospital stay was analyzed. Overall, the median hospital stay was 3 days (1-43 days, mean: 3.21 days). In surgical procedures without complication (n=100), the median hospital stay was 2 days (2-13 days, mean: 2.94 days) (figure S1). In surgical procedures followed by complication(s) (n=336), the median hospital stay was 3 days (1-43 days, mean: 3.29 days) (figure S2). One patient stayed in hospital for 43 days because of complications from chronic lung disease unrelated to parotid surgery.

Discussion
In head and neck surgery, the heterogeneity of tumors and management induces large variance in outcome data among the institutions. [11,12]  adverse-events, not only related to the surgical procedure. [13] In addition, the fear that a high rate of complications could be interpreted in the medical community as evidence of poor quality of care contributes to inaccurate reporting of adverse events. [12] A consensus is clearly needed to report surgical complications using uniform definitions and registration system to assure reliable outcome data in a standardized and reproducible way, building a strong basis for comparison. The goal of our study was to analyze complications occurring during the perioperative period.
Indeed, little is known about the true prevalence and severity of acute complications occurring during the first days following parotidectomy when long-term complications (6-24 months postoperatively) and sequellae have been extensively studied in the literature [14][15][16]. However, providing data about the prevalence and severity of short-term complications following parotidectomy is paramount to inform the patients properly about the risks related to surgery.
Perioperative complications may have an impact on the duration of hospital stay and related costs and, last but not least, their recognition may lead to modifications and improvements in the surgical management. We selected the Clavien-Dindo classification because it seemed to us as the most suitable for identifying and assessing short-term postoperative complications. The high rate of reported complications can be explained by using a standardized grading scheme where even the most minor complications were recorded whereas they are not usually reported with other systems. We report a high rate of 61.7% of acute postoperative facial paralysis. In the literature, the rate of facial paralysis reported in the immediate postoperative period is extremely variable, ranging from 9.3 to 68%. [19][20][21][22][23][24][25][26][27][28] This large variability can be explained by the lack of consensus regarding the timing of facial function assessment. Indeed, even when a discrete weakness is frequently observed during the first postoperative days, spontaneous improvement occurs a few weeks later. Most of those patients are generally rated House-Brackmann grade I (normal facial function) when they are assessed a few months after surgery. [29,30] Therefore, facial function evaluation performed during the first postoperative days will be more severe on the rate of immediate paralysis. In our series, a complete facial nerve recovery at 3, 6 and 12 months was observed in 86.9%, 93.7% and 98.1% respectively. These results are in line with those reported in the literature. [23,26,27,29,30] In our study, partial superficial parotidectomy is associated with a lower risk of postoperative facial paralysis. In the literature, the extent of surgical resection in the parotid gland is a well-identified factor increasing the risk of postoperative facial paralysis. [19,23,24,27,29,31] In our series, a longer duration of surgery is associated with a higher risk of postoperative complications, as it has been reported by others. [19] We are not able to demonstrate that facial nerve monitoring use of is associated with a reduction of perioperative facial paralysis. This result may be biased because during the major part of the study period, intraoperative facial nerve monitoring was mostly used in cases where difficulty to identifying the facial nerve was anticipated. Currently, routine use of neuromonitoring in parotid gland surgery decreases the duration of the intervention and, accordingly, the risk of complications Other factors with a significant impact on the rate of 30-day postoperative complications were identified. An increase in BMI slightly increased the risk of healing disorders. In the whole series, the rate of seromas (and sialoceles) is higher (19.8%) than reported by others including sialoceles alone in partial superficial parotidectomy exclusively. [32] We show that use of active suction drainage increases the risk of developing a seroma. A recent Danish study reported that the risk of seroma and hematoma after superficial parotidectomy increased with secretion beyond 25 ml/24 hours, questioning the use of routine drainage after superficial parotidectomy. [33] The median hospital stay is shorter in patients without complication than in patients with perioperative complications than in patients with complications. A recent study reported that partial superficial parotidectomy was associated with a shorter hospital stay and fewer complications especially transient facial paralysis than superficial parotidectomy. [31] Longer hospital stay is also observed in patients who had perioperative complications using non parametric analysis. Of note, patients who developed a seroma had a statistically significantly shorter hospital stay than those who did not. The occurrence of seroma could be related to a premature ablation of the drainage of the surgical site.
In our study, ASA score > 1 is not associated with a higher risk of complications, suggesting that preexisting patient comorbidities has no influence on acute postoperative complication rates. The specific correlation of ASA scores with operating times, hospital length of stay, postoperative infection rates, overall morbidity and mortality rates following gastrointestinal, cardiac, and genitourinary surgery has been extensively studied. [34][35][36][37][38] We were not able to show any correlation between ASA score and complications rates. Of note, 90% of our patients were scored ASA 1 and ASA 2. It is however important in similar studies to take in consideration the comorbidities to avoid biased comparison between institutions. Outcome measures need to be riskadjusted before they are benchmarked.
Limitations to this study are first related to the retrospective nature of our analysis leading to variability in reporting complication practices meaning that many definitions were open to interpretation. This was minimized by looking at all data sources available, including recorded reports from the senior surgeons who performed all procedures, laboratory values and radiological findings. Next, a study of this magnitude is particularly laborious and time-consuming and was only possible thanks to reliance upon institutional electronic medical records. Last, although we have focused primarily on early postoperative complications, long term patient-centered clinical (and oncologic) outcomes need to be measured to assess quality of care following parotidectomy. [39]

Conclusions
Use of a standardized, scaled classification of postoperative complications shows that parotid gland surgery are surgical procedures followed by a rate of 30-day postoperative complications higher than that usually reported. Longer hospital stay is observed in patients with perioperative complications.
These informations must be mitigated because almost all of these complications are minor with a limited consequence on the duration of the hospital stay and with no long-term sequelae. It is