The surgical treatment of advanced oral cancer often requires extensive resections in the head and neck area and the oral cavity. This type of cancer is collectively referred to as Major Oral and Maxillofacial Cancer. In such cases microvascular free flaps are the gold standard treatment of choice for defect reconstruction, with an overall flap survival rate of approximately 90–95%.
The surgical treatment of advanced oral cancer often requires extensive resections in the head and neck area and the oral cavity 
. Major oral cancer surgery with free flap reconstruction can be complex, highly invasive, lengthy, and exhausting 
and, therefore, may necessitate prolonged invasive ventilation, post-operative cardio-pulmonary monitoring and/or sedation 
Although optimal measures for post-operative care following head and neck free flap reconstructions have already been discussed in the literature, and current trends are moving from routine ICU admission to immediate specialty unit recovery, the post-operative ICU admission rates and requirements still vary from one clinical center to another and, even within clinical institutions 
. In this regard, it was shown that post-operative patient management in these complex head and neck cancer surgery patients can be performed safely in non-ICU specialty wards 
, however, that the majority of reconstructive surgeons will still send their patients to the ICU for the immediate post-operative period 
If the patient is admitted to an ICU post-operatively the ICU management hours or length of stay (LOS), which is the time until the patient is discharged from ICU, is a medically, as well as an economically relevant factor for both the patient and the clinical center 
. For that reason, several studies have already focused on ICU-LOS and overall hospital LOS regarding specific advantages and disadvantages of ICU vs. non-ICU specialty wards, different sedation protocols, risk factors for post-operative complications, the effects of ICU staffing, the incidence of post-operative delirium and complex co-morbidity and mortality scores 
However, so far only a few studies have directly investigated the effects of separate pre-operative parameters on the post-operative ICU-LOS in major oral cancer surgery, independently from the already well-known incidence of post-operative delirium or anesthesiologic co-morbidity and mortality scores, that summarize many separate parameters to one single number and, are usually not determined within the routine pre-operative clinical assessment.
2. Effects of Pre-Operative Risk Factors on Intensive Care Unit Length of Stay (ICU-LOS)
Advanced head, neck, and oral cancer surgery with free flap reconstruction often necessitate patient admission to ICU post-operatively or, at the very least, a step-down/intermediate care unit, admission 
. The high clinical relevance of identifying prognostic parameters for a prolonged ICU-LOS has repeatedly been shown in the literature 
It has to be highlighted that post-operative ICU admission is not the standard of care at many centers. However, clinically appropriate post-operative patient management still varies widely between centers 
, and a defined consensus, of specific criteria to determine the need for post-operative ICU versus non-ICU admission, especially in at-risk patients remains incomplete 
ICU admission depends upon the patient’s pre-operative comorbid status, the intra-operative complication rates, the reconstructive surgeon’s preference, and potentially also on the human and financial resources of the clinical center 
. Regarding the postoperative care in major head and neck cancer patients, it was shown that in patients with pre-operatively present co-morbidities, high ASA grades, cardio-pulmonary or renal functional impairments and/or other risk factors a post-operative ICU admission can be considered 
ICU-LOS is both a highly relevant medical and economic factor, which correlates with an increased incidence of pneumonia, use of narcotics, and also with increased health costs and staffing resources 
. We found that one-third of patients had their primary tumor site located in the floor or anterior base of the mouth. A similar distribution was also described by Sundermann et al., in a large-scale evaluation of oral cavity carcinoma localization 
. We also observed similarities in our study population regarding age, blood loss, and urinary output during surgery comparable to other reported cohorts in this field 
. The mean ICU-LOS (~3.6 days) was found to be within a similar range compared to other published protocols, which indicate that most ICU-LOS admissions are between 24 and 72 h for the major head, neck, and maxillofacial patients with free flap reconstruction 
. The duration of surgery was slightly higher in this study (~11.4 h) than in similar investigations, however, with a mean operation time of three hours more, it is still in a comparable range 
Several parameters were found to significantly prolong ICU-LOS. These were: (1) pre-operatively diagnosed PVD, (2) increasing grades of post-operative complications and especially, (3) the presence of relevant renal dysfunction, and (4) increasing NYHA grade categories. These parameters showed statistically significant results in both the regression model and the single testing calculations, including high effect sizes and positive correlation coefficients. Additional to these parameters, associated concurrent postoperative delirium was not seen as a systematic bias mainly responsible for a significant prolonged ICU-LOS. This is due to anesthesiologic medication and substitutions (narcotics and others) only being administered according to anesthesiologic standards and protocols to minimize and limit the delirium rate.
Some other variables also showed significance. Increased BMI correlated with significance in the regression model and, the patient’s age, length of surgery, tumor size, intra-operative blood transfusions, COPD, the ASA performance status, and type of neck dissection were significant in the single testing calculations.
In this context, a higher amount of intra-operatively given blood transfusion was also associated with a prolonged ICU-LOS by Rempel et al., and the parameter age was already found to be an independent factor for prolonged ICU-LOS by Kesting et al., in head and neck carcinoma surgery 
. However, the significant effect of BMI on ICU-LOS may be negated, as this parameter showed a nearly non-existent correlation towards zero and, in addition, very high BMI values (adiposity) were not found to be significant. Furthermore, only moderate correlations were found for the parameters “tumor size” and “age” and the weak effect size was found for the parameter “ASA performance status”.
Increasing patient age and prolonged operative length have already been established as risk factors for the occurrence of post-operative delirium. In addition, increasing patient age and tumor size were identified as parameters that correlate significantly with increased ICU-LOS, following head and neck free flap reconstruction 
. According to our results, the aforementioned parameters, especially age over 70, were found to correlate in this study with a prolonged ICU-LOS, however, more as confounders in combination with other variables, rather than as separate significant risk factors alone. These findings are in accordance with the results published by Bhama et al. 
In all parameters that were identified to significantly correlate with ICU-LOS, mean ICU-LOS was increased by at least 60% (50 h or more). The highest correlation with ICU-LOS was observed in the parameters “renal dysfunction” (GFR < 60 mL/min) and the extent of heart failure (NYHA classification), meaning that these parameters most strongly affect ICU-LOS. This may be explained through the fact that relevant renal dysfunction leads to a decreased elimination rate of certain toxins in the blood plasma, creating multi-organ damage on a cellular level and further impairs cardio-pulmonary function. Unstable renal and cardio-pulmonary systems have both crucial consequences on the overall health condition of the patient and, increase the overall morbidity and mortality 
. This may be especially true for the immediate post-operative period in major surgical cases.
It was reported that a prolonged ICU-LOS negatively affects the patient’s overall health condition and 5-year mortality 
, and in addition, prolonged ICU-LOS (of approximately 50 h) also results in an additional 5400. Euros financial health care cost per patient. This stands in accordance with other reports evaluating ICU hospital costs 
At-risk patients are prone to needing significantly longer ICU-management periods than others. These patients are those with pre-operative severe renal dysfunction, PVD, and/or high NYHA stage categories. Confounding parameters that contribute to a prolonged ICU-LOS in combination with other variables were identified as higher age, prolonged operative time, COPD, and intra-operatively transfused blood.
The early-stage identification of relevant risk factors in all patients scheduled for major oral, head and neck, and maxillofacial cancer resection, before surgery, can decrease the post-operative management period spent in ICU and, may improve the general pre- and post-operative health condition of the patient, the overall 5-year mortality rate and the overall therapy status outcome.
Pre-operative initiation of risk factor optimization at the earliest possible time point, and the concurrent present health issue compensation, following identification of potential predictors for a prolonged post-operative management period, is essential: it is even more important than during or after surgery.
Especially in at-risk patients, the presence of close medical support and appropriately trained nurse staff ratios (patient-to-nurse 1:1, or at least 1:2) should be ensured, more so than in not-at-risk patients, due to an expected prolonged need and complexity of immediate postoperative care. In the absence of specialized intermediate care, step-down units or high-nursing wards, these at-risk patients can be considered for admission to an “open” (low intensity) ICU for the immediate postoperative period. This will ensure safe and appropriate patient care after major oral, head and neck, and maxillofacial surgery, with adjuvant complex free flap reconstruction.