Predictions of surgery duration (SD) are used to schedule planned/elective surgeries so that utilization rate of operating theatres be optimized (maximized subject to policy constraints). An example for a constraint is that a pre-specified tolerance for the percentage of postponed surgeries (due to non-available operating room (OR) or recovery room space) not be exceeded. The tight linkage between SD prediction and surgery scheduling is the reason that most often scientific research related to scheduling methods addresses also SD predictive methods and vice versa. Durations of surgeries are known to have large variability. Therefore, SD predictive methods attempt, on the one hand, to reduce variability (via stratification and covariates , as detailed later), and on the other employ best available methods to produce SD predictions. The more accurate the predictions, the better the scheduling of surgeries (in terms of the required OR utilization optimization).
An SD predictive method would ideally deliver a predicted SD statistical distribution (specifying the distribution and estimating its parameters). Once SD distribution is completely specified, various desired types of information could be extracted thereof, for example, the most probable duration (mode), or the probability that SD does not exceed a certain threshold value. In less ambitious circumstance, the predictive method would at least predict some of the basic properties of the distribution, like location and scale parameters (mean, median, mode, standard deviation or coefficient of variation, CV). Certain desired percentiles of the distribution may also be the objective of estimation and prediction. Experts estimates, empirical histograms of the distribution (based on historical computer records), data mining and knowledge discovery techniques often replace the ideal objective of fully specifying SD theoretical distribution.
Reducing SD variability prior to prediction (as alluded to earlier) is commonly regarded as part and parcel of SD predictive method. Most probably, SD has, in addition to random variation, also a systematic component, namely, SD distribution may be affected by various related factors (like medical specialty, patient condition or age, professional experience and size of medical team, number of surgeries a surgeon has to perform in a shift, type of anesthetic administered). Accounting for these factors (via stratification or covariates) would diminish SD variability and enhance the accuracy of the predictive method. Incorporating expert estimates (like those of surgeons) in the predictive model may also contribute to diminish the uncertainty of data-based SD prediction. Often, statistically significant covariates (also related to as factors, predictors or explanatory variables) — are first identified (for example, via simple techniques like linear regression and knowledge discovery), and only later more advanced big-data techniques are employed, like Artificial Intelligence and Machine Learning, to produce the final prediction.
Literature reviews of studies addressing surgeries scheduling most often also address related SD predictive methods. Here are some examples (latest first). [1] [2] [3] [4]
The rest of this entry review various perspectives associated with the process of producing SD predictions — SD statistical distributions, Methods to reduce SD variability (stratification and covariates), Predictive models and methods, and Surgery as a work-process. The latter addresses surgery characterization as a work-process (repetitive, semi-repetitive or memoryless) and its effect on SD distributional shape.
A most straightforward SD predictive method comprises specifying a set of existent statistical distributions, and based on available data and distribution-fitting criteria select the most fitting distribution. There is a large volume of comparative studies that attempt to select the most fitting models for SD distribution. Distributions most frequently addressed are the normal, the three-parameter lognormal, gamma (including the exponential) and Weibull. Less frequent "trial" distributions (for fitting purposes) are the loglogistic model, Burr, generalized gamma and the piecewise-constant hazard model. Attempts to presenting SD distribution as a mixture-distribution have also been reported (normal-normal, lognormal-lognormal and Weibull–Gamma mixtures). Occasionally, predictive methods are developed that are valid for a general SD distribution, or more advanced techniques, like Kernel Density Estimation (KDE), are used instead of the traditional methods (like distribution-fitting or regression-oriented methods). There is broad consensus that the three-parameter lognormal describes best most SD distributions. A new family of SD distributions, which includes the normal, lognormal and exponential as exact special cases, has recently been developed. Here are some examples (latest first). [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]
As an alternative to specifying a theoretical distribution as model for SD, one may use records to construct a histogram of available data, and use the related empirical distribution function (the cumulative plot) to estimate various required percentiles (like the median or the third quartile). Historical records/expert estimates may also be used to specify location and scale parameters, without specifying a model for SD distribution.
These methods have recently gained traction as an alternative to specifying in-advance a theoretical model to describe SD distribution for all types of surgeries. Examples are detailed below ("Predictive models and methods").
To enhance SD prediction accuracy, two major approaches are pursued to reduce SD data variability: Stratification and covariates (incorporated in the predictive model). Covariates are often referred to in the literature also as factors, effects, explanatory variables or predictors.
The term means that available data are divided (stratified) into subgroups, according to a criterion statistically shown to affect SD distribution. The predictive method then aims to produce SD prediction for specified subgroups, having SD with appreciably reduced variability. Examples for stratification criteria are medical specialty, Procedure Code systems, patient-severity condition or hospital/surgeon/technology (with resulting models related to as hospital-specific, surgeon-specific or technology-specific). Examples for implementation are Current Procedural Terminology (CPT) and ICD-9-CM Diagnosis and Procedure Codes (International Classification of Diseases, 9th Revision, Clinical Modification). [5] [15] [16] [17]
This approach to reduce variability incorporates covariates in the prediction model. The same predictive method may then be more generally applied, with covariates assuming different values for different levels of the factors shown to affect SD distribution (usually by affecting a location parameter, like the mean, and, more rarely, also a scale parameter, like the variance). A most basic method to incorporate covariates into a predictive method is to assume that SD distribution is lognormally distributed. The logged data (taking log of SD data) then represent a normally distributed population, allowing use of multiple- linear-regression to detect statistically significant factors. Other regression methods, which do not require data normality or are robust to its violation (generalized linear models, nonlinear regression) and artificial intelligence methods have also been used (references sorted chronologically, latest first). [14] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30]
Following is a representative (non-exhaustive) list of models and methods employed to produce SD predictions (in no particular order). These, or a mixture thereof, may be found in the sample of representative references below:
Linear regression (LR); Multivariate adaptive regression splines (MARS); Random forests (RF); Machine learning; Data mining (rough sets, neural networks); Knowledge discovery in databases (KDD); Data warehouse model (used to extract data from various, possibly non-interacting, databases); Kernel density estimation (KDE); Jackknife; Monte Carlo simulation. [31] [32] [33] [34] [35] [2] [36] [37] [38] [39] [40]
Surgery is a work process, and likewise it requires inputs to achieve the desired output, a recuperating post-surgery patient. Examples of work-process inputs, from Production Engineering, are the five M's — "money, manpower, materials, machinery, methods" (where "manpower" refers to the human element in general). Like all work-processes in industry and the services, surgeries also have a certain characteristic work-content, which may be unstable to various degrees (within the defined statistical population to which the prediction method aims). This generates a source for SD variability that affects SD distributional shape (from the normal distribution, for purely repetitive processes, to the exponential, for purely memoryless processes). Ignoring this source may confound its variability with that due to covariates (as detailed earlier). Therefore, as all work-processes may be partitioned into three types (repetitive, semi-repetitive, memoryless), surgeries may be similarly partitioned. A stochastic model that takes account of work-content instability has recently been developed, which delivers a family of distributions, with the normal/lognormal and exponential as exact special cases. This model was applied to construct a statistical process control scheme for SD. [5] [41] [42]
Neurosurgery or neurological surgery, known in common parlance as brain surgery, is the medical specialty concerned with the surgical treatment of disorders which affect any portion of the nervous system including the brain, spinal cord and peripheral nervous system.
Surgery is a medical specialty that uses manual and/or instrumental techniques to physically reach into a subject's body in order to investigate or treat pathological conditions such as a disease or injury, to alter bodily functions, to improve appearance, or to remove/replace unwanted tissues or foreign bodies. The subject receiving the surgery is typically a person, but can also be a non-human animal.
Laparoscopy is an operation performed in the abdomen or pelvis using small incisions with the aid of a camera. The laparoscope aids diagnosis or therapeutic interventions with a few small cuts in the abdomen.
In probability theory, a log-normal (or lognormal) distribution is a continuous probability distribution of a random variable whose logarithm is normally distributed. Thus, if the random variable X is log-normally distributed, then Y = ln(X) has a normal distribution. Equivalently, if Y has a normal distribution, then the exponential function of Y, X = exp(Y), has a log-normal distribution. A random variable which is log-normally distributed takes only positive real values. It is a convenient and useful model for measurements in exact and engineering sciences, as well as medicine, economics and other topics (e.g., energies, concentrations, lengths, prices of financial instruments, and other metrics).
Cross-validation, sometimes called rotation estimation or out-of-sample testing, is any of various similar model validation techniques for assessing how the results of a statistical analysis will generalize to an independent data set. Cross-validation is a resampling method that uses different portions of the data to test and train a model on different iterations. It is mainly used in settings where the goal is prediction, and one wants to estimate how accurately a predictive model will perform in practice. In a prediction problem, a model is usually given a dataset of known data on which training is run, and a dataset of unknown data against which the model is tested. The goal of cross-validation is to test the model's ability to predict new data that was not used in estimating it, in order to flag problems like overfitting or selection bias and to give an insight on how the model will generalize to an independent dataset.
Orthopedic surgery or orthopedics is the branch of surgery concerned with conditions involving the musculoskeletal system. Orthopedic surgeons use both surgical and nonsurgical means to treat musculoskeletal trauma, spine diseases, sports injuries, degenerative diseases, infections, tumors, and congenital disorders.
A Nissen fundoplication, or laparoscopic Nissen fundoplication when performed via laparoscopic surgery, is a surgical procedure to treat gastroesophageal reflux disease (GERD) and hiatal hernia. In GERD, it is usually performed when medical therapy has failed; but, with a Type II (paraesophageal) hiatus hernia, it is the first-line procedure. The Nissen fundoplication is total (360°), but partial fundoplications known as Thal, Belsey, Dor, Lind, and Toupet fundoplications are alternative procedures with somewhat different indications and outcomes.
A receiver operating characteristic curve, or ROC curve, is a graphical plot that illustrates the performance of a binary classifier model at varying threshold values.
Perioperative mortality has been defined as any death, regardless of cause, occurring within 30 days after surgery in or out of the hospital. Globally, 4.2 million people are estimated to die within 30 days of surgery each year. An important consideration in the decision to perform any surgical procedure is to weigh the benefits against the risks. Anesthesiologists and surgeons employ various methods in assessing whether a patient is in optimal condition from a medical standpoint prior to undertaking surgery, and various statistical tools are available. ASA score is the most well known of these.
Regression dilution, also known as regression attenuation, is the biasing of the linear regression slope towards zero, caused by errors in the independent variable.
Robot-assisted surgery or robotic surgery are any types of surgical procedures that are performed using robotic systems. Robotically assisted surgery was developed to try to overcome the limitations of pre-existing minimally-invasive surgical procedures and to enhance the capabilities of surgeons performing open surgery.
Computer-assisted orthopedic surgery or computer-assisted orthopaedic surgery is a discipline where computer technology is applied pre-, intra- and/or post-operatively to improve the outcome of orthopedic surgical procedures. Although records show that it has been implemented since the 1990s, CAOS is still an active research discipline which brings together orthopedic practitioners with traditionally technical disciplines, such as engineering, computer science and robotics.
Proportional hazards models are a class of survival models in statistics. Survival models relate the time that passes, before some event occurs, to one or more covariates that may be associated with that quantity of time. In a proportional hazards model, the unique effect of a unit increase in a covariate is multiplicative with respect to the hazard rate. For example, taking a drug may halve one's hazard rate for a stroke occurring, or, changing the material from which a manufactured component is constructed may double its hazard rate for failure. Other types of survival models such as accelerated failure time models do not exhibit proportional hazards. The accelerated failure time model describes a situation where the biological or mechanical life history of an event is accelerated.
Computer-assisted surgery (CAS) represents a surgical concept and set of methods, that use computer technology for surgical planning, and for guiding or performing surgical interventions. CAS is also known as computer-aided surgery, computer-assisted intervention, image-guided surgery, digital surgery and surgical navigation, but these are terms that are more or less synonymous with CAS. CAS has been a leading factor in the development of robotic surgery.
In statistics and machine learning, lasso is a regression analysis method that performs both variable selection and regularization in order to enhance the prediction accuracy and interpretability of the resulting statistical model. It was originally introduced in geophysics, and later by Robert Tibshirani, who coined the term.
Aesthetic medicine is a branch of modern medicine that focuses on altering cosmetic appearance through the treatment of conditions including scars, skin laxity, wrinkles, moles, liver spots, excess fat, cellulite, unwanted hair, skin discoloration, and spider veins. Traditionally, it includes dermatology, oral and maxillofacial surgery, reconstructive surgery and plastic surgery, surgical procedures, non-surgical procedures, and a combination of both. Aesthetic medicine procedures are usually elective. There is a long history of aesthetic medicine procedures, dating back to many notable cases in the 19th century, though techniques have developed much since then.
Surgical stress is the systemic response to surgical injury and is characterized by activation of the sympathetic nervous system, endocrine responses as well as immunological and haematological changes. Measurement of surgical stress is used in anaesthesia, physiology and surgery.
In statistics, linear regression is a linear approach for modelling a predictive relationship between a scalar response and one or more explanatory variables, which are measured without error. The case of one explanatory variable is called simple linear regression; for more than one, the process is called multiple linear regression. This term is distinct from multivariate linear regression, where multiple correlated dependent variables are predicted, rather than a single scalar variable.If the explanatory variables are measured with error then errors in variables models are required, also known as measurement error models.
Steven D. Wexner is an American surgeon and physician. He is Director of the Ellen Leifer Shulman and Steven Shulman Digestive Disease Center at Cleveland Clinic Florida. Wexner has received numerous regional, national, and international research awards. Through his multiple academic appointments, Wexner personally trains 15-20 surgeons each year, and he educates thousands more around the world through conferences and lectures. He is a resource for his colleagues from around the world for referral of patients with challenging or complex problems. In 2020, he was elected vice-chair of the Board of Regents of the American College of Surgeons for a one-year term. Since 1990. he has served as Symposium Director of the Cleveland Clinic Annual International Colorectal Disease Symposium. The Symposium was held in Fort Lauderdale or Boca Raton every year from 1990 to 2019. Since 2020, the Symposium has expanded to include host locations outside of the US with interruptions during the pandemic years of 2021–2022.
Conor P. Delaney MD, MCh, PhD, FRCSI, FACS, FASCRS, FRCSI (Hon.) is an Irish-American colorectal surgeon, CEO and President of the Cleveland Clinic Florida, the Robert and Suzanne Tomsich Distinguished Chair in Healthcare Innovation, and Professor of Surgery at the Cleveland Clinic Lerner College of Medicine. He is also the current President of the American Society of Colon and Rectal Surgeons (ASCRS). He was previously Chairman of the Digestive Disease & Surgery Institute at the Cleveland Clinic. He is both a Fellow and Honorary Fellow of the Royal College of Surgeons in Ireland and a Fellow of both the American College of Surgeons and American Society of Colon and Rectal Surgeons.