For estimation of outcome after anaesthesia it is evident that the impact of surgery must also be taken into account. In contrast to various grading systems that we have for the assessment of preoperative morbidity and risk, such as Goldman’s Cardiac Risk Index or the ASA classification, there is no comparably simple and practical scale to quantify the invasiveness of surgical interventions. Therefore, any post-anaesthesia outcome assessment remains incomplete and of limited informative value as long as the impact of the surgical procedure is not incorporated into this evaluation. In particular, there is no simple quantification tool that encompasses spatial and temporal aspects of a surgical intervention. Nowadays surgical interventions may be judged according to the involved surgeon’s ‘gut-feeling’, which is not only subjective, but far from yielding a quantitative aspect. There are some means to evaluate surgical stress such as the ‘Surgical Apgar Score’ (SAS), which is based on parameters also related to the pre-existing morbidity. Alternatively, there is the Surgical Stress Index (SSI) that is deducted from finger plethysmographic waveform amplitudes and pulse-to-pulse intervals. This technique is objective, but it remains more dependent on the amount and quality of anaesthesia than on the impact of surgery.
In contrast to these evaluation systems of surgical impact, we propose a tool intended to assess the invasiveness of surgery alone, which includes all stressing effects of the intervention on the targeted organs. Its result is expressed as a numerical value that is applicable to any kind of surgery. Thus, this novel scoring system is called the ‘Universal Surgical Invasiveness Score’ (USIS). This solely observational assessment tool is based on plausible considerations and experience, while it explicitly avoids stress-related parameters that have to be provided by invasive procedures. USIS should be suitable to assess all kinds of surgical interventions on adults. However, its actual main limitation is that its components still lack clinical validation, for which reason the prefix ‘preliminary’ should been added to its recently used name resulting in ‘Preliminary Universal Surgical Invasiveness Score’ (pUSIS).
In order to establish a viable version of this scale, a 3-phased plan of action has been drawn: 1) a pilot study is a first step to prove the feasibility of pUSIS on a limited number of routine elective surgical cases; 2) a ‘Delphi Exercise’ for which a group of experienced surgeons and anaesthesiologists will discuss and (re)-evaluate the components of pUSIS in light of the results from this pilot study; and 3) a prospective multicentre validation study on a large number of cases, which will lead to the final version of the scoring system. Actually, the first step, consisting of the collection of real life pUSIS data from a group of different types of surgery, has been concluded in a pilot study in 80 cases. This investigation was devised to obtain real-life data about the magnitude, distribution, and spread of values among the investigated interventions and the effort necessary to calculate the final score.1
The pUSIS is composed of 3 parts: 1. Surgical access: considering location and size of the incisions as well as the type of access to the targeted operation site. 2. The magnitude of the targeted organ/tissue trauma due to surgical manipulation by considering location and time duration of the surgical activity on the affected organ/tissue. 3. Associated factors that have an impact on postoperative outcomes such as blood loss and the location and number of inserted drain tubes. The sum of the collected points from these 3 parts yields the final score. In the pilot study, the anaesthesiologist in charge of the assessed surgery calculated pUSIS towards the conclusion of the operation. In 6 different surgical centres in 3 countries, a group of 8 distinct types of surgical interventions were chosen to be investigated; for each type of surgery, 10 consecutive individual cases were included.
Individual pUSIS values ranged from 8 in a laparoscopic cholecystectomy as the lowest value to 36 in a total hip replacement as the highest one. The lowest median pUSIS value of 11.5 was found for laparoscopic cholecystectomy and the highest was 24.5 for open thoracic surgery. The correlation between pUSIS values and duration of surgery resulted in a tight linear regression (R2 = 0.6419). The lowest mean (±SD) difficulty level to obtain pUSIS values was 1.6±0.6 for sleeve gastrectomy and the highest was 2.9±0.6 for knee replacement. The time duration to finalise the calculations was 4.1±1.1 min for video-assisted thoracoscopy (VATS) to 9.4±1.3 min for sleeve gastrectomy.
We concluded that pUSIS has the potential to be a useful, simply obtainable, universal assessment tool for quantification of the magnitude and invasiveness of individual surgical operations with the benefit of having a means for quantification of surgical interventions for outcome research and evaluation of surgical performance.