In-hospital mortality and failure to rescue following hepatobiliary surgery in Germany - a nationwide analysis

This study was based on individual inpatient data of the nationwide DRG (diagnosis-related groups) statistics that are provided by the Research Data Centers of the Federal Statistical Office and the state statistical offices [18]. Details on this nationwide database that is accessible via controlled remote data analysis have been described elsewhere. Every inpatient episode was assigned to the treating hospital based on an anonymized hospital identifier and included data from the years 2009 to 2015. Reporting of this study adheres to the REporting of studies Conducted using Observational Routinely-collected health Data (RECORD) statement [19].

This article does not contain any studies with human participants or animals performed by any of the authors. In accordance with the German guideline for conducting administrative data analyses ‚Good Practice in Secondary Data Analysis (GPS)’, no ethical approval was required for this study [20].

This study used administrative data provided by the Research Data Centre of the German Federal Statistical Office. In accordance with the terms of use regarding microdata provided by the Research Data Centers of the Federal Statistical Office and the Statistical Offices of the Federal States, no informed consent was required for this study https://​www.​forschungsdatenz​entrum.​de/​en/​terms-use.

All inpatient episodes with the following types of liver resections from 2009 through 2015: Trisectionectomy (TS), hemihepatectomy (HH), multiple segmental resection (MSR) and bisegmentectomy (BS) were identified using appropriate procedure codes. Of these, TS and HH were defined as major resections, while MSR and BS were considered minor resections (Fig. 1). Surgeries such as atypical resections were excluded from this analysis, as the German operation procedure code (OPS) insufficiently separates larger atypical resections from small excision biopsies. All procedures were analyzed in hierarchical order within the same inpatient case in order to avoid double-counting a case as described previously [14]. Patients under the age of 20 and cases with procedure codes for post-mortem hepatectomy, liver transplantation, and liver graft resection were excluded from the analysis. Four groups of principal diagnoses (‘metastatic disease’, ‘primary malignant hepatobiliary neoplasm’ [including hepatocellular and cholangiocellular carcinoma], ‘benign neoplasm of the hepatobiliary system’ and ‘other medical indication’) were defined to stratify the analyses by medical indication. Inclusion and exclusion criteria as well as the definitions of medical indications and surgical procedures are listed in the Supplemental file 1.

Volume of hepatobiliary resections performed by a hospital was calculated for each year of observation. After ranking hospitals according to increasing hospital volumes, five volume categories were established by the selection of whole number cutoff points for annual volume. To allow a more precise breakdown of lower hospital volumes, these cut-offs were self-defined as follows: 1–10 resections = ‘very low’, 11–20 resections = ‘low’, 21–40 resections = ‘medium’, 41–100 resections = ‘high’ and > 100 = ‘very high’. The hospital ranking was based on all hepatobiliary resections and done for each year in order to allow adjustments of individual hospital ranks, if volume changed from 1 year to another.

Patient characteristics and all outcome measures were analyzed according to the volume categories and to the extent of hepatobiliary resection (minor and major resections). In-hospital mortality, defined as death before discharge, was studied as primary outcome measure. Observed and risk-adjusted mortality were stratified by volume categories. Risk-adjusted mortality for each volume category was calculated by multiplying the ratio of observed to expected mortality by the overall mortality. Expected mortality and risk-adjusted odds ratios (ORs) were calculated using logistic regression models that accounted for clustering and risk-adjustment as previously described in detail [14]. The exact definitions of covariates for risk adjustment (age, sex, year of treatment, comorbidities, medical indication, type of surgical procedure and extent of surgery) and associated odds ratios of in-hospital death are displayed in Supplemental file 2.

Failure to rescue (FTR) was studied as a secondary outcome, defined as in-hospital mortality among patients with complications or interventions required for complications, within each volume category. Three types of severe complications that are associated with a high risk of death were analyzed via secondary diagnosis codes (severe cardiovascular events [including myocardial infarction, stroke and pulmonary embolism], septic complications [including Peritonitis and Sepsis] and liver failure). Wherever possible, German operation procedure codes (OPS) of interventions required for complications were preferably used over ICD-10 codes of complications in order to increase reliability of the FTR analysis (eg, blood transfusion [6 or more units] instead of postoperative bleeding, mechanical ventilation [> 48 h] instead of acute respiratory insufficiency and hemodialysis [> 72 h] instead of acute renal failure). This approach is based on the fact that OPS codes are more relevant for reimbursement and thus better documented in administrative discharge data. In addition, the rate of percutaneous abdominal drainage was determined. Since a single patient case could involve more than one complication or intervention, a pooled rate of FTR was created representing all patient cases with at least one type of complication or intervention. Besides the observed FTR, the risk-adjusted FTR for these patients was calculated by means described above. The definitions of complications are displayed in Supplemental file 3.

The level of statistical significance was set to .05. The data analyses were conducted using SAS Version 9.3 (SAS Institute Inc., Cary, NC, USA).

Between the years 2009 and 2015, a total of 31,114 inpatient cases with hepatobiliary resections were identified at the national level in Germany according to the above-mentioned including criteria. Of all procedures, 82.7% (n = 25,735) were performed for malignant indications including metastases. Benign disease and other diagnoses made up 7.9% (n = 2456) and 9.4% (n = 2923), respectively. More than half of all resections were TS and HH (10.6 and 45.0%, n = 17.273).

The annual absolute number of inpatient cases rose slightly from 4090 to 4432 over the 7-year time period (Table 1). The relative distribution of inpatient cases across hospital volume categories did not significantly vary between 2009 and 2015. Hospitals of the very low volume category (1–10 resections per year) treated 31.3% of all patients. The annual number of hospitals performing at least one hepatobiliary resection per year did not change over time. 81% of all hospitals did not perform more than 10 hepatobiliary resections per year.

On average 3 liver resections per year were performed by hospitals in the lowest volume category comprising between 392 and 428 institutions during the study period, while the small number of hospitals in the highest volume category (between 4 and 7 during the study period) performed 120 resections annually (Table 2 and Supplemental file 7). The rate of patients being transferred to another hospital did not differ between volume categories. Patients undergoing hepatobiliary resections in lower volume hospitals were older than those being treated in higher volume hospitals (Table 2). Notably, the proportion of patients aged 65 years or above was higher in low volume hospitals than in high volume hospitals (eg, very low: 58.4% vs. very high: 44.1%). The rate of metastatic disease as underlying disease was higher in lower volume hospitals, while benign diseases and malignant neoplasms were more frequently found in the higher volume categories. HH and TS were performed more often in high volume hospitals than in low volume hospitals (eg, very high: 67.67% vs. very low: 43.23%), as well as concomitant resections of visceral vessels (eg, very high: 7.62% vs. very low: 1.22%) and creations of hepatojejunal anastomosis (eg, very high: 18.11% vs. very low: 3.32%). BS and multiple segment resections were more frequent in very low volume hospitals compared to the other volume categories (eg, very high: 32.26% vs. very low: 56.77%). The frequency of coexisting conditions differed between volume categories regardless of whether minor or major resections were performed. A stratification of patient characteristics according to the extent of hepatobiliary resections (minor and major resections) is given in the Supplemental files 4 and 5.

Overall in-hospital mortality was 7.5%. In the groups of minor and major resections, in-hospital mortality was on average 3.9 and 10.3%, respectively. TS were associated with the highest mortality, ranging from 8.6% in metastatic disease to 21.7% in case of malignant neoplasms (Table 3). Lowest mortality was found in patients undergoing BS for metastatic disease (1.0%).

In-hospital mortality rates according to type of hepatobiliary resection and hospital volume categories are given in Supplemental file 8. Observed in-hospital mortality was inversely associated with hospital volume categories following major resections, ranging from 9.9% in the very high volume category to 11.6% in the very low volume category (Table 4). After risk adjustment the differences were clearly amplified and statistically significant (eg, very high: 7.4% [95% CI 6.6–8.2] vs. very low: 11.4% [95% CI 10.4–12.5]). In contrast, risk-adjusted rates of in-hospital mortality following minor resections did not significantly differ between low and high volume hospitals (eg, very high: 3.3% [95% CI 2.5–4.2] vs. very low: 4.5% [95% CI 4.0–5.1]) (Table 4). Further stratification according to the underlying diseases showed that the hospital volume effect found for major resections was primarily based on patients treated for malignant hepatobiliary neoplasms and metastatic disease (Table 5).

After inclusion of hospital volume categories in the statistical model comprising relevant covariates, each higher volume category was associated with lower odds of in-hospital death when compared to the very low volume category in case of major resections. Such a distinct inverse relationship between hospital volume and odds of in-hospital death was not present in minor hepatobiliary surgery (Fig. 2). For major resections, the risk of dying was nearly halved (OR 0.59 [95% CI 0.4–0.9]) in hospitals with very high volumes as compared to hospitals with very low volumes. Still, the estimated reduction in mortality risk was 35% (OR 0.65 [95% CI 0.5–0.8]) and 27% (OR 0.73 [95% CI 0.6–0.9]) in hospitals with high and medium volumes, respectively. In case of minor resections, there was no significant reduction of the mortality risk except for the comparison of the very low category with the low volume (OR 0.7 [95% CI 0.5–0.9]) and very high volume category (OR 0.68 [95% CI 0.5–0.9]).

Incidence of complications in patients undergoing major hepatobiliary resections was higher than of those undergoing minor hepatobiliary surgeries. Overall, more than 29.3% of all patients had at least one complication. Rates of in-hospital mortality of patients with complications (failure to rescue) varied widely, ranging from 23% in patients with adverse vascular events (stroke or acute infarction or pulmonary embolism) to 90.7% in patients with a combination of adverse vascular events, septic disease and liver failure. In contrast, in-hospital mortality was only 2.6% in patients without complications.

The incidences of complications and observed mortality rates of patients with complications did not distinctively differ across hospital volume strata regardless of whether the patient received a minor or major resection (Supplemental file 6). However, observed mortality rates of patients with complications decreased with higher volumes. In case of major resections the risk-adjusted mortality of patients with at least one complication (pooled FTR) was significantly lower in very high volume hospitals (21.38 [95% CI 19.2–23.8) compared to low volume hospitals (27.13 [95% CI 23.9–30.7]) and very low volume hospitals (29.38 [95% CI 26.7–32.2], Table 4).