The study was conducted at Austin Health, a tertiary teaching hospital affiliated with the University of Melbourne in Melbourne, Victoria, Australia. Austin Health performs approximately 38,000 surgical procedures annually, including complex cardiothoracic surgery, hepatobiliary-pancreatic surgery, liver transplantation, and major spinal and orthopedic surgery. The orthopedic surgical unit provides services to over 15,000 outpatients annually and performs over 2,500 operations per year, of which approximately 650 are major hip operations.
Following approval from the Austin Health Human Research Ethics Committee (LNR/17/Austin/616), we performed a retrospective cohort study of patients who required RRT activation following major hip surgery between September 2014 and November 2017. The need for informed written consent from participants was waived due to the observational and retrospective nature of the study.
The RRT at our institution is an intensive care–led service introduced in 2000. The RRT is governed by the Department of Intensive Care Medicine, and the RRT team comprises an intensive care registrar and critical care nurse. The RRT is also accompanied by the patient’s admitting unit at every activation. Escalation of medical resources to assist with RRT activation are immediately available if required (e.g., anesthesia support for airway management). At our institution, the RRT is activated whenever a patient meets predetermined criteria, which include acute changes in any of the following: obstructed airway, noisy breathing or stridor, problems with a tracheostomy tube, any difficulty in breathing, respiratory rate < 8 or > 25 breaths/min, oxygen saturation < 90% despite oxygen administration, heart rate (< 40 or > 120 beats/min), systolic blood pressure < 90 mmHg, urine output < 50 mL over 4 hours, sudden change in conscious state, patient cannot be roused, or if any member of staff is worried about imminent deterioration of the patient. Additionally, an RRT is activated for any “code blue.” A “code blue” is activated whenever a patient suffers a cardiac or respiratory arrest. Our institution’s RRT reviews approximately 3,000 patients annually, of which the majority are post-surgery.
For inclusion in our study, patients had to be adults (age > 18 years) undergoing major hip surgery who had an RRT or “code blue” activation post-surgery and were within the index hospital admission. In the case of multiple RRT activations, we only analyzed the first event. We used the following procedures as listed in the International Statistical Classification of Diseases (10th revision) to select patients: total hip arthroplasty, partial hip replacement/hemiarthroplasty (unipolar or bipolar femoral head), revision of hip replacement not otherwise specified, arthrotomy for removal of prosthesis, revision of hip replacement (both acetabular and femoral components), revision of hip replacements (acetabular liner), resurfacing hip (total acetabulum and femoral head), resurfacing hip (partial femoral head or acetabulum), and insertion or removal of any internal fixation device. We excluded superficial procedures of the hip joint including joint arthrocentesis and wound debridement.
As part of routine perioperative care for major hip surgery, patients were assessed by a multidisciplinary team consisting of a surgeon, anesthetist, perioperative physician, and ortho-geriatrician (if over 70 years of age). Routine preoperative investigations included biochemical, hematological, and coagulation tests, and where necessary, all patients were optimized from a cardiorespiratory perspective prior to surgery. All patients underwent preoperative hemoglobin optimization, based on the National Blood Authority of Australia’s patient blood management initiative (8). When appropriate, standard perioperative care included strict transfusion practice in accordance with these guidelines. Further, as part of the Diabetes Discovery Initiative, all patients with a HbA1c of 8.3% (67 mmol/mol) and above were seen by the endocrinology unit, which generated a personalized plan for glycemic control according to our institution’s guidelines. Patients with a HbA1c between 7.5% (58 mmol/mol) and 8.2% (66 mmol/mol), and those with newly diagnosed diabetes, were seen by a general physician. All patients were managed according to the hospital’s perioperative guidelines for patients with diabetes, with an inpatient blood glucose target of 5–10 mmol/L based on the Australian Diabetes Society guidelines (9). In addition, for patients with decision-making capacity, an advance care plan was undertaken, which allowed patients to communicate their future preferences relating to medical treatment to their families, friends, and health professionals. In accordance with existing legislation, a legally defined “person responsible” was appointed to make medical decisions on behalf of a patient who lacks the capacity to give their own consent to treatment.
Data were extracted from the patient’s electronic medical records and from Austin Hospital’s computerized laboratory results by two independent study investigators. Austin Health uses Cerner electronic medical records, which allows comprehensive electronic data capture and access to patient health information from the perioperative setting. We collected a priori–defined data on patient characteristics, comorbidities, and preoperative management. All other comorbidities were extracted from patient medical records. Patient comorbidity was further defined using the Charlson Comorbidity Index (CCI), a validated metric that predicts 1-year patient mortality (10). For the calculation of the CCI, moderate/severe chronic kidney disease was defined as an estimated glomerular filtration rate of less than 60 mL/min (Stage 3 or worse), and chronic liver disease was defined based on the Child–Pugh classification (11). Congestive cardiac failure was defined as “heart failure with preserved ejection fraction” (i.e. diagnosed by combination of clinical acumen combined with either echocardiographic features of diastolic dysfunction, or elevated plasma B-type natriuretic peptide concentrations) and “heart failure with reduced ejection fraction” (i.e. left ventricle ejection fraction <40%), regardless of etiology. We used a modified Canadian Study of Health and Aging Clinical Frailty Scale to determine frailty (12).
Intraoperatively, we recorded the type of procedure, anesthesia (regional and/or general), as well as the use of fluids, and vasoactive and opioid medications. Furthermore, the number of epochs of intraoperative hypotension, and the magnitude of each hypotensive event, were recorded. Similar data were collected from the post-anesthesia care unit (PACU). A hypotensive event was defined as any reduction in systolic, diastolic, or mean arterial pressure by 30% or more as compared to preoperative values; severe hypotension was defined as a reduction in any of the above-mentioned blood pressures by 50% or more. The duration of hypotensive episodes was not assessed, and each hypotensive measure was counted as a discrete epoch. Postoperatively, we collected postsurgical discharge destination, indication for RRT activation, time to RRT activation from surgery, as well as length of stay and in-hospital mortality.
Due to the exploratory and observational design of this study, our primary objectives were to describe the demographic and perioperative profile of patients who required RRT activation after major hip surgery. We also compared the perioperative characteristics of patients who survived the index hospital admission to those who did not. Specifically, we further explored differences between these two groups with respect to the following a priori variables: i) preoperative comorbidities (including frailty), ii) type of anesthesia (general and/or regional), iii) surgical presentation (selective or emergency), iv) perioperative hypotension, and v) use of opioids and vasoactive drugs.
Continuous variables were tested for normality and normally distributed data were expressed as means and standard deviations (SD) and compared using a Student’s t test; non-normally distributed data were expressed as medians and interquartile ranges (IQRs) and compared using the Mann–Whitney U test. Categorical variables were described as proportions and compared using the chi-square test or the Fisher’s exact test. All p values of less than 0.05 were treated as indicative of statistical significance, and no correction for multiplicity of testing was undertaken due to the exploratory nature of the study. We reported this study using the STROBE guidelines for reporting observational studies (13). Analyses were performed using GraphPad Prism (version 7.00 for Mac, GraphPad Software, La Jolla, California, United States).