The relationship between pre‐operative hypertension and intra‐operative haemodynamic changes known to be associated with postoperative morbidity

Hypertension is not consistently associated with postoperative cardiovascular morbidity and is therefore not considered a major peri‐operative risk factor. However, hypertension may predispose to peri‐operative haemodynamic changes known to be associated with peri‐operative morbidity and mortality, such as intra‐operative hypotension and tachycardia. The objective of this study was to determine whether pre‐operative hypertension was independently associated with haemodynamic changes known to be associated with adverse peri‐operative outcomes. We performed a five‐day multicentre, prospective, observational cohort study which included all adult inpatients undergoing elective, non‐cardiac, non‐obstetric surgery. We recruited 343 patients of whom 164 (47.8%) were hypertensive. An intra‐operative mean arterial pressure of < 55 mmHg occurred in 59 (18.2%) patients, of which 25 (42.4%) were hypertensive. Intra‐operative tachycardia (heart rate> 100 beats.min^?1) occurred in 126 (38.9%) patients, of whom 61 (48.4%) were hypertensive. Multivariable logistic regression did not show an independent association between the stage of hypertension and either clinically significant hypotension or tachycardia, when controlled for ASA physical status, functional status, major surgery, duration of surgery or blood transfusion. There was no association between pre‐operative hypertension and peri‐operative haemodynamic changes known to be associated with major morbidity and mortality. These data, therefore, support the recommendation of the Joint Guidelines of the Association of Anaesthetists of Great Britain and Ireland (AAGBI) and the British Hypertension Society to proceed with elective surgery if a patient's blood pressure is < 180/110 mmHg.     

Association between peri‐operative angiotensin‐converting enzyme inhibitors and angiotensin‐2 receptor blockers and acute kidney injury in major elective non‐cardiac surgery: a multicentre,prospective cohort study

The peri‐operative use of angiotensin‐converting enzyme inhibitors or angiotensin‐2 receptor blockers is thought to be associated with an increased risk of postoperative acute kidney injury. To reduce this risk, these agents are commonly withheld during the peri‐operative period. This study aimed to investigate if withholding angiotensin‐converting enzyme inhibitors or angiotensin‐2 receptor blockers peri‐operatively reduces the risk of acute kidney injury following major non‐cardiac surgery. Patients undergoing elective major surgery on the gastrointestinal tract and/or the liver were eligible for inclusion in this prospective study. The primary outcome was the development of acute kidney injury within seven days of operation. Adjusted multi‐level models were used to account for centre‐level effects and propensity score matching was used to reduce the effects of selection bias between treatment groups. A total of 949 patients were included from 160 centres across the UK and Republic of Ireland. From this population, 573 (60.4%) patients had their angiotensin‐converting enzyme inhibitors or angiotensin‐2 receptor blockers withheld during the peri‐operative period. One hundred and seventy‐five (18.4%) patients developed acute kidney injury; there was no difference in the incidence of acute kidney injury between patients who had their angiotensin‐converting enzyme inhibitors or angiotensin‐2 receptor blockers continued or withheld (107 (18.7%) vs. 68 (18.1%), respectively; p = 0.914). Following propensity matching, withholding angiotensin‐converting enzyme inhibitors or angiotensin‐2 receptor blockers did not demonstrate a protective effect against the development of postoperative acute kidney injury (OR (95%CI) 0.89 (0.58–1.34); p = 0.567).     

A review of echocardiography in anaesthetic and peri‐operative practice. Part 1: impact and utility

Echocardiography is migrating rapidly across speciality boundaries and clinical demand is expanding. Echocardiography shows promise for evolving applications in the peri‐operative assessment and therapeutic management of patients undergoing non‐cardiac surgery, whether it be elective or emergency. Although evidence is limited with regard to significant impact on outcomes from anaesthesia and surgery, there is little doubt about the validity and power of two‐dimensional real‐time viewing of cardiac anatomy and function. Echocardiography can be used to assist in decision‐making along the entire peri‐operative pathway, and is increasingly delivered by the previously referring physicians. The discussion around more widespread incorporation of cardiac ultrasound into anaesthetic practice must take into account competency, training and governance. Failure to do so adequately may mean that the use of echocardiography is poorly applied and costly.     

Peri‐operative management of patients with type‐2 diabetes mellitus undergoing non‐cardiac surgery using liraglutide,glucose–insulin–potassium infusion or intravenous insulin bolus regimens: a randomised controlled trial

In this open‐label multicentre randomised controlled trial, we investigated three peri‐operative treatment strategies to lower glucose and reduce the need for rescue insulin in patients aged 18–75 years with type‐2 diabetes mellitus undergoing non‐cardiac surgery. Patients were randomly allocated using a web‐based randomisation program to premedication with liraglutide (liraglutide group), glucose–insulin–potassium infusion (insulin infusion group) or insulin bolus regimen (insulin bolus group), targeting a glucose < 8.0 mmol.l^?1. The primary outcome was the between group difference in median glucose levels 1 h after surgery. We analysed 150 patients (liraglutide group n = 44, insulin infusion group n = 53, insulin bolus group n = 53) according to the intention‐to‐treat principle. Median (IQR [range]) plasma glucose 1 h postoperatively was lower in the liraglutide group compared with the insulin infusion and insulin bolus groups (6.6 (5.6–7.7 [4.2–13.5]) mmol.l^?1 vs. 7.5 (6.4–8.3 [3.9–16.6]) mmol.l^?1 (p = 0.026) and 7.6 (6.4–8.9 [4.7–13.2]) mmol.l^?1) p = 0.006, respectively). The incidence of hypoglycaemia and postoperative complications did not differ between the groups. Six patients had pre‐operative nausea in the liraglutide group, of which two had severe nausea, compared with no patients in the insulin infusion and insulin bolus groups (p = 0.007). The pre‐operative administration of liraglutide stabilised peri‐operative plasma glucose levels and reduced peri‐operative insulin requirements, at the expense of increased pre‐operative nausea rates.     

Cardiac biomarkers in the prediction of risk in the non‐cardiac surgery setting

B‐Type natriuretic peptides and troponin measurements have potential in predicting risk in patients undergoing non‐cardiac surgery. Using the American Heart Association framework for the evaluation of novel biomarkers, we review the current evidence supporting the peri‐operative use of these two biomarkers. In patients having major non‐cardiac surgery who are risk stratified using clinical risk scores, the measurement of natriuretic peptides and troponin, both before and after surgery, significantly improves risk stratification. However, only pre‐ and postoperative natriuretic peptide measurement and postoperative troponin measurement have shown clinical utility. It is now important for trials to be conducted to determine whether integrating pre‐ and postoperative natriuretic peptide and postoperative troponin measurement into clinical practice is able to improve clinical outcomes in patients undergoing non‐cardiac surgery.     

Pulmonary hypertension and its management in patients undergoing non‐cardiac surgery

Pulmonary hypertension is a complex disorder of the pulmonary vasculature that leads to increased peri‐operative morbidity and mortality. Non‐cardiac surgery constitutes a significant risk in patients with pulmonary hypertension. The management of right ventricular failure is inherently challenging and fraught with life‐threatening consequences. A thorough understanding of the pathophysiology, the severity of the disease and its treatment modalities is required to deliver optimal peri‐operative care. This review provides an evidence‐based overview of the definition, classification, pathophysiology, diagnosis and treatment of pulmonary hypertension and focuses on the peri‐operative management and treatment of pulmonary hypertensive crises in a non‐cardiac setting.     

Fast‐track surgery for bariatric laparoscopic gastric bypass with focus on anaesthesia and peri‐operative care. Experience with 500 cases

Background: Bariatric surgery for morbid obesity implies challenges in anaesthesiological handling. We report our experience from 500 consecutive patients during 3 years. Methods: The patients were due for laparoscopic Roux–en–Y gastric bypass and enteral bypass. Sleep was induced after pre‐oxygenation with target control infusions (TCI) of remifentanil and propofol; vecuronium was supplied for facilitating endotracheal intubation. The propofol infusion was stopped and desflurane 3–6% was given for BIS‐titrated anaesthetic maintenance together with remifentanil TCI. Antiemetic prophylaxis was supplied with intravenous (IV) droperidol, ondansetron and dexamethasone; post‐operative pain prophylaxis was IV paracetamol, parecoxib and bupivacaine infiltration. The patients were extubated in the operating room and kept in the post‐operative care unit for 3–4 h, being tested for a 20 m walk before discharge to the ward. Results: The procedure was uncomplicated peri‐operatively in all 500 cases and in 497 patients (99.4%) post‐operatively. Three patients had one complication, which resolved without sequelae: oesophageal rupture from gastric tubing, reoperation for anastomosis leakage and pneumonia. The mean duration of surgery was 57 min (range 37–91). The mean time from the start of anaesthesia until the start of surgery and time from the end of surgery until the end of anaesthesia were both significantly reduced throughout the study period, from 23 to 7.8 and 5.8 to 1.9 min, respectively (P<0.001). The mean total hospital stay was reduced from 3 days at start to 2 days in the end of the series (P<0.05). Conclusion: Safe bariatric short‐stay surgery is feasible with a dedicated anaesthesiological concept in an expert surgical team.     

A survey of UK peri‐operative medicine: pre‐operative care

The majority of UK hospitals now have a Local Lead for Peri‐operative Medicine (n = 115). They were asked to take part in an online survey to identify provision and practice of pre‐operative assessment and optimisation in the UK. We received 86 completed questionnaires (response rate 75%). Our results demonstrate strengths in provision of shared decision‐making clinics. Fifty‐seven (65%, 95%CI 55.8–75.4%) had clinics for high‐risk surgical patients. However, 80 (93%, 70.2–87.2%) expressed a desire for support and training in shared decision‐making. We asked about management of pre‐operative anaemia, and identified that 69 (80%, 71.5–88.1%) had a screening process for anaemia, with 72% and 68% having access to oral and intravenous iron therapy, respectively. A need for peri‐operative support in managing frailty and cognitive impairment was identified, as few (24%, 6.5–34.5%) respondents indicated that they had access to specific interventions. Respondents were asked to rank their ‘top five’ priority topics in Peri‐operative Medicine from a list of 22. These were: shared decision‐making; peri‐operative team development; frailty screening and its management; postoperative morbidity prediction; and primary care collaboration. We found variation in practice across the UK, and propose to further explore this variation by examining barriers and facilitators to improvement, and highlighting examples of good practice.     

Intra‐operative colloid administration increases the clearance of a post‐operative fluid load

Background: It is unknown whether an intra‐operative colloid infusion alters the dynamics of a crystalloid load administered post‐operatively. Methods: Ten patients received 12.5 ml/kg of Ringer's lactate over 30 min 1–3 days before and 4 h after laparoscopic cholecystectomy, during which 10 ml/kg of a colloid solution, hydroxyethylstarch (HES 130/0.4), was infused. The total body clearance of the pre‐ and post‐operative test infusions was taken as the ratio between the urinary excretion and the Hb‐derived dilution of venous plasma over 150 min. The plasma clearance of the infused fluid was calculated using volume kinetics based on the plasma dilution alone. The pre‐operative plasma clearance was compared with the post‐operative plasma clearance and patients served as their own control. Results: The urinary excretion averaged 350 ml for the pre‐operative infusion and 612 ml post‐operatively, which corresponds to 46% and 68% of the pre‐ and post‐operative infusions, respectively. The total body clearance of the crystalloid fluid was 30 ml/min before surgery and 124 ml/min after surgery (P<0.01). The plasma clearance, as obtained from the plasma dilution alone, was 28 and 412 ml/min, respectively. The maximal increase in plasma volume was 410 ml pre‐operatively vs. 220 ml post‐operatively. Conclusions: Infusion of a colloid solution in combination with a crystalloid during laparoscopic cholecystectomy increased the plasma clearance of a post‐operative crystalloid infusion.     

Thromboelastography to monitor the intra‐operative effects of low‐molecular weight heparin following bridging anticoagulation in a child with normal renal function*

Paediatric patients who require anticoagulation with therapeutic doses of low‐molecular weight heparin are at risk of having a residual anticoagulant effect at the time of surgery, even if managed according to current peri‐operative guidelines. Testing for residual effect is not currently recommended in such circumstances. A 15‐year‐old child with a mechanical aortic valve replacement requiring long‐term warfarin treatment, as well as underlying coagulation defects, was administered low‐molecular weight heparin for bridging anticoagulation before kyphoscoliosis surgery. Thromboelastography was used intra‐operatively to diagnose residual heparinisation, which was demonstrated by a prolonged reaction (R) time of 16.0 min in the plain cup, compared with 9.2 min in the heparinase cup. Subsequently, thromboelastography was also used to monitor haemostatic therapy, which consisted of protamine 2 mg.kg^?1 and 500 IU cryoprecipitate. Thromboelastography was used intra‐operatively to allow rapid testing of coagulation status and guide therapy, thereby minimising use of blood products and reducing complications.     

Peri‐operative management of the obese surgical patient 2015

Guidelines are presented for the organisational and clinical peri‐operative management of anaesthesia and surgery for patients who are obese, along with a summary of the problems that obesity may cause peri‐operatively. The advice presented is based on previously published advice, clinical studies and expert opinion.     

Anaesthesia‐associated hypersensitivity reactions: seven years' data from a British bi‐specialty clinic

Our bi‐specialty clinic was established to systematically investigate patients with suspected peri‐operative hypersensitivity reactions. Four hundred and ten patients were studied; 316 following an intra‐operative reaction (‘postoperative’ group) and 94 with a previous history of reaction, referred before undergoing anaesthesia (‘pre‐operative’ group). In the postoperative group, 173 (54.7%) were diagnosed with IgE‐mediated reactions: 65 (37.6%) to neuromuscular blocking drugs; 54 (31.2%) antibiotics; 15 (8.7%) chlorhexidine and 12 (6.9%) patent blue dye. Reactions were severe in 114 patients (65.9%). All reactions to patent blue dye were severe. We identified IgE sensitisation in 22 (13.2%) cases with isolated mucocutaneous reactions. Only 173 (54.7%) patients had serum tryptase samples taken. Referrers' suspected causal agent was confirmed in only 37.2% of patients. Of 94 patients reviewed ‘pre‐operatively’, 29 (30.8%) were diagnosed with IgE‐mediated hypersensitivity reactions, reinforcing the importance of investigating this group of patients. Knowledge of the range of causative agents identified in our study should guide the investigation of suspected peri‐operative hypersensitivity reactions.     

The efficacy of peri‐operative interventions to decrease postoperative delirium in non‐cardiac surgery: a systematic review and meta‐analysis.

The purpose of this meta‐analysis was to determine the efficacy of peri‐operative interventions in decreasing the incidence of postoperative delirium. An electronic search of four databases was conducted. The Preferred Reporting Items for Systematic Reviews and Meta‐Analyses (PRISMA) guidelines were adhered to. We included randomised controlled trials of non‐cardiac surgery with a peri‐operative intervention and that reported postoperative delirium, and identified 29 trials. Meta‐analysis revealed that peri‐operative geriatric consultation (OR 0.46, 95% CI 0.32–0.67) and lighter anaesthesia (OR 2.66, 95% CI 1.27–5.56) were associated with a decreased incidence of postoperative delirium. For the other interventions, the point estimate suggested possible protection with prophylactic haloperidol (OR 0.62, 95% CI 0.36–1.05), bright light therapy (OR 0.20, 95% CI 0.03–1.19) and general as opposed to regional anaesthesia (OR 0.76, 95% CI 0.47–1.23). This meta‐analysis has shown that peri‐operative geriatric consultations with multicomponent interventions and lighter anaesthesia are potentially effective in decreasing the incidence of postoperative delirium.     

Pilot multi‐centre randomised trial of the impact of pre‐operative focused cardiac ultrasound on mortality and morbidity in patients having surgery for femoral neck fractures (ECHONOF‐2 pilot)

Hip fracture surgery is common, usually occurs in elderly patients who have multiple comorbidities, and is associated with high morbidity and mortality. Pre‐operative focused cardiac ultrasound can alter diagnosis and management, but its impact on outcome remains uncertain. This pilot study assessed feasibility and group separation for a proposed large randomised clinical trial of the impact of pre‐operative focused cardiac ultrasound on patient outcome after hip fracture surgery. Adult patients requiring hip fracture surgery in four teaching hospitals in Australia were randomly allocated to receive focused cardiac ultrasound before surgery or not. The primary composite outcome was any death, acute kidney injury, non‐fatal myocardial infarction, cerebrovascular accident, pulmonary embolism or cardiopulmonary arrest within 30 days of surgery. Of the 175 patients screened, 100 were included as trial participants (screening:recruitment ratio 1.7:1), 49 in the ultrasound group and 51 as controls. There was one protocol failure among those recruited. The primary composite outcome occurred in seven of the ultrasound group patients and 12 of the control group patients (relative group separation 39%). Death, acute kidney injury and cerebrovascular accident were recorded, but no cases of myocardial infarction, pulmonary embolism or cardiopulmonary arrest ocurred. Focused cardiac ultrasound altered the management of 17 participants, suggesting an effect mechanism. This pilot study demonstrated that enrolment and the protocol are feasible, that the primary composite outcome is appropriate, and that there is a treatment effect favouring focused cardiac ultrasound – and therefore supports a large randomised clinical trial.     

Postoperative outcomes following cardiac surgery in non‐anaemic iron‐replete and iron‐deficient patients – an exploratory study

Iron deficiency anaemia is strongly associated with poor outcomes after cardiac surgery. However, pre‐operative non‐anaemic iron deficiency (a probable anaemia precursor) has not been comprehensively examined in patients undergoing cardiac surgery, despite biological plausibility and evidence from other patient populations of negative effect on outcome. This exploratory retrospective cohort study aimed to compare an iron‐deficient group of patients undergoing cardiac surgery with an iron‐replete group. Consecutive non‐anaemic patients undergoing elective coronary artery bypass grafting or single valve replacement in our institution between January 2013 and December 2015 were considered for inclusion. Data from a total of 277 patients were analysed, and were categorised by iron status and blood haemoglobin concentration into iron‐deficient (n = 109) and iron‐replete (n = 168) groups. Compared with the iron‐replete group, patients in the iron‐deficient group were more likely to be female (43% vs. 12%, iron‐replete, respectively); older, mean (SD) age 64.4 (9.7) vs. 63.2 (10.3) years; and to have a higher pre‐operative EuroSCORE (median IQR [range]) 3 (2–5 [0–10]) vs. 3 (2–4 [0–9]), with a lower preoperative haemoglobin of 141.6 (11.6) vs. 148.3 (11.7) g.l^?1. Univariate analysis suggested that iron‐deficient patients had a longer hospital length of stay (7 (6–9 [2–40]) vs. 7 (5–8 [4–23]) days; p = 0.013) and fewer days alive and out of hospital at postoperative day 90 (83 (80–84 [0–87]) vs. 83 (81–85 [34–86]), p = 0.009). There was no evidence of an association between iron deficiency and either lower nadir haemoglobin or higher requirement for blood products during inpatient stay. After adjusting the model for pre‐operative age, sex, renal function, EuroSCORE and haemoglobin, the mean increase in hospital length of stay in the iron‐deficient group relative to the iron‐replete group was 0.86 days (bootstrapped 95%CI ?0.37 to 2.22, p = 0.098). This exploratory study suggests there is weak evidence of an association between non‐anaemic iron deficiency and outcome after cardiac surgery after controlling for potentially confounding variables.     

The pathophysiology of peri‐operative myocardial infarction

It is generally believed that plaque rupture and myocardial oxygen supply‐demand imbalance contribute approximately equally to the burden of peri‐operative myocardial infarction. This review critically analyses data of post‐mortem, pre‐operative coronary angiography, troponin surveillance, other pre‐operative non‐invasive investigations, and peri‐operative haemodynamic predictors of myocardial ischaemia and/or myocardial infarction. The current evidence suggests that myocardial oxygen supply‐demand imbalance predominates in the early postoperative period. It is likely that flow stagnation and thrombus formation is an important pathway in the development of a peri‐operative myocardial infarction, in addition to the more commonly recognised role of peri‐operative tachycardia. Research and therapeutic interventions should be focused on the prediction and therapy of flow stagnation and thrombus formation. Plaque rupture appears to be a more random event, distributed over the entire peri‐operative admission.     

Pre‐operative dietary restriction is feasible in live‐kidney donors

van Ginhoven TM, de Bruin RWF, Timmermans M, Mitchell JR, Hoeijmakers JHJ, IJzermans JNM. Preoperative dietary restriction is feasible in live kidney donors.
Clin Transplant 2011: 25: 486–494. © 2010 John Wiley & Sons A/S. Abstract: Dietary restriction (DR), defined as reduced energy intake without malnutrition, confers protection against renal ischemia and reperfusion injury in animal models. This pilot study investigates for the first time the feasibility of pre‐operative DR in the clinical setting. Live‐kidney donors were randomized between pre‐operative DR or ad libitum intake. Seventeen participants were instructed to follow a 30% calorie‐restricted diet, followed by one day of water‐only fasting prior to surgery. Thirteen participants were allowed to eat ad libitum pre‐operatively. Ninety‐four percent of the donors adhered to the diet, 31.4% reduction in caloric intake was achieved. Post‐operative well‐being, appetite and ability to perform daily tasks were not different between both groups. There was no difference in post‐transplant graft function of kidneys obtained from DR donors or control donors as determined by serum creatinine levels during the first post‐operative month and renograms at post‐operative day one. This study shows that mild dietary restriction is feasible in the setting of live‐kidney donation. No effect was observed regarding post‐operative graft function. Additional studies are warranted to investigate the appropriate regimen of dietary restriction to protecting against ischemia and reperfusion injury, such as increasing the magnitude and/or duration of the reduction in daily caloric intake.     

Pre‐operative haemoglobin levels and iron status in a large multicentre cohort of patients undergoing major elective surgery

Pre‐operative anaemia in patients undergoing major surgical procedures has been linked to poor outcomes. Therefore, early detection and treatment of pre‐operative anaemia is recommended. However, to effectively implement a pre‐operative anaemia management protocol, an estimation of its prevalence and main causes is needed. We analysed data from 3342 patients (44.5% female) scheduled for either: elective orthopaedic surgery (n = 1286); cardiac surgery (n = 691); colorectal cancer resection (n = 735); radical prostatectomy (n = 362); gynaecological surgery (n = 203) or resection of liver metastases (n = 122). For both sexes, anaemia was defined by a haemoglobin level < 130 g.l^?1; absolute iron deficiency by ferritin < 30 ng.ml^?1 (< 100 ng.ml^?1, if transferrin saturation < 20% or C‐reactive protein > 5 mg.l^?1); iron sequestration by transferrin saturation < 20% and ferritin > 100 ng.ml^?1; and low iron stores by transferrin saturation > 20% and ferritin 30–100 ng.ml^?1. The overall prevalence of anaemia was 36%, with differences according to the type of surgery. Laboratory parameters allowing classification of iron status were available for 2884 patients. Among those with anaemia (n = 986), 677 (69%) were women, 608 (62%) presented with absolute iron deficiency, 101 (10%) with iron sequestration; and 150 (5%) with low iron stores. Iron status alterations were similar in women with haemoglobin < 130 g.l^?1 or < 120 g.l^?1. For those who were not anaemic (n = 1898), corresponding figures were 656 (35%), 621 (33%), 165 (9%) and 518 (27%), respectively. Anaemia was present in one‐third of patients undergoing major elective procedures. Over two‐thirds of anaemic patients presented with absolute iron deficiency or iron sequestration. Over half of non‐anaemic patients presented with absolute iron deficiency or low iron stores. We consider these data useful for planning pre‐operative management of patients scheduled for major elective surgery.     

The association between peri‐operative acute risk change (ARC) and long‐term survival after cardiac surgery

Acute risk change has been described as the difference in calculated mortality risk between the pre‐operative and postoperative periods of cardiac surgery. We aimed to assess whether this was associated with long‐term survival after cardiac surgery. We retrospectively analysed 22,570 cardiac surgical patients, with minimum and maximum follow‐up of 1.0 and 6.7 years. Acute risk change was calculated as the arithmetic difference between pre‐ and postoperative mortality risk. ‘Rising risk’ represented an increase in risk from pre‐ to postoperative phase. The primary outcome was one‐year mortality. Secondary outcomes included mortality at 3 and 5 years and time to death. Univariable and multivariable analyses were undertaken to examine the relationship between acute risk change and outcomes. Rising risk was associated with higher mortality (5.6% vs. 3.5%, p < 0.001). After adjusting for baseline risk, rising risk was independently associated with increased 1‐year mortality (OR 2.6, 95%CI 2.2–3.0, p < 0.001). The association of rising risk with long‐term survival was greatest in patients with highest baseline risk. Cox regression confirmed rising risk was associated with shorter time to death (HR 1.86, 1.68–2.05, p < 0.001). Acute risk change may represent peri‐operative clinical events in combination with unmeasured patient risk and noise. Measuring risk change could potentially identify patterns of events that may be amenable to investigation and intervention. Further work with case review, and risk scoring with shared variables, may identify mechanisms, including the interaction between miscalibration of risk and true differences in peri‐operative care.