Evaluation of prognostic risk models for postoperative pulmonary complications in adult patients undergoing major abdominal surgery: a systematic review and international external validation cohort study

BACKGROUND

Stratifying risk of postoperative pulmonary complications after major abdominal surgery allows clinicians to modify risk through targeted interventions and enhanced monitoring. In this study, we aimed to identify and validate prognostic models against a new consensus definition of postoperative pulmonary complications.

METHODS

We did a systematic review and international external validation cohort study. The systematic review was done in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. We searched MEDLINE and Embase on March 1, 2020, for articles published in English that reported on risk prediction models for postoperative pulmonary complications following abdominal surgery. External validation of existing models was done within a prospective international cohort study of adult patients (≥18 years) undergoing major abdominal surgery. Data were collected between Jan 1, 2019, and April 30, 2019, in the UK, Ireland, and Australia. Discriminative ability and prognostic accuracy summary statistics were compared between models for the 30-day postoperative pulmonary complication rate as defined by the Standardised Endpoints in Perioperative Medicine Core Outcome Measures in Perioperative and Anaesthetic Care (StEP-COMPAC). Model performance was compared using the area under the receiver operating characteristic curve (AUROCC).

FINDINGS

In total, we identified 2903 records from our literature search; of which, 2514 (86·6%) unique records were screened, 121 (4·8%) of 2514 full texts were assessed for eligibility, and 29 unique prognostic models were identified. Nine (31·0%) of 29 models had score development reported only, 19 (65·5%) had undergone internal validation, and only four (13·8%) had been externally validated. Data to validate six eligible models were collected in the international external validation cohort study. Data from 11 591 patients were available, with an overall postoperative pulmonary complication rate of 7·8% (n=903). None of the six models showed good discrimination (defined as AUROCC ≥0·70) for identifying postoperative pulmonary complications, with the Assess Respiratory Risk in Surgical Patients in Catalonia score showing the best discrimination (AUROCC 0·700 [95% CI 0·683-0·717]).

INTERPRETATION

In the pre-COVID-19 pandemic data, variability in the risk of pulmonary complications (StEP-COMPAC definition) following major abdominal surgery was poorly described by existing prognostication tools. To improve surgical safety during the COVID-19 pandemic recovery and beyond, novel risk stratification tools are required.

FUNDING

British Journal of Surgery Society.

1536 Neuroanatomy, Not Just for Budding Neurosurgeons. Motivations for Participating in An Extra-Curricular Neuroanatomy Course for Undergraduates

Introduction

Extra-curricular activities form an important part of undergraduate education as they give students the opportunity to explore subjects of interest. There is significant demand within the undergraduate population for further teaching in neuro-related specialities. The aim of this online twelve-week course was to provide neuroanatomy teaching in greater breadth and detail than possible in the undergraduate curriculum. We sought to gauge motivations for involvement.

Method

Delegates (n = 166) from six UK universities were asked to complete a short questionnaire examining motivations and future career plans prior to the course beginning, only those who consented were involved further in the analysis (n = 98).

Results

Motivations for involvement were predominantly to develop a greater understanding of neuroanatomy (63.3%), to support career plans (13.3%) or to support preparation for an examination or competition (8.2%). The majority (56.1%) had no particular speciality in mind. For those who did, a range of specialities including neurosurgery (24.5%), neurology (8.2%) was given.

Conclusions

There is clear interest within the undergraduate population for more specialised extra-curricular activities in addition to conventional experiences such as conferences. Online courses run over multiple weeks provide further scope for depth and exploration of subjects in further detail. In this course, the majority of delegates did not have a particular speciality in mind, demonstrating neuroanatomy to be a popular subject regardless of potential career plans. For students looking to pursue a career in neuro-related specialities, courses are perceived as important opportunities to support future career development.

1520 Decoding Neurophobia – Insights from an Undergraduate Neuroanatomy Course

Introduction

Neurophobia is a common multifaceted issue amongst students studying medical sciences at an undergraduate level associated with difficulty in understanding neuroscience topics and ongoing negative perceptions of clinical neurosciences. We sought to examine whether neurophobia was present even amongst students who participated in an extracurricular neuroanatomy teaching course.

Method

Prior to the beginning of a twelve-week online neuroanatomy course, delegates were asked to complete a short questionnaire examining perceptions of neurophobia and specialities of interest. This was repeated after the course. This course was open to all undergraduate students in the UK and covered material beyond the remits of the undergraduate curriculum.

Results

From the 166 signups, 98 students completed the pre-course questionnaire. As expected, the majority of students (n = 83) taking part did not identify as neurophobic, describing the subject area as ‘interesting’, ‘enjoyable’ and ‘challenging’. Students who identified as neurophobic described neuroanatomy as ‘complex’ or ‘overwhelming’. Some students (n = 12) continued to describe themselves as neurophobic at the end of the course, despite this 7 of those students continue to consider a future career in a neuro-related speciality.

Conclusions

The fact that students with Neurophobia attended this extra-curricular course speaks volumes of how perception and self-motivation of a student are important for learning a subject. All students who participated in this course recognised the complexity and interesting nature of neuroanatomy. This experience highlights the challenge of medical educators to provide teaching experiences that are stimulating and enjoyable, but not overwhelming.

Successful percutaneous treatment of anomalous left coronary artery from pulmonary artery

Anomalous origin of the left main coronary artery from the pulmonary artery (ALCAPA) is an uncommon congenital condition seen in the adult population, with most patients developing symptoms in infancy. We describe successful closure of an ALCAPA in an adult using a percutaneous transcatheter approach in a patient with evidence of anterior wall ischemia believed to be the consequence of myocardial steal. A 30-year-old female was noted to have continuous flow in the right ventricular septum on transthoracic echocardiography, with subsequent imaging confirming the presence of an ALCAPA. Myocardial perfusion imaging confirmed anterior wall ischemia, and as a strategy to optimize coronary perfusion pressure, the patient underwent percutaneous ALCAPA closure using an Amplatzer vascular plug. The procedure was well tolerated, with no evidence of anterior ischemia or myocardial dysfunction. Follow up perfusion imaging demonstrated no residual anterior wall ischemia. Transcatheter closure of an ALCAPA is a potentially safe and effective alternative treatment strategy in this patient population.

Pregnancy complicated by heart disease: a review of Canadian experience

The physiological adaptations to pregnancy can potentially worsen the prognosis in women whose pregnancy is complicated by heart disease. A comprehensive systematic approach to risk identification is desirable. The ability to predict a subgroup of women that are at a particularly increased risk of pregnancy-related complications can enhance the obstetric care we provide to this population. A retrospective review of 276 pregnancies associated with pre-existing heart disease was undertaken in three Toronto teaching institutions. During the course of the pregnancy, 45 (18%) of 252 completed gestations were complicated by adverse cardiovascular events (congestive heart failure, arrhythmia and stroke). Poor maternal functional class or cyanosis, myocardial dysfunction, left heart obstruction, prior arrhythmia and prior cardiac events were predictive of maternal cardiac complications. These predictors were converted into a point score. If a point score was 0, 1 or more than 1, the risk of a given patient running into cardiovascular complication was 3%, 30% and 66%, respectively. The Canadian Prospective Multicenter Study offered the validation of this prediction rule. In this study, 13 centres recruited prospectively 599 patients with completed gestations. Similar factors were identified in their ability to predict adverse cardiac events. In addition, neonatal complications (20% of pregnancies) were associated with poor functional class or cyanosis, left heart obstruction, anticoagulation, smoking and multiple gestation. A sample of this prospective cohort (302 pregnancies) was compared to 572 matched pregnancies with no underlying heart disease. The neonatal complication rate was higher in the study group when compared to controls, 18% versus 7%, respectively. The highest neonatal complication rate (33%) was seen in gravidas with underlying heart disease who had previously identified cardiac risk factors, were at both extremes of reproductive age, had obstetrical risk factors, smoked or received anticoagulants. Both maternal and neonatal morbidity are increased significantly in gravidas with pre-existing heart disease, although mortality is low. Factors that place the mother and the neonate at risk can be identified before pregnancy. This allows informed counselling and development of a patient-specific management plan.

Early detection of protein depletion in alcoholic cirrhosis: role of body composition analysis

BACKGROUND

Malnutrition is common in alcoholic cirrhosis. Bedside nutritional assessment techniques may be unreliable in patients with chronic liver disease. The aim of this study was to quantify changes in body composition and compare methods for measuring body composition in alcoholic cirrhosis.

METHODS

Thirty-eight men with alcoholic cirrhosis were compared with 16 age-matched healthy men. Body composition was assessed using anthropometry and bioelectrical impedance to determine fat-free mass and body fat, deuterium oxide dilution to measure total body water, in vivo neutron activation analysis to measure total body protein, and dual energy x-ray absorptiometry to measure bone mineral content and total body fat mass.

RESULTS

With increasing severity of cirrhosis, total body water increased, whereas total body protein decreased with a significant decrease in serum albumin levels. Total body protein levels, expressed as an index, were a more sensitive indicator of protein depletion than serum albumin levels. When patients were assessed by anthropometry and bioelectrical impedance for fat-free mass, there was no reduction compared with controls.

CONCLUSIONS

Anthropometry and bioelectrical impedance do not accurately reflect changes in body composition associated with chronic liver disease. Quantification of body composition changes in alcoholic cirrhosis requires the use of direct methods such as in vivo neutron activation analysis, dual energy x-ray absorptiometry, or deuterium oxide dilution.

Glomerular hyperfiltration in patients with well-compensated alcoholic cirrhosis

BACKGROUND

Peripheral and splanchnic arteriolar tone is often decreased in patients with cirrhosis. The responsible circulating vasodilator(s) would be expected to also lower renal vascular resistance. To examine this possibility we have undertaken a hemodynamic study of the renal circulation in patients with stable, well characterized, compensated cirrhosis and in healthy controls of similar age and sex.

METHODS

Clearance techniques were used to assess splanchnic and renal hemodynamics and hepatocellular function.

RESULTS

Renal vascular resistance was significantly reduced in the cirrhotic patients (P = 0.048) and was accompanied by a significant (P = 0.014) and proportional (r = -0.45; P = 0.016) increase in glomerular filtration rate. The hepatic extraction of indocyanine green, a measure of functional intrahepatic portasystemic shunts, was the only independent predictor of glomerular filtration rate (r = -0.65; P = 0.002).

CONCLUSIONS

The results support the hypothesis that, in patients with cirrhosis, the presence of portasystemic shunts results in an increased delivery of endogenous vasodilator(s) into the systemic circulation where their principal action on the renal circulation is to preferentially decrease afferent arteriolar tone. The resultant glomerular hyperfiltration may contribute to the pathogenesis of cirrhotic glomerulosclerosis.

Increased sympathetic nervous activity and the effects of its inhibition with clonidine in alcoholic cirrhosis

OBJECTIVE

To study disturbances in sympathetic nervous system function in patients with alcoholic cirrhosis and the effect of clonidine on such disturbances.

DESIGN

Cross-sectional physiologic and neurochemical evaluation of patients with cirrhosis and of healthy controls; an uncontrolled trial of intravenous clonidine in the cirrhotic patients.

PATIENTS

Forty-four hospitalized patients with biopsy-proven alcoholic cirrhosis and 31 healthy controls.

INTERVENTIONS

Intravenous clonidine.

MAIN OUTCOME MEASURES

Radiotracer-derived measures of norepinephrine release to plasma, central hemodynamics, wedge hepatic vein pressure, and measures of renal function.

MAIN RESULTS

In patients with cirrhosis, clonidine reduced previously elevated norepinephrine overflow rates for the whole body, kidneys, and hepatomesenteric circulation. This sympathetic inhibition was accompanied by the following potentially clinically beneficial effects: the lowering of renal vascular resistance (median reduction, 24%; 95% CI, 14% to 31%), the elevation of glomerular filtration rate (median increase, 27%; CI, 14% to 39%), and the reduction of portal venous pressure (median reduction, 25%; CI, 18% to 32%). The norepinephrine and hemodynamic responses to graded clonidine dosing (1, 2, and 3 micrograms/kg body weight intravenously) indicated that the sympathetic outflow to the hepatomesenteric circulation was more sensitive to pharmacologic suppression with clonidine than was the sympathetic outflow to the systemic circulation.

CONCLUSIONS

The sympathetic nerves to the kidneys, heart, and hepatomesenteric circulation are stimulated in patients with cirrhosis. Clonidine inhibits these activated sympathetic outflows differentially, which could possibly provide a basis for the selective pharmacologic treatment of portal hypertension in patients with cirrhosis.

Normal diet NaCl variation can affect the renal set-point for plasma pH-(HCO3-) maintenance

In humans who are ingesting abundant NaCl, blood pH (pHb) and plasma bicarbonate concentration [HCO3-)p) change little or imperceptibly in response to the ingestion of alkali salts. We tested the hypothesis that such tight homeostatic regulation is an artifact of eating a culturally imposed NaCl-enriched diet, not a fundamental physiological trait of humans. In five normal men ingesting a constant acid-producing diet with a low intrinsic NaCl content (0.15 mEq/kg of body weight per day), we measured plasma and urine acid-base composition during four 7-day periods in which the diet was supplemented as follows: no supplements----NaHCO3 only----NaHCO3 plus NaCl----NaCl only. Each sodium supplement was 2.0 mmol/kg body weight per day. With no supplements, pHb was 7.43 +/- 0.005 and (HCO3-)p was 25.0 +/- 0.4 mEq/L. When NaHCO3 only was added, pHb rose 0.02 (to 7.45 +/- 0.004; P less than 0.01) and (HCO3-)p rose nearly 4 mEq/L (to 28.9 +/- 0.6 mEq/L, P less than 0.001). The rise in (HCO3-)p was sustained predominantly by an increased rate of renal bicarbonate reabsorption. When NaCl was added, (HCO3-)p returned to the earlier level, despite continued NaHCO3 supplementation (24.9 +/- 0.6 mEq/L), and remained there when NaHCO3 supplementation was subsequently stopped (24.1 +/- 0.5 mEq/L). Thus, tight homeostatic regulation of plasma acid-base composition in response to a change in dietary base occurred only when dietary NaCl was abundant. To our knowledge, this is the first study in normal humans that demonstrates that diet NaCl variations within the normal range significantly influence plasma acid-base composition.(ABSTRACT TRUNCATED AT 250 WORDS)

Dietary potassium influences kidney maintenance of serum phosphorus concentration

In studying the metabolic effects of diet potassium (K+) variation in normal humans, we noted that varying diet K+ within its normal range influenced inorganic phosphorus (Pi) homeostasis and serum calcitriol (1,25-dihydroxyvitamin D) levels. In six men who ingested a constant whole-foods diet containing (per 70 kg body wt) 27 mmol/day Pi and 52 mEq/day K+, we increased diet K+ to 156 mmol/day with supplements first of potassium bicarbonate (KHCO3) alone and then of potassium chloride (KCL) alone, each for eight days interrupted by an eight-day recovery period of no K+ supplement. Urine Pi decreased promptly with either K(+)-salt, each inducing a persisting retention of 7 to 10 mmoles Pi, which was dumped during recovery. Fasting serum [Pi] increased with either K+ supplement (P = 0.022, repeated measures analysis of variance); the composite mean serum [Pi] for the two K(+)-supplement periods exceeded that for the two periods without supplements (P less than 0.01, paired t-test). Conversely, the concentrations of serum calcitriol decreased with either K+ supplement (P = 0.020). Among subjects, the diet K(+)-induced increases in serum [Pi] correlated with those in plasma [K+] (r = 0.64, P = 0.027); the decreases in serum calcitriol concentration correlated with the increases in serum [Pi] (r = -0.69, P = 0.014). There were no significant differences among periods in serum parathyroid hormone, ionized calcium, urine cyclic AMP excretion, plasma renin activity, body weight, serum albumin, or creatinine clearance; plasma volume decreased slightly during KCL but not during KHCO3 periods.(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatic extraction of morphine is impaired in cirrhosis

Using hepatic vein catheterization this study has provided the first direct measurement of morphine hepatic extraction in 8 controls and 8 cirrhotics. The extraction ratio was 0.52 in the control group and was reduced by 25% in the cirrhotics. This reduction is due to impaired enzyme capacity rather than reduced blood flow. The effect of cirrhosis is less than that reported in similar studies of high clearance oxidized drugs and this lends support to the concept that glucuronidation may be relatively spared in cirrhosis. A discrepancy between the systemic clearance and the hepatic clearance provides indirect support for extra-hepatic metabolism of morphine.

Serial assessment of glomerular filtration rate in lupus nephropathy

In patients with lupus nephropathy (LN), previous studies have shown that creatinine clearance (CCr) overestimates true glomerular filtration rate as measured by inulin clearance (CIn), and that among patients the degree of overestimation is highly variable. We sought to determine whether the discrepancy between CCr and CIn remains constant over time (months, years) in each individual patient, and therefore whether serial measurements of CCr reliably reflect the direction and magnitude of change in CIn. Twenty-five patients with LN underwent simultaneous determinations of CCr and CIn performed two to four (mean 3.3) times over three years. In a given patient, it was found that the ratio of CCr/CIn changed substantially over time (mean SD 0.16 with 95% confidence interval of 0.12 to 0.20). Thus, in about 32% of cases the ratio of CCr/CIn will vary more than +/- 16% from a previously measured value of CCr/CIn. Patients with both high and low values of CIn showed similar variability in CCR/CIn over time. Variability in CCr/CIn was found regardless of whether CIn was increasing, decreasing, or constant over time. In nearly one-half of all measurements of CCr, the corresponding change in CIn was directionally discordant. Iothalamate and technetium-DTPA renal clearances correlated highly with CIn (R2 = 0.99). We conclude that the discrepancy between CCr and CIn can vary greatly over time in an individual patient. Consequently, serial CCr does not accurately measure the direction or magnitude of change in glomerular filtration rate in lupus nephropathy.

Dietary NaCl determines severity of potassium depletion-induced metabolic alkalosis

It is uncertain whether, in humans, potassium depletion can cause or sustain metabolic alkalosis of clinically important degree in the absence of coexisting known alkalosis-producing conditions. Previously we found, in normal humans ingesting abundant NaCl, that dietary K+ depletion alone can induce and sustain a small decrease in blood acidity and increase in plasma bicarbonate concentration; we hypothesized that more severe alkalosis was prevented by mitigating mechanisms initiated by renal retention of dietary NaCl that was induced by K+ depletion. To ascertain the acid-base response to dietary K+ depletion under conditions in which the availability of NaCl for retention is greatly limited, in the present study of six normal men we restricted dietary K+ as in the previous study except that intake of NaCl was maintained low (2 to 7 mEq/day, Low NaCl Group) instead of high (126 mEq/day, High NaCl Group). Plasma acid-base composition and renal net-acid excretion (NAE) did not differ significantly between groups during the control period. In the steady state of K+ depletion (days 11 to 15 of K+ restriction), neither plasma K+ concentration (2.9 +/- 0.9 mEq/liter vs. 3.0 +/- 0.1 mEq/liter) nor cumulative K+ deficit (399 +/- 59 mEq vs. 466 +/- 48 mEq) differed significantly between groups. During K+ restriction, persisting metabolic alkalosis developed in both groups, which was more severe in the Low NaCl Group: increment in [HCO3-]p, 7.5 +/- 1.0 mEq/liter versus 2.0 +/- 0.3 mEq/liter, P less than 0.001; decrement in [H+]p, 5.5 +/- 0.6 nEq/liter versus 2.9 +/- 0.4 nEq/liter, P less than 0.003. A significantly more severe alkalosis in the Low NaCl Group was evident at all degrees of K+ deficiency achieved during the course of the 15 days of K+ restriction, and the severity of alkalosis in the Low NaCl Group correlated with the degree of K+ deficiency. During the generation of alkalosis (days 1 to 7 of K+ restriction), NAE increased in the Low NaCl Group whereas it decreased in the High NaCl Group. During the maintenance of alkalosis (days 11 to 15), NAE stabilized in both groups after it returned to values approximating the control values. In both groups, urine Cl- excretion decreased during K+ restriction even though Cl- intake had not been changed, with the result that body Cl- content increased negligibly in the Low NaCl Group (28 +/- 6 mEq) and substantially in the High NaCl Group (355 +/- 64 mEq).(ABSTRACT TRUNCATED AT 400 WORDS)

The management of acutely bleeding varices by injection sclerotherapy

Acutely bleeding varices present a therapeutic dilemma because of the limited efficacy and high complication rates of conventional treatments. Over a period of 26 months, 56 episodes of acutely bleeding varices were treated with injection sclerotherapy as the initial management. Immediate control of haemorrhage was achieved in 91% of patients and control of bleeding during the hospital admission in 84%. Balloon tamponade and surgery were reserved for those patients in whom bleeding was not controlled by sclerotherapy; in 66% of patients the bleeding was controlled by sclerotherapy alone. Of the 56 episodes, 75% survived their admission to hospital. Acute injection sclerotherapy is as least as effective as conventional therapies in the control of bleeding with a low incidence of complications. The technique can be used in all patients irrespective of the severity of their liver disease and, when bleeding is controlled, allows the physician the choice of all the available prophylactic therapies.

Hypocomplementaemia fails to prevent acute-phase stimulation of fibrinogen synthesis

Fibrinogen synthesis rates of normocomplementaemic and hypocomplementaemic rats were measured after turpentine injection using the 14C-carbonate technique and a liver perfusion system. In both groups of animals turpentine administration caused a significant increase (P less than 0,01) in fibrinogen synthesis rates, but no significant difference was observed between the two groups. These results suggest that complement does not play an important role in the genesis of the fibrinogen acute-phase reaction.

Neutropenia fails to prevent the acute phase stimulation of fibrinogen synthesis

This study evaluates the role of neutrophil granulocytes in mediating acute phase stimulation of fibrinogen synthesis. Turpentine was administered to neutropenic and non-neutropenic rats and fibrinogen synthetic rates measured in an isolated liver perfusion system. Using the (14C) carbonate technique for the measurement of the absolute synthetic rates of liver produced plasma proteins it was observed that the rates of fibrinogen synthesis of the neutropenic and non-neutropenic rats were significantly greater (p less than 0.01) than those of normal control animals, but were not significantly different from each other. These results suggest that the neutrophil granulocyte may not be of major importance in mediating acute phase stimulation of fibrinogen synthesis.

Papilledema without peripheral neuropathy in a patient taking perhexiline maleate

Perhexiline maleate is an agent currently under investigation in Canada that is used for angina unresponsive to other treatment. This paper describes a possible side effect previously unreported--papilledema not associated with peripheral neuropathy.