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Acute kidney injury following elective endovascular abdominal aortic aneurysm repair

J. C. Roberts, O. Harryman, P. S. Lancaster, R. Hartley, F. Serracino-Inglott, F. Farquharson and A. C. Pichel

Manchester Royal Infirmary, Manchester, UK

The development of acute kidney injury (AKI) is known to be associated with increased morbidity and mortality. The purpose of this single centre study was to determine the incidence of AKI following endovascular abdominal aortic aneurysm repair (EVAR), identify independent risk factors and describe the relationship between AKI and early and late mortality.

Methods

We collected data prospectively from 267 patients who underwent elective EVAR. Grade of AKI was determined using the Risk, Injury, Failure, Loss and End-stage (RIFLE) consensus criteria. A logistic regression model was selected to identify independent risk factors for AKI and to identify the relationship between peri-operative variables, the development of AKI and outcome.

Results

A total of 25/267 (9.4%) patients developed AKI. There was a significantly higher risk in patients with pre-operative renal impairment (OR 3.7, 95% CI 1.5–8.8, p = 0.002). Patients who developed AKI received a significantly greater volume of radiological contrast compared to those who did not (p = 0.016). Development of any grade of AKI was associated with increased risk of death in hospital (OR 14.5, 95% CI 4.0–51.8).

Discussion

Our study has shown that the incidence of AKI after elective EVAR in our institution was high. Patients with an estimated glomerular filtration rate < 60 ml.min−1 (chronic kidney disease stage 3, 4 and 5) were more likely to develop AKI. The most easily modifiable risk factor in our patients was the dose of contrast agent administered. Institution of local risk assessment and preventative strategies should be undertaken in all patients undergoing EVAR.

Difference in blood pressure measurements between arms in vascular patients

J. Durrand, B. Goodman, E. Kothmann, V. Whittaker and G. Danjoux

James Cook University Hospital and Teesside University, Middlesbrough, UK

Primary care evidence has shown that an inter-arm systolic blood pressure difference (SBPD) ≥15 mmHg occurs in 9.1% of hypertensive patients in the UK, and that this is associated with increased risk of cardiovascular events and all-cause mortality over a 10-year period [1]. National guidelines recommend bilateral BP measurement, with treatment targeted to the higher recording arm [2]. Identification of a discrepancy is critical both to guide secondary risk reduction in the primary care setting, and to facilitate accurate peri-operative monitoring and risk management. The aim of our study was two-fold: to identify the prevalence of a SBPD ≥15 mmHg in vascular surgical patients and to calculate a missed difference number-needed-to-harm (NNH) through the checking of BP in one arm alone at random.

Methods

Vascular pre-assessment at our institution routinely involves contemporaneous BP measurement in both arms, performed using a non-invasive automated calibrated device. We retrospectively reviewed data from patients attending the clinic between 2004 and 2012.

Results

A total of 946 patients were identified, with 245 (25.9%) demonstrating significant SBPD (Table 1). Measurement of BP in only a single arm chosen at random resulted in a NNH of 8 (95% CI 7.1–8.4) to miss a SBPD of ≥15 mmHg.

Table 1. Inter-arm systolic blood pressure difference (SBPD). Values are median (IQR [range]) or number (proportion)
Planned surgeryRevascularisation procedure (n = 222)Carotid endarterectomy (n = 165)Aneurysm repair (n = 545)Other (n = 14)Total (n = 946)
SBPD; mmHg11 (4–18 [0–58])7 (3–14) [0–77])8 (3–14) [0–72])7 (3–11) [1–21])8 (3–15)[ 0–77])
SBPD ≥15 mmHg79 (36%)41 (25%)123 (23%)2 (14%)245 (26%)

Discussion

We have identified a markedly increased prevalence of significant SBPD in vascular patients compared to the general hypertensive population. Failing to identify this peri-operatively could lead to misleading information intra-operatively, and affect BP management. We therefore recommend adhering to NICE guidance [2] in both the primary care and peri-operative setting.

References

  1. Clark CE, Taylor RS, Shore AC, Campbell JL. The difference in blood pressure readings between arms and survival: Primary care cohort study. British Medical Journal 2012; 344: e1327.
  2. National Institute for Health and Clinical Excellence. Hypertension: clinical management of primary hypertension in adults. CG127. NICE, London, UK 2012.

Oxygen consumption before and after major vascular surgery

J. Koch, M. T. Royds, A. F. Nimmo, A. J. Thomson and G. B. Drummond

Royal Infirmary, Edinburgh, UK

Some previous studies have found that resting oxygen uptake (inline image) increases after surgery. For example, in a study using the inverse Fick principle, Older [1] et al reported a 44% increase in inline image after abdominal surgery. This increase has been suggested as a reason why pre-operative cardiopulmonary exercise testing is a useful predictor of outcome. However, other studies do not report an increase in inline image after surgery [2].

Methods

We measured inline image in 26 patients at rest on the evening before, and again about 24 hours after vascular surgery (abdominal aortic aneurysm (AAA) repair or femoral-popliteal bypass (FPB)). Patients breathed air via a tight-fitting face mask attached to a non-rebreathing valve (Hans Rudolph, Shawnee, KS, USA). Expired gases were mixed, dried, and passed through a dry gas meter. Mixed expired O2 (Servomex paramagnetic O2 analyser, Crowborough, E. Sussex, UK), and CO2 (Datex-Ohmeda Normocap capnograph, GE Medical, Hatfield, Herts, UK) fractions were measured at steady state. Expired gas volume was measured over five minutes and inline image was calculated as follows [3]:

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Results

In patients undergoing AAA repair, we found a reduction in mean inline image of 11.4% (95%CI: −23.2 to +0.3%); whereas in patients undergoing FPB mean inline image increased by 1.8% (95%CI: −12.0 to 15.7%) (Figure 1). Beta-blockers were given to 12 out of the 26 patients. inline image did not increase even in patients not on beta blockers.

image

Figure 1. Difference in inline image measurements before and after surgery in individual patients.

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Discussion

We did not observe a rise in inline image after major vascular surgery.

References

  1. Older P, Smith R. Experience with the preoperative invasive measurement of haemodynamic, respiratory and renal function in 100 elderly patients scheduled for major abdominal surgery. Anaesthesia and Intensive Care 1988; 16: 389–95.
  2. Ellison LT, Duke JF, Strickland GW, et al. Oxygen requirements in the early postoperative period (48 hours): ventilation and respiratory exchange. Annals of Surgery 1966; 163: 559–66.
  3. Ultman JS, Bursztein S. Analysis of error in the determination of respiratory gas exchange at varying FIO2. Journal of Applied Physiology 1981; 50: 210–6.

Peri-operative antiplatelet therapy for carotid endarterectomy

C. Halloran, R. Kukreja and R. Heames

University Hospital Southampton, Southampton, UK

The role and urgency of carotid endarterectomy (CEA) in the prevention of stroke is clearly recognised [1]. There are no specific guidelines regarding the management of antiplatelet agents in the peri-operative period for patients undergoing CEA. We carried out a national survey to establish the degree of variation in prescribing practice throughout the UK.

Methods

Vascular Anaesthesia Society members were asked to complete a survey of their antiplatelet prescribing practice in the CEA peri-operative period.

Results

A total of 44 surveys were completed (Table 2).

Table 2. Survey results regarding timings of cessation of antiplatelet agents in patients undergoing carotid endarterectomy. Values are number (proportion)
Single agent
1 week5 days1 dayDo not stop
Aspirin0 (0%)1 (2%)1 (2%)42 (96%) (42)
Dipyridamole8 (20%)4 (10%)1 (2%)27 (68%)
Clopidogrel14 (33%)1 (2%)2 (5%)26 (60%)
Dual agent (aspirin plus)
Dipyridamole11 (26%)4 (9%)1 (2%)27 (63%)
Clopidogrel16 (37%)2 (5%)2 (5%)23 (53%)

Discussion

Our survey showed significant variation in antiplatelet prescribing in patients undergoing CEA. We advocate the continuation of established antiplatelet agents to prevent peri-operative stroke, the benefit of which we feel outweighs the risk of bleeding during surgery. This survey highlights the need for data collection on stroke rates between differing antiplatelet prescribing practices to formulate a national prescribing guideline.

Reference

  1. National Institute for Health and Clinical Excellence. Stroke: Diagnosis and initial management of acute stroke and transient ischaemic attack (TIA). CG 68. NICE, London, UK 2008.

Predicting respiratory failure in abdominal aortic aneurysm Repair

J. Whing, S. Grant and C. McCollum

University Hospital of South Manchester, Manchester, UK

Our study aims to develop a multivariate risk prediction model for postoperative respiratory failure following abdominal aortic aneurysm (AAA) repair.

Methods

Data was collected on consecutive patients undergoing AAA repair between September 2000 and June 2011 in the North West of England. Data was split randomly in a 70:30 ratio into development and validation datasets. Logistic regression analysis was performed on development datasets for all AAA repairs and open repairs to identify risk factors for postoperative respiratory failure. The area under the receiver-operator curve (ROC) was used to assess the performance of the models. Data on a sub-cohort of patients who underwent preoperative cardiopulmonary exercise testing was also analysed using univariate and multivariate statistical techniques.

Results

A total of 164 patients (8.9%) had respiratory failure. Independent variables found to be associated with postoperative respiratory failure were respiratory disease, open repair and antihypertensive medication. The risk factors in open repair only were age > 75 years, antihypertensive medication and respiratory disease. The area under the ROC curve for all repairs was 0.72 and 0.71 for the developmental and validation data sets respectively and 0.65 and 0.63 for open repairs, indicating moderate discriminatory ability. Analysis of the cardiopulmonary exercise testing database showed that 15.7% of patients undergoing open repair developed postoperative respiratory failure and FeV1/FVC < 75% was the only predicting factor.

Discussion

Our multivariate prediction model predicted respiratory failure in both the developmental and validation subsets, however it is limited by the impact of missing data in the validation dataset.

Randomised trial of fibrinogen concentrate in major aortic surgery

J. Koch, G. A. Morrison, M. T. Royds, R. T. A. Chalmers, D. McGee and A. F. Nimmo

Royal Infirmary, Edinburgh, UK

During thoraco-abdominal aortic aneurysm (TAAA) repair, massive haemorrhage is common; this may result from both surgical bleeding and coagulopathy. After major blood loss, a low fibrinogen concentration is typically the first abnormality that impairs haemostasis. Fresh frozen plasma (FFP) and/or cryoprecipitate are commonly used to correct hypofibrinogenaemia. An alternative is to use a freeze-dried fibrinogen concentrate.

Methods

After ethics committee approval and with informed consent, patients undergoing repair of extent-4 TAAA (without the use of a bypass circuit) were randomised to receive either a continuous infusion of fibrinogen concentrate (RiaSTAP®, CSL Behring, Marburg, Germany) or FFP to treat hypofibrinogenaemia. Low fibrinogen concentration and other causes of impaired haemostasis were diagnosed by point-of-care ROTEM® thromboelastometry analysis (TEM Intl, Munich, Germany) performed every 30–60 min during surgery, and at two and 24 h after the end of surgery. Platelets were transfused on the basis of ROTEM results and a pre-defined protocol. In the fibrinogen group, FFP was also given according to a pre-defined protocol if a ROTEM result during surgery indicated markedly reduced concentrations of coagulation factors other than fibrinogen or if the prothrombin (PT) and/or activated partial thromboplastin time (APTT) results after surgery were more than twice normal.

Results

To date, seven patients have been randomised to receive fibrinogen concentrate and 5 to receive FFP. There have been no deaths. One patient required re-operation for haemorrhage immediately after surgery and a bleeding artery was found. There were no other postoperative bleeding or thrombotic complications (Table 3).

Table 3. Patients randomised to fresh frozen plasma (FFP) or fibrinogen concentrate (FIB) during major vascular surgery. HDU, high dependency unit; ICU, intensive care unit
Blood loss; lRed cells; unitsPlatelets; unitsFIB; gFFP;units in theatreFFP;units in HDU/ICU
FFP8.5410120
FFP16.51330250
FFP4.9400100
FFP11.4620200
FFP9.3930160
FIB8.740800
FIB4.10011.800
FIB530800
FIB12.21211822
FIB11.88317.502
FIB6.330600
FIB9.7911001

Discussion

In extent 4-TAAA surgery with blood loss of up to approximately 10 litres, treatment with fibrinogen may be sufficient to correct impaired haemostasis without the need for FFP.

Renal protection with N-Acetylcysteine during endovascular surgery

P. Featherstone, A. Ercole and P. Bradley

Addenbrookes Hospital, Cambridge, UK

Many patients undergoing endovascular abdominal aortic aneurysm repair (EVAR) have pre-existing chronic kidney disease (CKD). Previous studies have demonstrated a high incidence of subclinical renal injury following EVAR [1] and approximately 2.5% of patients [2] experience a period of clinically significant renal dysfunction as defined by the Risk, Injury, Failure, Loss and End-stage (RIFLE) consensus criteria. The aetiology of renal injury in EVAR is multifactorial, but the use of contrast media during the procedure may be a contributory factor. Meta-analyses have shown that N-Acetylcysteine (NAC) reduces the incidence of contrast-induced nephropathy in patients with CKD undergoing contrast-enhanced computed tomography and coronary angiography [3]. Whilst no randomised controlled trials have examined the effectiveness of NAC in patients with CKD undergoing EVAR, its use in this patient population has become relatively common practice. We undertook a retrospective service evaluation to assess the effectiveness of this intervention.

Methods

This service evaluation was registered and approved by our institution. We identified 30 patients with pre-existing CKD stage-3 undergoing elective EVAR between 2007 and 2011 under the same pair of consultant vascular surgeon and anaesthetist. Patient case notes were reviewed and patients divided into those who had received standard care with or without 1.2 g intravenous NAC. Serum creatinine and estimated glomerular filtration rate (eGFR) measured pre-operatively and one day, three to six months, and one-year postoperatively were obtained where available.

Results

Notes were available for 28 patients, 12 of whom had received NAC. There were no significant differences in baseline demographics between the two groups. Pre- and day-one postoperative laboratory results were available for all patients; those at three to six months and one-year postoperatively were available for five patients receiving standard care and four receiving standard care and NAC. No patient developed clinically significant renal dysfunction. Statistical analysis was undertaken and we found no statistically significant differences in mean serum creatinine or eGFR within or between groups at any time point.

Discussion

This service evaluation showed neither clinical nor statistically significant benefit of NAC in patients with CKD undergoing EVAR and therefore its use cannot be recommended in this context.

References

  1. Moore NN, Lapsley M, Norden AG, et al. Does N-Acetylcysteine prevent contrast-induced nephropathy during endovascular AAA repair? A randomised controlled pilot study. Journal of Endovascular Therapy 2006; 13: 660–6.
  2. Boyle JR, Thompson MM. Endovascular abdominal aortic aneurysm repair is less invasive, now we must prove its efficacy. Journal of Endovascular Therapy 2003; 10: 16–9.
  3. Birck R, Krzossok S, Markowetz F, et al. Acetylcysteine for prevention of contrast-induced nephropathy: a meta-analysis. Lancet 2003; 362: 598–603.

Thoracic and fenestrated endovascular aortic repair: outcomes from a newly formed specialised vascular unit

J. L. Gross, A. Shida, B. Rodda and S. Loganathan

Royal Free Hospital, London, UK

Endovascular aortic repair (EVAR) may provide a treatment option for aortic aneurysm in patients unfit for open repair [1]. The majority of EVAR is undertaken infra-renally. Aortic repair more proximally provides a greater challenge and fenestrated grafts are required at the levels of the renal, superior mesenteric and coeliac branches to prevent renal dysfunction and bowel ischaemia. As the aorta supplies the spinal cord at this level, spinal cord ischaemia is a further significant risk. Outcome data on thoracic and fenestrated EVAR are sparse. We present results from our newly formed vascular unit, established on 1st April 2012.

Methods

All patients undergoing EVAR between 1st May and 15th July 2012 were prospectively analysed. Outcome data included: mean surgical time; intensive care unit (ICU) admission rate and length of stay (LOS); graft-related complications; postoperative acute kidney injury (AKI) as defined by the Risk, Injury, Failure, Loss and End-stage (RIFLE) consensus criteria; bowel ischaemia; lower limb weakness; hospital LOS; and in-hospital mortality. Patients were followed up until the time of hospital discharge.

Results

From the 28 patients undergoing EVAR, 12 patients (43%) underwent elective fenestrated EVAR (f-EVAR) and a further two patients (7%) had thoracic non-fenestrated EVAR (t-EVAR). In the f-EVAR group, 7 (58%) were male and mean (SD) age was 70.0 (9.4) years; 11 (92%) patients were ASA physical status 3 or 4. The remaining patient was ASA 2. Four patients (33%) had spinal drains inserted pre-operatively and duration of surgery was 8.0 (2.3) hours. Eleven patients (92%) were admitted to the ICU postoperatively with a length of stay (LOS) of 7.3 (11.3) days. With regards to outcome, three patients (25%) had endoleak (with one requiring immediate re-intervention), two (17%) had AKI, no patient developed bowel ischaemia and one patient developed paraplegia. This patient had repair involving the aortic arch following a 1st stage carotid to subclavian by-pass (a solitary case) who subsequently died. There was one other in-hospital death (8%). Mean (SD) hospital LOS was 8.8 (5.4) days amongst survivors. In the t-EVAR group, both patients were male with a mean (SD) age of 78.0 (11.3). One patient had a spinal drain, duration of surgery was 2.3 (0.4) hours and neither went to ICU post-operatively. There was no endoleak, AKI, bowel ischaemia or any other significant complication. Mean (SD) hospital LOS was 3.0 (1.4) days.

Discussion

Our results show short-term outcomes in a cohort of patients undergoing highly complex endovascular aortic repair. This may provide a treatment option in a new subset of patients that would otherwise be unsuitable or very high risk for open repair. The importance of continued surveillance and long-term follow-up in this patient group cannot be over-emphasised. Research should focus on factors that may improve outcome.

Reference

  1. The United Kingdom EVAR Trial Investigators. Endovascular Repair of Aortic Aneurysm in Patients Physically Ineligible for Open Repair. New England Journal of Medicine 2010; 362: 1872–80.