#4893 THE INCIDENCE, RISK FACTORS AND OUTCOMES OF ACUTE KIDNEY INJURY AFTER MINOR LOWER LIMB AMPUTATIONS
Authors: Agius Stefanie Marie , Balzan Deborah , Cassar Kevin , Buttigieg Jesmar 
Published: June 2023

Abstract

Background and Aims
Minor lower limb amputations (toe amputations and/or amputations distal to or through the tarsometatarsal joint), are limb and potentially lifesaving procedures. However, they are associated with serious adverse events including acute kidney injury (AKI). The aim of this study was to determine the incidence of AKI after such interventions, identify potential risk factors and assess impact on patient survival.

Method
This was a single centre retrospective study involving patients who underwent minor lower limb amputations at Mater Dei Hospital Malta between January and December 2019. Patient and procedure details were obtained from hospital records. Estimated glomerular filtration rate (eGFR) was calculated using the Modification of Diet in Renal Disease formula. Chronic kidney disease (CKD) was defined as per Kidney Disease: Improving Global Outcomes (KDIGO) criteria. AKI was defined using Acute Kidney Injury Network (AKIN) criteria or KDIGO criteria if day 7 serum creatinine was available. Statistical analysis was performed using SPSS Statistics for Windows v21.0 (IBM Corp.).

Results
A total of 201 patients were included; males 69.7%, mean age 70.4 ±11.5 years, 87.1% had diabetes mellitus, 71.1% hypertension and 26.4% had ischemic heart disease. Pre-existing CKD was identified in 35.8%; 16.4% CKD stage 3a, 13.4% CKD stage 3b, 5.5% CKD 4 and 1 patient CKD 5. The majority (76.1%) underwent single toe amputations. Surgery was performed under loco-regional anaesthesia in 90% of patients, mostly in view of lower limb ulcers (64.7%) or gangrene (29.4%). A cohort of 54 (26.9%) patients received iodine based contrast within 7 days of procedure, including those who underwent bypass surgery (8%) and endarterectomy (4%). The incidence of AKI after minor lower limb amputations using AKIN criteria was 18.9%. An additional 12 patients were identified using KDIGO criteria (24.9%), however KDIGO criteria could only be applied for 123 patients as the rest did not have a day 7 serum creatinine. Most developed stage 1 AKI (18.4%), one patient developed stage 2 AKI and none developed stage 3 AKI using AKIN criteria. Only 1 patient needed temporary haemodialysis having developed AKI after day 3 post-operatively fulfilling KDIGO but not AKIN criteria. Recovery of kidney function occurred in all patients. All-cause mortality at 30 days, 60 days and 18 months (end of follow-up) was 2.0%, 5.5% and 19.9% respectively. None of the deaths were directly related to the AKI-amputation event. Patients who developed AKI, compared to those who did not, were more likely to have an eGFR &lt;45ml/min/1.73 m2 at the time of procedure (39.5% vs. 14.7%, p = 0.001). They were significantly older (73.0 ±10.4 vs. 68.5 ±11.8 years, p = 0.033), and more likely to have underlying chronic obstructive pulmonary disease (COPD) (28.9% vs. 13.5% p = 0.028). Use of loop and/or thiazide diuretics (68.4% vs. 49.1%, p = 0.049), fluoroquinolones (71.1% vs. 52.8% p = 0.047) and/or carbapenems (10.5% vs. 2.5%, p = 0.043) was also more frequent in this group. Use of iodine based contrast within 7 days of procedure did not effect incidence of AKI. Hospital length of stay and all-cause mortality were not significantly higher in patients with AKI. An eGFR &lt;45ml/min/1.73 m2 was established as a strong independent predictor for the development of AKI (odds ratio [OR] 3.24, confidence interval [CI]: 1.40–7.52, p = 0.006), as were use of fluoroquinolones (OR: 3.19, CI: 1.30–7.82, p = 0.012) and day 1 C-reactive protein (CRP) (OR: 1.01, CI: 1.00–1.01, p = 0.009). Cumulative survival censored at the end of follow-up was not significantly lower in patients who developed AKI (log rank: 0.45, p = 0.50).

Conclusion
In our study, 18.9% of patients developed AKI after minor lower limb amputations using AKIN criteria. One patient required acute haemodialysis. Age, COPD, diuretics, fluoroquinolones and carbapenems were associated with increased incidence of AKI. An eGFR &lt;45ml/min/1.73 m2, day 1 CRP and fluoroquinolone use were independent risk factors for the development of AKI. In this small patient cohort, AKI was not associated with higher all-cause mortality, and none of the deaths were directly related to the AKI-amputation event.