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Acute kidney injury in post operative cardiac surgery patients is seen in up to 40% of patients with 1% requiring hemodialysis long term and is associated with increased morbidity and mortality (M&M)7,8. Fluid overload in post operative cardiac surgery patients is also associated with increased M&M1,9. This perioperative “temporary kidney injury state” during post cardiac surgery has been studied extensively and is associated with increased need for resources, increased length of stay, urgent renal consultations, and a relatively higher failure to rescue (FTR) rate when compared to other complications2-4,9. The current options available for the treatment of AKI with or without fluid overload in post operative cardiac surgery patients are limited and include escalating diuretics, continuous renal replacement therapy (CRRT), simple ultrafiltration technology (to remove isotonic plasma) and hemodialysis, each with their associated risks and benefits. Modified ultrafiltration (MUF) was developed over the last two decades and used intraoperatively while on the cardiopulmonary bypass circuit to remove excess fluid in both adult and pediatric cardiac surgery patients. Simplified ultrafiltration technology using an extracorporeal circuit has been in clinical use for more than a decade and its efficiency has been extensively studied in heart failure clinical trials (i.e., UNLOAD, AVOID-HF, EUPHORIA)13. More recently, US clinical trials and the Food and Drug Administration approval were granted for the treatment of fluid overload in the pediatric population weighing ≥20 Kg. CRRT is the mode of choice over conventional hemodialysis for post operative cardiac surgery patients due to improved hemodynamic tolerance14.
Adult cardiac surgery patients mostly present acutely after many years of chronic medical conditions and modifiable risk factors including HTN, DM, obesity, hyperlipidemia, physical inactivity, and smoking. HTN and DM were seen in 88% and 76% of our 17 UF patients, respectively. The long-term deleterious effect of HTN and DM on renal function is underestimated in patients with cardiovascular diseases since both chronic diseases are found in most patients requiring hemodialysis. The term cardiorenal syndrome also describes the inter-organ pathophysiological relationships in the setting of fluid overload15,16. Mortality scoring systems and online calculators are used more frequently to risk stratify and predict outcomes of surgery. These scoring systems provide a guide and underscore the various phases of care, multi-disciplinary knowledge, available skills, hospital structure, processes, available equipment, staffing ratios and complexity that is inherent in cardiac surgery.
Coronary artery bypass grafting surgery is the most common open heart surgery procedure performed for the treatment of coronary artery disease and its outcomes are used as a quality indicator for the hospitals4. Since AKI has been reported to occur in up to 40% of patients undergoing cardiac surgery and has the highest failure to rescue rates of post cardiac surgery complications, more incite is needed to improve this quality metric3,7,8.
The care of these patients has evolved with the application of newer monitoring technology, devices, artificial intelligence, and processes to improve overall outcomes. Implementation of a cardiac Enhanced Recovery after Surgery (ERAS) protocol is one example of process improvement using goal directed therapy with emphasis on avoidance of excess sodium and water overload. Although prevention of fluid overload intra-operatively is preferable, it is still seen as a common denominator in post cardiac surgery patient’s complications. Fortunately, most cardiac ICUs in the immediate post-operative setting is equipped with hemodynamic monitoring, critical care expertise and protocols to care for any possible complication. Due to the high FTR rates for AKI, close monitoring of these patients is essential for improved survival.
Our entire CABG population (254 patients, which included the COVID-19 pandemic) had a mean STS mortality score of 2.5 ± 6.61% whereas, the subset (17 patients) that underwent UF therapy had a mean STS score of 5.7 ± 11.55%. Despite the higher mortality STS score for the UF group, there was a favorable survival outcome (100%). In addition to the mortality benefits, real time advantage of UF therapy (Table 4) include: quick set up (15 to 30 minutes) any time of day, night, weekend or holiday; no immediate need for renal consultation unless RRT is needed; use of existing venous access placed intra-operatively during the initial CABG procedure or a new peripheral cannula can be placed (see Figure 1 and 2), the set-up is very simple relative to other RRT devices and is done by the ICU bedside nurse with no additional nursing staff. The volume to be removed is adjustable (hour to hour as needed) and the machine records the amount of fluid removed every hour thereby improving ICU nursing labor efficiency without the need for volume calculations. The total extracorporeal blood is approximately 35cc within the circuit limiting blood loss if UF is discontinued. Of note, this study period included the COVID-19 pandemic period and the use of Aquadex UF system freed up CRRT/HD resources for other critical care patients since no increased nursing staff was needed to perform UF.
This small retrospective pilot study shows the safety of using this UF technology to remove excess isotonic plasma water from patients in a highly monitored setting in the post-operative phase of cardiac surgery care with great outcomes. A larger multi-institutional study including long term follow up of high-risk patient populations is warranted.
References:
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