Most people are born with a pair of kidneys, vital organs which are essential for health and survival. Kidneys function to filter blood of toxins that are produced from normal metabolism, regulate water and salt content within our body, and maintain our blood acid-base balance. The right and left kidneys usually receive 20% of the blood volume that is pumped out each cycle from the heart (cardiac output), then filters and regulate the blood, such that waste products are eliminated through urine production. This is a continuous process that occurs throughout the day. People who are born with only one (solitary) kidney or patients who lose a kidney from unfortunate events like traumatic injury or cancer resection can still live healthy lives if the remaining kidney function is preserved and not severely compromised. Conditions such as hypertension, diabetes, renal atherosclerosis, and polycystic kidney disease can deteriorate kidney function and contribute to Chronic Kidney Disease (CKD). In order of severity, CKD Stage 1 to 3 can be managed with careful monitoring and avoidance of further damage to the kidneys, e.g., exposure to nephrotoxic medications, intravenous contrast, etc. If further deterioration ensues as in CKD Stage 4, most patients will be counselled for Renal Replacement Therapy (RRT) and preparatory steps are undertaken in anticipation of starting RRT. Upon CKD Stage 5, if RRT is not started, most patients do not survive for long. Hence adequate planning and time allocation for preparation is important in caring for CKD patients.
RRT comes in the form of peritoneal (water) dialysis (PD) or hemodialysis (HD) where blood is filtered directly by a machine. PD utilizes the natural lining on the inside surface of our abdominal cavity called the peritoneum, as a filtration membrane for toxins and waste products to be excreted. A silicone tube (peritoneal catheter) is inserted into the abdomen through a minor surgical procedure that then exits the skin on one side of the lower abdomen. After the surgical incisions have had an opportunity to heal, the peritoneal catheter can be used to infuse or drain dialysate fluid. This sterile fluid when left within the abdominal cavity allows toxin and waste product diffusion across the peritoneum membrane, after a period of time of which the dialysate can be drained and discarded. PD comes in the form of Continuous Ambulatory Peritoneal Dialysis in Singapore (CAPD) or Automated Peritoneal Dialysis (APD) in Singapore. CAPD is conducted a few times a day where small volumes (1-2 liters) of dialysate is infused, retained, and then drained (i.e., one exchange), throughout the day as the patient carries on with their usual activities of living or work. Each exchange is approximately 30 to 60 minutes. APD differs where an infusion machine exchanges larger volumes of dialysate over 8 to 10 hours and occurs mostly at night when the patient is asleep. PD requires daily treatment and patients can be instructed on how to self-administer at home using sterile techniques.
Hemodialysis involves direct filtration of the patient’s blood using a synthetic exchange membrane, and in so doing, the hemodialysis machine also regulates the blood water and salt content, and pH (acid-base balance). HD requires fast and voluminous access to the patient’s blood which can be achieved in three ways: i) hemodialysis central venous catheter (CVC), ii) arteriovenous fistula (AVF), or iii) arteriovenous graft (AVG). A CVC is placed through the skin, directly into a large neck or arm vein that leads very close to the right heart chambers. The catheter has two ports, one for aspiration of blood to the HD machine, the other to return ‘cleansed’ blood to the patient. Tunneled CVCs can be placed as a more permanent access for hemodialysis but tend to have the higher infection (blood stream infections) and mechanical complication rates compared to AVF and AVG. Patients can also develop central venous narrowings or occlusions that complicate and limit their options for AVF and AVG in the future. It is generally not recommended to keep CVCs for HD for more than 6 months’ duration.
AVFs are the best long term HD access for patients, using the patient’s own artery and vein where a direct communication is created surgically. This allows increased blood to flow directly into a superficial vein, allowing it to distend and thicken (mature) over 6-weeks, such that it can support HD between 250 to 350 mls/min flow rate. Two needles are required, one for aspiration of blood the other for return, and each HD run is typically 4 hours. AVF has the lowest infection rates compared to CVC and AVG, and tend to last the longest (on average, approximately 3-years). AVFs are initially created at the most distal sites to maximize the number of circuits the patient may need in their lifetime on HD. For example, AVFs are created at the wrist, then forearm, and finally in the upper arm. For successful creation, maturation, and functionality of AVF, the initial vein size is recommended to be no smaller than 3mm. For patients who do not have adequate veins in their upper extremities for AVF creation, AVG is an alternative.
AVG uses a synthetic vascular graft or tube that is implanted underneath the skin of the forearm or arm, one end of which is connected to a main artery and the other to a draining vein. Conceptually similar to AVF, AVGs allow two needle cannulation and connection to the HD machine to deliver and return blood. Its infection risk is intermediate between CVC and AVF and it is slightly less durable than AVF (approximately 2 years duration). AVG also do not need to undergo a ‘maturation’ process like that of AVF and can usually be used 1-2 weeks post-operation. Newer early cannulation grafts allow almost immediate use of the AVG for HD.
Hemodialysis using CVC, AVF, or AVG are performed at HD centers and patients are typically dialyzed on alternate days, unlike PD which is performed daily. Most patients follow a Monday-Wednesday-Friday or Tuesday-Thursday-Saturday schedule. Travelling to-and-fro to HD centers may be problematic for some patients who live far away or have mobility/transport issues. Some patients are uncomfortable with needles and find AVF/AVG cannulation distressing but most patients get accustomed and feel little or no pain with time. Monitoring and pro-active intervention on failing AVF/AVG circuits can be done to extend to ‘lifespan’ of each circuit so that patients can receive uninterrupted and life-preserving dialysis in Singapore. Vascular specialists at PanAsia Surgery are readily available to counsel and assist patients with any of their RRT requirements.