Infections can be as frequent as once every 15 months (0.8 episodes per patient year). Compared to hemodialysis, PD allows greater patient mobility, produces fewer swings in symptoms due to its continuous nature, and phosphate compounds are better removed, but large amounts of albumin are removed which requires constant monitoring of nutritional status. The costs of PD are generally lower than those of HD in most parts of the world, this cost advantage is most apparent in developed economies. There is insufficient research to adequately compare the risks and benefits between CAPD and APD; a Cochrane Review of three small clinical trials found no difference in clinically important outcomes (i.e. morbidity or mortality) for patients with end stage renal disease, nor was there any advantage in preserving the functionality of the kidneys. The results suggested APD may have psychosocial advantages for younger patients and those who are employed or pursuing an education. Other complications include hypotension (due to excess fluid exchange and sodium removal), low back pain and hernia or leaking fluid due to high pressure within the abdomen. PD may also be used for patients with cardiac instability as it does not result in rapid and significant alterations to body fluids, and for patients with insulin-dependent diabetes mellitus due to the inability to control blood sugar levels through the catheter. Hypertriglyceridemia and obesity are also concerns due to the large volume of glucose in the fluid, which can add 500-1200 calories to the diet per day. Of the three types of connection and fluid exchange systems (standard, twin-bag and y-set; the latter two involving two bags and only one connection to the catheter, the y-set uses a single y-shaped connection between the bags involving emptying, flushing out then filling the peritoneum through the same connection) the twin-bag and y-set systems were found superior to conventional systems at preventing peritonitis. Best practices for peritoneal dialysis state that before peritoneal dialysis should be implemented, the person's understanding of the process and support systems should be assessed, with education on how to care for the catheter and to address any gaps in understanding that may exist. The person should receive ongoing monitoring to ensure adequate dialysis, and be regularly assessed for complications. Finally, they should be educated on the importance of infection control and an appropriate medical regimen established with their cooperation. The abdomen is cleaned in preparation for surgery and a catheter is surgically inserted with one end in the abdomen and the other protruding from the skin.