De la igualdad como principio básico, según Jhon Rawls, pero

Worldwide, studies comparing the dialysis population to the general population have consistently demonstrated that dialysis patients of all ages report a poorer quality of life in comparison to healthy controls or norm based scores (Kutner et al 2000b, Lamping et al 2000, Diaz-Buxo et al 2000, Allen et al 2002, Dwyer et al 2002, Knight et al 2003, Lowrie et al 2003, Perlman et al 2005, Altintepe et al 2006).

Evidence indicates that HD patients perceive their physical quality of life as being worse than their psychosocial (mental) quality of life, with their psychosocial quality of life closer to, and not always significantly different from, population norms. A perception that appears to apply more to older HD patients than younger HD patients (De Oro 1997, Diaz-Buxo et al 2000, Kutner et al 2000b, Lamping et al 2000, Tawney et al 2000, Mittal et al 2001, Allen et al 2002, Dwyer et al 2002, Lowrie et al; 2003, Knight et al 2003, Perlman et al 2005). Some studies, but not all, have also shown that HD patients have a poorer quality of life than PD patients or transplant patients (Merkus et al 1997, Diaz-Buxo et al 2000).

Few studies examining quality of life in CKD patients have been conducted in Europe or the UK. Those that have suggest that patients also report poorer levels of physical function than population norms (Blake et al 2000, Lamping et al 2000, Cleary & Drenman 2004) and may (Blake et al 2000) or may not (Lamping et al 2000, Cleary & Drenman 2004) report a poorer psychosocial quality of life. One study conducted in Scotland demonstrated that patients receiving HD or PD had both a lower physical and psychosocial quality of life than transplanted patients and a sample of the general population (Khan et al 1995).

Reasons for the reported differences in quality of life include the presence of comorbidities (Khan et al 1995, Merkus et al 1997, Diaz-Buxo et al 2000, Dwyer et al 2002), advancing age (Diaz-Buxo et al 2000), dialysis vintage (Rebello et al 1998), the presence of anaemia (Rebollo et al 1998, Kalantar-Zadeh et al 2001a, Perlman et al 2005) and low levels of physical activity (Kutner et al 2000, O’Hare et al 2003). Nutritional status has also been implicated in quality of life. In two observational studies of different HD populations by the same group, significant, but weak negative correlations with BMI and percentage body fat were found (Kalantar-Zadeh et al 2001a, Kalantar-(Kalantar-Zadeh et al 2006). Subjective global assessment (SGA), mid arm muscle circumference (MAMC) and serum albumin have also been found to positively correlate with quality of life (Laws et al 2000). Furthermore, in a large observational study of 1,545 HD patients, both calf circumference and serum creatinine were positively associated with perceived physical quality of life (Allen et al 2002). In addition, given that several large studies have found that both a poor psychosocial and physical self reported quality of life are associated with more frequent hospitalisation and increased mortality risk, interventions that improve quality of life may also have wider implications and therefore justifies the inclusion of

quality life as an outcome measure (DeOreo 1997, Kalantar-Zadeh et al 2001a, Knight et al 2003, Lowrie et al 2003, Mapes et al 2004).

1.3.1 Measuring quality of life

Although there is a lack of agreement in the literature regarding the concept of health related quality of life, it is commonly viewed as a multidimensional concept encompassing physical, psychological and social functioning, and a number of questionnaires have been developed on this premise (Kutner 1994, Cleary &

Drennan 2005).

In the majority of CKD studies the short form 36 (SF36) generic questionnaire has been utilised (Rettig et al 1997, Khan et al 1995, Blake et al 2000, Kutner et al 2000b, Lamping et al 2000, Diaz-Buxo et al 2000, Mittal et al 2001, Allen et al 2002, Dwyer et al 2002, Johansen et al 2003b, Knight et al 2003, Lowrie et al 2003, Cleary

& Drenman 2004, Burrowes et al 2005, Perlman et al 2005, Altintepe et al 2006).

While the kidney disease quality of life short form (KDQOL-SF), a disease specific questionnaire for dialysis patients exists, which incorporates the SF36 dimensions, it is more complex and takes twice the amount of time to complete (Phillips, Davies &

White 2001). In addition, it has not been widely used in intervention studies of function and quality of life in HD patients.

Whilst the SF36 is a generic questionnaire and not specific to HD patients, it is considered to have construct validity in a range of patient groups including CKD (Brazier et al 1992, Garratt, Ruta & Abdalla1993, Neto et al 2000). Evidence also suggests that the SF36 is suitable for self administration within 5 to10 minutes and has a high degree of acceptability in the general population, as well as European,

UK and Scottish renal populations of various ages (Khan et al 1995, Blake et al 2000, Lamping 2000, Cleary & Drenman 2004).

The SF36 provides a profile of two health component summary measures, the physical component score (PCS) and the mental component score (MCS). It also provides information on eight health domain scales which are, physical functioning (PF), role physical (RP), bodily pain (BP), general health (GH), vitality (VT), social functioning (SF), role-emotional (RE), and mental health (MH). Whilst the PCS &

MCS are considered to provide a reliable, valid and broad overview of perceived physical and psychosocial morbidity, the domain scales provide information on specific aspects of physical and psychosocial well being which may or may not be similarly affected as a consequence of disease or interventions (Ware et al 2007).

The MH, RE and SF domains and the MCS have been shown to be the most valid of the SF-36 scales for measuring mental health in both cross cultural and longitudinal studies. The PF, RP and BP domains of the PCS have been shown to be the most valid SF-36 scales for measuring physical health. Further to this, the PF scale has been shown to be the best all round valid measure of physical health and the MH scale has been shown to be the most valid measure of mental health in studies to date (Ware et al 2007).

Reliability testing of the SF36 has been reported over a wide range of conditions including HD. In a HD population the internal consistency of the eight domain scales ranges from 0.82 and 0.92, which compares favourably with reported internal consistency for other populations (Cleary & Drennan 2004).The SF-36v2, the later improved version of the original short form-36 is easier to understand and complete.

It is considered to have comparable reliability and validity and it is this version that is

now recommended for use. However, the use of norm based scores allows ongoing comparability between studies using the SF-36 (Ware et al 2007).