Nutrition Important for Physical Functioning in CKD Patients

Nutrition Important for Physical Functioning in CKD Patients
Alison Steiber, PhD, RD, LDJanuary 11 2011
Adequate physical functioning is essential for individuals to live independently and have good quality of life (QoL). The etiologies of suboptimal physical functioning in hemodialysis (HD) patients are varied. Acid-base imbalances (Nephron. 1987;46:57-62), poor oxygen capacity (Ren Fail. 2002;24:337-345), inadequate dialysis dose (Am J Nephrol. 199;18:399-403), low carnitine concentrations (Ren Fail. 1996;18:91-96), and poor nutritional status (Nephrology. 2010;15:454-463) are some of the reported causes. Regardless of the cause, poor muscle functioning affects the daily lives of HD patients.

Measurement of physical functioning is not routinely done in most dialysis facilities and has many challenges. However, in a recent review article (Sports Med. 2010;40:1055-1074), Pelagia Koufaki, PhD, and Evangelia Kouidi state, “It is important that physical functioning of patients across discrete stages of renal function is comprehensively and accurately characterized based on sound outcome measures.” Historically, caregivers have used perceived QoL assessment tools such as the Medical Outcomes Short Form-36 (SF36) that have been strongly correlated with mortality and morbidity outcomes in HD patients (J Am Soc Nephrol. 2001:12:2797-2806). Significant correlations have been found between QoL scores and muscle strength and maximal oxygen consumption (Am J Kidney Dis. 2002;39:257-265). Furthermore, physical performance measures can be predictors of loss of independence, placement in institutions, and low morale (Kidney Int. 2001;60:1586-1591). Resistance training, exercise regimes, and oral carnitine have been shown to improve both physical functioning measures and perceived QoL scores (Am J Kidney Dis. 2002;40: 355-364; Am J Kidney Dis. 2002;39:257-265).

Nutrition is an important factor contributing to a patient's physical functioning. In a study on muscle quality and quantity, hypoalbuminemia, and low body mass index account for 32% of the variance in predicting muscle cross sectional area, an indicator of muscle quantity. This study is evidence that poor nutritional status impacts muscle functioning and thus physical functioning, and, ultimately, QoL. To date, a nutrition intervention trial has not been done where physical functioning outcomes were measured for improvement. However, in a clinical setting it makes sense to assess patients simultaneously for both physical functioning ability and nutritional status. Furthermore, interventions need to address both the patients' nutrition status and their physical ability.

There are a variety of ways to define and measure physical performance. Some of the common measures are muscle strength, muscle fatigue and muscle function. Koufaki and Kouidi suggest that the physical functioning to be concerned with in chronic kidney disease (CKD) is health-related physical function. This type of physical function is defined as a component of health-related fitness (cardiorespiratory/muscular fitness, body composition, and flexibility) that is concerned with characterizing an individual's ability to perform and participate in life activities necessary for normal physical, emotional, mental and social function. A number of tools are available for physical function assessment, but there is no consensus regarding which one is best for clinical or research purposes.

Assessments that can be done with limited space and time and have been shown to provide valuable information are the sit-to-stand and gait-speed tests. In the sit-to-stand test, a patient must start from a sitting position on a chair and stand up without the use of hands or chair arms. Patients who can stand up even once have been shown to have significantly better nutritional status. The gait-speed test can also be done in a small amount of space. Twenty feet are measured off and a clinician then times how long it takes a patient to walk the distance. Longer times reflect worse functioning. Researchers have used these measures in clinical trials with HD patients and demonstrated improvements with exercise programs. Additionally, surveys such as the SF36 can be used to corroborate the findings, allowing clinicians to design effective interventions.

In conclusion, many factors contribute to a patient's physical functioning, including nutrition status. Poor physical functioning is associated with outcomes in CKD patients and should be assessed in a routine manner.

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