Abstract

The aim of this study was to analyze and assess the association between functional status (FS) and muscle strength (MS) in young adults, adults and older adults in an intensive care unit (ICU). We conducted a prospective cohort study with 48 patients. FS was assessed using the Functional Status Score for the Intensive Care Unit (FSS-ICU) and MS was measured using the Medical Research Council Sum-Score (MRC-SS) and by testing handgrip strength (HS). The assessments were performed on awakening and ICU discharge. The data were analyzed using the Kruskall-Wallis, chi-squared, Wilcoxon and Spearman’s correlation tests. FS and MRC-SS scores were higher on ICU discharge in all groups. Gains were lowest in the older adult group. HS was greater in both hands on ICU discharge in all groups except the adults. FSS-ICU on both awakening and ICU discharge was highest in the adults; HS-R was lowest in the older adults. There was a strong association between FS and MS in the young adults and adults. FS and MS showed progressive improvement during ICU stay. Gains in FS and MS on awakening and ICU discharge were lowest among the older adults. Important associations were found between these variables in all groups except the older adults. This can be explained by the multifactorial nature of illness and incapacity in this group.

Key words:
Health assessment; Intensive care unit; Physical function; Muscle strength; Older persons

Introduction

Technological advances and interdisciplinary intensive care have improved the survival of critical patients. Critically ill patients are subject to prolonged bed rest, leading to a decline in physical function, muscle strength and cognitive functioning¹1 Barbosa BR, Almeida JM, Barbosa MR, Rossi-Barbosa LAR. Avaliação da capacidade funcional dos idosos e fatores associados à incapacidade. Cien Saude Colet 2014; 19(8):3317-3325.

2 Hartley P, Costello P, Fenner R, Gibbins N, Quinn E, Kuhn I, Keevi VL, Romero-Ortuno R. Change in skeletal muscle associated with unplanned hospital admissions in adult patients: A systematic review and meta-analysis. PLoS ONE 2019; 14(1):1-21.^-33 González-Seguel F, Corner EJ, Merino-Osorio C. International classification of functioning, disability, and health domains of 60 physical functioning measurement instruments used during the adult intensive care unit stay: a scoping review. Phys Ther 2019; 99(5):627-640.. In older patients, these changes may be more pronounced due to physical and mental limitations resulting from aging, which is a multifactorial process⁴4 Valenzuela PL, Javier S, Morales JS, Pareja-Galeano H, Izquierdo M, Enzo Emanuele E, Villa P, Lucia A. Physical strategies to prevent disuse-induced functional decline in the Elderly. Ageing Res Rev 2018; 47:80-88.^,55 Pišot R, Marusic U, Biolo G, Mazzucco S, Lazzer S, Grassi B, Reggiani C, Toniolo L, di Prampero PE, Passaro A, NArici M, Mohammed S, Rittweger J, GAsparini M, Gabrijelcic BM, Simunic B. Greater loss in muscle mass and function but smaller metabolic alterations in older compared with younger men following 2 wk of bed rest and recovery. J Appl Physiol 2016; 120(8):922-929..

Immobility during hospitalization gives rise to early rapid loss of muscle in critical patients from different age groups, promoting a reduction in type II muscle fiber and contractile properties and an increase in inflammatory cytokines and muscle proteolysis⁵5 Pišot R, Marusic U, Biolo G, Mazzucco S, Lazzer S, Grassi B, Reggiani C, Toniolo L, di Prampero PE, Passaro A, NArici M, Mohammed S, Rittweger J, GAsparini M, Gabrijelcic BM, Simunic B. Greater loss in muscle mass and function but smaller metabolic alterations in older compared with younger men following 2 wk of bed rest and recovery. J Appl Physiol 2016; 120(8):922-929.

6 Parry S, Puthucheary Z. The impact of extended bed rest on the musculoskeletal system in the critical care environment. Extrem Physiol Med 2015; 4:16.

7 Morten V, Jorgensen MG, Andreasen J, Rathleff MS, Molgaard CM. Very low levels of physical activity in older patients during hospitalization at an acute geriatric ward: a prospective cohort study. J Aging and Phys Act 2015; 23:542-549.

8 Tanner RE, Brunker LB, Agergaard J, Barrows KM, Briggs RA, Kwon OS, Young LM, Hopkins PN, Volpi E, Marcus RL, LAStayo PC, Drumond MJ. Age-related differences in lean mass, protein synthesis and skeletal muscle markers of proteolysis after bed rest and exercise rehabilitation. J Physiol 2015; 593:4259-4273.^-99 Coker RH, Hays NP, Williams RH, Wolfe RR, Evans WJ. Bed rest promotes reductions in walking speed, functional parameters, and aerobic fitness in older, healthy adults. J Gerontol A Biol Sci Med Sci 2015; 70(1):91-96.. These changes are responsible for around a 40% loss of muscle strength during the first week of immobilization in the intensive care unit (ICU), leading to ICU-acquired weakness (ICU-AW)⁶6 Parry S, Puthucheary Z. The impact of extended bed rest on the musculoskeletal system in the critical care environment. Extrem Physiol Med 2015; 4:16.^,77 Morten V, Jorgensen MG, Andreasen J, Rathleff MS, Molgaard CM. Very low levels of physical activity in older patients during hospitalization at an acute geriatric ward: a prospective cohort study. J Aging and Phys Act 2015; 23:542-549..

Persistence of muscle weakness is associated with a reduction in aerobic capacity, negatively affecting quality of life and activities of daily living²2 Hartley P, Costello P, Fenner R, Gibbins N, Quinn E, Kuhn I, Keevi VL, Romero-Ortuno R. Change in skeletal muscle associated with unplanned hospital admissions in adult patients: A systematic review and meta-analysis. PLoS ONE 2019; 14(1):1-21., and an increase in the number of re-hospitalizations and mortality¹⁰10 Doiron KA, Hoffmann TC, Beller EM. Early intervention (mobilization or active exercise) for critically ill adults in the intensive care unit. Cochrane Database Syst Rev 2018; 27(3):CD010754.

11 Welch C, Hassan-Smith ZK, Greig CA, Lord JM, Jackson TA. Acute sarcopenia secondary to hospitalisation - an emerging condition affecting older adults. Aging Dis 2018; 9(1):151-164.

12 Nydahl P, Sricharoenchai T, Chandra S Kundt FS, Huamg M, FischillM, Needham DM. Safety of patient mobilization and rehabilitation in the intensive care unit. Systematic review with meta-analysis. Ann Am Thorac Soc 2017; 14:766-777.^-1313 Van Ancum, Scheerman K, Jonkman NH, Smeenk HE, Kruizinga RC, Meskers CGM, Maier AB. Change in muscle strength and muscle mass in older hospitalized patients: A systematic review and meta-analysis. Exp Gerontol 2017; 92:34-41.. A recent systematic review³3 González-Seguel F, Corner EJ, Merino-Osorio C. International classification of functioning, disability, and health domains of 60 physical functioning measurement instruments used during the adult intensive care unit stay: a scoping review. Phys Ther 2019; 99(5):627-640. highlighted that the assessment of physical function and muscle strength during ICU stay is extremely important and that these factors should be assessed early in order to identify patients potentially at risk of physical and functional impairment.

Some studies^10,13-19 have shown changes in physical function in critically ill patients. However, these studies do not describe changes in physical function by age group. Given the wide age range of patients admitted to ICUs, this information is extremely important to help optimize individualized treatment planning in order to ensure early treatment, including the ICU as the first stage of rehabilition¹²12 Nydahl P, Sricharoenchai T, Chandra S Kundt FS, Huamg M, FischillM, Needham DM. Safety of patient mobilization and rehabilitation in the intensive care unit. Systematic review with meta-analysis. Ann Am Thorac Soc 2017; 14:766-777.. The aim of this study was therefore to analyze functional status in young adults, adults and older adults on awakening and ICU discharge and assess the association between functional status and muscle strength.

Methods

Study characteristics

We conducted a prospective cohort study following the guidelines of the STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) statement²⁰20 Von Elm E, Altman DG, Egger M, Pocock SJ, Gotzche PC, Vandenbroucke JP. The strengthening the reporting of observational studies in epidemiology (STROBE) statement: guidelines for reporting observational studies. Bull World Health Organ 2007; 85:867-872.. The study was carried out in the adult ICU of a public hospital in Ceilândia (Ceilândia Regional Hospital), Brasília, Federal District of Brazil between March 2015 and July 2016.

The study was approved by the Health Sciences Teaching and Research Foundation’s research ethics commit. All the subjects and/or legally responsible parties were informed about the study protocol and signed an informed consent form.

Participants

Participants were recruited from critical patients using convenience sampling. Eligible patients were any patients of both sexes aged 18 years and over with a level of consciousness score of above 8 based on the Glasgow Coma Scale.

Patients with unstable fractures, motor and/or neurological impairments prior to ICU admission, wounds and/or other conditions that prevented them from sitting, and receiving palliative care were excluded.

Assessment protocol

The following clinical data was gathered from the electronic patient record system: sex; age; comorbidities prior to ICU admission; ICU admission diagnosis; clinical report of sepsis; body mass index (BMI); disease severity, measured by the Acute Physiology and Chronic Health Evaluation II (APACHE II); medications (length of time using corticosteroids, sedatives and vasoactive drugs); days on mechanical ventilation (MV); and pre-ICU and ICU length of stay.

All participants underwent an assessment of functional status (FS) and muscle strength (MS) on awakening and ICU discharge. The participants were divided into three groups: young adults, adults and older adults. Awakening was defined as the first day in which individuals responded to at least three of the following orders proposed by De Jonghe et al.¹⁶16 De Jonghe B, Sharshar T, Lefaucheur JP, Authier FJ, Durand-Zaleski I, Boussarsar M, Cerf C, Renaud E, Mesrati F, Carlet J, Raphaël JC, Outin H, Bastuji-Garin S. Paresis acquired in the intensive care unit: a prospective multicenter study. JAMA 2002; 288(2): 2859-2867.: “Open (close) your eyes”, “Look at me”, “Open your mouth and put your tongue out”, “Nod your head”, and “Raise your eyebrows when I have counted up to five”.

The assessments were performed by a team of physical therapists, who were previously trained to administer the scales and assessment instruments. The ICU had 24-hour physical therapy care and all patients had at least two physical therapy sessions a day, in accordance with the IUC protocol.

Functional status (FS) was assessed using the Functional Status Score for the Intensive Care Unit (FSS-ICU), a measure designed for ICU settings. Translated and adapted for use in Brazil, the instrument examines the patient’s ability to perform the following five tasks: 1) rolling, 2) transfer from supine to sit, 3) sitting at the edge of the bed, 4) transfer from sit to stand, and 5) walking²¹21 Huang M, Chan KS, Zanni JM, Parry SM, Neto SG, Neto JA, da Silva VZ, Kho ME, Needham DM. Functional Status Score for the ICU: An international clinimetric analysis of validity, responsiveness, and minimal important difference. Crit Care Med 2016; 20(30):1-10.^,2222 Silva VZ, Neto JAA, Cipriano JG, Pinedo M, Needham DM, Zanni JM, Guimarães FSS. Versão brasileira da Escala de Estado Funcional em UTI: tradução e adaptação transcultural. Rev Bras Ter Intens 2017; 29(1):34-38..

Participants were instructed to perform the tasks on the bed as independently as possible. If the patient was unable to complete the task, the examiner offered assistance. At the end of each movement, a score was assigned based on the assistance required to perform the task. Each task was scored on an eight-point scale ranging from 0 (unable to attempt or complete the task) to 7 (completely independent), resulting in a maximum total score of 35, where the higher the score, the better FS²¹21 Huang M, Chan KS, Zanni JM, Parry SM, Neto SG, Neto JA, da Silva VZ, Kho ME, Needham DM. Functional Status Score for the ICU: An international clinimetric analysis of validity, responsiveness, and minimal important difference. Crit Care Med 2016; 20(30):1-10..

Muscle strength was measured using the Medical Research Council Sum-Score (MRC-SS) and handgrip strength (HS) measured using a hand-held dynamometer. The MRC-SS assesses six muscle groups: shoulder abductors, elbow flexors, wrist extensors, hip flexors, knee extensors and foot dorsiflexors¹⁷17 De Jonghe B, Bastuji-Garin S, Durand MC, Malissin I, Rodrigues P, Cerf C, Outin H, Sharshar T. Respiratory weakness is associated with limb weakness and delayed weaning in critical illness. Crit Care Med 2007; 35(9):2007-2015.^,1818 Parry SM, Berney S, Granger CL, Dunlop DL, Murphy L, El-Ansary D, Koopman R, Denehy L. A new two-tier strength assessment approach to the diagnosis of weakness in intensive care: an observational study. Crit Care 2015; 19(52):1-10..

The MRC-SS was initially performed with the patient’s arm positioned against gravity. The examiner demonstrated the desired movement and then requested the patient to repeat the motion. If the patient was unable to perform the movement against gravity, the position was modified to reduce load²³23 Ciesla N, Dinglas V, Fan E, Kho M, Kuramoto J, Needham D. Manual muscle testing: a method of measuring extremity muscle strength applied to critically ill patients. J Vis Exp 2011; 12(50):2632.. An isometric hold was applied at the end of the range in order to test each grade of MS, as described by Parry¹⁸18 Parry SM, Berney S, Granger CL, Dunlop DL, Murphy L, El-Ansary D, Koopman R, Denehy L. A new two-tier strength assessment approach to the diagnosis of weakness in intensive care: an observational study. Crit Care 2015; 19(52):1-10.. Each muscle group was scored between 0 (total paralysis) and 5 (normal strength), with a minimum and maximum final score of 0 and 60, respectively¹⁷17 De Jonghe B, Bastuji-Garin S, Durand MC, Malissin I, Rodrigues P, Cerf C, Outin H, Sharshar T. Respiratory weakness is associated with limb weakness and delayed weaning in critical illness. Crit Care Med 2007; 35(9):2007-2015.. A final score of less than 48 was considered indicative of ICU-AW²⁴24 Hermans G, Clerckx B, Vanhullebusch T, Segers J, Vanpee G, Robbeets C; Casaer MP, Wouters P, Gosselink R, Van Den Berghe G. interobserver agreement of medical research council sum- score and handgrip strength in the intensive care unit. Muscle Nerve 2012; 45:18-25..

HS was measured using a digital dynamometer (Jamar Plus®, Patterson Medical Ltd, Illinois, USA). The participants were sat with their elbow flexed at a 90-degree angle and forearms in a neutral position. The patients were then instructed to squeeze as hard as possible, making three attempts with each hand. The final measure was taken to be the mean of the three measures¹⁹19 Ali NA, O'Brien JM Jr, Hoffmann SP, Phillips G, Garland A, Finley JC, Almoosa K, Hejal R, Wolf KM, Lemeshow S, Connors AF Jr, Marsh CB; Midwest. Acquired weakness, handgrip strength, and mortality in critically ill Patients. Am J Respir Crit Care Med 2008; 178:261-268.^,2424 Hermans G, Clerckx B, Vanhullebusch T, Segers J, Vanpee G, Robbeets C; Casaer MP, Wouters P, Gosselink R, Van Den Berghe G. interobserver agreement of medical research council sum- score and handgrip strength in the intensive care unit. Muscle Nerve 2012; 45:18-25.. The examiner held the device and verbal encouragement was given during the attempts.

Statistical analysis

The categorical data were presented as total (n) and relative (%) frequencies and the continuous data were described as medians and interquartile range. The data were assessed for normality using the Kolmogorov-Smirnov statistic. All tests were bilateral and a significance level of 5% was adopted (a=0.05).

The overall sample was divided into three groups: young adults (≥18 to 39 years), adults (≥40 to 59 years) and older adults (≥60 years). To compare the clinical characteristics, FS and MS across the groups, we used the Kruskal-Wallis test with Muller-Dunn post-hoc testing for numerical variables and the Chi-squared test for categorical variables.

FS and MS on awakening and ICU discharge were analyzed using the Wilcoxon test. The correlation between the FSS-SS and MRC-SS and HS measures on awakening and ICU discharge was assessed using Spearman’s correlation test.

Statistical analysis was performed using GraphPad Prism 5 for MAC and SPSS V.24 for MAC.

Sample size

Sample size was calculated based on the evolution of the FSS-SS and MRC-SS measures between awakening and ICU discharge, adopting a clinically significant difference of one-half standard deviation (effect size = 0.5), 95% significance level, power of 80% and dropout rate of 20%, resulting in a minimum sample of 40 patients.

Results

Forty-eight of the 54 eligible patients were assessed for FS and FM on awakening and ICU discharge: 16 young adults, 17 adults and 15 older adults. The median age (IQR) of the overall sample was 47 (36-62) years. The sample was predominantly male (62%) and the most common cause of admission to the ICU was respiratory disease (27%) (Figure 1).

The APACHE II score was higher among older adults than in adults and young adults [25 (19-29) vs 17 (14-24) vs 16 (14-19); p= 0.077] and the most common comorbidity was high blood pressure (100%). Frequency of use of invasive ventilation and ICU length of stay were similar across the groups (75%, 71% and 80%, respectively; p=0.828 and 9 (5-21) vs 11 (7-20) vs 12 (8-21); p=0.653).

Duration of MV was similar across groups [5 (0-12) vs 6 (0-11) vs 7 (31-12); p=0.824)]. Incidence of ICU-AW on awakening was higher in older adults (93%) than in young adults and adults (50% and 59%, respectively; p=0.026) (Table 1).

In the overall sample, there were significant differences in FSS-ICU [15 (7-24) vs 26 (16-32); p=0.001)], MRC-SS [44 (37-53) vs 52 (44-56); p=0.000 )], HS-R [14 (11-25) vs 18 (11-25); p=0.002)] and HS-L [13 (8-22) vs 16 (10-23); p=0.004)] between awakening and ICU discharge. These measures show a gradual increase between awakening and discharge (Table 2).

The data show a considerable increase in FSS-ICU between awakening and discharge in the different age groups [17 (7-28) vs 21 (10-34), p=0.048; 18 (9-30) vs 32 (27-34), p=0.001; 11 (6-18) vs 23 (13-28), p=0.003)]. Similar results were found for MRC-SS [48 (32-56) vs 53 (36-60), p=0.050; 46 (39-56) vs 55 (45-56), p= 0.031; 40 (34-46) vs 48 (44-52), p=0.003)]. With regard to HS-R and HS-L, changes were observed in all groups except the adults (p=0.211; p=0.244). The right hand was the dominant hand in 75% of the young adults, 71% of the adults and 80% of the older adults. The data are shown in Table 2.

Significant differences in FSS-ICU were observed between young adults, adults and older adults both on awakening and on ICU discharge: awakening - 17 (7-28) vs 18 (9-30) vs 11 (6-18), p=0.040; discharge - 21 (10-34) vs 32 (27-34) vs 23 (13-28), p=0.013. HS-R was higher on awakening among all groups [17 (7-27); 18 (14-38); 12 (11-14); p=0.050] (Figure 2).

There was strong correlation between FSS-ICU and MRC-SS on both awakening (r=0.74; p=0.001) and discharge (r=0.75; p=0.001) in the overall sample. The findings also show a moderate correlation between FSS-ICU and HS-R and HS-L on both awakening and discharge: awakening - r=0.61; p=0.00 and r=0.57; p=0.001, respectively; discharge - r=0.57; p=0.007 and r=0.50; p=0.001, respectively.

A strong correlation was found between FSS-ICU and MRC-SS on awakening in young adults and adults. The correlation between FSS-ICU and HS-D was moderate in young adults and strong among adults, while the correlation between FSS-ICU and HS-L was moderate among both young adults and adults. The correlation between FSS-ICU and MRC-SS on ICU discharge was strong in young adults and adults, while the correlation between FSS-ICU and HS-R and HS-L was moderate and strong, respectively, in both these groups (r=0.80; p=0.001). Among older adults, the association between FS and MS was weak both on awakening and on discharge (Figure 3).

Discussion

The findings show a gradual change in functional status and muscle strength in patients between awakening and ICU discharge. The older adults showed lower gains in physical function and muscle strength. Important associations were found between functional status and muscle strength among young adults and adults. These findings can help guide therapeutic actions according to the specific clinical needs of each age group, indicating that older adults need tailored preventive therapy to minimize the negative effects of ICU admission.

Functional decline in critical patients during ICU admission, regardless of age group, is a prominent topic in the literature. Previous systematic literature reviews^{2, 25-27} highlight impairment of cardiovascular and musculoskeletal systems, posing a potential health risk, meaning that early identification of these problems is important to ensure timely interventions.

Our sample was predominantly male, which is consistent with the findings of international studies²¹21 Huang M, Chan KS, Zanni JM, Parry SM, Neto SG, Neto JA, da Silva VZ, Kho ME, Needham DM. Functional Status Score for the ICU: An international clinimetric analysis of validity, responsiveness, and minimal important difference. Crit Care Med 2016; 20(30):1-10.^,2828 Brauner YO, Adi N, Shahar BT, Yehezkel E, Carmeli E. Effect of physical therapy on muscle strength, respiratory muscles and functional parameters in patients with intensive care unit-acquired weakness. The Clin Respir J 2015; 9(1):1-6. with critical patients in ICUs. Men show low adherence to preventive and curative measures because they take less care of their health than women as they dedicate themselves more to work, therefore tending to seek care in more critical situations when symptoms are more severe²⁹29 Tipping CJ, Bailey MJ, Bellomo R, Berney S, Buhr H, Denehy L, Harrold M, Holland A, Higgins AM, Iwashyna TJ, Needham D, Presneill J, Saxena M, Skinner EH, Webb S, Young P, Zanni J, Hodgson CL. The ICU mobility scale has construct and predictive validity and is responsive: a multicenter observational study. Ann Am Thorac Soc 2016; 13(6):887-893.^,3030 Costa JFM, Maia ACB. Concepções de homens hospitalizados sobre a relação entre gênero e saúde. Psic: Teor e Pesq 2009; 25(1):55-63..

In addition, from a cultural perspective, men tend to be taught from a young age to display their masculinity, strength and virility, meaning that physical frailty and being absent from work does not cause as much unease among women as it does in men³¹31 Costa Junior, Couto MT, Maia ACB. Género y atención en la salud: puntos de vista de los profesionales que trabajan en el hospital y ambulatorio. Sex Salud Soc 2016; 23:97-117..

Although chronic comorbidities such as high blood pressure and diabetes mellitus were present in all age groups, the prevalence of these conditions was higher among the older adults. This may be attributed to an increase in life expectancy in recent years, directly affecting the prevalence of chronic diseases. The latter are key factors in cardiovascular risk, which can lead to an increase in fatal and non-fatal cardiovascular outcomes, influencing hospital admission rates among older adults³²32 Costa AF, Flor MR, Campos MR, Oliveira AF, Costa MFS, Silva RS, Lobato LCP, Scramm JMA. Carga do diabetes mellitus tipo 2 no Brasil. Cad Saude Publica 2017; 33(2):1-14.^,3333 Lobo LA, Canuto R, Dias-da-Costa JS, Pattussi MP. Tendência temporal da prevalência de hipertensão arterial sistêmica no Brasil. Cad Saude Publica 2017; 33(6): 1-13..

Most of the patients in our study needed mechanical ventilation. Duration of ventilation was longer among the older adults. These findings are similar to those reported by Dietrich et al.³⁴34 Dietrich C, Cardoso JR,Vargas F, Sanchez EC, Dutra FH, Moreira M. Capacidade funcional em idosos e idosos mais velhos após alta da unidade de terapia intensiva. Coorte prospectiva. Rev Bras Ter Intensiva 2017; 29(3):293-302., who showed that mean duration of ventilation among older adults (61-79 years) was 8.0 ± 11.2 days. The findings of the current study show that mean ICU length of stay was above seven days, which is consistent with the findings of international and Brazilian studies¹⁸18 Parry SM, Berney S, Granger CL, Dunlop DL, Murphy L, El-Ansary D, Koopman R, Denehy L. A new two-tier strength assessment approach to the diagnosis of weakness in intensive care: an observational study. Crit Care 2015; 19(52):1-10.^,2929 Tipping CJ, Bailey MJ, Bellomo R, Berney S, Buhr H, Denehy L, Harrold M, Holland A, Higgins AM, Iwashyna TJ, Needham D, Presneill J, Saxena M, Skinner EH, Webb S, Young P, Zanni J, Hodgson CL. The ICU mobility scale has construct and predictive validity and is responsive: a multicenter observational study. Ann Am Thorac Soc 2016; 13(6):887-893.^,3434 Dietrich C, Cardoso JR,Vargas F, Sanchez EC, Dutra FH, Moreira M. Capacidade funcional em idosos e idosos mais velhos após alta da unidade de terapia intensiva. Coorte prospectiva. Rev Bras Ter Intensiva 2017; 29(3):293-302.^,3535 Jesus FS, Paim DM, Brito JO, Barros IA, Nogueira TB, Prata B, Pires Q. Declínio da mobilidade dos pacientes internados em unidade de terapia intensiva. Rev Bras Ter Intensiva 2016; 28(2);114-119.. This is explained by illness severity and patient condition, meaning that length of stay can range from hours to weeks, depending on patient response to therapy²⁷27 Parry SM, Granger CL, Berney S, Jones J, Beach L, El- Ansary D, Koopman R, Denehy L. Assessment of impairment and activity limitations in the critically ill: a systematic review of measurement instruments and their clinimetric properties. Intens Care Med 2015; 41(5):744-762..

In older adults, immobility in the ICU (associated with the course of the disease and age-related physiologic changes) can result in significant limitations that lead to loss of respiratory muscle strength, making critical patients more susceptible to respiratory complications, prolonged use of MV, dysphagia and post-extubation foreign body aspiration, ultimately resulting in increased mortality and health care costs³⁶36 Stieff KV, Lim F, Chen L. Factors Influencing Weaning Older Adults from Mechanical Ventilation: An Integrative Review. Crit Care Nurs Q 2017; 40(2):165-177.. According to Yanping Ye et al.³⁷37 Yanping Ye, Bo Zhu, Li Jiang, Qi Jiang, Meiping Wang, Lin Hua, Xiuming Xi. A contemporary assessment of acute mechanical ventilation in Beijing: description, costs, and outcomes. Crit Care Med 2017;45(7):1160-1167., mean daily ICU costs per patient can be up to US$1,212. Therefore, although MV may be necessary, it is important to seek strategies that optimize its use in order to minimize potential complications. The prevalence of ICU-AW in the current study was high in older adults. This is a common complication and recurring problem in the acute phase of the disease in this age group³⁸38 Latronico N, Gosselink R. Abordagem dirigida para o diagnóstico de fraqueza muscular grave na unidade de terapia intensiva. Rev Bras Ter Intensiva 2015; 27(3):199-201.. Evidence²2 Hartley P, Costello P, Fenner R, Gibbins N, Quinn E, Kuhn I, Keevi VL, Romero-Ortuno R. Change in skeletal muscle associated with unplanned hospital admissions in adult patients: A systematic review and meta-analysis. PLoS ONE 2019; 14(1):1-21.^,2929 Tipping CJ, Bailey MJ, Bellomo R, Berney S, Buhr H, Denehy L, Harrold M, Holland A, Higgins AM, Iwashyna TJ, Needham D, Presneill J, Saxena M, Skinner EH, Webb S, Young P, Zanni J, Hodgson CL. The ICU mobility scale has construct and predictive validity and is responsive: a multicenter observational study. Ann Am Thorac Soc 2016; 13(6):887-893.^,3939 Solverson KJ, Grant C, Doing CJ. Assessment and predictors of physical functioning post-hospital discharge in survivors of critical illness. Anm Intens Care 2016; 6(1):92.

40 Wieske L, Dettling-Ihnenfeldt D, Verhamme C, Nollet F, Schaik IN, Schultz M, Horn J, van der Schaaf M. Impact of ICU-acquired weakness on post-ICU physical functioning: a follow-up study. Critical Care 2015; 19:196.^-4141 Dettling-Ihnenfeldt D, Wieske L, Horn J, Nollet F, Van-der-Schaaf M. Functional Recovery in Patients with and Without Intensive Care Unit-Acquired Weakness. Amer J Phys Med Rehabil 2017; 96(4):297-242. shows that ICU-AW reduces physical function and bedside mobility and can be a predictor of poor functional health status for up to one year after ICU discharge. Patel et al.⁴² demonstrated that both increasing age and severity of illness are risk factors for developing ICU-AW. Decline in physical and mental functioning in comparison with performance prior to admission is particularly evident in critically ill patients. These changes can be accentuated by prolonged ICU length of stay, use of MV, sepsis, multiple organ dysfunction, immobility, the use of systemic corticosteroids, ICU-AW, slow recovery from lung injury and age¹¹11 Welch C, Hassan-Smith ZK, Greig CA, Lord JM, Jackson TA. Acute sarcopenia secondary to hospitalisation - an emerging condition affecting older adults. Aging Dis 2018; 9(1):151-164.

12 Nydahl P, Sricharoenchai T, Chandra S Kundt FS, Huamg M, FischillM, Needham DM. Safety of patient mobilization and rehabilitation in the intensive care unit. Systematic review with meta-analysis. Ann Am Thorac Soc 2017; 14:766-777.

13 Van Ancum, Scheerman K, Jonkman NH, Smeenk HE, Kruizinga RC, Meskers CGM, Maier AB. Change in muscle strength and muscle mass in older hospitalized patients: A systematic review and meta-analysis. Exp Gerontol 2017; 92:34-41.^-1414 Zanni JM, Korupolu R, Fan E, Pradhan P, Janjua K, Palmer JB, Brower RG, Needham DM. Rehabilitation therapy and outcomes in acute respiratory failure: an observational pilot project. J Crit Care 2010; 25:254-262.^,1616 De Jonghe B, Sharshar T, Lefaucheur JP, Authier FJ, Durand-Zaleski I, Boussarsar M, Cerf C, Renaud E, Mesrati F, Carlet J, Raphaël JC, Outin H, Bastuji-Garin S. Paresis acquired in the intensive care unit: a prospective multicenter study. JAMA 2002; 288(2): 2859-2867.^,2626 Welch C, Hassan-Smith ZK, Greig CA, Lord JM, Jackson TA. Acute sarcopenia secondary to hospitalisation - an emerging condition affecting older adults. Aging Dis 2018; 9(1):151-164.^,2828 Brauner YO, Adi N, Shahar BT, Yehezkel E, Carmeli E. Effect of physical therapy on muscle strength, respiratory muscles and functional parameters in patients with intensive care unit-acquired weakness. The Clin Respir J 2015; 9(1):1-6..

Reduced functional status was observed on awakening, followed by a gradual increase in parameters up to ICU discharge. These findings were similar to those found in previous research assessing functional status and muscle strength in critical patients using FSS-ICU, MRC-SS and dynamometry¹⁴14 Zanni JM, Korupolu R, Fan E, Pradhan P, Janjua K, Palmer JB, Brower RG, Needham DM. Rehabilitation therapy and outcomes in acute respiratory failure: an observational pilot project. J Crit Care 2010; 25:254-262.^,1515 Thrush A, Rozek M, Dekerlegand JL. The clinical utility of the functional status score for the intensive care unit (FSS-ICU) at a long-term acute care hospital: a prospective cohort study. Phys Ther 2012; 92(12):1536-1545.^,4343 Nordon-Craft A, Schenkman M, Edbrooke L, Malone DJ, Moss M, Denehy L. The physical function intensive care test: implementation in survivors of critical illness. Physical Therapy 2014; 94(10):1499-1507.^,4444 Silva PE, Maldaner V, Vieira L, Carvalho KL, Gomes H, Melo P, Babault N, Cipriano Jr, Durigan JLQ. Neuromuscular electrophysiological disorders and muscle atrophy in mechanically ventilated traumatic brain injury patients: new insights from a prospective observational study. J Crit Care 2018; 44:87-94.. These studies showed a considerable increase in physical function and muscle strength during ICU stay. A study by Zanni et al.¹⁴14 Zanni JM, Korupolu R, Fan E, Pradhan P, Janjua K, Palmer JB, Brower RG, Needham DM. Rehabilitation therapy and outcomes in acute respiratory failure: an observational pilot project. J Crit Care 2010; 25:254-262. reported a four-point increase in the FSS-ICU score between the pre-hospitalization baseline and ICU discharge, while Thrush et al.¹⁵15 Thrush A, Rozek M, Dekerlegand JL. The clinical utility of the functional status score for the intensive care unit (FSS-ICU) at a long-term acute care hospital: a prospective cohort study. Phys Ther 2012; 92(12):1536-1545. showed that median cumulative FSS-ICU scores increased by five points. Furthermore, an international clinimetric assessment of FSS-ICU involving the United States, Australia and Brazil found an effect size of 2.02 from awakening to ICU discharge.

Our findings show a progressive increase in muscle strength during ICU stay, with slow progress towards achieving prior baseline strength⁴⁵45 Norman K, Stobäus N, Kulka K, Schulzke J. Effect of inflammation on handgrip strength in the non-critically ill is independent from age, gender and body composition. Eur J Clin Nut 2014; 68(2):155-158.. A recent study by Dietch et al.³⁴34 Dietrich C, Cardoso JR,Vargas F, Sanchez EC, Dutra FH, Moreira M. Capacidade funcional em idosos e idosos mais velhos após alta da unidade de terapia intensiva. Coorte prospectiva. Rev Bras Ter Intensiva 2017; 29(3):293-302. showed differences in MRC-SS and HS in older persons aged between 61-79 years and ≥80 years between ICU admission and discharge.

Functional decline was more accentuated in the older adults because aging is a contributing factor. In this regard, key ICU risk factors related to immobility give rise to an imbalance between muscle protein synthesis and degradation. This in turn is associated with myofibril necrosis, leading to a reduction in muscle mass and bone mineral density⁴⁶46 Corner EJ, Wood H, Englebretsen C, Thomas A, Grant RL, Nikoletou D, Soni N. The Chelsea Critical Care Physical Assessment Tool (CPAx): validation of an innovative new tool to measure physical morbidity in the general adult critical care population; an observational proof-of. concept pilot study. Physiotherapy 2013; 99(1):33-41.^,4747 Corner EJ, Wood H, Englebretsen C, Thomas A, Grant Parry S, Puthucheary Z. The impact of extended bed rest on the musculoskeletal system in the critical care environment. Extrem Physiol Med 2015; 4:16..

However, the estimate of improvement in functional status and muscle strength in the older adults was high, demonstrating potential improvement in frailer individuals. This shows that developing preventive strategies in this age group is important to provide significant beneficial effects⁴⁷47 Corner EJ, Wood H, Englebretsen C, Thomas A, Grant Parry S, Puthucheary Z. The impact of extended bed rest on the musculoskeletal system in the critical care environment. Extrem Physiol Med 2015; 4:16.. Preventive and curative measures should therefore focus on clinical strategies that have an impact on modifiable characteristics, seeking to adopt an individualized approach directed at maintaining or gaining global muscle strength, mobility and physical function according to patients’ specific needs⁴⁸48 Peek K, Carey M, Sanson-Fisher R, Mackenzie L. Physiotherapists' perceptions of patient adherence to prescribed self-management strategies: a cross-sectional survey of Australian physiotherapists. Disabil Rehabil 2016; 39(19):1932-1938..

FSS-ICU showed a correlation with the two measures of muscle strength on both awakening and ICU discharge. Similar results were found in the literature²¹21 Huang M, Chan KS, Zanni JM, Parry SM, Neto SG, Neto JA, da Silva VZ, Kho ME, Needham DM. Functional Status Score for the ICU: An international clinimetric analysis of validity, responsiveness, and minimal important difference. Crit Care Med 2016; 20(30):1-10.^,4949 Parry SM, Denehy L, Beach LJ, Berney S, Williamson HC, Granger CL. Functional outcomes in ICU - what should we be using? - an observational study. Crit Care 2015; 29(19):127., with studies pointing to an association between FSS-ICU and MRC-SS, HS, ICU Mobility Scale, Activities of Daily Living (ADL) and Physical Function in Intensive Care Test-scored (PFIT-s) scores. However, there was a week association between physical function and muscle strength in the older adults. In this regard, it is probable that functional decline in older adults does not occur only due to a reduction in muscle strength, but also as result of deficiencies in multiple body systems that may be related to illnesses diagnosed prior to admission⁵⁰50 Denehy L, Lanphere J, Needham DL. Ten reasons why ICU patients should be mobilized early. Intens Care Med 2017; 43:86-90.^,5151 Cerri AP, Bellelli G, Mazzone A, Pittella F, Landi F, Zambon A, Annoni G. Sarcopenia and malnutrition in acutely ill hospitalized elderly: Prevalence and outcomes. Clin Nutr 2015; 34(4):745-751..

This study has some limitations. The data do not show functional status and muscle strength prior to ICU admission. The fact that the admissions were emergency admissions made it difficult to assess this information, thus limiting comparisons between the measures and baseline data. Although we achieved the minimum sample size, caution should be taken when generalizing the findings to other ICUs due to the specific characteristics of the study sample.

Future observational and interventional studies should be conducted with older critically ill patients in different ICU settings to explore other factors associated with functional decline in older adults. The findings of such studies can inform early interventions tailored to the specific needs of frailer patients in order to minimize the adverse effects of ICU admission and post-ICU discharge, promoting an independent return to activities of daily living.

Conclusion

Functional status and muscle strength showed progressive improvement during ICU stay. The older adults showed a smaller gain in functional status and muscle strength after awakening. There was an important association between these variables in the young adults and adults, characterizing an interaction between the different domains of the functional status of the adults. With regard to the older adults, the variables were not correlated due to multi-morbidities and the multifactorial nature of illness and incapacity in this group.

Acknowledgements

We are grateful to the physical therapy students from the University of Brasília for their contribution to data collection and to all the volunteers and family members who participated in this study. We would also like to thank the following organizations for providing funding for this study: the Fundação de Apoio à Pesquisa do Distrito Federal (FAP/DF), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), and the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) master’s scholarship program.

References

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