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Evaluation of peripheral muscle strength of patients undergoing elective cardiac surgery: a longitudinal study

Kelli Maria Souza SantosI; Manoel Luiz de Cerqueira NetoII; Vitor Oliveira CarvalhoII; Valter Joviniano de Santana FilhoIII; Walderi Monteiro da Silva JuniorIII; Amaro Afrânio Araújo FilhoV; Telma Cristina Fontes CerqueiraVI; Lucas de Assis Pereira CacauIV

DOI: 10.5935/1678-9741.20140043


CABG: Coronary Artery Bypass Grafting

FBHC: Fundação de Beneficência Hospital de Cirurgia

PMS: Peripheral muscle force


Cardiovascular diseases are responsible for high rates of morbidity and mortality in Brazil and in the world[1]. For treatment of many of these cardiac conditions, surgery is the main resource[2]. Although very safe, heart surgery is a procedure considered large and is accompanied by the need for general anesthesia, cardiopulmonary bypass, mechanical ventilation and relative restriction to bed rest[3].

The heart disease patients showed loss of functional capacity resulting from decreased oxidative capacity of skeletal muscle and reduced muscle perfusion, such loss being aggravated in case of hospitalization for bed rest, impacting loss of peripheral muscle function[4]. Peripheral muscle strength (PMS) can be considered as a predictor of overall muscular strength, and is associated with functional and nutritional presentation[4]. The PMS is of great interest to cardiac rehabilitation, but it has been little explored in the current literature[5].

The aim of this study was to assess peripheral muscle strength in patients undergoing elective heart surgery.



Study design

This is a pilot, observational, longitudinal study performed at the Fundação de Beneficência Hospital de Cirurgia (FBHC) in the city of Aracaju - SE. The patients' assessments were performed at three time points: preoperatively (a day before surgery) (M1), on the 1st day after ICU discharge (M2) and the day of discharge (M3), in the form of lower limb isometrics.

All study participants received physiotherapy (physical and respiratory therapy), in the pre- and postoperative periods, twice a day for every day of hospitalization in the morning and afternoon. The treatment protocol included: breathing exercises (ventilatory), lung re-expansion maneuvers, bronchial hygiene, postural drainage, exercises to prevent deep vein thrombosis, deambulation, walking up and down stairs, active-assisted and active kinesiotherapy of upper and lower limbs, and muscle stretching. The rehabilitation protocol followed the guidelines of the Brazilian Consensus on Cardiovascular Rehabilitation[6].

Study Population

Patients were recruited from a tertiary hospital of Cardiology between September and November 2012. Patients undergoing elective cardiac surgery (both genders and aged between 18 and 80 years) were eligible for this study. Inclusion criteria were: absence of neurocognitive decline or dementia that could influence the process of communication, absence of musculoskeletal disorder and previous pulmonary diseases (chronic obstructive pulmonary disease), presence of hemodynamic instability (Mean Arterial Pressure >60 mmHg), dyspnea with oxygen saturation less than 90%. The patient, who refused to sign the Written Informed Consent and those who had the time of stay in the ICU more than 7 days were excluded from the study.

This research protocol was approved by the Research Ethics Committee of our institution (CAAE nº 01521012.2.0000.0058). All patients signed a written informed consent prior to participation in this research.

Data collected from medical records

Clinical history, diagnosis, vital signs, type of surgery, total days ofhospital and ICU stay, time of cardiopulmonary bypass and mechanical ventilation time were collected, as well as the patient's characteristics involved in the study (Table 1).


Assessment of peripheral muscle strength

The PMS was assessed at three different time points: preoperatively (day before surgery) (M1), on the 1st day after ICU discharge (M2) and the day of discharge (M3), in the form of isometrics for extension and flexion of the right and left knees. The instrument used in this assessment was the portable digital dynamometer, IMPAC®, IP-90DI model with scale in kgf, associated with an anatomical adapter for better coupling of the lower end segment[7].

In the assessment of knee isometric strength was observed muscle performance in flexion and extension, bilaterally. The procedure followed in the following standardization: the patient remained seated, hips at 90º of flexion and abduction at shoulder width. Patients performed the movements required under verbal command of the evaluator, exerting a continuous isometric force for 5 seconds. Three independent measurements and with one-minute interval between them for each movement and collection of averaging of such measurements were performed. The digital dynamometer remained leaning against a flat surface in order to maintain the stability of the instrument under the pressure exerted by the subject at the time of isometrics. Patients were instructed not to perform the Valsalva maneuver. The analgesic therapy in the study patients was standardized.

Statistical analysis

Data arepresented as mean and standard deviation. The data presented normal behavior (Shapiro Wilk test) and for the analysis of PMS at different times, we used one-way ANOVA test and Bonferroni post-test with 95% confidence interval. We consider the level of less than 5% (P<0.05) significance. For statistical analysis we used SPSS (Chicago IL, USA) version 13.0.



In this study, 31 patients were listed for surgery of which 22 met the inclusion criteria. Nine patients were excluded and 22 were assessed until the end of the study (Figure 1, Table 1).


Concerning body composition of the sample, BMI (Body Mass Index) had values classified as normal weight (37.5% men, 64.29% women), overweight (50% men, 14.29% women) and obesity grade 1 (12.5% men, 21.42% women). All subjects were considered physically inactive with respect to the level of physical activity after submission to the specific questionnaire.

The preoperative values of peripheral muscle strength for knee extension found in study patients (3.5±8.94) were nearly 50% lower than predicted for the healthy population with the same mean age (18.2±2.3)[8].

There was a 29% reduction in the PMS for the movement of knee flexion in the interval between assessments of M1 (7.06±2.8), CI=(3.30, 14.50) and M2 (5.29±1.9) CI (2.55, 10.67) (P=0.056). Comparing M1 and M3 (6.35±2.4), CI=(3.05, 12.82) there is still a deficit of PMS of 10% for movement of knee flexion (P=0.99).

For movement of knee extension, there was also a 25% reduction of M1 (8.94±3.5), CI=(5.10, 20.45) for M2 (6.34 ± 2.24), CI=(2.34, 11.92) (P=0.016) and further reduction of 13% when comparing M1 with M3 (7.74±3), CI=(3.91, 17.19) (P=0.057) (Figure 2).



The main finding of our study was the reduction in muscle strength of the lower limbs of patients undergoing elective cardiac surgery procedure.

Some studies have reported that postoperative complications of cardiac surgery may contribute to the increased staying time of intensive care unit[3], especially respiratory and metabolic complications[9]. Nevertheless, decrease in postoperative functionality of these patients has been reported[10].

Among the postoperative respiratory complications, one aggravating factor is the loss of respiratory muscle strength[11], but so far, it is unknown whether such loss is also reproduced in peripheral muscle strength.

Peripheral muscle force (PMS) can be regarded as a predictor of overall muscular strength, and is associated with functional and nutritional presentation of the patient[12,13]. Nevertheless, the PMS has been little explored in the literature, especially in the context of complications from surgery, the reason why the study was proposed.

Diffuse neuromuscular abnormalities have been reported in 50% of patients admitted to the ICU after staying on mechanical ventilation, with the primary clinical sign the physical deconditioning and muscle weakness[14].

Immobility in bed following surgical procedures, the use of cardiopulmonary bypass (CPB) and mechanical ventilation, the pain caused by sternotomy and saphenectomy, the presence of drains and venous access, peripheral edema, among other factors, are conditions that limit mobility in bed and consequently the functionality[6].

It is known that the functionality of cardiac patients can be severely limited by the reduction of muscle mass and strength, decreased oxidative capacity and a significant deficit in blood flow affecting the energy intake to the muscle[6].

In the present study, after ten days, on average, CABG patients were discharged from hospital (M3) and currently has detected an increase in the PMS values compared to the values listed in M2, demonstrating loss of only 10% when compared with M1.

Even with the limitation of the study, taking into consideration the design and duration of patient follow-up, it is not possible to identify the causes of incomplete restoration of PMS in patients postoperatively, but it is noteworthy that the patients had a good recovery of strength muscle, which was demonstrated by the absence of significant differences when comparing the previous values with the day of discharge.

However, it is clear that the moment of greatest restriction on the bed (due to the drains, access and pain) is closely linked to the largest deficit in muscle strength (M2), emphasizing the need for early inclusion of this patient in cardiac rehabilitation protocols with supervised physical exercise.

Limitations of the study

The fact that this was a pilot study limits the interpretation of some data. Even in the absence of a gold standard for assessment of peripheral muscle strength, dynamometry is an effective, practical and reproducible method has demonstrated in the literature[15].



Patients undergoing cardiac surgical procedures may present reduction in peripheral muscle strength in the immediate postoperative period, with a tendency to gain strength in subsequent days until the day of discharge.

Potential conflict of interest

There was no potential relevant conflict of interest.


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No financial support.

Authors' roles & responsibilities

KMSS: Data collection

MLCN: Editing

VOC: Guidance, supervision

VJSF: scientific writing and supervision

WMSJ: training and supervision of staff

AAAF: Data Collection

TCFC: Evaluation of patients

LAPC: Coordination and guidance

Article receive on Wednesday, September 4, 2013

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