Increased resting heart rate
Early increased cardiac stroke
Reduced tidal volume
Potential permanent restrictive pulmonary disease due to fixed contractures of the costovertebral joints
Reduced FVC and FEV1
Loss of elastic recoil as a result of structural changes within the lungs
Tendency for mucus to pool in the lower part of the airway
Collapse of airways and small areas of lung tissue (atelectasis), which reduces the area available for gaseous exchange
Atrophy of postural muscles, leading to an increased risk of falls and disability 
Reduction of bone mass in the spine and lower limbs
Decreased gastric bicarbonate secretion and increased acidity within the stomach
Symptoms associated with gastroesophageal reflux disease (GERD)
Increased transit time and constipation
Release of ANP and increased diuresis
Transient increase in plasma and urinary urea, a decrease in plasma creatinine, and no change in urinary creatinine
Rise of urinary calcium excretion
Incomplete emptying and urinary stasis, due to weakened abdominal and pelvic floor musculature
Renal and bladder stones and infections
Higher risk of pressure sores
Depressed levels of aldosterone and antidiuretic hormone
Sodium loss during diuresis and hyponatremia with subsequent increased plasma renin activity and increased plasma aldosterone levels
Progressive loss of potassium in the urine due to aldosterone secretion
Increased cortisol secretion, onset of insulin resistance, impaired glucose tolerance, and the subsequent development of type 2 diabetes
Central and peripheral nervous system
Dysfunctions in mental status (confusion, sleep disorders, drowsiness)
Difficulties in posture and balance in sitting and standing position
Development of polyneuropathies
8.2 Prevention of Bed Rest Syndrome
Patients in the intensive care unit (ICU) could be the paradigm of the management of bed rest via mobilization. They are often sedated, critical/frail patients, with obvious difficulty in changing position, sitting or walking. Immobilization in complex patients in the ICU, together with systemic inflammation, is a strong independent risk factor for the development of intensive care unit-acquired weakness (ICUAW) .
Evidence indicates that functionally significant joint limitations are shown by more than a third of patients admitted to ICU for over 2 weeks.
It is noteworthy that enough damage to create the basis for a decubitus ulcer is done after as little as 2 h of immobility. Susceptibility to pressure ulcers comes from a combination of external factors (pressure, friction, shear force, and moisture) and internal factors (e.g., fever, malnutrition, anemia, and endothelial dysfunction).
Although a few years ago, early physical rehabilitation of critically ill patients was considered unsafe, in the last decade growing literature has shown the safety and feasibility of mobilizing ICU patients to prevent impairments, adverse events, in-hospital infections, and functional limitations .
In order to address these aspects, components of the ABCDE bundle include: Awaken from sedation, Breathe independently without a ventilator, Choice of sedation, Delirium management, and Early mobilization .
While preliminary data regarding early mobilization of ICU patients has been shown to be safe, feasible, and beneficial, in one multicenter, observational Italian study, postural changes and early mobilization were prescribed in about two thirds of the cases, suggesting that these treatments are not yet widely practiced .