Clinical Consequences of Prolonged MV
As a consequence of weaning failure, patients will undergo prolonged ventilator dependence, a component of the 'chronic respiratory illness'. Besides prolonged ventilator dependence, chronic critical illness comprises additional features such as weakness due to myopathy and neuropathy, and body composition alterations such as loss of lean body mass, increased adiposity and anasarca. Other features of this syndrome include specific neuroendocrine changes of anterior pituitary hormones, such as growth hormone, thyrotrophin and prolactin, contributing to low target organ hormone levels and impaired anabolism;[19,20] increased susceptibility to difficult-to-eradicate infections;[21,22] coma or protracted or permanent delirium; nutritional deficiency-associated skin breakdown, edema, incontinence and prolonged immobility.
Some of these features (e.g., brain dysfunction and symptom distress) may also be present in the acute critical illness (or other conditions). Other features (e.g., changes in body composition and neuroendocrine patterns) have only been described in the chronic phase. Chronic critical illness is defined by the presence of this clinical constellation associated with prolonged dependence on MV. Although currently available bedside methods of assessment of respiratory and peripheral muscle function in critically ill patients may be considered somewhat inadequate, evidence suggests that respiratory muscles may be relatively spared from damage resulting from immobility, prolonged MV and systemic inflammation in critical illness. Furthermore, the consciousness of total or partial dependence on a machine for breathing may induce emotional stress in patients requiring prolonged MV (and in their caregivers). The stress may negatively impact ventilator weaning and survival. Depressive disorders have been diagnosed in 42% of difficult-to-wean patients, and patients with depressive disorders seem to be more likely to suffer from weaning failure and reduced survival.
Expert Rev Resp Med. 2010;4(5):685-692. © 2010 Expert Reviews Ltd.
Cite this: The Difficult-to-wean Patient - Medscape - Oct 01, 2010.