Sleep During Mechanical Ventilation
Sleep During Mechanical Ventilation
Purpose of Review: This review addresses the growing interest in the study of sleep during critical illness.
Recent Findings: We know that sleep, in all of its measurable aspects, is severely deranged in critically ill patients during mechanical ventilation. There is growing evidence that mode of mechanical ventilation, medications, and acuity of illness may contribute to such sleep derangements and that conventional factors such as noise and health care delivery may be playing a much smaller role than previously thought. Alternatively, changes in sleep-wakefulness state can alter patient-ventilator interaction, which may in turn influence physicians' decision-making. Sleep organization may predict functional outcome in patients with head trauma. Additionally, there is evidence that poor sleep is an important factor influencing long-term quality of life in survivors of critical illness.
Summary: A more complete understanding of the etiopathogenesis of sleep derangements during mechanical ventilation may identify new interventions to help improve sleep, and possibly favorably influence short-term and long-term outcomes.
Over the last 30 years, our understanding of the interaction between sleep and breathing in ambulatory patients has evolved significantly. More recently, considerable attention has been directed at cardiovascular morbidities associated with untreated sleep-disordered breathing and potential benefits of treating such disorders. Although knowledge of sleep and breathing in ambulatory patients has evolved, very little is known about sleep in critically ill patients. Critically ill patients, especially those receiving mechanical ventilation, may be more susceptible to the cardiovascular and other physiologic consequences of derangements in sleep and breathing. Therefore, studies aimed at understanding sleep derangements in critically ill patients may be of major importance. The purpose of this review is to highlight recent developments in this new and growing field of study.
An understanding of normal sleep and the effect of medications-especially sedatives-on sleep is vital to help evaluate sleep derangements in critically ill patients. Also, in the study of sleep during mechanical ventilation, it is important to define sleep and sedation clearly. A critically ill patient who is recumbent and quiescent with eyes closed is more likely to be noted to be asleep by a sleep physician, but an intensivist may refer to the patient as being sedated. Sleep is a physiologic state of the brain. Sedation, however, can signify an artificial and augmented state of sleep or, alternatively, may be used to report the degree of unresponsiveness-as in level of sedation. It is this author's belief that such semantics, although arcane at face value, reflect the differing approaches and biases of these two groups of physicians. Both approaches are essential in understanding sleep during mechanical ventilation.
Sleep in critically ill patients can be assessed in terms of quantitative and qualitative aspects such as sleep fragmentation (arousals and awakenings) and proportion of time spent in various sleep stages (rapid eye movement [REM] and non-REM [stages 1, 2, 3, and 4]). Certain aspects of these sleep stages are of particular interest in the critical care setting. During REM sleep, the irregularities in respiration and heart rate and the accompanying paralysis of respiratory muscles excepting the diaphragm may influence mechanical ventilation. Alternatively, during slow wave sleep (stages 3 and 4), the associated growth hormone secretion and protein anabolism may be important. Lastly, circadian rhythm can be measured using movement (actigraphy), body temperature, or urinary metabolites of melatonin.
Purpose of Review: This review addresses the growing interest in the study of sleep during critical illness.
Recent Findings: We know that sleep, in all of its measurable aspects, is severely deranged in critically ill patients during mechanical ventilation. There is growing evidence that mode of mechanical ventilation, medications, and acuity of illness may contribute to such sleep derangements and that conventional factors such as noise and health care delivery may be playing a much smaller role than previously thought. Alternatively, changes in sleep-wakefulness state can alter patient-ventilator interaction, which may in turn influence physicians' decision-making. Sleep organization may predict functional outcome in patients with head trauma. Additionally, there is evidence that poor sleep is an important factor influencing long-term quality of life in survivors of critical illness.
Summary: A more complete understanding of the etiopathogenesis of sleep derangements during mechanical ventilation may identify new interventions to help improve sleep, and possibly favorably influence short-term and long-term outcomes.
Over the last 30 years, our understanding of the interaction between sleep and breathing in ambulatory patients has evolved significantly. More recently, considerable attention has been directed at cardiovascular morbidities associated with untreated sleep-disordered breathing and potential benefits of treating such disorders. Although knowledge of sleep and breathing in ambulatory patients has evolved, very little is known about sleep in critically ill patients. Critically ill patients, especially those receiving mechanical ventilation, may be more susceptible to the cardiovascular and other physiologic consequences of derangements in sleep and breathing. Therefore, studies aimed at understanding sleep derangements in critically ill patients may be of major importance. The purpose of this review is to highlight recent developments in this new and growing field of study.
An understanding of normal sleep and the effect of medications-especially sedatives-on sleep is vital to help evaluate sleep derangements in critically ill patients. Also, in the study of sleep during mechanical ventilation, it is important to define sleep and sedation clearly. A critically ill patient who is recumbent and quiescent with eyes closed is more likely to be noted to be asleep by a sleep physician, but an intensivist may refer to the patient as being sedated. Sleep is a physiologic state of the brain. Sedation, however, can signify an artificial and augmented state of sleep or, alternatively, may be used to report the degree of unresponsiveness-as in level of sedation. It is this author's belief that such semantics, although arcane at face value, reflect the differing approaches and biases of these two groups of physicians. Both approaches are essential in understanding sleep during mechanical ventilation.
Sleep in critically ill patients can be assessed in terms of quantitative and qualitative aspects such as sleep fragmentation (arousals and awakenings) and proportion of time spent in various sleep stages (rapid eye movement [REM] and non-REM [stages 1, 2, 3, and 4]). Certain aspects of these sleep stages are of particular interest in the critical care setting. During REM sleep, the irregularities in respiration and heart rate and the accompanying paralysis of respiratory muscles excepting the diaphragm may influence mechanical ventilation. Alternatively, during slow wave sleep (stages 3 and 4), the associated growth hormone secretion and protein anabolism may be important. Lastly, circadian rhythm can be measured using movement (actigraphy), body temperature, or urinary metabolites of melatonin.
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