Page 255 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

CHAPTER 23: Sleep 159

in the 24-hour pattern of blood pressure, heart rate, body tempera- Patient care activities are obvious and frequent causes of sleep disrup-
ture, and spontaneous motor activity. A recent study that analyzed tion. Countless examples exist: nursing and physician assessments, blood
26
6-sulfatoxymelatonin excretion patterns from samples collected hourly draws, bathing, wound changes, endotracheal suctioning, radiography,
showed that while the circadian rhythms of critically ill patients receiv- transportation, automated blood pressure monitoring, etc. In a study of
ing mechanical ventilation and continuous intravenous sedation were ICU survivors vital sign measurement and phlebotomy were considered
usually preserved, abnormalities in timing were frequent, most com- more disruptive than noise. While in certain cases the timing of par-
33
monly in the form of a phase delay. 27 ticular patient care activities cannot or should not be modified, there
The relative contribution of disease, medications, and the ICU envi- are numerous other activities—bathing and chest radiography being two
ronment to the development of these abnormalities is unknown. Even if obvious examples—that are typically performed at times that have less
the circadian rhythms of critically ill patients are abnormal at the time to do with the patient’s condition and more to do with the organization
of admission to the ICU, the results of the preceding studies suggest that of work activities by the ICU or by the ancillary service involved. These
they do not synchronize effectively to the ICU environment. This may activities represent obvious opportunities for improving patient sleep.
be partly due to weak light-dark and activity cycles in modern ICUs. It While the effects of sedatives and narcotics on sleep are considered
is also possible that entrainment is inhibited by sedative-induced eye separately below, it is important to remember that many other medica-
closure, which limits retinal exposure to ambient light. In addition, it is tions administered to ICU patients have the potential to affect sleep.
34
not known whether the dispersion of sleep-like activity from sedation For instance, vasoactive drugs like norepinephrine, phenylephrine,
over a 24-hour period itself affects circadian rhythmicity. Conceivably, and epinephrine reduce N3 and REM sleep. Beta-blockers can cause
appropriately timed light exposure could help normalize circadian tim- sleep disturbances including reduced REM sleep and vivid nightmares.
ing in such individuals similar to its use in ambulatory patients with cir- Antihistamines and tricyclic antidepressants can cause sleepiness while
cadian rhythm disorders; however, this remains to be studied. Overall, also reducing sleep quality in some subjects. Corticosteroids can cause
much work remains to be done to elucidate the causes and clinical insomnia and nightmares and reduce REM sleep and sleep continuity.
significance of these abnormalities in circadian rhythmicity. Acute illness may itself affect sleep quality, whether though indirect
means of inducing pain, breathlessness, or anxiety, or through direct
SLEEP IN THE CRITICALLY ILL PATIENT means, as in the sleep-wake cycle reversal that may complicate the early
stages of hepatic encephalopathy. Some illnesses are associated with
■ OVERVIEW OF SLEEP ARCHITECTURE altered states of consciousness and electroencephalographic abnormali-
AND POTENTIAL DISRUPTERS TO SLEEP ties that defy discrete classification into wakefulness or sleep. Indeed, in
a study performed by Freedman et al, patients with sepsis exhibited EEG
Considered together, studies of sleep in critical illness have shown a abnormalities prior to the clinical recognition of sepsis. 31
variety of abnormalities (Table 23-3). The sleep of patients receiving In summary, most critically ill patients experience significant and fre-
more than trivial amounts of sedation is difficult to assess and is dis- quently profound sleep disruption that is the result of varying degrees of
cussed below. Similarly, critically ill patients are subject to a host of toxic patient care activities, underlying illness, environmental disruption, and
and metabolic encephalopathies that confound normal sleep scoring. medications. Patients receiving mechanical ventilation are exposed to
28
When these patients are excluded, the polysomnographically assessed an additional form of sleep disruption, while the effects of intravenous
sleep of critically ill patients has been shown to be highly fragmented sedation on sleep are complex and not well understood. The effects of
and nonconsolidated and dispersed over a 24-hour period. The more these treatments are considered in more detail below.
29
restorative stages of N3 sleep and REM sleep are severely reduced or
even absent in many studies. Collectively, these studies suggest that ICU ■
patients experience severe sleep disruption. MECHANICAL VENTILATION AND SLEEP
There are many potential causes of sleep disruption in the critically Studies on mechanical ventilation and sleep are relatively few but are
ill patient, ranging from those that originate from the patient’s underly- growing in number. Because it is challenging, if not impossible, to study
ing condition to environmental light and noise to patient care activities. the isolated effects of mechanical ventilation on sleep in patients who
Early efforts focused on the role of the ICU environment. Indeed, the are receiving sedation, the discussion below is drawn upon those studies
typical ICU is excessively noisy, exceeding Environmental Protection that have been performed in patients receiving little to no sedation at the
Agency guidelines and capable of inducing sleep disruption in healthy time they were studied.
individuals exposed to recordings of ICU activity. However, several Broadly speaking, mechanical ventilatory support itself—as opposed
30
studies employing continuous polysomnography have shown that envi- to the sleep-disrupting activities that may attend it, like suctioning—
ronmental noise probably does not cause more than about 20% of all may be associated with poor sleep if the level of support is inadequate,
arousals and awakenings 31,32 : a significant problem, but far from the only, causing dyspnea and arousal; if it is excessive, leading to hypocapnia
or even the most important, one. It is also true that many studies have and central apneas; or if there are significant differences between the
demonstrated excessive light levels at night; however, ICU survivors timing and duration of neural and mechanical inspiratory time. Indeed,
have generally ranked light disruption lower than noise and patient care ventilator settings that may be perfectly appropriate for a patient during
activities where sleep disruption is concerned. Interestingly, the biggest wakefulness may be ill-suited for sleep, given the reduction in respira-
problem with light in the ICU may have to do with inadequate exposure tory drive that attends sleep. This concept is exemplified by a study
to light during the day, as discussed previously. performed by Meza and colleagues, who showed that periodic breathing
and repetitive central apneas could be induced in normal volunteers
with increases in pressure support, and was associated with a decrease in
35
TABLE 23-3 Sleep Abnormalities in Critically Ill Patients Who Are Not Deeply Sedated arterial P CO 2 below the apnea threshold. Similarly, a study performed by
Fanfulla et al in patients with stable chronic respiratory failure or noc-
Total sleep quantity is highly variable
turnal hypoventilation due to neuromuscular disease showed that pres-
Sleep is highly fragmented and nonconsolidated and distributed over 24 hours sure support settings that were tailored to the patient’s respiratory effort
Sleep is lighter: predominantly composed of Stages N1 N3 and REM sleep resulted in improved sleep quality over the patient’s usual home settings,
and N2 and with reduced or absent Stage which were titrated on simple clinical parameters. Interestingly, the
36
Increased arousals and awakenings improvement was associated with a reduction in ineffective efforts, an
effect that may have been achieved through a reduction in dynamically
Circadian rhythms frequently disturbed determined intrinsic PEEP, thereby aiding ventilator triggering.

section02.indd 159 1/13/2015 2:05:07 PM