In their study, 6 of 11 patients had congestive heart failure likely contributing to the central apneas associated with PS ventilation. Our patient population consisted mainly of individuals with COPD and pneumonia leading to respiratory failure. Although none of our patients were receiving assist-control ventilation, 12 patients received SIMV with mechanical ventilator rates and there was no difference in arousals or awakenings compared with the 6 patients with PS or SIMV changed to PS ventilation. Our patients may have been more critically ill and were also receiving sedation, which may have contributed to the decreased effect of ventilator mode on sleep fragmentation.
All patients demonstrated increased delta activity. Until recently, studies have excluded patients who were receiving sedation or who were critically ill. Cooper and colleagues investigated sleep patterns in 20 critically ill patients receiving mechanical ventilation who received CS and describe a large proportion of patients with increased delta activity. Patients were retrospectively categorized into three patient groups based on the following EEG features: disrupted sleep (all stages of sleep were present); atypical sleep where abnormal sleep stage transition was present (absent stage 2 sleep); or the presence of coma (> 50% delta waves). canadian health and care mall
The patients with disrupted sleep showed predominately stages 1 and 2 sleep in agreement with other studies. However, the other two groups of patients demonstrated marked increases in delta activity. They reported that 12 of their 20 patients had “unidentifiable electrophysi-ologic sleep.” Seven of the patients had > 50% delta activity thought to be consistent with encephalopathy or coma, and five patients had atypical EEG patterns (no stage 2). Severity of illness scores, sedatives, and narcotic doses were higher among these patients, although no discernable etiology was identified to explain the increase in delta activity.
In agreement with the study by Cooper et al, we demonstrated increased delta activity in all three groups by both scoring methods. Our patients who received CS had larger amounts of delta activity than patients who received only IS. Patients in the IS group had less slowing of the delta waves and slightly higher amplitude compared to the CS and CS/ NMBA groups (Fig 1, 2). Only four of our patients (three patients were in the CS group) had > 50% delta activity, and all of these patients were intermittently observed to be awake or with spontaneous movement, which does not appear to support coma as the etiology. All patients in the CS and Cs/NMBA groups demonstrated variability in EEG with intermittent changes in wave frequency, sustained periods of a activity, or a superimposed on the delta activity.
Figure 1. mDelta activity in patients receiving CS and NMBAs. Shown are polysomnographic 30-s epoch representations of low-voltage, low-frequency delta activity scored as SWS using the 50-^V amplitude criterion in a patient receiving sedation and NMBA. Each box represents 80 |j,V and 1 s. EMG = electromyogram.
Figure 2. mDelta activity in patients receiving IS. See Figure 1 for expansion of abbreviation.