We believe that the actual amount of sleep enjoyed by
the patients was very much less than the nurses' assessment
which was based on the only available criterion of
"not obviously awake". In addition we believe that the
patients' own estimates were confounded by the inability
to distinguish between sleep and times of "non-sleep"
which could not be recalled. Recent studies suggest that
total sleep time/24 hours in this ICU is of the order of
two hours/24 hours [2].