Describe the stages of sleep (50% of marks).
Describe the respiratory physiological changes that occur in sleep (50% of marks).
Few candidates demonstrated a good knowledge of this topic. Few answers described the EEG changes associated with the stages of sleep. Respiratory changes in sleep were more commonly known though many candidates made no reference to the change in resistance associated with reduction in upper airway tone.
Confusion existed about the tidal volume changes in sleep. The question asked specifically for respiratory changes and marks were not awarded for discussion about cardiovascular or metabolic responses.
Considering that even grown-ass intensivists are usually unable to interpret and report polysomnography data, it seems unreasonable to expect their juniormost trainees to need to know the EEG criteria for different sleep stages. One can only assume that, in order to pass, the trainees were expected to regurgitate the names of memorised EEG patterns, which they cannot possibly be expected to ever recognise.
Stages of sleep:
|NREM N1||lightest stage, easiest to rouse||
|NREM N2||50% of normal sleep||
|NREM N3||difficult to rouse||
|REM||Characterised by rapid phasic eye movements and minimal muscle tone||
Respiratory physiological changes during sleep:
|Parameters||NREM sleep||REM sleep|
|Respiratory rate||Decreases||Variable, with apnoeas|
|Minute volume||Decreases||Decreases further|
|Alveolar ventilation||Decreases||Decreases further|
|PaCO2||Increases slightly||Increases more|
|PaO2||Decreases slightly||Decreases more|
|Hypoxic ventilatory response||Decreases||Decreases further|
|Hypercapnic ventilatory response||Decreases||Decreases further|
|Upper airway muscle tone||Decreases slightly||Decreases further|
|Upper airway resistance||Increases||Increases further|
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