Other senses, such as hearing, vision, touch, and proprioception, are impaired in
addition to the sensation of pain being reduced. The pupils are normal in appearance
and contract when a light is shone into them. The peri-oral musculature, so often
tensed involuntarily by the patient during treatment, is more easily retracted when the
dental surgeon attempts to obtain good access for operative work. The absence of any
side-effects makes this an extremely useful plane when working on moderately
anxious patients.
Plane 2: dissociation sedation and analgesia
This plane is usually obtained with concentrations of 20-55% nitrous oxide (80-45%
oxygen). As with plane 1, patients do not always experience all the symptoms. This
should be remembered when reassuring and encouraging them.
As the patient enters this plane, psychological symptoms, described as dissociation or
detachment from the environment, are experienced. Sometimes this dissociation is
minimal, at other times it is profound. It may also take the form of a euphoria similar
to alcoholic intoxication (witness the laughing gas parties of the mid-nineteenth
century). The patient may feel suffused by a warm wave, and may experience a slight
humming or buzzing in the ears, and a drowsiness or light-headedness sometimes
described by the patient as a 'floaty' or 'woozy' feeling.
The overall demeanour of the patient will be relaxed and acquiescent. Apart from the
overall appearance of relaxation, one of the few tangible physical signs is a reduction
in the blink rate. At the deeper level of this plane of sedation the psychological effects
become more pronounced. Occasionally, a patient will repeat words or phrases
several times in succession. The words repeated may or may not make sense.
There is a noticeable tendency for the patient to dream, the dreams usually being of a
pleasant nature. It is believed by many operators that the dreams experienced by the
patient are to some extent conditioned by the ideas and thoughts introduced by the
dental surgeon during the induction phase of sedation. The sedative effect is
considerably pronounced, with both psychosedation and somatic sedation being
present.
The psychosedation takes the form of a relaxed demeanour, and a willingness on the
part of the previously unwilling patient to allow treatment regarded as frightening or
especially traumatic. The somatic sedation takes the form of physical relaxation,
unresisting peri-oral musculature, and occasionally an arm or leg sliding off the side
of the dental chair indicating profound relaxation. The analgesic effect is probably
accentuated by the sedation and sense of detachment. The patient is still able to
respond to questions and commands, although there may be a considerable mental
effort involved in thinking out the answer. The response is usually delayed and
sluggish. Paraesthesia may be more pronounced and cover a greater area of the body
than in plane 1. The patient is nevertheless obviously conscious and can demonstrate
this by keeping the mouth wide open to assist the dental surgeon during operative
treatment. On recovery, the patient may exhibit total amnesia. Nausea is a rare side-
effect and very occasionally (in less than 0.003% of administrations) a patient may
vomit.