sufficient. For patients with ASA III or IV, treatment within a hospital environment
and pulse oximetry, blood pressure cuff, and/or electrocardiograph monitoring would
be prudent. This applies to only a very small proportion of patients such as those with
cystic fibrosis with marked lung scarring or children with severe congenital cardiac
disease where there is high blood pressure or cyanosis.
The patient
The clinician should pay careful attention to the patient's level of anxiety. This is
achieved by assessing the patient's responses to an operative stimulus such as the
dental drill. The level of sedation is assessed by the patient's demeanour compared
with his or her presedation behaviour. It is important to note that different patients
exhibit similar levels of impairment at different concentrations of nitrous oxide. If the
patient appears to be too heavily sedated then the concentration of nitrous oxide
should be reduced. There is no need to use pulse oximetry or capnography (to
measure exhaled carbon dioxide levels) as is currently recommended for patients
being sedated with intravenously administered drugs.
The machinery
At all stages of inhalation sedation, it is necessary to monitor intermittently the
oxygen and nitrous oxide flow meters to verify that the machine is delivering the
gases as required. In addition, it is essential to look at the reservoir bag to confirm that
the patient is continuing to breathe through the nose the nitrous oxide gas mixture.
Little or no movement of the reservoir bag suggests that the patient is mouth
breathing, or that there is a gross leak, for example, a poorly fitting nasal mask.
Key Points
For nitrous oxide inhalation sedation:
- set the flow;
- slowly titrate the dose;
- monitor the patient's response;
- monitor the equipment.
4.11.7 The planes of inhalation sedation
The administration of oxygen-nitrous oxide gas mixture for sedating child patients
induces three levels or planes of analgesia and sedation.
Plane 1: moderate sedation and analgesia
This plane is usually obtained with concentrations of 5-25% nitrous oxide (95-75%
oxygen). As the patient is being encouraged to inhale the mixture of gases through the
nose, it is necessary to reassure him or her that the sensations described by the
clinician may not always be experienced. The patient may feel tingling in the fingers,
toes, cheeks, tongue, back, head, or chest. There is a marked sense of relaxation, the
pain threshold is raised, and there is a diminution of fear and anxiety. The patient will
be obviously relaxed and will respond clearly and sensibly to questions and
commands.