51
4. The studies have shown that the Korotkoff Sound Method has the worst accuracy when it comes to mea-
surement of hypotension, while the oscillating method has worse accuracy when it comes to measurement
of controlled hypertension relief.
8.2.2 Factors affecting NIBP measuring
• Select a cuff of appropriate size according to the size of the subject.
• The cuff width should be 2/3 of the length of the upper arm. The cuff inflation part should be long enough to
wrap around 50-80% of the limb concerned.
• Prior to use of the cuff, empty the cuff of any residual air inside it to ensure accurate measurement.
• Locate the cuff in such a way that the mark “
φ
” is in the position where artery pulsates clearly for best effect.
• The lower part of the cuff should be 2cm above the elbow joint.
• Do not wrap the cuff over thick clothing;
• The patient should lie in bed or sit in a chair, in order for the cuff and heart to be at the same level and the
most accurate measurement to be taken. Other postures may lead to inaccurate results;
• During measuring, do not move the arm or the cuff;
• The measuring interval shall longer than 2 minutes, in continuous measurement, too short interval may cause
arm extrusion, blood quantity increases, then cause blood pressure increases.
• Keep the patient still and calm before and during measuring as the patient’s state also affect the measuring
result, e.g. when excited or anxious, their blood pressure will go up.
• Results will also be affected by the time of day, tending to be lower in the morning and higher in the evening;
8.2.3 Clinical Limitations and Contraindications
1. Serious angiospasm, vasoconstriction, or too weak pulse.
2. Extremely low or high heart rate or serious arrhythmia (especially auricular fibrillation) will lead to unreliable
measurements or an inability to take a reading.
3. Patients connected to an artificial heart-lung machine.
4. Patient taking diuretics or vasodilators.
5. With patient suffering from major hemorrhage, hypovolemic shock and other conditions with rapid blood
pressure change or when the body temperature is too low, the readings will not be reliable, as reduced pe-
ripheral blood flow will lead to reduced arterial pulsation.
6. Patient with hyperadiposis;
In addition, statistics show that 37% people report blood pressure difference of no less than 0.80kPa (6mmHg)
between the left and right arms, and 13% people report difference of no less than 1.47kPa (11mmHg).
Note:
Some practitioners may report big discreteness or abnormal value of the blood pressure measures
when the oscillating method is used. As a matter of fact, the so-called “big discreteness” must be a term in
the sense of statistical significance of mass data. Abnormal data may be observed in some individual cases.
It is normal in the scientific experiments. It may be caused by an apparent reason, or by an unknown factor
in some cases. Such individual doubtful experimental data may be identified and eliminated using the special
statistical technique. It is not a part of this manual. The practitioner may eliminate the apparently unreasonable
data according to the experience.
8.3 SpO
2
Monitoring
8.3.1 Measuring Principle
Based on Lamber-Beer law, the light absorbance of a given substance is directly proportional with its density
or concentration. When the light with certain wavelength emits on human tissue, the measured intensity of light
after absorption, reflecting and attenuation in tissue can reflect the structure character of the tissue by which
the light passes.
Due to that oxygenated hemoglobin (HbO2) and deoxygenated hemoglobin (Hb) have different absorption
character in the spectrum range from red to infrared light (600nm~1000nm wavelength), by using these cha-
racteristics, SpO
2
can be determined. SpO
2
measured by this Gima Vital Signs Monitor is the functional
oxygen saturation -- a percentage of the hemoglobin that can transport oxygen. In contrast, hemoximeters
report fractional oxygen saturation – a percentage of all measured hemoglobin, including dysfunctional hemo-
globin, such as carboxyhemoglobin or metahemoglobin.
8.3.2 Sources of interference for SpO
2
Measurement
• Intravascular dyes such as indocyanine green or methylene blue.
• Exposure to excessive illumination, such as surgical lamps, bilirubin lamps, fluorescent lights, infrared hea-
ting lamps, or direct sunlight.
• Vascular dyes or external used colouring producta such as nail polish or tinted skin care.