International System of Units (SI)

• The International System of Units (SI) is a globally accepted system of measurement units, established in 1960.
• It is based on seven fundamental units from which all other units are derived.
• The SI system provides a consistent and standardized way of measuring quantities.
• The SI system is crucial for scientific, medical, and technological advancement.

Seven Fundamental SI Units

• Meter (m) measures length
• Kilogram (kg) measures mass
• Second (s) measures time
• Ampere (A) measures electric current
• Kelvin (K) measures temperature
• Mole (mol) measures the amount of substance
• Candela (cd) measures luminous intensity
• Standardized units ensure measurements and calculations are consistent, accurate, and universally understood in medicine.

Importance of SI Units in Medicine

• Medical practice relies on precise measurements for diagnosis, treatment, and patient monitoring.
• SI units ensure accuracy, reducing the risk of errors in drug dosages, blood pressure, temperature, and critical health parameters.
• SI units are standardized globally, allowing consistency in medical research, clinical practices, and international health guidelines.
• Consistency is crucial when comparing medical data from different countries or conducting global clinical trials.
• Accurate dosages of medications are vital for patient safety; overdose or underdose can be avoided by following standardized units.
• Doctors, researchers, and healthcare professionals worldwide use SI units.
• In radiology, radiation doses are expressed in gray (Gy) or sieverts (Sv), which are standardized SI units.

Medical Applications of SI Units

• The SI unit for temperature is the Kelvin (K), but in medical practice, temperature is commonly measured in Celsius (°C). Normal body temperature is around 37°C.
• Fever is typically defined as a body temperature over 38°C, and temperatures exceeding 40°C can be dangerous.
• Blood pressure is measured in millimeters of mercury (mmHg).
• mmHg is derived from the SI unit of pressure—the Pascal (Pa).
• mmHg is used in clinical practice to measure systolic and diastolic pressure with a typical blood pressure reading of 120/80 mmHg.
• The SI unit for mass is the kilogram (kg).
• A patient's weight is often measured in kilograms in clinical practice.
• Medication dosages are calculated based on weight, and standardized units ensure correct dosage prescriptions.
• Medications are often prescribed in milligrams (mg), micrograms (µg), or milliliters (mL).
• By using the correct SI units for drug dosages it helps to avoid harmful errors.
• For a drug requiring a dosage of 5 mg, using precise SI units ensures the patient receives the correct amount.
• Radiation dosage is measured in gray (Gy) for absorbed dose and sievert (Sv) for the biological effect of radiation.
• X-ray doses and other forms of medical imaging require standardized measurements with strict limits placed on exposure to ensure patient safety.
• Oxygen saturation is commonly measured in percent (%).
• The underlying measurements often relate to partial pressures of gases (Pa) in the blood, based on the SI unit of pressure (Pascal, Pa).
• The SI unit of concentration is moles per liter (mol/L) and in medical practice, this is often expressed in millimoles per liter (mmol/L) for easier interpretation.

Advantages of Using SI Units in Medicine

• International Standardization
• Reduced Ambiguity
• Improved Patient Outcomes
• Regulatory Compliance