Did You Know?
Chemical Indicators Are Used to Monitor Packs During Sterilization ❓❓❓
Chemical indicators allow us to assess whether the sterilization conditions have been achieved inside a pack (the instruments to be sterilized). ❓
By evaluating the results of chemical indicators, we can determine:
✅ Whether instrument preparation procedures, especially drying, meet the required standards.
✅ The appropriateness of packaging – whether the pack is overloaded or if the chosen packaging method aligns with the sterilization program used.
✅ Whether loading and arrangement of items in the sterilizer chamber follow the correct procedure and do not obstruct sterilant penetration.
✅ The operational performance of the sterilizer, including technical parameters (temperature, time, steam saturation), and whether they meet necessary conditions.
🔎 Therefore, chemical indicators play a critical role in early detection of any abnormalities throughout the entire processing cycle – from preparation, packaging, and chamber loading to sterilizer operation.
📌 Minimum usage: One chemical indicator per pack (Decision No. 3671/QĐ-BYT, 27/09/2012, Ministry of Health; and ANSI/AAMI ST79:2017)
📌 According to ISO 11140, there are six types, but Type 4 and Type 5 chemical indicators are the most commonly used for monitoring inside packs:
1️⃣ Multi-parameter chemical indicator (Type 4) – Stated Value (SV) at 121°C: 15 minutes
2️⃣ Integrated chemical indicator (Type 5) – SV at 121°C ≥ 16.5 minutes
📍 In practice, reputable brands’ Type 5 integrated indicators often have SV values higher than the minimum.
🌿 Example: a Type 5 bar-type indicator may have an SV at 121°C ranging from 20–25 minutes. This means the indicator will only show PASS after 20–25 minutes of exposure at 121°C.
📍 Hence, Type 5 indicators are harder to achieve than Type 4. This can be challenging for some 121°C sterilization programs in hospitals, especially for machines with sterilization times of 16–20 minutes (even though they meet EN 285 standards – minimum sterilization time at 121°C is 15 minutes).
➡️ SV (Stated Value) of a chemical indicator is the process parameter required for the indicator to change to a PASS state. For example, a Type 4 indicator according to ISO 11140 has an SV of 15 minutes at 121°C. If exposed to 121°C steam for 15 minutes, the indicator color will change to PASS according to the manufacturer’s instructions.
⚠️ Important considerations when selecting and using chemical indicators:
✅ Follow the manufacturer’s instructions, especially regarding storage conditions suitable for Vietnam’s hot and humid climate. Proper storage ensures stability and accuracy, protecting indicators from temperature and humidity:
🌿 Terragene chemical indicators: 30–80% RH
🌿 3M (Solventum) chemical indicators: 40–60% RH
✅ Indicators packaged in resealable pouches are easier to store.
🌿 Example: Terragene chemical indicators come in aluminum foil pouches with zip-lock, allowing partial use without moisture exposure.
✅ Selection should be based on SV value appropriate to the sterilization program.
🌿 Example: For a 121°C sterilization program lasting 16 minutes, a Type 4 indicator with SV 15 min is suitable.
❌ Conversely, using a Type 5 indicator with SV 20 min at 121°C may result in a FAIL, not because the machine is faulty or the indicator is poor quality, but because sterilization conditions are insufficient for the indicator to reach its designed SV. This may lead to misinterpretation of sterilization effectiveness.
📍 Place the indicator at the most difficult-to-reach point for the sterilant inside the pack (ANSI/AAMI ST79:2017).
🚨 What to do if a chemical indicator fails?
According to ANSI/AAMI ST79:2017:
1️⃣ Do not use the pack; report and return it to the sterilization center.
2️⃣ Analyze possible causes based on:
👉 Machine parameters (temperature, pressure, printout)
👉 Results of chemical indicators in other packs of the same sterilization load
👉 Biological indicators (if available)
❗ If only a few packs fail → do not consider the entire batch invalid.
⚠️ Common causes of chemical indicator failure:
1️⃣ Instruments not fully dried, moisture remaining in the pack
2️⃣ Packaging issues: overloading, tightly packed fabric packs preventing steam penetration, filter or valve issues in sterilization containers
3️⃣ Overloaded sterilizer chamber
4️⃣ Incorrect indicator placement, blocked by instruments or packaging material
5️⃣ Instruments left overnight before sterilization → indicator absorbs environmental moisture
6️⃣ Wrong indicator type selected (SV not suitable)
📌 For Plasma/H₂O₂ sterilization: if instruments are wet → the cycle may fail, and the indicator may not show PASS due to moisture diluting H₂O₂, reducing concentration to change indicator color.
✅ Chemical indicators are crucial evidence to ensure instruments meet sterilization conditions.
➡️ Place correctly – choose correctly – store correctly – read results correctly.
Content responsibility: Dr. Phạm Thị Thanh Thủy
📌 For more information, contact hotline: 093 955 66 66 or 084 880 1708