Q The humidity in our ORs recently was more than 70 percent, and we postponed some surgery while we brought it down to the recommended 50 to 60 percent. However, I have yet to find a textbook that states whether it is higher or the lower humidity that should concern us. Should we hold up surgery if humidity levels are either too high or too low?

A Delaying surgery for humidity levels that are extremely high or low can prevent many infection control and safety problems involving healthcare workers and patients.

The recommendations for humidity's being kept in the 50 to 60 percent range is essentially derived from the concept of human comfort. It is well known that very low humidity causes dehydration and high humidity causes bronchial/respiratory problems. But those aren't the only reasons to maintain OR humidity in this range:

• Low humidity can create an environment ripe for potential errant electrosurgical sparks and static discharges.
• Low humidity makes fabrics dehydrate, joining surfaces shrink and liquids evaporate.
• Excess dryness can be a serious problem in anesthesia administration. Patients benefit from breathing warm and humid gases during anesthesia, because warm gases typically help maintain body temperature and help prevent airway and bronchial drying during intubation.
• Humidity must be controlled for all forms of sterilization. Fabrics and devices need to be stabilized/pre-conditioned to a relative humidity of 50 percent for effective normal sterilization cycles.
• High humidity does not cause problems unless it condenses into moisture, which then will carry any "bugs" it runs into. Condensation can form in high humidity for several reasons. For example, introducing something cold will cause condensation to form, and stagnant air (such as you might find in the corners of the room) can accumulate enough moisture that it eventually condenses. High humidity also causes doctors and nurses to sweat, which produces moisture.

Q While it's true having your hands below waist level does not, in itself, contaminate anything, isn't it also true that if you can't see something, you can't guarantee its sterility?

A I don't buy the "being seen" premise. Many sterile items in a sterile field are not always seen or easily visible. Being seen also means an item has a greater potential to be contaminated by airborne bacteria. For example, dust will settle on the top of the Mayo stand but not on the sides that hang down - yet the top is considered sterile, while the sides are not because they can't be "seen." The front of a surgeon's gown will always be more highly contaminated than the back when the procedure starts and becomes more so as time passes, yet the front is considered sterile, the back is not. This "being seen" premise is behind the rule that a sterile field set-up that is delayed will remain sterile as long as someone is there to watch it. But the mere fact of someone's being there adds potential contamination to the field.