Pocket Warming of Epidural Medication

Studies have shown that warmed epidural medication resulted in a mean analgesic onset of 9.2
minutes as compared to a mean onset of 16 minutes for the same medication at room
temperature. Onset time for pain medication during labor is important to a great many
participants, thus techniques to shorten analgesic onset are relevant to daily clinical
practice. Combined-spinal epidural (CSE) techniques have been used to improve the onset and
reliability of labor analgesia compared to epidural techniques; however, CSEs have risks
associated with their usage. Firstly, is not always possible to administer a spinal dose
despite successful loss-of resistance with CSE techniques, providing less satisfactory labor
analgesia, and secondly, the CSE technique has been associated with a greater incidence of
non-reassuring fetal heart tones (FHT), uterine hyperactivity, maternal pruritis, and greater
incidence of neurologic sequelae compared to epidural analgesia. Further, CSE labor analgesia
is more likely to result in prolonged FHT decelerations if there is FHT abnormalities prior
to the neuraxial procedure. Given these potential limitations of CSE techniques for labor
analgesia, epidural medication warming may represent an effective alternative for safe and
satisfactory labor analgesia.

Previous studies in obstetric and non-obstetric patients undergoing surgery have demonstrated
a more rapid onset of sensory blockade in patients receiving body temperature (37 °C)
epidural medication compared to room temperature medication, though other reports have found
no significant difference in the onset of sensory blockade when comparing body temperature to
room temperature epidural medications. To the knowledge of the investigators, there are few
studies examining the effect of warmed epidural medications for patients receiving epidural
labor analgesia.

In the experience of the investigators' colleagues, the close proximity to the body has a
warming effect on the epidural medication and ultimately leads to quicker onset of pain
relief once administered. Pocket warming does not warm the medications to the same extent as
an incubator, but is certainly less expensive and is readily available to every obstetric
anesthesia practice.

The investigators have previously measured the temperature of five 10mL syringes of normal
saline at room temperature and at baseline the average was 21.7 °C (range 21.5-21.9 °C), and
increased to an average of 29.7 °C (range 29.1 - 30.2 °C) after 1.5 hours of pocket warming.
It has not been studied and is unknown if this degree of warming would be effective in
enhancing the onset of labor analgesia, but such information is valuable given that an
approximate 30 °C temperature may be accomplished by simple pocket warming and is within
manufacturer recommended storage temperatures of 15-30 °C.

The investigators also assessed the potential for epidural medication cooling by measuring
the temperature of one of the investigator's 10mL saline syringes for twenty minutes after
removal from the warm pocket environment. The initial temperature of 30.0 °C had cooled to
27.0 °C by five minutes, 24.7 °C by ten minutes, 22.9 °C by fifteen minutes, and had returned
to baseline room temperature by twenty minutes. The time between medication removal and
dosing is important to consider given that significant cooling may occur and negate any
potential benefits of warming the medication. This cooling effect makes use of a centralized
warmer less promising, as it could take 10-20 minutes to position the patient and complete
placement of the epidural catheter prior to dosing the medication. The use of a bedside
incubator or a pocket warming technique would be useful in this regard, because the
medication could be administered immediately after removal from the warm environment.

The investigators hypothesize that pocket warming in the front, upper pocket would be
beneficial in enhancing onset of labor analgesia relative to room temperature medication.

Inclusion Criteria:

1. Women with a single vertex presentation fetus at term (38-42 weeks)

2. Intact fetal membranes or membrane rupture <6 hours previously

3. Request to have an epidural for labor analgesia

4. Provide written consent for the study.

Exclusion Criteria:

1. Patients being treated/managed for chronic pain

2. Allergies or significant adverse reactions to local anesthetic or opioid medications

3. Contraindication to labor epidural placement

4. Patients with history of spine abnormalities or spine surgery

5. Clinical signs or symptoms of infection

6. Baseline temperature > 37.6 °C

7. Non-English speaking

8. Prisoners

9. Age less than 18 years old