Peripheral Skin Temperature Changes Following Spinal Anaesthesia for Category 4 LSCS

Regional anaesthesia of the lower limbs blocks sympathetic nerve fibres as well as sensory and motor fibres. It has been documented previously in the non-pregnant population that the blockade of sympathetic nerve fibres by regional anaesthesia (including spinal, epidural and lumbar plexus anaesthesia) results in vasodilation of peripheral blood vessels and an increase in the blood flow to the skin, increasing the peripheral skin temperature. Additionally thermoregulation has been found to be impaired more by spinal anaesthesia than epidural anaesthesia. The aim of the study is to measure peripheral skin temperature changes occurring in the lower limbs following spinal anaesthesia in the pregnant obstetric population undergoing category 4 lower segment caesarean section. The hypothesis is that peripheral skin temperature will rise following spinal anaesthesia and that this temperature change could be used as a measure of bilateral sympathetic block which may be an indicator of potential success of spinal anaesthesia. Future follow up studies could then potentially determine if peripheral skin temperature can also be used as a marker to determine the success of epidural analgesia for labour.

The study will involve temperature measurement by Covidien Mon-a-Therm skin temperature probes and Braun Welch Allyn tympanic membrane thermometer devices on the dorsum of the right and left feet. The study will last from the time the parturient arrives in theatre for their lower segment caesarean section until the parturient leaves the recovery area.

The hypothesis is that peripheral skin temperature will rise following spinal anaesthesia and that this temperature change could be used as an indicator of potential success of spinal anaesthesia.

This is an observational study. The investigators will obtain ethics committee approval for conducting the study. ASA 1 and 2 full term (37-42 weeks), parturients with singleton pregnancy, normal placental position, scheduled for category 4 LSCS under 'single-shot' spinal anaesthesia will be recruited. The investigators intend to recruit 60 parturients. The parturients will undergo an informed consent process including an explanation of the methods and risks of the study. A patient information leaflet will be provided for the parturients.

The data will be collected on a password protected spread-sheet with no patient identifiable information. A grant for funding has been granted from the Obstetric Anaesthetists' Association.

Prior to establishment of spinal anaesthesia, the skin temperature of the parturient's feet will be measured on the dorsum of the right and left feet above space between the 2nd and 3rd metatarsal bones while the parturient is lying supine with left lateral tilt. The temperature will be measured by Covidien Mon-a-Therm skin temperature probes and a Braun Welch Allyn tympanic membrane thermometer device. Following spinal injection when the parturient is lying supine with lateral tilt, the temperature will be re-measured by Covidien Mon-a-Therm skin temperature probes and a Braun Welch Allyn tympanic membrane thermometer device. The skin temperature of the parturient's feet will be monitored continuously by the Covidien Mon-a-Therm skin temperature probes using the GE Healthcare monitor with readings transcribed every 1 minute by the research investigator until transfer onto the bed at the end of surgery. The skin temperature of the parturient's feet will be measured and recorded every 1 minute using a Braun Welch Allyn tympanic membrane thermometer device until the sterile drapes are applied prior to commencing the operation and then again after removal of the drapes prior to transfer onto the bed. Following transfer to the post-operative recovery area, the skin temperature of the parturient's feet will be measured and recorded every 10 minutes using a Braun Welch Allyn tympanic membrane thermometer device until discharged to the ward from the recovery area (usually 2 hours from departmental guidelines).

Theatre room temperature will be measured and recorded at the start of anaesthesia and at the end of surgery using a room thermometer. Surgical drapes will be applied over the parturient's lower limbs during the caesarean section procedure as per the investigators routine practice. The ambient temperature under the surgical drapes will be measured and recorded at the start of anaesthesia and at the end of surgery using a room thermometer.

Tympanic temperature will be measured by a Braun Welch Allyn tympanic membrane thermometer device before spinal anaesthesia and then every 30 minutes until the end of surgery as per NICE clinical guideline 65.

Spinal anaesthesia will be conducted as per usual practice. All intravenous fluids will be given through a fluid warmer.

Parturient data to be recorded will include: Age, Weight, Height, BMI, total dose of intra-operative vasopressor given, highest estimated dermatome level of anaesthesia to cold (ethyl chloride spray) bilaterally prior to commencing surgery, level motor block using straight leg raise as per normal practice when anaesthesia ready for surgery, duration of surgery, estimated blood loss, total volume of intravenous fluids given (including any blood products). Dermatome level of anaesthesia will be measured to cold (ethyl chloride spray) level and motor block will be measured using straight leg raise as per normal practice, in recovery, every 30 minutes.

6 parturients will be recruited as a control group. The skin temperature of these parturient's feet will be measured on the dorsum of the right and left feet above space between the 2nd and 3rd metatarsal bones while the parturient is lying supine with left lateral tilt in theatre. The temperature will be measured by Covidien Mon-a-Therm skin temperature probes and a Braun Welch Allyn tympanic membrane thermometer device. The sterile drapes will be applied and the skin temperature of the parturient's feet will be monitored continuously by the Covidien Mon-a-Therm skin temperature probes using the GE Healthcare monitor with readings transcribed every 1 minute by the research investigator for 30 minutes. After 30 minutes, the skin temperature of the parturient's feet will be measured and recorded every 1 minute using a Braun Welch Allyn tympanic membrane thermometer device for 5 minutes. Theatre room temperature will be measured and recorded for this control group of parturients. The ambient temperature under the surgical drapes will be measured and recorded using a room thermometer.

Inclusions / exclusions:

Parturients will be excluded from the study if the parturient refuses or if they have medical conditions that may affect peripheral temperature and therefore the results of the study. The exclusion criteria are: Parturients converted to other forms of anaesthesia (not just spinal anaesthesia); Parturients with a pyrexia / sepsis; Parturients with peripheral vascular disease (including Raynauds); Parturients with cardiovascular disease; Parturients with diabetes mellitus (gestational, type 1 or 2); Hypertensive disorders of pregnancy; ASA 3+ Parturients; BMI \>40 or \<18; Parturient refusal.

Eligibility Criteria:
Inclusion Criteria:

* Full term (37-42 weeks) parturients
* ASA 1 and 2
* Singleton pregnancy
* Normal placental position
* Scheduled for category 4 LSCS
* 'Single-shot' spinal anaesthesia
* Signed informed consent
* Received a patient information leaflet

Exclusion Criteria:

* Any medical conditions that may affect peripheral temperature
* Parturients converted to other forms of anaesthesia (not just spinal anaesthesia)
* Parturients with a pyrexia / sepsis
* Parturients with peripheral vascular disease (including Raynauds)
* Parturients with cardiovascular disease
* Parturients with diabetes mellitus (gestational, type 1 or 2)
* Parturients with hypertensive disorders of pregnancy
* ASA 3+ Parturients
* BMI \>40 or \<18
* Parturient refusal.