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Cooling - therapeutic hypothermia in the neonate

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Overview

Cooling has been recognised as an effective intervention to decrease adverse neuro-developmental outcomes following perinatal asphyxia. There are no studies that have performed direct comparison between selective head cooling and whole body cooling and it is generally considered that both techniques provide neuroprotection.

Indications

For indications see NZCYCN Guideline on Neonatal Encephalopathy.

Application of Cooling

Care is taken to not overheat the infant prior to cooling.

  • Infant should be nursed on a radiant heat table
  • Turn off radiant heat source and allow to cool passively
  • Umbilical venous and arterial lines should be inserted as venous access may not be easy to establish once the infant is cooled and frequent blood samples +/- invasive BP monitoring may be required
  • Insert approved rectal probe to 5 cm
  • Turn off radiant heat source and allow to cool passively
  • Follow link to specific instructions for Criticool body cooling or selective head cooling set up and instructions.
  • Cooling (core temperature between 33.0 and 34.0°C) normally continues for a period of 72 hours before careful rewarming. Infants with severe PPHN may require warming earlier.
  • Infants are nil by mouth for the duration of cooling and inotropic support (until evidence suggests it is safe).
  • Infants do not need to be routinely intubated and ventilated during therapeutic cooling. This should be assessed on an individual case basis.

Set up and initiating whole body cooling

Initiating whole body cooling is the responsibility of the senior medical staff. Ideally ensure that the Criticool device is plugged into the red uninterrupted power supply (UPS)

  1. Assemble the Criticool device according to Reference Guide
  2. Ensure radiant heater is off & mattress either off or set at 33.5° C
  3. Before use, perform a System Calibration.
    Before performing system calibration test, check the reservoir is filled to between 1500ml and 2 litres with tap water. Top up to max after calibration is complete
    Connect to power source and turn the system on (make sure the tubes and sensors are disconnected).
    The unit will perform a self test then automatically default to cooling operational mode.
  4. To perform a System Calibration:
    Cooling mode is highlighted
    Press OK

    Cooling 1

    Check the default mode is set to NEONATAL and the temperature is 33.5° c.
    Push MENU

    Cooling 2

    Scroll down using arrows until PREFERENCE is highlighted
    Press ENTER

    Cooling 3

    System calibration should now be highlighted
    Press the up arrow
    Calibration will commence

    Cooling 4

    Calibration takes about 10 minutes.
    When the process is complete, a message appears on the screen "SYSTEM CALIBRATION COMPLETED".
    Switch to operation mode and commence cooling or go to standby mode until ready to commence cooling.
    Top up the water tank to the maximum allowable level.
  5. Insert the approved rectal core temperature probe to 5cm, secure to inner thigh of infant and connect to the device.
    Position a skin temperature probe on the infant in an area outside of the garment (i.e. upper chest, arm or leg) and connect to the device.
  6. Place the infant on the wrap
    Connect water tubes to wrap and to the CritiCool unit - the wrap automatically fills up.
    Check all garment clamps are open and a clicking sound is heard.
    Ensure the baby has a nappy on (consider urinary catheterisation).
  7. Monitor the garment closely while it fills. If it leaks, change it.
    Once the wrap has finished filling, wrap the infant in the garment, ensuring no folds, bends or areas of pressure that may interfere with the flow of water causing leaks or damage the infants' skin.
  8. Circulation is confirmed when the "flow icon" (top right of display) is turning.
  9. Ensure you have core and surface temperature readings - the infants' temperature should now be managed by the CritiCool.

Monitoring and Assessment

  1. For the period of hypothermia all infants require the following monitoring and recording:
    - Continuous rectal temperature measuring
    - Continuous heart rate, respiratory rate, pulse oximetry
    - Invasive blood pressure monitoring, if possible
    - Recording of the real time core, skin and set temperature as displayed on the therapy control panel
    *The heart rate may reduce during hypothermia so alarms must be adjusted accordingly*
  2. Continuous amplitude integrated electroencephalogram [BRAINZ] monitoring may be requested by the SMO and should be set up according to the NICU protocol.
  3. General management of the infant is provided according to the routine clinical practice guidelines and protocols such as:
    - respiratory support
    - cardiovascular support
    - management of seizures
    - infection
    - fluid and electrolyte balance
  4. Staff caring for the infant being cooled should contact the Level 3 Reg/NSANP if there are any problems reaching or maintaining a rectal temperature of between 33.5°c and 34° c throughout the 72 hour period of hypothermia.

Rewarming using the criticool device

Rewarming is initiated by the SMO. The SMO needs to decide if using CONTROLLED REWARMING mode or MANUAL rewarming.

Controlled Rewarming

  1. Firstly, the mode will need to be changed to ADULT mode.
    From the MENU page, select PREFERENCE , press ENTER.
    Scroll down to select ADULT, exit MENU.
    The display will now read ADULT COOLING.
    From the menu page, select SELECT MODE
  2. Use the UP/ DOWN arrow keys to highlight CONTROLLED REWARM and press OK
  3. The message CORE READOUT TOO LOW CHECK CORE AND OPERATE appears - the water will no longer be circulating in the wrap!
  4. Confirm the CORE reading and the TARGET TEMPERATURE (default is 36.5° c)
  5. Set TARGET TEMPERATURE (between 36° c and 38° c)
  6. Press MENU button and use UP/DOWN arrow keys to select OPERATION
  7. Once OPERATION highlighted, press ENTER button to confirm

The CritiCool heats the water, and starts circulation - the flow icon starts to rotate.

N.B If the device is set to rewarm in the NEONATAL mode, rewarming is 0.2 degrees per 30 minutes - rewarming will take about 7.5 hours. If the device is set to ADULT mode, this rewarms at the rate of 0.2 degrees per 60 minutes - rewarming will take about 15 hours.

Manual Rewarming

  1. Select NORMOTHERMIA on the control panel.
    The sun icon will replace the snow flake icon
    An alarm will sound alerting that the core temperature readout is too low - / acknowledge / select OK
  2. The set point is increased by 0.1° c every 20 minutes: this ensures an overall increase in temperature of 0.3° c every 1 hour.
  3. It will take approximately 10 hours to rewarm an infant
  4. Seizure activity may be encountered during this phase.
  5. When the core temperature reaches 36.5° c remove the garment. Turn the RHT on to baby mode to ensure the infant stays within the normothermic range.
  6. Remove the rectal probe when the core temperature has reached 37°c
  7. Once CritiCool disconnected from the infant, the system needs to be emptied.
    - Disconnect the wrap
    - Connect an emptying tube to the "water out" of the CritiCool and direct the tube into a container large enough for water collection.
    - Change the mode to empty
    - Wait for the water to empty from the system

    The CritiCool is now ready for storage until next procedure.

Follow up of baby after cooling completed

See NZCYCN Guideline on Neonatal Encephalopathy for more information about cooling and follow-up

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Document Control

  • Date last published: 18 October 2018
  • Document type: Clinical Guideline
  • Services responsible: Neonatology
  • Owner: Newborn Services Clinical Practice Committee
  • Editor: Sarah Bellhouse
  • Review frequency: 2 years