Date: 22 Jan 97 21:55:51 EST
From: Mike Darwin <>
Subject: Temperature Monitoring of Cryopatients

The following is a BioPreservation Technical Briefing 
discussing the rationale for multi-site core temperature 
monitoring in human cryopreservation patients.  This brief 
also discusses the procedures for application of specific 
(and in some cases proprietary) temperature monitoring equipment.

Temperature Monitoring in the Human Cryopreservation 
Patient: Theoretical Considerations and Practical Techniques

by Michael Darwin

Note that the tympanic temperature data collected on C-2150 
indicates that cerebral perfusion probably continued for 
approximately 50 minutes into transport.  This data is 
especially meaningful (and impressive) when it is considered 
in light of data obtained in the dog lab simulating external 
and intracorporeal cooling during CPR: cerebral perfusion 
has usually failed by 15 minutes, and earlier (as assessed by 
 intravascular dye administration) in normothermic dogs 
undergoing prolonged CPR. 

Impact of Cooling Modalities on Selection of Temperature 
Monitoring Sites

	The choice and availability of cooling modalities will 
to a great extent determine the utility of the previously 
discussed sites for patient core temperature monitoring.  If 
gastric and colonic lavage are used, particularly if they 
are used repeatedly, rectal and esophageal temperature data 
will not be meaningful until after lavaging has stopped and 
thermal equilibrium of the most deeply cooled tissues (i.e., 
the mucosa of the esophagus and rectum where the temperature 
probes are placed) is restored. In such situations the use 
of tympanic and nasopharyngeal temperature monitoring will 
be critical.  

Similarly, extensive experience with dogs has shown that 
rapid intrapulmonary loading to vital capacity with CryoVent 
at 1-2 degrees C results in a disproportionate drop in 
esophageal temperature which persists for 4 to 6 minutes 
after liquid loading is complete.  Continuous sweep flow 
liquid ventilation also decreases esophageal temperature 
well below that of central venous, tympanic and rectal 
temperatures.  In cases where pulmonary heat exchange via 
liquid ventilation is being used in conjunction with 
peritoneal and/or colonic lavage cooling, the only reliable 
indicators of brain temperature will be tympanic 
temperatures and central venous temperature (the latter if 
an SVO2 or pulmonary artery thermodilution catheter are in 
position at the time of arrest, or have been placed post 
arrest by the transport team).

	Monitoring of the temperature of both tympanic membranes 
is important for several reasons. First, malpositioning or 
dislodgment of one of the probes will still leave the other 
as a back-up. Second, in patients with severe 
atherosclerotic disease of the carotid bulb and accompanying 
stenosis, or other unilateral compromise to carotid and/or 
cerebral hemisphere blood flow (i.e., lateralized trauma to 
the brain parenchyma or its vasculature) this reduction in 
blood flow will be evident by the reduced rate of cooling of 
the affected hemisphere.

	Similarly, in situations where endotracheal intubation 
is not possible and the DEGTA must be used, or where 
infectious disease or logistics renders use of gastric, 
colonic and/or peritoneal lavage impossible, then esophageal 
and rectal temperature probes may be reliably used.

	The procedures for using all of these temperature 
monitoring approaches are discussed in detail below, 
beginning with the simplest scenarios and progressing to 
consideration of the most complicated ones.  

Figure 8-3:  DEGTA with Thermocouple Probe:
A) Thermocouple line/connector,
B) Esophageal obturator,
C) Thermocouple probe tip,
D) Esophageal balloon,
E) Mask,
F) Esophageal balloon inflation/pressure monitoring assembly.

Placing an Esophageal Probe

	If endotracheal intubation is not possible or must be 
delayed, the Darwin Esophageal Gastric Tube Airway (DEGTA) 
should be placed to secure the airway and begin mechanical 

	The thermocouple probe on the DEGTA will be placed at 
the same time as the DEGTA since it is an integral part of 
it (follow the protocol for placement of the DEGTA outlined 
in Chapter 4).  If a DEGTA is not used, it will be necessary 
to place an esophageal thermocouple probe using the 
following approach:

1)	Connect the probe to the temperature monitor by inserting 
the male mini-plug connection on the probe into the female 
connector on the meter or the switch box.

2)	Immerse the probe in a (preferably insulated) container 
of crushed ice with a small amount of water and check the 
calibration of the meter by turning it on and measuring the 
temperature.  Agitate the probe in the ice slush while being 
careful to keep the probe away from the (warmer) wall of the 
container. Set the meter to read a temperature of 0 C. If 
there are problems calibrating the meter, check the front 
display for the LO BATT signal. The battery is a 9 volt cell 
which can be easily replaced by opening the battery 
compartment on the rear of the unit.

3)	Uncoil the probe and set the meter or switch box to read 
the temperature in degrees Celsius. Set the meter to read 
"Type T" (Copper-Constantan) thermocouples. This last 
instruction is very important, as it is easily overlooked 
and the "default" setting on recently manufactured meters is 
now "Type K" as opposed to "Type T."  Look at the reading on 
the meter and see if it appears to be displaying a reading 
which is reasonably close to that of the ambient 
temperature. Further check the probe/connection by 
momentarily holding the probe between thumb and forefinger 
and observing the meter for a temperature increase.

4)	Insert the probe through the mouth to a depth of 6 in. 
(15 cm.).

5)	Secure the probe with plastic or adhesive tape by looping 
it up and taping it to the patient's forehead.

6)	Read and record the patient's temperature and the time it 
was taken on the Transport Data Collection Sheet. 
Temperature readings should be taken no less than every 5 
minutes and more often is possible: preferably ever 1-2 
minutes, especially during the first hour of CPR and at the 
start of extracorporeal support.

Figure 8-7:  Photograph of the Darwin Rectal Probe.

Placing the Nasopharyngeal Probe

	The nasopharyngeal probe consists of a vinyl  or teflon 
coated thermocouple with a smooth, beaded end which is stiff 
enough to hold its shape under gravity but can be easily 
deformed under pressure. The procedure for placing the probe 
is to follow steps 1-3 above, under the heading Placing an 
Esophageal Probe and then:

Figure 8-8: Photograph of the Nasopharyngeal or Esophageal 
Probe shown with DigiSense thermocouple thermometer.

1) Pass the probe through either the right or left nare and 
gently explore the nasal fossa with the probe until an 
opening is found which allows the probe to be advanced.  
Advanced the probe into the opening 2-3 cm but no further.  
It is not desirable to advance the probe until it projects 
into the oropharynx or esophagus as temperature measured at 
these locations may influenced by ice water contact from the 

2) Secure the probe to the patient's forehead, the exterior 
of the nare or other appropriate location.  Skin staples may 
be used to do this if the patient is wet and adhesive tape 
will not stick.

3) Pack both nares with silicone putty to exclude ice water 
or other refrigerating liquid from entering the nares and 

4) Read and record the patient's temperature and the time it 
was taken on the Transport Data Collection Sheet. 
Temperature readings should be taken no less than every 5 
minutes and preferably more often: every 1-2 minutes if 
possible, especially during the first hour of CPR and at the 
start of extracorporeal support.

Placing the Rectal Probe

	If a Darwin Rectal Probe is used it can be either a 
closed, obdurator type, with  retention balloon, or a 
cannula type designed to be used in conjunction with colonic 
lavage.  In the event iced colonic lavage is being used, the 
accuracy of the rectal probe in the first minute to hour or 
so after the lavage in reflecting true core temperature will 
be questionable.  If colonic lavage is to be used, an 
initial DRP reading should be taken after placement of the 
probe and inflation of the retention balloon prior to 
initiating lavage with cold fluid.  Following lavage, 
priority given to taking subsequent readings from the rectal 
probe should be low compared with that in obtaining readings 
from tympanic probes, or those at other sites where 
localized cooling will not render the data suspect or 

	A DRP may be placed by following steps 1 through 3 above, then:

4)	Lubricating the tip of the probe with K-Y, Surgi-Lube, or 
other lubricating jelly.  This may be done most effectively 
by squeezing the lubricant onto a paper towel and dipping 
the probe in it.

5)	Using gloved hands, inserting the probe into the rectum 
to a depth of at least 3 in. (7.5 cm).  If necessary, the 
index finger may be inserted into the rectum to dilate it.

6)	Once the probe is in position, inflate the cuff of the 
balloon with 50 cc of air to prevent the probe from being 
dislodged and to prevent leakage of fecal matter into the 
water of the PIB.

7)	Securing the probe cable to the patient's thigh with 
adhesive or plastic tape.

8)	Reading and recording the patient's temperature and the 
time it was taken on the Transport Data Collection Sheet 
(Chapter 2). Temperature readings should be taken no less 
frequently than every 10 minutes, more often if possible.

	Probes should be checked frequently to insure that they 
have not become dislodged during transport or as a 
consequence of the addition of ice to the PIB or shifting 
ice packs.  Any unusual plateau or pause in temperature 
descent, or any sudden acceleration in temperature descent, 
should prompt a recheck of the probe's position.

_Remember to deflate the balloon of the DRP before removing it._

Placing The Tympanic Probes

	To facilitate proper placement and retention of tympanic 
probes and to allow continuous measurement of tympanic 
temperature a specialized apparatus has been developed, the 
Darwin Bilateral Tympanic Temperature Monitor (DBTTM). This 
device is shown in Figure 8-9 and consists of a headset with 
two tapered ear cones which are covered with water-proof 
sealing putty.  The cones are positioned in each auditory 
meatus (external ear canal) and are advanced down the meatus 
until the putty forms a tight seal.  The thermocouple probes 
are then advanced down the ear cones until they are seated 
on the tympanic membrane. The probes and the headset are 
then secured to patient's head by a slightly compressive 
elastic Velcro strap which encircles the head at the level 
between the nose and mouth. Both probes are held in position 
against the tympanic membranes, both of the meatuses are 
sealed from contact with cold water or other external 
refrigerant, and both probes are anchored securely to the 
patient's head.  

Figure 8-9: Diagram of The Darwin Bilateral Tympanic 
Temperature Monitor

	The major barriers to accurate and repeatable tympanic 
temperature monitoring are technique and the presence of 
cerumen in the ear canal. The latter is less of a problem 
with continuous direct contact thermocouple thermometry than 
is the case with infrared tympanic thermometry. In cases 
where there is access to the patient during terminal care or 
the agonal process, it is strongly recommended that patient 
core temperature be monitored using a commercially available 
tympanic temperature device such as the Thermoscan Tympanic 
Temperature Thermometer available over-the-counter at most 
pharmacies in the United States and Europe.  

	Early use of the Thermoscan or a similar device will 
familiarize the Transport Technician with each patient's 
unique ear anatomy and help to determine the angle and 
approach required for placement of the ear cones of the 
DBTTM. Furthermore, in order to use an infrared tympanic 
thermometer it is necessary that the ear canals be free of 
cerumen. This is best accomplished by gentle and careful 
cleaning of the ear canal before cardiac arrest occurs. 
Since temperature measurement is a standard part of basic 
home or hospital care it is wise to direct the home health 
care providers toward the use of tympanic thermometry not 
only because of its benefit to the cryopreservation process, 
but also because it is less irritating, less invasive and 
generally far better tolerated by patients than is oral or 
rectal or axial thermometry.

	In most cases cleaning of the ear canal can be 
accomplished by gentle and conservative use of a cotton 
tipped applicator. In cases of severe build up of cerumen it 
may be necessary to use one of the over-the-counter cerumen 
dissolving preparations available at pharmacies or home 
health care stores. On no account should vigorous or 
invasive probing of the auditory meatus be undertaken prior 
to pronouncement of the patient. Whenever possible the 
medical staff or home health care personnel responsible for 
the patient's care should be asked to clean the meatus if it 
is necessary to do so. In most cases where the patient is 
being cared for in a medical facility, tympanic temperature 
monitoring will already be in use, as it is now the standard 
of care for most hospitals and nursing homes, and it is 
being used in home hospice situations with increasing 

	Post arrest application of the DBTTM should be 
accomplished using the following steps:

1) Follow calibration procedure for both probes of DBTTM as 
outlined above for other Copper-Constantan thermocouple 

2) If access to the patient during the agonal period is 
possible and there are cooperative and supportive family 
members the patient's auditory meatus should be cleaned as 
part of routine mouth and facial care. This is done using 
cotton tipped applicators. When cardiac arrest appears 
imminent (last few hours of shock) the meatus may be further 
prepared by gently cleaning it with cotton tipped 
applicators dipped in rubbing alcohol, with the excess 
alcohol blotted on a tissue.  This maneuver will help to 
insure a good seal between the meatus and the putty.

3) If premortem access is not possible, any grossly visible 
cerumen is removed with the special cotton tipped 
applicators provided with the DBTTM for this purpose. A 
small bottle of skin defatting liquid for use with the 
applicators is also provided, and this may be used to clean 
the ear canals post-pronouncement.

4) The "headset" of DBTTM is placed on the patient's head 
exactly as if it were a stereo headset being positioned to 
listen to music.

5) The ear cones are introduced into the meatus at the 
proper angle and advanced until they are seated and the 
putty-seal is made, one ear at a time.

6) When both ear cones are positioned and maximally 
advanced, the thermocouple probes are gently advanced down 
the ear cone until the first resistance is felt.  

7) The probes wires are then bent downwards at a 90o angle 
and the Velcro securing strap is tightened.

8) Each probe is connected to the switch-box of the 
thermocouple meter and the initial readings taken and 


1)   White N, Baird S, et al.  A comparison of tympanic 
temperature readings to pulmonary artery catheter core 
temperature recordings.  Appl Nurs Res   1994;7:165-169.

2)   Moriya K, Sekitani T, et al. Tympanic Temperature in a 
patient with vertigo.  Acta Otolaryngol Suppl   1993;506:24-25.

3)   Klein, DG, Mitchell C, et al.  A comparison of 
pulmonary artery, rectal, and tympanic membrane temperature 
measurement in the ICU.   Heart Lung   1993;22:435-441.

4)   Mariak Z, Bondyra Z, et al.  The temperature within the 
circle of Willis versus tympanic temperature in resting 
normothermic humans.   Eur. J Appl Physiol   1993;66:518-520.

5)   Eleff SM, Kim H, et al.  Effect of cerebral blood flow 
generated during cardiopulmonary resuscitation on 
maintenance versus recovery of ATP and pH.   Stroke   

6)   Kwon S, Per Vaagenes L, et al.   Effect of cardiac 
arrest time on cortical cerebral blood flow during 
subsequent standard external cardiopulmonary resuscitation 
in humans.

Selected Bibliography

1) Waring KS.  Insuring Intensive Care.  Horsham, PA: 
Intermed Communications, Inc. 1981.

2) Operators Manual for Cole-Parmer Digi-Sense Thermometers. 
Barnant Instrument Co. Chicago, IL. 1992.

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