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 ventilation. 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 PIB. 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 sinuses. 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 meaningless. 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 frequency. 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 probes. 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 documented. References 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 1993;24:2066-2073. 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. BioPreservation, Inc 10743 Civic Center Drive Rancho Cucamonga, CA 91730 (909)97-3883