Binks and colleagues, in the second national survey on therapeutic hypothermia following cardiac arrest, demonstrated an impressive increase in levels of implementation of the International Liaison Committee on Resuscitation guidelines (from 28% to 85.6%) [1]. The survey has a very good response rate, thus reflecting practice across the country.
One important aspect of practical implementation of therapeutic hypothermia remains unexplored. How many of the 208 intensive care units using therapeutic hypothermia post-cardiac arrest monitor ‘core temperature continuously’ during the cooling and rewarming period? The gold standard for true core temperature is the temperature of blood measured using a pulmonary artery catheter [2]. However, such invasive monitoring is rarely warranted, and core temperature is frequently measured at sites such as the oesophagus, nasopharynx, rectum, bladder and tympanic membrane, all of which have variable levels of accuracy. The oesophagus and nasopharynx offer more accurate estimates of core temperature than the rectum and bladder, with tympanic membrane readings being the least accurate [3]. Temperature measurement at all these sites induces a time lag between registered and measured core temperature, which may lead to an overshoot of core temperature below the desired target temperature [3]. Intermittent temperature measurement via the tympanic membrane, and continuous temperature measurement via axillary probes remain popular choices of temperature monitoring in intensive care units, even when therapeutic hypothermia is being implemented. The survey by Binks did not assess methods of monitoring hypothermia. In view of the potential to induce inaccuracies, continuous core temperature monitoring via either a pulmonary artery catheter (if already in situ), or at one of the other sites (bladder, oesophagus, nasopharynx or rectum) is an integral part of therapeutic hypothermia after cardiac arrest [4].
The failure to assess the methods of temperature monitoring issue is not a criticism of this survey, but I feel this should be incorporated into future studies or surveys on therapeutic hypothermia post-cardiac arrest.
No external funding and no conflicts of interest declared
V Sharma
John Radcliffe Hospital
Oxford, UK.
E-mail: drvvs@rediffmail.com
References
1 Binks AC, Murphy RE, Prout RE, et al. Therapeutic hypothermia after cardiac arrest- implementation in UK intensive care units. Anaesthesia 2010; 65: 260-5.
2 Akata T, Setoguchi H, Shirozu K, et al. Reliability of temperatures measured at standard monitoring sites as an index of brain temperature during deep hypothermic cardiopulmonary bypass conducted for thoracic aortic reconstruction. Journal of Thoracic and Cardiovasccular Surgery 2007; 133: 1559-65.
3 Polderman KH, Herold I. Therapeutic hypothermia and controlled normothermia in the intensive care unit: practical considerations, side effects, and cooling methods. Critical Care Med 2009; 37: 1101-20.
4 Nolan JP, Morley PT, Vanden Hoek TL, et al. Therapeutic hypothermia after cardiac arrest: an advisory statement by the advanced life support task force of the International Liaison Committee on Resuscitation. Circulation 2003; 108: 118-21.