Hypothermia: an adverse effect or a missing partner?

Abstract

Hypothermia is mainly discussed in the literature with regard to its side-effects [1], while the contributions pointing out its potential advantages are few and far between [2,3]. This state of affairs indicates that this variable needs to be studied with a view to reassessing the potential role of hypothermia in intensive care.There is little doubt that lowering metabolic activity should prove advantageous in countering many pathological features, and indeed hypothermia is one of the easiest methods for lowering exactly that activity. Some of the experimental and clinical reports available give the impression that the basic flaw is related to an uncontrolled approach which does not adequately cater for problems in thermal recovery [4].Clearly, anti-physiological practices cannot be applied on animals or humans without anaesthesia and paralysis. Indeed, the application of respiratory pattern modifications, haemodilution and controlled hypotension requires deep sedation and paralysis. Similarly, anaesthesia and paralysis are required during the induction of hypothermia as well as during rewarming in order to avoid ªcold stressº.It is a well-known fact that during prolonged surgery ªlight hypothermiaº (33±35°C) provides good stabilisation of vital signs as well as good tolerance of a deep level of normovolaemia anaemia. Nevertheless, this situation reveals its negative effects when the patient becomes conscious and undergoes ªcold stressº. However, an important example of what hypothermia could actually offer is related to the side-effects induced by the most recent therapeutic approach for treating patients with the acute respiratory distress syndrome (ARDS), i. e. permissive hypercapnia [5]. The rationale behind the use of this technique is based upon some well-known pathophysiological considerations ± namely, the scientific community's general acceptance of the ªbaby lungº concept in ARDS. In such circumstances, it is possible that, during conventional treatment, most of the ventilation will reach healthy regions, resulting in overdistension which can actually worsen lung injury. Under such conditions, ventilation has to be driven by the mechanical characteristics of the lung and not by gas exchange targets. In order to achieve a good mechanical result the tidal volume (V T ) and the ventilatory rate both have to be lowered. The mechanical advantages of this technique are universally acknowledged. In other words, although it is definitely proper to avoid barotrauma in patients, the side-effects of this strategy involve gas exchange with hypoxia (occasionally) and hypercapnia (always). Subsequently, intra-and extracellular acidosis is enhanced with theoretical multisystem damage proportionate to the hypercapnia level.In the 1980s the scientific community spent a lot of time and energy trying to avoid hypercapnia by removing CO 2 in a variety of ways [6]. The most famous method, which is still used, is low frequency positive pressure ventilation with extracorporeal CO 2 removal (LFPPV-ECCO 2 R) [7]. Lately, this a...