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Minerva Anestesiologica 2004 July-August;70(7-8):617-24

Copyright © 2004 EDIZIONI MINERVA MEDICA

language: English, Italian

Heat stress: characteristics, pathophysiology and avoidable mistakes

Caspani M. L., Savioli M., Crotti S., Bruzzone P., Gattinoni L.

Intensive Care Unit IRCCS Ospedale Maggiore Policlinico Department of Anesthesia and Intensive Care University of Milan, Milan, Italy


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In August 2003 an excep­tion­al heat­wave was record­ed in Europe. The ­authors ­would ­like to ­describe 6 ­patients for ­which the inten­si­vist was ­called as a con­sul­tant. All ­patients had a ­skin tem­per­a­ture >40°C, cen­tral ner­vous ­system impair­ment, ­severe hypo­na­tre­mia [124.7 mEq/l±5.6 (­range 117-130)] and ­severe meta­bol­ic aci­do­sis [BE -6.28 mEq/l±3.55 (­range -9.5-0), HCO3- 17.75 mEq/l±3.25 (­range 13.4-21.9)]. All ­patients had ­decreased plate­let ­count and coag­u­la­tion abnor­mal­ities. Two ­patients ­were hyper­ten­sive, 4 hypo­ten­sive. The ­heat ­stress due to the hot envi­ron­ment is char­ac­ter­ized by system­ic inflam­ma­to­ry ­response (as in severe sep­sis) and hemo­dy­nam­ic impair­ment (as in hypo­vo­lem­ic ­shock). The asso­ci­a­tion ­between hypo­vo­le­mia and ­altered micro­cir­cu­la­tion ­leads to ­cell ener­gy fail­ure ­with meta­bol­ic lac­tic aci­do­sis. The ener­gy fail­ure may ­induce struc­tu­ral irre­ver­sible dam­age of mito­chon­dria. It is pos­sible to dif­fer­en­tiate, dur­ing ener­gy fail­ure, the irre­ver­sible or rever­sible con­di­tion by vol­ume load­ing and vasoac­tive ­drugs chal­lenge ­tests. In ­fact, if the hemo­dy­nam­ic cor­rec­tion is asso­ciat­ed ­with nor­mal­iza­tion of SvO2 ­with dis­ap­pear­ance of meta­bol­ic aci­do­sis, ­this sug­gests hemo­dy­nam­ic impair­ment ­with ­intact mit­o­chon­dri­al func­tion. In contrast, if the hemo­dy­nam­ic improve­ment ­with nor­mal­iza­tion of SvO2 is asso­ciat­ed and aci­do­sis per­sists, ­this sug­gests irre­ver­sible struc­tu­ral mit­o­chon­dri­al dam­age. The thresh­old ­between rever­sibil­ity and irre­ver­sibil­ity is like­ly ­time depen­dent, as sug­gest­ed by bio­chem­i­cal con­sid­er­a­tion and by 2 ­large ran­dom­ized stud­ies on hemo­dy­nam­ic treat­ment. The com­par­a­tive anal­y­sis of ­these 2 stud­ies sug­gests ­that the ­time of inter­ven­tion may ­lead to sig­nif­i­cant dif­fer­enc­es in mor­tal­ity. In ­these ­patients ­time is essen­tial.

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