Pretty rare.
Prehosp Emerg Care. 2008 Apr-Jun;12(2):162-8.
Paramedic use of needle thoracostomy in the prehospital environment.
Warner KJ, Copass MK, Bulger EM.
Seattle Medic One performed 39 in a one year period. 22 were in cardiac arrest (10 being trauma and the others being PEA arrests). All but one of the remaining were trauma. Of those not in arrest only 6 had both hypotension and decreased breath sounds. 8 seemed to be simple pneumos
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Prehosp Emerg Care. 1998 Apr-Jun;2(2):132-5.
Needle thoracostomy in the prehospital setting.
Eckstein M, Suyehara D.
108 patients in a 1 year period at one level 1 trauma center in the LA area.
2 were found to not have reached the pleural cavity and another were determined to have cause an iatrogenic pneumo. So, who knows how many were actually tension pneumos.
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J Ultrasound Med. 2010 Sep;29(9):1285-9.
Inadequate needle thoracostomy rate in the prehospital setting for presumed pneumothorax: an ultrasound study.
Blaivas M.
57 NT over a 3 year period - 15 found to not be pneumos.