ETC02 monitoring

The other night my crew and I had a 300 lb. intoxicated, intubated patient who fell off a cliff or was assaulted, laceration to the right temporal area, GCS 3 according to the ED doc. He was brought to the ED via BLS ambulance. He was immediately immobilized by the ED and intubated. RSI drugs as follows: Etomidate 20mg, Succinylcholine 12mg, Lidocaine 100mg and Versed 2mg. ETT 7.5 24mm at the teeth, placement was good verified by the post intubation x ray. Vent settings AC Pressure Support VT 750 Rate 14 FI02 100% PEEP 0. I duplicated the vent settings on the transport vent. We use Zoll monitors that require comping the monitor for 02 greater than 60%. That being done the ETC02 cable was zeroed. My initial reading was 37mm Hg. Vital signs were stable and within normal limits, no chest trauma noted on x ray or physical exam, lungs clear and equal. The sending facility does not monitor ETC02 nor did they get ABGs. Lab values were within normal limits except for a blood alcohol of .496 (this could be his normal value. We all know the type).
Shortly after leaving the building I noticed the ETC02 had dropped to 20-22 mm Hg, SA02 100%, no tube disgorgement, no changes in the patients status, equipment was functioning normally. The ambient temperature was mid 20's.
My question is for those of you working in cold climates does the ETC02 value change/drop with drops in temperatures? Is the ETC02 affected by ETOH?
I have been scouring the internet to find the answers but have come up short as has our QI manager. Any suggestions or comments?