A five-year old presents to your A & E with trouble breathing after being struck in the chest by a hockey stick. The child’s vital signs are: Blood pressure 80/50, pulse 130, respirations 28 and labored with unequal rise and fall of the chest. The child is lethargic, responding to painful stimuli only, his skin is pale, diaphoretic and cool. When you auscultate the patients lung sounds you notice absent lung sounds over the left chest and a bruise with fractured ribs on the left thorax. What is the best initial treatment for this patient?