B737-800
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe
Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Took Evasive Action
Aircraft
Shortly after reaching cruise; Left Bleed trip off light illuminated. Reset per QRH; within minutes same issue [recurred]; reset again and light remained out. Noted a large split duct pressure. Shortly after descent from FL380; the RT Bleed trip light illuminated. Began checklist to reset light; [but it] appeared not to reset. We advised ATC we may have a pressurization problem and needed a descent lower than FL240 already assigned. This was granted.Shortly after that the Captain noted a spike in cabin [altitude] and told me to declare an emergency with ATC; and we started an emergency descent. I notified ATC and coordinated with the Captain setting up a direct route to [destination] from present position. O2 masks were donned during this process; cabin was uncontrollable and we were now in a descent to 10;000 FT.  At 10;000 FT we were able to stabilize and assess the situation; and prepare for an arrival after 3 gate changes and ATC notifications for medical personnel to meet us.A history of bleed malfunctions [had been] documented [on this aircraft] prior to this flight.
B737-800 FO reported loss of cabin pressure at FL380.