My mother diagnosed by covid 19 in April and she recovered after 15 days. Treatment was given in home isolation. On 16th June she slip on left leg  floor hip ball fracture. Before surgery her in hrct scan ( ct severity index 5) And (ct severity score 1-8 mild) Recent her hip ball fracture surgery completed on 30/June after 15 days of injury. After  surgery time her hemoglobin levels are at 8.5 Then 2 packets of Blood given. After blood transfusion her oxygen levels are decreasing.. without ventilation her O2 levels are 88-95. Could you explain the cause of O2 level decreasing in the covid time her O2 levels are good.