A 70 year old female presents to ED with a 1 month history of vomiting and diarrhoea.

Over the last few days she has started to feel increasingly weak and had a few episodes of confusion. The patient has a background history of  one previous  episode small bowel colitis for which she was treated with a short course of steroids 2 years ago. On examination HR 102 BP 90/540 Apyrexial Sats 97% RA RR18. She has dry mucous membranes and decreased skin turgor and CPR 3 seconds.

VBG

pH 7.557                                                  Na 122 mmol/l

pCO2 44 mmHg                                      K 2.0 mmol/l

HCO3 37 mmol/l                                      Cl 74 mmol/l

BE 12.9                                                    Cr 85 umol/l

Lactate 2.6                                               BSL 5.5 mmol/l

1. Describe and interpret the VBG
2. What are the likely causes of low sodium in this case?
3. How would you manage this patients fluid replacement?