This is nearly impossible: You can determine oxygen saturation by photometry and oxygen pressure by equilibration with known gas pressure (calculated from O2 concentration in the gas and atmospheric pressure), but you need also at least a pH meter. 

Thank you Dieter for giving clarity to my ideas. But, I would also like to know whether SO2 measured by pulse oximetry alone can be sufficiently utilised to derive P50 from equations.  

No, you always need additionally at least PO2 to obtain one point on the curve. Using a plausible value of Hill's n you can calculate the curve. But you should also know pH, if you want to apply the curve for changing in vivo conditions (lungs and consuming tissues). 

 But, I need your help further. Are these equations as written below used to calculate P50?

S = ((23,400((PO2)3+ 150PO2)-1) + 1)-1

P50 = 26.7PO2(obs)/PO2(7.4)

I would like you to be a part of the research that may contribute for familial polycythemia in Nepali population. There are no physiology labs that conduct ODC in blood sample, and I am giving a try to it perhaps for the first time in Nepal. Will you guide me further?

From where did you get the equations? You can see that you need saturation, PO2 and pH. To measure standard P5o or the whole curve you need in any case a blood gas analyzer. Perhaps somebody may apply for a project and travel to Kathmandu for measurements with transportable apparatus. There are many  altitude investigators who work in the Mount Everest region and have a stopover in Kathmandu. A specialist for oxygen dissociation curves is Prof. Walter Schmidt from Bayreuth, a former assistant of mine, who also often performs experiments in higfh mountains (walter.schmidt@uni-bayreuth).. In addition you might measure biphosphoglycerate in red cells photometrically and send samples to a specialist for hemoglobin typing.

Good luck

Dieter Böning 

High powered discussion !

Thank you Professor Dieter for your valuable suggestions. 

Sincerely,

Ojashwi.

I agree with Dieter.The P50 values of  Haemoglobin solutions can be very accurately  measured using the Gill-cell metod.

See publication: Haemoglobin-oxygen affinity and acid-base properties of blood from the fossorial mole=rat, Cryptomys hottentotus pretoriae. Comp. Biochem. and Physiol. Part A 147 (2007) 50-56 9Available online at www.sciencedirect.com

W.J. van Aardt et al.

sounds good enough.

Ojashwi -

Not sure if you already have your answers. You will need PO2, PH, SO2 to calculate p50 from a sample. There are online and excel spreadsheet tools available in which you just put the values and it calculates the p50 for you (if you prefer an easy way).  Please keep in mind that you must measure blood gas in a fresh sample (never do it in a stored sample); you can keep the sample in heparinized tube max for 10mins if the blood gas analyzer is located at a different place. Factors like temperature, time between blood extraction and analysis, storage, age etc. affects the level of blood gases.  PO2 can be more than 100 if the blood draw is from a patient on oxygen therapy or extracted from a patient under anesthesia. Always consider PO2/FiO2 ratio because PO2 alone is not enough.  I hope this is helpful.  

Thank you Bharat for the answer. This is helpful indeed.