Fig. 2. Oxygen–hemoglobin dissociation curve for standard hemoglobin (Hb) at pH of 7.4 and base excess of 0, and hemoglobin M (Milwaukee) at arterial carbon dioxide tension (Paco2) of 42 mmHg, pH of 7.34, and base excess of −2.8 in our patient. The equation for the curve fit is given. The Hill coefficient (n) and thus oxygen affinity are reduced in hemoglobin M (Milwaukee) but appear similar for higher and lower Paco2. Note that dependent on the patient’s methemoglobin level of approximately 15% maximal saturation of the available reduced hemoglobin is reached at a fractional oxygen saturation (Sao2) of approximately 85%. Pao2 50 = oxygen tension at Sao2= 50%; Pao2: arterial oxygen tension; Sao2 max = maximal Sao2= 100%.