Introduction

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Disclaimer

One should keep in mind that the current opinion in Europe may differ from the one in Australia or in the U.S. Having an international readership, it might be difficult to satisfy everybody with the given answers or the suggestions for additional reading. In order to assure the accuracy of this section, all the questions and especially the answers will be reviewed by several international members of the editorial board. Nevertheless, it is difficult to ensure that all the information given is entirely accurate for all circumstances. The publishers disclaim any liability, loss, or damage occurred as consequence, directly or indirectly, of the use and application of any of the content of this section.

Question 1

Question 2

What is P-50 in the oxyhemoglobin dissociation curve?

Question 3

What are the absolute and relative contraindications for spinal anesthesia?

Answer 1

Answer 2

P-50 is the oxygen tension (PaO2) associated with 50% hemoglobin saturation. Under normal conditions (pH 7.4, PaCo2 40 mmHg, 37 degree C) it has a value of 26.6 mmHg.

A left shift of the curve caused by alkalosis, hypothermia, abnormal Hb, hypocarbia, and low 2,3 DPG-levels results in a greater affinity of hemoglobin for oxygen (oxygen is less likely to be released into the tissue).

A right shift of the curve caused by acidosis, hyperthermia, hypercarbia, and high 2,3 DPG-levels results in a lower affinity of hemoglobin for oxygen (oxygen is more likely to be released into the tissue).

Answer 3

Absolute contraindications:

Relative contraindications: