Chart — Fundamentals
Oxyhemoglobin Dissociation Curve Shifts
The oxyhemoglobin dissociation curve relates arterial oxygen tension (PaO₂) to hemoglobin saturation (SaO₂). A right shift means hemoglobin gives up oxygen more readily (good for the tissues); a left shift means hemoglobin holds onto oxygen more tightly (poor unloading). Read the landmarks first, then use the shift table to predict which way a patient’s curve has moved and why.
Written by Apex Respiratory Editorial Team
Educational use only. This material supports respiratory therapy education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional protocols, or physician orders. Always follow facility policies and current provider orders, and verify calculations independently before clinical use.
Left Shift vs. Right Shift
| Property | Left Shift | Right Shift |
|---|---|---|
| Hemoglobin affinity for O₂ | Increased (holds O₂) | Decreased (releases O₂) |
| P50 | Decreased (under 27 mmHg) | Increased (over 27 mmHg) |
| O₂ unloading to tissue | Less (impaired delivery) | More (enhanced delivery) |
| pH | Alkalosis (increased pH) | Acidosis (decreased pH) — the Bohr effect |
| PaCO₂ | Decreased | Increased |
| Temperature | Decreased (hypothermia) | Increased (fever) |
| 2,3-DPG | Decreased | Increased |
| Other causes | Carbon monoxide, methemoglobin, fetal hemoglobin, stored (banked) blood | Exercise, chronic hypoxemia |
Key Curve Landmarks
| PaO₂ (mmHg) | SaO₂ (%) | Note |
|---|---|---|
| 27 | 50 | The P50 (the point of 50% saturation) |
| 40 | 75 | Normal mixed venous point |
| 50 | 85 | Steep part of the curve |
| 60 | 90 | The “shoulder”; usual supplemental-oxygen threshold |
| 80-100 | 95-98 | Normal arterial range |
Memory Aid
Right shift — “CADET, face Right!” — CO₂, Acid, 2,3-DPG, Exercise, and Temperature all INCREASED shift the curve to the Right and unload oxygen to the tissues.
How to Use This Chart
- A right shift helps tissues extract oxygen and is appropriate during fever, acidosis, and exercise.
- A left shift (banked blood low in 2,3-DPG, alkalosis, hypothermia, carbon monoxide) makes hemoglobin cling to oxygen and impairs delivery despite a reassuring saturation.
- Carbon monoxide is a double hit: it displaces oxygen from hemoglobin AND left-shifts the curve, so the oxygen that remains bound is harder to release.
Related Resources
Sources
- Kacmarek RM, Stoller JK, Heuer AJ. Egan's Fundamentals of Respiratory Care. 12th ed. Elsevier; 2021. Oxygen transport chapter.
- West JB, Luks AM. West's Respiratory Physiology: The Essentials. 11th ed. Wolters Kluwer; 2021.