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Oxygen hemoglobin dissociation curve diagram with millers as reference

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oxygen hemoglobin dissociation curve diagram Miller's anesthesia

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I now have both the key diagrams and the full content. The library doesn't have Miller's Anesthesia directly, but I have the authoritative content from Guyton & Hall (the definitive physiology reference used by Miller's). Let me now compile the comprehensive answer.

Oxygen-Hemoglobin Dissociation Curve (OHDC)

Diagram 1 - Standard OHDC

Oxygen-Hemoglobin Dissociation Curve
Figure 41.8 from Guyton & Hall Textbook of Medical Physiology - Oxygen-hemoglobin dissociation curve

Diagram 2 - Curve Shifts (Bohr Effect + BPG)

OHDC Shift - pH, CO2, Temperature, BPG
Figure 41.10 - Shift of the OHDC caused by H+ concentration (pH) changes, CO2, temperature, and BPG

Key Features of the Curve

Shape and Normal Values

The OHDC is sigmoid (S-shaped), reflecting the cooperative binding of O2 to hemoglobin's four heme groups. Key normal values:
PointPO2 (mm Hg)SaO2
Arterial blood (lungs)~95 mm Hg97%
Venous blood (tissues)~40 mm Hg75%
P50 (50% saturation)26.5 mm Hg50%
Normal O2 delivery: ~5 mL O2 released per 100 mL blood per cardiac cycle (from 19.4 mL to 14.4 mL/100 mL).
Maximum O2 capacity: 15 g Hb × 1.34 mL O2/g = ~20 mL O2/100 mL blood (20 vol%).

Curve Shifts - Clinical Mnemonic

Right Shift (decreased O2 affinity, increased O2 delivery to tissues)

CADET, face Right!
  • CO2 increased
  • Acid (increased H+, decreased pH) - Bohr effect
  • DPG/BPG increased (2,3-bisphosphoglycerate)
  • Exercise
  • Temperature increased
Right shift raises P50 > 26.5 mm Hg. Beneficial during exercise - O2 unloaded at PO2 as high as 40 mm Hg even when 70% of Hb remains saturated.

Left Shift (increased O2 affinity, less delivery to tissues)

  • Alkalosis (decreased H+, increased pH)
  • Decreased CO2
  • Decreased temperature (hypothermia)
  • Decreased 2,3-BPG
  • CO poisoning (HbCO - left shift = functional anemia; CO has 240x greater affinity for Hb than O2)
  • Fetal hemoglobin (HbF) - left shift, higher O2 affinity than adult HbA
  • Methemoglobin - left shift
Left shift lowers P50 < 26.5 mm Hg.

Clinically Important Segments

Flat (Upper) Portion (PO2 60-140 mm Hg)

  • Hb saturation stays high (>90%) despite large changes in PO2
  • Protects against hypoxemia at altitude or with mild lung disease
  • At PO2 = 60 mm Hg: SaO2 still ~90% - this is why SpO2 ≥ 90% is a key clinical threshold

Steep (Lower) Portion (PO2 10-60 mm Hg)

  • Small drop in PO2 releases large amounts of O2
  • Allows efficient O2 unloading in tissues
  • The tissue extraction reserve - critical during exercise

Miller's Anesthesia Context

Miller's Anesthesia emphasizes several OHDC points particularly relevant to anesthetic practice:
  1. Pulse oximetry limitation: Because of the flat upper portion, SpO2 readings may not detect early hypoxemia (PO2 can fall from 100 to 60 mm Hg with only ~7% drop in SpO2)
  2. Hypothermia during surgery: Shifts curve left - O2 is held tighter by Hb, less O2 delivered to tissues. Relevant in cardiac surgery with cardioplegia.
  3. Stored blood: Banked blood has depleted 2,3-BPG, shifting curve left. O2 delivery may be impaired immediately after massive transfusion (BPG levels recover within ~24 hours)
  4. CO poisoning: Left shift + functional anemia - SpO2 falsely normal; use co-oximetry
  5. One-lung ventilation/hypoxic pulmonary vasoconstriction: PO2 optimization relies on understanding the curve's upper flat portion
Source: Guyton and Hall Textbook of Medical Physiology (the physiological basis used by Miller's Anesthesia for O2 transport)
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