DIFUSSION AND PERFUSION
- Jennifer de la Cruz
- Mar 5
- 2 min read
By: J. de la Cruz
Aim:
To explain the difference between diffusion and perfusion= the two processes involved in oxygenation. To add physiological reasoning to task-based nursing practice.
Background:
Oxygenation is at the heart of perianaesthesia care, yet the difference between diffusion and perfusion is still a blind spot for many clinicians at the bedside.
Diffusion is the gas exchange in the lungs, so anything that thickens, floods or collapses alveoli in the lungs will impair diffusion and reduce oxygen content in the arteries even when perfusion is normal. The common perioperative threats to diffusion include:
atelectasis from muscle relaxant, high fraction of inspired oxygen or supine positioning;
pulmonary oedema;
aspiration pneumonia
pre-exisitng lung disease
Perfusion describes how effectively oxygen rich blood is delivered to tissues. Even with 100% diffusion, tissues can be profoundly hypoxic if perfusion is inadequate. Perioperative threats to perfusion include:
Anaemia and low oxygen carrying capacity of blood
Hypovolaemia and low cardiac output
Vasoconstriction
Prolonged hypotension during major surgery
Diffusion-perfusion (V/Q) mismatch example scenarios:
The “normal blood pressure, falling saturation” post operative (abdominal laparoscopic) patient supine, muscle relaxant was used & reversed, minimal pain, SpO₂ drifting from 96% to 88% on room air. Here, perfusion is okay but diffusion is compromised, often by atelectasis and reduced functional residual capacity.
The “perfect sats, poor patient” scenario: Elderly patient post major abdominal surgery on 6 L/min via mask, SpO₂ 100%, but drowsy, hypotensive (low blood pressure) and oliguric (low urine output). Diffusion looks fine; perfusion and oxygen delivery are failing.
The high‑risk hypoxic cluster: Patients with obesity, OSA, cardiac failure or significant lung disease are at greatest risk of both diffusion and perfusion failure postoperatively and may benefit from strategies diaphgramatic breathing , high flow nasal prongs, or triflow (physio recommendation) .
References
Lumb, A. B., & Nunn, J. F. (2019). Nunn's applied respiratory physiology (9th ed.). Elsevier.
West, J. B. (2021). Respiratory physiology: The essentials (11th ed.). Wolters Kluwer.
Zbigniew Putowski, Jan Bakker, Eduardo Kattan, Glenn Hernández, Hafid Ait-Oufella, Wojciech Szczeklik, Philippe Guerci (2025),Tissue perfusion as the ultimate target of hemodynamic interventions in the perioperative period, Journal of Clinical Anesthesia,
DISCLAIMER:
The information presented here is provided for general educational and informational purposes only. It does not constitute medical advice and is not a clinical protocol. Readers must always refer to their institutional policies and clinical guidelines and consult with qualified healthcare professionals for individual patient care. The author and this site disclaim any liability for adverse outcomes that may result from the use or application of the information provided.
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