What French (Fr) size corresponds to an 18‑gauge (18 G) catheter?

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Equivalencia de Catéter 18G a French

Un catéter 18 gauge (18G) equivale aproximadamente a 6 French (Fr).

Conversión Estándar Gauge a French

  • La escala French define 1 Fr como 0.33 mm de diámetro externo, según la American Society of Anesthesiologists 1
  • Un catéter 18G tiene un diámetro externo de aproximadamente 1.27 mm, lo que corresponde a aproximadamente 3.8-4.0 mm en circunferencia externa
  • Aplicando la fórmula de conversión (diámetro en mm ÷ 0.33 = French), un catéter 18G equivale a aproximadamente 6 Fr 1

Contexto Clínico de Uso del 18G

Para Administración de Contraste en TC

  • Los catéteres 18G periféricos se recomiendan para angiografía por TC de tórax cuando se requieren tasas de flujo de 5-6 mL/s, según el consenso clínico del European Heart Journal 2
  • Un catéter 18G tradicional permite tasas de infusión de 5.0-7.5 mL/s, comparable a un catéter fenestrado 20G más moderno 2
  • Para estudios de angiografía coronaria por TC, un catéter 18G no fenestrado logra tasas de infusión promedio de 5.3 mL/s 3

Para Transfusión Sanguínea

  • Los catéteres 18G son apropiados y preferibles para transfusión sanguínea en adultos, según las guías MAGIC 4
  • Importante: Un catéter 20G (aproximadamente 5 Fr) es suficiente para transfusión rutinaria de adultos y no debe considerarse inadecuado 4

Para Procedimientos Ginecológicos

  • Como alternativa para anestesia intrauterina cuando no hay catéteres de hidrosonografía disponibles, se puede usar un angiocatéter 18G, según el American Journal of Obstetrics and Gynecology 2

Consideraciones Prácticas Importantes

  • El rendimiento real de flujo es significativamente menor que las especificaciones del fabricante: un estudio demostró que un 18G infunde a 35.6 mL/min en promedio, muy por debajo de los 105 mL/min estimados por el fabricante 5
  • La longitud del catéter afecta significativamente la resistencia al flujo; catéteres más cortos mejoran el flujo independientemente del calibre 6
  • Más allá de 18 Fr en catéteres urinarios, el aumento de tamaño proporciona rendimientos marginales decrecientes en flujo 6

References

1
Guideline

Introducer Sheath Selection Guidelines

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

2
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

4
Guideline

Peripheral IV Catheter Selection for Blood Transfusion

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

5
Research

Are 2 smaller intravenous catheters as good as 1 larger intravenous catheter?

The American journal of emergency medicine, 2010

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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