# Physiologic changes in microgravity may lead to unpredictable effects of spinal anesthesia

## TL;DR

Spinal anesthesia may behave unpredictably in space due to microgravity's effects on body physiology.

## Contribution

This paper identifies how microgravity alters spinal anesthesia mechanisms and highlights research needs for space missions.

## Key findings

- Microgravity changes spinal geometry and cerebrospinal fluid dynamics, affecting anesthetic spread.
- Current assumptions about spinal anesthesia may not apply in microgravity conditions.
- Research is needed to develop safe anesthesia protocols for space missions.

## Abstract

Regional techniques such as spinal anesthesia may offer advantages over general anesthesia for autonomous medical care during long-duration space missions, yet their behaviour in microgravity remains largely uncharacterised. On Earth, intrathecal anesthetic spread depends on baricity, posture, spinal curvature, and cerebrospinal fluid dynamics. Microgravity alters these determinants by diminishing gravity-dependent density gradients, modifying spinal geometry through paraspinal atrophy and elongation, and inducing cardiovascular and neurophysiologic adaptations that may affect block characteristics and hemodynamic tolerance. This Mini Review synthesises current evidence on spinal anesthetic mechanisms and spaceflight physiology to identify where terrestrial assumptions may fail in microgravity. Key knowledge gaps and research priorities are highlighted to inform the development of safe neuraxial anesthesia protocols for exploration-class missions.