Feasibility of Ultrasound-Guided Nerve Blocks in Simulated Microgravity: A Proof-of-Concept Study for Regional Anaesthesia During Deep Space Missions

Academic Background

With crewed deep space exploration on the horizon, preparing for potential astronaut health crises during space missions has become a critical issue. The administration of anaesthesia and analgesia in space presents numerous challenges, including physiological and ergonomic issues associated with microgravity, as well as non-specific factors such as isolation and limited supplies. Regional anaesthesia is considered one of the safest options; however, researchers hypothesize that the ergonomic challenges of microgravity may compromise the ease and accuracy of nerve blocks.

During deep space missions, astronauts may face severe traumatic injuries, such as fractures, crush injuries, and burns. While injured astronauts in low Earth orbit (LEO) missions may be returned to Earth for treatment, this is highly unlikely in deep space missions. Therefore, developing strategies for medical interventions in space has become essential. Regional anaesthesia, as a method of pain management and anaesthesia that does not require airway intervention, can provide effective pain relief while maintaining the cognitive function of astronauts, making it a potential solution.

However, the feasibility of regional anaesthesia in microgravity has not yet been verified. This study aims to evaluate the feasibility of ultrasound-guided nerve blocks in a simulated microgravity environment, providing a scientific basis for regional anaesthesia in future deep space missions.

Source of the Paper

This paper was co-authored by Mathew B. Kiberd, Regan Brownbridge, Matthew Mackin, Daniel Werry, Sally Bird, Garrett Barry, and Jonathan G. Bailey, all from the Department of Anesthesia, Pain Management & Perioperative Medicine at Dalhousie University, Canada. The paper was published on September 25, 2024, in the British Journal of Anaesthesia, titled Feasibility of Ultrasound-Guided Nerve Blocks in Simulated Microgravity: A Proof-of-Concept Study for Regional Anaesthesia During Deep Space Missions.

Research Process

1. Study Design and Model Preparation

This study used a meat model (bovine muscle) to simulate the environment for nerve blocks. Researchers cut bovine muscle into approximately 10×10×3 cm pieces and embedded a tendon to simulate a nerve structure. To enhance the fidelity of the model, the meat was encased in ballistic gel, creating a high-fidelity regional anaesthesia model.

2. Simulated Microgravity Environment

To simulate microgravity, researchers used free-floating underwater conditions. Underwater training is a common method for preparing astronauts for space missions, providing an environment close to microgravity. The meat model was placed in a buoyant mannequin, tethered approximately 2 meters from the bottom of a swimming pool. Both the operator and assistant were in a free-floating state, simulating the microgravity environment of space.

3. Experimental Procedure

A total of 40 meat models were randomized for injection under simulated microgravity and normal gravity conditions. Each model was operated on by four anaesthesiologists with varying levels of regional anaesthesia experience, with each anaesthesiologist performing five injections under each condition. Operators used a wireless high-frequency linear ultrasound transducer and a 22G 50 mm echogenic needle to inject a mixture of water and methylene blue dye. After successful injection, the models were frozen for 24 hours, then dissected by two blinded assessors to determine the accuracy of the injection.

4. Evaluation Metrics

The study evaluated the following metrics: - Time to block: The time from when the ultrasound transducer touched the model until the needle was removed. - Ease of image acquisition: Assessed using a 5-point Likert scale (1=very difficult, 5=very easy). - Ease of needle placement: Also assessed using a 5-point Likert scale. - Success rate of injection: Determined by whether the methylene blue dye was accurately injected around the tendon. - Rate of accidental intraneural injection: Assessed by whether the dye mistakenly entered the tendon.

Main Results

1. Time to Block

The median time to block was 27 seconds (interquartile range 21-69 seconds) under normal gravity and 35 seconds (interquartile range 22-48 seconds) under simulated microgravity. There was no significant difference between the two conditions (p=0.751).

2. Ease of Image Acquisition and Needle Placement

There was no significant difference in the ease of image acquisition or needle placement between the two conditions. The ease of image acquisition scored 4.0 (interquartile range 3.0-5.0) under normal gravity and 5.0 (interquartile range 4.0-5.0) under simulated microgravity (p=0.070). The ease of needle placement scored 4.5 (interquartile range 4.0-5.0) under normal gravity and 4.0 (interquartile range 3.0-4.0) under simulated microgravity (p=0.067).

3. Success Rate and Rate of Accidental Intraneural Injection

The success rate of injection was 80% (¹⁶⁄₂₀) under normal gravity and 85% (¹⁷⁄₂₀) under simulated microgravity, with no significant difference (p>0.999). The rate of accidental intraneural injection was 5% (¹⁄₂₀) in both conditions, also showing no significant difference.

Conclusion

This study is the first to evaluate the feasibility of regional anaesthesia in a simulated microgravity environment. The results indicate that, despite the ergonomic challenges of microgravity, experienced anaesthesiologists can successfully perform nerve blocks under simulated microgravity conditions. There were no significant differences in the time to block, ease of image acquisition, or ease of needle placement between the two conditions, and the success rate and rate of accidental intraneural injection were comparable.

This finding provides important proof-of-concept for regional anaesthesia in future deep space missions. Although the meat model used in this study has limitations and cannot fully replicate the complexities of actual space conditions, it lays the groundwork for future research. Regional anaesthesia, as a portable, safe, and effective method of pain management and anaesthesia, has the potential to play a significant role in deep space missions.

Research Highlights

1. First evaluation of regional anaesthesia feasibility in simulated microgravity: This study fills a gap in space medicine research by providing scientific evidence for regional anaesthesia in future deep space missions.
2. Use of a high-fidelity meat model: Researchers developed a high-fidelity meat model that effectively simulates the environment for nerve blocks, offering a reference for future simulation studies.
3. Feasibility of regional anaesthesia in microgravity confirmed: The results show that, despite the ergonomic challenges of microgravity, experienced anaesthesiologists can successfully perform nerve blocks.

Significance and Value of the Research

The scientific value of this study lies in its first-time verification of the feasibility of regional anaesthesia in a simulated microgravity environment, providing important theoretical support for medical interventions in future deep space missions. Regional anaesthesia, as a portable, safe, and effective method of pain management and anaesthesia, has the potential to play a crucial role in deep space missions, particularly in providing effective pain relief for astronauts suffering from traumatic injuries while maintaining their cognitive function.

Furthermore, this study opens new directions for future space medicine research, particularly in evaluating the feasibility of complex medical procedures in simulated microgravity environments. As human deep space exploration advances, space medicine will become a key area in ensuring the health and safety of astronauts, with regional anaesthesia playing an increasingly important role in future deep space missions.