Aerospace Medicine · Supplementary · from Aerospace Medicine

Case 2: Decompression Sickness in Astronaut

Patient Presentation

Demographics: 42-year-old female astronaut and mission specialist (PhD Biomedical Engineering)

Chief Complaint: "I'm having severe joint pain in my right shoulder and my skin feels tingly — it started 30 minutes into the EVA."

History of Present Illness: Dr. S.K. was performing an extravehicular activity (EVA) during a space station maintenance mission when she developed progressive right shoulder pain described as deep, boring, and aching. The pain began approximately 30 minutes into the EVA despite completing the standard pre-breathe protocol (2 hours of 100% O2 at cabin pressure followed by suit pressurization at 4.3 psi). She initially attributed the pain to suit ergonomics but it intensified and was accompanied by cutaneous mottling and paresthesias over the right upper extremity.

The EVA was terminated early and the astronaut returned to the airlock. Upon repressurization to cabin pressure (14.7 psi), symptoms partially improved but did not resolve. She subsequently developed mild cognitive difficulty with word-finding problems noted by crew members. No chest pain, dyspnea, or visual changes were reported.

Review of the pre-breathe protocol revealed that Dr. S.K. had performed moderate exercise (resistance training) approximately 4 hours before the EVA, which may have increased tissue nitrogen loading. Additionally, she had been on the station for only 3 weeks, arriving from Earth where higher ambient pressure exposure may have contributed to residual nitrogen stores.

Past Medical History:

• One prior episode of mild Type I DCS (skin bends only) during altitude chamber training, resolved with descent — 8 years ago
• Patent foramen ovale (PFO) screening: bubble study equivocal (trace shunt detected under Valsalva)
• Otherwise medically qualified for spaceflight

Medications:

• Multivitamin
• Melatonin 3 mg PRN for circadian adjustment

Social History:

• Non-smoker, no alcohol use during mission
• Recreational SCUBA diver (certified, 40+ dives, no DCS history with diving)
• Third spaceflight; two prior EVAs without incident

Family History:

• Non-contributory

Physical Examination

• Vital Signs: BP 124/78 mmHg, HR 92 bpm, RR 16, SpO2 98% on cabin air, Temp 36.9°C
• General: Alert but mildly anxious, intermittent word-finding pauses noted
• Skin: Cutis marmorata (mottled, marbled appearance) over right shoulder and proximal upper arm; mild subcutaneous crepitus palpated over right deltoid region
• Musculoskeletal: Tenderness to palpation over right glenohumeral joint; pain worsened with movement; no effusion
• Neurological: Oriented to person, place, time; word-finding difficulty on formal testing; cranial nerves intact; motor strength 5/5 bilateral upper and lower extremities; sensation intact to light touch and pinprick; proprioception normal
• Cardiovascular: Tachycardic, regular rhythm, no murmurs
• Pulmonary: Clear to auscultation bilaterally

Workup and Results

Laboratory Studies:

Imaging/Additional Studies:

• Portable ultrasound (ISS): No pneumothorax; no joint effusion in right shoulder; echogenic foci noted in right subclavian vein (venous gas emboli)
• Transcranial Doppler (TCD): Multiple high-intensity transient signals (HITS) detected bilaterally, consistent with cerebral microemboli
• Neurocognitive testing (ISS protocol): Mild impairment in verbal fluency and working memory compared to pre-flight baseline

Clinical Image

Illustration showing nitrogen bubble formation in tissues and vasculature during EVA decompression from 14.7 psi cabin pressure to 4.3 psi suit pressure in microgravity. Source: Educational illustration.

Diagnosis

Decompression Sickness, Type II (Neurological Involvement) with Type I Features (Musculoskeletal and Cutaneous)

Key Diagnostic Criteria:

• Symptom onset during EVA with decompression from 14.7 psi to 4.3 psi
• Musculoskeletal pain (the "bends") in right shoulder
• Cutaneous manifestations (cutis marmorata) indicating skin involvement
• Neurological symptoms (word-finding difficulty) elevating to Type II classification
• Venous gas emboli confirmed on ultrasound with cerebral microemboli on TCD
• Possible right-to-left shunt via PFO as mechanism for arterial gas embolism and neurological involvement

Treatment Plan

1. Immediate 100% oxygen via mask (continuous until symptoms resolve)
2. IV fluid resuscitation with normal saline (1.5 L bolus, then 125 mL/hr) to reduce hemoconcentration and improve microcirculation
3. Oral aspirin 325 mg (if no contraindications) for antiplatelet effect
4. ISS hyperbaric treatment protocol: repressurization of affected module if capability exists; consultation with ground-based hyperbaric medicine specialists
5. Serial neurocognitive assessments every 6 hours
6. If symptoms persist or worsen: emergency medical evacuation via Soyuz/Crew Dragon for ground-based hyperbaric oxygen therapy (USN Treatment Table 6)
7. Formal PFO evaluation with transesophageal echocardiography upon return to Earth
8. Restriction from future EVA activities pending aeromedical board review

Key Learning Points

• Decompression sickness in spaceflight occurs due to the pressure differential between cabin atmosphere (14.7 psi) and EVA suit pressure (4.3 psi), a ratio of 3.4:1 that exceeds safe decompression limits without pre-breathe
• The standard pre-breathe protocol (100% O2 for 2-4 hours) reduces but does not eliminate DCS risk; exercise before EVA can paradoxically increase tissue nitrogen loading
• Type II DCS involves the central nervous system and requires more aggressive treatment; the presence of a PFO creates a pathway for venous gas emboli to reach the arterial circulation (paradoxical embolism)
• In-flight treatment of DCS on the ISS is limited; definitive hyperbaric oxygen therapy requires return to Earth, making prevention paramount
• Prior history of DCS, even mild, is a risk factor for recurrence and should prompt thorough PFO screening

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