Decompression Sickness (DCS)

Overview

Epidemiology

• Population statistics:
  • Sports diving: 3 cases per 10,000 dives
  • Commercial diving: 1.5–10 cases per 10,000 dives
  • 2.5 times more likely in men than women 
• Risk factors:
  • Dive details:
    • Depth
    • Duration
    • Number of dives
    • Interval surface time between dives
    • Water conditions
  • Diver: 
    • Weight (obesity is predisposing)
    • History of lung or cardiac disease
    • Right-to-left cardiac shunts (e.g., patent foramen ovale)
    • Inexperienced divers are more commonly affected.
    • Rate of ascent
    • Length of time between low altitude (scuba dive) and high altitude (air travel or ground ascent)

Etiology

Decompression sickness (DCS) comprises varied symptoms caused by gas bubbles that come out of solution in the body after ascending from a deep dive.

• Most likely to occur when: 
  • Scuba diving is followed closely by travel to high altitudes 
  • Divers do not adhere to dive protocols 
• Panic can make divers ascend too quickly.

Classification

Based on severity of symptoms and location of gas bubbles:

• Type I: mild bubbles form in:
  • Lymphatic system 
  • Skin
  • Muscles and joints
• Type II: severe/lethal bubbles form in:
  • Heart
  • Lungs
  • Central nervous system

Pathophysiology

• Descent: gas in body under higher atmospheric pressure → dissolves into tissues and blood
• Rapid ascent: partial pressure of gas > ambient pressure → gas comes out of solution → formation of bubbles
• Bubbles affect:
  • Organ tissue
    • Mechanical disruption/damage to tissue 
    • Alteration of the functionality of important structures
  • Venous circulation → picks gas up from tissues
    • In ↓ quantities → bubbles are asymptomatic and filtered in pulmonary capillaries
    • In ↑ quantities, bubbles can cause:
      • Inflammatory response
      • Activation of coagulation cascades
      • Damage to endothelium
      • Activation of platelet aggregation
      • Occlusion of blood flow
      • Capillary leakage

Clinical Presentation

• Nonspecific, depending on:
  • Location of gas bubbles
  • Compressibility of gases in body
• Quicker onset of symptoms = ↑ severity
  • Severe cases start < 30 minutes after surfacing.
  • Mild symptoms can take 6 hours to appear.
  • 75% of cases show symptoms in < 1 hour.
• Most cases are mild.
• Pulmonary/cardiovascular manifestations can be lethal.

Diagnosis

Diagnosis is based on: 

• History: relationship of symptoms to a diving event
  • DCS should be considered in any diver manifesting symptoms that cannot be explained by other mechanisms.
• Imaging:
  • Computed tomography (CT) scan can be used to detect vacuum phenomenon of trapped gas.
  • Magnetic resonance imaging (MRI): most accurate for detection of brain and spinal cord lesions

Management and Prognosis

The main goal of therapy is to dissolve bubbles and recompress gas in body fluids.

First aid

• Trendelenburg positioning → puts right ventricular outflow tract below right ventricular cavity → air migrates up and out of way of flow of blood
• Intravenous (IV) fluids
• Supplementary oxygen → accelerates inert gas washout

Definitive therapy

• Recompression therapy in hyperbaric treatment facility
  • Hyperbaric oxygen
  • Should never be withheld, even if initiation is delayed 
• IV fluids
• A consult with diving medicine/hyperbaric oxygen specialist is required, even if symptoms resolve.

Prevention

• Diver education
• Pre-dive medical screening and dive planning
• Strict adherence to dive course, timing, and depths
• Slow and controlled ascent (decompression stops: Experienced divers control their ascent using algorithms that indicate when ascent has to stop at different depths to allow for gas washout.)
• Recommendation to avoid high altitudes for 24 hours after a dive

Contraindications to deep-sea diving

• Active asthma
• Reduced pulmonary function
• Lung cysts
• Recent thoracic trauma or pneumothorax
• Cardiovascular disease
• History of bowel obstruction
• Recent brain or eye surgery
• Seizures
• Diabetes mellitus and hypoglycemic episodes
• History of syncope

Prognosis

• 75% of cases completely resolve.
• 16% of cases may have residual symptoms for up to 3 months.
• Spinal cord involvement often causes permanent damage.

Clinical Relevance

The following conditions greatly increase the likelihood of developing decompression sickness:

• Asthma: a chronic inflammatory condition of the airways characterized by bronchial hyperreactivity, which presents as wheezing, cough, and dyspnea. People with asthma have increased risk for pulmonary barotrauma and decompression sickness, which can lead to a pneumothorax and breathing difficulties. Treatment often requires intubation. 
• Pneumothorax: a collection of air in the pleural space that can occur due to dysbarism, causing shortness of breath and hypoxia. Treatment is with thoracostomy (chest tube) placement and oxygen.
• Bowel obstruction: the interruption of the normal transit of intestinal contents either due to a functional decrease in peristalsis or mechanical obstruction. Over-pressurization of the bowels can result in gastric rupture, bowel perforation, or pneumoperitoneum. Treatment often requires surgery.