Decompression Sickness, Emergency Medicine

Basics

Description

Multisystemic disease process resulting from escape of inert gas bubbles (nitrogen) out of solution into body fluids and tissues

Etiology

Mechanism:

Pathophysiology:
- Increases in ambient pressure cause increase in partial pressure of nitrogen inspired (as per Henry law, below).
- Nitrogen accumulates in tissues in increasing concentrations the longer ambient pressures remain elevated.
- Decompression sickness (DCS) results when ambient pressure keeping nitrogen in solution decreases too rapidly (on ascent), preventing gradual removal of excess body burden of nitrogen.
- As the nitrogen removal gradient is overwhelmed, tissues become supersaturated and bubble formation occurs.
Henry law:
- Amount of gas that will dissolve in a solution at a given temperature is directly proportional to partial pressure of that gas.
- Increases in partial pressure result in larger amount of gas dissolved in tissue.
- Decreases in partial pressure result in gas coming out of solution.
Bubbles are viewed as foreign material by body inciting inflammatory and coagulation responses
- Leads to increased vascular permeability and decreased intravascular volume and hemoconcentration
Bubble location determines clinical effects:
- Blood flow and lymphatic obstruction leading to ischemia, infarction, or lymphedema
- Mechanical distention of tissues leading to pain
Risk factors for DCS:
- Dive factors:
  - Greater depth
  - Longer bottom time
  - Multiple dives in a day
  - Rapid ascent
  - Cold water
- Human factors:
  - Obesity
  - Intercurrent illness
  - Pulmonary disease
  - Dehydration
- Proper use of dive tables and computers does not eliminate risk for DCS.
- Predive vigorous exercise may reduce risk
50% of patients develop symptoms in 1 hr, 90% develop symptoms within 6 hr.
Airplane flight following diving can precipitate DCS owing to lower cabin pressure.

Diagnosis

Signs and Symptoms

Cutaneous:
- Scarlatiniform, erysipeloid, or mottled rash:
  - Mottling (Cutis marmorata) often indicates more severe disease
- Peau d'orange appearance owing to lymphatic obstruction
Musculoskeletal (the bends):
- Pain:
  - Dull, deep muscular aching
  - Often in a joint (elbow and shoulder most common)
  - Typically not exacerbated by movement or reproduced with palpation
GI:
- Nausea and vomiting
- Abdominal pain
Pulmonary (the chokes):
- Pulmonary vasculature obstruction from bubble burden (venous gas embolism)
- Acute respiratory distress
  - Substernal chest pain/pressure
  - Cough
  - Dyspnea
  - Hypoxia
CNS:
- Weakness and fatigue
- Numbness and paresthesia
- Agitation
- Headache
- Dizziness
- Vertigo
- Convulsion
- Bladder and/or bowel incontinence
- Lethargy
- Visual disturbances
- Most commonly affects spinal cord (lower thoracic and lumbar regions)
Inner ear (the staggers):
- Vestibular damage
- Dizziness, vertigo, tinnitus, nausea
- Similar symptoms to inner ear barotrauma but with worse prognosis

History
Meticulous dive history including time at depth, ascent history, and onset of symptoms.
Physical Exam
Thorough physical exam including a detailed neurologic exam

Essential Workup

Clinical diagnosis: Recognize risk factors and various clinical presentations.
Careful neurologic exam to document possible waning symptoms
Trial of pressure:
- Rapid relief of symptoms upon recompression in a hyperbaric chamber may be the only way to diagnose DCS conclusively.

Diagnosis Tests & Interpretation

Lab

CBC:
- Increased hematocrit secondary to hemoconcentration
Electrolytes, BUN, creatinine, glucose
Urinalysis
- Increased specific gravity may indicate intravascular volume depletion
ABG and pulse oximetry:
- Monitor oxygenation

Imaging

CXR:
- Concomitant pulmonary barotrauma
- Noncardiogenic pulmonary edema from DCS
Extremity x-ray
- Rule out trauma as cause of pain
Head CT when altered mental status or neurologic deficit

Differential Diagnosis

Musculoskeletal injury unrelated to bubble formation
Inner or middle ear barotraumas
Arterial gas embolism
Cerebrovascular accident (CVA)
Trauma

Treatment

Pre-Hospital

Cautions:
- Recognize DCS:
  - Postdive extremity pain often attributed to muscle strain
  - Serious neurologic complaints often minimized because diver does not consider DCS
- If air evacuation required:
  - Limit altitude to less than 1,000 ft or use pressurized aircraft
Controversies:
- In-water recompression:
  - Return injured diver/patient to depth where symptoms are ameliorated.
  - Extremely difficult
  - Need large amount of surface support

Initial Stabilization/Therapy

Airway, breathing, and circulation management (ABCs)
Provide normobaric (100%) oxygen via mask or endotracheal tube (ETT):
- Increases inert gas (nitrogen) elimination from tissues, reducing gas bubble size
- Increases oxygen delivery to injured tissue
Maintain patient in supine position to prevent further cerebral involvement
Early recompression in hyperbaric chamber

Ed Treatment/Procedures

IV rehydration with 0.9% normal saline (NS) to maintain goal urine output of 1-2 mL/kg/h:
- Diver usually dehydrated owing to diuretic effect of pressure, exercise, breathing dry compressed air, and increased vascular permeability
- Increased fluid assists with gas removal and dissolution of nitrogen
Hyperbaric oxygen recompression therapy (see Hyperbaric Oxygen Therapy):
- Arrange transportation to nearest hyperbaric facility.
- Prophylactic chest tube for simple pneumothorax to prevent conversion to tension pneumothorax in chamber
- Fill endotracheal and Foley catheter balloons with water or saline to avoid shrinkage/damage during recompression.
- Recompression therapy protocols found in US Navy diving manual
Divers Alert Network (DAN):
- Provides 24-hr emergency hotline for medical consultation on treatment of dive-related injuries and for referrals to hyperbaric chambers ([919] 684-9111)
Analgesics and antiemetics
Diazepam (Valium) for severe vertigo
Adjunctive therapy with NSAIDs and/or heliox may reduce number of recompression treatments required

Follow-Up

Disposition

Admission Criteria
Refer all patients with suspected or diagnosed DCS for hyperbaric therapy.
Discharge Criteria

Stable patients with mild symptoms may be discharged posthyperbaric oxygen treatment.
Air travel may exacerbate symptoms as ambient pressure decreases.

Followup Recommendations

Hyperbaric referral

Pearls and Pitfalls

Difficult to distinguish musculoskeletal DCS from musculoskeletal pain
Significant fatigue may be the only symptom of DCS
Even minor symptoms or resolving symptoms suspected of being DCS should be treated with hyperbaric recompression therapy
Do not delay recompression therapy for lab testing and imaging when DCS is most likely diagnosis
Avoid in-water recompression therapy.

Additional Reading

Bennett MH, Lehm JP, Mitchell SJ, et al. Recompression and adjunctive therapy for decompression illness. Cochrane Database Syst Rev. 2012;5:CD005277. doi:10.1002/14651858.CD005277.pub3.
Divers Alert Network [Homepage]. Available at www.diversalertnetwork.org.
Hawes J, Massey EW. Neurologic injuries from scuba diving. Neurol Clin. 2008;26:297-308.
Levett DZ, Millar IL. Bubble trouble: A review of diving physiology and disease. Postgrad Med J. 2008;84:571-578.
Lynch JH, Bove AA. Diving medicine: A review of current evidence. J Am Board Fam Med. 2009;22:399-407.

Codes

ICD9

993.3 Caisson disease

ICD10

T70.3XXA Caisson disease [decompression sickness], initial encounter

SNOMED

89684003 Bends

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