Decompression Sickness PDF

DECOMPRESSION SICKNESS Date: 18 Jan 2022 Revision no. 01 Decompression Sickness Bends Disease • Group of effects produced by exposure to altitude. Classically, the main manifestations are limb pain (the bends), respiratory disturbances (the chokes), skin changes, various disturbances of the CNS &...

DECOMPRESSION SICKNESS Date: 18 Jan 2022 Revision no. 01 Decompression Sickness Bends Disease • Group of effects produced by exposure to altitude. Classically, the main manifestations are limb pain (the bends), respiratory disturbances (the chokes), skin changes, various disturbances of the CNS & cardiovascular collapse. • All these disturbances are always disappear on recompression to ground level. • The symptoms of decompression sickness was described first in the 19th century with divers (Caisson disease). • Mechanism of D.S. depends on Henry's Law that deals with the solubility of gases in liquids & it stated: "The quantity of gas dissolved in 1 cm³ of a liquid is proportional to the partial pressure of the gas in contact with the liquid". BUBBLE FORMATION: • A person living at sea level & breathing atmospheric air will have a dissolved nitrogen pressure PN2 of 573 mmHg in all body tissues & fluids. • Assuming that PB is 760 mmHg, PO2 is 100 mmHg, PCO2 is 40 mmHg & PH2O is 47mmHg PB = PN2 + PO2 + PCO2 + PH2O 760 = PN2 + 100 + 40 + 47 :: PN2 = 760 - 100 - 40 - 47 =573 mmHg • If that person is rapidly decompressed to altitude, a state of super saturation will be produced when the total barometric pressure became less than 573 mmHg (this occurred at 7500 feet altitude). Thus, above this altitude, an individual will encounter super saturation upon rapid decompression (Altitude Threshold). • The lowest altitude where a sea-level acclimatized person has encountered symptoms of D.S. is approximately 18000 feet (PB is 372 mmHg) PN2 R = 573 = PB = 372 1.54 (Critical super saturation ratio) Pathophysiology of Bubbles: Gas bubbles that form in body tissues & blood have 2 effects: 1. The direct mechanical effect of bubbles, which distort & disrupt tissues & cause pain & blocks circulation, causing ischemia & possible infarction. 2. The biochemical changes occurring at the blood bubble interface. Platelet aggregation occurs, with the release of vasoactive substances such as serotonin & epinephrine leading to vasoconstriction. The release of platelet factors accelerate clotting & lead to further circulatory embarrassment. Blood viscosity increases with a concomitant rise in capillary flow resistance & capillary pressure. This effect coupled with Hypoxic loss of capillary wall integrity, leads to large shifts of fluid from the intravascular to the extra vascular space & a further hemoconcentration. Protection & Predisposing factors • Protection against D.S. is based on controlling the tissue N2 to ambient pressure ratio (PN2/ PB). • When N2 is breathed, the tension of the gas dissolved in tissue/ fluids increases until equilibrium with partial pressure of the gas in the air is reached. • In decompression (Pressure reduction) & as per Henry's Law, N2 will separate from blood & other tissues & create bubbles that result in decompression sickness. The Aviator can be protected from D.S. in 2 ways: 1. A/C pressurization  With adequate A/C pressurization, the occupants are not exposed to reduced Barometric pressure where bubbles can form & protect from D.S. exists because PN2/PB ratio remains below the critical threshold as the value of PB remains high. 2. Denitrogenation  It is a method by which one breathe 100% O2 for the purpose of eliminating N2 from the body before going to altitude (Nitrogen washout) so PN2 will be low. Manifestation of Decompression Sickness • Bubbles in D.S. can form in all parts of the body. • Some target organs will be affected more. 1. BENDS:  Manifested by pain only.  Seen in 65-70% of cases of altitude induced D.S.  The pain tends to be localized in & around large joints.  Interphalangeal small joints sometimes affected particularly when perform an active movements.  Bends pain is deep & aching in character & ranges from mild to so severe that the patient does not wish to move the affected joint.  Active or passive movement of the joint will aggravate the pain.  This pain will be relieved by descent, if not relieved after reaching the ground, Hyperbaric O2 therapy will be the definitive treatment. 2. CHOKES  A symptom of D.S.  It is rare in both diving & aviation (manifested in less than 2% of D.S. cases).  It is a life-threatening disorder.  The mechanism, it is multiple pulmonary gas emboli.  The clinical picture consists of Substernal chest pain, Dyspnea & Dry non-productive cough.  In most cases, the pain is made worse on inhalation.  Patient feels generally & severely ill.  If the altitude maintained, patient will progress to collapse.  If not relieved by descent to ground level, hyperbaric chamber therapy should be applied as quickly as possible.  Chokes secondary to diving, also required the same therapy. 3. NEUROLOGIC SYMPTOMS • The involvement of the CNS occurs in 5-7% of cases of D.S. either from diving or altitude exposure. • In cases of altitude D.S., The symptoms that sometimes, not relieved totally by descent, the neurologic ones of these symptoms are about 35 to 50% of the cases. • The neurologic symptoms of D.S. presents in one of 2 forms: A. SPINAL CORD FORM: • Seen usually following diving & rarely following altitude exposure. • The first symptom is the insidious onset of numbness or paresthesia in the feet which may spread upward, accompanied by an ascending weakness or paralysis to the level of the spinal lesion. • In other cases may show girdling abdominal or thoracic pain. MECHANISM: • The lesion is due to bubbles formed in or embolized to the paraspinal venous plexus. • Poorly collateralized segmental venous drainage of the spinal cord & sluggish blood flow through the paraspinal venous plexus can result quickly in mechanical blockage of the venous drainage by bubbles. • This blockage, in turn, results in a congestive, or "red" infarct of the spinal cord B. BRAIN FORM: • May presented by headache, visual disturbances consisting of scotomas, tunnel vision, diplopia, or blurring. • Sometimes extreme fatigue or personality changes that ranges from emotional ability (changes in mood) to significantly flattened affect. • These symptoms are referred to a brain lesion due to bubble effect. 4. CIRCULATORY MANIFESTATION: • Could be manifested as shock following the development of chokes, severe bends, or severe neurologic impairment (secondary collapse). • MECHANISM of circulatory collapse either "Direct involvement of the vasomotor regulatory center" or "Massive blood vessel endothelial damage by bubbles with subsequent loss of intravascular volume". 5. SKIN MANIFESTATION: • Skin bends is a disorder that present as pruritus or formication (sensation of bugs are crawling on your skin). • This sensation will pass within 30 minutes & does not require treatment. 6. PITTING EDEMA: • May be manifested, it is a minor manifestation of D.S. & will resolve spontaneously without sequela arise from lymphatic blockage by bubbles. 7. CHRONIC EFFECT: • With divers only, sometimes a permanent neurologic deficits result from spinal cord D.S. even with proper & rapid treatment. • 15% of patients who have suffered spinal cord D.S. will manifest some degree of permanent neurologic deficits from minor sensory & motor losses to complete paraplegic. DIAGNOSIS and MANAGEMENT of DECOMPRESSION SICKNESS When D.S. Occurs? • Rarely occurs unless one of the following condition exists: 1. Diving deeper than 10m (33ft) of sea water & the diver fail to follow repetitive dive decompression schedule. 2. Exposure to altitude greater than 18000 Ft after exposure to compressed gas breathing (Aviation). 3. Exposure to altitude shortly following exposure to compressed gas breathing (scuba diving or hyperbaric chamber exposure flying with less than 3 hours). After scuba diving, D.S. may occur at a cabin altitude as low as 4500 feet. 4. Sudden decompression at high altitude.  Most cases of D.S. occurring at altitude will be completely relieved by descent to ground level, approximately 2% of cases will persist. The following procedures should be followed when D.S. is diagnosed: 1. 100% O2 should be administered. 2. If hyperbaric chamber is on site. Patient should be immediately treated according to the H.B.O. protocol. 3. 100% O2 should be continue if there no on-site hyperbaric chamber. The patient may improve & may not. 4. With signs & symptoms of Neurologic manifestations, chokes, or circulatory collapse, the only treatment required is immediate hyperbaric O2 therapy. 5. Return to flying no earlier the 72 hours after resolution. HYPERBARIC O2 THERAPHY • Once the diagnosis of D.S. has been made, hyperbaric therapy is required. It is never acceptable to waste time & continue observation of the patient. • The use of O2 at 1 ATA (outside the hyperbaric chamber) should be restricted to the period of initial observation/ examining, the time required for transportation to the chamber, & the time required to prepare the chamber, only. • When long delays between the onset of D.S. & treatment occur, the manifestation of D.S. will become more serious. Thank you