Page 653 - ACCCN's Critical Care Nursing

630 S P E C I A LT Y P R A C T I C E I N C R I T I C A L C A R E

way through, while incomplete fractures only involve unit for assessment and treatment, including mechanical
part of the bone. Fractures are also classified according to ventilation.
the direction of the fracture line, and include linear, Internationally, there continues to be disagreement
oblique, spiral and transverse fractures.
regarding the pathophysiological changes associated with
A fracture causes disruption to the periosteum, blood FES, although there is general consensus on the following
vessels, marrow and surrounding soft tissue, resulting principles. It has been accepted that there is a mechanical
in a loss of mechanical integrity of the bone. Bone is component to the changes that take place in FES, where
one of only two sites (the other being the liver) that fat is physically forced into the venous system and causes
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will reform itself, not forming scar tissue when it heals. physical obstruction of the vasculature. Although marrow
When a fracture occurs, there is initial bleeding and pressure is normally 30–50 mmHg, it can be increased
soft tissue damage around the site, with haematoma up to 600 mmHg during intramedullary reaming (the
formation within the medullary canal. The healing process where the medullary cavity of the bone is surgi-
sequence that follows a fracture depends on the type cally enlarged to fit a surgical implant such as a tibial
of fracture fixation that is used. When a fracture is fixed nail), consequently reaching a pressure significantly
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in a method that eliminates the interfragmentary gap above pressures throughout the vasculature. A second
and provides stability to the site, such as in screwing theory, associated with the biochemical changes that
or wiring, primary healing takes place. When a fracture occur during trauma, proposes that trauma is associated
is fixed in a manner that reduces but does not eliminate with a higher level of circulating free fatty acids, which
movement around the fracture site, secondary healing cause destabilisation of circulating fats and/or direct tox-
takes place. 48 icity to specific tissues, including pulmonary and vascular
endothelium. 49
In primary healing, also referred to as direct union,
the haematoma that initially formed is eliminated by the
apposition of fracture ends during reduction. Once the Rhabdomyolysis
bone ends are intact, osteoclasts form cutting cones that Rhabdomyolysis is the breakdown of muscle fibres result-
in turn form new haversian canals across the fracture gap. ing in the distribution of the cellular contents of the
These contain blood vessels that are essential to primary affected muscle throughout the circulation, and occurs
bone healing. By 5–6 weeks after the fracture, osteoblasts during the reperfusion of injured muscle. The cellular
will fill the canals with osteons, which are the basic contents that are circulated include potassium, phos-
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structure of the new bone. Although the bone is now phate, organic acids, myoglobin, creatine kinase and
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formed, the strength and shape continues to develop over thromboplastin. Two phases of injury are essential for
coming weeks. the development of rhabdomyolysis: the first is when
muscle ischaemia occurs, and the second is with reperfu-
In contrast to primary healing, secondary healing is char- sion of the injured muscle. The length of time that muscle
acterised by an intermediate phase, where a callus of is ischaemic affects the development of rhabdomyolysis,
connective tissue is first formed and then replaced by with periods of less than 2 hours generally not producing
bone. 47,49 The secondary healing phase begins with an permanent damage, but periods above this time resulting
inflammatory phase in which the haematoma clots and in irreversible anatomical and functional changes. The
44
provides initial support, then inflammatory cells invade clinical sequelae of rhabdomyolysis include electrolyte
the haematoma to remove necrosed bone and debris. The abnormalities such as hypocalcaemia, hyperkalaemia and
reparative phase begins 1–2 weeks after the fracture and acidosis, hypovolaemia, acute renal failure and multi-
consists of immature woven bone being laid down and organ failure.
strengthened through a process known as mineralisation.
The final remodelling stage consists of replacement of the
woven bone by lamellar bone, through osteoblasts secret- Clinical Manifestations
ing osteoid that is mineralised and forms interstitial Common forms of skeletal trauma include the
lamellae. The remodelling of these structures occurs in following:
response to appropriate levels of mechanical loading l Long bone fractures. The long bones are the humerus,
during this phase. 47,48
radius, ulna, femur, tibia and fibula. Fractures of these
bones are serious and can carry a high level of morbid-
Fat embolism ity, especially if they involve a joint such as a trimal-
Fat embolism syndrome (FES) may occur in patients who leolar fracture of the ankle (distal tibia and fibula). In
have experienced a fracture of a long bone, particularly if many cases definitive surgical management is required,
multiple fractures or fractures to the middle or proximal with internal fixation.
parts of the femur are experienced. Fractures to the pelvis l Dislocations. All joints are at risk of traumatic dis-
can also lead to a fat embolism. Incidence of FES is low location, depending on the mechanism of injury. Dis-
(<1%). FES consists of fat in the blood circulation associ- locations can be limb-threatening if they cause
ated with an identifiable pattern of clinical signs and neurovascular compromise. Reduction of traumatic
symptoms that include hypoxaemia, neurological symp- dislocation is a medical emergency.
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toms and a petechial rash. Patients generally present l Open fractures (compound). Any break in the skin
12–48 hours after they have experienced a relevant that communicates directly with the fracture is classi-
fracture and often require admission to a critical care fied as an open fracture. Open fractures carry a higher