LIFE-THREATENING PROBLEMS - Medicine for Mountaineering and Other Wilderness Activities - page 28

Hemorrhagic Shock
Hemorrhage or acute blood loss is the most common cause of shock after injury. The
acute blood loss may be from obvious open wounds but is more typically the result of
bleedingfrominternalorgans( Chapter10:AbdominalInjuries ) .Thesignsofshockdepend
on the magnitude of blood loss and the rate of bleeding. The amount of external blood loss
is usually overestimated, particularly on snow, whereas rapid internal bleeding may not be
evidentwhenitoccursinthechest,abdomen,orpelvis.Withsignificantreductionofcircu-
lating blood volume, compensatory mechanisms occur that attempt to preserve blood flow
to vital organs: Arteries in the skin and muscle constrict to divert blood to critical organs,
and the heart pumps at an increased rate to circulate the blood faster and allow a smaller
volume of blood to carry more oxygen. At the same time, the rate of breathing is increased
to enhance the loading of oxygen as blood transverses the lungs.
The American College of Surgeons provides a classification of hemorrhagic shock into
progressive levels I to IV based on the magnitude of acute blood loss ( Table 3-2 ). Circulat-
ing blood volume is best estimated by body weight:
7% x ideal body weight in kg = approximate blood volume in ml
Thus, a person 6 feet (180 cm) tall and weighing 175 pounds (80 kg) has a circulating
blood volume of roughly 6000 ml, whereas an individual 5 feet 2 inches (155 cm) tall and
weighing 110 pounds (50 kg) has a blood volume of about 4000 ml.
Although this classification is designed to assist in the management of shock in the hos-
pital, the relative class of shock may be helpful to a rescue team to determine the urgency
ofevacuation,suchascallingforhelicoptertransportorrecognizingthelikelihoodofdeath
when prompt evacuation is impossible.
The vital organ affected early by inadequate oxygen delivery is the brain. The earliest
manifestation of shock is anxiety, and the most objective measure of significant blood loss
is a rapid heart rate. An injured person who is restless with a sustained heart rate greater
than 120 per minute and cool extremities should be assumed to have life-threatening acute
bloodloss.Ascompensatorymechanismsfailwithcontinuedbloodloss,theinjuredperson
deteriorates from confusion to lethargy.
Measuring blood pressure with a blood pressure cuff and a stethoscope would be one
way to evaluate the severity of shock, but if this equipment is not available a rough estim-
ate of blood pressure can be made by palpating for pulses at different areas. (Normal blood
pressure is approximately 120 mmHg systolic and 80 mmHg diastolic.) If a pulse can be
felt at the wrist (radial pulse), the systolic blood pressure is usually at least 80 mmHg. If
the radial pulse cannot be detected but a pulse can be felt in the groin (femoral pulse), the
systolicbloodpressureisapproximately 70mmHg.Ifthefemoralpulsecannotbedetected
but a pulse can be felt in a carotid artery, the systolic blood pressure is approximately 60
mmHg.