shock

1. shock

2. Definition: shock is a condition of reduced tissue perfusion, resulting in the inadequate delivery of oxygen and nutrients that are necessary for cellular function.

3. On a multicellular level, the definition of shock becomes more difficult because not all tissues and organs will experience the same amount of oxygen imbalance for a given clinical disturbance.

4. The 4 classes of shock, as proposed by Alfred Blalock, are as follows • Hypovolemic • Vasogenic (septic) • Cardiogenic • Neurogenic

5. Hemorrhage: A cut loss of circulating blood volume. The risk factor for hemorrhagic shock: • Pt age. • Severity of injury with anatomical postion. • Time lapse between injury and intiation of treatment. • Prehospital fluid therapy & application of PACG. • Medication used for chronic condition

7. Hypovolemic shock • the most common type, results from a loss of circulating blood volume from clinical etiologies, such as penetrating and blunt trauma, gastrointestinal bleeding, and obstetrical bleeding. • Humans are able to compensate for a significant hemorrhage through various neural and hormonal mechanisms.

8. Pathophysiology • these responses act to systematically divert circulating volume away from non vital organ systems so that blood volume may be conserved for vital organ function. • Acute hemorrhage causes a decreased cardiac output and decreased pulse pressure.

9. These changes are sensed by baroreceptors in the aortic arch and atrium. • With a decrease in the circulating volume, neural reflexes cause an increased sympathetic outflow to the heart and other organs.

10. The response is an increase in heart rate, vasoconstriction, and redistribution of blood flow away from certain non vital organs, such as the skin, gastrointestinal tract, and kidneys. • a multisystem hormonal response to acute hemorrhage occurs.

11. Corticotropin-releasing hormone is stimulated directly. This eventually leads to glucocorticoid and beta-endorphin release. • Vasopressin from the posterior pituitary is released, causing water retention at the distal tubules.

12. Renin is released by the juxtamedullary complex in response to decreased mean arterial pressure, leading to increased aldosterone levels and eventually to sodium and water resorption. • Hyperglycemia commonly is associated with acute hemorrhage.

13. This is due to a glucagon and growth hormone–induced increase in gluconeogenesis and glycogenolysis. • Circulating catecholamines relatively inhibit insulin release and activity, leading to increased plasma glucose.

14. In addition to these global changes, many organ-specific responses occur. • The brain has remarkable autoregulation that keeps cerebral blood flow constant over a wide range of systemic mean arterial blood pressures.

15. The kidneys can tolerate a 90% decrease in total blood flow for short periods of time. • With significant decreases in circulatory volume, intestinal blood flow is dramatically reduced by splanchnic vasoconstriction. • Early and appropriate resuscitation may avert damage to individual organs as adaptive mechanisms act to preserve the organism.

16. Age • Hemorrhagic shock is tolerated differently, depending on the preexisting physiologic state and, to some extent, the age of the patient. • Very young and very old people are more prone to early decompensation after loss of circulating volume.

17. Pediatric patients have smaller total blood volumes and, therefore, are at risk to lose greater percentage of blood on an equivalent-volume basis during exsanguination compared to adults. • The kidneys of children younger than 2 years are not mature; they have a blunted ability to concentrate solute.

18. Younger children cannot conserve circulating volume as effectively as older children. • Also, the body surface area is increased relative to the weight, allowing for rapid heat loss and early hypothermia, possibly leading to coagulopathy.

19. Elderly people may have both altered physiology and preexisting medical conditions that may severely impair their ability to compensate for acute blood loss. • Atherosclerosis and decreased elastin cause arterial vessels to be less compliant, leading to blunted vascular compensation, decreased cardiac arteriolar vasodilation, and angina or infarction when myocardial oxygen demand is increased.

20. Older patients are less able to mount a tachycardia in response to decreased stroke volume because of decreased beta-adrenergic receptors in the heart and a decreased effective volume of pacing myocytes within the sinoatrial node.

21. Also, these patients frequently are treated with a variety of cardiotropic medications that may blunt the normal physiological response to shock. • These include beta-adrenergic blockers, nitroglycerin, calcium channel blockers, and antiarrhythmics.

22. The kidneys also undergo age-related atrophy, and many older patients have significantly decreased creatinine clearance in the presence of near-normal serum creatinine. • Concentrating ability may be impaired by a relative insensitivity to antidiuretic hormone.

23. These changes in the heart, vessels, and kidneys can lead to early decompensation after blood loss. • All of these factors in concert with comorbid conditions make management of elderly patients with hemorrhage quite challenging.

24. Causes • The most common clinical etiologies are penetrating and blunt trauma, gastrointestinal bleeding, and obstetrical bleeding.

25. Clinical • History: -No single historical feature is diagnostic of shock. Some patients may report fatigue, generalized lethargy, or lower back pain (ruptured abdominal aortic aneurysm). - Others may arrive by ambulance or in the custody of law enforcement for the evaluation of bizarre behavior.

26. Obtaining a clear history of the type, amount, and duration of bleeding is very important. • Many decisions in regard to diagnostic tests and treatments are based on knowing the amount of blood loss that has occurred over a specific time period. • If the bleeding occurred at home or in the field, an estimate of how much blood was lost is helpful.

27. For GI bleeding, knowing if the blood was per rectum or per os is important. Because it is hard to quantitate lower GI bleeding, all episodes of bright red blood per rectum should be considered major bleeding until proven otherwise.

28. Bleeding because of trauma is not always identified easily. • The pleural space, abdominal cavity, mediastinum, and retroperitoneum are all spaces that can hold enough blood to cause death from exsanguination. • External bleeding from trauma can be significant and can be underestimated by emergency medical personnel.

29. Multiple open fractures can lead to the loss of several units of blood. • Scalp lacerations are notorious for causing large underestimated blood loss.

30. Physical • The physical examination in patients with hemorrhagic shock is a directed process. • Often, the examination will be paramount in locating the source of bleeding and will provide a sense of the severity of blood loss.

31. The hallmark clinical indicators of shock have generally been the presence of abnormal vital signs, such as hypotension, tachycardia, decreased urine output, and altered mental status. • These findings represent secondary effects of circulatory failure, not the primary etiologic event

32. Because of compensatory mechanisms, the effects of age, and use of certain medications, some patients in shock will present with a normal blood pressure and pulse. • The general appearance of a patient in shock can be very dramatic. The skin may have a pale & usually with diaphoresis.The patient may appear confused or agitated and may become obtunded.

33. The pulse first becomes rapid and then becomes dampened as the pulse pressure diminishes. Systolic blood pressure may be in the normal range during compensated shock. • The conjunctivae are inspected for paleness, a sign of chronic anemia. The nose and pharynx are inspected for blood.

34. The chest is auscultated and percussed to evaluate for hemothorax. This would lead to loss of breath sounds and dullness to percussion on the side of bleeding. • The abdominal examination searches for signs of intra-abdominal bleeding, such as distention, pain with palpation, and dullness to percussion.

35. The flanks are inspected for ecchymosis, a sign of retroperitoneal bleeding. Ruptured aortic aneurysms are one of the most common conditions that cause patients to present in unheralded shock.

36. Signs that can be associated with a rupture are a palpable pulsatile mass in the abdomen, scrotal enlargement from retroperitoneal blood tracking, lower extremity mottling, and diminished femoral pulses.

37. The rectum is inspected. If blood is noted, take care to identify internal or external hemorrhoids. On rare occasion, these are a source of significant bleeding, most notably in patients with portal hypertension. • Patients with a history of vaginal bleeding undergo a full pelvic examination. A pregnancy test is warranted to rule out ectopic pregnancy.

38. Trauma patients are approached systematically, using the principles of the primary and secondary examination. • Trauma patients may have multiple injuries that need attention concurrently, and hemorrhage may accompany other types of insults, such as neurogenic shock.

39. The primary survey is a quick maneuver that attempts to identify life-threatening problems. • To assess the airway, ask the patient's name. If the answer is articulated clearly, the airway is patent. • The oral pharynx is inspected for blood or foreign materials. • The neck is inspected for hematomas or tracheal deviation.

40. The lungs are auscultated and percussed for signs of pneumothorax or hemothorax. • The radial and femoral pulses are palpated for strength and rate. • A quick inspection is made to rule out any external sources of bleeding. • A gross neurological examination is performed by asking the patient to squeeze each hand and dorsiflex both feet against pressure. • The patient then is exposed completely, taking care to maintain thermoregulation with blankets and external warming devices.

41. The secondary examination is a head-to-toe, careful examination that attempts to identify all injuries. • The scalp is inspected for bleeding. Any active bleeding from the scalp should be controlled before proceeding with the examination. • The mouth and pharynx are examined for blood.

42. The abdomen is inspected and palpated. Distention, pain on palpation, and external ecchymosis are indications of intra-abdominal bleeding. • The pelvis is palpated for stability. Crepitus or instability may be an indication of a pelvis fracture, which can cause life-threatening hemorrhage into the retroperitoneum.

43. Long bone fractures are noted by localized pain to palpation and boney crepitus at the site of fracture. All long bone fractures should be straightened and splinted to prevent ongoing bleeding at the sites. • Femur fractures are especially prone to large blood losses and should be immobilized immediately in a traction splint.

44. Workup • Laboratory Studies: laboratory values are not helpful in acute hemorrhage because values do not change from normal until redistribution of interstitial fluid into the blood plasma occurs after 8-12 hours.

45. Hemoglobin and hematocrit values remain unchanged from baseline immediately after acute blood loss. • During the course of resuscitation, the hematocrit may fall secondary to crystalloid infusion and re-equilibration of extracellular fluid into the intravascular space.

46. No absolute threshold hematocrit or hemoglobin level that should prompt transfusion exists. A hemoglobin concentration of less than 7 g/dL in the acute setting in a patient that was otherwise healthy is concerning only because the value most likely will drop considerably after re-equilibration.

47. In the absence of preexisting disease, transfusions can be withheld until significant clinical symptoms are present or the rate of hemorrhage is enough to indicate ongoing need for transfusion. • Patients with significant heart disease are at higher risk of myocardial ischemia with anemia, and transfusion should be considered when values drop below 7 mg/dL.

48. Arterial blood gas may the most important laboratory value in the patient in severe shock. • Acidosis is the best indicator in early shock of ongoing oxygen imbalance at the tissue level. A blood gas with a pH of 7.30-7.35 is abnormal but tolerable in the acute setting. • The mild acidosis helps unload oxygen at the peripheral tissues and does not interfere with hemodynamics.

49. A pH below 7.25 may begin to interfere with catecholamine action and cause hypotension unresponsive to inotropics. • Metabolic acidosis is a sign of underlying lack of adequate oxygen delivery or consumption and should be treated with more aggressive resuscitation, not exogenous bicarbonate

50. Life-threatening acidemia (pH <7.2) initially may be buffered by the administration of sodium bicarbonate to improve the pH. However, be aware that no survival benefit to this practice has been documented.