Hypotension / Shock
Shock is a life-threatening situation. In most cases, shock is due to poor tissue perfusion with impaired cellular metabolism, leading to progressive organ failure which if not reversed results in irreversible organ damage and death. Rapid and effective intervention is required to impede the progression of this serious disorder and ultimately impact patient survival.
Diagnosing shock in a timely way is an important training problem for third year medical students because accurate diagnosis requires prudent selection and interpretation of common diagnostic studies. Also, determining appropriate management strategies for shock under significant pressure is important because of its impact on patient morbidity and on health care cost.
Describe and discuss:
- anatomy and physiology of the cardiovascular and respiratory systems
- pathophysiology of disorders of the cardiovascular and respiratory systems
- physiologic principles that govern normal blood pressure and hemodynamic homeostasis
- relationship between tissue oxygen delivery and utilization
- mechanisms of hypoxemia and hemoglobin-oxygen dissociation curve
- complete medical history
- basic physical examination
- basic communication skills, including other health professionals and patients from diverse backgrounds
Apply Medical Knowledge in the Clinical Encounter
1. Describe and discuss the signs and symptoms, distinguishing clinical characteristics, and typical clinical course of the different types of shock:
- hypovolemic shock
- cardiogenic shock
- extracardiac obstructive shock
- distributive shock (profound decrease in systemic vascular tone)
2. Describe and discuss the distinguishing features of the different stages of shock:
- stage I – early, reversible and compensatory shock
- stage II – intermediate or progressive shock
- stage III – refractory or irreversible shock
3. Describe and discuss conditions in which shock is common:
- severe bleeding
- heart attacks
- severe burns
- severe bacterial infections
- abdominal emergencies
- excessive loss of body fluids
- crush injuries
4. Describe and discuss diagnostic tests:
- vital signs
- chest x-rays
- Central Venous Pressure
- arterial blood gases
- pulmonary capillary wedge (Swann-Ganz)
5. Describe and discuss priorities and specific goals of resuscitation for each form of shock:
- define goals of and priorities in resuscitation (ABCs)
- defend choice of fluids
- discuss indications for transfusion
- discuss management of acute coagulopathy
- discuss indications for invasive monitoring
- discuss use of inotropes, afterload reduction in management
6. Describe vasopressors used in shock states.
7. Identify and describe strategies that would prevent a patient from developing shock.
8. Psychosocial, ethical, and legal issues relevant to patients suffering from shock.
1. Obtain, document and present an age-appropriate medical history that differentiates among etiologies of disease, including:
- known cardiac disease (coronary disease, CHF, pericarditis)
- recent fever or infection (leading to sepsis)
- drugs (excess diuretics or antihypertensives)
- conditions predisposing for pulmonary embolism
- possible bleeding from any site, particularly GI tract
2. Perform a focused physical exam to include neck veins, cardiac, pulmonary, establish the diagnosis and severity of disease. It is necessary to:
- know that jugular veins are flat in oligemic or distributive shock; jugular venous distention (JVD) suggests cardiogenic shock; JVD in presence of paradoxical pulse may reflect cardiac tamponade
- look for evidence of CHF, murmurs of aortic stenosis, acute regurgitation (mitral or aortic), ventricular septal defect
- check for asymmetry of pulses (aortic dissection)
- recognize that tenderness or rebound in abdomen may indicate peritonitis or pancreatitis; high-pitched bowel sounds suggest intestinal obstruction; stool guaiac tests can rule out GI bleeding
- know that fever and chills usually accompany septic shock; sepsis may not cause fever in elderly, uremic, or alcoholic patients.
- recognize skin lesions that may suggest specific pathogens in septic shock: petechiae orpurpura (Neisseria meningitidis), erythyma gangrenosum (Pseudomonas aeru ginosa), generalized erythroderma (toxic shock due to Staphylococcus aureus or Streptococcus pyogenes).
3. Generate a differential diagnosis recognizing specific history and physical exam findings that suggest a specific etiology.
4. Recommend when to order diagnostic and laboratory tests and be able to interpret them (with consultation), both prior to and after initiating treatment based on the differential diagnosis. Consider test cost and performance characteristics as well as patient preferences.
- Obtain hematocrit, WBC, electrolytes. If actively bleeding, check platelet count, PT, PTT, DIC screen.
- Arterial blood gas usually shows metabolic acidosis (in septic shock, respiratory alkalosis precedes metabolic acidosis).
- If sepsis suspected, draw blood cultures, perform urinalysis and obtain Gram stain and cultures of sputum, urine, and other suspected sites.
- Obtain ECG (myocardial ischemia or acute arrhythmia), chest x-ray (CHF, tension pneumothorax, aortic dissection, pneumonia). Echocardiogram may be helpful (cardiac tamponade, CHF).
- Central venous pressure or pulmonary capillary wedge (PCW) pressure measurements may be necessary to distinguish between different categories of shock:
- Mean PCW _ 6 mmHg suggests oligemic or distributive shock
- PCW _ 20 mmHg suggests left ventricular failure
- Cardiac output (thermodilution) is decreased in cardiogenic and oligemic shock, and usually increased initially in septic shock.
5. Demonstrate skill in the placement of large-bore intravenous access (Seldinger technique).
6. Identify the patient’s problem from all of the problems listed in the differential diagnosis by combining scientific knowledge, information obtained in the clinical encounter and collective experience with similar patients.
7. Communicate the diagnosis to the patient.
8. Record, present, research, critique, and manage clinical information.
9. Access and use appropriate information systems and resources to help delineate issues related to shock.
Develop a Management Plan
Make decisions about what to include from the following items and explain why each item selected should be included:
1. Manage airway control, breathing and circulatory support including:
- rapid improvement of tissue hypoperfusion and respiratory impairment: serial measurements of bp (intraarterial line preferred), heart rate, continuous ECG monitor, urine output, pulse oximetry, blood studies: Hct, electrolytes, creatinine, BUN, ABGs, calcium, phosphate, lactate, urine Na concentration (20 mmol/L suggests volume depletion)
- continuous monitoring of CVP and/or pulmonary artery pressure, with serial PCW pressures.
- supplemental oxygen therapy may be needed; intubation may be needed if consciousness is an issue.
2. Insert Foley catheter to monitor urine flow.
3. Assess mental status frequently.
4. Augment systolic bp to _100 mmHg:
- place in reverse Trendelenburg position;
- IV volume infusion (500- to 1000-mL bolus), unless cardiogenic shock suspected (begin with normal saline, then whole blood, dextran, or packed RBCs, if anemic); continue volume replacement as needed to restore vascular volume.
5. Add vasoactive drugs after intravascular volume is optimized; administer vasopressors if systemic vascular resistance (SVR) is decreased (begin with norepinephrine or dopamine; for persistent hypotension add phenylephrine or vasopressin).
6. If CHF present, add inotropic agents (usually dobutamine) aim to maintain cardiac index _ 2.2 (L/m2)/min [ _4.0 (L/m2)/min in septic shock].
7. Administer 100% O2; intubate with mechanical ventilation if PO _ 70 2mmHga.
8. If severe metabolic acidosis present (pH _ 7.15), administer NaHCO3 (44.6–89.2 mmol).
9. Identify and treat underlying cause of shock.
- Emergent coronary revascularization may be lifesaving if persistent ischemia is present.
- Consider cardiac tamponade.
10. Manage infection if sepsis present.
- volume depletion (e.g., vomiting, diarrhea, diuretic over-usage, ketoacidosis, third spacing such as burns)
- internal sequestration (ascites, pancreatitis, intestinal obstruction)
- myopathic (acute MI, dilated cardiomyopathy)
- mechanical (acute mitral regurgitation, ventricular septal defect, severe aortic stenosis, tampanode)
Extracardiac obstructive shock
- pericardial tamponade
- massive pulmonary embolism
- tension pneumothorax
Distributive shock (profound decrease in systemic vascular tone)
- toxic overdoses
- neurogenic (e.g., spinal cord injury)
- endocrinologic (Addison’s disease, myxedema)