Chapter 32 Diagnosis and Management of Hypotension and Shock in the Intensive Care Unit
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Diagnosis and Management of Hypotension and Shock in the Intensive Care Unit Chapter 32 DIAGNOSIS AND MANAGEMENT OF HYPOTENSION AND SHOCK IN THE INTENSIVE CARE UNIT JESSICA BUNIN, MD* INTRODUCTION PATHOPHYSIOLOGY AND CLINICAL PRESENTATION CATEGORIES OF SHOCK GENERAL DIAGNOSTIC APPROACH FOR HYPOTENSION GENERAL PRINCIPLES OF MANAGEMENT OF THE HYPOTENSIVE INTENSIVE CARE UNIT PATIENT MANAGEMENT OF SPECIFIC TYPES OF SHOCK Hypovolemic Shock Cardiogenic Shock Distributive Shock Obstructive Shock SUMMARY *Lieutenant Colonel, Medical Corps, US Army; Chief of the Critical Care Medicine Service, Department of Medicine, Walter Reed National Military Medical Center, 8901 Wisconsin Avenue, Bethesda, Maryland 20889 327 Combat Anesthesia: The First 24 Hours INTRODUCTION Shock is a state of impaired tissue oxygenation and than 30% of blood volume has been lost. Although perfusion that can be caused by decreased oxygen hypotension and shock are not synonymous, the goals delivery, poor tissue perfusion, or impaired oxygen of treatment are the same: to restore the body’s oxygen utilization. Hypotension is a sign of shock and an indi- balance and correct hypoperfusion. This chapter will cator of advanced derangement, requiring immediate address the categories of shock, initial evaluation of a evaluation and management. For example, in hemor- hypotensive patient, general principles of shock man- rhagic shock, hypotension is not present until greater agement, and management for specific causes of shock. PATHOPHYSIOLOGY AND CLINICAL PRESENTATION Shock represents a state of hypoperfusion that vital of organs—the heart and the brain—because of can be the final pathway for a number of conditions. the opening of arteriovenous connections to bypass Hypoperfusion from any cause results in an inflamma- capillary flow.2 tory response. A normal physiologic compensation to As these compensatory mechanisms begin to fail, improve perfusion of vital organs is sympathetic vaso- the clinical signs and symptoms of shock become evi- constriction resulting in an elevated diastolic pressure, dent. The most commonly discussed signs of shock narrow pulse pressure, and peripheral hypothermia. are hypotension, altered mental status, and oligura, There is also a sympathetically mediated tachycardia but dysfunction of any end organ can result. Labora- that helps maintain cardiac output. Hypoperfusion tory abnormalities include lactic acidosis, elevated also causes an acidosis induced by lactate production base deficit, hypoxia, elevated blood urea nitrogen and resulting in compensatory tachypnea as the body and creatinine, elevated liver-associated enzymes attempts to offset the resulting acidosis. The other and bilirubin, and coagulation abnormalities. Lactic major effect of the acidosis is a rightward shift of the acidosis and base deficit are more sensitive indicators oxyhemoglobin curve,1 allowing more of the oxygen of severity and prognosis than are blood pressure and that is bound to hemoglobin to be released. Addition- urine output (these will be covered in greater detail ally, there is increased shunting of blood to the most later in this chapter).3,4 CATEGORIES OF SHOCK It is helpful to place shock in one of the following pressure are elevated in cardiogenic shock. In this state, four distinct categories: (1) hypovolemic, (2) cardiogen- the volume is available, but pump failure causes inad- ic, (3) distributive, and (4) obstructive. Hypovolemic equate blood circulation. Physical exam is significant shock can result from hemorrhage or other forms of for distended neck veins, pulmonary edema, and a intravascular fluid loss such as capillary leak, gastroin- possible S3 gallop. testinal losses, or renal losses. Its hemodynamic profile Distributive shock is often referred to as high out- is significant for increased heart rate (HR), decreased put or hyperdynamic shock because, unlike the other cardiac output (CO), increased systemic vascular forms of shock, the cardiac output is normal to elevat- resistance (SVR), decreased cardiac filling pressures, ed. The loss of vascular tone that defines distributive decreased pulse pressures (PPs), and decreased central shock results in decreased SVR and an increased pulse venous oxygen saturation (ScvO2). Simply stated, the pressure caused by decreased diastolic pressure. Many circulatory system cannot maintain adequate blood causes of distributive shock exist, including early septic flow and the body is compensating by increasing HR shock, neurogenic shock, and anaphylactic shock. in an effort to increase CO and SVR to maintain perfu- Obstructive shock shares the hemodynamic profile sion. On physical exam, one would expect to see pallor of cardiogenic shock, and the two are often lumped and flat neck veins. together. The most significant difference between Cardiogenic shock is most often caused by a myo- the two is the cause. Obstructive shock is caused by cardial infarction, but it can have other causes such impaired cardiac filling as in cardiac tamponade, or ex- as myocardial contusion. Like hypovolemic shock, its cessive afterload as in a massive pulmonary embolus. hemodynamic profile shows increased HR, decreased Management lies in relieving the obstruction, which CO, increased SVR, and decreased ScvO2. It differs, is often readily treatable if identified, but can be fatal however, in that cardiac-filling pressures, central ve- if not detected. nous pressure (CVP), and pulmonary artery occlusion One must be cognizant that the categorization of 328 Diagnosis and Management of Hypotension and Shock in the Intensive Care Unit SHOCK Hypodynamic-Low CO Hyperdynamic-Low SVR Pulmonary Edema? No Yes JVD? No Yes Sepsis RV Failure Cardiogenic Shock Hypovolemia Neurogenic PE LV Failure Hemorrhage Adrenal Insuff Tamponade MI Dehydration Anaphylaxis Tension PTX Valve Disease Medication Treatment Treatment Treatment Treatment Hemostasis Fluids Fluid Optimization Fluid Fluids Inotropes Intropes Pressors Blood Specific TX IABP Early Goal Revascularization Directed Figure 32-1. Diagnosing and treating various forms of hypotension. CO: cardiac output; IABP: intra-aortic balloon pump; JVD: jugular vein distension; LV: left ventricular; MI: myocardial infarction; PE: pulmonary embolism; PTX: pneumothorax; RV: right ventricular; SVR: systemic vascular resistance; TX: therapeutics shock is not always clear cut and overlap often oc- have cardiac tamponade or a pneumothorax, resulting curs. For example, while septic shock is considered in obstructive shock. Additionally, shock is a dynamic distributive shock, there is often a large component state so the dominant component may change over of hypovolemia present from third spacing of fluid. time or with treatment. An overview of the causes and Alternatively, a thoracic trauma patient may suffer treatments of the various forms of shock can be seen hemorrhage, causing hypovolemic shock, but may also in Figure 32-1. GENERAL DIAGNOSTIC APPROACH FOR HYPOTENSION As with any medical illness, diagnosing the source neck veins, auscultation of cardiac and breath sounds, of hypotension should begin with a history and physi- sources of external bleeding, assessment of possible cal examination. The importance of a thorough but internal sources of bleeding, and neurologic status. focused physical exam must not be underestimated. Noninvasive vital signs are not adequate to de- Vital signs should be obtained. Airway, breathing, and termine the severity of illness or injury. Tachycardia, circulation should be immediately assessed and the tachypnea, and hypotension are highly concerning patient must be fully disrobed and inspected, front and findings, but they likely represent an advanced stage of back. Specific findings that may guide the investigation disease. Consequently, invasive monitoring and labo- are vital signs, level of consciousness, appearance of ratory evaluation should be obtained.4 CVP and ScvO2 329 Combat Anesthesia: The First 24 Hours can assist with determining the type of shock. Arterial including medication effect, altered mental status, and catheterization may be helpful in maintaining a more distracting injuries. Therefore, to improve diagnostic accurate blood pressure as well as in determining re- accuracy, many trauma centers routinely include Fo- spiratory variation of pressures. There is no apparent cused Assessment Sonography for Trauma (FAST) as benefit to using a pulmonary artery catheter.5 Lactate part of the physical exam.11 and base deficit are important values to obtain.3,4 They The FAST exam consists of four sonographic views will not assist in determining the cause of hypotension, to evaluate for pericardial and peritoneal free fluid: but they will aid in assessing severity and adequacy of (1) pericardial, (2) perisplenic, (3) perihepatic, and (4) resuscitation. Base deficit has been shown to correlate pelvic.11 This exam is most helpful when free fluid is with greater fluid requirements, ongoing blood loss,6 identified. A negative exam is less helpful because of and mortality.7 Lactate has been shown to correlate a lower sensitivity. Therefore, the Eastern Association with the development of multiorgan failure.8 for the Surgery of Trauma guidelines recommend re- Although obtaining a thorough history is not a peat exams and at least 6 hours of monitoring before requirement when assessing a hypotensive critically accepting a negative exam.10 Similarly, Advanced ill patient, at a minimum one must be aware of aller- Trauma Life Support recommends a repeat exam in gies and medications.