CLINICAL CASE SCENARIO OF SEPTIC SHOCK
A 44-year-old woman is admitted to the ICU after having undergone a 3-hour abdominal operation for the debridement of infected necrotizing pancreatitis (infected pancreas necrosis). The operation resulted in 800 mL of blood loss, and she received 3000 mL of crystalloid, 2 units of packed RBC, and 2 units of fresh frozen plasma during the operation. Prior to the surgery, she was receiving imipenem, itraconazole, and micafungin for Gram-negative bacteremia and fungemia. The patient’s skin appears warm and pink. She is intubated and mechanically ventilated. Her vital signs are pulse rate of 110 beats/minute, blood pressure of 94/60 mm Hg, and temperature of 39.1°C (102.4°F). Her breath sounds are present bilaterally and her abdomen is soft and distended. A chest radiograph reveals bibasilar atelectasis. A 12-lead ECG reveals sinus tachycardia. Complete blood count reveals WBC 24,000/mm3, hemoglobin 11 g/dL, and hematocrit 38%.
Likely causes of low blood pressure: Probably a combination of sepsis and blood loss.
Next steps in the management: Initial efforts should be to restore intravascular volume with crystalloid fluids and blood products. The addition of a vasoconstrictive medication should be considered if volume replacement does not normalize her blood pressure and improve end-organ perfusion.
Best methods to provide ongoing assessment: Place a central venous catheter for continuous CVP monitoring and an arterial catheter for ongoing blood pressure monitoring. Trans-thoracic echocardiography can be valuable to assess intravascular volume and evaluate cardiac functions. Serial measurements of serum lactate levels can be helpful to monitor progress during the resuscitation process.
CLINICAL APPROACH TO SHOCK
Hypotension leading to shock can result from decreased intravascular volume, cardiac pump failure, and/or acute vasodilation without sufficient increase in intravascular volume. Persistent hypotension leads to deficits of perfusion to organ systems and predisposes to multiple organ dysfunction syndrome (MODS). A systematic approach to the hypotensive patient is important to minimize the duration and severity of organ hypoperfusion. The cardiovascular system can be considered as an arrangement of pump, pipes, and fluid volume. This simplistic idea translates to the three primary components of cardiovascular physiology: namely, cardiac output (pump), vascular tone (pipes), and intravascular volume (fluid). All components of the system need to be intact to maintain normal perfusion. Dysfunction in one or more of these components will often contribute to hypotension and shock. Evaluation of a patient with postoperative hypotension should include a review of the pertinent history including medications, a careful physical examination, the trend in vital signs and urine output.
DEFINITIONS
SHOCK: A condition where the perfusion of end-organs is inadequate. Shock can be caused by insufficient intravascular volume such as during hemorrhagic shock or hypovolemic shock due to excess fluid loss or insufficient fluid intake. Shock can also be due to inappropriate distribution of circulatory volume, such as with neurogenic shock (loss of regulation in vascular tone) or with septic shock (vasodilation due to circulating endogenous vasodilators).
CENTRAL VENOUS CATHETER: An intravenous catheter of sufficient length to measure the pressures in the superior vena cava when placed through the internal jugular vein or subclavian vein.
ECHOCARDIOGRAPHY: Noninvasive imaging modality that can provide information about cardiac contractility, regional wall motion abnormalities, valvular abnormalities, and intravascular volume status. This imaging modality can be quite useful for the evaluation of critically ill, hemodynamically unstable patients.
SERUM LACTATE: When this end-product of anaerobic metabolism is elevated, it generally suggests a global deficit in oxygen delivery. Serum lactate can also become elevated as the result of inadequate clearance, such as with renal dysfunction.
PULMONARY ARTERY CATHETER: A centrally placed catheter that can measure left ventricular end-diastolic pressure and pulmonary artery pressures. These pressure measurements can help gauge the patients’ left ventricular functions. Because of the invasive nature of this device and the limited information that it provides in comparison to CVP catheters, PA catheters are rarely used in the ICU settings now. The real advantage of a PA catheter over a CVP catheter is for the monitoring of patients with poor cardiac functions who are maintained on inotropic agents (such as acute heart failure patients).
Sepsis
Sepsis refers to the hyperdynamic and febrile responses to infections. Severe sepsis is defined as the occurrence of infection with septic host response and at least one end-organ dysfunction. Septic shock is defined as sepsis with persistent hypotension despite fluid administration. Early Goal-Directed Therapy is a treatment approach for sepsis that was introduced during the early 2000s; this approach is directed at early recognition of sepsis and early aggressive treatment to restore or minimize tissue hypoperfusion. It is important to recognize that severe sepsis can carry a mortality of 25% to 30% and septic shock can carry a mortality of 50%. The two major treatment goals in septic shock are to identify and address the source of infection (source control), and to restore tissue perfusion as soon as possible to minimize remote organ hypoperfusion that can lead to organ dysfunction. Ideally, these treatment priorities should be addressed simultaneously. Time to antibiotic initiation has been well documented to influence outcomes associated with sepsis; therefore, every effort should be made to select and administer the appropriate antimicrobial treatments as soon as sepsis is recognized. The recommended end-points of resuscitation are
target CVP of 8 to 12 mm Hg,
a mean arterial pressure of >65 mm Hg, and
urine output of >0.5 mL/kg/h.
If fluids alone are insufficient to achieve the blood pressure goals, a norepinephrine drip is recommended to help achieve the target blood pressures once intravascular volume depletion has been corrected. If continued increases in norepinephrine infusion fail to achieve target blood pressures, a continuous infusion of vasopressin at a constant rate of 0.03 U/min can be initiated to help improve catecholamine receptor responsiveness. The use of physiologic doses of corticosteroids can be considered for individuals with septic shock who do not achieve sufficient responses to source control, fluid administration, and vasopressors.
