An intraaortic balloon pump is most likely needed to assist the heart in propelling blood through the aorta. Fluid volume walks a tight rope between too much and too little. Hemodynamic monitoring is essential to regulate the intravenous fluids given to the patient. Enough fluid must be administered to keep the preload (ventricular filling pressure) sufficient and yet not too much to overburden an already taxed system. Correction of dysrhythmias and the use of inotropic agents (e.g., dopamine) may be necessary for maintaining blood pressure; however, decreasing the workload of the heart by decreasing afterload (systemic vascular resistance) through vasodilators (e.g., nitroglycerin) is also important.

Hypovolemic shock occurs when approximately 15-20% of the blood volume is lost. It may occur with trauma in which hemorrhaging and a loss of whole blood occurs, with burns and a loss of plasma, or with a loss of extracellular fluid such as with the gastrointestinal system fluid loss through excessive vomiting or diarrhea. Third spacing, the shifting of fluid from the vascular compartment to the interstitial or intracellular, or internal hemorrhaging also may cause hypovolemic shock.

Inadequate perfusion, the ultimate outcome of hypovolemic shock, starts with a decreased blood return to the heart and results in a decreased cardiac output and circulatory insufficiency. The compensatory mechanisms of sympathetic nervous system (SNS) stimulation, renin-angiotensin activation, and antidiuretic hormone stimulation attempt to maintain the blood pressure and cardiac output.

Treatment involves rapid fluid replacement. Surgical intervention may be needed if the insult is related to trauma. Success is achieved when blood pressure and cardiac output return to normal. A urine output of approximately 30 cc/hr indicates fluid balance has been achieved.

Obstructive shock is related to some type of mechanical obstruction that interrupts blood flow through the circulation, heart, or lungs. Situations involving dissecting aortic aneurysm, cardiac tamponade, or pulmonary embolism are some of the more common factors causing obstructive shock. The
obstruction of blood flow causes the pressures of the right side of the heart to elevate and impairs the return of blood to the heart, resulting in jugular vein distention and an elevated central venous pressure.

Treatment includes correcting the problem and returning blood flow to normal. Maintaining blood pressure and cardiac output during this type of shock is difficult because blood flow is obstructed. Thrombolytics may work with pulmonary embolism, although multiple contraindications such as age, cardiopulmonary resuscitation, and recent surgery may prevent use of this therapy. Surgical repair of an aneurysm or removing fluid from the pericardial sac with tamponade may help to alleviate the blockage.

Neurogenic shock occurs secondary to a loss of vasomotor tone that brings about vasodilation. Neurogenic shock may be caused by brain or spinal cord injury from a diving accident or a bullet wound, lack of glucose to the brain, overdose of drugs, or anesthesia. In neurogenic shock the skin is warm and dry. Cervical spinal cord injuries, at or above the fifth thoracic vertebra, result in the loss of SNS vasoconstrictor tone, causing an uncompensated massive vasodilation. In addition, hypotension occurs because of an unopposed parasympathetic nervous system action, allowing for bradycardia, unlike other shock states where tachycardia is a compensatory mechanism. Often, the patient with spinal injury has hypothalamic dysfunction that causes a temperature dysfunction called
poikilothermia (temperature of the environment); when combined with the vasodilation, the patient’s temperature becomes even cooler.

Neurogenic shock is rare, and if the cause is known the condition may be corrected; for example, neurogenic shock related to anesthesia can be reversed. Temporary administration of vasoconstrictors such as dopamine may be indicated. An insulin reaction causing decreased glucose availability for the brain can also be easily reversed through administration of glucose. Spinal cord injury is permanent, and treatment of the shock state is comprehensive. Neurogenic shock related to spinal cord injury can develop immediately after the injury and last for days to weeks. Treatment involves fluid resuscitation and vasopressors such as dopamine to maintain cardiac output and tissue perfusion, phenylephrine or norepinephrine to increase the systemic vascular resistance, and management of the hypothermia with heating blankets.

Anaphylactic shock occurs when vasodilators such as histamine are released into the circulation as a result of an allergic reaction to drugs, foods, insect stings, or antitoxins. The release of vasoactive mediators causes the vasodilation of arterioles and venules and makes the capillary wall permeable, which results in the leaking of fluid from the vascular to the interstitial space.