Tissue perfusion

Although blood pressure control follows Ohm s law and seems to be simple, it underlies a complex circuit of interrelated systems. Hence, numerous physiologic systems that have pleiotropic effects and interact in complex fashion have been found to modulate blood pressure. Because of their number and complexity it is beyond the scope of the current account to cover all mechanisms and feedback circuits involved in blood pressure control. Rather, an overview of the clinically most relevant ones is presented. These systems include the heart, the blood vessels, the extracellular volume, the kidneys, the nervous system, a variety of humoral factors, and molecular events at the cellular level. They are intertwined to maintain adequate tissue perfusion and nutrition. Normal blood pressure control can be related to cardiac output and the total peripheral resistance. The stroke volume and the heart rate determine cardiac output. Each cycle of cardiac contraction propels a bolus of about 70 ml blood into the systemic arterial system. As one example of the interaction of these multiple systems, the stroke volume is dependent in part on intravascular volume regulated by the kidneys as well as on myocardial contractility. The latter is, in turn, a complex function involving sympathetic and parasympathetic control of heart rate intrinsic activity of the cardiac conduction system complex membrane transport and cellular events requiring influx of calcium, which lead to myocardial fibre shortening and relaxation and affects the humoral substances (e.g., catecholamines) in stimulation heart rate and myocardial fibre tension. 

D Ineffective Tissue Perfusion Renal related to adverse drug readions ot the aminoglycosides... 

INEFFECTIVE TISSUE PERFUSION RENAL The patient taking an aminoglycoside is at risk for nephrotoxicity. The nurse measures and records the intake and output and notifies the primary health care provider if the output is less than 750 ml/day. It is important to keep a record of the fluid intake and output as well as a daily weight to assess hydration and renal function. The nurse encourages fluid intake to 2000 ml/day (if the patient s condition permits). Any changes in the intake and output ratio or in the appearance of the urine may indicate nephrotoxicity. The nurse reports these types of changes to the primary health care provider promptly. The primary health care provider may order daily laboratory tests (ie, serum creatinine and blood urea nitrogen [BUN]) to monitor renal function. The nurse reports any elevation in the creatinine or BUN level to tiie primary health care provider because an elevation may indicate renal dysfunction. 

RISK FOR INEFFECTIVE TISSUE PERFUSION RENAL When the patient is taking a drag tiiat is potentially toxic to die kidneys, die nurse must carefully monitor fluid intake and output. In some instances, die nurse may need to perform hourly measurements of die urinary output. Periodic laboratory tests are usually ordered to monitor the patient s response to therapy and to detect toxic drag reactions. Seram creatinine levels and BUN levels are checked frequentiy during the course of therapy to monitor kidney function. If the BUN exceeds 40 mg dL or if the serum creatinine level exceeds 3 mg cIL, the primary health care provider may discontinue the drug therapy or reduce the dosage until renal function improves. 

Occurs as a result of circulatory insufficiency associated with overwhelming infection Occurs when obstruction of blood flow results in inadequate tissue perfusion. Examples include a severe reduction of blood flow as the result of massive pulmonary embolism, pericardial tamponade, restrictive pericarditis, and severe cardiac valve dysfunction Occurs as a result of blockade of neurohum oral outflow. Examples include from a pharmacological source (ie, spinal anesthesia) or direct injury to the spinal cord. This type of shock is rare. 

Ineffective Tissue Perfusion related to hypovolemia, blood loss, impaired distribution of fluid, impaired circulation, impaired transport of oxygen across alveolar and capillary bed, other (specify)... 

MAINTAINING ADEQUATE TISSUE PERFUSION. When a patient is in shock and experiencing ineffective tissue perfusion tiiere is a decrease in oxygen resulting in an inability of die body to nourish its cells at die capillary level. If die patient has marked hypotension die administration of a vasopressor (a drug diat raises die blood pressure because of its ability to constrict blood vessels) is required. The primary health care provider determines die cause of die hypotension and then selects the best mediod of treatment. Some hypotensive episodes require die use of a less potent vasopressor, such as metaraminol, whereas at other times a more potent vasopressor, such as dobutamine (Dobutrex), dopamine (Intropin), or norepinephrine (Levoplied) is necessary. 

Q Ineffective Tissue Perfusion Peripheral related to adverse drug response (hypotension)... 

D Ineffective Tissue Perfusion Cardiopulmonary related to myocardial ischemia... 

D Risk for Injury related to adverse drug elfeds D Ineffective Tissue Perfusion related to adverse drug reactions... 

Ineffective Tissue Perfusion related to adverse drug effects... 

By far, the most widely used and most empirically studied tissue viability imaging techniques are those that study tissue perfusion, and discussion of perfusion imaging techniques will dominate this section. We will also mention a few emerging techniques that currently are not as widely used in the acute stroke setting, but show promise for the future. 

A basic grasp of normal cardiac function sets the stage for understanding the pathophysiologic processes leading to HF and selecting appropriate therapy for HF. Cardiac output is defined as the volume of blood ejected per unit of time (liters per minute) and is a major determinant of tissue perfusion. Cardiac output is the product of heart rate (HR) and stroke volume (SV) CO = HR x SV. The following describes how each parameter relates to CO. 

When determining the appropriate fluid to be utilized, it is important to first determine the type of fluid problem (TBW versus ECF depletion), and start therapy accordingly. For patients demonstrating signs of impaired tissue perfusion, the immediate therapeutic goal is to increase the intravascular volume and restore tissue perfusion. The standard therapy is normal saline given at 150 to 500 mL/hour until perfusion is optimized. Although LR is a therapeutic alternative, lactic... 

For peritonitis, early and aggressive intravenous fluid resuscitation and electrolyte replacement therapy are essential. A common cause of early death is hypovolemic shock caused by inadequate intravascular volume expansion and tissue perfusion. 

In the early phase of serious intraabdominal infections, attention should be given to preserving major organ system function. With generalized peritonitis, large volumes of intravenous (IV) fluids are required to maintain intravascular volume, to improve cardiovascular function, and to ensure adequate tissue perfusion and oxygenation. Adequate urine output should be maintained to ensure appropriate fluid resuscitation and to preserve renal function. A common cause of early death is hypovolemic shock caused by inadequate intravascular volume expansion and tissue perfusion. 

Shock refers to conditions manifested by hemodynamic alterations (e.g., hypotension, tachycardia, low cardiac output [CO], and oliguria) caused by intravascular volume deficit (hypovolemic shock), myocardial pump failure (cardiogenic shock), or peripheral vasodilation (septic, anaphylactic, or neurogenic shock). The underlying problem in these situations is inadequate tissue perfusion resulting from circulatory failure. 

FIGURE 12-1. (Continued) B. Ongoing management of inadequate tissue perfusion. (CHF, congestive heart failure LR, lactated Ringer s solution.)... 

With generalized peritonitis, large volumes of IV fluids are required to restore vascular volume, to improve cardiovascular function, and to maintain adequate tissue perfusion and oxygenation. 

Aggressive fluid repletion and management are required for the purposes of achieving or maintaining proper intravascular volume to ensure adequate cardiac output, tissue perfusion, and correction of acidosis. 

Rapid fluid resuscitation is the best initial therapeutic intervention for treatment of hypotension in sepsis. The goal is to maximize cardiac output by increasing the left ventricular preload, which will ultimately restore tissue perfusion. 

When fluid resuscitation is insufficient to maintain tissue perfusion, the use of inotropes and vasoactive drugs is necessary. Selection and dosage are based on the pharmacologic properties of various catecholamines and how they influence hemodynamic parameters (Table 45-5). 

Fluid status is assessed by monitoring urine output and specific gravity, serum electrolytes, and weight changes. An hourly urine output of at least 1 mL/kg for children and 50 mL for adults is needed to ensure tissue perfusion. 

Supportive care goals include maintenance of adequate cardiac output and blood pressure to optimize tissue perfusion while restoring renal function to pre-ARF baseline. 

Preparation of Hepatocytes. In general, the harvesting of hepatocytes from the liver or fiver specimen is performed by tissue perfusion using a peristaltic pump with two... 

Pearce JA, Thomsen S (1999) Kinetic models of tissue perfusion processes. Proceedings of Laser Surgery (SPIE) Advanced Characterization, Therapeutics, and Systems III 1643 251. 

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