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Fluids & Electrolytes
SIMILAR TO DIALYSIS, ultrafiltration is a type of renal replacement therapy that may be indicated for patients with heart failure (HF) who have significant volume overload despite outpatient diuretic therapy. Performed with compact, portable machinery, ultrafiltration can be safely managed in any telemetry unit or even in an outpatient treatment area that has appropriately trained personnel. It isn't a first-line treatment for patients in acute respiratory distress as a result of fluid overload due to HF.
This article discusses nursing responsibilities for patients who are candidates for ultrafiltration. The following scenario illustrates a typical case.
Ms. W, age 69, was brought to the ED by paramedics who had inserted an 18-gauge peripheral venous access device and administered 80 mg of furosemide following a directive from the medical control physician. Her chief complaint is progressively increasing shortness of breath over the past 5 days. On initial assessment, her heart rate is 84; respiratory rate, 26; and BP, 168/92. Her SpO2 was 92% on room air but is now 97% on 100% oxygen via non-rebreather mask. Bibasilar crackles are noted on auscultation and the cardiac monitor shows a normal sinus rhythm (NSR). Her pain intensity rating is 0/0-10.
Her medical history includes type 2 diabetes mellitus and myocardial infarction. She states she's become increasingly short of breath, gained 15 lb (6.8 kg) over the last 5 days, and noticed that her "water pill" hasn't been working as well as usual.
Her medications include low-dose aspirin, furosemide, simvastatin, lisinopril, and a multivitamin. She has no known drug allergies.
On arrival at the treatment room, she's awake, alert, and oriented but able to speak only in short sentences. Her respiratory rate is now 22. Her heart rate is 88 bpm with an S3 gallop, NSR. Her BP is 174/94. She has bilateral jugular venous distension and 3+/0-4+ pitting edema of her feet, ankles, and calves.
Blood work results are within the normal range except for brain natriuretic peptide (BNP), which is 4,000 pg/mL (normal, less than 100 pg/mL; values tend to increase with age and are higher in women than men).1
The 12-lead ECG is unremarkable. A chest X-ray demonstrates increased pulmonary vascular markings and cardiomegaly. Her urine output has been 120 mL since she received the I.V. diuretic about 3 hours ago.
After examination by her cardiologist, Ms. W is diagnosed with acute decompensated HF refractory to loop diuretics, and ultrafiltration is planned. (See Zeroing in on HF.)
In general, the term ultrafiltration describes the separation of solids (solute) from liquids (solvent) by a semipermeable membrane. When used to manage HF, ultrafiltration removes excess fluid without significant disturbance of the patient's vital signs, serum electrolytes, or renal function, and without depleting intravascular volume.2 First used for intractable pulmonary edema in the 1950s, ultrafiltration led to the development of a modified dialysis circuit in the 1970s.
Using diffusion, osmosis, and ultrafiltration, hemodialysis corrects electrolyte imbalances and removes waste products in addition to sodium and water. In contrast, ultrafiltration uses convection in response to a transmembrane pressure gradient to remove sodium and water.3-5
Although modified continuous renal replacement therapies and conventional hemodialysis systems may be used to treat fluid overload, newer methods employ isolated ultrafiltration systems. These isolated systems consist of a compact, portable machine; disposable filter; specialized circuit of tubing; and blood access devices. (See A detailed look at the ultrafiltration process.)
Blood is removed, filtered, and returned to the patient via peripheral venous access using one of the following:
* a pair of large-bore short peripheral catheters
* peripheral venous access via a midline catheter and a large-bore short peripheral catheter
* a central venous access device such as one used for hemodialysis.
The method used to access the venous system is determined by the prescribing healthcare provider. Despite being considered the least reliable method of vascular access for ultrafiltration, short peripheral venous catheters shouldn't be excluded as a treatment option. Short peripheral venous catheters can be inserted by the nursing staff; are less invasive; and are associated with fewer insertion-related complications than central or midline catheters. Other advantages include less discomfort, decreased financial impact, and increased patient satisfaction.
Although the rate depends on the patient's clinical condition and specific healthcare provider instructions, blood is usually withdrawn from the patient through a specially designed circuit at a rate of approximately 40 mL/minute. The circuit consists of anticoagulated tubing (usually primed with a standard mix of heparin) and a disposable filter that contains less than 40 mL of blood at any given time.
The filter is made of a fibrous membrane containing many tiny pores. As blood passes through it, a transmembrane pressure gradient develops. With the pressure inside the filter higher than the pressure outside the filter, the pressure gradient promotes an outward flow of excess water, sodium, and other small molecules through the membrane's tiny pores. This removal process is known as convective transport.
The excess fluid and molecules, or solute, is routed to a collection bag while the remaining fluid, blood cells, proteins, and other larger molecules that can't pass through the membrane are returned to the patient. Because the specialized circuit produces no forces or pressures other than the transmembrane pressure gradient, sodium can pass freely across the fibrous membrane, allowing the concentrations on each side to equalize. The sodium concentration of the fluid deposited into the collection bag remains isotonic to the blood returned to the patient.3,5-8
The ultrafiltration machine is programmed to remove an exact amount of excess fluid at a precise rate determined by the prescribing healthcare provider. Fluid is removed at a maximum volume of 500 mL/hour over a period usually ranging from 8 to 24 hours.4,9 All parameters are set by carefully correlating the clinical status of the patient with the overall goals of therapy. The disposable filter and tubing are anticoagulated to prevent filter thrombosis.5,10
Because the circuit removes excess fluid without disturbing the patient's electrolyte balance, ultrafiltration has been shown to permit the removal of excess sodium at a concentration of 140 mEq/L while removing only about 4 mEq/L of potassium. In comparison, patients treated with diuretics such as furosemide or bumetanide lose sodium at a concentration no greater than 90 mEq/L but can lose potassium at a concentration of up to 30 mEq/L, resulting in a significant and potentially dangerous electrolyte imbalance.3,9
One of the greatest benefits of ultrafiltration is its lack of impact on the patient's overall volemic state. The premise behind ultrafiltration is to remove intravascular volume while at the same time allowing the shift of extravascular fluid to the intravascular compartment at an equal rate-the plasma refill rate. If the intravascular fluid is removed at a rate that's greater than the shift of extravascular fluid to the intravascular space (a plasma refill mismatch), hypotension ensues.8,11 Ultimately, a reduction in central venous pressure (CVP) will occur. Isolated CVP elevations (a negative outcome) can impact renal function resulting in greater sodium retention. Because ultrafiltration produces a higher sodium-yielding filtrate than diuretic therapy, improved renal functioning from this enhanced sodium removal can result in an increased renal perfusion pressure. Renal function can also improve due to decreased venous congestion from intra-abdominal pressure reduction.9,12,13 If CVP can't be monitored via a central line, a decreasing CVP can be evidenced by improved urinary output, reduced respiratory effort, decreased peripheral edema, and normalized vital signs. See Benefits offered by ultrafiltration for additional positive outcomes.
Although acute kidney injury is possible with ultrafiltration, changes in renal function are generally minimal and can be compared with those experienced by patients treated only with diuretics.9,12,13 Ultrafiltration can impair renal perfusion and its sodium-sparing activity. Several potential ultrafiltration pitfalls can lead to renal failure. If fluid is removed from the intravascular space too quickly, the resulting hypovolemic state can lead to hypotension, renal hypoperfusion, prerenal azotemia, and then acute renal failure. In turn, patients with chronic HF who have malnutrition-inflammation complex syndrome can have a resultant hypoalbuminemia, inflammatory state, and myocardial dysfunction that impedes the plasma refill rate needed for successful outcomes.12,13
Some clinical studies haven't shown improvements in renal function as evidenced by static (unchanged) serum creatinine levels. In fact, some studies have shown worsening renal function demonstrated by increasing serum creatinine levels.14,15 Additional studies need to be performed to investigate ultrafiltration's full impact on renal function in patients with HF.
While ultrafiltration results in many positive outcomes, several undesirable effects can occur as well. These include the following:
* vascular access-related complications (such as infection or thrombosis)
* hemorrhage, from either circuit disconnection or anticoagulation
* air embolism
* hemolysis and hyperkalemia
* worsening prerenal azotemia or acute kidney injury
* rarely, an allergic reaction related to immunoglobulin E reactions or to ethylene oxide used to sterilize the extracorporeal circuit.8,12,13
Other considerations include the costs involved with the procedure, as well as the additional nursing education and staffing required.
Patients must meet specific criteria to be considered as candidates for ultrafiltration. Adults with HF and signs and symptoms of significant volume overload despite outpatient diuretic therapy and prior hospitalization for HF may be considered for ultrafiltration.8,11
Resistance to diuretics, commonly seen in patients with severe left ventricular dysfunction, can be defined as continued edema despite increasing the dosages of oral or I.V. diuretics or a change in diuretic; for example, changing from a loop to a thiazide diuretic or using a combination.8,16
In patients with HF, tolerance to conventional doses of diuretics is the result of the kidneys' declining ability to filter sodium and overall increases in angiotensin II and aldosterone (which result in increased sodium levels in plasma).12,13
Patients who are most likely to benefit from ultrafiltration include those who have a stable systolic BP greater than 90 mm Hg and at least 1 L fluid excess and can tolerate the required procedural anticoagulation.16
Hemodynamically unstable patients and those experiencing an acute coronary event, such as myocardial infarction, should be excluded from ultrafiltration. In addition, ultrafiltration is contraindicated in patients with an elevated serum creatinine (greater than 3.0 mg/dL) or a hematocrit greater than 45%, and in those who don't have adequate venous access.4
Ultrafiltration isn't a complicated procedure, and most patients remain hemodynamically stable. Treatment with ultrafiltration should be prescribed by a healthcare provider educated in ultrafiltration practices and performed by a nurse who's received training in extracorporeal therapies. In most instances, basic training in using the ultrafiltration system, including adequate hands-on time, can be accomplished in less than 8 hours.5,11 The primary nurse should do the following.
* Ensure that the patient has given informed consent for ultrafiltration vascular access placement and treatment according to facility guidelines.
* Document measurements of the patient's calves, thighs, and abdomen before and after treatment to evaluate effectiveness of extracorporeal therapy.
* Document the patient's weight before and after treatment.
* Continuously monitor the patient's vital signs, cardiac rhythm, overall clinical status, and response to treatment.
* Obtain diagnostic study results, including serum electrolytes, as prescribed by the healthcare provider.
* Ensure adequate vascular access for withdrawal and infusion.
* Label the ultrafiltration line "for ultrafiltration only."
* Prime the ultrafiltration cassette with heparin (unless contraindicated) as prescribed by the healthcare provider.
* Start ultrafiltration according to the manufacturer's usage guidelines.
* Set ultrafiltration removal rate and blood flow rate as prescribed. A typical blood flow rate is 30 to 40 mL/minute and a typical ultrafiltration rate is 300 to 500 mL/hour, adjustable in increments of 10 mL/hour.
* Assess the patient and monitor the equipment's function continuously for at least the first 10 minutes.
* Following institutional protocol, monitor vital signs until ultrafiltration treatment is complete. Notify the healthcare provider about changes in the patient's clinical status, such as respiratory distress, symptomatic bradycardia or tachycardia, and/or a 10 mm Hg drop in systolic BP from baseline.
* For unexpected outcomes that indicate actual or potential patient hemodynamic instability, such as hypotension or anticoagulation complications, call the prescribing healthcare provider immediately and stop the ultrafiltration by setting its rate to 0 mL/hour for 30 minutes or as needed until the patient's heart rate and/or BP stabilizes.
* Meticulously document intake and output. Maintain prescribed fluid restrictions and educate the patient and the family of their importance.
* Empty the ultrafiltration bag when full, after collecting 1 L, or every shift.
* Use an indwelling urinary catheter only when absolutely necessary and remove it as soon as it's no longer clinically indicated.
* Assess the venous access site every 2 hours for erythema, tenderness, pain, edema, drainage, or bleeding, and perform dressing changes according to facility policy.
* Initiate venous thromboembolism prophylaxis according to facility protocol or healthcare provider prescription.
* For bleeding complications, stop the ultrafiltration and heparin infusion (if one was prescribed by the provider) and notify the healthcare provider for further instructions.7,11,14,17
Educate patients about ultrafiltration, stressing the importance of these instructions.
* Notify the nurse if the ultrafiltration machine alarms.
* Protect the ultrafiltration tubing; for example, make sure it doesn't get caught on anything and that it isn't kinked or compressed, restricting the flow. Make sure the tubing doesn't become disconnected because this could lead to bleeding.
* Call for assistance when performing activities of daily living such as bathing, toileting, getting out of bed, or doing anything requiring excessive movement that might interfere with the functioning of the ultrafiltration tubing or the flow of filtrate.
* Report signs and symptoms of dehydration, such as palpitations, dizziness, or lightheadedness.
* Adhere to sodium and fluid restrictions as prescribed.
* Inform the nurse before urinating so that your urine can be collected, measured, and documented.
When ultrafiltration is provided to the volume-overloaded patient with HF who's refractory to diuretics, it can safely and effectively reduce adverse reactions and outcomes, as well as decrease length of stay and hospital readmission rates.
About 5.8 million people in the United States have HF, with almost 700,000 of them being newly diagnosed. HF accounts for 1 million hospitalizations yearly. For patients over age 65, acute HF is the most common reason for hospitalization.
After their initial hospitalization for HF, about 50% of patients will be rehospitalized within 6 months for another episode. Over 280,000 people will die each year from HF, with one in five dying within the first year and 50% within 5 years of their diagnosis.
In addition to generally improved renal function, ultrafiltration has these benefits:
* diuretic responsiveness that's temporarily restored for approximately 30 days along with the removal of proinflammatory cytokines and toxins
* shortened length of stay for hospitalizations due to HF and decreased hospital readmissions in the 3 months following ultrafiltration
* successful sodium removal without enhanced renal renin secretion or intravascular hypovolemia
* improved cardiac output and lowered right atrial and pulmonary arterial wedge pressures
* decreased neurohormone levels
* decreased risk of electrolyte abnormalities, such as hypokalemia, and correction of hyponatremia
* more rapid removal of fluid excess and improvement in symptoms along with minimal changes in heart rate and BP
* lack of activation of the neurohormonal and sympathetic nervous system
* diminished requirement for diuretics.
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