Bongard Frederic , Darryl Sue. Diagnosis and Treatment Critical Care

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removal. “High flux” dialyzers provide the most rapid solute

clearance, but their use requires dialysis equipment with vol-

umetric control of fluid removal.

In general, urea removal during hemodialysis follows

first-order kinetics and assumes that urea is distributed

throughout total body water. Under normal operating condi-

tions, a 4-hour dialysis will lower pretreatment urea levels by

approximately 50–70%. Factors that may decrease treatment

efficiency include inadequate blood flow to the dialyzer,

access recirculation, and dialyzer clotting.

Vascular Access

Efficient hemodialysis requires blood flows of at least

200–300 mL/min and a relatively large-bore vascular access.

In the acute setting, the most widely used method is the per-

cutaneous cannulation of either the femoral or subclavian

vein with double-lumen catheters. Regardless of placement

site, the use of double-lumen catheters may allow a certain

percentage of dialyzed blood leaving the efferent lumen to

reenter the afferent lumen. This process is known as recircu-

lation and may reach values of 50% or more, resulting in

extremely inefficient dialysis treatment.

Percutaneous placement of a double-lumen catheter in

the femoral vein is the most widely used method for achiev-

ing rapid access for hemodialysis. Extensive experience has

shown this method to be safe and well tolerated despite the

necessity for repeated punctures. A disadvantage is that the

catheter limits the patient’s mobility, and an unresolved issue

is the length of time a single catheter can be left in place

safely. Ideally, the catheter should be removed after every

procedure; however, this is often impractical or impossible.

In any event, prolonged catheter placement should be

avoided. When alternative access sites are unavailable,

catheters may be replaced over a guidewire, and the removed

catheter tip sent for culture. Careful attention to sterile tech-

nique during placement and meticulous care of the access

site are essential. The most serious complications of femoral

vein access are retroperitoneal hemorrhage and pulmonary

embolism. Retroperitoneal hemorrhage may result from iliac

vein rupture and has been associated with difficult guidewire

placement. Pulmonary emboli are the result of catheter-

related thrombi and are most apt to occur with catheters left

in situ for prolonged periods. Other complications include

hematomas, thrombophlebitis, arteriovenous fistulas, sepsis,

and access-site infection.

Subclavian vein access allows for unhindered patient

mobility, and catheters in the subclavian vein have been left

in place safely for prolonged periods. The major disadvan-

tage is the increased risk of life-threatening complications

during placement. Radiologic evaluation for catheter place-

ment is required prior to the first treatment. Sharp angula-

tions of the distal catheter tip necessitate catheter

repositioning to avoid vessel rupture. Massive hemothorax

and pericardial tamponade are among the most serious com-

plications. These complications can occur even after previously

successful treatments. Cardiac arrhythmias, throm-

bophlebitis, sepsis, air embolism, pneumothorax, and access-

site infection are other complications. It has been

demonstrated that prolonged cannulation can lead to signif-

icant subclavian vein stenosis, thus rendering the ipsilateral

arm incapable of supporting subsequent permanent hemo-

access. Given this risk, use of this access site is to be avoided

in patients for whom there is a high probability of perma-

nent renal failure (eg, diabetic patients with preexisting renal

dysfunction suffering from subsequent acute renal injury).

The right internal jugular vein offers an alternative to

subclavian cannulation. A potential advantage of this

method is that the catheter’s route is relatively straight, thus

avoiding the sharp angulations associated with the subcla-

vian route. Nonetheless, retrograde cannulation of the sub-

clavian vein is possible, and radiologic evaluation of

placement is required. A drawback to this technique is the

relatively awkward placement and the difficulty of access-site

care. “Tunneled” access to the internal jugular is becoming

more popular and allows for much easier access-site care.

Anticoagulation

The need for anticoagulation can be the most significant dis-

advantage associated with hemodialysis. Several methods

have been proposed for reducing hemorrhagic risks.

Regional heparinization is performed by infusing heparin

into the blood before it reaches the filter with continuous

neutralization with protamine into the blood after the filter,

but this procedure has fallen out of favor because of the

“heparin rebound” effect, which may appear up to 10 hours

after treatment.

Low-dose heparin (10–20 units/kg per hour) and bedside

monitoring of coagulation status have been shown to be

superior to regional heparinization in controlling hemor-

rhagic risks. Low-molecular-weight heparin has been pro-

posed because of its limited effect on platelet function.

Unfortunately, these low-molecular-weight fragments have a

prolonged half-life (18 hours) and are not neutralized by

protamine.

Citrate anticoagulation has been used successfully but

requires careful attention to dialysate calcium concentration

and may require substantial amounts of sodium and fluid

infusions.

Because of their short half-life, prostacyclin and its deriv-

atives have been used. Although employed successfully in sta-

ble patients, prostacyclin may be inappropriate for the

critically ill. Aside from a considerable list of potentially

troublesome secondary effects, including flushing, nausea,

headache, and abdominal pain, the antiplatelet action of

prostacyclin is still demonstrable up to 2 hours after cessa-

tion of infusion, and there is no known method for reversing

the effect.

An increasingly popular approach is to completely avoid

anticoagulation by using high blood flows and frequent

saline flushes of the filter (200 mL every 20 minutes). The

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new, more porous dialyzers have ultrafiltration capabilities

that will easily remove the excess fluid administered.

Complications

Although hemodialysis is performed by specially trained

nursing personnel and is directed by a nephrologist, compli-

cations may occur in the ICU setting when the intensivist is

the first physician to evaluate the situation. During treat-

ment, the most commonly encountered complication is

hypotension. Other complications include cardiac arrhyth-

mias, hypoxemia, hemorrhage, air embolism, pyrogenic reac-

tions, and dysequilibrium syndromes.

A. Hypotension—Poorly tolerated fluid removal is the most

obvious cause of hypotension, but several more subtle mech-

anisms may play a role in some patients. Relative intolerance

to acetate can cause hypotension, and bicarbonate-based

dialysates are now used commonly for any patient in whom

vascular instability is considered a potential difficulty. The

relative bioincompatibility of cuprophane- and cellulose-

based membranes can, in rare cases, cause enhanced activa-

tion of complement and the acute onset of severe respiratory

distress and hypotension resistant to volume replacement.

This constellation of symptoms has been called the first-use

syndrome and has been managed with intravenous amino-

phylline or subcutaneous epinephrine. Once a patient’s sus-

ceptibility is established, the syndrome will occur at the

initiation of every treatment with an unused dialyzer, usually

within 15–20 minutes. Definitive management consists of

switching to a more biocompatible membrane.

More recently, a similar anaphylactoid type syndrome has

been described involving the use of polyacrylonitrile dialyzers

(AN-69) in patients treated with angiotensin-converting

enzyme (ACE) inhibitors. Regardless of the cause, sympto-

matic hypotension during dialysis should be treated initially by

lowering the transmembrane pressure, decreasing blood flow,

evaluating for cardiogenic causes, and administering normal

saline, albumin, or hypertonic glucose. If significant wheezing

is present, the first-use syndrome should be suspected.

B. Cardiac Arrhythmias—Several abnormalities increase

the risk of cardiac arrhythmias during dialysis. Of these, the

best-established is digitalis toxicity initiated by the rapid low-

ering of serum potassium levels. Many dialysate baths con-

tain 2 mmol/L of potassium or less; dialysate baths

containing 3.5 mmol/L of potassium have been shown to

reduce the risk of digitalis toxicity. Other causes of arrhyth-

mias include abnormalities of magnesium or calcium,

hypoxia, pericarditis, myocardial infarction, acetate toxicity,

and complications of subclavian catheterization.

C. Hypoxemia—The hemodialysis procedure can induce

hypoxemia by at least two mechanisms. The more benign of

these involves the loss of CO

through the dialyzer with sub-

sequent decrease in respiratory drive. This complication

occurs with acetate-buffered dialysate solutions, which are

currently being replaced with bicarbonate-based solutions.

When this type of hypoxia does occur, it can be managed eas-

ily with supplemental oxygen. A more ominous cause

involves the first-use syndrome (see above), with rapid acti-

vation of complement leading to leukoagglutination in the

lung and severe bronchospasm. This presentation calls for

termination of treatment and the potential need for amino-

phylline or epinephrine. Subsequent treatments must be per-

formed with a more biocompatible membrane.

D. Hemorrhage—If serious hemorrhage occurs during dial-

ysis, previously administered heparin should be neutralized

with protamine. A rational starting dose would be 1 mg pro-

tamine for every 100 units heparin administered. If possible,

protamine infusions should be limited to no more than 15

mg over 5 minutes to minimize the risk of anaphylactoid

reactions. There is considerable individual variation in prot-

amine requirements, and normalization of the partial

thromboplastin time should be sought. There is also the pos-

sibility of a “heparin rebound” effect occurring up to 10

hours after successful neutralization.

E. Dialysis Dysequilibrium—This syndrome of headache,

nausea, muscle irritability, obtundation, and delirium or

seizures may be associated with rapid correction of severe

uremia. To decrease the risk, short, gentle treatments (blood

flows <200 mL/min) should be prescribed until BUN levels

approach 100 mg/dL (36 mmol/L).

Beathard GA: Catheter management protocol for catheter-related

bacteremia prophylaxis. Semin Dial 2003;16:403–5. [PMID:

12969396]

Brunet P et al: Anaphylactoid reactions during hemodialysis and

hemofiltration: Role of associating AN69 membrane and

angiotensin I converting enzyme inhibitors. Am J Kidney Dis

1992;19:444–7. [PMID: 1585932]

Deshpande KS et al: The incidence of infectious complications of

central venous catheters at the subclavian, internal jugular, and

femoral sites in an intensive care unit population. Crit Care

Med 2005;33:13–20. [PMID: 15644643]

Marshall MR et al: Sustained low-efficiency daily diafiltration

(SLEDD-f) for critically ill patients requiring renal replacement

therapy: Toward an adequate therapy. Nephrol Dial Transplant

2004;19:877–84. [PMID: 15031344]

2. Peritoneal Dialysis

Peritoneal dialysis offers the best method of renal replace-

ment for the patient in whom it is difficult or impossible to

obtain adequate hemoaccess. In contrast, patients with

recent abdominal surgery may be poor candidates owing

to the risks of abdominal wound dehiscence and infection

of recently implanted vascular grafts. In patients with pre-

vious abdominal surgery, intraperitoneal adhesions may

limit dialysate distribution, thus causing decreased ultra-

filtration and decreased solute removal. A major advan-

tage of this technique is that no anticoagulation is

required. Disadvantages include substantial protein loss

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339

(see Table 13–12), risks of peritonitis, drainage difficulties,

compromised pulmonary function owing to elevated

diaphragms, hydrothorax, glucose and electrolyte abnormal-

ities, and a relatively immobile patient.

Capabilities

Solute removal with this technique depends mostly on

dialysate volume and how long the dialysate is allowed to stay

in the peritoneal space before drainage (dwell time). A rea-

sonably aggressive schedule incorporates 2-L exchanges every

2 hours. Assuming a 50% equilibration between serum and

dialysate urea levels during a 2-hour dwell time, this schedule

provides 12 L of urea clearance per day. A more modest

schedule would be similar to that of chronic ambulatory peri-

toneal dialysis (CAPD), with 2-L exchanges every 4–6 hours.

Assuming a 100% equilibration of urea after a 6-hour dwell

time, four 2-L exchanges yield 8 L of urea clearance per day.

Associated net filtration of approximately 2 L/day will add to

these predicted values. Peritonitis hastens equilibration

between serum and dialysate, thus yielding greater solute

clearance during the more rapid exchange schedules.

Fluid removal depends directly on the concentration of

glucose in the dialysate and the dwell times allowed. With

1.5% dextrose solution, a 2-L exchange performed every

hour can extract 100–200 mL of fluid. A 4.25% solution pro-

vides 500 mL of filtrate per hour. Prolonging dwell times

decreases net filtration rate because of an increasing equili-

bration of dialysate glucose with serum levels, thus decreas-

ing the osmotic drive for fluid removal. The onset of

peritonitis markedly limits ultrafiltration because of rapid

absorption of dialysate glucose.

Access

There are two widely used methods for obtaining access to

the peritoneal cavity. Bedside placement of a stiff Teflon

catheter is the most rapid means of access. Complications

include bowel perforation, bladder perforation, pericatheter

leakage, hemorrhage, and infection. Foley catheter placement

to ensure bladder decompression prior to insertion is

strongly recommended. A major drawback is that the patient

must be bedridden, and drainage problems are not uncom-

mon. Patients with previous abdominal surgery may have

adhesions of bowel to the abdominal wall, thus increasing

the risk of perforation. Bowel perforation sometimes may

be managed successfully by repositioning the catheter and

initiating empirical antibiotic therapy in the dialysate

(Table 13–13). Abdominal wall infection should be consid-

ered a contraindication to catheter placement.

The surgical placement of a pliable Silastic catheter

(Tenckhoff type) is the safest method of obtaining access.

Drawbacks are catheter malposition, abdominal pain, and

delays in catheter placement. When initiating treatment,

low-volume exchanges may limit the risk of suture-line

dehiscence.

Complications

The most common complication of peritoneal dialysis is fail-

ure to drain or insufficient drainage. Identification of the

cause often can be aided by determining if the ability to

infuse fluid through the catheter is maintained. If fluid infu-

sion is obstructed, the catheter may suffer from intrinsic

blockage, and an attempt at declotting may be appropriate

with saline flushes or thrombolysis with urokinase or tissue

plasminogen activator. If declotting is impossible, catheter

replacement is necessary. A catheter that allows unimpeded

fluid infusion but not outflow may be malpositioned or may

be suffering from a “ball valve” effect caused by omentum

wrapped around its pores. Initial management of this prob-

lem consists of having the patient move from side to side or

be placed in the Trendelenburg position. On occasion, an

enema may yield dramatic results. If these initial efforts fail,

catheter position must be determined by radiographic tech-

nique and repositioned, either with an intracatheter

guidewire or by surgical revision.

Organism Initial Dose (per 2 L) Maintenance Dose (per 2 L)

∗

Staphylococcus epidermidis

Vancomycin 1 g

Cefazolin 1 g

1 g every 5 days × 3

500 mg per exchange x 14 days

Staphylococcus aureus

Vancomycin 1 g 1 g every 5 days × 3

Escherichia coli

Ampicillin 500 mg 100 mg per exchange × 14 days

Pseudomonas aeruginosa

Gentamicin 70–100 mg 15 mg per exchange × 14 days

∗

Dosing appropriate for four exchanges per day.

Modified from Holley JL, Piraino BM: Complications of peritoneal dialysis: Diagnosis and management. Semin

Dialysis 1990;3:245–48, with permission from Blackwell Publishing.

Table 13–13. Intraperitoneal doses of antibiotics for dialysis-related peritonitis.

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Peritonitis arises most often from contamination during

bag exchanges, although intraperitoneal contamination also

can occur as a result of intraabdominal disease. Clinical signs

of peritonitis include abdominal pain, nausea, cloudy dialysate

effluent, and loss of ultrafiltration (decreased fluid output per

exchange). As opposed to spontaneously occurring peritonitis,

peritoneal infection in the context of peritoneal dialysis may

be managed successfully with intraperitoneal antibiotics (see

Table 13–13). A reasonable diagnostic plan would include

evaluation of white blood cell count in the effluent (with peri-

tonitis, >100 granulocytes/μL) and Gram staining and empir-

ical treatment until the results of culture of the effluent

are reported. Common antibiotic regimens are listed in

Table 13–13. Treatment should be continued for at least 10 days.

Fungal peritonitis most often requires removal of the catheter

and is best treated with cessation of peritoneal dialysis.

In the immediate period after catheter placement, the

dialysate effluent can be blood-tinged. The intraperitoneal

administration of heparin (500–1000 units per 2-L bag) may

limit the formation of fibrin clots but is unlikely to cause sys-

temic anticoagulation. Open drainage systems are associated

with a high rate of peritonitis, and a closed system, with bag-

to-bag connections similar to those used in chronic ambula-

tory peritoneal dialysis, is preferred. Spent dialysate should

be monitored daily for cell count. If granulocyte counts

begin to increase above 100/μL, empirical antibiotic therapy

should be initiated pending culture results. Massive protein

losses are associated with peritonitis but also may occur

without infection (see Table 13–12). These losses should be

measured, and protein intake should be adjusted upward.

Substantial glucose absorption can lead to hyperglycemia

and can be controlled with intraperitoneal insulin. A reason-

able starting dose would be 5–10 units per 2-L dialysate bag.

Goldberg L et al: Initial treatment of peritoneal dialysis peritonitis

without vancomycin with a once-daily cefazolin-based regimen.

Am J Kidney Dis 2001;37:49–55. [PMID: 11136167]

Piraino B et al: ISPD Ad Hoc Advisory Committee: Peritoneal

dialysis-related infections recommendations—2005 update.

Perit Dial Int 2005;25:107–31. [PMID: 15796137]

Gokal R. Dialysis techniques: Peritoneal dialysis. In: Hörl WH et al

(eds), Replacement of Renal Function by Dialysis, 5th ed. Berlin:

Springer, 2004.

3. Continuous Renal Replacement Therapy

(CRRT)

The term continuous renal replacement therapy (CRRT ) has

been applied to a wide array of extracorporeal techniques for

supporting the critically ill patient with acute renal failure.

Originally proposed as a simple method of filtration pow-

ered by arteriovenous circuits and known as continuous arte-

riovenous hemofiltration (CAVH), filtrate outputs provided

by a patient’s unstable blood pressure were found to be inad-

equate for removing the large amounts of nitrogenous wastes

associated with the hypercatabolic patient. In an attempt to

deal with this inadequacy, several technical modifications

have been developed to enhance the efficiency of the treat-

ment. These include the addition of a diffusive component to

solute removal, known as continuous arteriovenous hemodial-

ysis (CAVHD), and the development of specialized machines

for providing continuous pumped filtration—allowing for a

new set of extremely efficient techniques that do not require

arterial access and that no longer depend on the variability of

the patient’s changing blood pressure—continuous venove-

nous hemofiltration (CVVH), continuous venovenous

hemodialysis (CVVHD), and continuous venovenous

hemodiafiltration (CVVHDF).

The continuous therapies have several potential advan-

tages over intermittent dialytic techniques. The most obvious

is that the treatment is continuous, allowing for a constant

readjustment of fluid and electrolyte therapy and the admin-

istration of large amounts of parenteral nutrition without

the risk of interdialytic volume overload. Second among the

advantages—at least for the hemofiltration-based treatments

(ie, CAVH and CVVH)—is its convective mode of solute

transport, known to increase middle-molecule clearance

compared with diffusion-based dialytic techniques. When

compared with peritoneal dialysis, CRRT is not contraindi-

cated in patients with prior abdominal surgery and offers

isovolumetric fluid removal without the risk of peritonitis.

The major drawbacks are the need for continuous anticoag-

ulation and that the patient must remain bedridden during

the treatment.

Issues that arise when considering the application of

CRRT include the amount of solute clearance required, the

type of replacement fluid or dialysate to administer, the type

of anticoagulation to be employed, the amount of nutrition

to be infused, the amount of nutrients lost in the filtrate or

dialysate, and the impact of the treatment on drug dosing,

and the complications likely to be encountered. Each of these

issues may have a substantial impact on outcome. For exam-

ple, a recent study demonstrated that patients receiving fil-

tration rates of 35 mL/kg per hour (approximately 2.5 L/h)

had a significantly increased survival when compared with

patients receiving filtration rates of 20 mL/kg per hour

(approximately 1 L/h). One also must consider who is going

to monitor the treatment and how these personnel are

trained.

The following techniques for continuous renal replace-

ment therapy are available. Each technique has advantages

and disadvantages, and some are more practical or effec-

tive in patients with hypotension, those requiring large

volume of fluid removal, or those needing dialysis as well as

ultrafiltration.

Continuous Arteriovenous Hemofiltration (CAVH)

The standard CAVH circuit allows blood to flow from an

arterial access through a tubing circuit to a low-resistance

hemofilter and back to a venous access. Filtrate, which is rel-

atively protein-free, is produced at a rate of several hundred

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milliliters per hour and is collected into a bag connected to

the ultrafiltrate port of the filter. In the postdilution mode,

the replacement fluid is infused into the venous tubing.

Continuous anticoagulation is administered through a pre-

filter tubing connection.

Management of the circuit and maintenance of its

patency are subject to a variety of procedural choices such as

how often to rinse the system with saline, how often to

change the filters and tubing, and how to achieve hemoac-

cess. These issues often depend on the clinical setting and

the type of system components being employed. Owing to

the need for arterial access and the inconsistent output pro-

vided by blood pressure-driven filtration, the popularity of

CAVH has decreased, and this arteriovenous method is

being replaced with blood pump-driven venovenous sys-

tems (see below).

Slow Continuous Ultrafiltration (SCUF)

Blood pressure-driven filtration is a means of providing con-

tinuous isoosmotic fluid removal for aid in the management

of oliguric patients. The circuit is similar to that of CAVH,

but no replacement fluid is administered. Although insuffi-

cient for adequate solute removal, this technique has been

found useful as a means of maintaining fluid balance in

patients intolerant of aggressive fluid removal and in those

with cardiodynamic instability such as may be seen during

aortic balloon pumping or during open-heart surgery.

Continuous Arteriovenous Hemodialysis

and Hemodiafiltration (CAVHD)

The circuit is essentially the same as that for CAVH but

with the addition of a constant infusion of dialysate pass-

ing through the filtrate compartment of the filter. At the

relatively slow blood flow rates encountered with an arte-

riovenous circuit, complete blood to dialysate equilibrium

of urea is achieved, and clearance rates increase linearly

with dialysate flow rates of up to 33.3 mL/min (2 L/h).

Further increases in dialysate flow up to 4 L/h can yield

urea clearances approaching 50 mL/min. In most clinical

situations, the dialysate flow rate is set at 1 L/h, resulting

in 17 mL/min of urea clearance by diffusion. The major

advantage of this system is the enhanced solute clearance,

which has allowed the technique to be applied to certain

intoxications.

An interesting issue common to all the diffusion-based

CRRT techniques (ie, CAVHD and CVVHD) is the amount

of backfiltration that can occur. About 60% of the dialysates

glucose is absorbed through the membrane. At the common

flow rate of 1 L/h, a standard 1.5% dextrose-containing

dialysate (such as is commonly used for peritoneal dialysis)

produces a net glucose transfer averaging 120 mg/min

(175 g/day), whereas a 4.25% solution yields approximately

415 mg/min (600 g/day). This amount of carbohydrate must

be accounted for when considering the patient’s nutritional

and insulin requirements.

Continuos Venovenous Hemofiltration (CVVH)

This circuit requires a blood pump and an air detector and is

often equipped with arterial and venous pressure monitors.

Equipment especially designed for this treatment is available.

This technique has the clear advantage of avoiding the poten-

tial complications of arterial access and is capable of provid-

ing a substantial amount of convection-based clearance.

Common output rates are between 1 and 2 L/h, replaced

with the appropriate replacement solution. Blood flow rates

between 100 and 150 mL/min allow for a decreased tendency

of filter clotting and limit the dosage requirements for anti-

coagulants.

Continuous Venovenous Hemodialysis

or Hemodiafiltration (CVVHD/F)

The addition of a diffusive component to the CVVH system

allows for the maximum clearance capabilities of any of the

continuous therapies. The basic circuit resembles that of

CVVH but allows a variable amount of dialysate to flow past

the filtrate compartment of the filter as with CAVHD. The

machines used are similar to those employed for CVVH.

Hemoaccess

The blood pressure-driven treatments (ie, CAVH and

CAVHD) require large-bore arterial and venous access. The

most widely used is the combined cannulation of the femoral

artery and vein. Hemoaccess for pump-driven continuous

therapies (ie, CVVH and CVVHD) does not require arterial

catheterization and uses the same access as for machine-

driven hemodialysis (see above).

Femoral artery and femoral vein cannulation is the most

widely used method for obtaining an arteriovenous circuit.

Adequate blood flows are best obtained with large-bore

catheters (0.3-cm luminal diameter) with minimal taper and

no sideholes. Standard hemodialysis catheters are often inad-

equate. Despite the apparent risk of arterial cannulation, the

reported complication rate is low. The successful use of these

catheters may be due to the common practice of restricting

their insertion to the well-trained, experienced operator.

Furthermore, access-site care is enhanced because of the con-

stant monitoring of the filter circuit. Potential complications

include retroperitoneal hemorrhage, vascular occlusion, sep-

sis, access-site infection, and hematomas.

Anticoagulation

The need for continuous anticoagulation is a major draw-

back to all methods of continuous therapy and has led to a

high incidence of hemorrhagic complications. It may be

helpful to use regional heparinization with the slow continu-

ous postfilter infusion of protamine. Starting dosage is usu-

ally 10 units/kg per hour of heparin, with a neutralizing dose

of protamine initially at 1 mg/h for every 100 units/h of

heparin. Dosages should be adjusted to provide partial throm-

boplastin times of 150 seconds or more in the postheparin

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circuit and approximately 50 seconds in the postprotamine

circuit. After establishing required dosing, the partial throm-

boplastin time should be monitored three times daily to

determine the need for further adjustments. In a patient with

a severe preexisting coagulopathy, reasonable filter life may

be achievable without any anticoagulation. The prefilter

infusion of replacement fluid also may help to prolong filter

life. Varying protocols for citrate anticoagulation have been

proposed. These techniques have been shown to provide suffi-

cient and safe anticoagulation, but alkalemia, hypernatremia,

and the risk of systemic hypocalcemia must be addressed for

each of the different protocols. Both prostacyclin and

low-molecular-weight heparin have been tried, but their use

retains the same drawbacks noted for hemodialysis—

notably, prolonged duration of action with no method for

rapid neutralization.

Predilution

The infusion of replacement fluid into the prefilter tubing

segment of the circuit dilutes the intraplasmatic urea concen-

tration and promotes the transfer of intraerythrocytic urea

into the plasma compartment, where it is available for

removal in the filtrate. The predilution technique also limits

the hemoconcentration that occurs at the venous side of the

hemofilter. The potential advantages of the predilution mode

include enhanced urea clearance and the possibility of

increasing filter patency by the prefilter dilution of hemat-

ocrit, clotting factors, and platelets. Disadvantages include the

increased cost of replacement fluid and inability to estimate

plasma electrolyte concentrations from analysis of the filtrate.

Replacement Fluids and Dialysate

All hemofiltration-based techniques (ie, CAVH and CVVH)

require large volumes of sterile, pyrogen-free replacement

fluid. A physiologic and relatively inexpensive formulation

consists of two easily prepared solutions given in alternating

fashion. The first solution is prepared by adding one 10-mL

ampule of 10% calcium gluconate to 1 L of 0.9% NaCl. The

second solution is prepared by adding 50 meq sodium bicar-

bonate to 1 L of 0.45% NaCl. When these two solutions are

given alternately, the net result is an electrolyte solution con-

taining sodium 141 meq/L, chloride 101 meq/L, bicarbonate

25 meq/L, and calcium 4 meq/L. Diffusion-based treatments

(ie, CAVHD and CVVHD) require dialysate solutions with

adequate buffering capacity. Common practice has been to

employ peritoneal dialysis solutions, but several premixed

solutions are now being marketed.

Careful attention to fluid balance is essential and can be

aided by connecting the filtrate output to a volumetric pump

or a balancing scale designed to match inputs and outputs.

Regardless of the CRRT technique employed, volume out-

puts and inputs can easily attain 25–50 L/day or more. Thus

even small percentage errors in fluid balance can lead to sub-

stantial changes in the patient’s volume status. Evaluation

with daily weights is essential.

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CRITICAL ILLNESS IN PATIENTS WITH CHRONIC

RENAL FAILURE

Patients receiving maintenance dialysis often require treat-

ment in the ICU. Cardiac disease, GI hemorrhage, and infec-

tions are the most common comorbid conditions. Standard

treatment options often must be modified for dialysis

patients. Unresponsiveness to standard diuretic regimens

means that fluid removal for pulmonary edema or severe

hypertension calls for ultrafiltration by dialytic means. For

upper GI hemorrhage, magnesium-containing antacids are

best avoided, and H

blockers may require dosage adjust-

ments. Antibiotic treatment actually may be facilitated in

that antibiotics normally cleared by the kidney may have

more prolonged therapeutic levels, and the nephrotoxicity

of certain medications is no longer a major consideration.

In general, however, management of the patient on dialysis

is similar to that of the patient with acute renal failure, with the

exception of several special considerations as outlined below.



Nutrition & Fluids

Fluid and Electrolyte Restrictions

Normal fluid restriction for a patient receiving maintenance

hemodialysis (three times weekly) often depends on the

patient’s tolerance for aggressive fluid removal during each

treatment. In general, fluid restriction should be 1–1.5 L/day

and is dictated by the patient’s tendency to develop hyperten-

sion or pulmonary congestion in the interdialysis period. A

certain degree of pedal edema is tolerated as long as hyper-

tension or pulmonary congestion is not present. A patient

maintained on chronic ambulatory peritoneal dialysis often

can tolerate a more liberal fluid restriction because dialysate

glucose concentrations can be adjusted to achieve greater

fluid removal on an ongoing basis. A restriction of 1.5–2 L/day

of fluid intake is often well tolerated, and that amount is

easily removed with the ongoing dialysis.

Nitrogen Balance and Caloric Requirements

Nitrogen balance studies in hemodialysis patients suggest that

protein requirements are between 1 and 1.2 g/kg per day. The

caloric requirement to maintain neutral nitrogen balance is



RENAL FAILURE

343

37 kcal/kg per day. Patients receiving chronic ambulatory

peritoneal dialysis lose a substantial amount of protein in the

dialysate (approximately 10 g/day), and their protein require-

ments approach 1.4 g/kg per day. Glucose absorption from

the dialysate is substantial but depends on the dialysate glu-

cose concentration and the length of the dialysate dwell time.

A gross estimate of the absorbed glucose can be calculated by

measuring the glucose concentration of the dialysate effluent

and comparing this figure with the infused concentration.



Vascular Access in Hemodialysis Patients

The hemodialysis patient’s permanent vascular access is the life-

line to adequate treatment, and these surgically implanted

access sites must be treated with care. There are two commonly

used means for creating a subcutaneous arteriovenous connec-

tion: surgical anastomosis of an artery and vein, often in the

wrist (primary arteriovenous fistula), and placement of a poly-

tetrafluoroethylene graft between artery and vein in the

brachial fossa. The primary arteriovenous fistula is more

resistant to infection and thrombosis, but it requires up to

6 weeks to mature, and its placement is surgically impossible

in many patients with inadequate distal vasculature.

Polytetrafluoroethylene grafts are available for use within

1–2 weeks but are more prone to infection and pseudoa-

neurysm formation. A properly functioning graft or fistula will

have a palpable thrill and a bruit audible with a stethoscope.

These findings should be checked daily. In general, the sites

should not be used for routine venipuncture, and blood pres-

sure readings should be taken on the contralateral arm. It is

not uncommon for a prolonged period of hypotension to

result in a thrombosed access. If an access site is found to be

clotted (inaudible bruit), vascular surgical consultation

should be sought immediately. In some cases, thrombolytic

therapy with urokinase or tissue plasminogen activator may

avoid the necessity for surgical revision. Angioplasty by

interventional radiology also may be successful.

Infection of the vascular access route is the most common

infectious complication in the hemodialysis population.

Erythema and tenderness over the site are the most common

signs; however, occult septicemia can result from an appar-

ently unaffected site. Access-site infection should be sus-

pected in all cases of systemic infection. Blood cultures from

the access site are a reasonable first step in diagnosing infec-

tion. As opposed to other infections with implantable grafts,

successful treatment without removal of the graft is possible

with prolonged administration of antibiotics. Most antibi-

otic regimens for access-site infections include vancomycin

because that agent is poorly dialyzable, and a single dose can

maintain adequate serum levels for 3–5 days.

Nassar GM, Ayus JC: Infectious complications of the hemodialysis

access. Kidney Int 2001;60:1–13. [PMID: 11422731]

Venkat A, Kaufmann KR,Venkat K: Care of the end-stage renal dis-

ease patient on dialysis in the ED. Am J Emerg Med

2006;24:847–58. [PMID: 17098110]



Chronic Ambulatory Peritoneal Dialysis

Patients

Chronic ambulatory peritoneal dialysis (CAPD) commonly

involves four 2-L exchanges per day. Net fluid removal

depends on the rate of exchange and the dialysate glucose

concentration (eg, 1.5%, 2.5%, or 4.25%). Peritoneal dialysis

catheters are surgically placed Silastic tubing with direct con-

nections to the intraperitoneal space. Strict sterility should

be maintained whenever the connection between the

catheter and the dialysate tubing is interrupted. Drainage

problems are not uncommon and may respond to moving

the catheter or turning the patient. On occasion, an enema

may cause sufficient intraabdominal movement to produce

adequate drainage. Standard intraperitoneal antibiotic ther-

apy for peritonitis is outlined in Table 13–13.



Renal Transplant Patients

The differential diagnosis of acute renal failure in the trans-

planted kidney was discussed earlier. Other commonly

encountered problems in the transplant recipient include

infections, GI complications, and hypertension.

Infections

Renal transplant patients require continuous immunosup-

pressive therapy that may include varying combinations of

corticosteroids, azathioprine, cyclosporine, mycophenolate

mofetil, and tacrolimus. The type of infection likely to occur

as a result of the immunocompromised state has been noted

to be somewhat bimodal in distribution. Whereas common

bacterial pathogens, including streptococci, staphylococci,

and gram-negative bacteria, seem to predominate in the

immediate posttransplant period, common opportunistic

infections with viral, protozoal, or fungal organisms seem to

occur 1 month or more after surgery. It is important to note

that the classic signs of infection, including fever, may be

masked by the anti-inflammatory corticosteroids. In general,

if a life-threatening infection is identified, it is often prudent

to discontinue immunosuppressive medication temporarily

despite the risk of graft rejection. In any event, close consul-

tation with the patient’s nephrologist or transplant surgeon

is essential.

Gastrointestinal Complications

Peptic ulcer disease, colonic perforation, and pancreatitis are

the most common GI complications in the renal transplant

patient. Bleeding or perforation of a peptic ulcer carries a

particularly high morbidity, and prophylactic use of H

antagonists, proton pump inhibitors, or antacids has been

found to be effective. Colonic perforations are uncommon

but are apt to be lethal if not identified quickly. Pancreatitis

is believed to be a result of long-term use of corticosteroids,

and severe sequelae including hemorrhagic pancreatitis and

pseudocyst formation have been reported.



CHAPTER 13

344

Hypertension

Hypertension can complicate up to 50% of all renal trans-

plants. Possible causes include renal artery stenosis of the

native or transplanted kidneys, allograft dysfunction,

cyclosporine, and recurrence of the original renal disease.

Renal artery stenosis of the grafted kidney may be treated

successfully by percutaneous angioplasty. Cyclosporine-

induced hypertension may result from the intrarenal vaso-

constriction associated with endothelin and may respond to

a decrease in dosage. In contrast, allograft dysfunction

related to ongoing infection may require decreased immuno-

suppression.

Kasiske BL et al: Recommendations for the outpatient surveillance

of renal transplant recipients. American Society of

Transplantation. J Am Soc Nephrol 2000;11:S1–86. [PMID:

11044969]

Silkensen JR: Long-term complications in renal transplantation. J

Am Soc Nephrol 2000;11:582–8. [PMID: 10703683]

Venkat KK, Venkat A: Care of the renal transplant recipient in the

emergency department. Ann Emerg Med 2004;44:330–41.

[PMID: 15459617]



345

0014

Gastrointestinal Failure

in the ICU

Gideon P. Naudé, MD

This chapter addresses the common causes that fall under the

broad category of gastrointestinal (GI) failure. Pancreatitis,

bowel obstruction, paralytic ileus, diarrhea, and malabsorp-

tion are discussed here. GI hemorrhage and specific GI dis-

eases are presented in other chapters. For an overview of

abdominal pathology, the reader is referred to Chapter 32,

which discusses the acute abdomen.



Pancreatitis

ESSENTIALS OF DIAGNOSIS



Severe abdominal pain, usually radiating to the back.



Nausea and vomiting.



Hemodynamic and respiratory compromise in severe

cases.



Elevated serum levels of pancreatic enzymes.



Pancreatic enlargements on CT scan.

General Considerations

Acute inflammation of the pancreas has a wide clinical spec-

trum from mild (eg, acute edematous pancreatitis) to very

severe (eg, necrotizing pancreatitis). Most patients have a

benign course, and recovery is uncomplicated. In approxi-

mately 30% of cases, the inflammatory process is aggressive

and associated with a mortality rate that approaches 50%. In

the latter group, management within the ICU is required.

Aggressive early resuscitation may prevent the onset of lethal

multisystem organ failure.

Acute pancreatitis is frequently precipitated by gallstone

obstruction of the pancreatic duct. Although identification

of a persisting stone within the common bile duct itself

(choledocholithiasis) is unusual, careful straining of stools

identifies a gallstone in up to 90% of patients who have had

an attack of pancreatitis within the preceding 10 days.

Pathogenesis may be related to obstruction of the pancreatic

duct during passage of the stone, which results in ductal

hypertension and causes breakdown of intracellular com-

partmentalization, leading to zymogen activation.

In the United States, alcohol consumption is responsible

for about 40% of cases of pancreatitis. Acute pancreatitis may

occur at any time in the course of ongoing excessive consump-

tion, although commonly the initial attack comes after several

years of alcohol abuse. The initial episode may be followed by

further attacks. The usual pattern is a severe first attack fol-

lowed by subsequent attacks that are less dramatic, presum-

ably because of the loss of active pancreatic tissue. Alcohol is

the etiologic factor most commonly associated with chronic

pancreatitis, and microscopic examination of the gland at first

acute presentation often demonstrates evidence of chronicity,

such as scarring and replacement of acinar elements with

fibrous tissue. This may have implications for pancreatic

endocrine function during subsequent acute attacks.

The mechanism of pancreatic damage by alcohol is

incompletely understood and may be idiosyncratic. Alcohol

has been shown to have ultrastructural effects on acinar cells.

It also may cause spasm of the sphincter of Oddi, producing

ductal hypertension.

Postoperative pancreatitis is seen most commonly follow-

ing operations on the biliary tree. The onset of atypical pain

or unexpected ileus following surgery raises the possibility of

pancreatitis. Because postoperative pancreatitis often lacks

the usual clinical features, early detection may be difficult.

Acute pancreatitis following endoscopic retrograde cholan-

giopancreatography (ERCP) is seen in approximately 2% of

cases and may be severe.

Acute pancreatitis may occur in conjunction with eleva-

tions of serum calcium, including transient hypercalcemic

states that may occur with intravenous infusions. Other

metabolic causes include hyperlipidemia, hypothermia, pro-

tein deficiency, and diabetes.



CHAPTER 14

346

Drugs and toxins probably account for more cases of

pancreatitis than is usually suspected. Common drugs

include furosemide, azathioprine, estrogen-containing con-

traceptives, tetracyclines, and corticosteroids. Scorpion

envenomation is a common cause in tropical environments

such as the Caribbean.

Blunt trauma may be associated with acute pancreatitis,

particularly if there is acute ductal obstruction caused by

hematoma. More commonly, chronic pancreatitis, pseudocyst

formation, or pancreatic fistulas result from blunt injury.

Pancreas divisum, ductal abnormalities, and pancreatic

carcinoma all have been suggested as etiologic factors for

acute pancreatitis. When pancreas divisum is present, the

narrow opening of the minor papilla may obstruct the flow

of pancreatic secretions. Unfortunately, sphincteroplasty of

the minor ampulla has mixed results.

Less common causes of acute pancreatitis include infec-

tious agents such as paramyxovirus (mumps), Epstein-Barr

virus, Mycoplasma species, hepatitis virus, and ascaris, as well

as autoimmune disorders, including systemic lupus erythe-

matosus, necrotizing angiitis, and thrombotic thrombocy-

topenic purpura. Recently, spinal surgery for scoliosis

resulted in a 15% incidence of pancreatitis in children and

young adults. In some patients, the etiologic factor is never

discovered.

Pathophysiology

The pancreas produces a wide variety of digestive enzymes

that have the potential for causing serious cellular and bio-

logic disruption. Proteases such as trypsin, chymotrypsin,

and elastase have been shown to activate proenzymes in the

inflammatory and complement cascades. Lipases such as

phospholipase A

can liberate phospholipid remnants. These

particles perpetuate the inflammatory response and may

have direct cellular toxicity. Normally, intrapancreatic

enzyme control is achieved by secretion of inactive proen-

zymes (zymogens) and intracellular enzyme inhibitors and

compartmentalization by storage of zymogens and enzyme

activators in separate cytosol granules. Once the integrity of

this protective process is breached, autodigestion initiates an

inflammatory process that is self-sustaining.

Acinar damage quickly disrupts normal organ function,

resulting in almost immediate cessation of exocrine secretion

and alteration of endocrine secretion. For this reason, ongo-

ing formation and leakage of pancreatic enzymes are proba-

bly only a minor factors in the perpetuation of acute

pancreatitis following the initial insult. Factors contributing

to progressive disease with severe inflammation and necrosis

are unknown, but organ ischemia and infection are likely to

be important.

Systemic toxicity and functional impairment of other

organ systems are related to the release of inflammatory

mediators such as interleukin-1 (IL-1), arachidonic acid

metabolites, kinins, and tumor necrosis factor (TNF).

There are profound changes in immune competence and

inappropriate activation of lymphocytes and polymor-

phonuclear neutrophils.

Clinical Features

Clinical evaluation of acute pancreatitis consists of confir-

mation of the diagnosis, estimation of severity, determina-

tion of prognosis, and identification of pancreatic necrosis.

A. Symptoms and Signs—Pain is the most constant symp-

tom, although its nature and severity are variable. Radiation to

the back is observed in 50% of patients, but no pattern can be

considered typical. The intensity of the pain does not correlate

with the degree of pancreatic inflammation. Occasionally,

other clinical features such as vomiting are dominant. The

diagnosis should be considered in all patients with abdominal

pain of recent onset, especially if associated with physiologic

compromise such as hypotension or hypoxia.

Various clinical signs have been described. Abdominal

distention and tenderness are common, but peritonitis is

rare. Abdominal findings do not indicate the severity of the

retroperitoneal process. If the inflammatory process has

extended beyond the pancreas, erythema around the flanks

may occur. The classic signs of hemorrhagic pancreatitis—

ecchymoses in the flank (Grey Turner’s sign) or umbilicus

(Cullen’s sign)—are not commonly present.

Signs of respiratory compromise may indicate incipient

respiratory failure. Tachypnea greater than 20 breaths/min

and a limited chest expansion on inspiration are important.

Clinical evidence of bilateral pleural effusion is found com-

monly in patients with severe pancreatic inflammation.

B. Laboratory Findings—Elevation of enzyme markers

such as amylase and lipase traditionally was considered diag-

nostic, but the sensitivity and specificity of these tests gener-

ally are inferior to those of CT scan. A normal serum amylase

level does not exclude the diagnosis, and enzyme elevation

may be observed in a number of other conditions, including

perforated or penetrating peptic ulcer, ruptured ectopic

pregnancy, and bowel obstruction or infarction.

Measurement of the renal clearance of amylase does not

enhance the sensitivity of this variable.

C. Imaging Studies—Organ imaging has replaced serum

biochemical analysis as the diagnostic modality of choice in

acute pancreatitis. In all but the mildest cases, imaging the

pancreas by CT scan or ultrasonography should be the initial

investigation. Demonstration of organ enlargement con-

firms the diagnosis. Enzyme levels frequently return to nor-

mal within a few days, whereas pancreatic radiologic

derangement persists for at least a week. Therefore, organ

imaging is also valuable in the retrospective diagnosis of this

condition. Very early in the disease, however, CT scan may be

unhelpful because macroscopic changes may take hours to

develop. During this brief period, measurement of enzyme

markers is preferable.

The value of CT scan versus ultrasonography is debated.

Actually, the procedures are complementary, and both