8.3 IV Fluids, IV Tubing, and Assessment of an IV System

Patients are prescribed an IV solution (fluids) based on their electrolyte and fluid volume status. IV fluids are commonly categorized as colloids and crystalloids. Colloid solutions contain large molecules that cannot pass through semi-permeable membranes and are used to expand intravascular volume by drawing fluid from extravascular space via high osmotic pressure. Examples of colloid solutions are albumin, dextrans, and hydroxyethyl starches (Crawford & Harris, ). Crystalloid solutions contain solutes such as electrolytes or dextrose, which are easily mixed and dissolvable in solution. Crystalloids contain small molecules that flow easily across semi-permeable membranes, which allows for transfer from the bloodstream into the cells and tissues (Crawford & Harris, ). They may increase fluid volume in interstitial and intravascular space. Examples of crystalloid solutions are isotonic, hypotonic, and hypertonic solutions.

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Isotonic solutions have an osomolality of 250 to 375 mOsm/L. Isotonic solutions have the same osmotic pressure as plasma, creating constant pressure inside and outside the cells, which causes the cells to remain the same (they will not shrink or swell) and does not cause any fluid shifts within compartments. Isotonic solutions are useful to increase intravascular volume, and are utilized to treat vomiting, diarrhea, shock, and metabolic acidosis, and for resuscitation purposes and the administration of blood and blood products. Examples of isotonic solutions include normal saline (0.9% sodium chloride), lactated Ringer&#;s solution, 5% dextrose in water (D5W), and Ringer&#;s solution. It is important to monitor patients receiving isotonic solutions for fluid volume overload (hypervolemia) (Crawford & Harris, ).

Hypotonic solutions have a lower concentration, or tonicity, of solutes and have an osomolality equal to or less than 250 mOsm/L. The infusion of hypotonic solutions lowers the osmolality within the vascular space and causes fluid to shift to the intracellular and interstitial space. Cells will swell but may also delete fluid within the vascular space. Examples of hypotonic solutions include 0.45% sodium chloride, 0.33% sodium chloride, 2.5% dextrose in water, and 0.2% sodium chloride. Monitor for hypovolemia and hypotension related to fluid shifting out of the vascular space, and do not administer to patients with increased intracranial pressure (ICP), as it may exacerbate cerebral edema. Use cautiously in patients with burns, liver failure, and traumas (Crawford & Harris, ).

Hypertonic solutions have a higher concentration, or tonicity, of solutes and have an osomolality equal to or greater than 375 mOsm/L. The osmotic pressure gradient draws water out of the intracellular space into the extracellular space. Examples of hypertonic solutions include D5W and 0.45% sodium chloride, D10W, and 3% sodium chloride. Hypertonic solutions may cause intravascular fluid volume overload and pulmonary edema, and they should not be used for an extended period of time. Hypertonic solutions should not be used in patients with heart or renal disease who are dehydrated (Crawford & Harris, ).

Although all IV fluids must be administered carefully, hypertonic solutions are additionally risky.

An order for IV fluids may be continuous or as a bolus, depending on the needs of the patient. IV solutions are available in 25 ml to ml bags. The frequency, duration, amount, and additives to solution must be ordered by a physician or nurse practitioner; for example, an order may be &#;give NS at 125 ml/hr.&#;

The most common types of solutions include normal saline (NS) and D5W. Patients may also have medications, such as potassium chloride, thiamine, and multivitamins, added to IV solutions. To discontinue an IV infusion, an order must be obtained from the physician or nurse practitioner (Perry et al., ).

IV Administration Equipment

When a peripheral vein has a cannula inserted, an extension tubing is connected to the hub on the cannula and flushed with normal saline to maintain patency of the cannula. Most peripheral intravenous cannulas will have extension tubing, a short, 20 cm tube with a positive fluid displacement/positive pressure cap attached to the hub of the cannula for ease of access and to decrease manipulation of the catheter hub (Vancouver Coastal Health, ). The extension tubing must be changed each time the peripheral catheter is changed. When the peripheral cannula is not in use, the extension tubing attached to the cannula is called a saline lock.

Intravenous fluids are administered through thin, flexible plastic tubing called an infusion set or primary infusion tubing/administration set (Perry et al., ). The infusion tubing/administration set connects to the bag of IV solution. Primary IV tubing is either a macro-drip solution administration set that delivers 10, 15, or 20 gtts/ml, or a micro-drip set that delivers 60 drops/ml. Macro-drip sets are used for routine primary infusions. Micro-drip IV tubing is used mostly in pediatric or neonatal care, when small amounts of fluids are to be administered over a long period of time (Perry et al., ). The drop factor can be located on the packaging of the IV tubing.

Primary IV tubing is used to infuse continuous or intermittent fluids or medication. It consists of the following parts:

• Backcheck valve: Prevents fluid or medication from travelling up the IV
• Access ports: Used to infuse secondary medications and give IV push medications
• Roller clamp: Used to regulate the speed of, or to stop or start, a gravity infusion
• Secondary IV tubing: Shorter in length than primary tubing, with no access ports or backcheck valve; when connected to a primary line via an access port, used to infuse intermittent medications or fluids. A secondary tubing administration set is used for secondary IV medication.

IV solution bags should have the date, time, and initials of the health care provider marked on them to be valid. Add-on devices (e.g., extension tubing or dead-enders) should be changed every 96 hours, if contaminated when administration set is replaced, or as per agency policy. Intravenous solution and IV tubing should be changed if:

• IV tubing is disconnected or becomes contaminated by touching a non-sterile surface
• Less than 100 ml is left in the IV solution bag
• Cloudiness or precipitate is found in the IV solution
• Equipment (date and time) is outdated
• IV solution is outdated (24 hours since opened)

Primary and secondary administration sets (see Figure 8.4) should be changed regularly to minimize risk and prevent infection (CDC, ; Fraser Health Authority, ). Change IV tubing according to agency policy. Table 8.5 lists the frequency of IV tubing change.

Table 8.5 Frequency of IV Tubing Changes

Safety considerations:

• All IV tubing must be changed using sterile technique.
• IV tubing is changed based on the type of tubing, time used, and the type of solution.
• If possible, coordinate IV tubing changes with IV solution changes.

Frequency of IV Tubing Change

Type of IV Tubing and Solution

Every 72 -96 hours Primary tubing with hypotonic, isotonic, or hypertonic continuous solution, when insertion site is changed, or when indicated by the type of solution or medication being administered. Every 24 hours Secondary or intermittent IV solution or medication. Rationale: When an intermittent infusion is repeatedly disconnected and reconnected for infusion, there is increased risk of contamination at the catheter hub, needleless connector, and the male Luer end of the administration set, potentially increasing risk for CR-BSI. Every 24 hours Infusions containing fat emulsions (IV solutions combined with glucose and amino acids infused separately or in a 3 in 1 admixture). Example: Total parenteral nutrition (TPN). 4 hours or 4 units, whichever comes first, or between products Blood and blood products Data source: CDC,

Infusing IV Fluids by Gravity or an Electronic Infusion Pump (EID)

To ensure therapeutic effectiveness of IV fluids, a constant, even flow is necessary to prevent complications from too much or too little fluid. A physician must order a rate of infusion for IV fluids or for medications. The rate of infusion for medications (given via a secondary or primary infusion) can be found in the Parenteral Drug Therapy Manual (PDTM). If an order for IV fluids is &#;to keep vein open&#; (TKVO), the minimum flow rate is 20 to 50 ml per hour, or according to physician&#;s orders (Fraser Heath Authority, ).

A health care provider is responsible for regulating and monitoring the amount of IV fluids being infused. IV fluid rates are regulated in one of two ways:

1. Gravity. The health care provider regulates the infusion rate by using a clamp on the IV tubing, which can either speed up or slow down the flow of IV fluids. An IV flow rate for gravity is calculated in gtts/min.
2. Electronic infusion device (EID) (see Figure 8.5). The infusion rate is regulated by an electronic pump to deliver the fluids at the correct rate and volume. All IV pumps regulate the rate of fluids in ml/hr. An IV pump (EID) is used for many types of patients, solutions, and medications (Vancouver Coastal Health, ).

An IV pump must be used for:

• All CVC devices
• All opioid infusions (use a patient-controlled analgesia)
• All pediatric patients
• All medication as described in the PDTM
• Infusion rates below 60 ml/hr
  

To calculate the drops per minute for an infusion by gravity, follow the steps in Table 8.6.

Table 8.6 Calculating the Drops per Minute (gtts/min) for an Infusion by Gravity

Steps

Additional Information

1. Verify the physician order. An order may read:

Example 1. Give NS IV 125 ml/hr

Example 2. Give ml of NS IV over 8 hours.

2. Determine the drop factor on the IV administration set. The drop factor is the amount of drops (gtts) per minute. IV tubing is either macro tubing (10, 15, or 20 gtts/min) or micro tubing (60 gtts/min). The drop factor (or calibration of the tubing) is always on the packaging of the IV tubing. 3. Complete the calculation using the formula. Use the formula: Infusion rate (ml/hr) × IV  drop factor (gtts/min) = drops per minute 60 (Administration time is always in minutes)

To calculate ml/hr, divide  ÷ 8 = 125 ml/hr.

Example: Infuse IV NS at 125 ml/hr. IV tubing drop factor is 20 gtts/min

125 × 20 = 41.6 gtts/min, round up to 42 gtts/min (Round down or up to the nearest whole number) 60 4. Regulate IV infusion using the roller clamp. Observe and count the drips in the drip chamber and regulate for 42 gtts/min (one full minute). Alternatively, divide 42 by 4 (rounded down from 10.4 to 10 gtts/min) to count for 15 seconds. The gtts/min should be assessed regularly to ensure the IV is infusing at the correct rate (e.g., every 1 to 2 hours, if the patient accidentally bumps the IV tubing, or if a patient returns from another department). Data source: Fulcher & Frazier, ; Perry et al.,

When an infusion is by gravity, there are several factors that may alter the flow/infusion rate (Fulcher & Frazier, ). In addition to regulating the flow rate, assess the IV system to ensure these factors are not increasing or decreasing the flow of the IV solution. These factors are listed in Table 8.7.

Table 8.7 Factors Influencing the Flow Rate of Infusions

Factors

Additional Information

Tube occlusion May occur if the tubing is kinked or bent. Tubing may become kinked if caught under the patient or on equipment, such as beds and bed rails. Vein spasms Irritating or chilled fluids (fluids stored in the fridge) may cause a reflex action that causes the vein to go into spasm at or near the intravenous infusion site. If fluids or medications are chilled, bring to room temperature prior to infusion. Height of the fluid container The IV tubing drip chamber should be approximately 3 feet above IV insertion site. Location/position of IV cannula If the cannula is located in an area of flexion (bend of an arm), the IV flow may be interrupted when the patient moves around. To avoid this issue, replace IV cannula. Infiltration or extravasation If the cannula punctures the vein, the fluid will leak into the surrounding tissue and slow or stop the flow, and swelling will develop. Accidental touching/bumping of the control clamp or raising arm above heart level Instruct the patient not to touch the roller clamp and to take care not to bump the clamp, as this may accidentally change the flow rate. Instruct patient to keep hand/arm below heart level; an elevated hand/arm will slow or stop an infusion running by gravity. Needle or cannula gauge/diameter The smaller the needle or cannula, the slower the fluid will flow. Data source: Fulcher & Frazier, ; Perry et al.,

Assessing an IV System

All patients with IV fluid therapy (PIV and CVC) are at risk for developing IV-related complications. The assessment of an IV system (including the IV site, tubing, rate, and solution) (see Figure 8.6) often depends on what is being infused, the patient&#;s age and medical condition, type of IV therapy (PIV or CVC), and agency policy. Generally, an IV system should be assessed as described in Checklist 65.

    Checklist 65: Assessing an IV System

Disclaimer: Always review and follow your hospital policy regarding this specific skill.

Safety considerations: 

• IV systems must be assessed every 1 to 2 hours or more frequently if required.
• An IV system should be assessed at the beginning of a shift, at the end of a shift, if the electronic infusion device alarms or sounds, or if a patient complains of pain, tenderness, or discomfort at the IV insertion site.
• Review the patient&#;s chart to determine insertion date and type of solution ordered.
• A peripherally inserted catheter is usually replaced every 72 to 96 hours, depending on agency policy.
• If the peripheral catheter or central venous catheter is not in use, or is being used intermittently, flushing is required to keep the site patent. Refer to agency policy for flushing guidelines.
• A not-in-use peripheral IV site is generally flushed every 12 hours with 3 to 5 ml of normal saline.
• Review the in-and-out sheet to determine expected amount in the IV solution bag.
• Patients with cardiac or renal disease, as well as pediatric patients, are at a higher risk for IV-related complications.
• Elderly patients often have fragile veins and may require closer monitoring.

Steps

 Additional Information

1. Perform hand hygiene. This step reduces the transmission of microorganisms. 2. Introduce yourself and explain the purpose of the assessment. This builds trust with patient and allows time for the patient to ask questions. 3. Confirm patient ID using two patient identifiers (e.g., name and date of birth), and compare the MAR printout with the patient&#;s wristband. This step ensures you have the correct patient and complies with agency standard for patient identification. 4. Apply non-sterile gloves (optional). This reduces the transmission of microorganisms. 5. Assess the IV insertion site and transparent dressing on IV site. Check IV insertion site for signs and symptoms of phlebitis or infection. Check for fluid leaking, redness, pain, tenderness, and swelling. IV site should be free from pain, tenderness, redness, or swelling.

Ensure patient is informed to alert the health care provider if they experience pain or notice swelling or redness at the IV site. If patient is unable to report pain at IV site, more frequent checks are required.

6. Inspect the patient&#;s arm for streaking or venous cords; assess skin temperature. Assess complications on hand and arm for signs and symptoms of phlebitis and infiltration/extravasation. 7. Assess IV tubing for kinks or bends. Kinks or bends in tubing may decrease or stop the flow of IV fluids. Ensure tubing is not caught on equipment or side rails on bed.

Tubing should be properly labelled with date and time.

8. Check the rate of infusion on the primary and secondary IV tubing. Verify infusion rate in physician orders or medication administration record (MAR). If IV solution is on gravity, calculate and count the drip rate for one minute.

If solution is on an IV pump, ensure the rate is correct and all clamps are open as per agency protocol.

If secondary IV medication is infusing, ensure clamp on secondary IV tubing is open. The EID is unable to distinguish if the primary bag or secondary bag is infusing.

9. Assess the type of solution and label it on bag. Check volume of solution in bag. IV solutions become outdated every 24 hours.

Ensure the correct solution is given.

If 100 ml of solution or less is left in the bag, change the IV solution and document on in-and-out sheet.

If an IV pump is used, ensure it is plugged into an outlet.

Ideally, the IV solution should be 90 cm above patient heart level.

10. Assist patient into comfortable position, place call bell in reach, and put up side rails on bed as per agency policy. These precautions prevent injury to the patient. 11. Perform hand hygiene. This step prevents the spread of microorganisms. 12. Document procedure and findings as per agency policy. Timely and accurate documentation promotes patient safety. Data source: Fulcher & Frazier, ; Perry et al.,

Critical Thinking Exercises

1. What are the signs and symptoms of phlebitis?
2. What types of patients should not receive hypotonic IV solutions?

CONTENTS

The illustration above may appear a bit amusing, but this actually mirrors various practices that I've encountered during my training and career. Several years ago, the ICU at Genius General Hospital transitioned from using normal saline to using mostly Lactated Ringers (spoiler alert: it was neither difficult nor dramatic). More recently, the use of pH-guided resuscitation has become increasingly common.

Fluid choice probably doesn't make much difference for most patients. However, fluid therapy is an extremely common intervention. When leveraged over the high number of patients receiving fluid, even small differences in efficacy can be important (e.g. NNT of 30 or 50). Finally, for occasional patients with significant pre-existing hyperkalemia or metabolic acidosis, fluid choice may be extremely important.

crystalloids versus colloids

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role of colloids (albumin)?

• The crystalloid vs. colloid debate will likely continue indefinitely, but it is dying down a bit. Despite theoretical support for albumin, there's no real evidentiary support. In practice, crystalloid is generally preferred because it is cheaper and more readily available.
• Currently, albumin seems to be indicated primarily for the purpose of supporting renal function among patients with cirrhosis, including:
  • Management of spontaneous bacterial peritonitis.
  • Management of hepatorenal syndrome.
  • Prophylaxis against hepatorenal syndrome after large volume paracentesis.

hetastarch is poison

• Hetastarch is a cheap, synthetic colloid.
• Numerous large high-quality RCTs have shown that it causes renal failure and may increase mortality in sepsis.
• Warnings have been issued by the FDA and also the European Medicines Agency not to use hetastarch.
• Strangely, this continues to be sold by pharmaceutical companies and remains on formulary at many hospitals.
• There is no medicolegal or evidence-based justification for using hetastarch.

step I: balanced crystalloid

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rationale for transitioning from normal saline to balanced crystalloids

• (1) There was never any physiologic rationale to use normal saline in the first place. Most reasons offered to support the use of saline aren't based on physiology or evidence (e.g. &#;it's cheap&#; or &#;it's what we're used to using&#;).
• (2) Normal saline exacerbates acidosis. This may be problematic &#; especially in patients who are severely acidotic to begin with (which isn't uncommon among critically ill patients).
• (3) Normal saline has been shown to exacerbate hyperkalemia (by causing acidosis which shifts potassium out of cells).,

  (, ).

• (4) In animal models, normal saline causes significant harm compared to balanced crystalloid (e.g. greater acidosis, impaired cardiac function, coagulopathy, impaired renal function, and mortality)., ), )
• (5) Hyperchloremia caused by normal saline may cause renal vasoconstriction, increasing the risk of kidney injury. This has been shown in a variety of studies, most recently the SALT-ED RCT.)
  • Interestingly, the SALT-ED trial showed benefit from balanced crystalloid, despite most patients' receiving relatively little fluid.

arguments for using saline & why they lack merit

• &#;Normal saline is cheaper.&#;
  • Lactated Ringers is only ~25 cents more expensive per liter, and the cost difference of Plasmalyte/Normosol isn't much greater. These differences simply aren't relevant in the context of a patient's hospital bill which will range in the thousands of dollars. Additionally, use of a balanced fluid may avoid the need for IV bicarbonate and/or dialysis &#; which would save a considerable amount of money.
• &#;I will give two liters of saline and then switch to a balanced fluid.&#;
  • First, nobody does that. Human beings aren't that well organized. If physicians and nurses in your unit are used to giving saline and a patient crashes, they're going to give saline. They're not going to check first to see how much saline the patient received.
  • Second, the SALT-ED trial suggested that clinical benefits from balanced crystalloid may occur even if only small volumes are used.
• &#;Lactated Ringers isn't safe in hyperkalemia.&#;
  • Lactated Ringers is fine in hyperkalemia. In fact, it is actually normal saline which is contraindicated in hyperkalemia (more on this here).
• &#;Lactated Ringers will elevate the lactate level.&#;
  • A 30 cc/kg bolus of Lactated Ringers might possibly raise the lactate level by ~0.5 mM.)
• &#;Lactated Ringers isn't compatible with some drugs (e.g. ceftriaxone).&#;
  • This shouldn't be a problem if the patient has adequate IV access. Furthermore, Plasmalyte doesn't contain calcium, so it's compatible with a wider variety of drugs.
• &#;Lactated Ringers isn't compatible with blood.&#;
  • This seems to be a myth. Lactated Ringers contains 1.5 mM of calcium. If this concentration of calcium caused blood to clot, then mild hypercalcemia would lead to lethal clotting problems (it doesn't). Several studies have found that Lactated Ringers may be compatible with blood transfusion., , )

ongoing studies on saline versus balanced crystalloids

• Further studies are ongoing regarding the selection of saline versus balanced crystalloids. However, it's dubious whether we really need any additional trials:)
  • There is zero physiologic rationale for using saline in most patients.
  • Nearly all available physiologic, animal, and clinical data suggests balanced crystalloids are superior.
  • It's well established that normal saline will cause acidosis and hyperchloremia (this is a fact).
• At this point, there are only two logically coherent strategies which exist, as shown below:

choice of balanced crystalloid

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discussion of various anions

• Sodium lactate
  • Historically, administration of lactate was feared (due to worsening of &#;lactic acidosis&#;). This isn't possible, because sodium lactate isn't an acid.
  • Lactate may function as a metabolic fuel for the heart, so if anything, lactate could be a good thing. Hypertonic sodium lactate infusion has been shown to improve cardiac function.)
  • In vivo, lactate will be very rapidly metabolized into bicarbonate by the liver (unless the patient has fulminant hepatic failure).
• Sodium acetate
  • Rapidly metabolized into bicarbonate.
  • Lacks lactate's beneficial cardiac effects. Excessive acetate levels may cause vasodilation and hypotension, but this doesn't seem to be clinically relevant (acetate will be rapidly metabolized and only transiently present).
• Sodium gluconate
  • Although often believed to be metabolized into bicarbonate, this doesn't seem to be the case &#; so sodium gluconate does not function as an alkali (unlike sodium acetate and sodium lactate). This means that Plasmalyte has the same exact pH effect as Lactated Ringers.
  • Sodium gluconate appears to be cleared unchanged from the kidneys. It could even function as an osmotic diuretic agent.

contraindications to Lactated Ringers

• These are not legitimate contraindications:
  • Hyperkalemia (more on this here).
  • Cirrhosis or liver injury (unless the patient has frank hepatic failure, it will be able to metabolize lactate).
• Legitimate contraindications (all relative however):

  • Elevated intracranial pressure

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    &#; Lactated Ringers could theoretically worsen this, because it is slightly hypotonic. Giving a liter of lactated ringers will have roughly the same effect as giving a liter of normal saline plus a dose of medication mixed in ~150 ml D5W. So this isn't a huge issue, but it's not ideal either. For a patient with known elevation of intracranial pressure, plasmalyte would be preferable.

  • Metformin-associated lactic acidosis

    &#; In this clinical scenario patients genuinely may have difficulty metabolizing the lactate. Note, however, that lactated ringers contains sodium lactate &#; so it will increase the lactate level without causing acidosis (more on this here).

  • Severe hypercalcemia

    &#; Lactated Ringers has 1.5 mM of calcium, which won't worsen hypercalcemia (if anything it could decrease the calcium level, because this will be a lower calcium concentration than the patient's blood). However, this isn't the optimal fluid here (more on this here).
• Overall, the contraindications to lactated ringers are generally uncommon and fairly mild. Outside of a neurological ICU, LR would be an excellent choice for ~95% of patients and a safe choice for nearly all patients.

choice of best balanced crystalloid?

• Differences between various balanced crystalloids are minor and probably of minimal clinical significance.
• Lactated Ringers is generally an outstanding choice as it is inexpensive, widely available, and physiologically sound (the choice of lactate as an anion is arguably superior to gluconate/acetate).
• Plasmalyte is also an excellent choice, which may be superior in situations where Lactated Ringers is relatively contraindicated (listed above).

general concept

• The transition from normal saline to balanced crystalloids (Step I, above) is focused largely on the avoidance of harm from fluid (e.g. hyperchloremia). However, we can take this concept a step further to use crystalloids to improve the pH status of selected patients.
  • Fluid should be viewed as a drug.
  • Just as we wouldn't give the patient &#;any antibiotic&#; we shouldn't give &#;any fluid&#; &#; the fluid should be selected to maximize benefit.
• Fluid resuscitation is a limited opportunity to manipulate pH status.
  • Large volumes of fluid can be used to affect the patient's pH status.
  • After the patient is volume resuscitated, this opportunity will be lost (because large volumes of fluid can no longer be given without causing volume overload).

pH abnormalities treatable with crystalloid

• (1) Non-anion-gap metabolic acidosis (NAGMA)

  • This essentially represents a bicarbonate deficit (whether bicarbonate has been lost in the stool or urine).
  • Patients with normal kidneys will eventually re-generate bicarbonate, but this takes time. Furthermore, critically ill patients frequently have renal insufficiency or renal tubular acidosis, which prolong recovery from NAGMA.
  • Exogenous bicarbonate administration is a physiologically logically and reasonably well-accepted treatment for NAGMA.

• (2) Uremic metabolic acidosis

  • Most forms of anion-gap metabolic acidosis (e.g. lactic acidosis or ketoacidosis) don't respond favorably to IV bicarbonate. One exception to this rubric may be uremic metabolic acidosis.
  • Exogenous bicarbonate has long been used by nephrologists in efforts to improve pH and avoid dialysis. This practice was recently validated in the BICAR-ICU trial, wherein bicarbonate administration decreased the requirement for dialysis in uremic patients (more on this here).

• (3) Acute metabolic alkalosis

  • Most forms of metabolic alkalosis seen in the ICU are chronic (e.g. chronic compensatory metabolic alkalosis in response to chronic respiratory acidosis). Compensatory alkalosis should be left alone.
  • Very rarely, acute metabolic alkalosis may be seen. For example, this may be caused by ingestion of large quantities of alkali, large volume diuresis (contraction alkalosis), or gastric losses (vomiting, continuous NG suction).
  • Normal saline is a rational therapy for acute metabolic alkalosis, because it will reduce the serum bicarbonate level back towards normal.
• Note that the following abnormalities are not treatable with crystalloid:
  • Chronic metabolic alkalosis which is compensatory for a chronic respiratory acidosis.
  • Anion-gap metabolic acidoses other than uremia (e.g. lactic acidosis or ketoacidosis).

pH-guided resuscitation

• This is pretty simple &#; it largely amounts to thinking about the patient's pH status and whether choice of IV fluid could improve it.
• When giving bicarbonate, the bicarbonate deficit may be a useful guide:
  • Bicarbonate deficit (in mEq) can be estimated this calculator from MDCalc.
  • Each liter of isotonic bicarbonate contains 150 mEq of bicarbonate (more on this below).
  • Generally, avoid giving the patient more than roughly ~80% of their bicarbonate deficit, to prevent over-correction of the metabolic acidosis.
• During a bicarbonate shortage, sodium acetate can be used in its place.

pH-guided resuscitation is most important in uremic metabolic acidosis

• This is probably the most common situation where pH-guided resuscitation is beneficial.
• Isotonic bicarbonate may improve the pH and help avoid dialysis. Alternatively, if the patient is resuscitated to a euvolemic state without isotonic bicarbonate, it will become impossible to provide them with an adequate amount of bicarbonate (these patients are often oliguric, so further fluid could provoke pulmonary edema).
• These patients are often hyperkalemic &#; a process which will also be alleviated by isotonic bicarbonate (discussed further in the chapter on hyperkalemia).
• Overall, there is a subset of patients with acute kidney injury, uremic metabolic acidosis, and hyperkalemia who will respond very favorably to isotonic bicarbonate with resolution of their electrolytic problems. This may buy them some time for their kidneys to recover, potentially avoiding the need for dialysis.

hypertonic & isotonic bicarbonate

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what is isotonic bicarbonate?

• Isotonic bicarbonate is generally formulated by adding 150 mEq of sodium bicarbonate to a liter of D5W (above).
• Although the bag of fluid will be hypertonic, glucose doesn't function as an effective osmole (since it readily enters cells). Therefore, in vivo this solution will behave as an isotonic fluid.
• D5W is used as the base solution because most hospitals don't have IV sterile water available. If your hospital does have IV sterile water, this would be preferable to D5W to produce a pure isotonic solution of bicarbonate.

isotonic bicarbonate vs. hypertonic bicarbonate

• The most commonly used forms of bicarbonate are hypertonic bicarbonate (undiluted ampules) and isotonic bicarbonate, as compared above.
• The amount of hypertonic bicarbonate which can be given is limited by the sodium concentration. Each 50-ml ampule of bicarbonate will increase the sodium concentration by roughly ~1-1.5 mEq/L. Caution needs to be exercised with repeated ampules, as eventually this may cause hypernatremia.
• The amount of isotonic bicarbonate which can be given is generally limited by volume overload. Each 150 mEq of bicarbonate comes along with a liter of volume.

dissolved CO2 & how rapidly can isotonic bicarbonate be given?

• Intravenous bicarbonate contains both bicarbonate and dissolved CO2. For example, the concentration of pCO2 in an ampule of bicarbonate may be ~100 mm.
• Following administration:
  • Dissolved CO2 will transiently increase the patient's pCO2. Over time, this will be breathed off and the patient will return to their prior pCO2 level. This will happen even if the patient is on mechanical ventilation (administered pCO2 increases the gradient driving CO2 out of the body &#; which increases CO2 clearance and eventually returns the patient to their baseline pCO2). The only situation where CO2 doesn't return to baseline is if the patient has died (e.g. cardiac arrest, with minimal effective circulation).
  • Bicarbonate will persist longer, after the pCO2 has been exhaled. This explains the alkalinizing effect of IV bicarbonate.
  • Fun fact: the pH of an ampule of bicarbonate is only 8. It's not that alkaline in the bottle (which contains both pCO2 and bicarbonate). The reason it causes alkalinization in vivo is because pCO2 is breathed off while bicarbonate remains.
• Ampules of sodium bicarbonate generally shouldn't be pushed over a few seconds. This may cause rapid pH shifts, including elevated pCO2. Thus, ampules of hypertonic bicarbonate should generally be pushed slowly over ~5-10 minutes if possible.
• Isotonic bicarbonate can be infused at rates similar to other crystalloids (e.g. 75-1,000 ml/hr). Given the lower concentration of CO2 in isotonic bicarbonate, rapidly loading the patient with CO2 isn't an issue here.

effect on potassium concentration

• Three factors are in play here:
  • (1) Hypertonicity causes potassium to shift out of cells (a process known as solute drag).
  • (2) Bicarbonate increases the pH, which shifts potassium into cells.
  • (3) Volume load of isotonic bicarbonate may directly dilute out potassium, thereby decreasing the potassium concentration.
• Hypertonic bicarbonate
  • Factors #1 & #2 cancel each other out.
  • Several RCTs have shown that hypertonic bicarbonate does not affect potassium level.
• Isotonic bicarbonate
  • Factors #2 & #3 both serve to reduce the potassium level.
  • Available data shows that isotonic bicarbonate decreases the potassium level among patients with metabolic acidosis., , )
• Clinical significance depends on what you're trying to achieve:
  • Hyperkalemia: If you're trying to reduce the potassium level, you need to use isotonic bicarbonate.
  • Hypokalemia: If you're trying to increase the pH without dropping the potassium, then hypertonic bicarbonate could have an advantage here. Alternatively you could use isotonic bicarbonate with simultaneous potassium supplementation.

hypocalcemia

• Increases in pH will tend to decrease the ionized calcium level (essentially removal of protons stuck to albumin renders albumin more negatively charged, leading to an increase in calcium-albumin binding).
• Increasing the pH to a normal range shouldn't cause hypocalcemia, but it may exacerbate pre-existing hypocalcemia.

common errors with bicarbonate

• In general, it's desirable to standardize this fluid in order to avoid medication errors:
  • (a) Don't mix up a solution with two ampules of bicarbonate. If you want to give the patient some additional D5W, it's preferable to run two simultaneous infusions (one with D5W and another with true isotonic bicarbonate).
  • (b) Don't mix up 3 ampules of bicarbonate in a liter of normal saline!
• Don't be afraid to run isotonic bicarbonate at the rate you need. For example, in a severely hypovolemic patient who needs fluid and bicarbonate, you may wish to run the isotonic bicarbonate at 250-1,000 ml/hr (to provide both volume and bicarbonate).
• Don't slam in an ampule of hypertonic bicarbonate (unless there is a really good reason, such as profound tricyclic intoxication).
• Don't use hypertonic bicarbonate to treat hyperkalemia (proven not to work).
• Don't bolus hypertonic bicarbonate for a patient in cardiac arrest (unless you suspect a toxicologic etiology).
• Don't use bicarbonate to treat lactic acidosis or ketoacidosis (this doesn't work and gives bicarbonate a bad reputation).

therapeutic alkalization to augment permissive hypercapnia

(back to contents)

basic concept

• Occasionally, intubated patients who are encountered who are extremely difficult to ventilate (typically due to status asthmaticus or severe ARDS).
• The safest approach to these patients may be to administer exogenous bicarbonate, with a goal of increasing the bicarbonate level to ~30-35 mEq/L
  • Note that the normal level of bicarbonate in blood is 22-28 mEq/L. Thus, a serum bicarbonate level of 30-35 mEq/L isn't terribly high.
• This will generally amount to shifting patients from a state of mild metabolic acidosis (most patients start off with a bicarbonate of ~20 mEq/L) to mild metabolic alkalosis. Higher serum bicarbonate makes it easier to safely ventilate patients (targeting a pH >7.15-7.20). Bicarbonate administration may be safer than increasing the respiratory rate or tidal volume (maneuvers which will increase mechanical force delivered to the lungs and may also increase the risk of pneumothorax).
  • Note that the development of a pneumothorax in a patient with profound ARDS or asthma may be a catastrophic event.
• Left to their own devices, patients with ARDS or status asthmaticus will often eventually compensate for their respiratory acidosis by mounting a compensatory metabolic alkalosis. Exogenous bicarbonate administration aims to achieve the same thing, merely accelerating this normal adaptation process.
• There is no high-quality evidence on this topic. The use of exogenous bicarbonate to balance out severe respiratory acidosis is a longstanding practice in critical care (e.g. utilized in the classic ARMA trial on ARDS.)

how to achieve therapeutic alkalization

• Depending on the patient's weight and baseline bicarbonate, this will generally involve administration of ~150-300 mEq sodium bicarbonate to target a serum bicarbonate level of ~30-35 mEq/L. This should generally be achieved gradually over a period of several hours.

• Hypertonic bicarbonate

  : Some or all of this exogenous bicarbonate may be administered in the form of hypertonic sodium bicarbonate (8.4%, described above). Hypertonic bicarbonate has the advantage of limiting added volume, but it will eventually cause hypernatremia.

• Isotonic bicarbonate

  : This may be useful in patients with hypovolemia or hypernatremia. In a patient with euvolemia and high-normal sodium, isotonic bicarbonate could be combined with diuretics (e.g. furosemide and thiazide diuretics) to achieve alkalinization without causing volume overload.
  • A thiazide diuretic may be useful here to promote sodium excretion and avoid hypernatremia (more on this here). Furosemide alone tends to cause excretion of dilute urine &#; so the combination of furosemide plus isotonic bicarbonate may still tend to increase the patient's sodium level.
• The optimal rate of alkalinization is unknown, and likely varies depending on the individual patient scenario. In most cases, gradual alkalization (e.g. 25-100 mEq bicarbonate per hour) is sufficient.
• Bicarbonate administration will cause a transient increase in pCO2 during its administration, which will cause a transient reduction in pH. However, once completed, pCO2 will decrease to baseline and the added bicarbonate will increase the pH.
  • If bicarbonate is administered more slowly, then transient pCO2 elevations are smaller. Of course, it will take longer to get to target pH.
  • This issue of dissolved CO2 is discussed further in the above section in IV bicarbonate.

Going further

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To keep this page small and fast, questions & discussion about this post can be found on another page here.

• Don't use normal saline as your default resuscitative fluid. There are many reasons for this, but one salient one is as follows: eventually you will wind up giving liters of saline to a hyperkalemic and acidotic patient, thereby pushing them off a pH cliff.
• Don't be afraid to use Lactated Ringers in patients with hyperkalemia or liver dysfunction. Don't be afraid to use Plasmalyte in any patient (there don't seem to be any legitimate contraindications to Plasmalyte).
• Don't miss opportunities to fix your patient's pH abnormalities using pH-guided resuscitation (especially for patients with uremic metabolic acidosis).
• Not understanding how to use various forms of bicarbonate.

Guide to emoji hyperlinks

• = Link to online calculator.
• = Link to Medscape monograph about a drug.
• = Link to IBCC section about a drug.
• = Link to IBCC section covering that topic.
• = Link to FOAMed site with related information.
• = Link to supplemental media.

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