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The Role of Lab Values in Clinical Decision Making and Patient Safety for the Acutely Ill Patient

The Role of Lab Values in Clinical Decision Making and Patient Safety for the Acutely Ill Patient
Adele Myszenski, PT, MPT
September 7, 2017
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Learning Outcomes

 
After this course, participants will be able to:
 
  • List at least three reasons why lab values and vital signs are essential clinical tools to determining the appropriateness of acute care rehab intervention.
  • List at least one of the normal values for each: BP, HR, SaO2, Hemoglobin, Potassium, Glucose, Platelets, Troponin, and CPK.
  • Describe the effects of abnormal lab values and discuss precautions and monitoring techniques.
  • List at least three ways to identify when to implement, modify or hold rehab interventions based on assessment of lab values and vital signs.

Introduction and Overview

 

Thank you for joining our webinar today on the role of lab values in clinical decision making and patient safety for the acutely ill patient. We're going to spend time introducing a few basic reasons why we look at lab values, go over some clinical reasoning, and then we'll dive deeper into each of the vital signs and lab values.

Definition

Laboratory diagnostic tests are one factor in determining the overall health of our patients. They evaluate the kidneys, liver, thyroid, heart, and other aspects of health. In acute care or subacute care, the most common blood tests that we see include complete blood count (CBC), and differential and basic metabolic profile or routine chemistry. The normal values at each institution are typically determined based on 95% of healthy people in a certain group. For many tests, the normal ranges will vary depending on age, gender, race, or other factors.

In a 1972 article, Lundberg defined a critical value as "a physiological state at such variance with normal as to be life threatening unless something is done promptly, and for which some corrective action can be taken." As critical values might evolve quickly in the acute care setting, it is important for us to frequently reassess to be sure that our patients are safe and we're providing effective patient management.

Another article by Amy Pawlik in 2013 deals with how patients with acute illness "require timely and accurate assessment and modification of activity by the intervening PT (or OT / assistant), and the titration of activity in response to changes in the physiological status." This is key to our lab values and understanding lab values and vital signs. We have to understand how they interact with our bodies and what the physiologic response is. Individual physicians may have guidelines that are based on their own clinical research or preference. It is always important to have discussions with your physicians for professional exchange, no matter what we're learning today.

Today, the abnormal values and the appropriateness for rehab intervention that we're going to discuss are based on evidence-based literature. They're also based on expert physician recommendations, in some cases where literature isn't as deep. At Henry Ford Hospital, a lab values manual was created in 1996 and has been revised many times over the years, including this year. We review it at least every two years, to assist PTs, OTs, PTAs, and COTAs in clinical decision making. Recently, the Academy of Acute Care Physical Therapy section gathered a task force to review the lab values resource they have published since 2011. Many of my slides and discussion today are based on this lab value resource. The link is included in my reference list and is available for anyone to access; you don't have to be a member of the Academy of Acute Care Physical Therapy. It is a convenient, comprehensive tool.  It is also a very customizable tool and they have a quick-reference guide as well.

Clinical Decision Making

To begin or continue interventions on patients that we're seeing in the acute care setting, we always need to use clinical decision making. The lab values alone may or may not determine whether you're going to intervene with a patient, or whether you're going to hold. In addition to looking at the lab values and determining whether they are within normal ranges or guidelines, clinical decision making also needs to be based on a thorough chart review, the trends of labs or vital signs, clinical discussion with the team, and the ability to monitor for clinical signs and hemodynamic stability during intervention.

Other things to consider when looking at the patient's big picture include:

  • Potential drug interactions
  • Meals the patient has consumed (which may have an effect on their most recently reported lab values)
  • Significant trends in the values over time
  • Electrolyte panels might change with intervenous infusions, medications, and diet
  • Chronic medical conditions (such as anemia) might be asymptomatic during exercise, while a patient with a precipitous drop in hemoglobin and hematocrit might require urgent medical attention 

It's always relative and no one has a crystal ball, so it is critical that we make sure to use our clinical judgment to decide. Of course, it's always important to document the rationale for treatment, whether you decide to hold, to modify, or to intervene with a patient. Documentation is key. 

Vital Signs

It's important to understand the normal values for vital signs, in order to monitor patients who have abnormal lab values. Furthermore, abnormal resting vital signs may also be an indicator for modifying or deferring intervention on any given day. Even if a patient's lab values are normal, the vital signs themselves might also be a reason why you might need to modify the intervention.

Guidelines

The normal resting values that have been determined are:

  • Heart rate (HR): 50 to 120 beats per minute
  • Systolic blood pressure (SBP): 80 to 180
  • Diastolic blood pressure (DBP): 40 to 110 mmHg
  • Oxygen saturation (SaO2): above 90%
  • Respiratory rate: 12 to 20 breaths per minute (BPM)

If you mobilize a patient whose vital signs fall outside of the "normal" parameters, treatment should be terminated if any of the following symptoms are observed (indicating that the patient is not tolerating our intervention):

  • Dizziness that is not resolved within 60 seconds of obtaining upright
  • An increase in the patient's heart rate of 30 BPM or more over baseline
  • A change in the patient's systolic blood pressure of 30 mmHg, or a change in the diastolic blood pressure of 10 mmHg
  • Blurred vision
  • Dilated pupils
  • Anginal pain
  • Shortness of breath

It is important to note that values outside of the listed guidelines do not automatically mean that we should defer treatment. There are other things to take into consideration.

  • What has been the trend over the last 24 hours?
  • Is the patient asymptomatic?
  • Are there other factors involved (i.e., pain, decreased hemoglobin, sepsis, or medications)?

Interventions provided by nursing may help with evaluation and treatment. For example, if the patient's heart rate is very high, that might be due to pain. Pain medicine or blood pressure medication might be able to help them. Paying attention to when the medication was administered will make a difference whether the blood pressure is high or low because perhaps they have a low blood pressure and they just received their medication. That would be a reason why you may want to consider taking caution. Suctioning, position change and anti-anxiety medications will also be some interventions provided by nursing that may impact whether or not you decide to see the patient.

On the other hand, a patient may have vital signs that fall within the normal values, but you still might decide to modify or defer treatment on the vital signs alone, again, based on the trend of the last 24 hours. Has it been consistent? Have trends in the last 24 hours significantly changed from baseline measures? For example, the patient's blood pressure is 120/80 in the morning and then ranges from 140/90 to 180/100 over the next few readings. Although the values are technically within our guidelines, the patient's blood pressure is gradually trending upward, so treatment might be deferred. This may also happen if there's a sudden or significant change in the lab values.

Clinical Examples

If you take a look at Figure 1, you will see that the patient's blood pressure went from 104/60 to 115/72, then from 102/58 to 87/59. You do want to consider what position the patient tested in and if blood pressure medications were given. Those might be reasons why the blood pressure reading is low right now. It may not be a time that you want to automatically defer treatment, but you would definitely want to take their blood pressure before you get him or her up out of bed.

Table of vital signs for clinical example 1 including BP, temp, heart rate, resp, and SpO2 over a 3 day period

Figure 1. Clinical example 1.

Figure 2 shows another clinical example. You can see that the patient's blood pressure is fluctuating. It starts off on the lower side and it's heading up. The latest reading is 150/82, which is still within our guidelines. Take a look at the heart rate: it is also fluctuating. They are tachycardic. If you're looking at the 1600 hour on 3/28, the HR is 131 beats per minute. It was likely taken at rest by the nurse (at our institution, those values are taken on the hour by the nurse assistant). They're also tachypneic. The latest respiratory reading is 23. You might want to consider holding treatment if the activity is going to increase their heart rate. You may also dig in a little deeper into the chart or speak with the physician about what's causing their tachycardia at this moment. Are they in AFib? It doesn't necessarily mean it's an automatic hold, but you definitely want to dig deeper here.

 

Table of vital signs for clinical example 2 including BP, temp, heart rate, resp, and SpO2 over a 4 day period

Figure 2. Clinical example 2.

Vital Signs Tips

For the most accurate BP reading, choose a manual blood pressure machine for patients who have a significantly low or high blood pressure. Many of our institutions now have electronic blood pressure machines. They should have manual cuffs available, should you need them. For those patients who you're seeing that are either regularly trending low or high, or in the moment, you would definitely want to utilize a manual cuff. The electronic machines tend to over-read when the blood pressures are low, and under-read at very high blood pressures.

When you're taking a manual blood pressure, make sure that the stethoscope ear pieces are rotated forward and following the channel of your ear canals to best hear the blood pressure. Of course, it is also important to choose the right size cuff. Too small of a cuff on a large arm will register an inaccurately high blood pressure.

Whether or not you choose to use a manual or an electronic blood pressure machine, you want to keep the patient's arm at the level of the heart to avoid hydrostatic and gravitational forces in the blood vessels. Instruct the patient to not move or talk; this is especially true of the electronic cuffs, which are sensitive to any motion in the arm and the hand. If you do need to reinflate the cuff (e.g., if you don't quite trust the reading, if it was extremely high or low, or if you're taking orthostatic pressure readings), you do want to wait at least a minute or two in between reinflating the cuffs so that the blood that was trapped in those vessels can be released and you can have an accurate blood pressure reading.

Orthostatic Hypotension

In our institution, we learned that we needed to refresh our memories on the definition of orthostatic hypotension, and what the clinical diagnosis means. It is defined as a decrease in systolic blood pressure of 20 mmHg or more or the diastolic blood pressure of 10 mmHg or more within three minutes of standing up. If within 60 seconds we see them having dizziness or issues that we identify are orthostatic, we are going to identify it as orthostatic hypotension, and we might have them sit down and rest. At that point, you should take the vital signs. The true diagnosis is to measure and document heart rate and blood pressure within two to three minutes between position changes. First, you have the patient supine. Take his/her blood pressure and heart rate and repeat that in sitting. You have the patient sit up two to three minutes. While sitting, you repeat the blood pressure and heart rate again. If the systolic blood pressure decreased more than 20mmHg or the diastolic blood pressure decreased more than 10mmHg, the patient is more likely to have an orthostatic response should you stand him or her. At that point, you would terminate treatment. You may have them sit in the chair if they can tolerate that, but you want to monitor them closely. If their blood pressure is stable when they're sitting, you would have them stand for two minutes. Typically, I have a walker in front of them if I'm doing this, or I have them holding onto my forearms. Then we take the blood pressure again; if it decreases more than 20 mmHg (if it goes from 100/80 to 75/45), clearly the patient is not tolerating upright. In sitting, I may have the patient do ankle pumps, march in place, anything to get their blood flowing back to their head if they're feeling a little bit dizzy. If it's not true orthostatic hypotension, that often will help the patient resolve their dizziness. In any case, it is always important to take the vital signs and have an objective measure to either report to the physician or for your own intervention, to determine how far you're going to progress the patient. 

Lab Values

In our discussion of lab values, we will break them down into categories:

  • Lab values related to blood and blood cells
  • Lab values related to electrolytes
  • Lab values related to cardiac markers
  • Lab values associated with deep vein thrombosis (DVT)
  • Other lab values

Hemoglobin

Hemoglobin is the red, iron-based pigment in the blood that carries oxygen. It is a major protein of erythrocytes that transports oxygen from the lungs to peripheral tissues, and therefore it is critical that we monitor hemoglobin. The normal values for hemoglobin differ between men and women. For a woman, a normal hemoglobin is between 12 and 16 Gm/dL. For a man, it's between 14 and 17.4 Gm/dL. Hemoglobin levels will also differ depending on the body size and the muscle mass. Furthermore, with almost all lab values, levels are slightly decreased in the elderly.

There are many causes of low hemoglobin. The three major causes are macrocytic anemia, microcytic anemia, and normocytic anemia.

  • Macrocytic anemia will be evident in patients with liver disease, hypothyroidism, vitamin B12 deficiency, folate deficiency, and myelodysplasia.
  • Microcytic anemia commonly occurs in patients with iron deficiencies, sickle cell anemia, and hemodilution (increased IV fluids or plasma).
  • Normocytic anemia is probably the most common reason we see low hemoglobin in the hospital setting, due to acute hemorrhage, surgery or trauma. Other causes include: early iron deficiency, anemia of chronic disease, hemolytic anemia, and bone marrow infiltrates.

There are several physiologic impacts of low hemoglobin. These include decreased exercise tolerance, increased fatigue, and tachycardia. When the blood has a low oxygen-carrying capacity, there are limited levels of actions that are available to the tissues. To get oxygen to the tissues, heart rate and cardiac output need to increase. This increases the work on the myocardium. 

APTA's Academy of Acute Care hemoglobin guidelines begins with monitoring vital signs, including oxygen saturation (Sp02) to predict tissue perfusion. Patients may present with tachycardia or orthostatic hypotension. If hemoglobin is less than eight grams per deciliter (<8 g/dL), APTA's guidelines are to conduct a symptoms-based approach when determining appropriateness for activity and to collaborate with the interprofessional team regarding the possible need for timing of transfusion prior to mobilization. Finally, it is imperative to consult the interprofessional team while monitoring signs and symptoms, since the blood levels and transfusions are individualized.

Henry Ford Hospital's hemoglobin guidelines are not absolute; it depends on the patient. Typically, patients with hemoglobin <7 gm/dL receive no OT or PT that day. One exception would be a patient who declines blood transfusions for religious reasons. In some cases, the length of stay is particularly dependent upon them clearing physical therapy and if they've already received their blood transfusion, they may request that we see the patient. It depends on the reasons why they had a drop in hemoglobin. If, for example, they don't know why the hemoglobin is dropping and they replaced the blood, we wouldn't necessarily want to see them before a new lab value came back, because if they're bleeding from an unidentified location, it's possible that they are still having a low hemoglobin level. For hemoglobin values above 7.1 but less than 7.9, we review the activity order with the patient's physician. We don't necessarily need them to write an order for us. We do use our clinical judgment, but if it's written in the chart that the patient has progressive mobility orders, we consider that activity order is clarified. However, the patient's heart rate and blood pressure must be monitored pre-, mid-, and post-PT intervention. We also require that the oxygen saturation be above 90% prior to beginning treatment, and treatment will be terminated if any of the following symptoms are observed (as stated earlier): if dizziness is not resolved within 60 seconds, if heart rate goes up more than 30 BPM over baseline, if they have a change in their systolic or diastolic blood pressure of 30 or 10, and blurred vision, dilated pupils, anginal pain or shortness of breath. If hemoglobin is greater than 8 gm/dL, we provide routine physical therapy for the patients. That may seem like a discrepancy where the normal is 12, but we're providing routine greater than eight. Of course, we're still monitoring for signs and symptoms, but we don't have a requirement for the vital signs.

For blood transfusions, we have a guideline that the patient must have a hemoglobin of seven or above to receive therapy. There are patients who have issues when they get blood transfusions. We say that we cannot mobilize the patient between the first 30 minutes of the transfusion for each bag of blood. The nurse is monitoring for transfusion reactions every five minutes of that first 30 minutes of each bag; as such, it doesn't make sense, unless it's a very specific case, for us to go in and mobilize the patient. It would not be workable for the patient. Typically, for general medicine patients who are hemodynamically stable, they may receive the transfusion if their hemoglobin drops to seven. However, post-surgical, cardiac, or orthopedic patients who have an underlying cardiovascular disease may transfuse at eight. In other words, they might not wait till it drops to seven to transfuse.

Hematocrit

Hematocrit is also found in the complete blood count, and it represents the percentage of whole blood volume composed of erythrocytes. It assesses for overall blood loss and fluid balance. The normal range for males is 42 to 52%; for females, it's 37 to 47%. It can be increased when there's hemoconcentration from dehydration, burns, vomiting, or extreme physical exercise. Decreased levels of hematocrit may occur in all of the same scenarios as hemoglobin, as stated earlier (macrocytic anemia, microcytic anemia, and normocytic anemia). 

The Academy of Acute Care does have some guidelines for hematocrit. They consider the low critical value <15 to 20%, indicating cardiac failure or imminent death. The high critical value would be greater than 60%, due to spontaneous blood clotting that would occur. Less than normal, monitor vitals to predict tissue perfusion. Greater than 25%, symptoms-based approach when determining appropriateness, collaborate with the interprofessional team regarding the need for or timing of the transfusion prior to mobilization.

At Henry Ford, we don't have a specific lab value for hematocrit. We have tried to keep things on the simpler side for some of these because we feel that if a patient's hematocrit is low, likely one of their other critical lab values is also low, and we are already modifying treatment based on the other lab values.

Oxygen, Partial Pressure (PaO2)

I feel it is beneficial to review this area because it relates to the oxygen supply that the patient needs. This may not be a lab value that you see very often on the general practice unit, but you may see it when you have a ventilated patient. It measures the oxygen tension, or the partial pressure in the arterial blood, and determines tissue oxygen supply, along with hemoglobin and blood supply. The normal range for the partial pressure of oxygen is greater than 80 mmHg. Of course, it's going to be increased in oxygen therapy and decreased when there is ventilation perfusion mismatching (e.g., asthma, COPD, atelectasis, PE, pneumonia, interstitial lung disease, airway obstruction), or any other alveoli hypoventilation, such as neuromuscular disease, head injury or stroke. There are some drugs that will also affect PaO2.

At Henry Ford, we choose not to provide PT or OT intervention if the partial pressure is less than 60. We arrived at that figure based on the oxyhemoglobin dissociation curve (Figure 3), which describes the relation between the partial pressure of oxygen (x axis) and the oxygen saturation (y axis). If you look at the peak where the curve is almost flat, that is at about 90% oxygen saturation. If you're taking a patient's oxygen saturation, and they have a partial pressure less than 60, you can see by the curve that it drops off dramatically. If they have a 60, you can be relatively certain that their oxygen saturation is going to stay above 80%. 

 

 

OxyHemoglobin dissaciation curve with oxygen partial pressure in the X axis and percent saturation on the y axis

Figure 3. OxyHemoglobin dissociation curve.

Potassium

Potassium is predominantly an intracellular ion whose plasma level is regulated by renal excretion. Plasma potassium concentration determines neuromuscular irritability. Elevated or depressed potassium concentration can interfere with muscle contraction, and also cardiac conductivity. The main thing to be worried about with an abnormal potassium is that the patient could have an arrhythmia. There are a couple different definitions of what is normal. The Merck manual suggests that normal potassium is 3.5 to 5.0 milliequivalents of solute per liter (mEq/L). The APTA reference says it's 3.7 to 5.1.

Potassium values can be increased (hyperkalemia) for several reasons. For example, if the patient has a massive hemolysis, if they have severe tissue damage, or rhabdomyolysis, acidosis, dehydration, acute or chronic renal failure, Addison disease, or if they are taking certain medications. Hyperkalemia is defined as a potassium level greater than 5.5 mEq/L. Potassium can be decreased (hypokalemia) if the patient has low potassium intake, if they've had prolonged vomiting or diarrhea, Cushing's disease, if they have hyperglycemia, alkalosis, trauma, or subarachnoid hemorrhage. Diuretics can also cause potassium levels to be reduced. Hypokalemia is defined as less than 3.5 mEq/L.

The Academy of Acute Care's guidelines divides this up in two ways. If the potassium is trending up (> 5 mEq/L), patients are at risk for cardiac issues. Best practice is to use symptom-based approach when determining appropriateness for activity. The patient might exhibit muscle weakness during an intervention. If the potassium is trending down, once again we would use a symptoms-based approach when determining appropriateness for activity. Severe hypokalemia is defined as < 2.5 mEq/L; at this level, you should collaborate with the interprofessional team.

At Henry Ford, we originally determined our ideal lab values for potassium based on collaboration with a cardiologist and nephrologist. We've been using this guideline for about five years. We conducted a study to validate that these lab values were appropriate, using the definitions that 3.5 to 5.0 is normal. Our policy is that we will not provide routine physical therapy or occupational therapy with values of less than three or greater than six. But if they have 3.1 to 3.4, or 5.1 to 5.9, we will review the chart, we'll note any orders if there is a cardiac workup. If it's pending or completed, typically they will have ordered troponins or another panel to determine whether there is cardiac involvement, and we will follow those guidelines (which we will cover coming up shortly).

If their vital signs are within normal resting values, we will provide therapy to the patient and monitor them pre-, mid-, and post-treatment. Again, their oxygen saturation needs to be greater than or equal to 90% prior to beginning mobility. Treatment will be terminated with the onset or increase of the following:

  • Dizziness not resolved/improved within 60 seconds of obtaining upright
  • Increase in the patient’s heart rate of 30 bpm over baseline or Bradycardia or arrhythmia
  • Change in the patient’s systolic blood pressure of 30 mm Hg or a change in the diastolic blood pressure of 10 mm Hg or orthostatic hypotension
  • Nausea/Vomiting
  • Paresthesia
  • Anginal pain

adele myszenski

Adele Myszenski, PT, MPT

Adele Myszenski, MPT is a supervisor at Henry Ford Hospital in Detroit, MI. HFH is a level 1 trauma, academic hospital and the recipient of the 2011 Malcomb Baldridge National Quality Award.  A 2001 graduate of Wayne State University, Adele practices primarily in the adult medical and surgical and neonatal ICUs.  She is responsible for creation, development and implementation of competencies across the service line for lab values, ICU, VAD and other areas.  In addition, Adele currently serves as expert superuser for EPIC and allied health site leader for CPM for EMR go-lives at HFHS.  Adele is an accomplished speaker at APTA Combined Sections meetings, PhysicalTherapy.com, OccupationalTherapy.com and Therapist Sea-Cruise..   Current areas of research include: validation of safe potassium levels in the acute care setting, early rehabilitation in the critical care patient and implementation of PT and OT pathway for transcatheter aortic valve replacement



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