Blood Gases

Core Lab

Synonym/Acronym

arterial blood gases (ABGs), venous blood gases (VBGs), capillary blood gases, cord blood gases.

Rationale

To assess oxygenation and acid-base balance.

This Core Lab Study is the gold standard for management of oxygenation levels and acid-base balance, especially in patients with severe illness. Understanding arterial blood gas results can be difficult and even complicated at times. Emergency, cardiac, and intensive care units commonly use results of ABGs and other core lab studies to inform the patient’s current clinical status and care plan.

Patient Preparation

There are no food, fluid, activity, or medication restrictions unless by medical direction. The Allen test should be performed prior to specimen collection from the radial artery. Information regarding how to perform the Allen test is presented with other general guidelines in Appendix A: Patient Preparation Specimen Collection.

Normal Findings

Method: Selective electrodes for pH, PCO₂, and PO₂.

Allen test		Note: Performed prior to use of radial artery for specimen collection
Normal Findings: Positive; where sufficient collateral blood flow in the ulnar artery is demonstrated		Note: Procedure for Allen test is described and pictured in Appendix A: Patient Preparation Specimen Collection.

Blood Gas Value (pH)	Arterial	Venous	Capillary
Scalp	—	—	7.25–7.35
Birth, cord, full term	7.11–7.36	7.25–7.45	7.32–7.49
Adult/child	7.35–7.45	7.32–7.43	7.35–7.45

Note: SI units (conversion factor × 1).

PCO₂	Arterial	SI Units (Conventional Units × 0.133)	Venous	SI Units (Conventional Units × 0.133)	Capillary	SI Units (Conventional Units × 0.133)
Scalp	—	—	—	—	40–50 mm Hg	5.3–6.6 kPa
Birth, cord, full term	32–66 mm Hg	4.3–8.8 kPa	27–49 mm Hg	3.6–6.5 kPa	—	—
Newborn–adult	35–45 mm Hg	4.7–6 kPa	41–51 mm Hg	5.4–6.8 kPa	26–41 mm Hg	3.5–5.4 kPa

PO₂	Arterial	SI Units (Conventional Units × 0.133)	Venous	SI Units (Conventional Units × 0.133)	Capillary	SI Units (Conventional Units × 0.133)
Scalp	—	—	—	—	20–30 mm Hg	2.7–4 kPa
Birth, cord, full term	8–24 mm Hg	1.1–3.2 kPa	17–41 mm Hg	2.3–5.4 kPa	—	—
0–1 hr	33–85 mm Hg	4.4–11.3 kPa	—	—	—	—
Greater than 1 hr–adult	80–95 mm Hg	10.6–12.6 kPa	20–49 mm Hg	2.7–6.5 kPa	80–95 mm Hg	10.6–12.6 kPa

HCO₃^-	Arterial Conventional and SI Units	Venous Conventional and SI Units	Capillary Conventional and SI Units
Birth, cord, full term	17–24 mmol/L	17–24 mmol/L	—
12 mo–2 yr	16–23 mmol/L	24–28 mmol/L	18–23 mmol/L
Adult	22–26 mmol/L	24–28 mmol/L	18–23 mmol/L

O₂ Sat	Arterial	Venous	Capillary
Birth, cord, full term	40%–90%	40%–70%	—
Adult/child	95%–99%	70%–75%	95%–98%

Values may be at the lower end of the normal range in older adults.

Oxygen Content: Arterial		Oxygen Content: Venous
6.6–9.7 mmol/L		4.9–7.1 mmol/L

TCO₂	Arterial Conventional and SI Units mmol/L	Venous Conventional and SI Units mmol/L
Birth, cord, full term	13–22 mmol/L	14–22 mmol/L
Adult/child	22–29 mmol/L	25–30 mmol/L

Base Excess Arterial		Conventional and SI Units
Birth, cord, full term		(–10) – (–2) mmol/L
Adult/child		(–2) – (+3) mmol/L

Critical Findings and Potential Interventions ⬆ ⬇

Timely notification to the requesting health-care provider (HCP) of any critical findings and related symptoms is a role expectation of the professional nurse. A listing of these findings varies among facilities.

Consideration may be given to verification of critical findings before action is taken. Policies vary among facilities and may include requesting recollection and retesting by the laboratory.

Arterial Blood Gas Parameter	Less Than	Greater Than
pH	7.2	7.6
HCO₃^-	10 mmol/L	40 mmol/L
PCO₂	20 mm Hg (SI: 2.7 kPa)	67 mm Hg (SI: 8.9 kPa)
PO₂	40 mm Hg (SI: 6 kPa)

Overview ⬆ ⬇

(Study type: Whole blood; related body system: Circulatory, respiratory, and urinary systems. Specimen volume and collection container may vary with collection method. See section titled “Teaching the patient what to expect” for specific collection instructions. Specimen should be tightly capped and transported in an ice slurry.)

Blood gas analysis is used to evaluate respiratory function and provide a measure for determining acid-base balance. Respiratory, renal, and cardiovascular system functions are integrated in order to maintain normal acid-base balance. Therefore, respiratory or metabolic disorders may cause abnormal blood gas findings. The blood gas measurements commonly reported are as follows:

pH
PCO₂ (partial pressure of carbon dioxide)
HCO₃^- (bicarbonate)
base excess (BE)
base deficit (BD)
PO₂ (partial pressure of oxygen)
O₂ saturation

What is pH and acid-base balance?

pH reflects the number of free hydrogen ions (H⁺) in the body. A pH less than 7.35 indicates acidosis. A pH greater than 7.45 indicates alkalosis. Changes in the ratio of free H⁺ to HCO₃ will result in a compensatory response from the lungs or kidneys to restore proper acid-base balance.

Extremes in acidosis are generally more life threatening than alkalosis. Acidosis can develop either very quickly (e.g., cardiac arrest) or over a longer period of time (e.g., chronic kidney disease). Infants can develop acidosis very quickly if they are not kept warm and given enough calories. Children with diabetes tend to go into acidosis more quickly than do adults who have been dealing with the disease over a longer period of time. In many cases, a venous or capillary specimen is satisfactory to obtain the necessary information regarding acid-base balance without subjecting the patient to an arterial puncture with its associated risks.

What is gas exchange and why is it important?

Normal body metabolism includes internal and external respiration. When we breathe oxygen from the air it diffuses into our lungs and is carried by the circulatory system to the cellular level where energy is generated for all body functions. Simultaneously, carbon dioxide, a waste product of cellular metabolism, diffuses from cells into the blood and is carried by the circulatory system to the lungs to be released into the air as we breathe out. The exchange of oxygen and carbon dioxide in the lungs is called external respiration. The exchange of oxygen and carbon dioxide into and out of the cells is called internal respiration. For additional information about the relationship between gas exchange and the body’s buffer systems; see the study titled “Hemoglobin and Hematocrit.”

Carbon Dioxide

Carbon dioxide has three modes of transportation from the tissues to the lungs by way of the circulatory system:

Direct dissolution into the blood (5%–7%)
Bound to proteins or hemoglobin in plasma (10%)
Chemical conversion to bicarbonate (primary mechanism—85%)

PCO₂ is an important indicator of ventilation. The level of PCO₂ is controlled primarily by the lungs and is referred to as the respiratory component of acid-base balance. The main buffer system in the body is the bicarbonate–carbonic acid system.

Bicarbonate

Bicarbonate is an important alkaline ion that participates along with other anions, such as hemoglobin, proteins, and phosphates, to neutralize acids. The main acid in the acid-base system is carbonic acid. It is the metabolic or nonrespiratory component of the acid-base system and is controlled by the kidney. For the body to maintain proper balance, there must be a ratio of 20 parts bicarbonate to one part carbonic acid (20:1).

The carbonic acid level is not measured directly but can be estimated because it is 3% of the PCO₂. Bicarbonate levels can either be measured directly or estimated from the measurement of total carbon dioxide content (TCO₂). For example, if the PCO₂ were 40, the carbonic acid would be calculated as (3% × 40),or 1.2, and the bicarbonate or HCO₃^- would be calculated as (20 × 1.2),or 24.

Base Excess (BE)

Blood gas reports generally use the term base excess, which is qualified by the use of the words positive and negative. BE reflects the number of anions available in the blood to help buffer changes in pH. Sometimes the term base deficit (BD) is used instead of (negative) BE. The normal range for BE (adult) is (–2) – (+3) mmol/L.

A positive BE is an excess in the amount of alkalinity (or base) in the blood, which is indicative of metabolic alkalosis.
A negative BE (or base deficit) is a deficit in the amount of alkalinity (or base), which is indicative of metabolic acidosis.

Oxygen

As seen in the table of reference ranges, PO₂ is lower in infants than in children and adults owing to the respective level of maturation of the lungs at birth. PO₂ tends to trail off after age 30 yr, decreasing by approximately 3 to 5 mm Hg per decade as the organs age and begin to lose elasticity. The formula used to approximate the relationship between age and PO₂ is PO₂ = 104 – (age × 0.27).

The oxygen-carrying capacity of the blood indicates how much oxygen could be carried if all the hemoglobin were saturated with oxygen. Percentage of oxygen saturation is [oxyhemoglobin concentration ÷ (oxyhemoglobin concentration + deoxyhemoglobin concentration)] × 100.

Like carbon dioxide, oxygen is carried in the body in a dissolved and combined (oxyhemoglobin) form. Most of the oxygen circulating in the body (98%) is bound to hemoglobin; the rest is dissolved. Oxygen content is the sum of the dissolved and combined oxygen. Because circulating blood may contain less oxygen than it is capable of carrying, it is useful to know the actual oxygen content. Oxygen content can be calculated on the basis of measured parameters (oxygen saturation, hemoglobin, and PO₂) and a solubility factor (0.003 is the Bunsen solubility factor for dissolved oxygen in blood). The oxygen content in arterial blood is calculated as CAO₂ = 1.34 (SAO₂ × Hgb) + 0.003 (PAO₂ ).The oxygen content of venous blood is calculated as CVO₂ = 1.34 (SVO₂ × Hgb) + 0.003 (PVO₂).

Specimen Types

Testing on specimens other than arterial blood is often ordered when oxygen measurements are not needed or when the information regarding oxygen can be obtained by noninvasive techniques such as pulse oximetry. Capillary blood is satisfactory for most purposes for pH and PCO₂; the use of capillary PO₂ is limited to the exclusion of hypoxia. Measurements involving oxygen are usually not useful when performed on venous samples; arterial blood is required to accurately measure PO₂ and oxygen saturation. Considerable evidence indicates that prolonged exposure to high levels of oxygen can result in injury, such as retinopathy of prematurity in infants or the drying of airways in any patient. Monitoring PO₂ from blood gases is especially appropriate under such circumstances.

Types of Acid-Base Imbalance

Acid-base status: Decreased pH indicates acidosis, increased pH indicates alkalosis, and restoration of pH to near-normal values is referred to as fully compensated balance. When pH values are moving in the same direction (i.e., increasing or decreasing) as the PCO₂ or HCO₃^-, the imbalance is metabolic. When the pH values are moving in the opposite direction from the PCO₂ or HCO₃^-, the imbalance is caused by respiratory disturbances.

Type of imbalance: To remember this concept, the following mnemonic can be useful: MetRO = Metabolic Together (pH, PCO₂ and HCO₃^- all moving in the same direction, i.e., increasing or decreasing); Respiratory Opposite (pH is moving in the opposite direction of PCO₂ and HCO₃^-, i.e., pH increases and the other two decrease or pH decreases and the other two increase).

Acid-Base Imbalance	pH	PCO₂ (Respiratory or Compensatory Response to Metabolic Imbalance)	HCO₃^- (Metabolic or Compensatory Response to Respiratory Imbalance)
Respiratory Acidosis
Uncompensated	Decreased	Increased	Normal
Partially compensated	Decreased	Increased	Increased
Fully compensated	Normal	Increased	Increased
Respiratory Alkalosis
Uncompensated	Increased	Decreased	Normal
Partially compensated	Increased	Decreased	Decreased
Compensated	Normal	Decreased	Decreased
Metabolic (Nonrespiratory) Acidosis
Uncompensated	Decreased	Normal	Decreased
Partially compensated	Decreased	Decreased	Decreased
Compensated	Normal	Decreased	Decreased
Metabolic (Nonrespiratory) Alkalosis
Uncompensated	Increased	Normal	Increased
Partially compensated	Increased	Increased	Increased
Compensated	Normal	Increased	Increased

Putting It All Together

Romanski method of evaluating blood gas scenarios

Determine whether the pH imbalance indicates acidosis or alkalosis.
1. Decreased pH indicates acidosis.
2. Increased pH indicates alkalosis.
3. When considering pH, use the midpoint of the normal range (7.4) as the cutoff; below 7.4 is acidosis, above 7.4 is alkalosis.
Determine whether the PCO₂ component indicates probability of respiratory cause or rules out respiratory cause.
1. Increased PCO₂ with decreased pH indicates respiratory acidosis because the blood becomes more acidotic when carbon dioxide is retained and production of carbonic acid increases.
2. Decreased PCO₂ with increased pH indicates respiratory alkalosis because the blood becomes alkalotic when more carbon dioxide is being “blown off” by the lungs than is staying in the blood.
3. If respiratory cause is ruled out, assume metabolic cause.
Determine which component is consistent with pH, i.e., the component indicating acidosis when the pH is decreased or the component indicating alkalosis when the pH is increased.
1. respiratory acidosis = increased PCO₂ with decreased pH
2. metabolic acidosis = HCO₃^- and pH are both decreased
3. respiratory alkalosis = decreased PCO₂ with increased pH
4. metabolic alkalosis = HCO₃^- and pH are both increased
Determine degree of compensation.
1. Uncompensated: The remaining component is normal, which indicates that the companion compensatory mechanism, respiratory or metabolic, was unable to compensate.
2. Partially compensated: Both the remaining component and the pH are either increased or decreased, which indicates that the companion compensatory mechanism, respiratory or metabolic, was able to partially compensate but not enough to resolve the acid-base imbalance.
3. Compensated: The remaining component is increased or decreased and the pH is normal, which indicates that the companion compensatory mechanism, respiratory or metabolic, was able to compensate and resolved the acid-base imbalance.

Examples of ABG Interpretations Using Steps 1 to 4 of Romanski Method (Explanations in Far Right Column)

	pH	PCO₂ (Respiratory Component)	HCO₃^- (Metabolic Component)	Steps 1–4 & Interpretation
Normal Range (NR)	7.35–7.45	35–45	22–26
Example 1:	7.22 ↓	40 NR	15 ↓	Interpretation: Metabolic acidosis (MeTRO); Uncompensated
• Determine pH imbalance	pH of 7.22 is less than 7.4; indicating acidosis			Step 1a—Acidosis
• Determine whether PCO₂ indicates or rules out respiratory component	Normal PCO₂ rules out respiratory and indicates a metabolic process			Step 2c—Metabolic
• Determine which component is in agreement with the pH imbalance	Decreased HCO₃^-*(indicates acidosis)* and decreased pH *(also indicates acidosis)*			Step 3b—HCO₃^- and pH are both in agreement for acidosis
• Determine the degree of compensation	The remaining component is PCO₂, and it is normal			Step 4a—Uncompensated—remaining component is normal
Normal Range	7.35–7.45	35–45	22–26
Example 2:	7.39 ↓	55 ↑	30 ↑	Interpretation: Respiratory acidosis (MeTRO); compensated
• Determine pH imbalance	pH of 7.39 is less than 7.4; indicating acidosis			Step 1a—Acidosis
• Determine whether PCO₂ indicates or rules out respiratory component	Significantly increased PCO₂ with decreased pH indicates respiratory process.			Step 2a—Respiratory
• Determine which component is in agreement with the pH imbalance	Significantly increased PCO₂*(indicates acidosis)* and decreased pH *(also indicates acidosis)*			Step 3a—PCO₂ and pH are in agreement for acidosis
• Determine the degree of compensation	The remaining component is HCO₃^- and it is increased; pH is in the normal range			Step 4c—Compensated—remaining component is increased or decreased and pH is normal
Normal Range	7.35–7.45	35–45	22–26
Example 3:	7.47 ↑	46 ↑	30 ↑	Interpretation: Metabolic alkalosis (MeTRO); partially compensated
• Determine pH imbalance	pH of 7.47 is greater than 7.4 indicating alkalosis			Step 1b—Alkalosis
• Determine whether PCO₂ indicates or rules out respiratory component	Increased PCO₂ coupled with an increased pH rules out a respiratory process and indicates a metabolic process			Step 2c—Metabolic
• Determine which component is in agreement with the pH imbalance	Increased PCO₂*(indicates alkalosis)* and increased pH(also indicates alkolosis)			Step 3d—PCO₂ and pH are in agreement for alkalosis
• Determine the degree of compensation	The remaining component is PCO₂ and it is increased; pH is also increased			Step 4b—Partially compensated—remaining component and pH are either increased or decreased
Normal Range	7.35–7.45	35–45	22–26
Example 4:	7.47 ↓	33 ↑	23 ↑	Interpretation: Respiratory alkalosis (MeTRO); uncompensated
• Determine pH imbalance	pH of 7.47 is greater than 7.4 indicating alkalosis			Step 1b—Alkalosis
• Determine whether PCO₂ indicates or rules out respiratory component	Decreased PCO₂ and increased pH indicate a respiratory process			Step 2b—Respiratory
• Determine which component is in agreement with the pH imbalance	Decreased PCO₂*(indicates alkalosis)* and increased pH *(also indicates alkolosis)*			Step 3c—Decreased PCO₂ and increased pH are in agreement for respiratory alkalosis
• Determine the degree of compensation	The remaining component is HCO₃^-, and it is normal			Step 4a—Uncompensated—remaining component is normal

Indications ⬆ ⬇

This group of tests is used to assess conditions such as asthma, chronic obstructive pulmonary disease (COPD), embolism (e.g., fatty or other embolism) during coronary arterial bypass surgery, and hypoxia. It is also used to assess the effectiveness of oxygen therapy or to assist in the diagnosis of respiratory failure, which is defined as a PO₂ less than 50 mm Hg and PCO₂ greater than 50 mm Hg. Blood gases can be valuable in the management of patients on ventilators or being weaned from ventilators. Blood gas values are used to determine acid-base status, the type of imbalance, and the degree of compensation as summarized in the following section. The interpretation of ABG values can be complicated by overlapping health conditions, effects of compensatory responses, and the physiological effects of other electrolytes/anion gap and oxygen levels/therapy at the time of measurement.

Contraindications ⬆ ⬇

Arterial puncture in any of the following circumstances:

Inadequate circulation, as evidenced by an abnormal (negative) Allen test or the absence of a radial artery pulse.

Significant or uncontrolled bleeding disorder, as the procedure may cause excessive bleeding; caution should be used when performing an arterial puncture on patients receiving anticoagulant therapy or thrombolytic medications.

Infection at the puncture site carries the potential for introducing bacteria from the skin surface into the bloodstream.

Congenital or acquired abnormalities of the skin or blood vessels in the area of the anticipated puncture site, such as arteriovenous fistulas, burns, tumors, vascular grafts.

Interfering Factors ⬆ ⬇

HCO₃^-

Drugs and other substances that may cause an increase in HCO₃^- include aminoglycosides, citrates, diuretics (loop and thiazide), glycyrrhiza (licorice), laxatives, and sodium bicarbonate, and penicillins.
Drugs that may cause a decrease in HCO₃^- include acetaminophen, acetazolamide, acetylsalicylic acid, aminoglycosides, amphotericin B, beta lactam penicillin, diazepam, ethyl alcohol, ethylene glycol, HAART—highly active antiretroviral therapy, isoniazid, linezolid, metformin, NSAIDs, paraldehyde, propofol, and xylitol.

PCO₂

Drugs and other substances that may cause an increase in PCO₂ include anesthetics, barbiturates, benzodiazepines, opiates, and sedatives.
Drugs and other substances that may cause a decrease in PCO₂ include acetylsalicylic acid, amphotericin B, cyclosporine, epinephrine, nicotine, progesterone, and theophylline.

PO₂

Drugs and other substances that may cause an increase in PO₂ include theophylline and urokinase.
Drugs and other substances that may cause a decrease in PO₂ include barbiturates and meperidine.

Other Factors

Specimens with extremely elevated white blood cell counts will undergo misleading decreases in pH, resulting from cellular metabolism, if transport to the laboratory is delayed.
Excessive amounts of heparin in the sample may falsely decrease pH, PCO₂, and PO₂.
A falsely increased O₂ saturation may occur because of elevated levels of carbon monoxide in the blood.
Recent blood transfusion may produce misleading values.
Specimens collected soon after a change in inspired oxygen has occurred will not accurately reflect the patient’s oxygenation status.
Specimens collected within 20 to 30 min of respiratory passage suctioning or other respiratory therapy will not be accurate.
Excessive differences in actual body temperature relative to normal body temperature will not be reflected in the results. Temperature affects the amount of gas in solution. Blood gas analyzers measure samples at 37°C (98.6°F); therefore, if the patient is hyperthermic or hypothermic, it is important to notify the laboratory of the patient’s actual body temperature at the time the specimen was collected. Fever will increase actual PO₂ and PCO₂ values; therefore, the uncorrected values measured at 37°C will be falsely decreased. Hypothermia decreases actual PO₂ and PCO₂ values; therefore, the uncorrected values measured at 37°C will be falsely increased.
O₂ saturation is a calculated parameter based on an assumption of 100% hemoglobin A. Values may be misleading when hemoglobin variants with different oxygen dissociation curves are present. Hemoglobin S will cause a shift to the right, indicating decreased oxygen binding. Fetal hemoglobin and methemoglobin will cause a shift to the left, indicating increased oxygen binding.
Citrates should never be used as an anticoagulant in evacuated collection tubes for venous blood gas determinations because citrates will cause a marked analytic decrease in pH.
Air bubbles or blood clots in the specimen are cause for rejection. Air bubbles in the specimen can falsely elevate or decrease the results depending on the patient’s blood gas status. If an evacuated tube is used for venous blood gas specimen collection, the tube must be removed from the needle before the needle is withdrawn from the arm or else the sample will be contaminated with room air.
Specimens should be placed in an ice slurry immediately after collection because blood cells continue to carry out metabolic processes in the specimen after it has been removed from the patient. These natural life processes can affect pH, PO₂, PCO₂, and the other calculated values in a short period of time. The cold temperature provided by the ice slurry will slow down, but not completely stop, metabolic changes occurring in the sample over time. Iced specimens not analyzed within 60 min of collection should be rejected for analysis. Electrolyte analysis from iced specimens should be carried out within 30 min of collection to avoid falsely elevated potassium values.

Potential Medical Diagnosis: Clinical Significance of Results ⬆ ⬇

Acid-base imbalance is determined by evaluating pH, PCO₂, and HCO₃^- values. pH less than 7.35 reflects an acidic state, whereas pH greater than 7.45 reflects alkalosis. PCO₂ and HCO₃^- determine whether the imbalance is respiratory or nonrespiratory (metabolic). Because a patient may have more than one imbalance and may also be in the process of compensating, the interpretation of blood gas values may not always seem straightforward.

Respiratory Acidosis

Respiratory conditions that interfere with normal breathing and cause CO₂ to be retained in the blood result in an increase of circulating carbonic acid and a corresponding acid pH. Conditions where there is either decreased alveolar gas exchange, decreased ventilation or perfusion, or premature mixing of venous and arterial blood will decrease blood pH. Examples include acute pulmonary edema, acute respiratory distress syndrome (newborns or adults), anemias (loss of blood, presence of abnormal hemoglobins), anesthesia, asthma, bronchiectasis, bronchitis (chronic), cancer, carbon monoxide exposure, cardiac disorders, cerebrovascular incident, compression or resection of lung, congenital heart defects, croup, COPD, cystic fibrosis (mucoviscidosis), drugs that depress the respiratory system (for therapeutic applications or by poisoning, e.g., opiates), head injury, hypoxia of high altitudes, near drowning, pneumonia, pulmonary infarction, sarcoidosis, and shock.

Respiratory Alkalosis

Respiratory conditions that increase the breathing rate cause CO₂ to be removed from the alveoli more rapidly than it is being produced. This results in an alkaline pH. Respiratory alkalosis may be seen with administration of drugs (e.g., salicylate and sulfa) that stimulate the respiratory system, in anxiety, artificial ventilation (excessive), central nervous system lesions or injury that result in stimulation of the respiratory system, fever, hepatic coma, hysteria, hyperthermia, hyperventilation, hypoxia of high altitude, pneumonia (early stage), pneumothorax, and pulmonary embolus.

Metabolic Acidosis

Metabolic (nonrespiratory) conditions that cause the excessive formation or decreased excretion of organic or inorganic acids result in metabolic acidosis. Some of these conditions include ingestion of salicylates, ethylene glycol, and methanol, as well as biliary or pancreatic fistula, diabetic ketoacidosis, shock, kidney disease, and starvation.

Metabolic Alkalosis

Metabolic alkalosis results from conditions that increase pH, as can be seen in alkali ingestion (excessive intake of antacids to treat gastritis or peptic ulcer), excessive administration of HCO₃^- (bicarbonate), cystic fibrosis, gastric suctioning, loss of stomach acid caused by protracted vomiting, and potassium and chloride deficiencies.

Nursing Implications ⬆

Potential Problems: Assessment & Nursing Diagnosis/Analysis

Problems		Signs and Symptoms
Gas exchange (inadequate—related to altered alveolar and capillary exchange, ventilation-perfusion mismatch, compromised oxygen supply, inadequate oxygen-carrying capacity of the blood)		Confusion; restlessness; hypoxia; irritability; shortness of breath; altered blood gases; orthopnea; cyanosis; increased heart rate, respiratory rate; use of respiratory accessory muscles; elevated blood pressure
Tissue perfusion (inadequate—related to compromised cardiac contractility, interrupted blood flow, inadequate oxygen transportation, decreased hemoglobin, hypoventilation, hypovolemia)		Hypotension; dizziness; cool extremities; capillary refill greater than 3 sec; weak pedal pulses; weak or absent peripheral pulses; altered level of consciousness; compromised sensation; poor healing; cool, clammy skin

Before the Study: Planning and Implementation

Teaching the Patient What to Expect

Review the procedure with the patient.
Discuss how this test can assist in assessing blood oxygen balance and oxygenation level.
Explain that a blood sample is needed for the test and that specimen collection and postprocedural care of the puncture site take about 10 to 15 min.
Advise resting for 30 min before specimen collection.
There may be some discomfort or pain during the arterial or venous puncture. Explain that the person performing the specimen collection may anesthetize the site with 1% to 2% lidocaine before puncture to decrease pain.

Procedural Information

It is important to notify the person collecting the specimen beforehand if the patient is receiving anticoagulant therapy or taking aspirin or other natural products that may prolong bleeding from the puncture site.

If the sample is to be collected by radial artery puncture, an Allen test is performed before puncture to ensure adequate blood flow to the hand. If the test result is positive (good blood return), the hand will quickly become warm and normal color will return. If the test result is negative (poor blood flow) the hand will remain pale and cool. Blood should only be collected from the hand with positive Allen test results.

General

The tightly capped arterial, venous, or cord blood sample is placed in an ice slurry immediately after collection.
Information on the specimen label is protected from water in the ice slurry by first placing the specimen in a protective plastic bag.
All types of blood gas specimens are promptly transported to the laboratory for processing and analysis.

Arterial

Perform an arterial puncture and collect the specimen in an air-free heparinized syringe.
There is no demonstrable difference in results between samples collected in plastic versus glass syringes.
Stopper the end of the syringe immediately after the needle is withdrawn and removed. It is very important that no room air be introduced into the collection container because the gases in the room and in the sample begin equilibrating immediately.
A pressure dressing is applied over the puncture site.
Samples are mixed by gently rolling the syringe between the hands to ensure proper mixing of the heparin with the sample, to prevent formation of small clots and to prevent sample rejection.

Venous

Central venous blood is collected in a heparinized syringe.
Venous blood is collected percutaneously by venipuncture in a 5-mL green-top (heparin) tube (for adult patients) or a heparinized Microtainer (for pediatric patients).
The vacuum collection tube must be removed from the needle before the needle is removed from the patient’s arm.
A pressure dressing is applied over the puncture site.
Samples are mixed by gently rolling the syringe between the hands to ensure proper mixing of the heparin with the sample, to prevent formation of small clots and to prevent sample rejection.

Capillary

A capillary puncture is performed and the specimen is collected in two 250-μL heparinized capillaries (scalp or heel for neonatal patients) or a heparinized Microtainer (for pediatric patients).
Capillary tubes are filled as much as possible and capped on both ends.
Some facilities recommend metal “fleas” be added to the capillary tube before the ends are capped.
During transport a magnet can be moved up and down the outside of the capillary tube using the flea to facilitate mixing, which prevents clot formation and sample rejection.
Laboratory or respiratory therapy staff must be notified of the number of fleas used, to account for each, and facilitate removal before the sample is introduced into the blood gas analyzers; the fleas can cause equipment damage.
Samples are mixed by gently rolling the capillary tube between the hands to ensure proper mixing of the heparin with the sample, to prevent formation of small clots and to prevent sample rejection.

Cord Blood

The sample is collected immediately after delivery from the clamped cord, using a heparinized syringe.

Fetal Scalp Sample

Samples for scalp pH are collected anaerobically before delivery in special scalp-sample collection capillaries and transported immediately to the laboratory for analysis.
The procedure takes approximately 5 min.
Positioning is in the supine position, with the feet in stirrups.
The cervix must be dilated at least 3 to 4 cm.
A plastic cone is placed in the vagina and fit snugly against the scalp of the fetus to provide access for visualization using an endoscope and to cleanse the site.
The site is pierced with a sharp blade.
Containment of the blood droplet can be aided by smearing a small amount of silicone cream on the fetal skin site.
The blood sample is collected in a thin, heparinized tube.
See preceding section on capillary collection for discussion of specimen mixing. Some facilities recommend small metal fleas be added to the scalp tube before the ends are capped.

Potential Nursing Actions

Validate the type of oxygen, mode of oxygen delivery, and delivery rate as part of the test requisition process and ensure there is a wait time of 30 min after a change in type or mode of oxygen delivery or rate for specimen collection.
Ensure an ice slurry in a cup or plastic bag is readily available for immediate transport of the specimen to the laboratory.

After the Study: Implementation & Evaluation Potential Nursing Actions

Avoiding Complications

Note that potential complications include bleeding, pain, hematoma.
Apply pressure to the puncture site for at least 5 min in the unanticoagulated patient, and for at least 15 min in the case of a patient taking natural products or medications with known anticoagulant, antiplatelet, or thrombolytic properties.
Apply pressure bandage. Observe/assess puncture site for bleeding or hematoma formation.

Treatment Considerations

Activity intolerance can be a concern. Symptoms of activity intolerance includes shortness of breath with activity, fatigue, inability to perform activity.
Interventions/actions related to activity intolerance include the following: Establish a baseline by asking how activity is normally tolerated. Gradually increase the level of activity and assist as needed. Pace activity, encourage periods of rest. Wear oxygen with activity as ordered. Discontinue activity with noted wheezing and shortness of breath.
Inadequate airway clearance can be a concern. Symptoms of inadequate airway clearance include an absent or ineffective cough, cyanosis, adventitious breath sounds, slow respiratory rate, diminished breath sounds, hypoxemia, nasal flare, subcostal retraction, elevated heart rate, agitation, use of accessory muscles to breath, increased difficulty breathing lying down, and purulent sputum.
Interventions/actions related to inadequate airway clearance include the following: Assess sputum for color, consistency, and amount. Administer ordered oxygen (humidified), monitor oxygenation with pulse oximetry. Place in semi-Fowler or position of comfort to facilitate breathing. Consult and collaborate with respiratory therapist and suction as appropriate. Encourage the patient to cough and do deep-breathing exercises every 2 hr. Assist in the use of incentive spirometry. Encourage fluids if not containdicated to decrease sputum viscosity. Splint chest with pillows to decrease pain with cough.
Altered breathing can be a concern. Symptoms of altered breathing include shortness of breath, rapid or slow breathing, nasal flare, use of accessory muscles, changes in respiratory effort and depth, cyanosis, pursed-lip breathing, bending forward to breathe easier.
Interventions/actions related to altered breathing include the following: Assess respiratory rate, rhythm, and depth including use of accessory muscles, nasal flare, and adventitious breath sounds. Administer prescribed oxygen, monitor and trend oxygen saturation with pulse oximetry. Collaborate to select positions to improve ventilation and oxygenation. Teach breathing exercises that will assist with exchange of oxygen and carbon dioxide, including breathing deeply and slowly. Consider future need for mechanical ventilation.
Decreased cardiac output can be a concern. Symptoms of decreased cardiac output include hypotension, increased heart rate, decreased cardiac output, decreased oxygen saturation, decreased peripheral pulses, decreased urinary output, cool and clammy skin, tachypnea, dyspnea, edema, altered level of consciousness, abnormal heart sounds, crackles in lungs, decreased activity tolerance, weight gain, fatigue, hypoxia, deceased ejection fraction (less than 55%).
Interventions/actions related to decreased cardiac output include the following: Monitor blood pressure and check for orthostatic changes. Assess respiratory rate, breath sounds, orthopnea, skin color and temperature, and level of consciousness. Assess peripheral pulses and capillary refill. Monitor urinary output, oxygen saturation with pulse oximetry, sodium and potassium levels, and B-type natriuretic peptide (BNP) levels. Administer ordered angiotensin-converting enzyme inhibitors, antidysrhythmics, diuretics, vasodilators, oxygen, and inotropics.
Fluid volume deficit can be a concern. Symptoms of fluid volume deficit includes dehydration, poor skin turgor, dry skin, thirst, sunken eyes, weakness, increased heart rate, decreased blood pressure, decreased urinary output, dry mucous membranes, altered level of consciousness, altered mental acuity.
Interventions/actions related to fluid volume deficit include the following: Encourage fluid intake, if not contraindicated. Monitor for urinary output less than 30mL/hr. Maintain IV fluid therapy. Measure daily weight at same time each day. Vigilant intake and output.
Note: Water balance needs to be closely monitored in patients with COPD. Fluid retention can lead to pulmonary edema.

Gas Exchange

Facilitate management of inadequate gas exchange.
Interventions/actions related to inadequate gas exchange include the following: Auscultate and trend breath sounds, adventitious breath sounds. Assess respiratory rate, rhythm, depth, accessory muscle use, symptoms of infection, atelectasis, consolidation, and pleural effusion. Monitor for restlessness, dizziness, lethargy, disorientation, confusion, and trend Hgb and Hct. Monitor chest x-ray reports, administer ordered oxygen, and oxygen saturation with pulse oximetry and consider preparation for intubation and/or mechanical ventilation. Trend ABG results. Administer ordered diuretics and vasodilators. Place the head of the bed in high Fowler position.
Observe/assess the patient for signs or symptoms of respiratory and metabolic disturbances.
- Symptoms of respiratory acidosis include: apprehension, coma, diaphoresis, disorientation, drowsiness, dyspnea, headache, hypertension, pallor, or tachycardia.
- Respiratory alkalosis presents with: tachypnea, restlessness, agitation, tetany, numbness, seizures, muscle cramps, dizziness, or tingling fingertips.
- Symptoms of metabolic acidosis include: rapid breathing, flushed skin, nausea, vomiting, dysrhythmias, coma, hypotension, hyperventilation, and restlessness.
- Metabolic alkalosis presents with: shallow breathing, weakness, dysrhythmias, tetany, hypokalemia, hyperactive reflexes, and excessive vomiting.

Tissue Perfusion

Facilitate management of inadequate tissue perfusion.
Interventions/actions related to inadequate tissue perfusion include the following: Monitor blood pressure (orthostatic). Assess dizziness, capillary refill, and pedal pulses. Monitor level of consciousness and check skin temperature for warmth. Administer prescribed IV fluids; vasodilator, antiplatelet, anticoagulant, inotropic drugs; and oxygen.

Nutritional Considerations

Stress the importance of following the prescribed diet.
Inadequate nutrition, periods of starvation, can result in hypophosphatemia (low phosphate), especially in the respiratory-dependent patient. Malnutrition is commonly seen in patients with severe respiratory disease related to fatigue, lack of appetite, and gastrointestinal distress.
Muscles used for breathing for COPD patients require a caloric intake 10 times higher than that of healthy individuals.
Adequate intake of vitamins A and C is important to prevent pulmonary infection and to decrease the extent of lung tissue damage.

Clinical Judgement

Consider how anxiety related to difficulty breathing can interfere with therapeutic interventions. What can be done to mitigate that?

Follow-Up Evaluation and Desired Outcomes

Demonstrates the ability to sustain an upright position to improve oxygenation.
Understands the importance of changing position every 2 hr to decrease the risk of atelectasis.
Acknowledges that oxygen therapy can improve hypoxia; uses oxygen, as prescribed, to support and improve oxygenation.

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