Assessment and Monitoring of the Perianesthesia Patient

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The primary purpose of the postanesthesia care unit (PACU) is the critical evaluation and stabilization of patients after procedures with an emphasis on the anticipation and prevention of complications that result from anesthesia or the operative or interventional procedure. A knowledgeable, skillful perianesthesia nurse must fully assess the condition of each patient not only at admission and discharge but also at frequent intervals throughout the postanesthesia period. Assessment must be a continuous and complete process that leads to sound nursing judgment and the implementation of therapeutic care. Assessment includes the gathering of information from direct observation of the patient (the primary source), from the health care providers, medical record, and the care plan.

Traditionally, perianesthesia nurses, with only limited information, have performed the role of caring for the surgical and procedural patients in the vulnerable postanesthesia state. However, for assessment of the perianesthesia patient and plan and implementation of appropriate care, preoperative information must be available as a basis for comparison with postoperative data. The perianesthesia nurse has a professional obligation to consider the patient’s history, clinical status, and psychosocial state. Preoperative patient information may be gathered with chart review, personal preoperative visit, clinical assessment, and consultation with other health care members who provide care to the patient. The nursing process is used to care for the patient undergoing surgery or invasive procedures, focused on assessment, planning, implementation, and evaluation. Assimilation of patient information is accomplished through an interdisciplinary team approach to patient care.

This chapter discusses the assessment of postprocedure patients and their common needs. Specific assessments related to patient age, the type of procedure, and problems that result from complicated diagnoses are addressed in following chapters. The assessment and management of postoperative pain are presented in Chapter 31.


Alveolar Artery Carbon Dioxide Differences The difference between the PaCO2 and the ETCO2 level is referred to as the alveolar-arterial CO2 difference (a-ADCO2).

Alveolar Dead Space Alveoli that do not participate in gas exchange because of a lack of blood flow.

Anatomic Dead Space Areas of the tracheobronchial tree not involved in gas exchange.

Capnography A continuous waveform display of carbon dioxide in respiratory gases. The analysis of capnography provides real-time assessment of the adequacy of ventilation.

Central Sleep Apnea A disorder in which breathing repeatedly stops and starts during sleep because the brain does not send proper signals to the muscles that control breathing. This condition is different from and occurs less often than obstructive sleep apnea (OSA).1

Dead Space Ventilation Includes anatomic, alveolar, and physiologic (total) dead space.

Electrocardiogram (ECG or EKG) A recording of the cardiac electrical activity from various views of the heart produced from electrodes placed on the body.

End-Tidal Carbon Dioxide (ETCO2) A noninvasive measure of the partial pressure of carbon dioxide at the end of an exhalation.

Flow-Directed Pulmonary Artery Catheter (FDPAC) Pulmonary artery thermodilution catheter used in hemodynamic monitoring.

Hyperthermia A core temperature greater than 38° C (100.4° F).

Hypothermia A core temperature less than 36° C (96.8° F).

Invasive Hemodynamic Monitoring The monitoring of blood flow through the use of invasive catheters to provide pressure measurements in the systemic and pulmonary circulations, arterial blood pressure, central veins, pulmonary capillary bed, and the right or left atrium as well as cardiac output (CO).

Left Atrial Pressure Measured with a catheter placed directly in the left atrium. Usually monitored only in open-heart cases when direct access to the left atrium can be reached. In the absence of mitral valve disease or left atrial tumor, left atrial pressure reflects left ventricular end-diastolic pressure and left ventricle preload.

Obstructive Sleep Apnea Breathing disorder distinguished by a pattern of repeated collapse of the upper airway and involuntary apnea during sleep.2

Physiologic Dead Space The sum of anatomic and alveolar dead space.

Pulmonary Artery Pressure Pressure in the pulmonary artery measured via an intravascular catheter inserted through a central vein to connect to the right side of the heart and advanced towards the pulmonary artery. A catheter in the pulmonary artery measures blood flow through the right side of the heart (right atrium and right ventricle) as well as pressures in the pulmonary artery and the filling pressure or wedge pressure of the left atrium.

Pulmonary Capillary Wedge Pressure (PCWP) Also known as the pulmonary capillary occlusion pressure; reflects the pressure in the left atrium.

Pulmonary Vascular Resistance (PVR) The resistance, impedance, or pressure the right ventricle must overcome to eject the blood into the pulmonary artery.

Pulse Oximetry Pulse oximetry (SpO2) is used for noninvasive measurement of arterial oxygen saturation (Sao2) in the blood.

Right Atrial Pressure Reflects venous return to the right side of the heart and right ventricular end-diastolic pressure (preload).

Systemic Vascular Resistance (SVR) The resistance, impedance, or pressure the left ventricle must overcome to eject the blood from the left ventricle.

Temporal Artery Temperatures Scanning of the forehead over the temporal artery with a noninvasive thermometer representing core temperature.

Preoperative assessments

The preoperative evaluation of the physical, psychosocial, and emotional status of the surgical and procedural patient is essential to patient-centered care, and nursing brings a unique perspective to this assessment. The scope of perianesthesia nursing practice involves the cultural, developmental, and age-specific assessment; diagnosis; intervention; and evaluation of patients within the perianesthesia continuum. The purpose of the perianesthesia assessment is to gather information necessary for the development of patient-specific interventions. The nursing assessment identifies risks for problems that can result from the administration of sedation/analgesia or anesthetic agents for surgical, diagnostic, or therapeutic procedures as well as the planned surgery/procedure.3 The perianesthesia nurse conducts the preoperative assessment and communicates essential information to the interdisciplinary health care team as appropriate. The collaboration between the perianesthesia nurse and other health care providers including the surgeon or proceduralist and anesthesia providers ensures a seamless perioperative process for the patient while also providing safe and efficient communication between health care providers. Standardized interdisciplinary communications are instrumental in the safe care of the patient.

There are several acceptable tools employed for standardizing communication at handoff. The SBAR tool—Situation, Background, Assessment, and Recommendations—is provided as an example. The SBAR handoff tool effectively structures communication between the anesthesia provider and the perianesthesia nurse (Box 27.1). Structured communication sets expectations for information to be shared during transitions of care and aids in improving communication and patient safety.

Box 27.1

The SBAR (Situation-Background-Assessment-Recommendation) technique provides a framework for communication among members of the health care team about a patient’s condition.

  •  S = Situation (a concise statement of the problem)
  •  B = Background (pertinent and brief information related to the situation)
  •  A = Assessment (analysis and considerations of options—what you found or think. What is your assessment of the situation?)
  •  R = Recommendation (action requested or recommended—specifically what you want)

From: Institute for Healthcare Improvement. SBAR Tool: Situation-Background-Assessment-Recommendation; Harding MM, Kwong J, Roberts D, et al. Lewis’s medical-surgical nursing: assessment and management of clinical problems. 11th ed. Elsevier; 2020; Ignatavicius DD, Workman ML, Rebar CR, Heimgartner NM. Medical-surgical nursing: concepts for interprofessional collaborative care. Elsevier; 2021.

Because many PACUs geographically include the preoperative holding area or share nursing staff with the preoperative holding area, the perianesthesia nurse often participates in the patient’s preoperative interview and assessment. A comprehensive preoperative nursing assessment includes relevant preoperative physical and psychosocial conditions, spiritual and cultural status, medical and surgical history (including anesthesia history), fasting duration, allergies, medication reconciliation, pain/comfort needs, providing education and ensuring understanding of the procedure and post procedure course, and the need for follow-up services. The preoperative physical assessment includes documentation of temperature, pulse, blood pressure, respirations, oxygen saturation, allergies, medication reconciliation, pain/comfort assessments, height, weight, and a review of systems. Nursing diagnoses are established on the analysis of data collected during the assessment phase and generation of an appropriate plan of care. The information obtained during the assessment should be documented within the patient’s health record and pertinent information should be communicated to the other health care providers as necessary. Preprocedure/preoperative patient teaching should be included in the assessment of all patients.

Admission observations

Physical assessment of the perianesthesia patient begins immediately upon admission to the PACU. The patient is accompanied from the procedure room to the PACU by the anesthesia provider or sedation nurse who provides handoff and a safe transfer of care to the perianesthesia nurse. The Joint Commission has attributed 80% of all medical errors to miscommunication between clinicians at the transfer of care.4 Best practices for handoff to the receiving nurse is standardized and includes information regarding the patient’s pertinent history and general condition, the procedure performed and any unexpected intraoperative events, the type of anesthesia or sedation administered, medications administered, fluid status, estimated blood loss, pain management plan, and plan for postoperative monitoring/location/discharge.

A description of the anesthesia type and medications administered is relayed to the perianesthesia nurse as many anesthetic agents depress respiratory and cardiovascular function (see Chapter 26). Careful assessment and monitoring is required to identify and manage any immediate postprocedural complications and ensure the patient’s return to normal homeostasis. For special precautions required for certain agents, review the chapters on anesthesia (see Chapters 1925).

Rapid assessment of the life-sustaining cardiorespiratory system is of initial concern. The perianesthesia nurse ensures that the airway is patent and that respirations are regular and unlabored; checks and records the patient’s blood pressure, pulse, rate of respiration, temperature, oxygen saturation, and ETCO2 level if applicable; and quickly inspects all dressings and drains for gross bleeding as well as any other surgery/procedure specific assessments. Baseline observations, which are made immediately on admission, should be relayed to the anesthesia or sedation provider in attendance and recorded in the admission note.

After initial observations are made, systematic assessment of the patient’s total condition is essential. Postoperative assessment can be made from head to toe or by a system review. Throughout the perioperative stay, ongoing assessment and documentation should include, but is not limited to, integration of the data received at the transfer of care, vital signs, pain/comfort assessment, intake and output, neuro assessment including neurovascular, sensory, and motor assessment; medication management; and safety needs and interventions.3

Respiratory function

As a result of the effect of anesthesia on the respiratory system, maintenance of adequate gas exchange is a crucial aspect of care in the PACU. Any change in respiratory function must be detected early so that appropriate measures can be taken to ensure adequate oxygenation and ventilation. The most significant respiratory problems encountered in the immediate postoperative period include hypoventilation, airway obstruction, aspiration, and atelectasis.

Respiratory assessment is coupled with the related responses of the cardiovascular and neurologic systems for total evaluation of the adequacy of gas exchange and ventilatory efficiency. Respiratory function is evaluated by using clinical assessment, monitor values, and laboratory data when pertinent. Pulse oximetry, a standard monitor, is used for assessment of Sao2 and correlates with the patient’s pulse. Capnography provides data for the evaluation of the adequacy of alveolar ventilation. Arterial blood gas measurements may be a part of the respiratory assessment (see Chapters 12, 29, and 30).

Clinical Assessment


The resting respiratory rate of a normal adult is approximately 12 to 20 beats/min. Infants and children have a higher respiratory rate and a lower tidal volume than adults (see Chapter 49). Respirations should be quiet and have a regular rate and rhythm. The chest should move freely as a unit, and expansion should be equal bilaterally. Alterations in symmetry can be caused by many factors, including pain that may cause splinting at the incision site, consolidation, and pneumothorax. Information of importance is the character of the respirations; intercostal retractions, bulging, nasal flaring, or use of the accessory respiratory muscles, which are signs of respiratory distress. The depth of respiration is as important as the rate. Shallow respirations are the cardinal sign of continuing depression from anesthesia or preoperative medications but can be caused by many other factors including incisional pain, obesity, tight binders, and dressings that restrict movements of the thoracic cage or abdomen. Shallow respirations and use of the neck and accessory muscles of respiration may also indicate residual neuromuscular blockade from the use of skeletal muscle relaxants, such as rocuronium, vecuronium, or cisatracurium. The presence of chest movements alone does not provide evidence that adequate gas exchange is occurring.

Airway obstruction is a blockage at any level of the airway and often occurs in the upper airway post anesthesia. Restlessness, confusion or anxiety, and apprehension are the earliest signs of hypoxemia and CO2 retention and require immediate attention for determination of cause. The patient’s color is regularly evaluated as a sign of adequate oxygenation and perfusion. Assessment of lips, inside of mouth, and nail beds provides important information about oxygenation of blood and may indirectly indicate a problem associated with respiratory or cardiovascular function.

Cyanosis is a late sign of severe tissue hypoxia, and, if it appears, immediate and vigorous efforts must be instituted to determine and correct the cause of hypoxia. The noninvasive monitors that are increasingly used in the PACU provide an effective means of continuous and objective assessment of gas exchange; pulse oximeters are used for monitoring hemoglobin oxygen saturation, and capnographs are used in evaluation of the adequacy of alveolar ventilation. A discussion of these monitors is forthcoming.

The presence of an artificial airway should be noted and documented; airways are used primarily to maintain a patent air passage so that respiratory exchange is not hampered. Five types of airways commonly used are: (1) the balloon-cuffed endotracheal tube (extends from the mouth through the glottis to a point above the bifurcation of the trachea); (2) the balloon-cuffed nasotracheal tube (extends from the nose to the trachea); (3) the supraglottic airway (examples include the laryngeal mask airway [LMA] or iGel) which comprises a tube component and a cuff/mask component inserted into the hypopharynx forming a low-pressure seal around the laryngeal inlet; (4) the oropharyngeal airway (extends from the mouth to the pharynx and displaces the tongue forward from the posterior pharyngeal wall preventing airway obstruction; and (5) the nasopharyngeal airway (extends from the nose to the pharynx).

The airway must be kept clear of secretions for adequate gas exchange to occur, and suctioning may be needed if secretions are excessive or if the patient is unable to manage their own secretions. The airway should not be removed until the laryngeal and pharyngeal reflexes return; these reflexes enable the patient to control the tongue, to cough, and to swallow. If the patient reacts to the airway by coughing or gagging, vomiting or aspiration may ensue. The airway should be removed as soon as clinically possible in this instance to avoid aspiration. The conscious or semiconscious patient will tolerate a nasal airway more readily than an oral airway; the oral airway carries inherently high risk for aspiration in the semiconscious or conscious patient due to elicitation of the gag reflex. The endotracheal tube or supraglottic can be removed as soon as the patient’s condition is adequately reversed, the patient can maintain an airway without the tube, and the risk for aspiration has subsided. Evaluation of readiness for removal of a supraglottic airway or endotracheal tube requires assessment of consciousness, return of reflexes, and return of neuromuscular function if applicable. If PACU policy permits removal of an airway, insertion of an airway should also be included, and both procedures should be accompanied by appropriate education, skill training, and competency.

Listening and Auscultation

First, the perianesthesia nurse should listen to the patient’s respirations. Normal respirations should be clear and heard bilaterally in the lungs. Noisy breathing may indicate a problem, including obstruction, secretions, stridor, or bronchospasm and should be assessed further. An accumulation of mucus or other secretions, evidenced by gurgling in any of the respiratory passages, can cause airway obstruction and should be removed immediately. Purposeful coughing with good expiratory airflow is the most effective method of clearing secretions. If the patient is not yet reactive enough to do this alone, the secretions may be suctioned orally and if appropriate, nasally as well. Obstruction can also occur from poor oropharyngeal muscle tone caused by residual neuromuscular blockade. Note that the absence of respiratory sounds should be addressed immediately.

Patients with OSA or central sleep apnea are prone to hypoventilation and airway obstruction and should not undergo extubation until they are fully awake. Tracheal extubation should be performed only when the patient is awake, exhibits the return of airway protective reflexes, and breathes spontaneously with adequate tidal volumes, oxygenation, and ventilation.2 To relieve airway obstruction, the chin lift or jaw thrust maneuver may be initiated by lifting the chin or providing anterior pressure support on the angle of the jaw to open the air passages.

Crowing, a sudden violent contraction of the vocal cords, may indicate laryngospasm and can result in complete or partial closure of the glottis. Other signs and symptoms of laryngospasm include inspiratory stridor, decreasing oxygen saturation, cyanosis, and respiratory obstruction. Total blockage of the airway caused by laryngospasm produces no sound because of the absence of moving air. Immediate recognition and treatment of laryngospasm is necessary as complete closure of the airway can be fatal. Treatment of laryngospasm includes firm and vigorous mobilization of the jaw backward, with aggressive pressure on the temporomandibular joint. At the same time, 100% oxygen and positive pressure via bag-valve-mask should be applied. If positive pressure and jaw thrust are not successful, succinylcholine 0.1mg/kg intravenously (IV) must be administered. Succinylcholine may be administered intramuscularly if a patent IV catheter is not available. Reintubation following administration of succinylcholine may be necessary.

If laryngospasm is untreated or prolonged, clinical manifestations of hypoxia will ensue including bradycardia. The perianesthesia nurse should prepare to administer atropine in the event of bradycardia secondary to hypoxia. Once laryngospasm has been successfully treated, evaluation and removal of causes is critical to prevent subsequent laryngospasm. Common causes of laryngospasm include secretions, blood in the airway, and decreased level of consciousness. Equipment and medications for management of a difficult airway should be readily available in the PACU.

Wheezing may indicate bronchospasm caused by a reflex reaction to an irritating mechanism. Bronchospasm occurs most often in patients with preexisting pulmonary disease, such as severe emphysema, reactive airway disease, pulmonary fibrosis, and radiation pneumonitis. Laryngeal edema after endotracheal intubation is not uncommon and can contribute significantly to airway obstruction. Wheezing coexistent with hives, tachycardia, and hypotension alert the nurse to a possible rare allergic reaction.

The perianesthesia nurse should auscultate the patient’s chest with a stethoscope for quality and intensity of breath sounds. Any abnormality should be identified and described in the patient’s medical record. Total absence of breath sounds on one side may signal the presence of pneumothorax (collapsed lung), obstruction, or fluid or blood within the pleural space. Auscultation of breath sounds in the PACU is often difficult because the patient usually cannot sit up or may not respond to commands to breathe deeply. Positioning the patient on alternating sides during assessment provides an opportunity for examination of the posterior lung field.


Palpation and inspection of the chest can be performed simultaneously for validation of observations such as symmetry of expansion. Crepitus and fremitus may be felt and heard. The temperature, the level of moisture and general turgor of the skin, and the presence of any edema should be noted.


The normal sound over the lungs is resonance. Dullness heard where normally resonance should be heard indicates consolidation or filling of the alveolar or pleural spaces by fluid.

Monitoring of Oxygenation with Pulse Oximetry

A pulse oximeter is used for noninvasive measurement of Sao2 in the blood (SpO2 when measured with pulse oximetry) and is a valuable adjunct to the clinical assessment of oxygenation. Many clinical indicators, such as the patient’s color and the characteristics of the respirations are subjective, and the physical signs of cyanosis are not evident until hypoxia is severe. Pulse oximetry monitoring is objective and continuous, providing data regarding development of hypoxemia. An early warning of developing hypoxemia allows intervention before severe signs of hypoxia appear. Consequently, pulse oximetry is the standard of care for PACU monitoring and patient management. As a confirmation of the importance of pulse oximetry, the American Society of PeriAnesthesia Nurses (ASPAN) 2021–2022 PeriAnesthesia Nursing Standards, Practice Recommendations and Interpretive Statements recommends evaluation of all PACU patients with pulse oximetry at admission, ongoing, and at discharge, and ASPAN recommends a pulse oximeter for every patient in all phases of perianesthesia nursing levels of care.3

A pulse oximeter technology consists of an electronic processor and a pair of small light-emitting diodes (LEDs) facing a photodiode through a translucent part of the patient’s body, usually a fingertip or an earlobe. In addition to an SpO2 display, most oximeters display the pulse rate and have an adjustable alarm system that sounds when values register outside a designated range. A variety of sensors are available in varying sizes and for specific anatomic application. The most common application site is a finger or toe (hand or foot in neonates); other sites include the nose, forehead, earlobe, or temple. Both reusable sensors and disposable adhesive sensors are available, and disposable sensors allow for patient-dedicated monitoring when infection control concerns are present.

Technology Overview

A pulse oximeter uses plethysmography for detection of the arterial pulse and spectrophotometry for determination of SpO2. The pulse oximetry sensor incorporates a red and an infrared LED as light sources and a photodiode as a light detector. In the most common type of sensor—a transmission sensor—the light sources and detector are positioned on opposite sides of an arterial bed such as around the finger. In a reflectance oximetry sensor, they are positioned on the same surface such as on the forehead.

With both transmission and reflectance sensors, red and infrared light passes into the tissue, and the detector measures the amount of light absorbed. Because oxyhemoglobin and deoxygenated hemoglobin differ in the absorption of red and infrared light, the detector can determine the percentage of oxyhemoglobin in the arterial pulse.

Pulse oximetry applications

Pulse oximetry is used in many clinical settings for safety monitoring and as a patient management tool. As a safety monitor, a pulse oximeter detects hypoxemia caused by unanticipated events such as severe atelectasis, bronchospasm, airway displacement, disconnections or kinks in the breathing circuit, and cardiac arrest. As a patient management tool, pulse oximetry is valuable in titrating oxygen therapy, weaning a patient from mechanical ventilation, and evaluating response to medications or other interventions intended for improvement of oxygenation.

In addition to these broad applications, certain uses of pulse oximetry are of particular value in the PACU. For example, patients after surgery can become significantly hypoxemic during transport to or from the PACU. Pulse oximetry during transport can be used to diagnose undetected hypoxemia and to identify a need for supplemental oxygen and more advanced airway management. Some patients in the PACU judged to be stable and ready for transfer on the basis of clinical evaluation alone have been found to be hypoxemic after evaluation with pulse oximetry.3 As indicated by the 2021–2022 ASPAN Standards, pulse oximetry is a valuable adjunct to clinical assessments in determination of readiness for PACU discharge.3

Interpretation of pulse oximetry measurements

Consideration of the mechanisms of oxygen transport is essential for adequate interpretation of SpO2. Approximately 98% of the oxygen in blood is bound to hemoglobin; Sao2 and SpO2 reflect this blood oxygen. The remaining blood oxygen is dissolved in plasma; blood gas analysis measures the partial pressure exerted by this oxygen dissolved in plasma (PaO2 = 80–100 mm Hg at sea level). The dissolved oxygen is used to meet immediate metabolic needs. The oxygen bound to hemoglobin serves as the reservoir that replenishes the pool of dissolved oxygen (see Chapter 12).

The rate at which oxygen binds to hemoglobin is primarily controlled by two factors: the PaO2 and the affinity of hemoglobin for oxygen. This relationship between PaO2 and Sao2 is represented by the oxyhemoglobin dissociation curve. The curve is sigmoid in shape, and its position is affected by a number of physiologic variables that change the affinity of hemoglobin for oxygen, including carbon dioxide concentration, pH, temperature, and the concentration of 2,3-diphosphoglycerate (Fig. 27.1).

Graph plots P sub C O 2 on the vertical axis against time on the horizontal axis. The curve has sigmoid shape. The curve again slopes down after forming the sigmoid shape with its three regions marked 1 through 3 (in Roman Numerals). The curve from the starting point to the end point is marked expiration. The lag and exponential phase are marked V sub app O S plus V sub ana D S. The complete curve from starting to end is marked P sub a c o 2. A leftward arrow labeled E T sub C O 2 points toward the end of sigmoid shape. The distance between P sub a C O 2 and E T sub C O 2 is marked V sub a V D S. All data are approximate.

Graph plots P sub C O 2 on the vertical axis against time on the horizontal axis. The curve has sigmoid shape. The curve again slopes down after forming the sigmoid shape with its three regions marked 1 through 3 (in Roman Numerals). The curve from the starting point to the end point is marked expiration. The lag and exponential phase are marked V sub app O S plus V sub ana D S. The complete curve from starting to end is marked P sub a c o 2. A leftward arrow labeled E T sub C O 2 points toward the end of sigmoid shape. The distance between P sub a C O 2 and E T sub C O 2 is marked V sub a V D S. All data are approximate.

Fig. 27.1 Normal capnogram. (From Pardo M, Miller R. Basics of Anesthesia. 7th ed. Philadelphia, PA: Churchill Livingstone; 2018, Chapter 20, Fig. 20.9.)

Many factors that shift the oxyhemoglobin dissociation curve are commonly seen in patients in the PACU. For example, a patient with hypothermia may have a left-shifted curve, thereby leading to hemoglobin binding more tightly to oxygen. In such a patient, a given SpO2 as measured with pulse oximetry may correspond to a lower-than-normal PaO2. Although oxygen saturation may be adequate, hemoglobin has a greater affinity for oxygen and is less willing to release oxygen to meet tissue needs. Warming the patient to a normothermic range facilitates oxygen unloading from the hemoglobin molecule and helps maintain adequate tissue oxygenation.

Clinical issues

As with any technology, important clinical issues must be considered for appropriate use of pulse oximetry. Shifts in the oxyhemoglobin dissociation curve caused by abnormal values of pH, temperature, partial pressure of carbon dioxide (Pco2), and 2,3-diphosphoglycerate must be considered. Consideration of the patient’s hemoglobin level is also important as pulse oximetry cannot detect depletion in the total amount of hemoglobin. When pulse oximetry is used on a postoperative patient with a low hemoglobin level, a high SpO2 value might not reflect adequate oxygenation. The amount of hemoglobin, although it is well saturated with oxygen, may be inadequate to meet tissue needs because fewer carriers are available to transport oxygen.

Adequate oxygenation is a factor of not only adequate oxygen saturation and hemoglobin values but also of adequate oxygen delivery, which necessitates appropriate CO and the ability of the tissues to effectively use oxygen. Tissue hypoxia results when oxygen demand exceeds oxygen supply. Pulse oximetry readings therefore should be assessed in conjunction with all other indices of oxygenation.

Dysfunctional hemoglobin, a variant of the hemoglobin molecule unable to transport oxygen, presents a similar problem. Despite the high SpO2 level, hemoglobin may be insufficient to carry oxygen. Carboxyhemoglobin is hemoglobin that is bound with carbon monoxide and therefore is unavailable for carrying oxygen. Its effect must be considered in patients with burns or in tobacco smokers with carbon monoxide poisoning. In methemoglobinemia, the iron molecule on the hemoglobin is oxidized from the ferrous to the ferric state. This form of iron is unable to transport oxygen. Methemoglobinemia, although rare, can occur in patients who receive nitrate-based and other drugs and in those who are exposed to a variety of toxins. When dysfunctional hemoglobins are suspected, assessment of oxygenation with pulse oximetry must be supplemented with arterial blood gas saturations measured with a laboratory co-oximeter to determine whether dyshemoglobins are present and oxygenation is adequate.

Perfusion at the sensor application site must be sufficient for the pulse oximeter to detect pulsatile flow, which is an important consideration for some patients in the PACU such as those treated with vasoconstrictors, those with marked hypothermia, and those with significantly reduced CO. A well-perfused site should be selected for application of the sensor. If in doubt, the pulse and adjacent capillary refill can be checked.

If the monitor cannot detect the pulse, the patient first is evaluated for adverse physiologic changes. Next, the perianesthesia nurse should ensure that blood flow is not restricted such as by a flexed extremity, a blood pressure cuff, an arterial line, any restraints, or a sensor applied too tightly. Local perfusion to the sensor site can be improved by covering the site with a warm towel or with the use of a forced air warming device. Certain sensors, such as nasal sensors, are designed for application to areas where perfusion is preserved even when peripheral perfusion is relatively poor. Finally, some pulse oximeters use an electrocardiographic signal as an aid in identification of the pulse, thus enhancing the instrument’s ability to detect a weak pulse.

Patient movement can produce false signals that interfere with the ability of the pulse oximeters to identify the true pulse, thus leading to unreliable SpO2 and pulse rate readings. The sensor should be properly and securely applied; a sensor that is loosely attached or incorrectly positioned can magnify the effect of motion. If the problem persists, consideration should be given to moving the sensor to a less active site. Pulse oximeters that use the electrocardiographic signal as an aid in identification of the pulse can have an enhanced ability to distinguish between the true pulse and artifacts produced by motion. The result is more reliable SpO2 readings.

Normally, venous blood is nonpulsatile and is not detected with a pulse oximeter. In the presence of venous pulsations, the SpO2 value provided by the pulse oximeter may be a composite of both arterial and venous saturations. Venous pulsations can occur in patients with severe right-sided heart failure or other pathophysiologic states that create venous congestion and in patients receiving high levels of positive end-expiratory pressure. They can also occur when the sensor is placed distal to a blood pressure cuff or occlusive dressing and when additional tape is wrapped tightly around the sensor. When venous pulsations are present, the perianesthesia nurse should take care in interpreting the SpO2 readings and, if possible, attempt to eliminate the cause.

Because pulse oximeters are optical measuring devices, the perianesthesia nurse must be aware of additional factors that can influence the reliability of SpO2 readings. To ensure good light reception, the sensor’s light sources and detector must always be positioned according to the manufacturer’s specifications. In the presence of bright lights, such as infrared warming devices, fluorescent lights, direct sunlight, and surgical lights, the sensor must be covered with an opaque material to prevent incorrect SpO2 readings. In addition, agents that significantly change the optical-absorbing properties of blood, such as recently administered intravascular dyes, can interfere with reliable SpO2 measurements. The use of pulse oximetry with certain nail polishes, especially those that are black, blue, green, and reddish-brown in color, can result in inaccurate readings. If nail polish in these shades cannot be removed, the sensor should be applied to an alternate unpolished site.

Monitoring of Ventilation with Capnography

Monitoring of ETCO2 in respiratory gases provides an early warning of physiologic and mechanical events that interfere with normal ventilation. Capnography, which measures ETCO2 at the patient’s airway, is increasingly used in the PACU. The ASPAN 2021–2022 PeriAnesthesia Nursing Standards, Practice Recommendations and Interpretive Statements recommends the use of ETCO2 if indicated and available.3 Capnography allows continuous assessment of the adequacy of alveolar ventilation, cardiopulmonary function, ventilator function, and the integrity of the airway and the breathing circuit. Consequently, it enables early detection of many potentially catastrophic events including the onset of malignant hyperthermia, esophageal intubation, hypoventilation, partial or complete airway obstruction, breathing circuit leaks or disconnections, a large pulmonary embolus, and cardiac arrest.

Two variants of the instrument are available. A capnometer provides numeric measurement of exhaled CO2 levels. A capnograph provides the same numeric information, and it also displays a CO2 waveform. Both types of instruments usually incorporate an adjustable alarm system and often have trending and printing capabilities. The following discussion focuses on the use of capnographs because they allow more complete and effective patient assessment than do capnometers. As discussed subsequently, changes in the shape of the CO2 waveform can provide crucial diagnostic information about ventilation, similar to the way in which the waveform provided with an ECG can provide crucial diagnostic information about the heart.

Technology Overview

For measurement of exhaled CO2, the most common type of capnograph passes infrared light at a wavelength that is absorbed by CO2 through a sample of the patient’s respiratory gas. The amount of light absorbed by the patient’s gas reflects the amount of CO2 in the sample.

Capnographs differ in the manner in which they obtain respiratory gas samples for analysis. Sidestream (or diverting) capnographs transport the sample through narrow-gauge tubing to a measuring chamber. Mainstream (or nondiverting) capnographs position a flow-through measurement chamber directly on the patient’s airway. Special adapters are available to allow sidestream capnographs to be used on patients who are not intubated. The sample adapter should be placed as close to the patient’s airway as possible.

Sidestream capnographs incorporate moisture-control features that are designed to minimize clogging of the sample tube, protect the measurement chamber from moisture-induced damage, and minimize the risk of cross-contamination. The design of these moisture-control systems significantly affects a monitor’s ease of use. Most systems rely on water traps, which must be emptied routinely. A new technology uses a special system of filters and tubing to dehumidify the sample and thus eliminate the need for water traps.

Capnographs also differ in calibration requirements. Many require removal of the patient from the respiratory circuit and adjustment of the instrument with special mixtures of calibration gases. Advanced capnographic technology includes automatic calibration and does not require any user calibration skills or time.

The normal capnogram

For effective use of capnography, it is important to understand the components of the normal CO2 waveform (capnogram)—a square-wave pattern with a plateau (Fig. 27.2). Early in exhalation, air from the anatomic dead space, which is virtually CO2 free, is measured with the instrument. As exhalation continues, alveolar gas reaches the sampling site, and the CO2 level increases rapidly. The CO2 concentration continues to increase throughout exhalation and reaches the alveolar plateau because alveolar gas dominates the sample. At the end of exhalation, the ETCO2 occurs, which in the normal lung is the best approximation of alveolar CO2 levels. The CO2 concentration then drops rapidly as the next inhalation of CO2-free gas begins.

Graph plots oxyhemoglobin saturation in percent ranging from 0 through 100, in increments of 10, on the vertical axis against O sub 2 partial pressure (millimeters of mercury) ranging from 0 through 100, in increments of 10, on the horizontal axis. A concave downward increasing curve marked arterial curve starts at (0, 0) and ends at (100, 96). Another concave downward increasing curve marked venous curve starts at the same point as that of the first curve, runs below the first curve, and ends at the same point as that of the first curve. A point on the second curve (42, 73) is marked venous point (P sub O 2 approximately equals 40 millimeters of mercury). A dashed vertical line connects horizontal axis at 27 to the first curve and a dashed horizontal line at 50 to the first curve. P sub 50 equals 26.8 millimeters of mercury. All data are approximate.

Graph plots oxyhemoglobin saturation in percent ranging from 0 through 100, in increments of 10, on the vertical axis against O sub 2 partial pressure (millimeters of mercury) ranging from 0 through 100, in increments of 10, on the horizontal axis. A concave downward increasing curve marked arterial curve starts at (0, 0) and ends at (100, 96). Another concave downward increasing curve marked venous curve starts at the same point as that of the first curve, runs below the first curve, and ends at the same point as that of the first curve. A point on the second curve (42, 73) is marked venous point (P sub O 2 approximately equals 40 millimeters of mercury). A dashed vertical line connects horizontal axis at 27 to the first curve and a dashed horizontal line at 50 to the first curve. P sub 50 equals 26.8 millimeters of mercury. All data are approximate.

Fig. 27.2 Normal oxyhemoglobin dissociation curve. (From Pardo M, Miller R. Basics of Anesthesia. 7th ed. Philadelphia, PA: Churchill Livingstone; 2018, Chapter 5, Fig. 5.5.)

End-tidal versus arterial carbon dioxide

In normal conditions, when ventilation and perfusion are well matched, ETCO2 closely approximates arterial CO2 (PaCO2). The difference between the PaCO2 and the ETCO2 level is the alveolar-arterial CO2 difference (a-ADCO2). ETCO2 is usually as much as 5 mm Hg lower than PaCO2. When the two measurements differ significantly, an anomaly in the patient’s physiology, breathing circuit, or capnograph is usually present. Significant divergence between ETCO2 and PaCO2 is often attributable to increased alveolar dead space. CO2-free gas from nonperfused alveoli mixes with gas from perfused regions, thus decreasing the ETCO2 measurement. Clinical conditions that cause increased dead space, such as pulmonary hypoperfusion, cardiac arrest, and embolic conditions (e.g., air, fat thrombus, amniotic fluid), can increase the a-ADCO2. Changes in the a-ADCO2 can be used in assessing the efficacy of the treatment; as the patient’s dead space improves, the partial pressure of the alveolar carbon dioxide minus the partial pressure of arterial carbon dioxide (PACO2 – PaCO2) narrows. Increases in dead space ventilation lower ETCO2 and therefore increase the PaCO2 – ETCO2 gradient. Widened PaCO2 – ETCO2 examples include embolic phenomena, hypoperfusion, and chronic obstructive pulmonary disease. Alternatively, a significant PACO2 – PaCO2 value can indicate incomplete alveolar emptying (e.g., with reactive airway disease), a leak in the gas-sampling system that allows loss of respiratory gas, and contamination of respiratory gas with fresh gas.5

Interpretation of changes in the capnogram

An abnormal capnogram provides an initial warning of many events that warrant immediate intervention. Abnormalities may be seen on a breath-by-breath basis or when the CO2 trend is examined. For this reason, visualization of both the real-time waveform and the CO2 trend on the monitor display is required. The following examples examine changes in ETCO2 produced by significant events that commonly occur in the PACU.

A sudden decrease in ETCO2 to a near-zero level indicates that the monitor is no longer detecting CO2 in exhaled gases (Fig. 27.3D). Immediate action is crucial for detection and correction of the cause of this loss of ventilation. Possible causes include a completely blocked endotracheal tube, esophageal intubation, a disconnected or kinked breathing circuit, and inadvertent extubation. The latter three possibilities are particularly likely if the decrease in ETCO2 coincides with movement of the patient’s head. First, after elimination of possible clinical causes for this decrease in ETCO2, a clogged sampling tube or instrument malfunction is investigated as the cause of the problem. Evaluation of the patient, including auscultation of breath sounds, should always precede an evaluation of equipment.

"Four capnography illustrations are marked A through C. A) Three inverted U-shaped troughs are formed with constant E T sub C O 2 and P sub a C O 2. B) Three inverted V-shaped troughs are formed with constant E T sub C O 2 and P sub a C O 2. C) Three inverted U-shaped troughs are formed with increasing E T sub C O 2 and P sub a C O 2. Second and third trough are not touching the horizontal axis. D) Three inverted U-shaped troughs of unequal sizes are formed with decreasing E T sub C O 2 and increasing P sub a C O 2.

“Four capnography illustrations are marked A through C. A) Three inverted U-shaped troughs are formed with constant E T sub C O 2 and P sub a C O 2. B) Three inverted V-shaped troughs are formed with constant E T sub C O 2 and P sub a C O 2. C) Three inverted U-shaped troughs are formed with increasing E T sub C O 2 and P sub a C O 2. Second and third trough are not touching the horizontal axis. D) Three inverted U-shaped troughs of unequal sizes are formed with decreasing E T sub C O 2 and increasing P sub a C O 2.

Fig. 27.3 Capnogram abnormalities. (A) The normal Paco2 to ETco2 gradient is 2 to 5 mm Hg. (B) This rightward slant of the initiation of the alveolar gas detection is seen when there is the presence of asthma or chronic obstructive pulmonary disease. The greater the slant to the right, the worse the expiratory airway resistance. The gradient of Paco2 to ETco2 has increased. (C) This waveform shows a progressive rise in the baseline CO2 value; that is, there is a progressive increase in inspiratory carbon dioxide, noting a CO2 rebreathing most commonly due to an exhausted CO2 absorber. (D) This waveform signifies a progressive drop in the ETco2, that is, a decrease in the height of the waveform. This form is noted whenever there is abrupt reduction in pulmonary blood flow (cardiac output), as occurs with a pulmonary embolism or a cardiac arrest. ETco2, End-tidal carbon dioxide. (From Pardo M, Miller R. Basics of Anesthesia. 7th ed. Philadelphia, PA: Churchill Livingstone; 2018, Chapter 20, Fig. 20.10A–D.)

An exponential decrease in ETCO2 over a small number of breaths usually signals a life-threatening cardiopulmonary event that has dramatically increased dead space ventilation (Fig. 27.3D). Sudden hypotension, pulmonary embolism, and circulatory arrest with continued ventilation must be considered.

A gradual increase in the ETCO2 level while the capnogram retains its normal shape usually indicates that ventilation is inadequate to eliminate the CO2 that is produced. This situation can be the result of a small ventilator leak or a partial airway obstruction that reduces minute ventilation. It can also reflect increased CO2 production associated with increased body temperature, the onset of sepsis, or shivering. Of particular importance, a large increase in ETCO2, resistant to an increase in minute ventilation, can be one of the earliest signs of malignant hyperthermia, which may not begin until after emergence from anesthesia.

A gradual decrease in the ETCO2 level commonly occurs in the patient who is anesthetized, narcotized, hyperventilated, or hypothermic. Assessment of the capnogram can reveal information about the quality of alveolar emptying. For example, the patient with bronchospasm is unable to completely empty the alveoli, and the resulting capnogram does not have an alveolar plateau (Fig. 27.3B). The ETCO2 reported by the capnograph in this instance is not a good estimate of alveolar CO2. Effective administration of bronchodilator therapy commonly improves alveolar emptying and results in a more normal capnogram.

Clinical issues

In addition to the diagnostic usefulness of changes in the capnogram, some specific applications of capnography are particularly valuable in the PACU. Of primary importance is its ability to provide early warning of hypoventilation that, in the PACU, may be the result of anesthesia, sedation, analgesia, or pain. A falling ETCO2 value may indicate pulmonary hypoperfusion from blood loss or hypotension. During rewarming, ETCO2 values are likely to increase as metabolic activity increases.

Capnography can signal when shivering produces an unacceptable increase in oxygen consumption and metabolic rate. During ventilator weaning, capnography is valuable in assessing adequacy of ventilation. ETCO2 measurements, which decrease during cardiac arrest, typically reach approximately 50% of normal levels during effective cardiopulmonary resuscitation (CPR). Capnography has been shown to demonstrate efficacy of CPR, specifically a level of >20 mm Hg which indicates that compressions are generating perfusion.6 When spontaneous circulation is restored, ETCO2 values increase dramatically. The presence and persistence of normal ETCO2 values are also useful determinants in confirming tracheal intubation because persistent CO2 is not found in the esophagus. However, capnography cannot be substituted for chest auscultation and radiography in elimination of the possibility of bronchial intubation.

Importantly in the PACU, capnography can provide critical information about the patient’s ventilatory status, including an early warning of apnea that results in overall patient safety.2,7 Deterioration of a patient is discernible 2 to 3 minutes earlier in a patient with an ETCO2 reading than with oxygen saturation. Therefore, capnography is a helpful assessment for patients who are extremely sedated, who require high doses of opioids, or who have OSA.2,7,8 See EBP Box.

Evidence-Based Practice3,21,22,23

Capnography in Acute Care Settings

The prevalence of OSA is substantial in North America. Postoperative patients with OSA are at risk for respiratory complications, although approximately 60% of surgical patients with this condition go undiagnosed.21 Evidence demonstrates the utility of capnography in acute care settings, particularly to mitigate and prevent acute postoperative respiratory events related to hypoventilation and OSA.22 The 2019 American Society for Pain Management Nursing (ASPMN) Guidelines validate that sufficient evidence exists identifying capnography as an effective method to monitor for respiratory compromise and highlight that capnography is more sensitive in identifying respiratory compromise than intermittent pulse oximetry assessments.22 The ASPMN 2019 Guideline also recommends trend monitoring rather than threshold monitoring when assessing patient respiratory status.22 Noted revisions from the 2011 ASPMN guidelines on Monitoring for Opioid-Induced Advancing Sedation and Respiratory Depression include: (1) multiparameter nursing assessment, including respiratory rate and quality, pulse oximetry, and level of sedation before opioid and again at peak effect; (2) clinician reassessments comparing present patient data to previous data to assess change over time (trend monitoring); (3) the consideration for continuous electronic respiratory monitoring during the first 24 hours after surgery or initiation of parenteral opioid medications; and (4) patient-centric selection of type of electronic monitoring device.22

The ASPAN also recommends the use of technology-supported monitoring based on individual and iatrogenic risk factors.3 This recommendation suggests that capnography can be a useful indicator of respiratory depression in high-risk patients.3 The application of capnography in patients with OSA, respiratory disease, obesity, opioid use, and who have undergone major thoracic or abdominal surgery has been identified as appropriate use of this technology. Capnography may be instituted in patients who are intubated and connected noninvasively for patients receiving oxygen via nasal cannula or simple face mask.3

Implications for Practice

Perianesthesia patients are at increased risk for respiratory compromise secondary to the administration of anesthetic medications, including volatile anesthetics, sedatives, and opioids. Additionally, patient-specific comorbidities present increased risk for postoperative respiratory events, including OSA. The perianesthesia nurse uses multiple assessment strategies, including physical assessment and monitoring. The use of trend monitoring will highlight changes in patient status from baseline and warn perianesthesia nurses of impending events. Evidence has demonstrated an increase in perianesthesia nurses’ confidence and compliance with technology following the implementation of an evidence-based guideline recommending the application of capnography in the postoperative arena.23 In this study, pragmatic adoption of this new practice was due to comprehensive nurse education, familiarity with the monitoring process, and the nurses’ value for patient safety.

Perianesthesia nurses are well positioned to implement a patient-centric approach to the use of capnography in at-risk patients to reduce hypercarbic states and respiratory compromise.

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May 20, 2023 | Posted by in NURSING | Comments Off on Assessment and Monitoring of the Perianesthesia Patient
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