Chapter 17

Clinical Monitoring II

Respiratory and Metabolic Systems

“Every breath you take, every move you make…I’ll be watching you.”

(Sting, 1983)¹

The lyrics to the song, “Every Breath You Take” were written decades ago and refer to a stalking, obsession-based relationship and yet, when considered in an anesthesia monitoring context, they succinctly define the contract between the nurse anesthetist and the patient undergoing anesthesia care. Clinical monitoring in the perioperative setting is the process of observing physiologic responses to surgery and anesthesia. It is the essence of what the Certified Registered Nurse Anesthetist (CRNA) does to ensure an optimal, safe outcome.

It is important to note that the modalities chosen to obtain physiologic feedback may or may not lead to a reduction in patient morbidity and mortality.² Research provides rationale to support the standardization of minimal monitoring modalities. Standards are available to the anesthesia provider from both the American Association of Nurse Anesthetists (AANA) and the American Society of Anesthesiologists (ASA).^3,4 It is a matter of clinical judgment by the anesthetist that determines what modalities beyond those minimally required will provide useful information when added to the anesthetic plan of care. It is through this evidence-based approach that best practices are developed.

It is important to emphasize that despite advancements in technology, human vigilance must be maintained and considered primary in assessing patient responses to anesthesia. Human error is always possible and often associated with adverse outcomes. Monitoring alone cannot prevent adverse outcomes, but a timely response to warnings can have a positive impact.⁵ It cannot be emphasized enough that reliance on technology must never be allowed to lull the clinician into complacency. Although accuracy and reliability of monitors continue to improve, the potential for machine malfunction and artifact is ever present. Timely human response to intraoperative events remains the key to predicting, avoiding, and managing untoward responses to anesthesia and surgery. The basic human senses of sight, hearing, touch, and even smell remain the primary tools in clinical monitoring. The patient is the primary source of assessment data.

This chapter reviews current monitoring standards as outlined by the AANA. In addition, a practical systems approach to monitoring is presented as it relates to the avoidance of critical incidents. Respiratory monitoring is reviewed as it relates to the ongoing assessment of airway and breathing using not only the human senses but also technologic tools used by nurse anesthetists. The modalities to be discussed in this chapter include the precordial stethoscope, carbon dioxide detection devices, and pulse oximetry. Thermoregulation is significantly altered under anesthesia, so temperature monitoring modalities are reviewed in this chapter. Finally, implications for the education of nurse anesthetists and the future of clinical monitoring are visited.

Monitoring Standards

Monitoring standards are published and reviewed by anesthesia professional associations so that minimal standards in the provision and monitoring of care can be recommended. Such standards are intended to provide guidance to anesthesia providers and healthcare facilities in evaluating quality care and developing and improving the safety of practice while educating the public regarding patient rights and expectations. Standard V of the AANA Scope and Standards for Nurse Anesthesia Practice outlines specific monitoring requirements necessary for compliance (Table 17-1).⁴ The standards acknowledge the importance of vigilant monitoring as the basis of safety in anesthesia practice. In addition, the standards point out that the CRNA must constantly be in attendance of the patient until the responsibility for care can be safely transferred to another qualified healthcare provider. They further state that these are intended to be minimum requirements and should be exceeded as deemed necessary in the judgment of the anesthetist. In most cases, when certain monitoring modalities are not used, they must be at least immediately available. The AANA interpretation specifically indicates that alarm limit parameters and audible warning systems should be used, and a specific statement is made recommending the use of variable pitch alarms. The value of variable pitch commonly used in pulse oximetry equipment has been widely appreciated for its ability to provide information regarding subtle changes in oxygen saturation using the sense of hearing, prior to visualizing the monitor. Alarms are designed to protect the patient by alerting the practitioner that the individual is at increased risk and needs immediate assistance.

TABLE 17-1

Scope and Standards for Nurse Anesthesia Practice

Adapted from the American Association of Nurse Anesthetists. Scope and Standards for Nurse Anesthesia Practice; 2010. Available at http://www.aana.com.

An area of concern related to electronic monitoring devices is a phenomenon referred to as alarm fatigue. Alarm fatigue can be defined as a type of human error occurring when a practitioner is desensitized to alarms or alerts.5,6 The ideal alarm would be easy to localize and recognize. It would be evident despite other noises and alarms, yet would allow for effective communication between care providers. The ideal monitoring device would also elicit a minimal number of false alarms. Alarms in many medical devices fall short of the ideal and as a result are subject to being ignored or even disabled by the practitioner—a very dangerous practice. Biomedical specialists continue to develop and perfect alarms to improve their usefulness in alerting the clinician to significant changes in patient status.⁷

The ever changing and developing technologic capabilities warrant that these standards also allow for consideration of new monitoring modalities as they are introduced. It is important to note that the type of anesthetic given may influence the specific monitoring needed but should not be a factor in considering the level of vigilance or accessibility of advanced monitoring and interventional equipment.

Systematic Approach to Monitoring

A systematic, evidence-based process shown to be effective in reducing anesthetic morbidity and mortality should be the goal when planning appropriate monitoring to be used. As monitoring standards guide practice by prescribing minimums to be adhered to, other processes can be helpful in defining how monitoring should occur and which modalities should be used. In the spirit of learning from previous errors or untoward events, closed-claim studies can provide valuable insight into monitoring techniques and habits that could be useful in preventing future anesthesia mishaps. Incident monitoring systems and practices can be used to collect data for practitioners to use to develop safer processes as in the often referenced analogies made to the aviation industry.⁸ In a manner of speaking, clinical monitoring can be thought of as a means to avoid critical incidents.

The act of administering anesthesia results in a physiologic response to the pharmacodynamics and pharmacokinetics of each substance given. The insult of the surgical or diagnostic procedure performed also results in a physiologic response. As such, observation of the human systems response is the monitoring of the pharmacology of the agents used and the physiology of the human system. As the science and process for quality assurance and improvement have evolved, much has been learned and written about the value of a systematic approach to the analysis of critical incidents and crisis management. The concepts used in quality assurance management are therefore easily applied to anesthesia monitoring because a primary function of the nurse anesthetist is to prevent or respond to critical incidents. A systematic approach to clinical monitoring provides a means of ensuring timely responses to physiologic changes presented by the patient.

Many algorithms and protocols have been written to guide the practitioner through the monitoring process and ensure thorough, vigilant observation. Simple, systematic approaches to crisis management are often focused on or derived from the common algorithm “ABC,” representing airway, breathing, and circulation. In an anesthesia context, additional foci for monitoring can include color (i.e., cyanosis), oxygen and oxygen analyzers, ventilation, vaporizer or pump settings and status, endotracheal tube patency and placement, monitors and equipment, and drug effects, thereby expanding the crises response algorithm to COVERABCD (Table 17-2).⁹ There is an enormous value in developing a systematic approach to monitoring. The habit sometimes referred to as “sweeping” the anesthesia field to visualize the patient, with the eyes following a path to the anesthesia machine via the airway and breathing circuit and progressing to the monitoring modalities used, has long been taught as a means of increasing vigilance and attention to detail.

TABLE 17-2

Crisis Management Algorithm

Algorithm	Descriptor
C—Circulation, Color	Determine adequacy of circulation, check pulse, blood pressure; ECG notes oxygenation through assessment and oximetry
O—Oxygen, Oxygen analyzer	Check oxygen delivery system, hypoxic guard
V—Ventilation, Vaporizer	Ventilate by hand to assess breathing circuit and airway patency, assess chest excursion and auscultation; assess ETco₂; check vaporizer function
E—Endotracheal tube	Systematic assessment of ETT if used, including patency, seal, etc
R—Review monitors, Review equipment	Review all monitors in use, assure appropriate calibration and maintenance, review any and all equipment in contact with the patient
A—Airway	Check patency of the unintubated airway, assess for laryngospasm, foreign body, etc
B—Breathing	Assess pattern, rate, and depth of respirations; examine, auscultate, and review ETco₂ and pulse oximeter monitors
C—Circulation	Repeat assessment of circulation
D—Drugs	Review drugs given; consider needed pharmacologic intervention; consider possibility of medication administration error

ECG, Electrocardiogram; ETco₂, end-tidal carbon dioxide concentration; ETT, endotracheal tube.

Adapted from Runciman WB, Merry AF. Crises in clinical care: an approach to management. Qual Safe Health Care. 2005; 14(3):156-163.

Review of critical incidents has provided insight into how clinicians can enhance safety and prevent mishaps through their use of monitors with alarms. Closed-claims review of various databases supports the notion that vigilance remains a key point, and respiratory events are of particular concern.¹⁰ It has been suggested that in cases in which anesthesia is provided outside of the operating room, (e.g., a rapidly growing practice in which monitoring may not be as focused as in a standard anesthetizing area), the number and severity of liability claims may be increased.¹¹ The well known mantra of the ABCs—observing the Airway, Breathing (respiration), and Circulation—remains foremost and critical in anesthesia clinical monitoring. Monitoring drug effects completes the basic monitoring approach. The monitoring of cardiovascular circulation is addressed in Chapter 16. The monitoring of the neurologic system can be found in Chapter 18.

The means to measure CO₂ level must be based on the patient’s condition, the type of anesthetic administered, and the complexity of the surgical procedure. The continuous measurement of carbon dioxide in expired gas provides a practical, noninvasive, and accurate reflection of arterial blood carbon dioxide and is the most common means of monitoring carbon dioxide levels in the anesthesia setting. It is also a monitoring standard of care during general anesthesia, for the patient being ventilated or whose ventilations are being assisted. In addition, the ASA monitoring standards state that “during moderate or deep sedation the adequacy of ventilation shall be evaluated by continual observation of qualitative clinical signs and monitoring for the presence of exhaled carbon dioxide unless precluded or invalidated by the nature of the patient, procedure, or equipment.”³ Accuracy of ETco₂ as a correlation with arterial carbon dioxide has been well documented. End-tidal CO₂ is said to be approximately 2 to 5 torr lower than arterial CO₂ in patients who have no cardiac or pulmonary abnormalities.¹⁴ Capnometry is a term that encompasses all means of measuring carbon dioxide, whereas capnography refers to the recording of the measurement. The term capnogram is used to describe a continuous display of carbon dioxide during the phases of ventilation. The continuous measurement of ETco₂ is accomplished through the use of infrared analysis. When a gas mixture containing more than one substance, (e.g., an exhaled gas sample) is analyzed, a quantitative measurement can be made to determine the proportional contents. Each gas in the mixture absorbs infrared radiation at a different wavelength. The amount of CO₂ is measured by detecting its absorbance at specific wavelengths and filtering the absorbance related to other component gases. Older monitors had difficulty distinguishing between nitrous oxide and CO₂, but this fault is corrected in current models.¹²

Sampling of ETco₂ can be accomplished through either a nondiverting (also known as mainstream) or diverting (also known as sidestream) monitor. A nondiverting monitor measures gas directly within the breathing system. Gas passes through a wide-chambered sensor that fits over a connector between the anesthesia circuit and mask adapter. The sensor is connected to the monitor by a cable. Nondiverting monitors offer several advantages. They have minimal sampling-time delays, use few disposable items, and do not require scavenging because gas is not removed from the system. Disadvantages include the inability to measure gases other than CO₂ and nitrous oxide, an increase in circuit deadspace by the adapter, and greater risk of interference by condensation and secretions. Also, because the sensor and cable are attached in proximity to the patient, the added weight may cause traction on the tube, increase the risk of circuit disconnect, and make sampling in a nonintubated patient difficult.

The other more commonly used CO₂ monitor type is the diverting monitor. The diverting monitor extracts gas from sample tubing attached near the patient end of the circuit and pumps it to the monitor. Disadvantages include the need for scavenging of sampled gases because they are removed from the circuit and some risk of contamination by condensation or secretions exists. Advantages of the diverting system include minimal increase in deadspace and versatility in gas analysis because the sample can also be sent to anesthetic agent monitors. In addition, the small, lightweight tubing can be adapted to sample awake, spontaneously breathing patients through the mouth, nares, or simple mask.¹⁴

It has become common to adapt the sampling line of a diverting ETco₂ monitor to trace a capnogram in awake or sedated, spontaneously breathing patients receiving O₂ via simple mask or nasal cannula. Nasal cannula tubing already equipped with a sampling line is commercially available. It has been shown that sampling ETco₂ in the spontaneously breathing patient’s hypopharynx is reliable and accurate and that the exact position and use of supplemental O₂ flow will not affect reliability.¹⁵ The use of ETco₂ monitoring as a warning of hypoventilation or excess sedation has gained attention outside of the anesthesia setting. For example, ETco₂ monitoring has been shown to be a more sensitive indicator of hypoventilation than clinical observation or pulse oximetry when used during sedation in the emergency department setting.¹⁶ Other studies note the value of ETco₂ monitoring during sedation as well and note the advantage over pulse oximetry alone in detecting hypoventilation in patients receiving supplemental O₂. It has been suggested that like pulse oximetry, ETco₂ monitoring should be considered a standard of care for patients receiving sedation outside the operating room.¹⁷

End-Tidal Carbon Dioxide Capnography

Capnography can record CO₂ as a component of expired lung volume or as a measure of CO₂ alone throughout the phases of respiration plotted against time. Time capnography is most commonly used in the perioperative setting. Basic interpretation of the ETco₂ capnogram is a necessary skill. The capnogram can differentiate between normal and abnormal patterns of ventilation that result from patient pathologies, anesthesia system problems, or unexpected patient responses during anesthesia.

The normal time capnogram can be recorded at varying speeds. A fast speed setting of approximately 12.5 mm/second allows interpretation of individual respiratory components and short-term changes, whereas a slow speed of approximately 25 mm/minute displays long-term changes.¹⁸ Although no standard descriptions exist for the components of the capnogram, it is typically described as encompassing four basic phases (Figure 17-1). These phases are often displayed in a classic waveform shape best recorded during mechanical ventilation in an intubated patient. It is important to note that the basic shape of the wave form will vary depending on the mode of airway management used (endotracheal tube, laryngeal mask airway, simple mask, nasal cannula, etc.) as well as in comparison to the spontaneously breathing patient.