Resuscitate Your Anesthesia Monitoring: Don’t Let Poor Patient Monitoring Flatline Your Practice

by Jennifer Sager, BS, CVT, VTS (Anesthesia/Analgesia, ECC)

My first foray into veterinary anesthesia monitoring was standing in the corner of the operating room while my doctor asked me to turn the “blue knob” to a certain level, the “green knob” to another level, and “listen through this stethoscope to see if there is a heartbeat.” I was young and inexperienced, and we boasted that nothing ever died on our watch.

Knowing what I know now through education, my technician certification, specialty training in anesthesia/analgesia, and 20 years of experience, I am mortified that the bar was set so low. Should we, as patient advocates, base our success on the lack of “apparent” patient complications? Certainly not.

Tailoring anesthetic plans to each patient is crucial to the quality of care we are providing to our clients and patients. This quality of care should be defined by the structure, process, and outcome of our practice, not by the old adage “No one has died yet, so I must not have a problem.”

Understanding the concept of veterinary anesthesia can be daunting, as it is constantly evolving with advances in medicine. However, anesthesia patient monitoring is practical, attainable, and required for maintaining best practices.

Anesthesia Standards

In human medicine, the position on monitored anesthesia care put forth in 1986 by the American Society of Anesthesiologists (2015) states, “Qualified anesthesia personnel shall be present in the room throughout the conduct of all general anesthetics, regional anesthetics and monitored anesthesia care.”

Continuous monitoring of the patient’s physiological parameters should include circulation, ventilation, oxygenation, and temperature. The guidelines from the American College of Veterinary Anesthesia and Analgesia (2009) mirrored these recommendations, shifting focus from the prevention of anesthetic mortality to the detection and prevention of anesthetic morbidity through vigilant patient monitoring throughout the perianesthetic period.

In 2011, AAHA published its first ever anesthesia guidelines, the 2011 AAHA Anesthesia Guidelines for Dogs and Cats, focusing on best practices for anesthesia. The 2020 update, published in the Mar/Apr issue of JAAHA, expands on the topics of patient considerations, anesthetic protocols, pain management, and anesthesia monitoring, with a focus on the continuum of care.

Anesthesia Patient Considerations

Preparing a patient for an anesthetic event, whether it is sedation or general anesthesia, should take into account many factors. Patient signalment, history, physical examination, laboratory analysis, type and length of procedure, pain management, and evaluation of any underlying comorbidities are key considerations. As stated in the American Association of Feline Practitioners anesthesia guidelines (AAFP 2018), the goal of the perianesthetic period should be to minimize stress, address pain, and anticipate anesthetic complications. All pharmacological anesthetic agents have the potential to affect the patient’s physiologic homeostasis, more specifically the cardiovascular and respiratory systems. Veterinary anesthesia mortality is at a rate of 1 in 1,000, compared with the human mortality rate of 1 in 10,000, with cats having a higher rate of complications, especially within the first three hours into anesthesia recovery (Brodbelt, et al. 2007). Therefore, the same anesthetic monitoring vigilance exercised to ensure a quality outcome should continue into the postoperative period for the patient.

Anesthesia Monitoring

One of the first monitoring concepts I teach students and technicians is to trust what you see, hear, and feel. Physical assessment of the patient’s physiological status (heart rate, mucous membrane color, respiratory rate, and jaw tone, to name a few) is crucial for a quick triage of your patient’s state. The use of multiparameter measurement devices provides supplemental data, which enables the anesthetist to fully evaluate the patient’s anesthetic depth and can identify common complications. Per the AAFP guidelines (2018), identification of these complications will allow for early intervention, increased patient safety, and reduced patient morbidity. Critical components of monitoring include the assessment of the circulatory, respiratory, and thermoregulation systems.

Circulation

Assessment of a patient’s circulatory system under anesthesia should focus on the patient’s overall cardiac output, which is influenced by many factors. Cardiac output is a product of heart rate and stroke volume, and it is a main component of blood pressure, along with systemic vascular resistance (Norkus 2018). Physical evaluation of the patient’s heart rate and rhythm via stethoscope, manual pulse pressure detection of flow, and monitoring of mucous membrane color and capillary refill time are real-time indicators of the patient’s cardiovascular system. Bradycardia in a patient could indicate an anesthetic overdose, hypothermia, metabolic derangement, or cardiovascular collapse. Tachycardia in a patient could indicate pain, a decrease in anesthetic depth, hypovolemia, or a change in ventilation status. A pulse deficit indicates a change in the cardiovascular system, warranting further investigation by the anesthetist, and it is often a rough but inaccurate clinical determinant of blood pressure. The use of an electrocardiogram and serial blood pressure monitoring will also provide the anesthetist more in-depth information regarding overall function.

Electrocardiograms (ECGs) are a tool often used to evaluate the patient’s heart rhythm; however, they indicate nothing about mechanical function of the heart. Dysrhythmias are important to evaluate because interruption in the electrical pathway of the heart can lead to a decline in cardiac output and collapse of the cardiovascular system. Interpretation of the ECG can be difficult and subject to interpretation, and it requires additional training of the staff member (AAFP 2018).

Blood pressure, whether indirect via Doppler or oscillometric device or direct via arterial catheter, is important in a variety of physiologic functions, such as oxygen and carbon dioxide transport and nutrient delivery to tissues. Hypotension, a mean arterial pressure less than 60 mmHg (Norkus 2018), can be caused by changes in cardiac output such as a decrease in preload, contractility, heart rate, and so on. Prolonged hypotension can lead to decreased tissue perfusion and hypoxemia, increasing a patient’s morbidity and mortality (AAFP 2018). A disadvantage of the use of the occlusion cuff is the potential for operator error in choosing the limb or size (ideally it should be on a circular part of the limb, 40% of the width of the diameter). A Doppler will allow the anesthetist to hear the patient’s heart rate but will only provide information about the systolic pressure of the patient (in case this is more correlated with the mean) (AAFP 2018). An arterial catheter is the gold standard for measuring real-time variations in the patient’s blood pressure, but it does require technique and specialized equipment.

Ventilation

The second major monitoring concept I teach students and technicians is, “If your patient is not breathing, they could die.” Seems intuitive, but measurement of a patient’s ventilation status is rapidly becoming one of the most critical tools in anesthetic monitoring. Respiratory system monitoring will include patient observation of respiratory rate and effort, as well as of thoracic auscultation. Direct visualization of the patient’s respiratory rate is, however, a poor indicator of true tidal volume in an anesthetized patient. Arterial blood gas analysis is the most reliable method of interpreting the patient’s arterial oxygen and carbon dioxide levels. However, samples can be difficult to obtain, and equipment may not be readily available in primary clinical settings. End-tidal carbon dioxide (EtCO2 ) measurements obtained via capnography are a very reliable tool to indirectly assess a patient’s ventilation as well as cardiac output status (Farry and Norkus 2018). The capnogram gives the anesthetist invaluable information regarding proper intubation, machine function, and ventilation function and is often the first monitoring parameter to fluctuate when a patient is experiencing respiratory and cardiovascular collapse. Hypocapnia, low EtCO2, can be indicative of an increase in the patient’s ventilation rate (light anesthetic depth, pain), secondary to cardiopulmonary disease, as well as improper anesthetic machine function (Norkus 2018). Conversely, hypercapnia, an increase in EtCO2, can also indicate improper anesthetic machine function (rebreathing of CO2 ), endobronchial intubation, and increases in cardiac output. The capnograph equipment can be expensive; however, if I only had one piece of monitoring equipment, it would be a capnograph.

Oxygenation

Pulse oximeters are relatively inexpensive, easy to use, tolerated well by awake and anesthetized patients, and one of the most frequently used monitoring devices in veterinary medicine. When a patient breathes in oxygen, it travels through the lungs and into the blood and is released into the tissue, where it binds with hemoglobin within the plasma. The pulse oximeter works via light absorption with red and infrared wavelengths. The difference between oxhemoglobin and deoxyhemoglobin (hemoglobin not saturated with oxygen) light absorption is displayed as a percentage. This information is important in terms of the oxyhemoglobin dissociation curve, and under general anesthesia, with 100% oxygen, it should be 95%–100% (Farry and Norkus 2018).

Clinically, this is a useful tool to indirectly assess a patient’s oxygen transport in terms of hemoglobin saturation as well as deliver an audible pulse rate. However, this is not a tool to assess how well a patient is breathing or their ventilation status. Another major limiting factor in the reliability of the pulse oximeter is tissue perfusion, as changes in peripheral circulation due to drug administration, hypothermia, shock, or other factors can alter the effectiveness of the pulse oximeter.

Temperature

Body temperature is a key physiologic parameter to monitor during the perioperative period. It is relatively easy to access in most patients, but it is also the parameter that is most often overlooked. Maintaining core body temperature in mammals specifically is a complex process that is part of the body’s physiologic homeostasis mechanism, regulated by the hypothalamus. Most patients will experience some degree of hypothermia during anesthetic procedures, whether under general anesthesia or sedation. Hypothermia, core body temperature less than 36°C (96°F), can result in myriad adverse effects, including delayed drug metabolism, cardiovascular dysfunction, impaired perfusion, decreased minute ventilation, cerebral depression, and the increased incidence of wound infection, to name a few (Farry and Norkus 2018).

However, hypothermia can begin before the anesthetic event. An example in anesthesia of evaporative heat loss would include respiration, applying cool liquids to shaved skin and exposed body cavities. The larger the exposed area, the larger the heat loss. Alcohol-based surgical solutions will accelerate heat loss, as compared with water-based solutions, via evaporation. Conductive heat loss occurs when heat is lost to an object surrounding or in contact with the patient that is colder than the normal body temperature of the patient: think cool metal tables, stainless-steel cages, and warm water bottles that have cooled. Convective heat loss is the transference of heat from the body as air passes over it, which can be accelerated by cool ambient temperatures, fans, and air conditioners. Radiation heat loss occurs when heat moves away from the body. This is a natural or passive process that occurs when heat is released from the body into the environment (specifically evident in colder room temperatures, less than 20°C or 68°F) (Haskins 2007). This type of heat loss is clinically significant because active warming measures do not affect the gradient of heat loss.

Conclusion

Patient monitoring is key to a successful outcome in any anesthesia procedure. Another piece of the puzzle, in terms of practice management, can be the development and training of staff members dedicated to performing the anesthetic care of our patients.
Before handing over the responsibility of patient monitoring to the staff, proper training is required. This training should include anesthetic machine setup and maintenance, drug pharmacology, and how to properly detect and respond to anesthetic emergencies. A trained employee within the surgical suite will allow for a more efficient workflow within the practice, enabling the practitioner to focus on the procedure. Untrained staff can lead to declines in customer service, as well as procedural mistakes that can cause adverse patient outcomes, dissatisfied clients, and a decrease in revenue. Sacrifices in patient care for workplace production will ultimately flatline your practice. 

References

American Society of Anesthesiologists. 2015. “Standards for Basic Anesthetic Monitoring.” asahq.org/standards-and-guidelines/standards-for-basic-anesthetic-monitoring.

American College of Veterinary Anesthesia and Analgesia. 2009. “ACVA Monitoring Guidelines Update.” acvaa.org/wp-content/uploads/2019/05/Small-Animal-Monitoring-Guidlines.pdf.

American Association of Feline Practitioners (AAFP). 2018. “2018 AAFP Feline Anesthesia Guidelines.” catvets.com/guidelines/practice-guidelines/anesthesia-guidelines.

Brodbelt, D. C., D. U. Pfeiffer, L. E. Young, and J. L. N. Wood. 2007. “Risk Factors for Anaesthetic-Related Death in Cats: Results from the Confidential Enquiry into Perioperative Small Animal Fatalities (CEPSAF).” British Journal of Anaesthesia 99, no. 5: 617–623.

Farry, T., and C. Norkus. 2018. “Monitoring the Critical Patient.” In Veterinary Technician’s Manual for Small Animal Emergency and Critical Care, 2nd ed., edited by C. Norkus, 261–266. Ames, IA: Blackwell.

Haskins, S. 2007. “Monitoring Anesthetized Patients.” In Lumb and Jones’ Veterinary Anesthesia and Analgesia, 4th ed., edited by W. J. Tranquilli, J. C. Thurmon, and K. G. Grim, 86–105. Ames, IA: Blackwell.

Norkus, C. 2018. “Cardiovascular Emergencies.” In Veterinary Technician’s Manual for Small Animal Emergency and Critical Care, 2nd ed., edited by C. Norkus, 87–109. Ames, IA: Blackwell.

Jennifer Sager, BS, CVT, VTS (Anesthesia/Analgesia, ECC), is the small-animal hospital education and training specialist at the University of Florida College of Veterinary Medicine and Veterinary Hospitals. In 2008, Sager attained her Veterinary Technician Specialty in Anesthesia and Analgesia, following up with a second VTS in 2009 in Emergency and Critical Care. She contributed to the American Association of Feline Practitioners anesthesia guidelines (2018) and is cochair of the 2020 AAHA Anesthesia and Monitoring Guidelines for Dogs and Cats, the first technician to help chair this type of document. Sager is the current president-elect of the Academy of Veterinary Technicians in Anesthesia and Analgesia.

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