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Anesthetic Monitoring: Your Questions Answered

Anesthetic Monitoring: Your Questions Answered

pdf_buttonJeff Ko, DVM, MS, Diplomate ACVA, and Rebecca Krimins, DVM

This article is the first one in a series that will discuss the goals of anesthetic monitoring as well as associated procedures and equipment. In this first article, the authors provide an overview of modern anesthetic monitoring and answer questions about why and how to provide cutting-edge anesthesia for your patients.

Noninvasive monitoring techniques in the anesthetized dog and cat have been described since the 1990s.1 More recently, major advances in technology have improved the efficiency and affordability of equipment. These advancements, in turn, have improved veterinarians’ and anesthetists ‘abilities to detect abnormalities in the anesthetized patient.

Advances in anesthetic monitoring have led to a “gold standard” approach that emphasizes:

  • Appropriate clinical evaluation
  • Training of personnel
  • Preanesthetic evaluation
  • Advanced monitoring techniques.

All of the above help minimize adverse side effects of anesthesia and surgery.

Links to Anesthesia Guidelines
To read the American College of Veterinary Anesthesiologists and American Animal Hospital Association anesthesia guidelines, go to acva.org/docs/Small_Animal_Monitoring_2009.doc and aahanet.org/PublicDocuments/Anesthesia_Guidelines_for_Dogs_and_Cats.pdf, respectively.

Why Monitor Anesthetized Patients?

Anesthetic agents coupled with invasive procedures can cause drastic hemodynamic changes in the patient’s cardiorespiratory system (Table 1). In addition, each patient exhibits different physiologic and pharmacologic responses to anesthetic agents. Because these responses are not always predictable, it is vital to monitor each patient closely.

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Prompt detection of respiratory or hemodynamic instability allows the anesthetist time to properly diagnose what is happening and intervene. This, in turn, prevents morbidity, such as cardiorespiratory collapse, which, if otherwise untreated, can lead to mortality. Furthermore, despite successful sophisticated surgery or diagnostic procedures, lack of a rapid and smooth recovery may defeat the purpose of performing them.

Saved by Monitoring (Case 1 and Case 2) describes how anesthetic monitoring made a difference in the surgical experience of two patients.


What Information Is Obtained During Anesthetic Monitoring?

By monitoring the anesthetized patient, the anesthetist obtains information in the following areas:

  1. Physiologic condition of the patient (eg, cardiovascular, respiratory, and metabolic systems)
  2. Patient’s response to anesthesia, including anesthetic depth and level of analgesia.

In addition, assessing the status of anesthetic equipment ensures its proper function, helping the anesthetist prevent iatrogenic crises that can jeopardize the patient’s health.

The information obtained via patient monitoring is used to achieve three goals:

  1. Ensure adequate tissue perfusion with well-oxygenated blood
  2. Prevent pain before, during, and after a surgical procedure
  3. Provide a smooth and rapid recovery from anesthesia/surgery.


Anesthesia Specialty for Veterinary Technicians

The Academy of Veterinary Technician Anesthetists (AVTA) is a recognized specialty of the National Association of Veterinary Technicians in America (NAVTA). The AVTA was officially recognized by NAVTA in January 1999, and became its second recognized specialty; the first being the Academy of Veterinary Emergency and Critical Care Technicians (1996).The AVTA focuses on:

  • Certifying technicians interested in specializing in veterinary anesthesia
  • Enhancing members’ knowledge in the care and management of anesthesia cases
  • Providing extensive information on sources of continuing education
  • Promoting patient safety, consumer protection, professionalism, and excellence in anesthesia care.

Applications for the AVTA certification examination are accepted each year. This year’s examination will take place September 8–12, 2012, at the 18th International Veterinary Emergency & Critical Care Symposium, San Antonio, Texas. Applications for this examination are due in January 2012.

To find out more about the AVTA, including how to become certified, go to avta-vts.org. A list of AVTA members, noted by the credentials VTS (Anesthesia), can be found on the homepage of the website.

What are the Target Physiologic Values for the Anesthetized Dog & Cat?

Physiologic and cardiorespiratory variables in anesthetized dogs and cats are listed in Table 2.

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What are Important Components of Anesthetic Monitoring?

  • Pre-anesthetic Evaluation: The monitoring process starts prior to premedication. It begins by obtaining a complete history of the patient, followed by a thorough physical examination, including blood analysis and indicated diagnostics. The patient is given an ASA (American Society of Anesthesiologists) classification based on assessment of its anesthetic risks (Table 3).

Deficits in homeostasis, such as dehydration, anemia, or any other significant abnormality (eg, low total protein, electrolyte imbalance, endocrine dysfunction, bleeding disorders) should be stabilized prior to any anesthetic procedure. A recent study has shown that mortality rates are higher in small animals with higher ASA status (ASA III–V) regardless of anesthetic agents used.2

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  • Monitoring All Anesthetic Phases: Once pre-anesthetic evaluation has been completed and the patient is approved for anesthesia, monitoring continues through:
    • Premedication
    • Induction
    • Maintenance
    • Recovery.
      Monitoring also applies to patients that have been prescribed take-home pain medication; this is accomplished through follow-up phone calls with the owner.
  • Sedated Patients: Sedated patients should also be monitored. Both the American College of Veterinary Anesthesiologists3 (ACVA) and the American Animal Hospital Association4 (AAHA) have monitoring guidelines, which emphasize that a sedated patient should receive the same quality of monitoring care as a patient under general anesthesia. To review these guidelines, see Links to Anesthesia Guidelines.
  • Personnel: There is no single piece of monitoring equipment that can replace the role of a capable and vigilant anesthetist monitoring an anesthetized patient. The ACVA monitoring guidelines recommend trained personnel be present for continuous evaluation of a sedated/anesthetized patient. See Anesthesia Specialty for Veterinary Technicians  for information on technician certification in veterinary anesthesia.
  • Documentation: When a patient is under general anesthesia, all vital signs must be evaluated and recorded on an anesthetic record at least once every 3 to 5 minutes. The anesthetic record becomes part of the patient’s medical record and legal documentation.

What Methods & Equipment are Used for Anesthetic Monitoring?

Priorities for monitoring an anesthetized patient include:

  • A physical assessment (Table 4) of the anesthetized patient by qualified personnel
  • Appropriate vital sign monitoring (Table 5).

Adverse side effects of anesthesia are minimized when the anesthetist systematically and regularly evaluates circulation, ventilation, oxygenation, and analgesia.

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In the next article in this series, anesthetic monitoring equipment and the physiologic components it measures will be discussed in-depth.

Read Part 2, Anesthetic Monitoring: Devices to Use and What the Results Mean, and Part 3, Anesthetic Monitoring: Therapeutic Actions.


  1. Ko JC. Noninvasive techniques in monitoring anesthetized patients. Vet Tech 1996; 17(5):301-307.
  2. Bille C, Auvigne V, Libermann S, et al. Risk of anesthetic mortality in dogs and cats: An observational cohort study of 3546 cases. Vet Anesth Analg 2012; 39:59-68.
  3. American College of Veterinary Anesthesiologists. Recommendations for monitoring anesthetized veterinary patients. JAVMA 1995; 206(7):936-937.
  4. American Animal Hospital Association. Anesthesia guidelines. JAAHA 2011; 47:378-385.

f02_KoJeff Ko, DVM, MS, Diplomate ACVA, is a professor in the Department of Veterinary Clinical Sciences at Purdue University College of Veterinary Medicine. He has authored numerous articles and book chapters in the field of anesthesia and pain management. Dr. Ko lectures extensively at regional, national, and international conferences. Dr. Ko can be reached at [email protected]


f02_kriminsRebecca Krimins, DVM, is currently a third-year anesthesia resident in the Department of Veterinary Clinical Sciences at Purdue University College of Veterinary Medicine. Dr. Krimins is a graduate of Ross University School of Veterinary Medicine.