What Is the Best Anesthesia Monitor?
Answer: Technology and Training Working Together
Wandering around the exhibit hall of any major veterinary conference, you may see a variety of colorful machines promising to make anesthesia safer for your patients. Often clinicians and practice owners will ask themselves: “Which anesthesia monitor is the best investment for my clinic?”
This question is a difficult one to answer. First, how many patients are you anesthetizing? What type of procedures are you preforming? What types of patients are you usually seeing (young and healthy or older with concurrent disease)? There are a bevy of available anesthesia multiparameter monitors on the market, but not one of them is a match for a well-trained veterinary technician whose sole purpose is to monitor anesthetic trends of each patient.
Compared with human medicine and surgery, veterinary medicine has a much higher mortality rate. Risk factors associated with anesthetic deaths in veterinary medicine include increased age, patients with higher ASA status (sicker patients), patients that are overweight, procedures performed during emergency hours with less staff, and accidental endotracheal intubation in cats. All these factors and more contribute to the increased anesthetic mortality rate—0.17% in dogs, 0.25% in cats, and 1.4% in rabbits as noted by several studies in veterinary medicine. One way to start decreasing anesthetic mortality in veterinary patients and providing safer anesthetics for our pets is to refer higher-risk cases such as the ones listed above to centers with an anesthesiologist and/or veterinary technician specialists in anesthesia. Another avenue is to use trained veterinary staff to educate clients on the risks and expectations associated with anesthesia.
The Human Factor
First, let’s focus on what a trained anesthesia technician armed with nothing but a stethoscope and their visual senses can bring to the table. Anesthesia technicians often perform client and patient intake exams prior to the surgical procedure and before medication. During this initial intake examination, technicians can obtain vital information that may have a bearing on anesthetic or sedation drug selection.
Palpation of the peripheral pulses is simple and inexpensive and can provide a wealth of information about heart rate and rhythm as well as pulse quality. When checking the patient’s mucous membranes, we can determine hydration or perfusion estimates. If a patient presents with muddy, pale, or even blueish mucous membranes, we become concerned about decreased oxygenation, the clinician is alerted, and more diagnostics can be obtained before anesthesia is administered.
By listening to the heart and lung fields, veterinary technicians can become aware of cardiovascular findings such as a heart murmur, an area of decreased sound, or “crackling” lung sounds. If detected before anesthesia, the attending clinician can be alerted to prevent elective anesthesia on a patient and avert serious complications.
I have personally had one patient come in for an ovariohysterectomy only to have a muffled chest auscultation postpone the surgery. We obtained radiographs of the patient, and it turned out she had a diaphragmatic hernia and was sent to a specialist for surgical correction and advanced anesthesia care.
When it comes to multiparameter monitors, most often clinicians are using ones that are able to measure the following values: oxygen saturation (SpO2%), end-tidal carbon dioxide (ETCO2), heart rhythm and electrical activity via electrocardiogram (ECG), respiration rate, temperature, and blood pressure.
Monitoring of all parameters during the anesthetic period is critical to prevention and early recognition of potentially lethal complications. Multiparameter monitors that include special algorithms for measuring ECG in animals are more capable because they are adjusted for the animal’s QRS complex, which differs significantly from the human QRS complex. Some of these monitors have increased trace sweep speeds, adding an additional tool for diagnosing abnormal ECGs in high-heart-rate animals such as rabbits or ferrets. Other parameters such as blood pressure monitoring are essential to ensure adequate blood flow to the kidneys and liver during the procedure.
The Importance of Capnography
A special note on ETCO2 monitoring: Most multiparameter monitors will have this as part of the package; however, stand-alone units for capnography are available as well (products such as the EMMA from Massimo or the AirMate from Sentier).
Waveform capnography represents the amount of carbon dioxide (CO2) during exhalation, which assesses ventilation. It consists of a number and a graph. The number represents a numerical capnometry value, which is the partial pressure of CO2 detected at the end of exhalation. The capnograph is the waveform that shows how much CO2 is present at each phase of the respiratory cycle, and it normally has a rectangular shape. This monitoring parameter in particular gives an additional level of safety as it will not only directly tell you about the patient’s ventilation status and breathing system but also indirectly clue you in to the patient’s cardiovascular status (cardiac output).
In fact, in a closed claim study, anesthesiologists who reviewed 1,175 anesthetic-related closed malpractice claims found capnography and pulse oximetry could have potentially prevented 93% of avoidable anesthetic mishaps.
Capnography is useful for troubleshooting anesthesia machine mishaps such as an exhausted carbon dioxide absorber, malfunctioning unidirectional valves, increasing dead space, kinked endotracheal tubes, and other equipment mistakes.
Immediate and effective response to complications during anesthesia is critical, and for additional training resources, the 2020 AAHA Anesthesia and Monitoring Guidelines for Dogs and Cats has a page dedicated to troubleshooting anesthetic complications such as hypotension, hypothermia, and hypoventilation.
The recovery period is another example where multiparameter monitors can aid the veterinary team in the prevention or detection of problematic events. According to AAHA’s anesthesia guidelines, there are several studies that point to recovery from anesthesia and the postoperative period as especially critical, with evidence of high mortality rates cited. AAHA does indicate that “increased monitoring and early diagnosis of physiologic changes and earlier intervention may reduce the risk of anesthetic death.”
The Future of Anesthesia
Looking into the future of anesthesia, there are some artificial intelligences already at work in the operating room. Pharmacological robots include the “McSleepy,” a machine that delivers IV sedation drugs such as propofol, narcotics, and muscle relaxants based on anesthesia team input. There is also the iControl-RP machine, described in The Washington Post as “a closed-loop system intravenous anesthetic delivery system which makes its own decisions regarding the IV administration of remifentanil and propofol based on continuous patient data.” This device monitors the patient’s EEG level of consciousness via a BIS monitor device as well as traditional vital signs. One of the machine’s developers, Mark Ansermino, MD, stated, “We are convinced the machine can do better than human anesthesiologists.”
While this seems far off for the foreseeable future in vet med, it only highlights the importance of a trained professional paired with technology. Most of the subjective determination of patient status is taken out of the equation with multiparameter monitoring systems or, allowing for more objective determination of patient status, as many of the parameters are continuous, with real-time reports of cardiopulmonary function (with ECG and ETCO2). The continuous and trending information from a multiparameter monitor together with a trained technician continuously assessing the patient’s physical parameters during surgery will provide the safest outcomes for our patients as possible.
When it comes to training staff on anesthesia monitoring, AAHA’s 2020 Anesthesia Guidelines for Dogs and Cats is a great resource. The website offers everything from an easy-to-use veterinary anesthesia monitoring form to a team anesthesia training checklist (downloadable PDF), preanesthesia client questionnaire, and much more to help your team become confident and successful during the anesthetic process.
Tasha McNerney, CVT, CVPP, VTS (Anesthesia and Analgesia), is a certified veterinary technician from Glenside, Pennsylvania. She is also a certified veterinary pain practitioner and works closely with the IVAPM to educate the public about animal pain awareness. McNerney has authored numerous articles on anesthesia and analgesia topics for veterinary professionals and pet owners.
Photo credits: Photo courtesy of Tasha McNerney