Monitoring of all parameters, including ECG, during the perianesthetic period is critical to prevention and early recognition of potentially lethal complications. Veterinary-specific multiparameter patient monitoring systems can play an invaluable role in diagnostics for companion animals during each phase of a surgical procedure, namely perioperative, operative, and postoperative. Many times, the trauma of surgery or the use of anesthetic agents can frequently induce heart issues in patients, expose undetected conditions, or activate other complications. Multiparameter monitoring allows veterinarians to make treatment decisions based on the entire surgical picture. Evaluating a patient’s vital signs with multiparameter monitors significantly increases a veterinarian’s ability to address the gamut of issues that can arise in a surgical scenario. Multiparameter monitors can detect irregular heart rates, arrhythmias, hypoventilation, systemic vasodilation, respiratory acidosis, and hypoxemia. Monitoring makes the veterinarian aware of the issue, but also helps them decide a course of action to either correct a problem or strategize the next steps for treatment. “Maintaining patient homeostasis during the entire perioperative period requires constant vigilance by the anesthetist,” says Kris Kruse-Elliott, DVM, PhD, DACVAA, president of the North American Veterinary Anesthesia Society (NAVAS). “Using a multiparameter monitor during induction, maintenance, and recovery from anesthesia provides needed information about cardiopulmonary status and function, and can often allow an anesthetist to anticipate and prevent problems.” Despite their accuracy, it is important to note multiparameter monitors do not preclude regular hands-on evaluation of surgical patients, particularly depth of anesthesia, including eye position and palpebral responses, jaw and muscle tone, and response to stimuli. There are a few scenarios where monitors do not detect abnormalities, and reliance on electrocardiogram (ECG) alone can be particularly misleading. For example, in electromechanical dissociation, a patient has electrical activity, but no mechanical activity or associated cardiac output. Evaluation of heart rate should be done by actual palpation of the pulse or auscultation of the heart, as the monitors that use a beat-to-beat interval to calculate heart rate can sometimes double count it if the ECG trace is somewhat isoelectric or other errors create an inaccurate reflection of heart rate. The bottom line is, direct contact and evaluation of the patient is part of appropriate anesthesia monitoring, regardless of the presence of a multiparameter monitor. As vigilant monitoring, interpretation, and response to the physiologic status of patients is critical, distinct situations where multiparameter monitoring is especially vital in the surgical window include heart issues, undetected conditions, and other complications. Heart issues Heart complications such as arrhythmias often occur in surgery. Some of the most difficult events to diagnose in relation to surgical events are cardiac dysrhythmias. These can be particularly challenging to recognize without ECG monitoring. At first, it may appear a patient has a respiratory sinus arrhythmia deemed “normal” upon physical exam. In reality, the animal may have a more irregular rhythm such as atrial fibrillation. Patients in ventricular bigeminy also may appear to have a normal rhythm when in fact they have alternating ventricular beats. Some patients (e.g. greyhounds) who develop hyperkalemia and an associated slowing of the heart rate will be difficult to diagnose based only on manual heart rate counts or the pulse oximeter. However, these conditions will become clear when a monitoring unit and ECG are connected to aid in diagnosis and proper treatment. “A common scenario is a patient who develops a profound vagally mediated bradycardia during surgery related to traction on the GI tract or manipulation of the orbit,” says NAVAS secretary Nancy Brock, DVM, DACVAA. “Recognizing these sudden drops in heart rate in response to surgical manipulation is critical to rapid treatment and prevention of worsening bradycardia and arrest. The reverse scenario is a patient who has an excessive sympathetic response to surgery with resultant catecholamine release and potential tachyarrhythmias. Profound tachycardia and tachyarrhythmias may have a negative impact on cardiac output and blood pressure, and can possibly also lead to arrest.” Monitoring of all parameters, including ECG, during the perianesthetic 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 animal QRS complex, which differs significantly from 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. Postoperative monitoring of patients also can be done with a telemetry system. A small transmitter is attached to the patient and wirelessly sends ECG information to a main central computer. Continuation of monitoring after surgery to detect any further heart abnormalities is critical for the safety of patients. Undetected conditions When a very thorough history is taken and a complete physical examination is performed, it is rare for something to be unmasked by anesthesia and surgery. Occasionally, undetected conditions can be diagnosed by chance when monitoring a patient during the surgical period. “Often, when something is unmasked at surgery, one can go back and get a better history or recognize that something, on initial or previous physical examination—such as an irregular heart rate—was a true issue. To be sure, monitoring during the perianesthetic period is yet another way to catch items missed on history or physical examination. While this reemphasizes the importance of monitoring, it does not preclude the need for being very thorough in taking history and performing a physical examination,” Dr. Kruse-Elliott says. With multiparameter monitoring, a broad range of conditions may be recognized during anesthesia and surgery. Monitoring should help the decision-making process in determining whether to continue with the surgery. Once stabilized, further evaluation, testing, and prescription of a treatment plan for managing the newly discovered condition should be implemented, after full recovery and healing from surgery is attained. Complications A broad range of conditions may be recognized during anesthesia and surgery. Some examples include: atrioventricular block that is not atropine-responsive; obstructive airway patterns demonstrated by capnography; previously undiagnosed hypertension; hypotension associated with unrecognized surgical blood loss; electrolyte abnormalities such as hyperkalemia impacting the ECG; and adverse reactions to anesthesia. One relatively common type of problem is the patient who has been endobronchially intubated inadvertently. When this occurs, mucous membrane color will certainly be an indicator—pale, bluish, or brick-red membranes are all signs of a problem. However, an abnormally low pulse oximeter oxygen saturation value also should be an alert to check the endotracheal tube length and placement in the patient. Prolonged recovery is another example where multiparameter monitors can aid veterinary surgeons in the prevention or detection of problematic events. According to guidelines published online by the American Animal Hospital Association (AAHA), when it comes to anesthetic-related deaths, there is limited data. However, AAHA cites 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.” When it comes to diagnosis in this critical stage, Kruse-Elliott adds, “while there are several differential diagnoses for prolonged recovery, one that can easily be missed is the hypoventilating patient who now has elevated arterial CO2 (up to 70 to 90 mm Hg). Often, these patients are left connected to a pulse oximeter and on oxygen, and the anesthetist has difficulty diagnosing the cause of prolonged recovery. Being sure to maintain monitoring during recovery allows for detection and correction of hypoventilation, as well as hypothermia, hypoxemia, and hypotension.” Troubleshooting problems and decision-making Perhaps the most common surgical complication that both monitoring and physical examination detects is blood loss with associated hypotension. Gradual loss of a significant amount of blood volume can be missed by all staff involved in a surgery, particularly in small patients. Careful and close patient observation for increasing heart rate in the face of unchanged or worsening pulse quality is recommended, along with monitoring for increasing heart rate in the face of gradual development of hypotension suddenly escalating to severe hypotension. If caught in progress with monitoring, appropriate treatment—including fluids and blood components—can be started before the patient becomes critical. Most of the subjective determination of patient status is taken out of the equation with multiparameter monitoring systems. There are other areas patient monitors can be useful for troubleshooting. A drop in EtCO₂ is often the first indicator to cardiopulmonary arrest. Pleth variability index (PVI) is a great tool in determining the patient’s hydration status. An increase in PVI could be an indication of hypovolemia. When problems are detected in a patient during surgical monitoring, decisions should involve directly checking the patient’s depth of anesthesia, pulse, and ventilation quality via the monitor, as well as noting mucous membrane color. Then, to determine the likely cause of the problem, a review of the patient history; physical status prior to anesthesia and surgery; any major problems; and the type of surgery and reason for it should all be seriously considered. Some questions to ask relative to history include: Is bradycardia a preexisting condition in this patient? Could the problem be induced by drugs? Is it related to hypoxemia? Could it be a vagally mediated response? Is there hypothermia? When the likely cause is determined, treatment can be initiated that relates directly to the problem and patient at hand. Monitoring is vital for better outcomes Most of the subjective determination of patient status is taken out of the equation with multiparameter monitoring systems, allowing for more objective determination of patient status, as many of the parameters are continuous, real-time reports of cardiopulmonary function. This is particularly important when training new, less experienced staff and when caring for patients with multiple complex disease conditions. “Multiparameter monitors are a vital component of perisurgical patient care. While physical observation remains a key piece of monitoring an anesthetized patient, the ability to have real-time measures of cardiopulmonary function is critical to the safe delivery of anesthesia in patients,” Dr. Brock says. Overall, veterinarians who utilize multiparameter patient monitoring of vital signs in their patients before, during, and after surgical procedures will attain full awareness of patient conditions. This approach will help them be prepared for emergency situations, avert crises, and minimize lasting damage to save lives and obtain better patient outcomes. Eduardo Miranda, BSEE, MSc, is a biomedical engineer and president of Digicare Animal Health, a manufacturer of veterinary-specific multiparameter monitoring systems and telemetry systems.
