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Anesthesia Safety Studies have shown that two-thirds of the human anesthesia-related deaths were considered preventable. Patient health, anesthetic monitoring, surgical skill, patient stress, and/or perioperative care likely influenced the outcome. Animal Studies In studies on veterinary patients, the main causes of death were human error leading to overdosage and hypoxia. Equipment malfunctions, hypothermia, and cardiovascular failure were also prevalent. In one study, the main risk factors identified were failure to obtain accurate body weights, failure to utilize premedications, and failure to intubate patients. Perianesthetic Monitoring Patients vary and accidents occur. This truth emphasizes the need for patient monitoring. Monitors designed specifically for veterinary patients have been made widely available resulting in an improved level of monitoring in veterinary practices. Monitoring is simply the process of collecting of data. These data are used by the anesthetist to formulate or modify the anesthetic plan to avoid or minimize risks to the patient. Obviously, anesthetic risk is directly related to the adequacy and accuracy of data collection and the knowledge and skill of the anesthetist to utilize the information. Automated monitoring (pulse oximetry, ECG, arterial blood pressure, end tidal CO2, arterial blood gases) provide more complete information and usually facilitate earlier detection of problems than manual monitoring alone (pulse palpation, mucous membrane color, respiration rate). Pulse oximeters are relatively inexpensive and provide continuous information about heart rate and hemoglobin saturation (oxygen level). Hemoglobin is the oxygen carrying component of blood. Pulse oximetry has limitations. For example, the monitor does not tell you about respiratory depression until respiratory function has deteriorated to the point hemoglobin desaturates. This occurs very near lethal respiratory failure when inspiring high concentrations of oxygen and may be accompanied by apnea. End-tidal CO2 increases very early and therefore is a much more useful indicator of respiratory function. Additionally, pulse oximeters are affected by motion and can be impaired by pigment. This leads to a relatively high rate of false alarms. ECG The electrocardiogram is a useful monitoring tool, but its proper use requires training. It provides a heart rate and a picture of the electrical activity of the heart muscle. The anesthetist should be trained to recognize many commonly encountered intraoperative arrhythmias. Blood Pressure End-tidal CO2 Capnography is numerical and graphical display of the end-tidal carbon dioxide partial pressure (the amount of carbon dioxide in the expelled air at the end of a breath). It is a non-invasive measurement of the ability of the respiratory system to excrete carbon dioxide (usually indicative of respiratory function). Most anesthetics are respiratory depressants and end-tidal CO2 allows early detection of respiratory impairment so appropriate intervention can occur (e.g., decreasing anesthetic dose or controlled ventilation) BEFORE the problem becomes significant (MUCH earlier than pulse oximetry) Blood Glucose, PCV, and Total Protein Blood glucose is a simple and rapid test to perform, but it is often under utilized in the perioperative period. Hypoglycemia may result in seizures, delayed anesthetic recovery, and severe hypoglycemia may cause death. Patients that are at risk for hypo- or hyperglycemia should have blood glucose measured before, during, and after anesthesia to facilitate maintenance of glucose levels that are compatible with good physiologic functions. Patients that are at risk for hypoglycemia include the very young, patients with paraneoplastic disease, anorexic animals, animals with impaired liver function, and diabetic animals receiving insulin. Hyperglycemia is usually better tolerated than hypoglycemia as long as the increase in osmolality of the blood does not cause disturbances in water distribution. However, animals with a history of diabetes mellitus should be monitored and appropriate intervention given if severe hyperglycemia occurs perianesthetically. Packed cell volume / hematocrit and total protein determination should be part of almost every preanesthetic workup. These values are important because red blood cells carry the majority of oxygen to the tissues and plasma proteins (albumin in particular) are important for maintaining physiologic fluid distribution between the vascular and interstitial / intercellular compartments. Supportive Care The topic of what is appropriate supportive care or anesthetic adjunctive therapies can stimulate passionate debate among veterinarians. A rational approach to selection of what is appropriate for a given case should start with identification of likely complications and risk factors. Hypothermia Hypothermia is very common during anesthesia. The causes are many, but some degree of hypothermia is almost always experienced. The goal of the anesthetist should be to minimize hypothermia through prevention of heat loss and providing supplemental heat from an appropriate device. Care should be taken when actively rewarming patients to avoid iatrogenic hyperthermia. Additionally, some devices may cause thermal injury (electric heating pads or hot plastic bottles) and should not be used. Following anesthesia, frequent monitoring of body temperature should be performed until body temperature approaches normal values. Fluid Therapy Intravenous fluid therapy is usually associated with minimal risk and a large benefit and is therefore probably warranted in most patients. Indwelling intravenous catheters are almost always warranted. They do add a small cost and can be associated with a small risk of infection or venous thrombosis; however the ease and speed with which they allow administration of emergency drugs, additional anesthetics, and intravenous fluids more than outweighs their risk for almost all procedures. Endotracheal Intubation Maintaining a patent airway is essential to safe anesthesia. When airway obstruction occurs, hypoxemia will rapidly develop. Delivery of inhalant anesthetics should almost always be via an endotracheal tube. Aspiration of saliva or gastric contents is another possible risk, especially if the animal was not fasted prior to anesthesia. One of the leading causes of anesthetic morbidity and mortality in humans has historically been airway obstruction and/or hypoxia. Attention to airway management and respiratory monitoring has improved human patient safety and would probably improve veterinary patient safety as well. Summary Good anesthesia is probably best defined as anesthetic protocols and practices which reduce patient morbidity and mortality risk to the lowest level that is reasonably possible while minimizing patient stress and pain. Anesthetic risk will likely never be eliminated, but there are many things that every practice can do to reduce it. At TenderCare Veterinary Center, we utilize the most up to date procedures, medications and equipment available to make your pet's experience as safe as possible. |
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