Critical care anesthesia (Proceedings)
Due to the fact that critical patients are more fragile than stabile patients, they require special nursing care. The same is true of these special patients under anesthesia. Using drugs that are reversible and drugs that have a short half life are a couple of specific ways to care for these patients. Unstable patients have a lower minimum alveolar concentration (MAC); therefore, close attention needs to be paid to the level of inhalant with which a patient is maintained.
The inclusion of multimodal anesthesia is helpful to decrease the volumes of particular agents such as inhalants. Multimodal anesthesia is the combination of multiple agents that have different mechanisms of action to achieve ideal analgesia. For example, combining hydromorphone dosed every four hours with ketamine as a constant rate infusion. Hydromorphone works at the mu opioid receptor, and ketamine works as an NMDA receptor antagonist. They work on different parts of the pain pathway.
Work UpA thorough pre-anesthetic work up is important in order to provide safe anesthesia for all patients. Critical patients especially benefit from an evaluation of both past medical history and current physical status. By working up patients pre-anesthetically, a greater sense of the patient's requirements can be achieved. Key components to a good work up include the following: history, physical exam, current blood work, and a plan for anesthesia.
The history may be as brief as HBC, previously healthy. Sometimes the history is much longer and contains medical conditions or diseases the patient has on top of the presenting complaint. The following could be included in a list of important questions to ask when working up a patient: what happened, when did it happen, how long has this been going on, and does the patient have any significant previous medical conditions. Has the patient received any medications? If so, what, how much, and when?
Current physical exam findings play a large role in the pre-anesthetic work up. What is the current TPR? Is the animal tachycardic? Why? Any arrhythmias? The patient should be auscultated for the presence of a murmur. If the patient is obese, drug calculations could be done based upon what the animal's lean body mass would be. Is the animal bright and alert or dull, recumbent and non-responsive? When touching the animal, does it seem painful somewhere? Was this pain response expected based upon the presenting complaint?
Because critical patients require such special handling, sometimes extra diagnostic testing is necessary before anesthesia. Current blood work for healthy patients usually means at least a big four (BUN/Azo, BG, PCV, TS) within the last month. The extra testing performed on critical patients typically depends upon a number of different criteria, the age of the patient, the current status of the patient, the procedure being performed, the tests that were previously performed, and the time elapsed since the last test. In house lab work is obviously preferred for critical patients in order to get fast results.
Included in an anesthetic plan should be the different anesthetic agents (injectable versus inhalant), and dosages required for premedication, induction, maintenance, and recovery. Additionally, the plan should cover any necessary monitoring equipment, whether a ventilator is indicated, type and rate of intravenous fluid administration, and catheters (intravenous and arterial). Emergency drugs should be calculated before anesthesia begins. When a patient arrests, it is difficult to think quickly and calculate the appropriate volume of drug; if these calculations were done prior to the arrest, it would save time and effort. For situations where an arrest is probable, having emergency drugs drawn up and ready is recommended. Preparation is the key to critical care anesthesia. Drugs and supplies should all be ready before inducing a critical patient.