Answering your questions: Sedating and anesthetizing patients that have organ system dysfunction - Veterinary Medicine
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Answering your questions: Sedating and anesthetizing patients that have organ system dysfunction
What agents and monitoring devices might be better in these patients? This anesthesiologist tells you how to handle common situations.


VETERINARY MEDICINE


Q: Are additional supportive measures needed in anesthetized patients with organ system dysfunction?

All patients can benefit from supportive measures such as providing intravenous access, fluid therapy, temperature homeostasis, and positive pressure ventilation. Patients with organ system dysfunction have decreased physiologic reserve, meaning they have a more limited capacity to tolerate the principal causes of morbidity and mortality we are trying to prevent (i.e. hypotension, hypovolemia, hypercapnia, hypoxemia, hypothermia, electrolyte and fluid imbalances). Ventilatory support (manual or mechanical) helps prevent respiratory acidosis, helps efficiently deliver inhalant anesthetics, and may improve airway monitoring. Intravenous fluid administration will help prevent hypovolemia, maintain a diuresis, and provide intravenous access for anesthetic agents or emergency medications. Warm-water or warm-air blankets can prevent hypothermia, excessive anesthetic depth, and prolonged recoveries. These types of support measures can make the difference necessary to prevent perioperative complications in patients.

As with monitoring practices, some support measures may be more valuable than others, and decisions can be tailored to the patient's presentation. The best supportive measure in all patients is providing continuous monitoring of the anesthetic equipment and anesthetic depth to avoid deep planes of anesthesia associated with decreased oxygen delivery to vital organs, hypothermia, and prolonged recoveries. This can only be accomplished by having an anesthetist devoted to monitoring the patient. This supportive measure determines the difference between being able to recognize that your patient is decompensating and being able to prevent it from happening in the first place. This additional supportive measure is needed in anesthetized patients with organ dysfunction.

It is common to forego special monitoring and support in patients that are only sedated and not anesthetized. Patients with organ system dysfunction will be particularly susceptible to hypoxemia, hypoventilation, and upper airway obstruction. In sedated patients, it is just as important to monitor the airway to make sure that the patient is moving air adequately. In general, if a patient can be intubated, the patient usually should be intubated. Oxygen supplementation should be considered whether or not the patient can be intubated.

Q: What anesthetic protocol and supportive measures do you recommend for a dog with a portosystemic shunt?

Patients with portosystemic shunts can be expected to have decreased ability to metabolize anesthetics dependent on liver function. Hypoalbuminemia may be present in these patients, and care should be taken to avoid excessive dilution of plasma proteins with crystalloid fluids. Colloids may be used. Coagulopathies and hypoglycemia are also potential concerns. Some of these patients will have hepatoencephalopathy and exaggerated responses to anesthetic agents (e.g. benzodiazepines). Acepromazine is usually avoided or used in low doses because it requires liver metabolism and may predispose a patient to hypotension and seizures. I usually administer only an opioid (often intravenously to obtain a greater effect) followed by mask induction with an inhalant to avoid using other medications that require hepatic metabolism. Monitoring blood pressure is essential to evaluate a patient's response to surgical correction. Ideally, blood pressure should be monitored invasively by using an arterial catheter. Hypothermia is a common complication; vaporizer settings should be appropriately turned down, warm-water or warm-air blankets should be used, and cold fluid administration should be avoided.

Q: How do you manage the delicate balance of fluid therapy during anesthesia in an animal with both renal and cardiac disease?

Fluid administration goals should include avoiding overhydration and maintaining urine output. Electrolyte abnormalities should be corrected before the procedure, if possible. Monitoring central venous pressure and performing chest auscultation to detect signs of pulmonary edema can help practitioners avoid excessive fluid administration in patients predisposed to volume overload. Some clinicians would prefer administering fluids with a lower sodium concentration rather than a balanced electrolyte solution in these patients. Urine output can be grossly evaluated by monitoring changes in urinary bladder size; however, a continuous closed monitoring system will provide a quantitative evaluation. Measuring the fluids administered and eliminated as well as monitoring body weight perioperatively may help maintain fluid homeostasis.

Using an anesthetic agent protocol that will minimize changes in cardiovascular performance (e.g. highly dependent on opioids for analgesia) will help prevent both pulmonary edema and inadequate perfusion of the kidneys. Maintaining mean arterial blood pressure above 70 mm Hg by using lower vaporizer settings will also help ensure renal perfusion. Continued monitoring well after recovery is prudent.

Q: How should we manage diabetic patients before surgery?

The goals of anesthesia in a patient with diabetes mellitus include avoiding both hypoglycemia and hyperglycemia. The patient's glucose concentration should be well-regulated before surgery. Eliminate ketoacidosis, dehydration, and electrolyte abnormalities before anesthesia.


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Source: VETERINARY MEDICINE,
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