Small Animal Surgical Emergencies. Группа авторов
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patient electrolyte status, and coagulation status. In the emergent situation, shock doses of isotonic crystalloids can be administered as intravenous boluses. The total shock dose for a dog is approximately equal to one blood volume, or 90 ml/kg body weight, with the shock dose for a cat being approximately 40–60 ml/kg body weight. One‐quarter of the total shock dose (20–25 ml/kg for dogs, 10–15 ml/kg for cats) may be administered over approximately 15 minutes, with repeated assessment of the patient's perfusion parameters. Once there is improvement and/or normalization of heart rate, pulse quality, mucous membrane color, and capillary refill time, fluid rates can be tapered accordingly.
Blood products including whole blood and packed red blood cells may be indicated in cases of acute hemorrhage, and/or when the hematocrit is below 20%, as there is inadequate oxygen delivery because of decreased oxygen‐carrying capacity. It is important to also recognize that dogs and cats can exsanguinate with a normal hematocrit. Furthermore, in acute hemorrhage, the hematocrit may in fact be normal and a decrease in total solids may be apparent first. With this in mind, early clinical identification of large volume blood loss, coupled with early intervention, is critical. This is especially relevant in patients with acute abdomen secondary to a bleeding abdominal mass or injured abdominal organ. In these patients, the source of hemorrhage must be identified and controlled while crystalloids and blood products are administered pre‐ and perioperatively as needed to maintain euvolemia and a hematocrit above 20%.
Hypertonic crystalloids can also be used for rapid intravascular volume expansion. Hypertonic crystalloid solutions (7–7.5% saline) are used to raise the intravascular concentration of sodium ions, which in turn draws water out of the interstitial space to increase intravascular fluid volume. Hypertonic saline should be administered slowly at a rate of not more than 1 ml/kg/minute for a total dose of 4 ml/kg. Administration of hypertonic saline should be followed with isotonic crystalloids to replace the interstitial volume as fluid shifts quickly into intracellular and interstitial spaces.
Stabilization of the patient in distributive shock also initially includes fluid resuscitation to optimize intravascular volume and oxygen supplementation. Fluid requirements are often very high owing to the vasodilation that may occur with severe systemic inflammation. Arterial blood pressure monitoring is helpful for guiding early goal‐directed fluid therapy. Even after appropriate fluid resuscitation, patients with distributive shock will often require circulatory support in the form of positive inotropes and/or pressor agents to increase cardiac output and/or blood pressure. If the source of distributive shock is infectious, identification and source control are critical. Early initiation of broad‐spectrum antimicrobial therapy is critical in all cases of suspected sepsis, in addition to taking necessary steps toward source identification and control (i.e., diagnostic abdominocentesis and abdominal exploratory surgery in cases of septic peritonitis).
Monitoring Response to Treatment
Monitoring the response to treatment should begin immediately and should be performed repeatedly throughout resuscitation. Frequent reassessment of heart rate, pulse rate and quality, mucous membrane color, capillary refill time, and level of consciousness should be made, in addition to repeated measurements of blood pressure, blood lactate, blood oxygen saturation via pulse oximetry, and electrocardiogram (ECG) monitoring. Positive responses to resuscitation are reflected by normalization of heart rate and pulse quality, return of mucous membrane color to pink, with a capillary refill time of less than two seconds, normalization of respiratory rate and effort, and an improved level of consciousness. Measured responses include normalization of blood pressure and lactate, stabilization and/or elevation of hematocrit, and blood oxygen saturation greater than 95%.
Systematic Approach to Initial Stabilization: Respiratory System
Emergency evaluation of the respiratory system should begin with an initial visual assessment of respiratory rate and effort to collect early information on patient condition, including observations of breathing with a restrictive pattern, abdominal effort, or paradoxical breathing. This, in conjunction with thorough auscultation to identify abnormal lung sounds indicative of pulmonary parenchymal disease or pleural space disease, is critical. Because vomiting is a common finding in acute abdomen patients, they may be at higher risk for aspiration pneumonitis and pneumonia, and may have increased ventral lung sounds. Pulmonary manifestations of sepsis, including septic pneumonitis, acute lung injury, and acute respiratory distress syndrome, may also be present. In addition, patients who have endured abdominal trauma may also have concurrent thoracic trauma, including rib fractures, pleural space disease, and pulmonary contusions. Even though physical examination is usually very effective in identifying clinically significant thoracic injuries, thoracic focused assessment with sonography for trauma ((FAST) and thoracic radiography are useful to confirm and/or differentiate between these causes.
Ancillary diagnostics to evaluate the respiratory system include pulse oximetry and arterial blood gas analysis. Pulse oximetry is a rapid, noninvasive way to measure oxygen saturation of the blood, with normal values ranging from 95% to 100%, and with severe hypoxemia indicated by levels less than 90%. Arterial blood gas analysis can be used to help distinguish the cause of severe hypoxemia, which occurs when the partial pressure of oxygen in arterial blood (PaO2) is less than 60 mmHg. Evaluation of ventilation status is necessary to differentiate between hypoventilation (hypoxemia combined with hypercapnia at a partial pressure of carbon dioxide in arterial blood, PaCO2, > 45 mmHg) and diffusion impairment, ventilation/perfusion mismatch or a shunt, all of which should have normal PaCO2. Oxygen responsiveness as indicated by improvement of PaO2 with supplementary oxygen challenge is supportive of ventilation/perfusion mismatch, decreased levels of inspired oxygen, or hypoventilation.
Oxygen therapy is provided by flow‐by supplementation, nasal cannulae (to include high‐flow oxygen therapy), or placement of the patient in an oxygen chamber. These methods all provide a fraction of inspired oxygen (FiO2) of approximately 30–100% and are often sufficient to help a patient maintain adequate oxygen saturation and normal arterial blood oxygen levels (PaO2 80–120 mmHg). In patients with pleural space disease, thoracocentesis is performed for both diagnostic and therapeutic purposes. Response to treatment is determined largely by serial pulse oximetry measurements, blood gas analysis, and repeated clinical assessment of patient respiratory effort and comfort. In patients who are persistently hypoxemic despite oxygen supplementation, or those with severe hypoventilation (PaCO2 > 60 mmHg) and/or respiratory fatigue, mechanical ventilation is indicated to provide ventilatory support to the patient while the underlying disease is addressed.
Systematic Approach to Initial Stabilization: Central Nervous System
Initial examination of the patient should include evaluation of the patient's mentation, posture, gait, as well as palpation for spinal or rectal pain. Decreased levels of consciousness, with increasing severity are depressed/dull, obtunded, stuporous, and comatose. The depressed/dull or obtunded patient will react normally to evoked stimuli, while the stuporous patient responds to only noxious stimuli, and the comatose patient is completely unresponsive except for reflex activity [5].
Animals with acute abdominal pain are sometimes described as having a hunched appearance or holding themselves in the “bow” or “praying position.” Painful spinal conditions including intervertebral disk disease, discospondylitis, spinal fractures, and spinal neoplasia may mimic this hunched positioning and be mistaken for abdominal pain. A complete neurologic examination should be performed before administration of pain medications to effectively rule out neurologic disease as the cause for pain. The use of opioids is preferred over other classes of drugs, including nonsteroidal anti‐inflammatory drugs (NSAIDs), owing to their rapid onset and better pain control, as well as the common findings of hypoperfusion and the potential for further adverse renal and gastrointestinal effects of NSAIDs.
Initial stabilization of patients with central nervous system (CNS) injury includes immobilization in the case of suspected spinal injuries and intravenous fluid support. Animals with a suspicion of spinal trauma should be immobilized by affixing to a board to prevent further injury.