INTRODUCTION

Careful assessment of the critically ill small animal patient can make the difference between surgical success or failure and, in particular, the difference between the animal’s life and death. The primary objective of evaluation of the preoperative patient is to recognize and treat any conditions that will increase the risk of anesthetic and surgical complications.^1,2 In addition, preoperative evaluation may provide some indication of the likely outcome for the patient (see Chapter 3, Survival Prediction Index).

Evaluation of the animal’s signalment, history, physical examination, diagnostic tests, and presumed anesthetic risk are essential. Triage and physical examination are of particular importance when evaluating the critically ill patient (see Chapters 1 and 2, Physical Examination and Patient Triage, respectively). The respiratory, cardiovascular and hematologic systems are of primary importance when considering anesthetic and surgical risks. The clinician should use a step-by-step approach to each patient, to ensure that all necessary information regarding these systems is obtained before anesthesia induction.

Part of the assessment of the preoperative patient is the choice of an appropriate anesthetic protocol (see Chapter 163, Anesthesia of the Critically Ill Patient).

RESPIRATORY RESUSCITATION

Any sign of respiratory distress and hypoxemia should be corrected with supplemental oxygen therapy. An arterial blood gas analysis may not be feasible and may cause untoward distress for the critically ill patient. Therefore noninvasive evaluation of respiratory status with pulse oximetry and visualization of the animal’s respiratory effort can be used to determine response to oxygen therapy. Once the animal is able to tolerate the procedure, thoracic radiographs should be performed to determine whether pulmonary parenchymal (contusions, pneumonia, pneumonia, edema), pleural space (pneumothorax, diaphragmatic hernia), or thoracic cage (rib fractures) abnormalities are present. Thoracic radiographs are always recommended before a major surgical procedure to rule out abnormalities that may affect the patient’s ability to tolerate anesthesia, as well as to look for evidence of neoplasia that may alter the prognosis and hence the owner’s expectations for the animal (see the Respiratory Disorders section of this text).

CARDIOVASCULAR RESUSCITATION

Hypovolemic shock is the most common cause of cardiovascular compromise in the critically ill patient and needs to be resolved before anesthesia induction. Clinical signs of hypovolemic shock include prolonged capillary refill time, tachycardia or bradycardia, hypotension, pale mucous membranes, and decreased urine output. A more thorough explanation regarding clinical signs and treatment of various forms of shock are listed elsewhere in this text. If pulse deficits, bradycardia, tachycardia, or an irregular heart rhythm is noted on physical examination, an electrocardiogram is indicated and specific therapy administered as appropriate (see Chapters 45, 46 and 47, Bradyarrhythmias and Conduction Abnormalities, Supraventricular Tachycardia, and Ventricular Tachyarrhythmias, respectively).

PAIN

Pain has numerous systemic consequences, slows recovery, and can prevent adequate assessment of the patient. Adequate analgesia is an essential aspect of stabilization of the critically ill patient. A variety of pain scoring systems have been used to document the severity of pain in animals.³ In some cases pain assessment is easy, when the animal exhibits obvious signs of distress such as yelping, splinting or guarding of the injured site, or lameness. Some individuals, however, appear more stoic and, rather than display abnormal behaviors, demonstrate a lack of normal behaviors as their only sign of discomfort (see Chapter 161, Pain and Sedation Assessment and Analgesia). Analgesic drugs should never be withheld, even in the most critically ill patient. Opioid drugs do not adversely affect the cardiovascular system and are safe to use in even the most critically ill animals. Administration of a preanesthetic drug not only acts as an analgesic, but also decreases the total dosage of drug(s) required for anesthesia induction and maintenance (see Chapters 162, 163 and 164, Sedation of the Critically Ill Patient, Anesthesia of the Critically Ill Patient, and Constant Rate Infusions, respectively).