Patient Assessment for Anesthesia

Stages of Anesthesia

• Preanesthesia Endpoint: The patient is a well-sedated animal, tranquil enough to allow for stress-free placement of an intravenous (IV) catheter, indicating readiness for the next steps in the anesthetic process.

• Induction Endpoint: The patient is successfully intubated (endotracheal tube placed into the trachea) and is in a lightly anesthetized state, sufficient for securing the airway and transitioning to maintenance anesthesia.

• Maintenance Endpoint: The animal is actively maintained in a safely anesthetized state, ensuring adequate depth for the surgical or diagnostic procedure while minimizing adverse effects. This is achieved either by inhalant anesthetics (e.g., isoflurane, sevoflurane) delivered via an anesthetic machine or by continuous intravenous injectable anesthesia (e.g., propofol, alfaxalone infusions).

• Recovery Endpoint: The animal has emerged from anesthesia, is in sternal recumbency (for small animals, SA) or standing (for large animals, LA), extubated (endotracheal tube removed), and breathing unassisted. The patient is stable and conscious enough to be left with less direct supervision, indicating a safe return to a physiological state.

Homework: History and Physical Exam Findings

• Review Homework – “Looking for Clues” for patient assessment.

• Homework questions:

  • What are typical questions asked prior to anesthesia? These questions are designed to gather crucial historical data on the patient's overall health, previous illnesses, medications, and any pre-existing conditions that might impact anesthetic safety.

  • What do particular physical exam findings tell us about our patient? Specific findings (e.g., heart murmur, pale mucous membranes, dehydration) provide vital clues regarding the patient's current physiological status and potential anesthetic risks.

• Note: Material is testable on the first Lecture exam, emphasizing its importance for foundational knowledge.

Legal Documentation

• A MUST! Comprehensive and accurate legal documentation is essential for client communication, patient safety, and medico-legal reasons.

• Owner info: Full name, address, and contact details for the animal's owner.

• Patient info: Full patient name, breed, age, sex/neuter status, and microchip number.

• Contact info for the day: Emergency contact numbers and preferred communication methods while the patient is hospitalized.

• Procedure(s) to be performed: Clear description of all planned surgeries, diagnostics, or treatments.

• Include details!!!!: Specifics regarding the anticipated procedure, potential complications, and expected outcomes.

• Consent – preop assessment: Signed owner consent form indicating understanding and approval of the anesthetic and surgical plan, based on a thorough pre-operative assessment of the patient's health.

• Advised of the risks: Documentation that the owner has been fully informed of potential anesthetic and surgical risks, including common complications and rare but serious adverse events.

System Overview: What do they look like? Clues from Hx and PE; Tests to run

• A systematic review of all body systems is critical for identifying potential anesthetic risks.

• What tests do you want to run? Diagnostic tests we can run to further assess and mitigate risks for specific systems:

  • Cardiovascular: To evaluate heart function, rhythm, and blood pressure.

  • Respiratory: To assess lung function and gas exchange capabilities.

  • Urinary: To check kidney function and hydration status.

  • Nervous: To evaluate central nervous system integrity and intracranial pressure.

• Most Important Systems for anesthesia: The cardiovascular and respiratory systems are paramount, as anesthetic agents directly affect their function, and their compromise can lead to life-threatening complications.

Signalment, Chief Complaint and History

• Signalment – Age, breed, sex, and reproductive status of the patient. This information provides initial clues about potential breed-specific diseases or age-related risks.

• Ill in the past 24 hours?: Recent changes in health can indicate acute conditions that might increase anesthetic risk.

• Previous illness: History of chronic diseases (e.g., diabetes, kidney disease) requires specific anesthetic management.

• Meds?: Current medications, including supplements or over-the-counter drugs, must be known due to potential drug interactions with anesthetics.

• Allergies/rxn: Any known allergies or adverse reactions to previous medications or anesthetics can guide drug selection.

• C, S, V, D: Assessing recent occurrences of coughing, sneezing, vomiting, or diarrhea can indicate respiratory issues, dehydration, or gastrointestinal upset, all of which impact anesthetic safety.

• Tolerate exercise?: Exercise intolerance can be a sign of underlying cardiac or respiratory disease.

• Vaccines current?: Vaccination status indicates general health and potential exposure to infectious diseases.

• Surgery/Diagnostics to be performed: Understanding the planned procedure helps anticipate duration, positioning, and specific anesthetic needs.

• Previous anesthesia: History of prior anesthetics, including any complications or smooth recoveries, is valuable for tailoring the current anesthetic plan.

System: Cardiovascular

• Hx and PE indicators:

  • Exercise intolerance, weakness: Can suggest poor cardiac output or underlying heart disease.

  • Cough, change in breathing: May indicate congestive heart failure (pulmonary edema) or pulmonary hypertension.

  • Abnormal heartbeat: Arrhythmias or murmurs detected on auscultation (listening with a stethoscope) suggest underlying cardiac disease.

  • Weak pulse, pulse deficits, prolonged CRT (Capillary Refill Time): Indicators of poor peripheral perfusion or cardiac output.

• Anesthetic concerns:

  • Arrhythmias, BP issues: Anesthetics can exacerbate pre-existing arrhythmias or cause hypotension (low blood pressure) or hypertension.

  • Watch preload (CVP - Central Venous Pressure): Careful management of intravenous fluid administration is crucial as fluids directly impact preload and cardiac output. Over- or under-hydration can be detrimental.

  • Vasoconstriction or vasodilation will change the workload of the heart (drug selection): Anesthetic drugs affect vascular tone, which alters systemic vascular resistance and thus the heart's workload. Drug choices should support cardiac function.

  • Increased sympathetic tone – stress an already damaged heart: Stress or pain can increase sympathetic nervous system activity, releasing catecholamines that may further compromise a diseased heart.

• Diagnostic tests:

  • BP: Non-invasive blood pressure measurement is essential to assess cardiovascular function and guide fluid/drug therapy.

  • EKG (Electrocardiogram): To evaluate heart rate, rhythm, and detect arrhythmias.

  • Chest X-ray: To assess heart size (cardiomegaly) and presence of pulmonary edema.

  • Echocardiogram: Ultrasound of the heart to evaluate cardiac structure, function, and valvular integrity.

System: Respiratory

• Hx and PE indicators:

  • Cough, sneezing, wheezing at home: Suggests chronic respiratory issues like bronchitis, asthma, or collapsing trachea.

  • Out of breath after exercise: Indicative of reduced respiratory reserve.

  • Observe breathing: Labored, cough, sneeze, wheeze, stridor (harsh sound on inspiration), excessive panting, mucous membrane color. These signs point to airway obstruction, altered breathing patterns, or hypoxemia.

  • Cat-open mouth?: Open-mouth breathing in cats is a critical sign of respiratory distress.

  • Nasal or ocular discharge?: Can indicate upper respiratory infection or inflammation.

• Diagnostic tests:

  • Chest X-ray: To assess lung parenchyma, airways, and pleural space.

  • Pulse oximetry (pulse ox): Measures oxygen saturation of hemoglobin ($SpO_2$) in arterial blood, indicating oxygenation status.

  • Oxygen trial: Administering supplemental oxygen to see if respiratory distress improves, helping differentiate cardiac vs. respiratory causes.

• Anesthetic concerns:

  • Gas exchange issues, may need assistance with ventilation: Patients with impaired lung function may struggle with oxygen uptake or carbon dioxide elimination, often requiring mechanical ventilation support during anesthesia.

  • Hypo- or hyperventilation will affect O2 and CO2 levels: Hypoventilation leads to hypercapnia ($PaCO_2$ elevation) and hypoxemia, while hyperventilation can lead to hypocapnia. Both can cause significant acid-base disturbances.

  • Monitor with pulse ox, capnograph, blood gases: These tools provide real-time assessment of oxygenation ($SpO<em>2$), ventilation ($ETCO</em>2$ via capnography), and acid-base status, allowing for timely intervention.

System: Genitourinary

• Hx and PE indicators:

  • Intact?: Unspayed females might be in estrus (heat) or pregnant, impacting drug sensitivity and uterine blood flow. Intact males are prone to prostatic issues.

  • Last Heat? (likely heat = heat cycle in breeding): Crucial for unspayed females due to potential for pseudopregnancy, pyometra, or increased vascularity of reproductive organs.

  • Bred?: Pregnancy significantly alters physiology, requiring extreme caution with drug selection and dose.

  • Changes in urination? “Do they pee??”: Polyuria (increased urination) or oliguria (decreased urination) can indicate kidney disease or dehydration. Assessing urination frequency and volume is key.

  • Inappropriate urination?: Can be a sign of urinary tract infection, bladder stones, or other renal issues.

  • Both testicles, vulvar discharge/swelling/right sex: Important for surgical planning (e.g., cryptorchid surgery) and detecting reproductive tract abnormalities.

  • Bladder palpation: To assess bladder size and ensure it's not distended, especially before abdominal procedures.

• Diagnostic tests:

  • Electrolytes: To assess hydration and kidney function, as imbalances (e.g., hyperkalemia in blocked cats) can be life-threatening.

  • UA (Urinalysis): To assess renal concentrating ability, presence of infection, or crystal formation.

  • Vaginal smear: To determine stage of estrus or diagnose vaginitis.

  • EKG if blocked: Urethral obstruction in male cats often leads to hyperkalemia, causing characteristic EKG changes.

  • X-ray: For detecting bladder stones or kidney size abnormalities.

  • U/S (Ultrasound): For detailed imaging of kidneys, bladder, and reproductive organs.

• Anesthetic concerns:

  • Monitor urine production: Essential during anesthesia to assess kidney perfusion and hydration status, often via a urinary catheter.

  • If cannot urinate – watch preload!!: In cases of urinary obstruction, inability to excrete fluid can rapidly lead to fluid overload and increased preload, impacting cardiac function. Careful fluid management is critical.

  • Urinary excretion of drugs: Many anesthetic drugs and their metabolites are excreted renally. Impaired kidney function can prolong drug effects and lead to accumulation.

  • Avoid hypotension – further injury to nephrons: The kidneys are highly susceptible to hypotensive episodes, which can lead to acute kidney injury (AKI) or worsen pre-existing renal disease.

System: Nervous

• Hx and PE indicators:

  • LOC changes – mentation: Alterations in level of consciousness (e.g., obtundation, stupor, coma) indicate neurological compromise.

  • Neuro exam – ocular changes (PLR, anisocoria): Pupillary light reflexes (PLR) and unequal pupil size (anisocoria) can provide clues about central nervous system health and intracranial pressure (ICP).

  • Changes in Respiratory: Respiratory pattern changes (e.g., Cheyne-Stokes, apneustic breathing) can indicate brainstem dysfunction or increased ICP.

  • Altered BP, HR (Cushing’s Reflex – associated with changes in Intracranial Pressure): Cushing's reflex is a classic sign of increased ICP, characterized by hypertension, bradycardia, and irregular respiration.

• Diagnostic Tests:

  • Baseline neuro exam: A complete neurological assessment prior to anesthesia is crucial for monitoring changes.

  • BP: To detect hypertension associated with Cushing's reflex or assess perfusion.

  • X-ray/CT/MRI: Imaging of the brain or spinal cord to identify structural lesions (e.g., tumors, herniation, trauma).

• Anesthetic concerns:

  • Fluids, BP, ventilation: Careful management of fluid rates, maintaining stable blood pressure (avoiding hypo- and hypertension), and controlling ventilation ($PaCO_2$) are critical to maintain cerebral perfusion pressure ($CPP = MAP - ICP$) and minimize increases in ICP.

System: Musculoskeletal

• Hx and PE indicators:

  • Slow to rise, favoring one limb: Suggests pain, weakness, or orthopedic issues.

  • Cry when picked up?: Indicates a painful area or generalized discomfort.

  • What meds/OTC?: Knowledge of NSAIDs or other pain medications being administered is important due to potential interactions or previous pain management.

  • Hunched, stiff: Postural changes can indicate back pain, abdominal pain, or other musculoskeletal discomfort.

• Diagnostic tests:

  • X-ray: For diagnosing fractures, arthritis, or other bony abnormalities.

  • Orthopedic exam: A thorough physical manipulation of joints and limbs to localize pain or instability.

• Special anesthesia/sx considerations??:

  • Positioning concerns: Patients with orthopedic issues (e.g., severe arthritis, fractures) require careful positioning during anesthesia to prevent further injury, nerve damage, or discomfort.

  • Chronic pain / wind up – will make it harder to manage pain: Chronic pain can lead to central sensitization (