Anesthesia for Patients withCardiovascular, Respiratory & Gastrointestinal Diseases

Lyon Lee DVM PhD DACVA

Patients with Cardiovascular Diseases

General considerations

• Most anesthetics produce some degree of cardiovascular depression 

• The patient with preexisting cardiovascular disease often has reduced cardiac reserve - less ability to compensate for anesthetic-induced depression 

• Usually patients with compensated cardiovascular disease (that is, not exhibiting any clinical symptoms of their disease) tolerate anesthesia fairly well 

• The cardiopulmonary system functions  to ensure that the rate of delivery of oxygen (DO2) meets or exceeds the consumption of oxygen (VO2) in the whole body (review Cardiopulmonary Physiology lecture)

• Effects of anesthetics on the cardiovascular system are 

  • Impairment of calcium utilization (inhalants, barbiturates) 

  • Alteration of systemic vascular resistance, heart rate, blood pressure

  • Development of intracellular acidosis (secondary to respiratory depression) 

• Many different types of cardiovascular disease may be encountered 

  • Congenital heart disease 

  • Acquired valvular disease 

  • Significant preexisting arrhythmias 

  • Hypotension/hypovolemia 

  • Dilated cardiomyopathy 

  • Anemia 

• Primary goals of anesthetic management in these patient groups are to

  • Avoid wide swings in heart rate 

  • Minimize changes in preload and afterload 

  • Prevent hypovolemia or overhydration

  • Minimize changes in inotropy (myocardial contractility)

Ways to support the cardiovascularly challenged patients 

• Stabilize heart rate & rhythm prior to anesthesia if possible 

• Optimize cardiac function prior to anesthesia if possible

• Physical examination: observe jugular distension, pulsation, palpate peripheral arterial pulse quality, auscultate heart for assessing characters of pulsation 

• Thorough cardiac evaluation prior to anesthesia - ECG, Doppler echocardiograph, thoracic radiographs, blood pressure measurement, ultrasonography, cardiac catheterization

• Laboratory evaluation -  PCV, TP, hemoglobin content, arterial blood gases, electrolytes

• Choose anesthetic agents that produce minimal cardiovascular changes and preferably have drugs of short duration of action or that are reversible 

• Preanesthetics: rely mostly on opioids +/- benzodiazepines: neuroleptanalgesic combination

• Anticholinergics are used judiciously

• Employ local anesthetic technique under sedation or even general anesthesia

• Induction: propofol, etomidate, ketamine, mask with inhalant 

• Maintenance: usually isoflurane or sevoflurane (rapid recovery and less cardiovascular depression than halothane)

• Monitor cardiovascular performance 

  • ECG: rate and rhythm 

  • Arterial blood pressure (BP = CO x SVR) 

  • Central venous pressure (preload) 

• Treat arrhythmias if they develop 

  • Significant VPC – lidocaine, beta-blockers 

  • Significant bradycardia or bradyarrhythmias – glycopyrrolate, atropine, isoproterenol or temporary pace maker implant if medically nonresponsive

• Support inotropy with 

  • Adrenergic agonists

    • Dobutamine 

    • Dopamine

    • Doepxamine 

    • Ephedrine

    • Norepinephrine

    • Epinephrine 

  • Phophodiesterase inhibitor

    • Milrinone

    • Amrinone

    • Enoximone

    • Theophylline

    • Pentoxyfylline

  • Calcium channel sensitizer

    • Levosimendan

    • Pimobendan

  • Digoxin

    • Calcium

    • Glucagon

Case example

• “Taylor” 

• Signalment: 6 month old intact male Maltese of 2kg in bwt

• History: presented for evaluation of inappetence, ataxia, weakness and exercise intolerance 

• Significant physical exam findings: ataxia, muscle weakness, heart murmur

• Laboratory finding: no abnormalities noted 

• Thoracic radiographs: enlarged heart shadow 

• Echocardiographic findings: patent ductus arteriosus 

• Presented for PDA surgical ligation

Patients with Respiratory Diseases

General considerations

• Many anesthetics produce some degree of respiratory depression

• The respiratory depression in combination with cardiovascular depression induced by most anesthetics, decreases oxygen availability in the tissues 

• Avoid heavy sedation that may induce excessive respiratory depression

• May have impairments of ventilation, oxygenation, or both 

• Ventilatory impairment affects acid/base balance 

• Oxygenation impairment affects oxygen delivery to tissues 

• Respiratory disease may be divided into upper or lower airway disease 

  • With upper airway disease, the key is to bypass the upper airway obstruction as quickly as possible 

  • With lower airway disease, our ability to correct/manage the problem may be more limited 

• Patient with poor compliance of the lung (restrictive disease such as pulmonary edema, fibrosis or effusion) tend to adopt rapid shallow ventilatory pattern

• Patients with obstructive disease (laryngeal paralysis, collapsing trachea, small airway disease) tend to adopt a slower pattern with increased respiratory effort

• Inspiratory dyspnea is usually associated with extrathoracic and expiratory dyspnea with intrathoracic lesion in origin.

• If pneumonic that can be treated with antibiotics and other supportive therapy, delay the surgery as long as possible until the symptom gets fully resolved

Preoperative evaluations 

• Thorough physical exam and ancillary investigation 

• Does the patient exhibit dyspnea at rest? with exercise/stress? 

• Is there stridor present? 

• Thorough auscultation of the lungs and trachea

• Radiographs/ultrasonography

• ECG

• Pulse oximetry

• Wright’s respirometer and tight fitting face mask to assess respiratory volume (tidal volume and minute ventilation) 

• Blood gas analysis 

Keys to anesthetic management 

• Preoxygenate, if possible 

• Thoracocentesis if needed (remove air, fluid, blood, etc...) 

• Minimize stress 

• Tranquilization/sedation with short acting or reversible drugs 

  • Opioids (resp. Depression) 

  • Benzodiazepines

  • Phenothiazines?

  • Avoid excessive doses so as to prevent resp depression 

• Rapid induction with short acting anesthetic agents 

  • Thiobarbiturates 

  • Propofol

  • Etomidate 

  • Ketamine  

• Minimize oxygen deficit period by allowing rapid intubation and ventilation 

• Control airway as quickly as possible, begin positive pressure ventilation (esp. with lower airway disease) 

• Nitrous oxide may be better avoided.

  • It diffuses into gaseous pocket and worsens symptoms such as pneumothorax 

  • It reduces the inspiratory fraction of oxygen

• Monitoring: 

  • ECG

  • Pulse oximetry

  • BP 

  • Capnography 

  • Serial blood gas analysis 

  • Tidal volume and peak airway pressure (thoracic compliance) 

  • Temperature

• Recovery 

  • Maintain ET tube in situ as long as possible 

  • Post-operative pulse oximetry

  • Support ventilation as long as possible 

  • Consider post anesthetic oxygen supplementation 

    • Mask 

    • Nasal catheter 

    • Oxygen cage 

  • Minimize stress, judicious use of tranquilizers/sedatives if needed 

  • If acute respiratory obstruction occurs post extubation, be prepared to reinduce anesthesia & reintubate rapidly

  • Treat chest pain so as to facilitate better use of respiratory muscle

Case example 1

• "Jake" 

• Signalment: 1 year old intact male Labrador retriever 

• History: presented for evaluation anorexia, listlessness of one week's duration 

• Significant physical exam findings: tachypnea, fever 

• Laboratory finding: elevated white blood cell count 

• Thoracic radiographs: pleural fluid, lung lobe collapse (suspect lung lobe torsion) 

• Presented for anesthesia 3/27 for thoracic exploratory 

Preanesthetic management?

Anesthetic induction?

Maintenance of anesthesia?

Monitoring?

Postoperative care?

Case example 2

• "Miss Genuines" 

• Signalment: 1 week old Quarter Horse filly 

• History: presented for choanal atresia 

• Significant physical exam findings: normal neonatal foal except for nasal obstruction 

• Laboratory finding: normal 

• Referring DVM had performed a tracheostomy shortly after birth 

• Presented for anesthesia 4/6 for laser surgical correction of choanal atresia 

Preanesthetic management?

Anesthetic induction?

Maintenance of anesthesia?

Monitoring?

Postoperative care?

Patients with Gastrointestinal Diseases

General considerations

• Variety of disease processes... 

• Malabsorption

• Derangement of electrolytes, acid-base status

• hypovolemia

• Preoperative stabilization of fluid balance, electrolyte balance important, if possible... 

Gastric dilitation/volvulus (GDV)

• Surgical emergency 

• Present with: 

  • Respiratory compromise 

  • Cardiovascular compromise 

  • Cardiac dysrhythmias (VPCs, V tach, tachycardia) 

  • Hypotension 

  • Hypoxemia 

  • Acid/base disturbances 

• If possible, decompress stomach prior to anesthesia 

• Large volumes of IV fluids rapidly (multiple large bore catheters) at 40-90 ml/kg 

• Acid/base evaluation helpful 

• Monitor & treat cardiac dysrhythmias as they present - lidocaine usually first line of defense 

• Anesthetic management 

  • Preanesthetic: opioids +/- benzodiazepines 

  • Induction: 

    • Rapid induction to gain control of airway quickly is preferable, initiate positive pressure ventilation 

    • May be able to intubate w/ neuroleptanalgesic combination (eg oxymorphone + diazepam) 

    • Propofol preferred 

    • Low dose thiopental may be used - but cautiously - potential for aggravating arrhythmias 

    • Mask induction w/ isoflurane/sevoflurane may be used - but it is still slower 

  • Maintenance 

    • Isoflurane/sevoflurane 

    • Supplemental opioids (eg oxymorphone, hydromorphone, fentanyl) IV to reduce inhalant concentration 

  • IPPV usually needed 

  • Monitor cardiovascular system closely 

    • ECG 

    • Blood pressure

Equine Colic

• One of our most common emergency surgical procedures 

• Patients present in a variety of conditions, from minimally to severely compromised 

  • Respiratory compromise 

  • Cardiovascular compromise 

  • Dehydration 

  • Hypotension 

  • Hypoxemia 

  • Electrolyte imbalances 

  • Acid/Base disturbances 

• Again, stabilize if possible 

  • Large volumes of fluids IV rapidly (multiple large bore catheters) 

  • Bicarbonate if acidotic 

  • Pain management (usually w/ alpha-2, NSAID such as Flunixin meglumine) 

• Our current anesthetic protocol 

  • Premedicate with xylazine + butorphanol or xylazine 

  • Induce with diazepam + ketamine or GGE + ketamine

  • Maintain with sevoflurane 

  • Monitor 

    • Invasive blood pressure 

    • ECG

    • Capnography

    • Serial blood gases and electrolytes 

  • Controlled ventilation (IPPV)

  • Multiple IV lines for rapid fluid administration 

  • Dobutamine or other positive inotropes to support BP and CO

  • Calcium supplementation if hypocalcemic 

  • Colloids if TP < 4 g/dl

• Recovery often slow - postoperative pain management should be considered