Anesthesia related complications Flashcards
Anesthesia related complications
-hypothermia
-hypotension
-hypoventilation (hypercapnia)
-hypoxemia
-bradycardia
Procedure related complications
-pain
-hemorrhage
Patient specific complications
-upper airway obstruction
-regurgitation/vomiting= aspiration
-hyperthermia
Causes of hypoxemia and low SpO2
-low inspired O2
-hypoventilation
-diffusion problem (pulmonary disease)
-ventilation perfusion (V/Q) mismatch
-right to left shunt
Mild Hypoxemia
SpO2 >80%
-activation of sympathetic nervous system
-increased HR, mild hypertension
Moderate Hypoxemia
SpO2 60-80%
-local vasodilation leading to hypotension
-reflex increase in HR
Severe Hypoxemia
SpO2 <60%
-local depressant effects predominate
-rapid decrease in BP leading to severe hypotension
-bradycardia, leading to ventricular fibrillation or cardiac arrest
Consequences of hypoxemia
-tissue hypoxia
-lactic acidosis
-organ failure
High risk patients for hypoxemia
-brachycephalics
-diaphragmatic hernia
-pneumothorax, pulmonary contusion
-upper airway obstruction
-pneumonia
-abdominal distension (GDV, C-section)
Low inspired O2 causing hypoxemia
-Check O2 supply
-endotracheal tube: check if tube is properly placed (esophageal, endobronchial)
-check that breathing system is tightly attached to ET tube
-airway obstruction (remove or bypass)
Hypoventilation causing hypoxemia
-check anesthetic depth
-administer O2
-intermittent positive pressure ventilation (IPPV)
Ventilation perfusion mismatch and intrapulmonary shunting leading to hypoxemia
Need to improve perfusion and ventilation
Specific ways to help with breathing under anesthesia
-Provide O2
-Position= sternal
-extend head and neck, pull out tongue
-Place Iv catheter and induce anesthesia
Stage 3, plane 1
Eye position=central
Palpebral reflex present
Stage 3 plane 3
Eye position= central
Absent palpebral reflex
Hypotension definition
SAP <80mmHg
MAP < 60mmHg
DAP <40mmHg
Driving force of Hypotension
MAP
MAP <60mmHg = compromised perfusion of visceral organs
Treating small animals with hypotension
-under 6mths have a physiologically low BP
-Geriatric: sub clinical organ impairment
TREAT earlier and more aggressive
Treating large animals with hypotension
Horses: minimum acceptable MAP 70mmHg (myopathy)
Treating severe hypotension
*sudden onset, MAP 35-45 mmHg)
Requires more aggressive diagnosis and correction
3 basic pathophysiological mechanisms leading to hypotension
- decreased vascular tone
- decreased CO
- hypovolemia
Hypotension and depth of anesthesia
Vasodilation: vasomotor center excessively depressed
-decrease vaporizer setting
-admin anesthetic sparing drugs
Anesthetic sparing drugs for hypotension
-Hydromorphone
-butorphanol
-morphine
-Continuous Rate Infusion of fentanyl, ketamine, lidocaine
Check HR during hypotension
Treat Bradycardia (1/2 rest HR), which can decrease CO
**slow normal heart rates do not usually affect CO
Anticholinergics: Atropine, Glycopyrrolate
Fluids for hypotension
- Crystalloid fluids
- Colloid bolus
- Hypertonic saline
Crystalloid fluids
-isotonic balance
-fluid bolus: 3ml/kg over 15mins for cats; 5ml/kg for dogs
**over 2-10mins if MAP <40mmHg
-repeat once if needed
Colloid bolus
Hypertonic saline
Ephedrine use for hypotension
Positive inotrope (Dobutamine) for persistent MAP <60 mmHg
Vasopressor for hypotension
**Last resort
-NE infusions and Vasopressin infusions
NE infusions
-alpha 1 vasoconstrictor
-may dimish visceral organ perfusion (liver, kidneys)
-try to limit emergency use only
-treatment for refractory hypotension (septic patients)
Vasopressin infusions
-non-catecholamines vasopressor (V1 receptors)
-used for refractory hypotension
-very sick patients or post cardiac arrest
Causes of bradycardia
-Drugs: alpha 2 agonists, opioids
-deep plane of anesthesia
-hypothermia
-vagal reflexes (oculo cardiac reflex)
-electrolyte imbalance
-sinus bradycardia
-AV block
Cardiac arrhythmias
Ventricular premature complexes
Sinus bradycardia with escape beat
Tachycardia
HR >180bpm in dog, or >200 bpm in cats
Causes of tachycardia
- Sympathetic response to:
-pain
-awareness
-hypotension
-hypoxemia
-hypercapnia
-hypovolemia - drug induced? Anticholinergics?
Regurgitation/Gastro-esophageal reflux (GER)
-Brown fluid from nose
ADD
Predisposing factors for Regurgitation
-brachycephalic breeds
-drugs relaxing lower esophageal sphincters (volatiles, opioids, anticholinergics, propofol)
-increased intra-abdominal pressure (pregnancy, obesity, surgery, head down position)
-prolonged anesthetic
Preventative measures for Regurgitation
-appropriate pre-anesthetic fasting
-pretreatment with omeprazole, maropitant, metoclopramide
-use of cuffed ET tube
Treatment of Regurgitation
-Secure airway in unconscious patient
-place suction catheter in esophagus
-suction refluxate and lavage with tap water
-instillation of 5-30ml Na-Citrate solution
-check and suction again prior to extubation
-Pantoprazole, famotidine
Hypercapnia
Normal: 35-45 mmHg
Mild: 45-60mmHg
-SNS stimulation= tachycardia, mild hypertension
Severe: >90mmHg
-severe CNS depression (narcosis)
-respiratory arrest (depression of brainstem)
Clinical signs when CO2 >60mmHg
- bounding pulses (high systolic, low diastolic)
- Vasodilation (brick red colour, capillary oozing)
Causes of hypercapnia
- hypoventilation
- equipment failure
- endobronchial intubation
- V/Q mismatch
- Apparatus dead space (overlong ET tube)
- increased CO2 production (hyperthermia)
Causes of hypoventilation
-respiratory depressant drugs
-positioning (dorsal)
-abdominal distension
-obesity
Equipment failure causing hypercapnia
-unidirectional valves (circle systems)
-CO2 absorber exhausted
-inadequate fresh gas flow (non-rebreathing systems)
Preventing Hypothermia
- insulation (towels bubble packs)
- Warming mats (circulating water, electrical, hot dogs, microwave bags of fluids, bean bags, snuggle safe)
- Warm air blankets (bair hugger)
- radiant heat lamps
- warm IV fluids/irritation fluids
Potential problems with warming devices
- patient cannot move away
- blood flow may not conduct heat away
- body pushed into heat source
- temperature must be monitored
- burns from direct contact to patient… use towel for insulation
Animals susceptible to hyperthermia
-heavy coated dogs on circle rebreathing system
-post op hyperthermic cats- linked to mu opioids, ketamine, intra-op hypothermia
-malignant hyperthermia
Treatment for hyperthermia
-turn off supplemental heat, remove blankets, ice packs
-water, alcohol to inguinal and axillary regions
-fans (but be careful of corneal ulcers)
-Acepromazine- causes vasodilation and resets hypothalamus temperature set point
Extubation of brachycephalic breeds
-Late extubation to avoid airway obstruction
**be patient, keep period between extubation and full alertness as short as possible
