Anesthetic complications Flashcards
What does a normal resp system look like in values
Normal PaO2: 80-110 mmHg (FiO2= 21%)
Saturation of hemoglobin (SpO2): 97-100%
Hypoxemia: PaO2: < 60mmHg, SpO2: <90%
PaO2= 5x FiO2
Causes of hypoxemia and low SpO2
Low inspired O2 (FiO2)
Hypoventilation
Diffusion problem (pulmonary disease)
Ventilation perfusion (V/Q) mismatch
Right to Left Shunt
What are the clinical effects of mild hypoxemia
SpO2 >80%
Activation of sympathetic nervous system
Increased heart rate, mild hypertension
What are the clinical effects of moderate hypoxemia
(SpO2: 60-80%)
Local vasodilatation → hypotension
Reflex increase in heart rate
What are the clinical effects of severe hypoxemia
SpO2 < 60%)
Local depressant effects predominate
Rapid decrease in blood pressure → severe hypotension
Bradycardia → ventricular fibrillation or cardiac arrest
What are the consequences of hypoxemia
Consequences: Tissue hypoxia, lactic acidosis, organ failure
What patients are at high risk for hypoxemia
Brachycephalics
Diaphragmatic hernia
Pneumothorax, pulmonary contusion
Upper airway obstruction
Pneumonia
Abdominal distension (GDV, C-section,…)
How do you reduce your chances of hypoxemia
PRE-OXYGENATION prior anesthesia induction
There is no contra -indication to oxygen!
What are the causes of hypoxemia
Low inspired O2
Hypoventilation
Ventilation perfusion mismatch and intrapulmonary shunting
- Improve perfusion and ventilation
How can you fix low inspired O2
Check O2 supply (O2 tank, flow meter..)
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
How do you fix hypoventialtion
Check anesthetic depth
Administer O2
Intermittent positive pressure ventilation (IPPV)
What is the definition of hypotension
SAP less than 80mmHg
MAP less than 60mmHg
DAP less than 40mmHg
What causes hypotension
Mean arterial pressure is driving force for perfusion
MAP < 60mmHg compromised perfusion of visceral organs
Hypotension with SA
< 6months have a physiologically lower BP
Geriatric: sub-clinical organ impairment
Hypotension should be treated earlier and more aggressive
Hypotension wiht LA
Horse: minimum acceptable MAP 70mmHg (myopathy)
Severe hypotension (with sudden onset) MAP (35-45mmHg)
Requires more aggressive diagnosis and correction
What are the common causes of hypotension
Three basic pathophysiological mechanism that lead to hypotension are decreased vascular tone, decreased cardiac output and hypovolemia.
What are the common reasons hypotension happens with peripheral vascular resistance
Decrease (vasodilation)
- Inhalant anesthetics, ace
- Sepsis
Increase (vasoconstriction)
- Alpha 2 agonists
- Pain
What are the common reasons preload decreases
Hypovolemia
+ pressure ventilation
Why would contractility decrese and cause hypotension
Resp/metablic acidosis
Hypoxemia
Why would HR decrese and cause hypotension
Baroreceptor reponse
Parasympathetic activity
Why would HR increase and cause hypotension
Baroreceptor response
Pain
Hypoxia
Hypercapnia
Hypotension – basic management MAP <60mmHg
Check depth of anethesia
Check HR
fluids
Ephedrine
Last resort add a vasopressor
how does anesthetic drugs affect BP
Vasodilation: vasomotor center excessively depressed
Decrease vaporizer setting
Administer anesthetic sparing drugs
- Hydromorphone (0.05-0.1mg/kg)
- Butorphanol (0.1-0.4mg/kg)
- Morphine (0.1-0.3mg/kg)
- CRI of fentanyl, ketamine, lidocaine
How do you treat HR issues that are causing hypotension
-Treat bradycardia (1/2 of resting heart rate)
- Bradycardia can decrease cardiac output
- Slow normal heart rates do not usually affect CO
- Anticholinergics: Atropine, glycopyrrolate
What fluids do you give for hypotension
Crystalloid fluids (isotonic balanced)
- Fluid bolus: 3 (cats)-5 (dogs) mL/kg over 15min (2-10min if MAP< 40mmHg)
- Increases intravascular volume and improves venous return
- Repeat once if needed
Colloid bolus
- Dogs: 2-5mL/kg, cats: 1-5mL/kg over 15 min
- If response to crystalloids is inadequate
- Maximum dose 20mL/kg/day (dilution of clotting factors, avoid in sepsis)
- Pentaspan 6% (60% eliminated in 24 hours)
Hypertonic Saline (7.5%)
- 4mL/kg over 10 min, duration 30-120 min
- Indication: blood loss, need of rapid volume expansion
Why would you give ephedrine for hypotension
Synthetic noncatecholamine, stimulates 𝛼1 and 𝛽1 receptors
Indirect acting: release of endogenous norepinephrine
Vasoconstrictor/venoconstrictor
Dose: 0.02-0.05mg/kg IV
50 mg/ml vials (dilute for week)
Effects last up to 15 minutes
How do you respond to persistent MAP <60 mmHg
Add Positive Inotrope-Dobutamine
- Βets 1 agonist (increases myocardial contractility)
- Useful for low cardiac output stages in patients with adequate intravascular volume
- Used as an infusion (short half life)
- 2-15μg/kg/min
- Less risk of cardiac arrhythmias
- Add 100 mg dobutamine to 500mL 5% dextrose (200mg/mL)
- Infuse 0.01–0.07 mL/kg/min
What should you do as a last resort when hypotension persists
- Non-catecholamine vasopressor (V1 receptors)
- Used for refractory hypotension
- Very sick patients or post cardiac arrest
What causes Bradycardia
Drugs: alpha 2 agonists, opioids
Deep plane anaesthesia
Hypothermia
Vagal reflexes (oculo-cardiac reflex)
Electrolyte imbalance
What are common heart arrythmias during ansthesia
Sinus bradycardia
Atrioventricular block
Sinus arrest
Ventricular escape beats
Asystole
How do you treat cardiac arrhythmias
anticholinergics
Atropine: 0.02-0.04mg/kg
Glycopyrrolate: 0.01mg/kg
Low normal HR – measure arterial BP before initiating treatment
Do not confuse ventricular escape rhythms with VPCs
How do you treat Ventricular premature complexes
lidocaine bolus 1-2,g/kg +/- CRI is recommended when complexes are multiform, causing hypotension, or occurring in significant runs
How do you treat sinus bradycardia with escape beats
atropine or glycopyrrolate. The goal is to increase the HR as the escape beat is due to the slow sinus rate
When is a HR considered tachycardic
Heart rate >180 bpm (dog)
HR >200 bpm (cat)
What causes tachycardia
Sympathetic response to
Pain
Awareness
Hypotension
Hypoxemia
Hypercapnia
Hypovolemia
Drug induced?
Correct underlying problem!
Regurgitation / gastro esophageal reflux (GER) is
Esophagitis, esophageal strictures in dogs/cats if ignored
Ruminants (no esophagitis)
Regurgitation/GER → aspiration of stomach contents
Aspiration of salvia, blood, mucus, GER
Bronchoconstriction
Hypoxia and cardiac arrest
Pneumonia
Can be silent (not observed)
What are the predisposing factor to GER
Brachycephalic breeds
Drugs relaxing lower esophageal sphincter: Volatiles, opioids, anticholinergics, propofol
Increased intra-abdominal pressure: Pregnancy, obesity, surgery, head-down position
Prolonged anesthesia
How do you prevent GER
Appropriate pre-anesthetic fasting
Pretreatment with omeprazole, maropitant, metoclopramide
Use of cuffed ET-tube
How do you treat GER
Secure airway in unconscious patient
Check cuff
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
What is/clinical signs of hypercapnia
Mild hypercapnia (45-60mmHg)
- SNS stimulation: tachycardia, mild hypertension
Clinical signs usually seen when PaCO2 > 60 mmHg
- Bounding pulses (high systolic, low diastolic)
- Vasodilation: brick red color, capillary oozing
Severe hypercapnia PaCO2 > 90 mmHg
- Severe CNS depression (narcosis)
- Respiratory arrest (depression of brainstem)
What are the causes of hypercapnia
Hypoventilation
Respiratory depressant drugs
Positioning (dorsal)
Abdominal distension
Obesity
Equipment failure
Uni-directional (one-way) valves (circle systems)
CO2 absorber exhausted
Inadequate fresh gas flow (non-rebreathing systems)
Endobronchial intubation (dogs, cats)
V/Q mismatch
Apparatus dead-space (overlong ET-tube)
Increased CO2 production (hyperthermia
How do you prevent hypothermia
Preventing heat loss is easier than treating
Insulation
Towels, bubble packing
Warming mats
Circulating warm water
Electrical, ‘Hot Dog’
Microwave bags of fluids, bean bags, snuggle safe
Warm air blankets ‘Bair Hugger’
Radiant Heat lamps
Warm IV fluids/irrigation fluids
Potential problems with warming devices
Patient cannot move away from source
Radiant heat source
Blood flow may not conduct heat away
Body pushed into heat source
Always observe and monitor temperature
Avoid direct contact to patient to avoid burns
Use towel for insulation
When is hyperthermia common in anesthesia cases
Heavy-coated dogs on circle rebreathing system
Post op hyperthermia cats:
μ-opioids, ketamine, intraop hypothermia
Malignant hyperthermia
How do you treat hyperthermia
Turn off supplemental heat, remove blankets, ice packs
Water, alcohol to inguinal and axillary regions
Fans–careful corneal ulcers
Acepromazine?
