3. Anesthetic Complications Flashcards
What are some causes of hypoxemia and low SpO2
low inspired O2 (FiO2)
hypoventilation
diffusion problem (pulmonary dz)
Ventilation perfusion (V/Q) mismatch
R > L shunt
Pao2 = 5x Fio2
FiO2 = Fraction of inspired oxygen
What are the clinical effects of hypoxemia?
Mild (spO2 >80%) - activation of sympathetic nervous system, inc HR, mild hypertension
Moderate (spo2 60-80%) - local vasodilation > hypotension, reflex inc in HR
Severe (spo2 <60%) - local depressant effects predominate, rapid dec in blood pressure > severe hypotension, bradycardia > netricular fibrillation or cardiac arrest
What is hypoxemia?
low oxygen
Can cause tissue hypoxia, lactic acidosis, organ failure
high risk patients: brachycephalics, diaphragmatic hernia, pneumothorax, pulmonary contusion, upper airway obstruction, pneumonia, abdominal distension (GDV, C-section)
What can cause hypoxemia?
low inspired O2
Check o2 supply (o2 tank, flow meter)
ETT: check placement (esophageal, endobronchial)
Check that breathing system is tightly attached to ETtube
airway obstruction: remove or bypass
Hypoventilation - check anesthetic depth, administer o2, intermittent pos pressure ventilation (IPPV)
Ventilation perfusion mismatch and intrapulmonary shunting - improve perfusion and ventilation
What are the minimal acceptable SAP, MAP and DAP
80/40 (60)
What is hypotension?
Low blood pressure
MAP is driving force for perfusion
MAP <60mmHg compromised perfusion of visceral organs
SA: <6mo have physiological lower BP
Geriatric: sub-clinical organ impairment - hypotension should be treated earlier and more aggressive
LA: horse - min MAP 70mmHg (myopathy)
Severe hypotension (with sudden onset) MAP (35-45mmHg) - more aggressive dx and correction
What are the 3 pathophysiological mechanisms that lead to hypotension?
dec vascular tone, dec cardiac output and hypovolemia
How should we treat hypotension?
Tx at the cause
Arterial blood pressure >(and peripheral vascular resistance) cardiac output > HR and Stroke volume (affects preload, contractility and afterload)
WHat might cause an inc/dec or peripheral vascular resistance?
dec (vasodilation): inhalant anesthetics, acepromazine
sepsis
Inc (vasoconstriction): a2 agonists, pain
WHat inc/dec HR in regards to hypotension?
dec: baoreceptor response (hypertension), parasympathetic activity
Inc: baroreceptor respons (hypotension,), pain, hypoxeia, hypercapnia
What can decrease preloand and contractility
contractility: resp/metabolic acidosis, hypoxemia
Preload: hypovolemia, positive pressure ventilation
How do we manage MAP <60mmHg?
Check anestetic depth
* 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, lidocain
2) Check heat rate
* 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
3) Add Positive Inotrope - Dobutamine
* β 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 fluids might we use with 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
How might ephedrine help with hypotension?
Ephedrine
* Synthetic noncatecholamine, stimulates 𝛼 1 and 𝛽 1 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
What is your last resort for a hypotensive animal?
Add a vasopressor
Norepinephrine infusions
* α 1 vasoconstrictor
* May diminish visceral organ perfusion (liver, kidneys)
* Try to limit to emergency use only
* Treatment for refractory hypotension (septic patients)
Vasopressin infusions
* Non-catecholamine vasopressor (V1 receptors)
* Used for refractory hypotension
* Very sick patients or post cardiac arrest
What can cause bradycardia during anesthesia?
half resting HR
drugs: A2 agonists, opioids
Deep plane of anesthesia
hypothermia
vagal reflexes (oculo-cardiac reflex), electrolyte imbalance
sinus bradycardia
AV block
How do we treat bradycardia?
anticholinergics
- Atropine: 0.02-0.04mg/kg (faster)
- Glycopyrrolate: 0.01mg/kg
Low normal hr - measure arterial BP before initiating tx
do not confuse ventricular escape rhythm w/ VPCs
What is ventricular premature complexes and sinus bradycardia w/ escaped beats? How do you treat it?
Ventricular Premature Complexes (very wide QRS)
* Treatment: Lidocaine bolus 1-2mg/kg +/- CRI is recommended when complexes are multiform, causing
hypotension, or occurring in significant runs
Sinus bradycardia with Escape beat (period where nothing is happening)
* Treatment: Atropine or glycopyrrolate. The goal is to increase the heart rate as the escape beat is
due to the slow sinus rate
What is tachycardia?
- Heart rate > 180 bpm (dog)
- Heart rate > 200 bpm (cat)
Sympathetic response to - Pain
- Awareness
- Hypotension
- Hypoxemia
- Hypercapnia
- Hypovolemia
- Drug induced? (anticholinergics…)
Correct underlying problem
What is regurgitation/gastro-esophageal reflux (GER)
- 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 can predispose regurgitation and GER, what can we do to prevent it?
Predisposing factors:
* Brachycephalic breeds
* Drugs relaxing lower esophageal sphincter: Volatiles, opioids, anticholinergics, propofol
* Increased intra-abdominal pressure: Pregnancy, obesity, surgery, head-down position
* Prolonged anesthesia
Preventive measures:
* Appropriate pre-anesthetic fasting
* Pretreatment with omeprazole, maropitant, metoclopramide
* Use of cuffed ET-tube
How do we treat regurgitation and 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 hypercapnia?
High ETCO Normal 35-45mmHg
* Mild hypercapnia (45-60mmHg)
- SNS stimulation: tachycardia, mild hypertension
* Clinical signs usually seen when PaCO 2 > 60 mmHg
- Bounding pulses (high systolic, low diastolic)
- Vasodilation: brick red color, capillary oozing
* Severe hypercapnia PaCO 2 > 90 mmHg
- Severe CNS depression (narcosis)
- Respiratory arrest (depression of brainstem
What can cause 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 (D/C)
V/Q mismatch
Apparatus deadspace (overlong Ettube)
inc Co2 production (hyperthermia)
How do we 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
What are some 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
What can cause hyperthermia? How do we treat it?
- Heavy-coated dogs on circle rebreathing system
- Post op hyperthermia cats:
- μ-opioids, ketamine, intra-op hypothermia
- Malignant hyperthermia
Treatment: - Turn off supplemental heat, remove blankets, ice packs
- Water, alcohol to inguinal and axillary regions
- Fans – careful corneal ulcers
- Acepromazine?
