Birds Flashcards
Temperature Regulation of Birds
○ Core body temps 39-42℃ (102-107.6℉) indicate HIGH metabolic rate
○ Low tolerance for low temps; significant effect of hypothermia
Functions of the Avian Respiratory System
○ Gaseous exchange
○ Vocalization
○ Thermoregulation
Main Features of Avian Respiratory System
Small lungs that undergo little change in volume when breathing
Air sacs DO not participate to gas exchange
What are the two main components of the avian pulmonary system?
Separate, distinct components
One for ventilation, one for GE
Tracheal Variations btw Species of Birds
1.Inflatable sac-like diverticulum
2. Double trachea (penguins, petrels)
3. Complex tracheal loops or coils within caudal neck in keep or within thorax/keel
–Fxn: large booming calls with low driving pressures
Larynx in Birds
○ Tracheal opening located at the base of the tongue
○ No epiglottis → easy visualization when tongue is gently pulled forward
Exception: Flamingo due to ventroflexion beak, large fleshy tongue
Trachea in Birds
Complete cartilaginous rings
Connects nares and mouth to the bronchi
Functions: warming, moisturizing, and screening particulate matter from inspired gas
Difference in trachea in between species:
Effect of Different Tracheal Anatomies in Birds?
Significant increase in tracheal dead space
Typical avian trachea vs trachea of comparably sized mammals 2.7 times longer BUT 1.29 times wider
= tracheal resistance to gas flow comparable
● Tracheal dead space volume in birds is ~ 4.5 times larger than that of comparably sized mammals, BUT relatively low respiratory frequency + larger tidal volume of birds decreases effect of larger tracheal dead space volume
● Avian minute tracheal ventilation = 1.5-1.9 times that of mammals
Syrinx
● Sound-producing organ
○ At junction of trachea and mainstem bronchi
○ Intubated birds can produce sounds, especially during PPV
Bronchi in Birds
3 orders of bronchial branching before gas exchange tissue reached
1. Primary bronchus (extra- and intrapulmonary)
2. Secondary bronchi
3. Tertiary bronchi or parabronchi
Role of Parabronchi, Surrounding Mantle of Tissue
Parabronchi, surrounding mantle of tissue (parabronchial mantle) = where gas exchange occurs, air capillaries within walls
Serve to connect ventrobronchi to dorsobronchi, laterobronchi
Primary Bronchi
–Enters junction of cranial, middle thirds of lung
–Gives rise to abdominal air sac, secondary bronchi
–Low columnar pseudostratified epithelium + well-developed internal circular smooth muscle layer + longitudinally oriented smooth muscles → contraction changes internal diameter
Movement of air only, no GE
Secondary Bronchi
–Arise from primary bronchus, same histology
–Arranged in four groups:
1. medioventral**
2. mediodorsal
3. lateroventral**
4. laterodorsal
Medioventral: gives rise to cranial air sacs
Lateroventral: gives rise of caudal thoracic air sacs
Air Sacs in Birds
9 Total
Arise from medioventral secondary bronchi: clavicular (1), cervical (2), cranial thoracic (2)
Arise from lateroventral secondary bronchi: caudal thoracic (2)
Arise from intrapulmonary bronchus (ie continuation of primary bronchus): abdominal (2)
How Group Air Sacs
-Cranial = cervical, clavicular, cranial thoracic
-Caudal = caudal thoracic, abdominal
Volume equally distributed btw cranial, caudal groups
Air Sac Structure and Function
Thin-walled structures composed of simple squamous epithelium, vessel poor
● Air sac do not contribute to gas exchange
Function: provide tidal flow of air to the relatively rigid avian lung [avian lung changes in volume by only 1.6%]
Air Sac Role During Movement of Gases
only volume-compliant structures in body cavity
inspiration → negative pressure within air sac →air flows from atmosphere into pulmonary system (air sacs + gas exchange surface areas of the lungs)
expiration → positive pressure within air sac →air flows from pulmonary system, air sacs to atmosphere
IInspiration in Birds
Contraction of Abdominal M
Elevation of Keel
Internal vol, thoracolumbar cavity increase
Negative intracoelomic pressure - air enters
BOTH INSPIRATION, EXPIRATION ACTIVE IN BIRDS
Intubation in Birds
can be difficult in small birds
Glottis can be difficult to visualize
Commercially available endotracheal tube manufactured for small birds do not exist
UNCUFFED TUBES
Use of IVC To Intubate Birds
do not possess same degree of flexibility, thermoplasticity of a commercially available ET tube
Can cause tracheal trauma (abrasion or puncture)
Must be of appropriate circumference: it needs to allow some degree of gas leak between tracheal wall and the catheter to avoid air sacs volutrauma or lung barotrauma
Bird Intubation: tube occlusion
Why:
–Small ETT diameter
-_Cold, dry FGF makes mucus thicker, more tenacious
Detection of Tube Obstruction in Birds
–Prolonged expiratory phase
–Gurgling on auscultation
Management of Airway Obstruction in Birds
● Extubating patient, cleaning tube, re-intubating, or by replacing with clean one
● Anticholinergic IM (atropine, 0.04 mg/kg, or glycopyrrolate 0.01 mg/kg) to reduce mucus production
Endotracheal Intubation and Risks in Birds
Because of complete cartilaginous tracheal rings, overly inflated cuff will injure tracheal mucosa or rupture tracheal rings
● Avian tracheal rings tend to rupture longitudinally
Larger birds (ostriches, emus) will need larger tubes: 10-18, 9-14
Ventilation in Emus
Tracheal cleft in emus does not complicate intubation, may make PPV difficult: can be overcome by placing snug wrap around distal third of neck
Body Position and Muscle Relaxation in Birds
body position may adversely affect ventilation (depending on species)
■ DORSAL RECUMBENCY IN CHICKEN (large breast muscles)
Weight of abdominal viscera →compress abdominal air sacs →reduced tidal volume
Anaesthesia causes myorelaxation → difficult to generate sufficient muscular effort to lift keel against gravity (in particular in birds with large heavy pectoral muscles) → reduced tidal volume
Sternal Recumbency in Birds
Sternal recumbency appears to be detrimental
How Manage Ventilation Challenges in Birds
Maintain light plane of anesthesia
Role of the Parabronchi
Increase total gas exchange, surface area
Basic unit for gas exchange: = Tertiary bronchus (parabronchus) + surrounding tissue (air capillaries + blood vessel)
Long, narrow tubes that anastomose profusely
■ Entrances guarded by smooth muscles
Tubular Parabronchi Subunits
- Atria
- Infundibula
Atria
opens into chambers, separated from one another via interatrial septa
–Bundle of SmM at opening, allow for SNS/PSNS control of air flow through parabronchi
Infundibula
funnel shaped duct arising from floor of atria, leads to air capillaries/meshwork with blood capillaries = site of GE
Infundibula
LaPlace’s Law and Avian Lungs
High surface tensions = air capillaries of small diameter → generate significant negative pressure across blood-gas barrier
■ This could lead to influx of fluid or collapsed tubules
Air, blood capillaries possess structural elements that preserve anatomy/gas exchange
What are the two types of parabronchial tissue?
- Paleo-pulmonic
- Neo-pulmonic
Paleo-pulmonic Parabronchial Tissue
found in all birds, consisting of parallel stacks of profusely anastomosing parabronchi
○ Unidirectional Gas Flow (aerodynamic valves)
Neopulmonic Parabronchial Tissue
meshwork of anastomosing parabronchi located in caudolateral portion of the lung; its degree of development = species-dependent
○ Bidirectional Gas Flow
What species only have paleopulmonic tissue?
Emus, penguins
Which species have 10-12% neopulmonic tissue?
Storks, swans, ducks, geese
Which species have 20-25% neopulmonic parabronchi?
Chickens, sparrows, other song birds
Gas Exchange Efficiency in Birds vs Mammals
More efficient, despite 27% smaller lung volume
MOA Increased Gas Exchange in Birds vs Mammals
Specific surface area of blood-gas tissue barrier is 15% greater
Ratio of tissue surface area to volume of exchange tissue is 17-35% greater
Mean thickness of tissue barrier in birds 56-67% less = less resistance to gas diffusion
○ Pulmonary capillary blood volume is 22% greater
Movement of Gases, Blood within Parabronchi
● Movement of gas within parabronchi, outwards into atria, infundibulae → convective flow and then by diffusion
● Blood flow from periphery → interparabronchial artery, arterioles → blood capillary → outward moving air
● Multicapillary serial arterialization system increases duration over which respiratory media (air and blood) exposed to each other
What creates the counter current exchange system?
○ inward flow of deoxygenated blood
○ outward flow of air from parabronchial lumen
Do birds have alveolar gas?
● No equivalent of alveolar gas because parabronchial gas continuously changes in composition as flows along length of parabronchus
Gas Flow through the PB as it relates to PO2, PCO2
As gas flows along a parabronchus, it receives CO2 and gives off O2
→ At INFLOW end of parabronchus, gas has low PCO2 and high PO2
→ At OUTFLOW end of parabronchus, gas has high PCO2 and low PO2
PeCO2 in End PB Gas
Can exceed PaCO2
PeO2 in End PB Gas
Can be less than PaO2
Cardiovascular System of Birds
Heart: four-chambered muscular pump that separate venous blood from arterial blood
Sympathetic, parasympathetic innervation
● NE, epi principal sympathetic NTs
● ACh principal parasympathetic NTs
Bird vs Mammal Hearts
Larger heart, lower heart rates, larger stroke volumes and slightly lower peripheral resistance = higher cardiac output
Total blood volume: 5-13% of body mass of birds
Higher blood pressure: arteries are stiffer → increased risk of fatality due to aortic rupture, heart failure and hemorrhage in stressed patients**
Higher oxygen demand
Do birds have a diaphragm?
liver lobes surround the apex of the heart
Conduction System in Birds
Sinoatrial node → atrioventricular node and its branches →Purkinje fibers
Purkinje fibers distribution within ventricular myocardium (complete from endocardium to epicardium), responsible for QRS morphology
Pattern of ventricular activation: Type2b → facilitates synchronous beating at high heart rates
Renal Portal System in Birds
Renal portal system like reptiles
CV Disease in Birds
Cardiovascular disease common in pet birds, 10%–15% prevalence
Atherosclerosis is considered the most common vascular disease in captive psittacine birds, with histological lesions appearing similar to those seen in people).
Clinical Signs of CV Dz in Birds
■ Dyspnoea
■ Lethargy
■ Weakness
■ Exercise intolerance
■ Abdominal distension
■ SUDDEN DEATH
Anesthetic Considerations for the Avian CV Stream
Avoid excitement because excitement = release epi, norepinephrine
In birds inhalant anesthetic (+++ halothane) synthesize myocardium to catecholamines induced arrhythmias
Birds ECG can be mistaken for ventricular tachycardia
Physical Exam of Birds - Distant Assessment
● Bird’s awareness of and attention to its surrounding environment
● Body form and posture
● Feather condition
● Respiratory rate
Hands on PE in Birds
● nares and mouth
● Heart and lung auscultation
● Sharpness of keel (good indicator of muscle mass and body fat)
Fasting in Birds
-Controversial: risk of hypoglycemia DT high metabolic rate vs risk of regurgitation
-Healthy birds: withhold food long enough for upper GI tract to empty
○ Overnight in large birds
○ 4-6 h in smaller birds (probably even less)
-Emergency procedure: bird with a full crop should be held upright during induction with a finger positioned below the mandible to block the esophagus
● Once anesthetized, empty crop
● At end of anesthesia check oral cavity
Fasting Guidelines: healthy birds
withhold food long enough for upper GI tract to empty
○ Overnight in large birds
○ 4-6 h in smaller birds (probably even less)
Fasting Guidelines in Emergency Situations/Sick Birds
bird with a full crop should be held upright during induction with a finger positioned below the mandible to block the esophagus
● Once anesthetized, empty crop
● At end of anesthesia check oral cavity
Physical Restraint in Birds
Improper restraint can cause trauma (wing/leg fracture) and/or physiologic stress
Excessive handling can cause overheating
Good restraint = wings and legs are controlled and not allowed to flap or kick
● long-necked birds: the neck must be gently controlled
Intubation
Patient should be intubated for most procedure
○ Maintain airway patent
○ Provide oxygen
○ Permit PPV
For brief procedure < 10 min, face mask sufficient
○ An ETT should always be ready
Air Sac Cannulation
Reduce o2 flow by 1/3
Can cannulate caudal thoracic or abdominal with placement of cannula just cranial or caudal to last rib
Induction
–Injectables rarely used as sole agents
–Mask or induction chamber - if chamber, can injure selves during involuntary excitement phase
Sevo preferred: less irritation, faster induction/recovert
Breathing Systems in Birds <10kg
○ Bain circuit
○ Norman elbow (Jackson Rees modification of Ayres T piece)
● Minimal resistance to patient ventilation
● Light weight (++ Bain)
● Oxygen flow 100-200 ml/kg/min
Breathing Circuits in Birds >10kg
○ Small animal breathing system (Emu and ostriches under 130 kg)
○ Large animal breathing system for larger
MAC in Birds
Differs to MAC minimal ALVEOLAR concentration as meant in mammals
○ Birds do not have alveolar lungs so MAC = minimal ANESTHETIC concentration
○ Defined as Minimal Anesthetic Concentration required to prevent gross purposeful movement in response to a painful stimulus and usually determined via a bracketing technique
MAC of Specific Agents in Birds
Similar to Mammals
Halothane: 0.85-1.05%
Isoflurane: 1.06-2.05%
Sevoflurane: 2.21-2.9% (2.39-3.94% not by bracketing technique)
Inhalant Maintenance of Anesthesia
Halothane, isoflurane and sevoflurane depress ventilation in birds in dose dependent manner
Hypoventilation: difficult to control plane of anesthetic, variety effects on cardiopulmonary function (arrhythmias)
When possible assist or control ventilation*
Apneic Index
measure of tendency of inhalant anesthetic to cause respiratory depression
● AI = [EtAA] / MAC
● LOWER the AI for anesthetic, GREATER its depressant effect on ventilation
Inhalant Effects on BP
–Iso: dose dependent decrease
–Halothane, Sevo: variable
N2O in Birds
● Not suitable as sole anesthetic
● 30% oxygen = generally accepted as minimum fraction of inspired oxygen
NO DIVING BIRDS
Contraindications for N2O in Birds
Do not use on diving birds (pelicans)
● Subcutaneous pockets of air that do not communicate with the respiratory system
● Use of N2O can results in subcutaneous emphysema
Injectable Drugs for Anesthesia - General Considerations
Risk of overdosing!!!
● Measure accurately the weight of the bird
● Dilution of drug concentration with sterile saline, insulin syringes
Other consideration:
○ They may delay onset of anesthesia
○ Species and individual variability
○ Cardio-respiratory depression
○ Slow induction
○ Prolonged recovery
Alfaxalone in Birds
○ Can be administered by several routes
○ IV = most predictable anesthesia with good muscle relaxation
○ Cardiac abnormalities reported
Propofol in Birds
○ Narrow safety of margin
○ 10 mg/kg to induce anesthesia and incremental doses of up to 3 mg/kg may be used to prolong anesthesia
○ Metabolised rapidly = rapid recovery
○ Respiratory depression and apnoea from overdose
Ketamine in Birds
Used in combination with other drugs to produce chemical restraint, analgesia
Anesthesia of 10-30 minutes duration 3-5 minutes after IM administration
○ Recovery variable from 30 minutes to 5 hours
Cardio-respiratory depression, thermoregulation affected
Careful in patients with hepatic and renal dysfunction
BZD + KET
○ Deep sedation or anesthesia with good muscle relaxation
○ Respiratory depression
NMBA in Birds
Two purposes in birds:
○ Whole-body SkM paralysis to facilitate surgical procedures
○ to produce mydriasis striated m in pupil
Vecuronium 0.2 mg/kg optimizes mydriasis
**DO NOT combine with agents promoting corneal penetration! -enhanced systemic uptake with potentially fatal effects
Local Anesthetics in Birds
Do not exceed 4mg/kg lido, 2mg/kg bupivacaine
○ Risk of seizures and cardiac arrest in small birds (inappropriate doses)
○ Provide local analgesia but do not relieve stress associated to physical restraint
Injection Sites in Birds: SQ
○ area of the back between the wings, the wing web, and the skinfold in the inguinal region
Injection Sites in Birds: IM
Pectoral, Thigh M
Injection Sites in Birds: IV
dorsal metatarsal vein and jugular vein (right jugular is larger and more visible)
Injection Sites in Birds: IO
○ Tibiotarsal (easier to place; harder to maintain)
○ Ulnar (harder to place; easier to maintain)
Do not place in pneumatic bones
Opioids in Birds
Butorphanol may be a more effective analgesic in birds then a µ-opioid such as morphine
Morphine seems to produce hyperalgesia
Butorphanol = analgesia and MAC sparing effect (2-4 mg/kg IV)
Fentanyl CRI - useful MAC reduction (3155%) in red tailed hawks
NSAIDS in Birds
Meloxicam: useful, muscle necrosis at doses needed to obtain analgesia, did not cause renal lesions
Ketoprofen: low bioavailability, tubular necrosis, mortality with eiders
Preferred NSAID = carprofen
Fluid Therapy in Birds
● Birds tend to have higher plasma Na, osmolality compared to mammals
● Fluids with close osmolarity to 300-320 mOm/L recommended
○ Normosol-R
○ Plasmalyte-R
○ Plasmalyte-A
○ NaCl 0.9%
Respiratory Monitoring in Birds
-High RR not assoc with depth: associated with small VT, greater proportion of dead space ventilation
–Monitor frequency, degree of motion of sternum, movements of reservoir bag
–Capnometry
Birds: Respiratory Pauses
Respiratory pauses > 10-15s treated by lightning plane of anesthesia and when possible, ventilate bird manually or mechanically
IPPV in Birds
When doing so do not exceed 15-20 cmH2O to prevent volutrauma to air sacs
RR 8-10 breaths/min, airway pressure of 10 cmH2O generally achieve desired goal to produce stable plane of anesthesia, acceptable minute volume for oxygenation/elimination of CO2
Oxygenation in Birds
-SpO2: designed to measure mammalian Hgb, subject to artifact
-Color and capillary refill time of mucous membrane, color of the cere, beak or bill, as well as coloration on head where lack of feathers
HR, Rhythm in Birds
■ Color and CRT of MM
■ Palpating peripheral pulse
■ ECG via hypodermic needles inserted through the skin at base of each wing, through skin at the level of each stifle
Blood Pressure in Birds
■ In birds > 4 kg
■ Doppler = values closer to mean arterial pressure
Temperature Monitoring in Birds
Electronic thermometer, long flexible thermistor probe into esophagus
Clinically acceptable range of core body temperature 38.3º-40.6º
Depth Assessment in Birds
M Relaxation
Recovery in Birds
● birds must be kept from flopping around
● lightly wrap the bird with a towel
● potential regurgitation risk: keep animal intubated until head control
Pneumatic Bones in Birds
skull, humerus, clavicle, keel (sternum), pelvic girdle, and the lumbar/sacral vertebrae, femur
Ketamine in Raptors
Avoid -no ketamine in vultures, caution with owls
PNBs in Birds
perform sciatic-femoral NB in raptors undergoing sx for pododermatitis
Motor responses following ENS both nerves consistent with those reported in mammalian species
BP blocks via palpation, US, nerve locators used with varying success
Epidurals in Waterfowl
Epidurals: synsacrococcygeal space, 55’ spinal ax with bupivacaine, 18’ with lidocaine
Lido 0.5-2mg/kg
75mm, 23g needle directed 10-20* cranially btw synasarcum, first free coccygeal vertebrae onset 1.5’, duration dose dependent
No AEs , all birds retained motor function
