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Toronto Notes 2019 Obstetrical Anesthesia Obstetrical Anesthesia
Anesthesia Considerations in Pregnancy
• airway
■ possible difficult airway as tissues becomes edematous and friable especially in labour
• respiratory
■ decreased FRC and increased O2 consumption cause more rapid desaturation during apnea
• cardiovascularsystem
■ increased blood volume > increased RBC mass results in mild anemia
■ decreased SVR proportionately greater than increased CO results in decreased BP
■ prone to decreased BP due to aortocaval compression (supine hypotensive syndrome) – therefore
for surgery, a pregnant patient is positioned in left uterine displacement (approximately 15 degrees)
using a wedge under her right flank • centralnervoussystem
■ decreased MAC due to hormonal effects
■ increased block height due to engorged epidural veins • gastrointestinalsystem
■ delayed gastric emptying
■ increased volume and acidity of gastric fluid
■ decreased LES tone
■ increased abdominal pressure
■ combined, these lead to an increased risk of aspiration – therefore for surgery, a pregnant patient is
given sodium citrate 30 cc PO immediately before surgery to neutralize gastric acidity
Options for Analgesia during Labour
• psychoprophylaxis–Lamazemethod
■ patterns of breathing and focused attention on fixed object
• systemicmedication
■ easy to administer, but risk of maternal or neonatal respiratory depression
■ opioids most commonly used if delivery is not expected within 4 h; fentanyl can be considered
• inhalationalanalgesia
■ easy to administer, makes uterine contractions more tolerable, but does not relieve pain completely ■ 50% nitrous oxide is insufficient alone but good safety profile for mother + child
• neuraxialanesthesia
■ provides excellent analgesia with minimal depressant effects
■ hypotension is the most common complication
■ maternal BP monitored q2-5min for 15-20 min after initiation and regularly thereafter ■ epidural usually given as it preferentially blocks sensation, leaving motor function intact
Options for Caesarean Section
• neuraxial:spinalorepidural
• general:usedifcontraindicationsortimeprecludesregionalblockade
Pediatric Anesthesia
Respiratory System
• incomparisontoadults,anatomicaldifferencesininfantsinclude:
■ large head, short trachea/neck, large tongue, adenoids, and tonsils
■ narrow nasal passages (obligate nasal breathers until 5 mo)
■ narrowest part of airway at the level of the cricoid vs. glottis in adults
■ epiglottis is longer, U shaped and angled at 45o; carina is wider and is at the level of T2 (T4 in adults)
• physiologicdifferencesinclude:
■ faster RR, immature respiratory centres which are depressed by hypoxia/hypercapnea (airway
closure occurs in the neonate at the end of expiration)
■ less oxygen reserve during apnea – decreased total lung volume, vital and functional reserve
capacity together with higher metabolic needs
■ greater V/Q mismatch – lower lung compliance due to immature alveoli (mature at 8 yr)
■ greater work of breathing – greater chest wall compliance, weaker intercostals/diaphragm, and
higher resistance to airflow
Cardiovascular System
• bloodvolumeatbirthisapproximately80mL/kg;transfusionshouldbestartedif>10%ofblood volume lost
• childrenhaveahighHRandlowBP
• COisdependentonHR,notstrokevolumebecauseoflowheartwallcompliance;therefore,
Anesthesia A27
Adult Upper Airway
Nasal cavity
Thyroid cartilage Cricoid cartilage Trachea
© Nicole Clough 2014
Nasal pharynx
Epiglottis Laryngeal pharynx
Vertebral body C6
Child Upper Airway
1 2
4
1. Large head
2. Newborns are obligate nasal breathers 3. Adenoid and tonsils
4. Larger tongue in proportion to mouth 5. Smaller pharynx
6. Larger and more flaccid epiglottis
7. Larynx is more superior and anterior 8. Narrowest point at cricoid cartilage
9. Trachea is more narrow and less rigid
Figure 16. Comparison of pediatric vs. adult airway
To increase alveolar minute ventilation in neonates, increase respiratory rate, not tidal volume.
Neonate: 30-40 breaths/min
Age 1-13: (24 – [age/2]) breaths/min
ETT Sizing in Pediatrics
Diameter (mm) of tracheal tube in children after 1 year = (age/4) + 4
Length (cm) of tracheal tube = (age/2) + 12
7 8
3 5 6
9
bradycardia severe compromise in CO
© Andrew Q. Tran 2014 (after Leanne Chan 2011)