Exam 4.docx

7\. The BBB is immature in an infant. How does this fact affect your anesthetic plan for an infant? The immature BBB allows drugs to cross more easily and higher concentrations of drugs resulting in a faster onset and higher levels of the drug in the brain. 8\. Explain why an increase in cerebral...

7\. The BBB is immature in an infant. How does this fact affect your anesthetic plan for an infant? The immature BBB allows drugs to cross more easily and higher concentrations of drugs resulting in a faster onset and higher levels of the drug in the brain. 8\. Explain why an increase in cerebral blood volume produces a rapid rise in ICP in an infant. Infants have an undeveloped CNS and therefore a lack of cerebral autoregulation. They are very sensitive to changes in cerebral blood volume, hence why an increase in cerebral blood volume results in a rapid rise in ICP. 9\. Why are the cranial sutures open in an infant? Sutures are open to allow for the rapid growth that occurs in utero (e.g. brain triples in weight in 1^st^ year of life) and to allow the brain to accommodate increased cerebral blood volume without increasing ICP. This is important due to underdeveloped cerebral autoregulation in infants. Anterior fontanelle closes by 2 years. Posterior fontanelle closes by 4 months. 10\. How can anesthesia providers use the fontanelles in the assessment of an infant? In other words, what information can they tell you? The anterior fontanelle can allow providers to assess hydration status and increased ICP. Sunken fontanelles indicate dehydration and bulging fontanelles indicate increased ICP. 11\. What are areas where open sutures converge called? Fontanelles 12\. Infants have a fixed SV. Explain why. The cardiac contractile elements (SR and T-tubules) are immature and therefore dependent on free ionized calcium for contractility. 13\. Given that infants have a fixed SV, how does the cardiac output of an infant increase? Infants increase their cardiac output by increasing their HR 14\. Infants also have blunted responses to catecholamines and decreased catecholamine stores. Describe the impact this would have when treating hypotension in an infant. When treating hypotension in an infant, catecholamines may be less effective due to the immaturity of their vasoactive receptors and infants may quickly experience hypotension when vasoactive substances are stopped due their decreased stores. Volume expansion is important in hypotensive infants. Calcium may be effective in treating infants that are not responsive to a fluid bolus. Epinephrine is better choice than atropine due to its inotropic and chronotropic properties. 15\. The larynx of an infant is higher, more superior, and is sits around the C3-4. The epiglottis is stiff/floppy, and the tongue is large. Based on this information, what considerations would you have when planning for the airway management and intubation of an infant? In terms of airway anatomy, it is easier to obstruct the airway of infants with minimal pressure on the submental space. Placing an infant in the sniffing position will worsen the laryngoscopic view due to position of the larynx. A shoulder roll is better used to align the laryngoscopic axes. Due to the dimensions of the epiglottis and tongue, placing an OPA can assist in mask ventilation. A Miller blade may be preferred due to its smaller profile and ability to directly lift the epiglottis. 16\. Based on the airway differences discussed in the lecture, why would it be wise to use an uncuffed ETT when intubating an infant? Cuffed ETT have been associated with increased airway resistance and tracheal damage from inflated cuffs. Extremely premature infant is born at or before 25 weeks Very preterm infant is born between 25-32 weeks gestation Moderately preterm infant is born between 32-34 weeks Late preterm infant is born between 34-36 weeks Pediatric patients have increased MAC, rapid induction and recovery Pediatric patients have larger Vd for water soluble drugs - Neonatal CV - Immature myocardium, noncompliant LV resulting in increased afterload and reduced CO - Fixed stroke volume so HR dependent for cardiac output - Faster HR - Epinephrine is better than atropine for bradycardia -- blunted response to exogenous catecholamines - Ensure adequate volume - Underdeveloped baroreceptor reflex -- don't respond to low volumes - Parasympathetic innervation - Fetal hemoglobin predominant - Higher affinity for O2 - Physiologic anemia of infancy -- peaks at 3-4 months of age due to decreased erythropoiesis and decreased life span of RBCs - Vitamin K and iron -- ensure infants have both for clotting - Decreased cord clamping - Neonatal respiratory characteristics - Type II pneumocytes and surfactant - Develops at 22-26 weeks - Peaks at 35-36 weeks - Lack leads to stiff, noncompliant lungs severe atelectasis V/Q mismatch hypoxia and hypercarbia - Infant's metabolic rate and O2 consumption are twice that of adults - Increased resistance to airflow - Obligate nose breathers - RR 37 in healthy newborn babies - Smaller babies, more work they have to do -- premature infants will have a greater RR than term infants - Vent settings - Low flow trigger so they don't exhaust themselves during the case and at the end, bring it back up - Don't use VC mode -- you'll blow their lungs - Neonatal airway anatomy - Large occiput - Neonatal larynx is small compared to mouth and pharynx - large tongue - short, small, stiff epiglottis - larynx - more cephalad and anterior - pointed toward nasopharynx nasal breathing - Why is this significant? Can't put them in the sniffing position - subglottic region is smaller than glottis opening - **cricoid cartilage is the narrowest part of the airway because it's non-expandable** - **Pediatric breathing mechanics decreased FRC** - Underdeveloped muscles and skeletal structure resulting in pliable chest - Horizontal ribs resulting in minimal assistance with chest expansion for inspiration paradoxical breathing where chest collapses in during inspiration - Exhalation limited by adductor muscles of larynx - Flat diaphragm... like COPD pts and both have to work hard to breathe - Diaphragm composed mainly of fast fatiguing fibers - Must assess for increased respiratory effort - Intervene to maintain oxygenation and prevent fatigue - **How do we overcome decreased FRC? Positive pressure** - Breathing control - Breathing controlled by PaO2 in carotid and aortic bodies, PaCo2, and pH - Initial response to decreased PaO2 is increase in ventilatory response quickly followed by decrease in ventilatory response impaired ability to compensate because of how quickly they fatigue - Hering-Breuer reflex - Nerve of Hering connected to carina - If lungs are overstretched, they send a vagal signal to the apneustic center of the pons to inhibit more inspiration triggering you to exhale - Periodic breathing -- pauses last up to 10 seconds - Stimulation of carina or SLN can cause this reflex - Pediatric nervous system - CNS development is incomplete at birth - Maturation of CNS continues until the end of the child's first year of life - Changes in CBF, cerebral blood volume, and ICP greatly affect each other monitor CPP - Autoregulation is easily impaired or disrupted can cause intraventricular hemorrhage - Impairments from positioning - Rate of ventilation -- acidosis - Immature blood brain barrier and neuromuscular junction - Immature BBB allows more drugs to cross - Immature NMJ allows easier depolarization i.e. more sensitive to NMBDs - Try to avoid depolarizing NMBDs - CNS is very vulnerable to trauma, hypoxia, hypoglycemia, and ischemia - Hypoglycemia BAD in neonates - Pain - Lack cerebral vascular autoregulation -- pain can cause response leading to intraventricular hemorrhage - Recommended limit infusions and doses of analgesics - Use multimodal methods - Liver of neonates - Immature hepatic biotransformation -- impaired metabolism - Decreased protein binding -- more free/unbound drug running around - **Increases in lipid solubility = increases in Vd = longer duration of action** - **Highly protein bound and highly lipid soluble -- leaves more drug to specifically target tissues** - **In high Vd -- initial drug is going to be rapid but maintenance doses may be lowered** - Drastic decrease in glycogen store in the first 3 weeks of life -- impaired ability to be NPO - Kidneys of neonates - Normal kidney function is not present until 6 months - Kidney function may not be that of an adult until age 2 - Neonates lack ability to regulate body temperature due to the following - Large surface area - Lack of subcutaneous tissue - Inability to shiver - Brown fat metabolism allows for non-shivering thermogenesis - What causes hypothermia? Cold rooms, cold fluids, cold gases, high FGF - Pharmacological considerations for the neonate - Rapid induction and recovery - Recovery may be impaired in TIVA/when drugs are hepatically metabolized - Increased MAC - Larger volume of distribution for water soluble drugs - Decreased protein binding in neonate until 5-6 months old - Decreased drug metabolism - Immature neuromuscular junction - Immature BBB - Implications of anatomical differences on airway management of pediatrics - Airways are smaller and tongue is larger -- increased chance for obstruction - Infants are mouth breathers until 3-6 months old -- increased chance of nasal obstruction causing respiratory distress - Openings for trachea and esophagus are closer together -- increased risk of aspiration - All airway branches are at a les acute angle --increased chance of intubating a bronchus - Proportionately more soft tissue in the airways -- increased edema in airways - Increased difficulty intubating due to larynx, epiglottis anatomy - Fewer alveoli and collateral airways -- decreased diffusions and increased shunting - Thoracic case is smaller and weaker giving a barrel shape to chest -- unable to increase depth of respiration - Diaphragm is flatter and children are primarily diaphragm breathers -- large of amount of abdominal contents produces a decrease in diaphragmatic movement - Increased metabolic rate -- increased O2 needs - Faster respiratory rate -- increased fluid loss - Presence of URI predisposes pt to coughing, laryngospasm, bronchospasm, airway edema - Snoring and noisy breathing can indicate tonsil/adenoid hypertrophy, OSA, pulmonary HTN - Recurrent pneumonia/respiratory infections can indicate frequent aspiration secondary to incompetent larynx, GERD, TEF, tracheobronchial fistula - Environmental allergies and secondhand smoke can increase airway reactivity - Assess for congenital abnormalities - Physically deformed ears i.e. microtia - Associated with mandibular hypoplasia - Bilateral microtia is associated with having a difficulty visualizing the larynx (grade 3-4 view) - Unilateral microtia is associated with less than 5% difficulty in visualizing the larynx - Ventilation management - PCP preferred method - Physiologic PEEP 4-5 - O2 -- risk of ROP until 44 weeks - N2O - Awake extubation - Pt is allowed to fully emerge from anesthesia and regain their protective airway reflexes - Advantages - Ability to protect airway against aspiration - Pt remains intubated during stage 2 and is protected from the possibility of laryngospasm due increased risk of laryngospasm during stage 2 - Disadvantage = ET will be irritating causing coughing and retching on emergence - Deep extubation - Pt is exubated while deeply anesthetized then allowed to emerge without an ETT in place - Advantages - Removal of ETT before stage 2 results in smoother emergence - Decreased coughing or retching puts less strain on incisions and suture lines - Disadvantages - Possibility of losing control of airway - Lack of protective reflexes may make pt more prone to aspiration - Not recommended for airway surgery where bloody drainage will be an issue - Presenting symptom of choanal is cyanosis at rest relieved by crying or insertion of an OPA