IV. ANESTHESIA FOR SURGICAL PROCEDURES AND SPECIAL POPULATIONS

ANESTHESIA FOR SPECIAL POPULATIONS

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Pediatrics

ANATOMY, PHYSIOLOGY, AND PATHOPHYSIOLOGY

NORMAL

  • Fetal circulation
    • Normal fetal shunts
      • Foramen ovale
        • Closes during first breath
      • Ductus arteriosus
        • Closes within a few days after birth
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Pulmonary

    • Functional residual capacity (FRC) is low in infants because of:
      • Small alveoli (lowered lung compliance)
      • Compliant chest wall (rib cage comprised of cartilage)
    • Compared to the adult airway, infants have a:
      • Larger head and tongue in relation to their body
      • Smaller nasal airways
      • Larynx that is anterior and cephalad
      • Cricoid cartilage that is the narrowest point of the pediatric airway
    • When compared to adults, infants have a higher alveolar ventilation along with the lower FRC, as previously mentioned. This increases their risk for atelectasis and hypoxemia. This also makes inhalational induction much faster.
      • Resting oxygen consumption is 7 mL/kg/min.
    • At birth, the oxyhemoglobin dissociation curve is shifted to the left. This means that the hemoglobin has an increased affinity for oxygen, making it less likely to be released to the tissues. Fetal hemoglobin reacts poorly with 2,3-DPG.

Airway

    • Narrow nasal passages
      • Because neonates are obligate nose breathers, nasal congestion has a greater impact on pediatrics.
    • Cricoid cartilage is the narrowest point, up to age 5.
    • Larynx is anterior and cephalad

Cardiac

AGE

RESPIRATORY RATE

HEART RATE

SYSTOLIC BP

DIASTOLIC BP

Neonate

40

140

65

40

12 months

30

120

95

65

3 years

25

100

100

70

12 years

20

80

110

60

  • Cardiac output relies upon heart rate because the left ventricle is not compliant.
  • Intravascular fluid deficit is evidenced by hypotension WITHOUT tachycardia
  • Temperature regulation
    • Infants are at a higher risk of hypothermia because of:
      • lower fat content
      • thin skin
      • the surface area compared to their weight is higher
      • Surgical variables-
        • Cold rooms, IV fluids, anesthetic gases are not humidified, and temperature regulation is altered by anesthetics
      • Low body temperature in infants can lead to slower waking times, heart and lung complications, altered drug reactions, and potential coagulopathies.
      • Newborns produce heat by non-shivering thermogenesis of brown fat metabolism. This is activated by the autonomic nervous system.
    • Spinal cord ends at L3.
    • Physiologic anemia
      • Hemoglobin levels at birth can be between 14-20 g/dL. Fetal hemoglobin levels rapidly decrease to their nadir at 2 to 3 months of age. Hemoglobin begins to level out after this until 2 years of age.
      • Prematurity can affect the physiologic anemia as well. It can cause the anemia dip to occur quicker and more severe than normal.

PREMATURITY

  • Less than 37 weeks gestation
  • At risk for pulmonary complications (such as apnea), hypothermia, immunocompromised
  • Respiratory distress syndrome can develop due to a lack of surfactant. Surfactant appears at 23-24 gestational weeks but increases in the last 10 weeks of gestation.
  • Shock or hypoxia that is prolonged can lead to bowel ischemia/inflammation.
  • Increased incidence of congenital anomalies
  • Retinopathy of prematurity
    • This is a fibrovascular proliferation that overlies the retina and can lead to progressive vision loss.
    • Titrate FiO2 down so that PaO2 is 60-80 mm Hg
    • Neonates less than 44 weeks postconception are at the highest risk.
  • Premature infants up to 60 weeks postconceptional age are at risk of apneic spells after surgery.

CONGENITAL ABNORMALITIES

  • COARCTATION OF THE AORTA
    • A narrowing of the descending aorta, usually at the junction of the ductus arteriosus into the aortic arch.
    • Can be preductal or postdual; preductal is pediatrics.
    • Blood pressure should be monitored on the right radial artery.
  • Persistent pulmonary hypertension
    • Caused by hypoxia, acidosis, pneumonia, and hypothermia.
    • Increased PVR and right-to-left shunting
  • Tetralogy of Fallot
    • Ventricular septal defect, right ventricular outflow tract obstruction, right ventricular hypertrophy, and dextroposition of the aorta with overriding of the VSD.
  • PATENT DUCTUS ARTERIOSUS
    • Ductus arteriosus remains open and creates a left-to-right shunt
    • Pulmonary congestion and CHF symptoms
    • Postligation cardiac syndrome (PLCS) can occur after correction of the PDA and lead to hypotension, decreased cardiac output, and increased PVR.
  • CONGENITAL DIAPHRAGMATIC HERNIA
    • Herniation of guts/bowel through the diaphragm into the chest cavity.
      • Bochdalek- can be right or left posterolateral
      • Morgagni- anterior
      • Left-sided is most common because the left side of the diaphragm closes later.
    • Symptoms:
      • Hypoxia, scaphoid abdomen, and bowel sounds in the thorax
    • Keep peak inspiratory pressures below 25 cm H2O to prevent pneumothorax in the good lung.
    • Chest tube may be required if lung compliance, blood pressure, or oxygenation drops unexpectedly.
  • TRACHEOESOPHAGEAL FISTULA AND ESOPHAGEAL ATRESIA
    • The most common type is C, where an upper esophagus ends in a blind pouch and a lower esophagus connects to the trachea. As you can imagine, breathing distends the stomach and feeding leads to choking/coughing/cyanosis (3 Cs).
    • Suspicions are raised when a catheter cannot be passed into the stomach. The diagnosis is confirmed by visualizing the catheter being coiled in the upper esophageal pouch.
    • Associated with VACTERL- Vertebral defects; Anal atresia; Cardiac anomalies; Tracheoesophageal fistula; Esophageal atresia; Radial dysplasia; Limb anomalies
  • NECROTIZING ENTEROCOLITIS
    • Intestinal inflammatory condition that is a life-threatening emergency.
    • Occurs in preterm babies, less than 32 weeks gestation, and less than 1500 g.
  • HYPERTROPHIC PYLORIC STENOSIS
    • Obstructive lesion (often described as “olive” shaped) in the pylorus muscle.
    • Interferes with gastric emptying
    • Unrelenting vomiting leads to:
      • Hyponatremia
      • Hypokalemia
      • Hypochloremia
      • Alkalosis
    • Hydrate with NaCl with potassium; NO lactated ringer’s
    • Postpone surgery until fluid and electrolytes are normalized.
  • INTESTINAL MALROTATION AND VOLVULUS
    • Spontaneous abnormal rotation of the midgut around the superior mesenteric artery.
    • True SURGICAL emergency
    • Patients are usually acidotic and hypovolemic- ketamine induction
    • Staged procedure and postoperative ventilation is likely so narcotic infusion may be considered
  • GASTROSCHISIS AND OMPHALOCELE
    • Defects in the abdominal wall with viscera that is herniated externally.

 

OMPHALOCELE

GASTROSCHISIS

HERNIA DEFECT LOCATION

Base of umbilicus

Lateral to the umbilicus

SAC

Yes

No

ASSOCIATION WITH OTHER ANOMALIES

Down’s syndrome, diaphragmatic hernia, and cardiac/bladder malformations

Isolated

  • Management is focused on:
    • Hypothermia
    • Infection
    • Dehydration
  • More problematic in gastroschisis
  • INGUINAL HERNIA
    • Can be present at birth and is common in preterm.
    • Concern is bowel incarceration or testicle involvement.
    • Ilioinguinal and iliohypogastric nerves are blocked.
  • NEONATAL HYDROCEPHALUS
    • An obstruction in CSF flow leads to increased ICP.
    • Ventriculoperitoneal (VP) shunt is required to move excess fluid to the gut.
  • MYELOMENINGOCELE
    • A form of spina bifida where the neural tube fails to close and leads to spinal cord and meningeal herniation through this defect.
    • Meningocele- herniation only contains meninges
    • Myelomeningocele- meninges and neural elements

PHARMACOLOGY

  • Rapid rise in FA/FI
    • Alveolar ventilation to FRC is much higher in pediatrics than in adults.
    • More of the cardiac output goes to the vessel-rich organs in the neonate.
    • Neonate has a greater cardiac output for their body size.
    • The infant also has a lower blood: gas partition coefficient.
  • Rapid induction and recovery
  • Increased MAC
    • Minimum alveolar concentration (MAC) is higher in infants than in neonates and adults for halogenated agents. Unlike other agents, sevoflurane has the same MAC in neonates and infants. Sevoflurane appears to have a greater therapeutic index than halothane and has become a preferred induction agent in pediatric anesthesia.
  •  

AGENT

NEONATES

INFANTS

CHILDREN

ADULTS

Halothane

0.87

1.1-1.2

0.87

0.75

Sevoflurane

3.2

3.2

2.5

2

Isoflurane

1.6

1.8-1.9

1.3-1.6

1.2

Desflurane

8-9

9-10

7-8

6

  • Immature hepatic biotransformation
    • IV anesthetics (propofol and thiopental) dosages are higher in children.
    • Opioids are more potent for various reasons, including immature, blood-brain barrier, increased sensitivity in respiratory centers, and decreased metabolism of drugs.
    • Decreased liver metabolism for the first month.
  • Protein binding
    • There is a decrease in protein which leads to an increase in free drugs. In turn, this results in an increased risk of toxicity.
  • Volume of distribution
    • Water is in greater proportion which increases the dosage for water-soluble medications.
    • Muscle relaxants have a shorter onset because of the shorter circulation times.
    • Fat content and muscle mass are decreased.
  • Neuromuscular junction
    • Hyperkalemia following succinylcholine administration is much more likely in this population. Extreme bradycardia and sinus node arrest can develop after the first dose without pretreating with an anticholinergic.
    • The neuromuscular junction is immature and leads to increased sensitivity to neuromuscular blockers. However, the volume of distribution is higher (meaning the extracellular compartment) and dilutes the drug. This contradiction can make the intended response variable of these medications.
  • Kidney function is not normal until 6 months of age; however, kidney function does not reach adult levels until 2 years of age.
  • Dosages (IV)
    • Cisatracurium 0.15 mg/kg (intubation)
    • Dexamethasone 0.25 mg/kg
    • Fentanyl 1-2 µg/kg
    • Glycopyrrolate 0.01 mg/kg
    • Ketamine 1-2 mg/kg (induction)
    • Metoclopramide 0.15 mg/kg
    • Midazolam 0.05 mg/kg (sedation)
    • Neostigmine 0.04-0.07 mg/kg
    • Ondansetron 0.1 mg/kg
    • Pancuronium 0.1 mg/kg
    • Propofol 2-3 mg/kg (induction); 60-200 µg/kg/min maintenance
    • Remifentanil 0.25-1 µg/kg; 0.05-2 µg/kg/min maintenance
    • Rocuronium 0.6-1.2 mg/kg (intubation)
    • Succinylcholine 2-3 mg/kg (intubation)
    • Vecuronium 0.1 mg/kg
  • Dosages (other routes)
    • Acetaminophen 10-20 mg/kg PO; 40 mg/kg rectal
    • Ketamine 6-10 mg/kg IM (induction)
    • Midazolam 0.5 mg/kg PO (premedication/sedation); up to 20 mg total
    • Succinylcholine 4-6 mg/kg IM (intubation)

Anesthesia Techniques / Procedures

  • Fluid requirements
    • Maintenance: 4-2-1 rule
      • 4 mL/kg/hour for the 1st 10 kg
      • 2 mL/kg/hour for the 2nd 10 kg
      • 1 mL/kg/hour for the remaining weight in kg
    • NPO deficit
      • Half infused the first hour
      • Quarter in the 2nd and 3rd hours
    • Evaporative/Replacement
      • According to surgical opening
        • 0-2 mL/kg/hour for minor procedures
        • 6-10 mL/kg/hour for major procedures
      • Blood loss
        • Maximum allowable blood loss (MABL)
          • EBV x ((Starting Hct) – (Desired Hct) / Starting Hct)
          • Premature neonates 100 mL/kg
          • Full-term neonates 85-90 mL/kg
          • Infants 80 mL/kg
          • Adults 65-75 mL/kg
        • IV fluid management and intraoperative blood loss is crucial. As mentioned above, a noncompliant heart and increased risk of hypothermia as well as a much smaller blood volume make the error margin much smaller.
  • Selecting tube size
    • (16 + age in years) / 4
    • (Age in years / 4) + 4
  • Depth of ETT
    • Height (in cm) / 10 + 5
    • Weight (in kg) / 5 + 12

 

Preterm

Term

6 mo

1 yr

2 yr

4 yr

6 yr

8 yr

10yr

ETT

2.5-3

3-3.5

3.5-4

4

4.5

5

5.5

6

6.5

Tube depth (cm)

7-8

9

11

12

13

14

15

16

17

LMA

 

1

1.5

1.5

2

2

2.5

2.5

2.5

Suction cath (F)

6

6

8

8

8

10

10

10

12

Nagelhout Nurse Anesthesia 7th edition, pages 1250-1251

MANAGEMENT OF COMPLICATIONS

HYPOXIA

  • Infants become bradycardic when hypoxic.

LARYNGOSPASM

  • Stimulation of the superior laryngeal nerve causes the laryngeal musculature to spasm.
  • Air is unable to pass through the vocal cords to the lungs for ventilation.
  • Most common between 1-3 months of age
  • Recent viral infection (less than a month) increases the risk of pulmonary complications.
  • Treatment:
    • Positive pressure
    • Jaw thrust
    • IV lidocaine 1-1.5 mg/kg
    • Succinylcholine 0.5-1 mg/kg IV or 4-6 mg/kg IM
    • Rocuronium 0.4 mg/kg

Acute epiglottitis/laryngotracheobronchitis

Age

6 months- 6 years

Any age

Symptoms

Barking cough

Inspiratory stridor

No cough; drooling; dysphagia

Worse supine

Onset

1-3 days

Rapid onset (hours)

Treatment

Dexamethasone 0.15-0.6 mg/kg orally

Nebulized racemic epi

Must be intubated in the operating room

Antibiotics; racemic epi

  • Recent viral infection should delay elective anesthesia/surgery for 2-4 weeks.

PIERRE-ROBIN SYNDROME

  • Facial abnormality associated with cleft palate and small face/glottis
  • Difficult intubation

TREACHER-COLLINS SYNDROME

  • Facial abnormality associated with a small mouth and is more severe than Pierre-Robin.

DOWN SYNDROME

  • Short neck, irregular dentition, mental retardation, hypotonia, and macroglossia
  • Other associated abnormalities: subglottic stenosis, seizures, heart disease, and lung infections

SCOLIOSIS

  • Lateral rotation/curvature of the vertebrae
  • If scoliosis is caused from muscular dystrophy, high risk of malignant hyperthermia
  • Can compromise heart/lung function
    • Pulmonary hypertension and right-sided heart hypertrophy

RIGHT-TO-LEFT SHUNTS

  • Slows inhalational induction
  • Speeds IV induction

LEFT-TO-RIGHT SHUNTS

  • Accelerates inhalational induction
  • Decreased IV induction

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Obstetrics

ANATOMY, PHYSIOLOGY, AND PATHOPHYSIOLOGY

PREGNANCY-INDUCED CHANGES

  • Pregnancy leads to increased oxygen consumption and the body must make necessary changes to accommodate.
  • Cardiac output increases the most when compared to heart rate, blood pressure, and SVR during pregnancy.
    • Cardiac output is increased by:
      • 30-40% during the first trimester
      • 50% at term
      • During labor, the cardiac output increases another
        • 10% to 15% during the latent phase
        • 25% to 30% during the active phase
        • 40% to 45% during the expulsive stage. The greatest increase in cardiac output occurs immediately after delivery of the newborn when the cardiac output can increase to greater than
      • The greatest increase is immediately after delivery, 75% to 80% above pre-labor values. This last increase is due to autotransfusion and increased venous return.
      • Cardiac output falls to pre-labor values within 2 days after delivery. But it takes about 2 weeks for the cardiac output to decrease to nonpregnant values.

PHYSIOLOGIC CHANGES OF PREGNANCY AT TERM

SYSTEMIC BLOOD PRESSURE

DOWN (minimal)

SVR

DOWN (minimal)

CARDIAC OUTPUT

UP (50%)

PLASMA VOLUME

UP (40%)

TOTAL BLOOD VOLUME

UP (40%)

HEMOGLOBIN

DOWN

FIBRINOGEN

UP (100%)

PLASMA CHOLINESTERASE

DOWN (25%)

OXYGEN USAGE

UP (20%)

ARTERIAL OXYGEN TENSION

UP (10 mm Hg)

MINUTE VENTILATION

UP (50%)

ALVEOLAR VENTILATION

UP (70%)

FUNCTIONAL RESIDUAL CAPACITY

DOWN (25%)

CARBON DIOXIDE PRODUCTION

UP (33%)

ARTERIAL CARBON DIOXIDE TENSION

DOWN (10 mm Hg)

MINIMUM ALVEOLAR CONC.

DOWN (33%)

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  • Parturients experience a decrease in glucose resorption in the renal tubules.

POST-PARTUM

  • Pseudocholinesterase levels are back to normal for the parturient 2-6 weeks after delivery.

PLACENTA

  • Factors effecting the transfer of medications:
    • Concentration gradient of free drug between the mother and child
    • Placental thickness and surface area
    • Blood flow
    • Molecular size, lipid solubility, pH, ionization, and protein binding
  • There are 3 layers in the placenta: trophoplasts, fetal connective tissue, and endothelium of the fetal capillaries.
    • Fetal trophoplasts consists of cytotrophoblast and Syncytiotrophoblast.
  • Blood flow is dependent on maternal blood pressure. It is not autoregulated.
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FETAL

  • Normal fetal heart rate is 140.
  • The fetal hemoglobin P50 is 20 mm Hg at term pregnancy.
  • Fetal ion trapping is increased with fetal acidosis.
    • The ions are unable to diffuse back into maternal circulation, leading to fetal drug accumulation.
  • At 6 weeks gestation, the growing fetus is most at-risk of teratogenic medications.
  • The normal term (about 3 kg) fetus has an oxygen consumption of 7 mL/kg/min or about 21 mL/min.
  • Maternal hyperventilation will lead to fetal hypoxia and acidosis.

LABOR

  • 1st stage of labor is associated with:
    • T10-L1
    • Visceral pain
    • Somatic afferent nerves
  • 2nd stage of labor is associated with:
    • Somatic pain
    • Pudendal nerve
  • Uterine blood flow is decreased by:
    • Uterine contractions
    • Maternal hypotension
    • Vasoconstriction of uterine vasculature
    • Extreme hypocarbia < 20 mm Hg
  • FETAL HEART RATE MONITORING
    • Normal fetal heart rate is 120-160 beats per minute with a 3-6 variability in beats per minute.
    • Early decelerations
      • Fetal head compression
      • Occur with each contraction
    • Late decelerations
      • Fetal hypoxia
      • Begin at the peak of contraction
    • Variable decelerations
      • Umbilical cord compression
    • FETAL HYPOTENSIVE SYNDROME
      • The gravid uterus compresses vessels in the supine position and decreases blood return to the heart. Left lateral decubitus corrects this.

PHARMACOLOGY

ANTI-HYPERTENSIVES and HYPOTENSION

  • Appropriate medications for a parturient with pre-eclampsia and symptomatic cerebral edema scheduled for a cesarean delivery are labetalol and hydralazine.
    • Hydralazine also helps to increase uteroplacental blood flow.
    • Avoid esmolol because of potential adverse fetal effects.
  • Exaggerated HTN in a parturient is likely after receiving a pure adrenergic agonist and receiving methylergonovine.
  • For the parturient with severe aortic stenosis that is experiencing hypotension, the appropriate medication is phenylephrine.
  • With an inverted uterus, inhalational agents are preferred over MAC or regional anesthesia. Nitroglycerin is also effective in relaxing the uterus for manipulation.

ANESTHETIC AGENTS

  • Nitrous oxide has no effect on uterine contractions at term pregnancy.
  • Ketamine 1 mg/kg will increase the uterine tone and could be harmful to the fetus.
  • The narcotic that also exhibits local anesthetic properties is meperidine.
  • IV narcotics, both through bolus and PCA administration, are commonly used for labor analgesia but the side effects (nausea, vomiting, respiratory depression, decreased beat-to-beat variability, etc.) make these medications less desirable.
  • Metoclopramide helps to prevent aspiration in emergency c-sections by increasing the lower esophageal sphincter tone.
  • Dense motor blockade via epidural is most associated with bupivacaine.
  • Chloroprocaine avoids accumulation in the fetus during periods of acidosis because of the rapid metabolism in fetal blood.
  • Bicitra increases gastric pH and helps decrease the risk of Mendelson’s syndrome.

OBSTETRIC SPECIFIC AGENTS

  • Ritodrine is a tocolytic in obstetrics by stimulating beta-2 receptors.
    • Monitor potassium levels because it can cause hypokalemia.
  • Treatment for postpartum hemorrhage

DRUG

Side-effects

Oxytocin

Hypotension and tachycardia

Methylergonovine

HTN, vasoconstriction; coronary vasospasm

Carboprost/Hemabate

Bronchospasm, increased PVR; nausea

Misoprostol

Fever, nausea

ANESTHESIA TECHNIQUES / PROCEDURES

  • Neuraxial techniques are preferred over general anesthesia because general anesthesia leads to a:
    • Higher risk of difficult intubation
    • Higher risk of aspiration
    • Transfer of medications to fetus that were intended for the parturient
    • Situation where the mother doesn’t get to immediately bond with the child
  • The airway can become edematous in pregnancy and make intubation more difficult. Other risk factors are associated: pre-eclampsia, pushing during vaginal delivery, and/or tocolytics.
    • The most common cause of anesthesia-related mortality in the obese obstetric patient is airway difficulties.
  • In the case of emergency, failed neuraxial, or contraindication, a rapid-sequence induction/intubation with cricoid pressure should be performed on the parturient that is ≥ 20 weeks gestation.
  • A T4 dermatome level should be achieved by neuraxial blockade for a cesarean delivery.
  • The epidural local anesthetic dose should be decreased during pregnancy because of:
    • Increased peripheral sensitivity to local anesthetics
    • Epidural space is smaller
    • Metabolism of local anesthesia is decreased
    • Venous engorgement of epidural space
  • Hypotension resulting from sympathectomy is the most common complication of neuraxial anesthesia.
  • Lower concentrations of local anesthetics via epidural are able to produce sensory analgesia while sparing motor blockade (this is called a differential blockade and is particularly useful in the laboring patient).
  • The most common side effect of intrathecal opioids is pruritus.
  • Postdural puncture headaches are more likely in the parturient because of their age and sex (younger age and female gender are risk factors).
  • Inhalational agents are responsible for the greatest amount of depression in APGAR scoring of the neonate. In fact, only 1 minute is needed for amounts to be detected in the umbilical vein and artery. Nitrous oxide, however, requires greater than 5-10 minutes of continuous inhalation delivery before transferring to the fetus.
  • Inhalational anesthesia is indicated for vaginal delivery when uterine relaxation is needed.
  • Paracervical block can be performed at the end of the second stage of labor. However, there is a risk of fetal bradycardia and acidosis.

HIGH-RISK PARTURIENTS

HYPERTENSION

  • SBP > 160 mm Hg OR DBP > 110 mm Hg
    • Treat immediately (30-60 minutes) with labetalol or hydralazine. Oral nifedipine is also used.
  • Types:
    • Chronic- pre-existing or develops before 20 weeks gestation
    • Gestational- develops after 20 weeks gestation
    • Pre-eclampsia- HTN with proteinuria
    • Chronic HTN with superimposed pre-eclampsia- development of pre-eclampsia in a patient with chronic HTN
    • Eclampsia- new-onset convulsions in a patient with HTN.

PRE-ECLAMPSIA

  • Hypertension
  • Mild pre-eclampsia
    • Proteinuria 2 g/24 hours
  • Proteinuria, greater than 5 grams of protein in the urine per day, is an indication of pre-eclampsia.
  • Pre-eclampsia is the 2nd leading cause of thrombocytopenia in parturients.
  • Pulmonary edema is the leading cause of death in pre-eclampsia.
  • Platelet aggregation is enhanced at sites of disrupted endothelium.
  • Patients with hydatidiform mole, obesity, polyhydramnios, or diabetes carry an increased incidence of pre-eclampsia.
  • There is a 6% chance of a parturient being diagnosed with pre-eclampsia during pregnancy.
  • Magnesium
    • Mainstay of seizure prevention in pre-eclampsia with severe features or eclampsia.
    • Therapeutic blood level: 4-6 mEq/L- facial flushing and nausea
    • Significant reduction in deep tendon reflexes may mean toxicity.
    • Patient will be sensitive to paralytics because magnesium depresses the CNS.
  • Start low-dose ASA (81 mg/day) between 12-28 weeks until delivery.
  • Expectant management up to 37 weeks gestation for those with HTN or pre-eclampsia without severe features.
  • Expectant management up to 34 weeks gestation for those with severe features.

ABNORMAL PLACENTATION

  • Placenta accreta
    • When the placenta adheres to, invades, or penetrates the uterine myometrium.
    • The likelihood a parturient will need a hysterectomy during the cesarean delivery is 67%.
    • Average blood loss is 3-5 L.
  • Placenta increta
  • Placenta percreta

PLACENTA PREVIA

  • Painless vaginal bleeding
  • Abnormal implantation on the lower uterine segment with partial-to-total occlusion of the internal cervical os.
  • Risk factors:
    • Prior c-section
    • Tobacco
    • Multiparous
  • Neuraxial is preferred

PLACENTAL ABRUPTION

  • Risk factors:
    • Tobacco and/or cocaine use
    • Trauma
    • Multiple gestation
    • HTN/pre-eclampsia
    • Premature rupture of membranes

NONOBSTETRIC SURGERY IN THE PARTURIENT

  • The most common adverse outcome in parturients undergoing surgery that is nonobstetric is teratogenic effects to the fetus.

MANAGEMENT OF COMPLICATIONS (e.g. AMNIOTIC FLUID EMBOLISM, HELLP SYNDROME)

VENOUS AIR EMBOLISM

  •  

UTERINE RUPTURE

  • Trial of labor after cesarean delivery (TOLAC) increases the risk of uterine rupture.

HELLP syndrome

  • Hemolysis, elevated liver enzymes, and low platelet count
  • A complication of pre-eclampsia resulting in progressive and/or sudden deterioration of mother and fetus.
  • Delivery of fetus is treatment.

AMNIOTIC FLUID EMBOLISM

  • Classic triad:
    • Gasping respirations
    • Cardiovascular collapse
    • Coagulopathy
  • Supportive management:
    • Airway
    • Hemodynamics- vasopressors, fluid resuscitation, blood products
  • A-OK
    • Atropine 1 mg IV- vagolytic
    • Ondansetron 8 mg IV- serotonin blocker
    • Ketorolac 30 mg IV- thromboxane blocker
  • If the baby has not been delivered, the mother should be placed in the left lateral position with head of bead elevated.

ANESTHETIC COMPLICATIONS

  • Pulmonary aspiration
    • Focus is on prevention
      • NPO
      • Bicitra and PPIs
      • Neuraxial anesthesia preferred
      • RSI if general anesthesia is necessary
    • Hypotension
      • Phenylephrine causes less fetal acidosis and is preferred over ephedrine for hypotension related to neuraxial anesthesia.
      • Ketamine is indicated for c-section induction at 1 mg/kg IV when the patient is hypovolemic.
    • Total spinal
      • Prevention is key during epidurally-administered agents. Test dose first and then dose incrementally.
      • Vasopressors, airway, life support
    • Local anesthetic systemic toxicity (LAST)
      • Prevention by adhering to the recommended local anesthetic doses.
      • Neurologic symptoms are seen before cardiac.
        • IV benzodiazepines for seizures.
      • Lipid emulsion (20%, 1.5 mL/kg over 1 minute, then 0.25 mL/kg/min for at least 10 minutes after the patient stabilizes)
    • Postdural puncture headache
      • Occurs typically due to an accidental dural puncture during epidural. Patients complaints of the “worst headache of my life;” worsens when standing, better lying in bed, photophobia, nausea, frontal/occipital
      • Conservative treatment
        • Bed rest, NSAIDs, caffeine, hydration
      • Blood patch
        • Aseptic withdrawal of 20 mL of patient’s blood is injected into the epidural space. The patient reports immediate relief of headache.

POSTPARTUM HEMORRHAGE

  • The average blood loss for a vaginal delivery is 600 mL.
  • The average blood loss for a cesarean section is 1000 mL.
  • The average blood loss, in units of blood, for an emergent hysterectomy during a cesarean delivery is 6.
  • Postpartum hemorrhage is blood loss of ≥ 1,000 mL after delivery.
    • Risk factors:
      • Multiple gestation
      • Induction or augmentation of labor
      • C-section
      • Polyhydramnios
      • Chorioamnionitis
      • HTN
    • Causes:
      • Uterine atony
      • Trauma
      • Retained products of conception
      • Abnormally invasive placenta (accreta, increta, percreta)
      • Coagulopathy
      • Inverted uterus
    • Antepartum hemorrhage occurs most commonly with placenta previa and placental abruption.

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Geriatrics

Anatomy, Physiology, and Pathophysiology

Cardiac

  • The heart and vascular system is less compliant, leading to a faster propagation of the pulse pressure waveform, increase in afterload, and an increase in SBP, leading to ventricular thickening (hypertrophy) and prolonged left ventricular ejection times. The combination of ventricular hypertrophy and slower myocardial relaxation often results in late diastolic filling and diastolic dysfunction. **this is verbatim from Nagelhout pages 1260-1261
  • They will labile blood pressures under anesthesia because of a noncompliant ventricle that is unable to adapt to low and high volumes.
  • Stroke volume doesn’t change in the elderly. Therefore, for cardiac output to increase, heart rate must increase.
  • Decreased receptor affinity and alterations in signal transduction cause the decrease in beta-receptor responsiveness in the geriatric population.
  • The heart rate, venous return, and systolic arterial pressure normally increase to preserve the preload reserve. This is due to beta-receptor-mediated properties.
  • However, the elderly response to stressor with a decrease in maximal heart rate and ejection fraction. This leads to increase the preload reserve, which makes them more likely to develop heart failure.
  • Elderly suffer from autonomic dysfunction. Specifically, when these patients change to the supine position, blood pools in the lower extremities. However, the heart rate does not increase because the autonomic responses that maintain cardiovascular and metabolic homeostasis are progressively impaired.

Respiratory

  • A ventilation/perfusion mismatch is normally created due to increased closing capacity and a loss of elastic recoil in the lung. This is evident in an increase in residual volume.
  • Arterial oxygen tension decreases with age, leaving a wide range of oxygen tension in elderly patients with emphysema. Oxygen tension falls an average of 0.35 mm Hg per year.
  • Laryngeal/pharyngeal support and reflexes decrease which can lead to airway obstruction and pulmonary aspiration.
  • Closing capacity exceeds functional residual capacity (FRC) at 65 years in the upright position and at 45 years in the supine position.
  • The central (medulla) and peripheral (carotid and aortic bodies) chemoreceptors affect ventilation with changes in pH, PaO2, and PaCO2. Their ventilatory response to hypoxemia and hypercarbia is decreased.
  • PaO2 decreases steadily with age; normal value of 80 mm Hg by age of 70. PaCO2 remains unchanged with age.
    • PaO2 = 102 – ( age / 3 )
  • FEV1 decreases with age due to loss of elastic recoil, decrease in small airway diameter, and airway collapse with forced expiration.

Renal

  • Glomerular filtration rate (GFR) decreases as we age, resulting in decreased renal drug clearance and less renal blood flow from 20 to 90 years of age. The combined effect is especially noticeable with decreased renal clearance of hydrophilic agents and hydrophilic metabolites of lipophilic agents.
  • Serum creatinine is unchanged because of an overall declining skeletal muscle mass related to aging. Creatinine clearance is the best indicator or drug clearance.

Hepatic

  • The liver decreases 20-40% with age. Hepatic changes seen as a result of aging are drug metabolism and protein binding.
  • Decreased metabolism, prolonged half-life, and altered distribution of medications.
  • Drug metabolism
    • Phase 1- oxidation, reduction, and hydrolysis
    • Phase 2- conjugation, sulfonic acid, and acetylation; not effected by age
  • Serum albumin decreases and alpha1– acid glycoprotein (AAG) increases.
    • Albumin binds acidic drugs and AAG binds basic drugs.

Endocrine

  • There is a decrease in pancreatic islet beta cells, leading to decreased insulin secretion.

Thermoregulation

  • Skeletal muscle mass decreases by half by the age of 80.
  • Body fat increases.
  • Blood volume lowers 20-30% by age 75.
  • Hypothermia is more pronounced and lasts longer because of a lower basal metabolic rate, a high ratio of surface to body area mass, and less effective peripheral vasoconstriction in response to cold.

Central Nervous System

  • There is a progressive loss of neurons and neuronal substance, decrease in neurotransmitter activity, and decreased brain volume. These losses are most prominent in the cerebral cortex.
  • Bispectral index monitoring may assist in guiding medication titration and inhalational agents, thus speeding recovery times and perhaps decreasing the incidence of postoperative delirium (POD) and postoperative cognitive dysfunction (POCD).

SYSTEM

PHYSICAL CHANGES

ANESTHESIA ASSOCIATION

Cardiovascular

– decreased beta response

– impaired baroreceptor response

– diastolic dysfunction

– decreased pacemaker ability

– Atrial enlargement

– Hemodynamic instability

– Volume overload

– More susceptible to arrhythmias

– Labile response to volume status

Pulmonary

– Increased chest wall stiffness

– Decreased response to low oxygen and high carbon dioxide

– Increased lung compliance

– decreased cough reflex and esophageal mobility

– Increased A-a gradient

– Hypercarbia and hypoxemia more likely

– Increased work of breathing

– Increased dead space ventilation

– Higher aspiration risk

CNS

– Decrease in the amount of neurotransmitters

– Increased risk of perioperative neurocognitive disorders

Endocrine

– Impaired glucose tolerance

– Increased risk of hyperglycemia

Thermoregulation

– Decreased muscle mass and vascular reactivity

– Hypothermia

Hepatic

– Decreased mass and blood flow

– Altered drug metabolism

Renal

– Decreased mass, glomeruli, and GFR

– Drug clearance is decreased

– Sodium excretion is impaired

– Decreased water retention and elimination efficiency

– Increased likelihood of acute kidney injury

  • Afterload increases in the elderly due to a decrease in arterial compliance. This leads to increased left ventricular wall thickness, left ventricular wall tension, cardiac workload, systolic blood pressure, and peripheral vascular resistance.
  • Circulation time is increased because of a weaker left ventricle pump.
  • Resting heart rate tends to drop as we age because of sinoatrial nodal cell loss and a decrease in adrenergic receptor sensitivity (leads to vagal tone overriding).

 

  • Pulmonary complications (such as aspiration and laryngospasm) increase due to an increased stimulus needed to close vocal cords and decreased sensation to clear secretions.
  • Other respiratory parameters that increase in geriatrics:
    • Dead space
    • Hypoxia risk
    • Functional residual capacity
    • Closing volume
    • Work of breathing
  • Geriatric lung tissues become stiffer leading to less complete inhalation/exhalation. This helps explain why FRC and dead space increases. Alveoli have less elasticity so they are more likely to close.
  • The ability to cough is decreased (and the stimulus need to cough is increased) resulting in an obvious increased risk of aspiration/pneumonia.

 

  • This age group also experiences an increased chance of hypothermia and insulin resistance.
  • Liver and kidney function normally declines with age.
  • Elderly men have less ability to metabolize benzodiazepines and succinylcholine (plasma cholinesterase) when compared to elderly women.

 

  • Geriatric neuraxial changes
    • Epidural motor blockade and duration of action is decreased.
    • Spinal anesthesia duration of action and sensory block is increased.
  • MAC and general anesthesia requirements decrease as we age.
Click image to view in a separate window. Created with BioRender.com
Click image to view in a separate window. Created with BioRender.com

Pharmacology

  • The geriatric population generally has an unchanged or decreased protein level. Plasma protein binding is often decreased, giving rise to a larger volume of distribution and a longer half-life.
  • Because of a decreased cardiac output, enlarged fat content, decreased protein binding, and decreased renal function, intravenous induction in the older population is slower.
  • Because of a decreased cardiac output, enlarged fat content, decreased protein binding, and decreased renal function, it’s obvious why this age group has a slower IV induction.
  • Aging increases the volume of distribution of all benzodiazepines, which prolongs their elimination half-lives. Diazepam’s elimination half-life may approach 36-72 hrs.  Elderly patients also exhibit enhanced sensitivity to benzodiazepines, which may lead to prolonged postoperative confusion.
  • Both dosage requirements for local and MAC of general anesthetics are reduced in the elderly. Epidural anesthesia results in a greater cephalad spread but a shorter duration of action; spinal anesthetics have a longer duration of action.
  • Medications
    • Decrease propofol bolus and infusion by 50%.
    • Decrease etomidate bolus by 50%.
    • Decrease opioids bolus by 50%.
    • Avoid or decrease midazolam by 75%.
    • There is no significant changes with the intubating dose of NDNMBs and succinylcholine.
  • Volume of distribution is decreased for water-soluble (hydrophilic) drugs and increased for lipid-soluble (lipophilic) drugs. The culprit for these changes are increased fat stores, decreased lean body mass, and decreased total body water.

 

Anesthesia techniques/procedures

Management of complications

  • Postoperative cognitive dysfunction

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Obesity

ANATOMY, PHYSIOLOGY, AND PATHOPHYSIOLOGY

CARDIAC

  • Obese patients are more likely to experience diastolic heart failure than systolic dysfunction.
  • The body fat distribution sub-category that is associated with an increased risk of ischemic heart disease and hypertension is android.
  • The body fat distribution sub-category that is associated with an increased risk of varicose vein development and joint disease is peripheral gynoid.
  • The waist circumference measurement in men that is associated with an increased risk of heart disease and diabetes is 40 inches.
  • The cause for cardiovascular pathophysiologic changes associated with obesity is progressive compensatory processes that evolve to meet the increased metabolic demands of fat.
  • The primary cause of morbidity and mortality in the obese population is coronary artery disease.
  • To meet the greater myocardial demand seen in obesity, compensatory changes must be made. Because heart rate normally stays the same, stroke volume is forced to increase. This eventually will lead to cardiomegaly, hypertension, and congestive heart failure.

PULMONARY

  • Obesity is an example of restrictive lung disease.
  • Closing capacity exceeds functional residual capacity in the extreme obesity patient.
  • Chest wall and lung compliance is decreased in the extreme obesity population.

CLASSIFICATION

  • Metabolic syndrome:
    • Blood pressure: 150/90 mm Hg
    • Fasting glucose: 120 mg/dL
    • High-density lipoprotein 40 mg/dL for a woman
  • Fat only contains 8-10% water and contributes less fluid to the total body water than muscle. Normally, TBW is 60-65% but in the severely obese it is reduced to 40%. So estimated blood volume is calculated according to 45-55 mL/kg.
  • Ideal body weight
    • Men- Height (in centimeters) – 100
    • Women- Height (in centimeters) – 105
  • Lean body weight- Ideal body weight x 1.3
  • Body mass index
    • Weight (in kilograms) / height (in meters)2
    • (Weight (in pounds) / height (in inches)2) x 703
  • Classifications
    • 25-29 OVERWEIGHT
    • 30-34.9 OBESITY Type 1
    • 35-39.9 OBESITY Type 2
    • >40 kg/m2 OBESITY Type 3
  • Obesity can also be defined as > 30 and severe obesity is > 40.
  • Extreme obesity is the term
  •  

PHARMACOLOGY

  • Water-soluble drugs are dosed according to ideal body weight and lipid-soluble drugs according to total body weight.
  • A pharmacokinetic change associated with obesity is increased volume of distribution of lipid-soluble drugs.
  • Succinylcholine is dosed according to total body weight.
  • Nondepolarizers are dosed according to ideal body weight.
  • Fentanyl is dosed according to total body weight.
  •  

ANESTHESIA TECHNIQUES/ PROCEDURES (including BARIATRIC)

  • Patients present for bariatric surgery with a BMI > 35 kg/m2, the likelihood of obstructive sleep apnea is 75%.
  • There are eight “yes/no” items to screen for obstructive sleep apnea. A score of ≥ 3 “yes’s” indicates a high risk of obstructive sleep apnea.
  • Because of the high risk of cardiovascular disease and diabetes, an electrocardiogram and glucose level are considered routine. Everything else is based on the individual patient’s history.
  • A neck circumference of 60 cm is associated with a 35% chance of difficult intubation.
  • By “ramping” the obese patient with blankets or pillows into the sniffing position, the intubation risk of obese patients is equal to the general population.
  • Large tidal volumes only minimally increase arterial oxygen tension. Reverse trendelenburg increases the functional residual capacity and prolongs apneic periods but does not increase oxygen levels. Tidal volumes of 6-10 mL/kg of IBW are recommended to avoid barotrauma but PEEP can increase both FRC and arterial oxygen tension.
  •  

MANAGEMENT OF COMPLICATIONS

  • Obesity hypoventilation syndrome:
    • Hypercapnia
    • Pulmonary capillary occlusion pressure 26 mm Hg
    • Right-sided heart failure
    • Central apnea
    • Polycythemia
  • Obstructive sleep apnea:
    • Normal pH
    • Normal pulmonary compliance
    • Normal carbon dioxide levels

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Substance Use Disorder Population

Medication-assisted therapy (MAT) (e.g., methadone, buprenorphine)

Pharmacologic interactions (e.g., acute intoxication)

Pain management

Management of complications

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Immune Compromised and Oncology Patients

  • Neutropenia is the absolute granulocyte count < 2000 µL.
    • < 500 µL significant risk of infection to skin, mouth, pharynx, and lungs.
    • < 100 µL sepsis or fungal infection
  •  Neutrophilia
    • The early response of granulocytes to a bacterial infection.
    • > 7000 µL
  •  Asthma
    • Extrinsic asthma is characterized by the activation of the immune system and release of IgE. Treated with beta agonists, anticholinergics, corticosteroids, and leukotriene inhibitors.
  •  Angioedema
    • Hereditary form is dysfunction of C1 esterase inhibitor
  • Immune-mediated allergic reactions:
    • Type I- IgE mediated and involve mast cells and basophils; e.g. anaphylaxis
    • Type II- IgG, IgM, and complement mediated cytotoxicity
    • Type III- tissue damage by immune complex formation or deposition
    • Type IV- exhibit T lymphocyte mediated delayed hypersensitivity
  •  Anaphylaxis
    • Life-threatening antigen-antibody interaction.
    • Mast cells and basophils are degranulated which causes symptomatology
    • Half of intravascular fluid is third-spaced due to marked capillary permeability

CANCER

  • Cellular proliferation of gene mutations accumulates and leads to cancer. Genes are involved in carcinogenesis by virtue of inherited traits that predispose to cancer:
    • Altered metabolism of potentially carcinogenic components
    • Decreased level of immune system function
    • Mutation of normal genes into oncogenes

PHARMACOLOGY

CANCER

  • Bleomycin
    • Antitumor antibiotic
    • Most common chemotherapeutic to cause pulmonary injury/toxicity
    • Most common adverse effect is interstitial fibrosis
    • Anesthesia problems occur postoperatively because of high FiO2
  • Methotrexate
    • Folic acid analog
    • Causes acute intracellular deficiency of folate
    • Treats leukemia, osteogenic sarcoma, psoriasis, etc.
    • Pulmonary toxicity has been reported with its use

REFERENCE: Nagelhout Nurse Anesthesia 7th edition, page 671

  • Cisplatin
    • Ototoxicity, peripheral neuropathy, and renal failure
  • Doxorubicin
    • Dose-dependent cardiomyopathy

ANESTHESIA TECHNIQUES/ PROCEDURES

CANCER

  • Acute pain in cancer patients are related to surgery, radiation, chemotherapy, pathologic fractures, and tumor invasion. A frequent source of pain is related to cancer metastasis, specifically to bone. Nerve compression or infiltration may be a cause of pain. Patients with cancer who experience frequent and significant pain exhibit signs of depression and anxiety.

 

  • 3 types of cancer pain:
    • somatic
    • visceral
    • neuropathic
      • Somatic responds to opioids, NSAIDs, and neural blockade.
        • Common opioids are morphine, hydromorphone, and methadone.
      • Visceral responds to sympathetic nerve blocks.
        • Neurolytic blocks for visceral pain
        • Celiac plexus
        • Superior hypogastric plexus
        • Ganglion impar
      • Neuropathic responds to antiepileptics, TCAs, and SNRIs.
        • Neuropathic pain is associated with sodium and calcium channel receptor changes.
          • Gabapentin and lamotrigine are common antiepileptics that work on these receptors.
          • TCAs, such as amitriptyline, doxepin, and nortriptyline, are commonly used.
        • These are considered first-line agents for neuropathic pain.
        • Second-line treatment involves topical capsaicin and lidocaine, and tramadol.
        • Cannabinoids may have some efficacy in neuropathic pain but the lack of evidence to confirm make its use controversial.
  • Opioids are the mainstay for cancer pain.

REFERENCE: Barash Clinical Anesthesia 9th edition, pages 1525-1530

IMMUNE-COMPROMISED

  • Most common triggers of anaphylaxis in the OR are muscle relaxants, latex, and antibiotics.

MANAGEMENT

CANCER

  • Knowing the chemotherapeutic agent used will help the CRNA to know potential adverse effects and/or organs to thoroughly assess.
  • The treatment of cancer with chemotherapy, pain medications, and adjuvant therapies are often associated with nausea and vomiting that can lead to nutrient deficiencies. Preoperative CMP testing will help guide identify potential electrolyte abnormalities.
  • Anemia and coagulopathy are frequently seen in cancer patients. Routine CBC testing should be initiated preoperatively to assess the current status of the hematologic system and whether blood products may be needed.
  • The most common cause of hypercalcemia in hospitalized patients is cancer. If hypercalcemia develops rapidly, decreased level of consciousness will be seen.

IMMUNE-COMPROMISED

  • In patients with hereditary angioedema, 2-4 units of FFP may be required to replenish the deficient enzyme.
  • The primary goals of anaphylaxis treatment are reversal of hypotension and hypoxemia, replacement of intravascular volume and inhibition of further cellular degranulation, and release of vasoactive mediators.
    • IV crystalloids, epinephrine, diphenhydramine, and corticosteroids are effective in the treatment.

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