Review Points Flashcards
Persistent Pulmonary Hypertension of the Newborn Definition
PPHN is persistence after birth of the high pulmonary arterial pressure (PPA), often suprasystemic, that is characteristic of the fetal circulation.
PPHN may occur with or without apparent pulmonary disease
Persistent Pulmonary Hypertension of the Newborn Pathology
In fetal life, pulmonary blood flow (Qp) is low (5-10% of cardiac output [CO]) due to high pulmonary vascular resistance (PVR) and shunts (i.e., foramen ovale, ductus arteriosus) which permit blood to bypass the pulmonary vascular bed. At birth, PVR normally falls dramatically (due to lung inflation and oxygenation), Qp increases to 100% of CO and, by 24 hours after birth, PPA has fallen to about 50% of systemic arterial pressure.
When this normal transition fails, PVR and PPA remain elevated, Qp stays low, right to left shunting occurs at the foramen ovale and ductus arteriosus, and hypoxemia results. Several factors influence PVR; among these, acidosis and alveolar hypoxia are potent pulmonary vasoconstrictors.
Clinical Causes of PPHN
Abnormal pulmonary vascular development (e.g., increased pulmonary vascular smooth muscle due to chronic fetal hypoxia, maternal diabetes, alveolar capillary dysplasia)
- Pulmonary hypoplasia with associated hypoplasia of pulmonary vasculature (e.g., congenital diaphragmatic hernia, Potter’s syndrome, prolonged oligohydramnios)
- Postnatal elevation in pulmonary vasoconstrictors (e.g., sepsis, pneumonia, aspiration syndromes, perinatal asphyxia)
- Congenital heart disease (e.g., total anomalous pulmonary venous return with obstruction).
Treatment of PPHN
Primary treatment is supplemental oxygen with high inspired oxygen concentrations- Start with 100% O2. Maintain pre-ductal PaO2at 90 to 100 mmHg.
Correct metabolic acidosis (NaHCO3, THAM).
Correct respiratory acidosis with assisted ventilation.
Inhaled nitric oxide (iNO): dose is 20 ppm
Adequate sedation, pharmacologic paralysis, as needed. Minimize handling
ECMO
Compare and describe the indications for mechanical ventilation for adult, pediatric and neonatal patients
All patient populations have the following indications: apnea, acute ventilatory failure, impending ventilatory failure and severe refractory hypoxemia.
The neonatal population also adds surfactant therapy and congenital defects/abnormalities as indications.
The differences are in the specific criteria required to meet the indication.
Acute ventilatory failure:
Adults/Peds: PaCO2> 55 mmHg with a pH < 7.25
Neonates: pH of < 7.25 despite the use of CPAP with supplemental oxygen of FiO2> 0.60
Impending ventilatory failure
Adults
Tachypnea, dyspnea, accessory muscle use, tracheal tug, pursed lip breathing etc.
May use objective measures (MIP, VC, Vt, Vd/Vt etc) to help quantify our findings.
Remember all of these things may not be done clinically and multiple factors are assessed (e.g. may measure MIPS on a neuromuscular patient but not do a Vd/Vt measurement)
Impending ventilatory failure
Ped
Young peds you will see similar signs and symptoms to the neonate, may include head bobbing
Older peds-more similar to adults
Impending ventilatory failure
Neo
retractions, expiratory grunting, nasal flaring, tachypnea, increasing oxygen requirements etc…
Non-invasive may be trialled if pH > 7.25
Severe refractory hypoxemia
Adults: use PF ratios (< 200 critical), A-a gradient (>350 critical), and PaO2/PAO2(<0.15 critical) to help define
Neonates: use guideline of a PaO2< 50 mmHg despite use of CPAP and supplemental oxygen (with FIO2≥0.6)
Ti dyn calculation on VC
TiDyn= VT/Flow (lps)
What are the normal goal ranges for ABGs in an adult patient?
Normal blood gas values for ventilation (pH 7.35-7.45, PaCO235-45 mmHg)
PaO260-100 mmHg (Note: remember this depends on what the patient’s underlying condition is, if they have normal lungs a higher PaO2would be desirable and expected, if they have a head injury would want to see PaO2’s in the 80-120 mmHg range.
Saturations³90% (see note above)
ABG Goals for ELBW (<28 week)
pH ≥7.25
PaCO2 45-65
PaO2 50-70
SaO2 85-92
ABG Goals for ELBW (<28 week)
pH ≥7.25
PaCO2 45-55
PaO2 45-65
SaO2 85-92
Lung Protective Strategies in Neo
pH ≥7.25 but use VT of ~ 4 mL/kg.
PaCO2is targeted at 45-55 mmHg initially.
PEEP is set to maintain recruitment but recruitment maneuvers are not used.
For Neonates PIPs are kept to < 25-30 cmH2O.
Lung Protective Strategies in Adults
pH ≥7.25 and goal VTin the 6-8 mL/kg range (potentially as low as 4 mL/kg depending on Pplat).
PaCO2 is allowed to rise slowly.
PEEP is set to maintain recruitment and recruitment maneuvers may be used.
Pplat generally kept < 30 cmH2O
Describe how auto-PEEP can interfere with patient-ventilator synchrony.
To trigger the ventilator a patient either has to inspire a certain set flow (for flow triggering) or cause a pressure drop below baseline in the circuit. When a patient has autoPEEP this creates an increased WOB as they must overcome the autoPEEP in their chest.
Eg. If pressure trigger set to -2 cmH2O, PEEP at 5 and autoPEEP is 10 cmH2O (and total PEEP is 15). The patient must reduce the circuit pressure to 3 cmH2O in order to trigger the ventilator meaning their inspiratory effort must reduce intrathoracic pressures from 15 cmH2O to at 3 cmH2O in order to trigger the vent.
Eg. If the flow trigger is set to 2 LPM, PEEP at 5 and autoPEEP is 10 cmH2O (and total PEEP is 15). The patient must still reduce intrathoracic pressure to less than 5 cmH2O in order to get a pressure gradient that results in flow into the patient and trigger the vent.
Describe the theory behind lung recruitment maneuvers.
Done primarily in the adult patient population
One technique to achieve “open lung ventilation”
Use high CPAP pressures for 30s to 60s (to 120 s in sustained maneuvers) unstable alveoli and alveoli with long time constants are recruited, opening the lung up.
After recruitment return patient to their conventional settings, if PEEP is set appropriately (to stabilize the newly recruited lung units), it will result in better V/Q matching and reduced risk of VILI (ventilator-induced lung injury).
Can also do recruitment maneuvers on patients who are spontaneously breathing that are at risk of atelectasis, pneumonia etc. (e.g. patients with neuromuscular diseases like ALS, MD or spinal cord injury)
