Unformatted text preview: Pediatric Resident Curriculum for the PICU UTHSCSA PRINCIPLES OF MECHANICAL
BLOOD GAS INTERPRETATION Pediatric Resident Curriculum for the PICU UTHSCSA Definitions
• Tidal Volume (TV): volume of each breath.
Rate: breaths per minute.
Minute Ventilation (MV): total ventilation per minute. MV = TV x Rate.
Flow: volume of gas per time.
Compliance: the distensibility of a system. The higher the compliance, the easier it is to inflate the lungs.
Resistance: impediment to airflow.
SIMV: patient breathes spontaneously between ventilator breaths. Allows patientventilator synchrony, making for a more comfortable experience. Pediatric Resident Curriculum for the PICU UTHSCSA Definitions
• PIP: maximum pressure measured by the ventilator during inspiration. • PEEP: pressure present in the airways at the end of expiration.
• CPAP: amount of pressure applied to the airway during all phases of the respiratory cycle.
• PS: amount of pressure applied to the airway during spontaneous inspiration by the patient.
• Itime: amount of time delegated to inspiration. Pediatric Resident Curriculum for the PICU UTHSCSA Types of Ventilation
• Volume Control
PressureRegulated Volume Control Pediatric Resident Curriculum for the PICU UTHSCSA Volume Control
• The patient is given a specific volume of air during inspiration.
• The ventilator uses a set flow for a set period of time to deliver the volume: TV (cc) = Flow (cc/sec) x itime (sec)
• The PIP observed is a product of the lung compliance, airway resistance and flow rate. The ventilator does not react to the PIP unless the alarm limits are violated.
• The PIP tends to be higher than during pressure control ventilation to deliver the same volume of air.
• With SIMV, the patient can breath spontaneously between vent breaths. This mode is often combined with PS. Pediatric Resident Curriculum for the PICU UTHSCSA Triggering the Ventilator Pediatric Resident Curriculum for the PICU UTHSCSA Pressure Control
Patient receives a breath at a fixed airway pressure.
The ventilator adjusts the flow to maintain the pressure.
Flow decreases throughout the inspiratory cycle.
The pressure is constant throughout inspiration.
Volume delivered depends upon the inspiratory pressure, I
time, pulmonary compliance and airway resistance.
• The delivered volume can vary from breathtobreath depending upon the above factors. MV not assured.
• Good mode to use if patient has large air leak, because the ventilator will increase the flow to compensate it.
• Pediatric Resident Curriculum for the PICU UTHSCSA Volume vs. Pressure Pediatric Resident Curriculum for the PICU UTHSCSA Changes in ARDS Volume Control Pressure Control Pediatric Resident Curriculum for the PICU UTHSCSA CPAPPressure Support
• No mandatory breaths
• Patient sets the rate, Itime, and respiratory effort.
• CPAP performs the same function as PEEP, except that it is constant throughout the inspiratory and expiratory cycle.
• Pressure Support (PS) helps to overcome airway resistance and inadequate pulmonary effort and is added on top of the CPAP during inspiration.
• The ventilator increases the flow during inspiration to reach the target pressure and make it easier for the patient to take a breath. Pediatric Resident Curriculum for the PICU UTHSCSA SIMV + PS Pediatric Resident Curriculum for the PICU UTHSCSA PressureRegulated Volume Control
• In this mode, a target minute ventilation is set. • The ventilator will adjust the flow to deliver the volume without exceeding a target inspiratory pressure. • Decelerating flow pattern.
• No change in minute ventilation if pulmonary conditions change.
• Can ventilate at a lower PIP than in regular volume control.
• Hard to use on a spontaneously breathing patient or one with a large air leak.
• Not a “weaning” mode. Pediatric Resident Curriculum for the PICU UTHSCSA Initial Ventilator Settings
• Rate: 2024 for infants and preschoolers 1620 for grade school kids 1216 for adolescents
• TV: 1015ml/kg
• PEEP: 35cm H2O
• FiO2: 100% • Itime: 0.7 sec for higher rates, 1sec for lower rates
• PIP (for pressure control): about 24cm H2O. • Pressure Support: 510cm H2O. Pediatric Resident Curriculum for the PICU UTHSCSA Adjusting The Ventilator
• pCO2 too high
• pCO2 too low
• pO2 too high
• pO2 too low • PIP too high Pediatric Resident Curriculum for the PICU UTHSCSA pCO2 Too High
Patient’s minute ventilation is too low.
Increase rate or TV or both.
If using PC ventilation, increase PIP.
If PIP too high, increase the rate instead.
If airtrapping is occurring, decrease the rate and the I
time and increase the TV to allow complete exhalation.
• Sometimes, you have to live with the high pCO2, so use THAM or bicarbonate to increase the pH to >7.20.
• Pediatric Resident Curriculum for the PICU UTHSCSA pCO2 Too Low
Minute ventilation is too high.
Lower either the rate or TV.
Don’t need to lower the TV if the PIP is <20.
PIP <24 is fine unless delivered TV is still >15ml/kg.
TV needs to be 8ml/kg or higher to prevent progressive atelectasis
• If patient is spontaneously breathing, consider lowering the pressure support if spontaneous TV >7ml/kg.
• Pediatric Resident Curriculum for the PICU UTHSCSA pO2 Too High
• Decrease the FiO2. • When FiO2 is less than 40%, decrease the PEEP to 35 cm H2O. • Wean the PEEP no faster than about 1 every 812 hours.
• While patient is on ventilator, don’t wean FiO2 to <25% to give the patient a margin of safety in case the ventilator quits. Pediatric Resident Curriculum for the PICU UTHSCSA pO2 Too Low
• Increase either the FiO2 or the mean airway pressure (MAP).
• Try to avoid FiO2 >70%.
• Increasing the PEEP is the most efficient way of increasing the MAP in the PICU.
• Can also increase the Itime to increase the MAP (PC).
• Can increase the PIP in Pressure Control to increase the MAP, but this generally doesn’t add much at rates <30bpm.
• May need to increase the PEEP to over 10, but try to stay <15 if possible. Pediatric Resident Curriculum for the PICU UTHSCSA PIP Too High
Decrease the PIP (PC) or the TV (VC).
Increase the Itime (VC).
Change to another mode of ventilation. Generally, pressure control achieves the same TV at a lower PIP than volume control.
• If the high PIP is due to high airway resistance, generally the lung is protected from barotrauma unless airtrapping occurs.
• Pediatric Resident Curriculum for the PICU UTHSCSA Weaning Priorities
• Wean PIP to <35cm H2O
• Wean FiO2 to <60% • Wean Itime to <50%
• Wean PEEP to <8cm H2O
• Wean FiO2 to <40% • Wean PEEP, PIP, Itime, and rate towards extubation settings.
• Can consider changing to volume control ventilation when PIP <35cm H2O. Pediatric Resident Curriculum for the PICU UTHSCSA Complications
Ventilatorinduced lung injury
Pneumothorax • Cardiac – Myocardial ischemia
– Reduced cardiac output • Gastrointestinal
Pneumoperiteneum • Renal – Fluid retention • Nutritional – Malnutrition
– Overfeeding Pediatric Resident Curriculum for the PICU UTHSCSA Acute Deterioration
• DIFFERENTIAL DIAGNOSES
Right mainstem intubation
Loss of airway
Air leak Pediatric Resident Curriculum for the PICU UTHSCSA Physical Exam
• Tracheal shift – Pneumothorax • Wheezing
Pulmonary thromboembolism • Asymmetric breath sounds
Mucus plugging with atelectasis • Decreased breath sounds bilaterally
– Tube occlusion
Loss of airway Pediatric Resident Curriculum for the PICU UTHSCSA Pressure Patterns
• Elevated peak and plateau pressures
Right mainstem intubation • Elevated peak pressure, normal plateau pressure
– Airflow obstruction
Partial tube occlusion –
– Cuff leak
Large bronchopleural fistula • Reduced peak and plateau pressure Pediatric Resident Curriculum for the PICU UTHSCSA Extubation Criteria
Pulmonary Pediatric Resident Curriculum for the PICU UTHSCSA Neurologic
• Patient must be able to protect his airway, e.g, have cough, gag, and swallow reflexes.
• Level of sedation should be low enough that the patient doesn’t become apneic once the ETT is removed.
• No apnea on the ventilator.
• Must be strong enough to generate a spontaneous TV of 5
7ml/kg on 510 cm H2O PS or have a negative inspiratory force (NIF) of 25cm H2O or higher.
• Being able to follow commands is preferred. Pediatric Resident Curriculum for the PICU UTHSCSA Cardiovascular
• Patient must be able to increase cardiac output to meet demands of work of breathing.
• Patient should have evidence of adequate cardiac output without being on significant inotropic support.
• Patient must be hemodynamically stable. Pediatric Resident Curriculum for the PICU UTHSCSA Pulmonary
• Patient should have a patent airway.
• If no air leak, consider decadron and racemic epinephrine.
• Pulmonary compliance and resistance should be near normal.
• Patient should have normal blood gas and workof
breathing on the following settings:
PEEP 35cm H2O
Rate: 6bpm for infants, 2bpm for toddlers, CPAP/PS for 1hr for older children and adolescents
– PS 58cm H2O
– Spontaneous TV of 57ml/kg
– Pediatric Resident Curriculum for the PICU UTHSCSA Blood Gas Interpretation
BE Arterial Venous Capillary 7.4 (7.387.42)
7.357.40 80100 mm Hg
3540 mm Hg 4560 mm Hg 3545 mm Hg
4152 mm Hg 4045 mm Hg >95% on RA
6080% on RA
>70% 2226 mEq/L 2226mEq/L
2226mEq/L 2 to +2
2 to +2
2 to +2 Pediatric Resident Curriculum for the PICU UTHSCSA Rules Of Interpretation
• ∆ in pCO2 of 10mm Hg should ∆ pH by 0.08. • pH ∆ of 0.15 is equal to ∆ in HCO3 of 10mEq/L. • Normal pCO2 in the face of respiratory distress is a sign of impending respiratory failure. Pediatric Resident Curriculum for the PICU UTHSCSA AcidBase Diagram From Goldberg, M.,
Green, S.B., Moss,
M.L., et al.: JAMA
223:269-275, Pediatric Resident Curriculum for the PICU UTHSCSA Respiratory Disturbances
• Acute respiratory acidosis occurs when CO2 is retained acutely.
• Chronic respiratory acidosis occurs when the retained CO2 gets buffered by renal retention of HCO3. The pH is higher than in acute respiratory acidosis, but it is still <7.4.
• Acute respiratory alkalosis occurs when CO2 is blown off acutely.
• Chronic respiratory alkalosis occurs when the reduction of CO2 is compensated for by the renal excretion of HCO3. The pH is lower than in acute respiratory alkalosis, but it is still >7.4. Pediatric Resident Curriculum for the PICU UTHSCSA Metabolic Disturbances
• Acute metabolic acidosis gets compensated by CO2 reduction within 1224 hours. The pH is still usually <7.4.
• Metabolic alkalosis is rare. Usual causes are pyloric stenosis, chronic diuretic use, and bicarbonate infusions.
• Otherwise healthy people do not usually retain CO2 to compensate for metabolic alkalosis.
• Patients who are severely dehydrated or have lung disease will retain CO2 to compensate for metabolic alkalosis. Pediatric Resident Curriculum for the PICU UTHSCSA Hypoxemia
There are five reasons for hypoxemia:
• FiO2 too low (high altitude)
• Global alveolar hypoventilation
Incomplete diffusion ...
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- Fall '11
- PICU, Pediatric Resident Curriculum