Acute Hypoxic/Hypercapnic Respiratory Failure Flashcards
Normal Inhalation
-Generated by negative intrathoracic pressure
-Increasing volume of the chest creates negative pressure, air moves down the pressure gradient
Normal Exhalation
-Passive process
-Recoil of chest wall, respiratory muscles and lungs themselves
Compliance
-“stiffness” of the lung and the chest wall
-Normally lungs expand easily, some conditions hinder this (e.g. Fibrotic lungs, morbid obesity)
Lung Compliance Equation
-Change in lung volume for a given change in intrathoracic pressure
-Compliance = ΔV/ΔP (normal ~100 mL/ 1 cm H2O)
Resistance
-Diameter of the airways
-Ex: COPD, Asthma, plugged airways (including artificial)
-Relatively small change in radius of airway = large change in resistance
Surface tension of alveoli
-Water lines the alveoli and creates surface tension
-Overcoming this surface tension requires a lot of pressure
Surfactant
-Acts as a detergent and breaks the surface tension
-Prevents nearly complete collapse of alveoli during exhalation
-Makes it easier to breath
Respiratory Centers in the Brain
-Chemo receptors in CNS
-CO2 Chemoreceptors in the aortic and carotid bodies
-Oxygen receptors in the aortic and carotid bodies
Chemoreceptors in the CNS
-Respiratory center in the brain
-Monitor pH of CSF – aggressively control the pH
-Metabolic acidosis compensation (e.g. lactic, ketoacidosis)
P/F Ratio
-An indirect estimate of shunt fraction
-PaO2/FiO2 = x Normal is above 400
Example: 100/0.21 = 476
Example: 90/0.5 = 180
Definition of Ventilation
How effectively CO2 is eliminated from the blood
Respiratory Failure: Hypoxic (Type I) VS. Hypercapnic/Hypercarbic (Type II)
-Respiratory failure may be acute, chronic or acute on chronic
-Multitude of reasons for resp failure
Signs and Symptoms of Hypoxia (Type I)
-Dyspnea
-Cyanosis
-Anxiety
-Restlessness
-Delirium
-Tachypnea
-Bradycardia
-Tachycardia
-Hypertension
-Cardiac Dysrhythmias
-Tremor
Signs and Symptoms of Hypercapnia
-Dyspnea
-Headache
-Htn
-Tachycardia
-Tachypnea
-Bradypnea
-Impaired LOC
-Papilledema
-AMS
Diagnostic Workup for Respiratory Failure
-H&P with physical exam
-ABG
-Labs (CBC, CMP, +/- BNP, D-dimer)
-EKG
-CXR (+/- chest CT, CT PE, V/Q scan)
-exam (pleural effusions, a-lines, b-lines, lung sliding) DVT exam, ascites, more…)
Normal ABG
-pH: 7.35 – 7.45 (7.40)
-Co2: 35 – 45 (40)
-PaO2: 70-90
-HCO3: 22-26
-Anion gap = Hidden acidosis
Compensation VS. Uncompensated of ABG
-Depends on pH
-Compensated = normal range
-uncompensated = outside normal range
-Regulated by opposing system.
-Respiratory = quickly adjusts (minutes)
-Renal = slow to adjust (hours to days)
Hypoxia Respiratory Failure: Definition and 4 umbrella causes
–PaO2 < 60 on arterial blood gas or SaO2 < 90% on pulse oximetry
-Hypoventilation
-V/Q mismatch (shunting)-COPD, PE
-Shunt: (ARDS, Pulmonary Edema, atelectasis)
-Diffusion defect (ILD, pulmonary fibrosis
Hypercapnic RF Definition and causes
-Definition: PaCO2 > 50 on ABG
-Acute –minutes to hours (drug overdose)
-Chronic – days to weeks (COPD, obesity hypoventilation syndrome)
-Acute on chronic (COPD exacerbation)
Important point
Saturations tell you NOTHING about the level of CO2 in the patient’s blood – get an ABG
-COPD, Asthma, neuromuscular disorders, chest wall abnormalities, drug overdose
ARDS DX criteria
-Respiratory distress
-Bilateral pulmonary infiltrates (doesn’t need to be diffuse)
-P/F ratio (hypoxemia) with minimum PEEP requirements
-Absence of other causes of acute hypoxic resp. failure and bilateral pulmonary infiltrates
ARDS Diagnostic Workup
-R/O HF
-R/O other conditions with similar presentations (DAH, aspiration pneumonitis, eosinophilic pneumonia)
-Lung biopsy-last resort
Berlin Criteria
-P/F ratio <300 = Mild ARDS
-P/F ratio <200 = Moderate ARDS
-P/F ratio <100 = Severe ARDS
10 P’s of Hypoxia: Before Intubation
-Position
-Pee (lasix?)
-Physiotherapy (deep breath, suction, cough)
-PEEP (Optiflo, HHFNC, CPAP/Bipap)
10 P’s of Hypoxia: After intubation
-Position (sitting up, prone?)
-Paralysis
-Pee (CRRT, Lasix)
-Prostaglandins (Nitric, pulmonary htn, flolan)
-PEEP: Increase, BiLevel, APRV
-Perfusion (improve BP, ECMO)
CPAP
-Continuous positive airway pressure
-Can deliver room air up to 100% FiO2
-Positive pressure helps raise mean airway pressure resulting in improved oxygenation
-Can improve work of breathing by “stenting” open airways
-Do not use in patients who are unable to protect their airway or have a large secretion burden
-Caution in patients who are at high aspiration risk
BiPAP
-BiPAP is CPAP with an inspiratory pressure on top of the continuous baseline pressure
-IPAP = inspiratory positive airway pressure
-EPAP = expiratory positive airway pressure
-Same features as CPAP, but gives inspiratory pressure to help offload some work of breathing
-IPAP – EPAP = pressure support (different than on vent)
-Can help decrease CO2 in a hypercapnia patient by augmenting their minute ventilation
-Same contraindications and cautions for BiPAP and CPAP
Assist Control on Ventilator
-Volume control vs. Pressure control
-Patient trigger breaths
Pressure Support
-Spontaneous (CPAP)
-Patient breathing “on their own”
5 = my mininum
Synchronized Intermittent Mechanical Ventilation (SIMV)
-Pressure support breaths when additional are taken
ASV (Adaptive Support Ventilation)
-Intelligent ventilation mode for passive and spontaneously breathing adult and pediatric patients
-Automatically adjusts ventilation to lung mechanics and applies lung-protective strategies.
Minute Ventilation
RR X TV
Auto PEEP/AIR Trapping
-Caused by obstruction
-Physiologic (COPD, Asthma)
-Mechanical (tube size, mucus plugs, biting down)
-Dynamic hyperinflation
-Hemodynamic compromise
-Disconnect ventilator – sigh of relief.
-Asses the Flow curve and graph
