Therapeutics Pulmonary Ronald Flashcard

Based on Arterial Blood Gas, how do you differentiate between Hypercapnic Respiratory Failure and Hypoxic Respiratory Failure?

Hypercapnic Respiratory Failure

  • Progressive increase in PaCO2 –> respiratory acidosis
  • PaCO2 > 50 mmHg and pH < 7.35

 

Hypoxic Respiratory Failure

  • Progressive decrease in PaO2 due to ventilation/perfusion (V/Q) mismatch
  • PaO2 < 60 mmHg

Hypercapnic Respiratory Failure: Etiologies

Increase CO2 Production

  • Fever
  • Seizures
  • Sepsis
  • Increased carbohydrate load

Can’t Breathe! (V/Q mismatch — increased dead space)

  • COPD
  • Asthma
  • Cystic Fibrosis
  • Pulmonary Fibrosis
  • Obstructive Sleep Apnea
  • Respiratory Muscle Fatigue

Won’t Breathe! (Hypoventilation — decrease minute ventilation)

  • Drug overdose
  • CNS disorders
  • Central Sleep Apnea

Hypoxic Respiratory Failure: Etiologies

Cardiogenic

  • Acute MI
  • Left Ventricular Failure
  • CHF exacerbation
  • Mitral stenosis
  • Mitral regurgitation
  • Diastolic dysfunction

Non-Cardiogenic

  • Pneumonia
  • Acute Respiratory Distress Syndrome (ARDs)
  • Sepsis/Septic Shock
  • Chemical Aspiration
  • Pulmonary embolism
  • Pancreatitis

Respiratory Terminology: Tidal Volume

  • The amount of air inhaled or exhaled with each normal breath
  • Avg healthy person (non-ventilated) = ~500 ml, or 5-7 ml/kg (IBW)
  • Estimated initial VT for ventilated patients = 6-10 ml/kg (IBW)
  • Excessively large tidal volumes can lead to hyperinflation of the lungs and ventilator-induced lung injury

Respiratory Terminology: Respiratory Rate

  • Breaths/min
  • Typical initial ventilator rate 12-16 bpm
  • Patients with restrictive lung disease may require higher initial respiratory rates (16-20 bpm)
  • Patients can set their own respiratory rate by breathing above the set number of breaths the ventilator provides
  • ↑ RR –> ↑ respired CO2 –> ↓ PaCO2

Respiratory Terminology: Fraction of Inspirated Oxygen

  • Percentage of O2 delivered to patient
  • Room air = FiO2 21%
  • On mechanical ventilation — FiO2 can range from 21-100%
  • GOAL — to provide lowest FiO2 to maintain adequate PaO2 (> 60 mmHg)
  • FiO2 is usually started at 100% and decreased to maintain an adequate PaO2 > 60-70 mmHg
  • High FiO2 for long periods of time increases the risk of O2 toxicity (direct lung injury, CNS effects, retinal effects)

Respiratory Terminology: Positive End-Expiratory Pressure

  • Pressure held in the lungs during exhaled
  • Helps to increase the surface area of the alveoli
  • Prevents the alveoli from collapsing during exhalation
  • PEEP can help reduce O2 requirements  — by increasing PEEP, you can decrease FiO2 due to increase surface area of alveoli recruited for oxygenation
  • Typically — PEEP < 5 cm H2O?????

Respiratory Terminology: Minute Ventilation

  • Amount of air inhaled or exhaled per one minute
  • Normal VE = 5-8 L/min
  • Increase minute ventilation = increased respiratory CO2 excretion (hyperventilation)

What are the different types of Non-Invasive Mechanical Ventilation?

  • Continuous Positive Airway Pressure (CPAP)
  • Bilevel Positive Airway Pressure (BiPAP)

Continuous Positive Airway Pressure

Non-Invasive Mechanical Ventilation

  • Constant level of positive pressure is applied throughout inspiration and expiration
  • An air splint that holds your airway open
  • Common use = obstructive sleep apnea
  • Typical setting = 2.5-15 cm H2O
  • Oxygen can be titrated into the circuit to alleviate hypoxemia

Bilevel Positive Airway Pressure

Non-Invasive Mechanical Ventilation

  • Continuous pressure that cycles between high and low pressure levels
  • Delivers CPAP but also senses when an inspiratory effort is being made and delivers a higher pressure during inspiration
  • When flow stops (end of inspiration), the pressure returns to the CPAP level
  • This positive pressure wave during inspiration unloads the diaphragm and decreases the work of breathing
  • A back up mandatory respiratory rate can be set (> 12 bpms)
  • Oxygen can be titrated into the circuit to help with hypoxemia

Indications for Bilevel Positive Airway Pressure

  • COPD with hypercapnea
  • Acute pulmonary edema (CHF exacerbation)
  • Those who refuse intubation
  • A step-down from the ventilator for COPD or CHF patients

What are the two pressures used in Bilevel Positive Airway Pressure?

  • Inspiratory Pressure — pressure support ventilation
  • Expiratory Pressure — CPAP level (air stent)

What are the types of Invasive Mechanical Ventilation?

  • Assist Control Ventilation (A/C) — Volume Control
  • Synchronized Intermittent Mandatory Ventilation
  • Pressure Support/Control Ventilation

Assist Control Ventilation

Invasive Mechanical Ventilation

  • Volume control
  • A predetermined respiratory rate and tidal volume are set on the ventilator
  • Chosen initially when starting invasive mechanical ventilation
  • Patient triggers a supported breath by beginning to inhale
  • On assisted breaths the work of breathing is shared between the patient and the ventilator
  • The machine delivers the set tidal volume on each breath — tidal volume is constant despite the breath being initiated by the patient or the machine
  • A back-up respiratory rate is set in case the patient makes a decreased effort to breathe or becomes apneic
  • The patient has the ability to control his/her own respiratory rate
  • Useful when intent is to have the ventilator assume most or all of the work of breathing

Synchronized Intermittent Mandatory Ventilation

Invasive Mechanical Ventilation

  • A predetermined respiratory rate and tidal volume are set on the ventilator
  • No assist from the ventilator is provided beyond the pre-set number of breaths initially set on the ventilator (RR)
  • If patient breaths > than the pre-set RR, those breaths will be whatever tidal volume the patient can achieve on their own
  • The patient can “breathe around” the ventilator and set his/her own respiratory rate
  • Synchronized = the machine-assisted breaths occur simultaneously with patient effort and prevents a ventilator-delivered breath in the middle of a patient-delivered breath

Pressure Support/Control Ventilation

Invasive Mechanical Ventilation

  • Ventilator responds to a patient’s inspiratory effort by increasing the pressure to a pre-specified level
  • Pressure is increased or decreased depending on patient’s ventilator status
  • Patient provides the needed work of breathing (respiratory rate and tidal volume)
  • Like breathing on a scuba tank
  • Used either as a primary ventilator support or as a tool for assessing a patient’s readiness for extubation from the ventilator

Parameters used to assess readiness for weaning

  • RR < 25-30 breaths/min
  • Tidal volume > 5 ml/kg
  • Minute ventilation < 10 L/min — takes both RR and Tidal Volume into account

For a patient on a ventilar, what would you need to change in order to alter the patients PaCO2 levels?

Tidal Volume or RR

 

Can change Tidal Volume or RR by increasing minute ventilation

For a patient on a ventilar, what would you need to change in order to alter the patient’s PaO2 levels?

Change PEEP and FiO2

 

Increasing both will increase PaO2

Effects of Positive Pressure Ventilation of Physiology

Cardiovascular

  • Decreased preload, stroke volume, and cardiac output
  • Putting positive pressure in the chest and pressure on the vena cava which can lead to a decrease in preload

GI

  • Incidence of stress ulcers and sedation-related ileus is increased

Neurological

  • May decrease venous return from the head, increasing intracranial pressure (caution in head injury) and worsening agitation, delirium, and sleep deprivation

Complications of Mechanical Ventilation

  • During Endotracheal Intubation — upperairway and nasal trauma, oral-pharyngeal lacerations, tooth avulsions, hematoma of vocal chords, etc.
  • Barotrauma
  • Volutrauma
  • Ventilator-Associated Pneumonia
  • Oxygen Toxicity
  • Auto-PEEP
  • Prolonged use of endotracheal tubes — sinusitis, tracheal necrosis or stenosis, glottic edema

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