Airway & Breathing Flashcards
Hypoxaemia
Definition
Causes
Effects
Low levels of oxygen in the blood.
Causes:
- impaired O2 intake - e.g. airway obstruction, lack of environmental O2.
-impaired gas exchange - e.g. alveoli collapse, pulmonary oedema.
- decreased Hb - e.g. anaemia, blood loss.
- cellular environment not supportive of O2 utilisation - e.g. metabolic acidosis.
Effects: hypoxia, impaired anaerobic metabolism and cellular dysfunction
Hypoxia
Definition
Signs/Symptoms
Inadequate supply of oxygen to tissues and vital organs.
Signs/symptoms arise first from organs at greatest risk:
- Brain - headache, confusion, decr. LOC.
- Heart - chest pain, tachy-arrhythmia, peripheral vasoconstriction.
-Lungs - tachypnoea, incr. WOB.
Respiratory Acidosis
Definition
ABGs
Causes
Elevated levels of CO2 and resultant decrease in pH (acidic).
ABGs = pH < 7.35 and PaCO2 > 45mmHg.
+/- HCO3 > 26mmol/L = metab. comp
Cause - inadequate alveolar ventilation = CO2 retention - e.g. espiratory depression, asthma, COPD.
Respiratory Alkalosis
Definition
ABGs
Causes
Low levels of CO2 (excess clearance) and resultant increase in pH (alkaline).
ABGs = pH > 7.45 and PaCO2 < 35mmHg.
+/- HCO3 < 22mmol/L = metab. comp
Causes- hyperventilation = excess CO2 clearance - e.g. anxiety/panic, pain, PE, pneumothorax, compensation for hypoxia.
Pulmonary Oedema
Definition
Causes
Patho
Abnormal build-up of fluid in alveoli resulting in impaired gas exchange.
Causes - viral/bacterial infection, PE, CHF, high altitudes, upper-airway obstruction.
Patho - impaired LV function OR build-up of infectious material > impaired lymphatic drainage in distazl lung > accumulation of fluid > impaired capillary diffusion.
Pneumonitis
Definition
Causes
Patho
Inflammation of alveoli resulting in impaired gas exchange.
Causes - airborne irritants, aspiration, infection or secondary to systemic events.
Patho - alveolar irritation > inflammatory response > altered pulmonary capillary permeability > haemorrhage and fluid leakage > neutrophil mediators > pulmonary vasoconstriction.
Metabolic Acidosis
Definition
ABGs
Causes
Elevated concentration of H+ ions in blood and resultant decrease in pH (acidic).
ABGs = pH <7.35, HCO3 < 22mmol/L and BE < -2mmol/L.
+/- CO2 < 35mmg = resp. comp
Causes
- increased H+ production - e.g. lactic acidosis, DKA.
- reduced H+ excretion - e.g. renal failure.
- increased HCO3 clearance - e.g. GIT losses, renal tubular disease, Addisons.
Metabolic Alkalosis
Definition
ABGs (+/- comp.)
Causes
Low concentration of H+ ions in blood and resultant increase in pH (alkaline).
ABGs = pH > 7.45, HCO3 > 26mmol/L and BE > +2mmol/L
+/- CO2> 45mmg = resp. comp
Causes:
- decreased H+ concentration - e.g. hypokalaemia.
- increased H+ excretion - e.g. GIT losses, diuretics
- decreased HCO3 clearance - e.g. liver cirrhosis.
Acidosis/Alkalosis Compensation
Aim - return pH to baseline by altering levels of CO2 or HCO3.
Lungs (rapid) -
Alkalosis - decr. RR > decr. CO2 clearance.
Acidosis - incr. RR > incr. CO2 clearance
Kidney (slow) -
Alkalosis - incr. excretion of HCO3 ions
Acidosis - incr. excretion of H+ ions, decr. excretion of HCO3 ions.
Mixed Respiratory/Metabolic Acidosis
ABGs
Causes
pH < 7.35
PaCO2 > 45
HCO3 < 22
*PaCO2 and HCO3 moving in opposite directions.
- Cardiac arrest
- MODS
Mixed Respiratory/Metabolic Alkalosis
ABGs
Causes
pH > 7.45
CO2 < 35
HCO3 > 26
*PaCO2 and HCO3 moving in opposite directions.
-Hyperventilation in COPD
-Hyperemesis gravidarum
- Liver cirrhosis and diuretic use
Internal Respiration
Exchange of gases between systemic blood capillaries and tissue cells. O2 transported in blood (bound to Hb molecules) from pulmonary capillaries via LV/aorta and systemic arteries. CO2 produced by tissue cells during anaerobic metabolism. O2 and CO2 diffuse via interstitial fluid in opposite directions according to diffusion gradient.
External Respiration
Exchange of gases between alveoli and pulmonary blood capillaries. O2 inhaled from atmospheric air. CO2 transported from tissues (as HCO3) to pulmonary capillaries via systemic veins, RV and pulmonary artery. O2 and CO2 diffuse via respiratory membrane in opposite directions according to diffusion gradient.
Respiratory Membrane
Basement membrane composed of single-cell layer of simple squamous epithelium fused to alveolar epithelial cells and pulmonary capillary endothelial cells. Site of gas exchange.
Inspiration
Movement of air into lungs via negative pressure created by diaphragm contraction and increasing lung volume. Active process involving contraction of diaphragm and external intercostals.
Expiration
Movement of air out of lungs via positive pressure and decrease lung volume . Passive process involving diaphragmatic relaxation, elastic recoil and surface tension (surfactant) of lungs to return to resting state.
Respiratory Centres
Medulla (PRIMARY CENTRE) - sends signals to muscles that stimulate inspiratory and expiratory movements AND controls reflexes for non-respiratory air movements (e.g. coughing, sneezing, swallowing).
Pons (SECONDARY CENTRE) - controls rate, speed and depth of involuntary respiration via two opposing regions.
Chemoreceptors - detect pH levels in blood and send signals to respiratory centres to adjust ventilation.
Tachypnoea
Definition
Causes
Abnormally rapid rate of respiration >20bpm.
Causes - EARLY SIGN OF CLINICAL DETERIORATION, respiratory distress, panic/anxiety, respiratory compensation (metabolic acidosis), hyperthermia.
Bradypnoea
Definition
Causes
Abnormally slow rate of respiration <12bpm.
Causes - EARLY SIGN OF CLINICAL DETERIORATION, respiratory depression (drugs/brain injury), respiratory compensation (metabolic alkalosis), hypothermia.
Orthopnoea
Difficulty maintaining ventilation in supine position due to non-compliance of lungs and/or pulmonary congestion.
Cheyne-Stokes Respirations
Periods of apnoea alternating with periods of hyperpnoea (forced respiration).
Causes - LVF, brain injury, end-of-life.
Kussmaul Breathing
Deep rapid respirations.
Causes - respiratory compensation for metabolic acidosis - e.g. DKA, lactic acidosis.
Oropharyngeal Airway
Definition
Sizing
Insertion
Hard plastic airway adjunct inserted into oral cavity upside down and rotated 180 degrees on contact with hard palate to prevent tongue from falling back and covering epiglottis.
Nasopharyngeal Airway
Thin/flexible airway adjunct inserted into a patient’s nostril to maintain patent airway by by-passing upper airway obstruction at level of nose, nasopharynx or base of tongue and preventing tongue falling backward on pharyngeal wall.
LMA
Supraglottic airway device with cuffed mask at one end that is inserted (unguided) through mouth and into the hypo-pharynx and inflated to create low-pressure seal around the laryngeal inlet/glottic opening and allow for ventilation.
NOT a definitive airway as does not protect against risk of aspiration.
ETT
Definitive airway device composed of PVC tube with tracheal cuff on one end that is inserted (guided) through larynx (between vocal cords) into lower trachea and inflated to maintain placement to maintain patent airway, allow for ventilation (including mechanical positive pressure), suction and protect against aspiration.
Tracheostomy
Small surgical opening into trachea and insertion of tracheostomy tube to allow air entry and exit.
Used where ETT is not available/contraindicated or long-term ventilation.
Mechanical Ventilation
Partial or complete provision of artificial ventilation via positive or negative pressure machines.
Invasive - involves insertion of definitive airway via trachea - e.g. ETT or tracheostomy.
Non-invasive - involves positive-pressure breathing support via face mask, nasal prongs, helmet - e.g. CPAP.
Negative Pressure Ventilators
Mechanism
Examples
Decrease pressure of air surrounding patient to create negative pressure vacuum that causes chest expansion and sucks air into lungs.
E.g. iron lung, jacket ventilators, cuirass ventilator.
Positive Pressure Ventilators (Invasive)
Mechanism
Ventilator initiates breath using positive pressure to deliver oxygen v into lungs. Ventilator terminates breath once set limit of inter-alveolar pressure is detected OR volume of gas is delivered. Expiration occurs passively.
Fraction of Inspire Oxygen (FiO2)
Concentration of O2 inhaled by the patient.
Tidal Volume
The amount of air that moves in OR out of the lungs with each respiratory cycle.
Average = 500ml (m) or 400ml (f)
Minute Ventilation
The total volume of air inhaled or exhaled in one minute.
MV = TV X RR
I:E Ratio
The proportions of each breath cycle spent in inspiratory and expiratory phases.
I:E = total inspiratory time/total expiratory time
Normal = 1:2
COPD = 1:3-1:5
Positive End Expiratory Pressure (PEEP)
Positive pressure that remains in airways at the end of the respiratory cycle. Greater than atmospheric pressure in mechanically ventilated patients to decreased WOB and maintain airway and alveolar patency.
Volume-Limited Assist Control
Breaths deliver predetermined tidal volume at set ventilator rate to guarantee minimum minute ventilation
Pressure-Limited Assist Control
Breaths deliver predetermine flow of air at set pressure limit and rate.
Pulmonary Barotrauma
Injury to lung tissues caused by positive-pressure ventilation.
Elevation of trans-alveolar pressure > differences in pressure of interstitial spaces >alveolar rupture leads > leakage of air into extra-alveolar tissue.
Ventilator-Associated Lung Injury
Acute lung injury caused or exacerbated by mechanical ventilation.
Alveolar over-distension, barotrauma, atelectotrauma and inflammation > increased alveolar permeability, alveolar oedema, haemorrhage > hyaline membrane formation > reduced functional surfactant > alveolar collapse.
Ventilator-Induced Pneumonia
A complication of invasive positive-pressure mechanical ventilation. Bacteria introduced into lungs via airway tubing and/or aspiration of secretions.
Ventilator Dependence
Failure to wean off mechanical ventilation and breathe independently; ongoing requirement for mechanical ventilation.
Long-term ventilation > reduction in diaphragm contractility > reduced inspiratory muscle function.
Non-Invasive Ventilation (BiPAP)
Definition
Indications
Initial settings
Delivery of oxygen into the lungs via positive pressure at different levels during inspiration and expiration, to reduce WOB on both inspiration and expiration.
iPAP > ePAP (Ventilation mainly provided by iPAP and ePAP recruits under-ventilated alveoli and allows removal of exhaled gas)
- COPD/Asthma with respiratory acidosis
- Respiratory failure type two (hypercapnic)
- Weaning from mechanical ventilation
CPAP
Definition
Indications
Delivery of oxygen via constant fixed positive pressure throughout inspiration and expiration to splint the airways open.
- Obstructive sleep apnoea
- Cardiogenic pulmonary oedema
- Chest wall trauma and hypoxia (not pneumothorax)
- Pneumonia (pre-ventilation)
NIV Care
- Use full face mask and ensure good seal
- Starting rates:
-BiPap - iPAP 10/ePAP4
-CPAP - 4cm H20 - Increase by 2-5cm/10min to achieve therapeutic response (NOT >25cm)
- Regular vital signs/GCS
- ABGs before and 1, 4, 12 hours post-initiation
- Complications - hypotension (+iPAP/ePAP), stomach inflation/aspiration (+iPAP), pressure sores.
Extracorporeal Membrane Oxygenation (ECMO)
Form of life support involving heart-and-lung by-pass machine that pumps and oxygenates blood outside the body, allowing heart and lungs to rest and heal.
Weaning
The gradual process of reducing mechanical ventilator support. Spontaneous breathing trials are used to assess patient’s ability to breathe with minimal-no support.
Delayed weaning risks - VALI, VAP, ventilator dependency.
Early weaning risks - loss of airway, impaired gas exchange, aspiration, respiratory fatigue, respiratory arrest.
Arterial Blood Gases (ABGs)
pH 7.35-7.45
PaO2 75-100mmHg
PaCO2 35-45mmHg
HCO3 22-26mmol/L
BE (-)2-(+)2
MET Criteria
Airway - THREATENED
Respiratory arrest
RR </=4 OR >36
ABG Interpretation
- PaO2 - Is the patient hypoxaemic?
(75 -100mmHg OR >10kPa) - pH - Is the patient acidic or alkalotic?
(7.35 - 7.45) - PaCO2 - Is the pH imbalance related to respiratory disturbance? (i.e. is there a CO2 disturbance that fits current pH?)
(35 - 45mmHg) - HCO3 - Is the pH imbalance related to metabolic disturbance?
(22-26mmol/L) - Base excess - Is there a disturbance in HCO3?
(-2 - +2 mEq/L)
*Note - are PaCO2 and HCO3 moving in opposite directions? = mixed acidosis/alkalosis.
