Reduced Lung Volume Flashcards
How is alveolar ventilation measured?
Respiratory rate x (tidal volume - deadspace)
What is regional ventilation?
Ventilation in specific regions of the lung
What is minute ventilation?
Respiratory rate x tidal volume
What is functional residual capacity?
Resting volume of the lung at the end of tidal breaths
What is the difference between atelectasis and lung collapse?
- Atelectasis is the collapse of alveoli
- Lung collapse is the collapse of whole regions of the lung
What is FRC a balance of?
- Inward elastic recoil of the lungs
- Springing out of the ribcage
What is closing capacity?
Volume of gas in the lungs at the time when small airways in the dependent portions (lower portions) of the lungs close during maximal exhalation
Why is pleural pressure less negative at the bottom of the lungs?
Because gravity pulls down the weight of the lung, making the space bigger (i.e. less pressure)
How is closing capacity measured?
Single breath nitrogen test
What factors does closing capacity increase with?
Age, COPD, smoking (loss of elastic recoil)
What is the relationship between closing capacity and body position?
- Higher when standing upright
- Lower when supine
What occurs when CC > FRC?
Dependent airway closure occurs during tidal breathing, i.e. much more likely to get lung collapse in those airways
What is the difference between CC and equal pressure point?
- CC is a volume
- EPP is where pleural pressure & pressure within alveoli are equal causing dynamic collapse (pressure-related, nothing to do with dependence/non-dependence)
What are the causes of reduced lung volume?
- External compression of lung tissue
- Reduced chest wall compliance
- Reduced central drive
- Decreased ability of respiratory muscles to generate force
- Loss of alveolar volume
What can cause external compression of lung tissue?
- Pleural space: Pleural effusion, empyema (pus), pneumothorax
- Abdomen: ascites (fluid), pregnancy, obesity
- Rib cage: Posture, flail segment, kyphoscoliosis
What causes reduced chest wall compliance?
- Kyphoscoliosis
- Obesity
- Pregnancy
- Age
What causes reduced central drive?
- Altered patterns of breathing
- Brainstem injury (medulla)
- Often causes reduction in tidal volume
What are some of the different patterns of reduced central drive?
- Cheyne-Stokes (just before death, breathing all over the place)
- Biot’s breathing
What decreases the ability of respiratory muscles to generate force?
- Neuromuscular disease (MND, stroke, spinal injury, phrenic nerve palsy)
- Deconditioning or fatigue (mechanical ventilation, COPD, illness)
What is required in order for the lungs to remain compliant?
- Elasticity
- Surfactant
What causes loss of alveolar volume?
- Post-op atelectasis
- Mucus plugging
- Removal of lung tissue
How is laparoscopic abdominal surgery different to open laparotomy?
- Less pain
- Less analgesic requirements
- Improved mobility
- Reduced hospital length of stay
- Lower incidence of post-op pulmonary complication (PPC)
What type of pain is laparoscopic surgery associated with?
Shoulder tip pain
- cause uncertain
- may be related to CO2 insufflation, irritation of diaphragm or peritoneum
- often worse with deep breathing
Why do physios not routinely assess patients following laparoscopic procedures?
They are low risk, shoulder tip pain is non-mechanical (i.e. can’t be fixed with physio)
What are examples of upper abdominal surgery?
- Splenectomy
- Liver resection
- Oesophagectomy (2 incisions, higher risk)
- Head of pancreas (2 incisions, higher risk)
What are examples of lower abdominal surgery?
- Colectomy
- Nephrectomy
What is an example of vascular abdominal surgery?
- Abdominal aortic aneurysm (AAA) repair & grafting
- High risk of PPC due to smoking history
What are some of the potential complications of surgery?
- Respiratory complications
- Wound infection
- Bleeding/haemorrhage
- Cardiovascular problems
- DVT
- Pulmonary embolus
- Renal failure
- Nausea/vomiting
- Psychosis
- Reduced gut mobility
- Musculoskeletal problems
- Exacerbation of pre-existing conditions
What surgeries are most commonly associated with PPCs?
Upper abdominal surgery & cardiothoracic surgery
What are the criteria for PPCs (requires 4 or more to be classified as PPC)?
- CXR report of collapse/consolidation
- Maximal oral temperature >38 deg for >1 consecutive days post op
- SpO2 <90% on >1 consecutive day post op
- Yellow/green sputum different to pre-op
- Infection on sputum culture report
- Unexplained high white cell count or prescription of antibiotic for respiratory infection
- New abnormal breath sounds
- Physician diagnosis of PPC
What are the 5 risk factors for PPC?
- Duration of anaesthesia >180 mins
- Surgery site (upper abdominal)
- Current smoker
- Respiratory co-morbidity
- Low fitness
What are the effects of UAS on lung volume?
Causes a restrictive ventilatory pattern Decreases - FRC - Tidal volume - Inspiratory capacity - Vital capacity
What causes reduced lung volume following UAS?
- Anaesthesia
- Analgesia
- Pain
- Diaphragm splinting
- Posture
- Mucus pooling
- Not being mobile
Why does anaesthesia cause reduced lung volume?
- Reduced phrenic nerve & diaphragm function
- Depressed hypercapnic drive & hypoxaemic response
- Supine posture
Why does analgesia cause reduced lung volume?
Decreases
- Respiratory drive
- Periodic sighs
- Cough reflex
- Breathing pattern
- Alveolar ventilation
Why does diaphragm splinting cause reduced lung volume?
- 60% reduction in diaphragm excursion
- Upper chest pattern of breathing
What are the consequences of reduced lung volume?
- Atelectasis
- Hypoxaemia (PaO2 < 80mmHg, SpO2 < 97%)
What auscultation findings can be expected in the presence of lung collapse?
- Reduced breath sounds
- Fine end inspiratory crackles
- Bronchial breath sounds
What are the signs of hypoxaemia?
- Restlessness
- Confusion
- Sweating
- Tachycardia
- Hypertension
- Cyanosis
What is compliance?
Volume change per unit pressure change
