ITE CA2 Respiratory Flashcards
Phase one criteria which predict poor perioperative outcome following pneumonectomy include:
Phase one criteria which predict poor perioperative outcome following pneumonectomy include: PaCO2 >45 mm Hg PaO2 < 50 mm Hg on room air FVC < 50% FEV1 < 2 L FEV1/FVC < 50% MVV(maximum voluntary ventilation) < 50% DLCO < 50
Respiratory acidosis Initial compensation
Homeostasis of body pH is complex and varies depending on the disturbance. Respiratory acidosis occurs when ventilation is inadequate. Initial compensation occurs though plasma protein buffers and is followed hours to days later by the renal response.
Urinary excretion of chloride ions occurs if respiratory acidosis continues. This is a much slower process and can take hours to days to help compensate for an acute respiratory acidosis.
Excretion of hydrogen ions is not an acute compensatory mechanism.
Renal retention of bicarbonate is important as a compensatory mechanism, however this does not occur immediately. The renal compensation for a respiratory acid-base disorder takes time to develop (usually hours to days depending on the clinical situation).
Half life of carbon monoxide
Half-life of CO at room air temperature is 3-4 hours. One hundred percent oxygen reduces the half-life to 30-90 minutes; hyperbaric oxygen at 2.5 atm with 100% oxygen reduces it to 15-23 minutes.
Estimated FRC
30-40 mL/kg
Rate of rise of CO2 in apnea awake
The PACO2 of an awake, preoxygenated adult with normal lungs rises 7 mm Hg/minute for the first 10 seconds, 2 mm Hg/min for the next 10 seconds, then 6 mm Hg/minute afterwards [Stock MC et. al. J Clin Anesth 1: 96, 1988], so essentially 6 mm Hg/min or 1 mm Hg every 10 seconds.
ph or alpha stat is temp corrected
ph stat
lung volume changes in obesity
Obesity is characterized by a marked decrease in expiratory reserve volume, leading to a decrease in lung compliance and FRC. Decreased FRC also leads to airway closure and decreased PaO2.
Lung volumes: obesity is characterized by a very marked decrease in expiratory reserve volume. In the presence of well-preserved residual volume, this is manifested as a reduction in functional residual capacity (FRC). Total lung capacity (TLC) is also reduced, but only modestly, thus inspiratory capacity (defined as TLC-FRC) is increased.
lung mechanics changes in obesity
Lung mechanics: the compliance of the respiratory system is decreased, mostly due to the fact that the tidal breathing occurs at smaller lung volumes.
airway function changes in obesity
Airway function: both FEV1 and FVC are decreased proportionally so that the FEV1/FVC ratio is preserved, i.e. obesity behaves like a restrictive defect.
gas exchange changes in obesity
Gas exchange: obese individuals have a normal closing capacity, but because FRC is decreased, airway closure occurs within the range of tidal breathing, leading to decreases in PaO2.
What increases FRC
Functional residual capacity increases with age due to loss of elastic lung tissue which acts as an inward force pulling the lungs closed. An increase will also be seen with increased height secondary to the larger lungs compared to short counterparts.
Causes of low FRC
FRC will go down with increased weight, decreased height, and in females compared with males. A decrease in FRC can also be seen in lung disease such as idiopathic fibrosis, pneumoconiosis, and different forms of granulomatosis and vasculitis. Following a lung resection a reduction in FRC will be seen; occasionally the remaining lung will expand to fill in some of the space left.
Other causes of low FRC are PANGOS: Pregnancy, Ascites, Neonatal, General anesthesia, Obesity, Supine position.
Capnogram in COPD with one transplanted lung
Double peak
During exhalation what part of lungs is emptied first
During forced exhalation, the lung apices are emptied first, and airway closure occurs first in the lung bases.
During exhalation, airway closure occurs first in what part of the lungs
During forced exhalation, the lung apices are emptied first, and airway closure occurs first in the lung bases.
PVR relative to Residual volume, FRC, total lung capacity
PVR increases with increasing and decreasing lung volumes on either side of functional residual capacity (FRC), as shown in the figure above
DLCO
definition
elevated/decreased in what conditions
The DLCO uses carbon monoxide diffusion to assess the parenchymal function of the lungs. DLCO is effected by cardiac output and hemoglobin concentration. The DLCO is elevated in conditions like: asthma, polycythemia, pulmonary hemorrhage, exercise, and left to right shunts. It is decreased in pulmonary embolism.
ABG in CO poisoning
An ABG from a patient with moderate to severe CO poisoning will most likely show a metabolic acidosis with a normal PaO2 and a falsely elevated calculated SaO2 and SpO2.
Differential for increased peak inspiratory pressure but unchanged Pplateau
AIRWAY RESISTANCE
- Airway compression
- Bronchospasm**
- Foreign body
- Kinked ET tube
- Mucus plug
- Secretions
- Asthma attack
Differential for increased peak insp pressure AND increased plateau pressure
PULMONARY COMPLIANCE (elastic resistance)
- Abdominal insufflation
- Ascites
- Intrinsic lung disease
- Obesity
- Pulmonary edema
- Tension pneumothorax
- Trendelenburg position?
- ARDS
- TRALI
manifestations of cystic fibrosis
Pulmonary manifestations of cystic fibrosis result from the inability to clear thickened airway mucus and from recurrent bacterial infections. Patients develop progressively worsening bronchiectasis and COPD with inspiratory and expiratory obstruction. Airway obstructions cause ventilation/perfusion mismatching which leads to hypoxemia. Chronic hypoxia then increases PVR and pulmonary hypertension which eventually leads to cor pulmonale. Patients also have a high propensity to develop spontaneous pneumothorax. Non-pulmonary complications include hepatobiliary tract disease, pancreatic insufficiency, malabsorption, diabetes, and azoospermia. Patients with cystic fibrosis (CF) tend to have greater bronchial reactivity to irritating stimuli and histamine than patients without CF.
Acute hypocarbia will result in
Acute hypocarbia will result in vasoconstriction, especially in the cerebral vasculature. It will also cause a respiratory alkalosis resulting in a decreased fraction of ionized calcium in the serum. This transient hypocalcemia may manifest as perioral numbness, muscle cramps, and tingling in the hands and feet.
