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.
Hypercarbia response
Hypercarbia will tend to cause an initial respiratory response according to the CO2 response curve. Progression of the hypercarbia will result in profound acidosis and resultant hypotension and cardiac arrhythmias. Sympathetic stimulation can lead to normalization of blood pressure or even hypertension with profound hypercarbia. Profound hypercarbic narcosis will tend to present around a partial pressure of 100-120 mmHg.
vasodilation
Cardiogenic pulmonary edema is most appropriately treated by
Cardiogenic pulmonary edema is most appropriately treated by supplemental oxygen, diuresis (especially loop diuretics), vasodilators, inotropes, and positive end-expiratory pressure (PEEP).
The expected amount of respiratory compensation for a given drop in pH due to a metabolic acidosis
The expected amount of respiratory compensation for a given drop in pH due to a metabolic acidosis can be calculated using the Winter formula: PCO2 = (1.5 * [HCO3]) + 8 +/- 2.
The ARDS Network demonstrated a 22% reduction in mortality when patients with ARDS were mechanically ventilated at tidal volumes using 6 mL/kg of PBW and what pressures
The ARDS Network demonstrated a 22% reduction in mortality when patients with ARDS were mechanically ventilated at tidal volumes using 6 mL/kg of PBW and plateau pressures ≤ 30 cm H2O.
CPAP effects
CPAP decreases surfactant depletion, increases total lung volume, increases minute ventilation, and generally decreases cardiac output.
relationship between surfactant, surface tension, and size of alveoli
Pulmonary surfactant more effectively reduces surface tension when it is more concentrated. As alveoli shrink, the surfactant concentration increases which more effectively reduces surface tension. On the other hand, as alveoli become more distended, the surfactant is stretched more thinly which results in a decrease in concentration. Subsequently, the surface tension will increase and favor a reduction in size.
LaPlace law formula for surface tension
The relationship of surface tension and size of the alveoli can be quantified with the LaPlace law:
Wall tension = (P*r)/2h
P pressure
r radius
h wall thickness
Pressure = 2 * T / r = (2 * surface tension) / radius
The pressure in above equation represents the pressure within the alveolus.
FRC
FRC = Residual Volume + Expiratory reserve volume
Or
FRC = Total lung capacity – Inspiratory capacity
Causes of low FRC
Causes of low FRC are PANGOS: Pregnancy, Ascites, Neonates, General anesthesia, Obesity, Supine position.
Factors that increase closing capacity
Factors that increase closing capacity are ACLS-SO: Age, Chronic bronchitis, LV failure, Smoking, Surgery, Obesity.
Normal adult values for the lung volumes and capacities measured by spirometry are as follows: TLC: VC: TV RV: FRC:
Normal adult values for the lung volumes and capacities measured by spirometry are as follows: TLC: 6-8 L VC: 4-6 L TV: 0.5 L RV: 1.5-2 L FRC: 2-2.5 L
Overdistension or high airway pressures more problematic
Overdistension of inflated alveoli may be more closely related to lung injury than the airway pressures themselves, especially in cases of decreased chest wall compliance where airway pressures may be increased due to increased chest wall pressures and not necessarily increased transpleural pressures.
Esophageal manometry
Esophageal manometry, while an old technology, has emerged in the last decade as a reasonable and viable means of monitoring pleural pressures and allowing for the calculation of a transpleural (also known as a transpulmonary) pressure gradient.
Fink effect
Diffusion hypoxia (“Fink effect”) is a well-documented effect since the 1950s that can be observed following the cessation of an inhaled anesthetic involving the use of high concentrations of nitrous oxide.
The low blood solubility of nitrous oxide, coupled by relatively low potency leads to large amounts of nitrous oxide being eliminated into the alveoli over a short period of time following cessation of anesthesia. This leads to displacement of oxygen and carbon dioxide in the alveoli. Supplemental oxygen should be provided to mitigate this effect
A positive response to a bronchodilator challenge during PFTs is
A positive response to a bronchodilator challenge during PFTs is a greater than 15% improvement in FEV1.
Decreased TLC is indicative of
Decreased TLC is indicative of restrictive pulmonary processes such as ARDS, pulmonary fibrosis, scoliosis/kyphosis, and certain neuromuscular diseases.
asthma restrictive or obstructive
obstructive
bronchiectasis restrictive or obstructive
bronchiectasis, which is an obstructive pulmonary disease
Anesthetic management of obstructive lung disease
Anesthetic management of obstructive lung disease includes bronchodilator therapy preoperatively, a higher concentration of inhalation anesthetics, and additional opioids to deepen anesthesia as ways to decrease airway reactivity. Obstructive lung disease can also lead to hypercapnia and management include slower ventilation rates and maintaining peak airway pressures below 40 cm H2O.
Restrictive lung disease anesthesia management
Restrictive lung disease is characterized by low lung compliance and stiff lung. Patients typically breathe rapidly and shallowly, and patients with severe restrictive lung disease can desaturate quickly during induction even with pre-oxygenation because of their decreased FRC. They are more likely to reach high peak airway pressures when given positive pressure ventilation because of their stiff lungs. Management of these patients includes lower mechanical tidal volumes to reduce the risk of barotrauma. Although lower mechanical tidal volumes at more rapid rates reduce the risk of barotrauma, it also increases the chances of developing atelectasis.
Restrictive lung dz FVC FEV1 FEV1/FVC FRC TLC
FVC decreased FEV1 decreased FEV1/FVC normal FRC decreased TLC decreased
Obstructive lung dz FVC FEV1 FEV1/FVC FRC TLC
FVC normal to slight increase FEV1 normal or slight decrease FEV1/FVC decreased FRC decreased TLC normal or slight increase if gas trapping
asbestosis restrictive or obstructive
restrictive
sarcoidosis restrictive or obstructive
restrictive
pulmonary fibrosis restrictive or obstructive
restrictive
bronchitis restrictive or obstructive
obstructive
cystic fibrosis restrictive or obstructive
Cystic fibrosis results in severe bronchiectasis in nearly all cases due to chronic cough, purulent sputum, and scarring of the bronchial airways; this produces an obstructive, not restrictive, lung disease pattern.
Transtracheal jet ventilation
Transtracheal jet ventilation can prove to be a life-saving invasive airway technique and involves placement of a large-bore catheter through the cricothyroid membrane using seldinger technique with a needle, then guidewire, then catheter. Pressures between 15 - 35 psi should be used, and adequate time should be allowed for passive expiration to reduce the risk of pneumothorax.
The minimum possible fresh gas flow rate that is compatible with a normoxic inhaled gas mixture by kg
The minimum possible fresh gas flow rate that is compatible with a normoxic inhaled gas mixture is the patient’s basal metabolic rate of oxygen consumption. This value is typically between 3 to 4 mL/kg/min in an adult but can be as high as 8-10 mL/kg/min in a premature infant or neonate.
compliance
Compliance, in general, can be thought of as ΔV/ΔP
static compliance
The Cstat of a tissue can be measured during an inspiratory hold. The formula uses plateau airway pressures since the value is measured during periods of no flow. The formula is Cstat = VT/(Pplat-PEEP).
where Cstat = static compliance, VT = tidal volume, Pplat = plateau pressure and PEEP = positive end-expiratory pressure. Note that the term plateau means “level”; this level area of minimal change would be a static measurement.
dynamic compliance
Dynamic compliance refers to compliance of lung tissue during gas flow. It can be calculated using the formula: Cdyn = VT/(PIP - PEEP)
Keep in mind: because PIP is always higher than Pplat, the Cdyn for any given lung tissue is always lower than the Cstat.
what is a “sigh”
recruitment maneuver
recruitment maneuver in ARDS
In large, multicenter studies, periodic recruitment maneuvers (or “sighs”) in patients with acute respiratory distress syndrome (ARDS) have been shown to produce only modest improvements in oxygenation without an improvement in mortality and with potentially significant hemodynamic and ventilatory complications.
