Respiratory for Anesthesia (62 cards) – Flashcards
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RESPIRATORY
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...
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What is the PANGOS mnemonic for?
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Decreased FRC.
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What are the PANGOS conditions?
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Pregnancy Ascites Neonates GA Obesity Supine position
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What effect does PEEP have on FRC?
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PEEP increases FRC (So does emphysema.)
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What happens when closing capacity > FRC?
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Shunting occurs during tidal breathing.
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What is the mnemonic ACLS-S for?
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Conditions which raise closing capacity.
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What are the ACLS-S conditions?
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Age Chronic bronchitis LV failure Surgery Smoking
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What is the effect of methemoglobin on the oxy-Hb dissociation curve?
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LEFT-SHIFT
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According to the Haldane effect, the more deoxygenated the blood...
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the more CO2 can be carried in the form of carbamino compounds, without increasing PaCO2.
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In general, ventilatory control is mediated by hypoxemic and hypercarbic influences. Where are these signals processed?
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Peripheral chemoreceptors in the carotid and aortic bodies respond to hypoxemia. Central chemoreceptors in the brainstem respond to H+ produced from the CO2 which crosses the BBB.
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To what, specifically, do peripheral chemoreceptors respond?
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PaO2. (Not to O2 content or saturation.)
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Is the CSF a good buffer?
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NO
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How long does it take for an increase in PaCO2 to cause a change in minute ventilation?
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1 minute
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What is the shape of the ventilatory response to PaCO2 from 20 - 80 mmHg?
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LINEAR
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What are two functions of HPV?
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1) Minimizes shunt 2) Improves PaO2
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What is the effect of anesthetics on HPV?
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Volatiles inhibit HPV. IV agents have not been shown to affect HPV.
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At low doses, which is more greatly impacted by NTG: venous or arterial resistance?
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Venous resistance
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What happens to V and Q, moving from the base of the lung to the apex?
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V and Q both decrease, but Q decreases more.
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What is normal V/Q?
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0.8
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Qs/Qt = ?
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(CcO2 - CaO2)/(CcO2 - CvO2)
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PaCO2 does not begin to increase until shunt fraction exceeds about...
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50%. This is due to the excellent solubility of CO2.
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Vd/Vt = ?
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(PaCO2 - PeCO2)/PaCO2
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What is PeCO2?
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Mixed expired CO2 partial pressure (not end tidal CO2)
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What is the V/Q presentation typical of pneumothorax?
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SHUNT (perfused, but not ventilated)
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What factors account for increased A-a gradient during anesthesia?
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Decreased CO, FRC, and compliance. Increased airway resistance.
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Where is ventilation greatest, in a supine patient under GA with paralytics?
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ANTERIORLY. Nondependent regions are better-ventilated following induction of GA, due to decreased FRC.
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In a supine patient breathing spontaneously, where is ventilation the greatest?
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POSTERIORLY
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What are the three cardinal effects of general anesthesia on the lung?
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Atelectasis Shunt Hypoxemia
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When is the perioperative decrease in FRC greatest?
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3 - 5 days after surgery (lasting 10 days to 2 weeks)
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If pulmonary edema develops secondary to cardiac causes, what will be the PCWP?
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>18 mmHg
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PVR = ?
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(Mean PAP - LAP) x 80/CO
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What is normal PVR?
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150 - 250 dyne-sec/cm^5
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How does the solubility of N2O in blood compare with that of N2?
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35-fold higher. This fact underlies the rapid elimination of N2O at the lungs at the conclusion of general anesthesia... which can lead to dilution of alveolar oxygen.
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What is methemoglobin?
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Hemoglobin in which the heme iron is in the oxidized (FERRIC) state.
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Smoking leads to increased carboxyhemoglobin. What is carboxyhemoglobin? What effect does it have on the oxy-Hb dissociation curve?
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CarboxyHb is Hb bound to CO. It causes a LEFT-SHIFT of the dissociation curve.
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What is the CO-Hb level in a smoker?
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10 - 15%
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How does the pulse oximeter interpret CO-Hb?
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As oxyhemoglobin!
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What are three effects of smoking on the airway?
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1) Increased irritability 2) Increased mucous 3) Decreased ciliary function
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What are the problems associated with smoking cessation immediately before surgery?
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There is no evidence of negative effects of quitting smoking too close to surgery.
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What is STOP-BANG?
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S = Snore T = Tired O = Observed apnea P = Pressure (HTN) B = BMI > 35 A = Age > 50 N = Neck > 40 cm G = Gender male?
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How is the STOP-BANG questionnaire scored?
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3+ = high risk Less than 3 = low risk
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Which airway abnormality associated with smoking takes longest to recover, upon smoking cessation?
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Mucociliary clearance
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With regard to reduction of postoperative pulmonary complications, when is the optimal time to quit smoking?
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> 6-8 weeks prior to surgery.
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What is the other name for nitric oxide (NO)?
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EDRF (endothelial-derived relaxing factor)
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What is the incidence of postoperative pulmonary complications?
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Postoperative pulmonary complications develop in 5% to 10% of patients in nonthoracic surgery and in 22% of high-risk patients. Up to 1/4 of deaths occurring within a week of surgery are 2/2 pulm complications. (second most common morbidity after cardiovascular adverse events)
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What are the established risk factors for postoperative pulmonary complications?
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Current smoking >40 pack-year hx ASA 3+ Age >70 COPD Neck, thoracic, upper abdominal, aortic, or neurologic surgery Surgery >2 hours GA (esp GETA) Albumin < 3 g/dL 30
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What is conspicuously NOT on the list of risk factors for postoperative pulmonary complications?
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Asthma ABG results PFT results
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What is the use of preoperative ABG results?
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ABGs can be used to predict pulmonary function after lung resection.
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What is the use of preoperative PFT results?
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PFTs can be used to diagnose disease, monitor management, and to determine which patients for lung resection will have adequate pulmonary reserve following surgery.
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How does nitric oxide become inactivated in the circulation?
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It binds avidly to hemoglobin (TESTED POINT)!!
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What is the effect of exogenous nitric oxide?
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Selective pulmonary vasodilation
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What is the dose of inhaled nitric oxide?
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20 - 40 ppm
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PEEP does not reduce...
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pulmonary edema.
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PEEP increases...
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FRC.
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What effect does PEEP have on pulmonary compliance?
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PEEP increases pulmonary compliance.
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What effect does PEEP have on dead space?
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PEEP increases dead space by overdistention of alveoli.
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What is often the effect of PEEP on cardiac output in patients with normal lungs?
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PEEP may increase cardiac output.
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Why should arterial oxygen levels not be used, alone, to monitor the effects of PEEP?
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Because these do not provide an accurate window upon the PEEP-induced effects on cardiac output. If PEEP results in improved oxygenation but reduced CO, then oxygen delivery may not be improved.
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What are two mechanisms by which PEEP is useful in pulmonary edema?
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1) Increased FRC, 2) Decreased shunt. Again, PEEP does not reduce the volume of pulmonary edema.
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Can PEEP be used to prevent ARDS or reduce mediastinal blood loss?
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NO.
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What is the major cardiac effect of PEEP?
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Decreased venous return.
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How does PEEP lead to fluid retention?
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PEEP triggers ADH release and decreases ANP.
