Anne Warner, MD, Harsh Desai, MD, and Frederick Giberson, MD Department of Surgery, Christiana Care Health Care System, Newark, DE, USA The use of positive end‐expiratory pressure (PEEP) as part of the ARDS ventilatory strategy has been shown to improve the functional residual capacity (FRC) above the closing pressure of alveoli, thereby preventing alveolar collapse. PEEP maximizes alveolar recruitment at end expiration, not inspiration. The addition of PEEP increases inflation pressure, thereby increasing peak alveolar pressure and ultimately mean airway pressure. Increased PEEP increases pulmonary vascular resistance impeding right vascular stroke volume and thereby left ventricular filling. It also decreases the transmural pressure – the pressure needed to be overcome in order to eject stroke volume – thereby decreasing left ventricular afterload. Answer: D Briel M, Meade M, Mercat A, et al. Higher vs lower positive end‐expiratory pressure in patients with acute lung injury and acute respiratory distress syndrome. JAMA. 2010; 303 (9): 865–873. Schmitt JM, Viellard‐Baron A, Augarde R, et al. Positive end‐expiratory pressure titration in acute respiratory distress syndrome patients: impact on right ventricular outflow impedance evaluated by pulmonary artery Doppler flow velocity measurements. Crit Care Med. 2001; 29: 1154–1158. The inflammatory cascade in ARDS is thought to be initiated by activation of circulating neutrophils by the release of IL‐1 and TNF by macrophages and monocytes. Endothelial dysregulation attracts and retains neutrophils with subsequent sequestration within the pulmonary microcirculation. This occurs through adhesion of neutrophils to endothelial cells and neutrophil stiffening. Neutrophils then move into lung parenchyma and degranulate propagating injury to the type I and II epithelial cells within the alveoli allowing for exudation of protein‐rich fluid, erythrocytes, and platelets into the distal airspaces. Answer: C Abraham E. Neutrophils and acute lung injury. Crit Care Med. 2003; 31(supp): S195–S199. The multiple uses of methylene blue have been established including use in methemoglobinemia treatment as well as potential use in vasoplegic syndrome. In the operating room, methylene blue is often used to evaluate renal function and for potential leak in urologic procedures. However, one of the adverse effects of methylene blue is to decrease pulse oximetry readings. Pulse oximeters are made up of a side containing two light emitting diodes that emit at 660nm and 940nm detecting deoxygenated and oxygenated hemoglobin, respectively. The light is captured after passing through the arteries in the finger by a probe on the other side of the oximeter. This is then passed through and alternating current amplifier to block nonpulsatile wave forms from veins. The ratio of oxygenated to total hemoglobin is used to calculate SpO2. When administered, methylene blue transiently decreases the detected oxygenated hemoglobin as the methemoglobin fraction, usually a small percentage of total circulating hemoglobin, increases until processed out through the renal system. Therefore, for this patient, aborting the procedure is not necessary. The desaturation is transient and not caused by mucus plugging, which may require bronchoscopy, pneumothorax, which would require tube thoracostomy, or significant atelectasis, which may require bag mask ventilation. Answer: E Clifton J and Leikin JB . Methylene blue. Am J Ther. 2003; 10(4): 289–291. Rong LQ, Mauer E, Mustapich TL, et al. Characterization of the rapid drop in pulse oximetry reading after intraoperative administration of methylene blue in open thoracoabdominal aortic repairs. Anesth Analg. 2019; 129(5): 142–145. Pulmonary function testing is often used in preoperative evaluation, particularly prior to thoracic procedures. These can be used, in addition to history and exam, to identify obstructive versus restrictive lung processes. Three of the important measures are the forced vital capacity (FVC) – the total volume forcefully expired after maximal inspiratory effort; forced expiratory volume in 1 second (FEV1) – the volume of air forcefully expired after maximal inspiratory effort in 1 second; the FEV1/FVC ratio. In evaluating spirometry results, first step is to interpret the FEV1/FVC ratio. If less than the lower limit of normal, an obstructive pattern is suspected. If greater than lower limit of normal, the FVC is evaluated and if less than lower limit of normal, a restrictive process is considered. Obstructive diseases include COPD, asthma, and emphysema while restrictive lung diseases include neuromuscular disorders and interstitial lung diseases. Answer: A Barreiro TJ and Perillo I . An approach to interpreting spirometry. Am Fam Physician. 2004; 69(5): 1107–1115. Pellegrino R, Viegi G, Brurasco V, et al. Interpretative strategies for lung function tests. Eur Respir J. 2005; 26:948–968. The relationship between alveolar pressure, pulmonary arterial pressure, and pulmonary venous pressure represents the West zones of the lung. Zone 1, not seen in normal physiology, signifies alveolar dead space secondary to increased alveolar pressure causing arterial collapse (PA > Pa > Pv). Zone 2 represents pulsatile perfusion (Pa > PA > Pv) typically the upper portions of lung in a typical, upright person. Zone 3 represents the bulk of healthy lung tissue with continuous blood flow without extrinsic compression (Pa > Pv > PA). In a hypovolemic individual, as in this patient, decreased circulating volume converts Zone 3 tissue to Zone 1 and 2, increasing dead space. Answer: C West JB and Dollery CT . Distribution of blood flow and the pressure‐flow relations of the whole lung. J Appl Physiol. 1965; 20(2): 175–183. For questions 7–10, use the following figure to match the clinical scenario to the appropriate flow volume loop:
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Respiratory and Cardiovascular Physiology
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