today's practice ot cardiopulmonary medicine Herbert P. Wiedemann, M.D., F.C.C.P., Michael A Matthay, M.D., F.C.C.P, Richard A Matthay, M.D., F.C.C.P.  CHEST  Volume 85, Issue 4, Pages 537-549 (April 1984) DOI: 10.1378/chest.85.4.537 Copyright © 1984 The American College of Chest Physicians Terms and Conditions

Figure 1 The methods of arterial cannulation. In the transfixation technique, the posterior wall of the artery is penetrated before the inner needle is withdrawn. Then, the outer plastic cannula is withdrawn slowly until blood flows freely from the end. The cannula can then be advanced farther up the arterial lumen. Direct insertion is also possible, but the tip must be positioned so that the cannula is entirely within the arterial lumen before advancing it over the needle. There is no difference in the incidence of local thrombosis or distal ischemia. (Reproduced from reference 33 with permission.) CHEST 1984 85, 537-549DOI: (10.1378/chest.85.4.537) Copyright © 1984 The American College of Chest Physicians Terms and Conditions

Figure 2 Photographs of the balloon of a 7 French Swan-Ganz catheter inflated with either 1.0 ml (A) or 1.5 ml (B) of air. Notice that the catheter tip protrudes beyond the inflated balloon if less than the full recommended volume is used. The exposed catheter tip may cause endocardial damage, induce ventricular arrhythmias, or damage the pulmonary artery. Also, using the recommended volume helps ensure a relatively proximal wedge position, which is important to lessen the risk of pulmonary infarction and to help maintain accuracy of thermodilution cardiac output and mixed venous Po2 determinations. (Reproduced from reference 28 with permission.) CHEST 1984 85, 537-549DOI: (10.1378/chest.85.4.537) Copyright © 1984 The American College of Chest Physicians Terms and Conditions

Figure 3 Representative recording of pressures as a Swan-Ganz catheter is inserted through the right side of the heart into the pulmonary artery. The first wave form is a right atrial tracing with characteristic a and v waves. The right ventricular, pulmonary artery, and pulmonary artery wedge tracings follow in sequence. The pressures and waveforms shown here are normal. Note that the wedge tracing shows a and v waves transmitted from the left atrium. In addition, the wedge pressure (mean) is less than pulmonary artery diastolic pressure. The wedge tracing is not always this distinct, but a very damped tracing or a mean wedge pressure greater than pulmonary artery diastolic pressure usually indicates some mechanical problem in the system (eg, air bubble in the connecting tubing, catheter tip “overwedged,” balloon inflated over distal orifice, catheter tip in zone 1 or zone 2, etc). In severe mitral regurgitation, the large transmitted left atrial v waves occasionally may cause the wedge tracing to resemble a pulmonary artery tracing. In such a case, careful analysis of the waveforms and attention to where the peak pressure occurs in relation to the ECG complex usually will avoid misinterpretation. (Reproduced from reference 20 with permission.) CHEST 1984 85, 537-549DOI: (10.1378/chest.85.4.537) Copyright © 1984 The American College of Chest Physicians Terms and Conditions

Figure 4 (A) Simplified representation of the pulmonary artery catheter in the “wedge” or pulmonary artery occlusion (PAO) position. With the balloon inflated, no flow exists. (B) By analogy to a “closed pipe” system, equal pressure readings are found for the wedge pressure, pulmonary venous (PV) pressure, and left atrial (LA) pressure. This simple model ignores the continuous flow of blood from nonoccluded pulmonary arteries to the PV and LA. These “flowing” columns are open to the “static” column at the level of the pulmonary venous (PV) system. Thus, mechanical obstruction to flow through the PV system (eg, tumor) will cause the wedge pressure to overestimate the LA pressure. (Reproduced from reference 29 with permission.) CHEST 1984 85, 537-549DOI: (10.1378/chest.85.4.537) Copyright © 1984 The American College of Chest Physicians Terms and Conditions

Figure 5 Relationship of pulmonary artery wedge pressure (PW) to left ventricular preload (left ventricular volume or “stretch”) in three situations. This figure illustrates the importance of considering pleural (juxtacardiac) pressure and ventricular compliance, along with PW, when making assumptions about left ventricular preload. The PW is elevated in each example and reflects the intracavitary left ventricular end-diastolic pressure. (A) The pleural pressure is increased, as might occur with PEEP therapy. Transmural left ventricular pressure is approximately normal, as is the preload. (B) The pleural pressure is normal. Transmural left ventricular pressure is elevated and preload is increased. (C) The ventricle is stiff, as might occur with myocardial ischemia. Although PW and pleural pressure are identical to example B, the preload in this instance is normal. (Reproduced from reference 33 with permission.) CHEST 1984 85, 537-549DOI: (10.1378/chest.85.4.537) Copyright © 1984 The American College of Chest Physicians Terms and Conditions

Figure 6 The zones of the lung, based on the relationship among pulmonary artery (Pa) pressure, alveolar pressure (PA), and pulmonary venous pressure (Pv). The zones are not constant. For instance, a decrease in Pv (eg, diuresis) or an increase in PA (eg, PEEP therapy) will convert some zone 3 area into zone 2 or zone 1. The pulmonary wedge pressure reflects Pv (and thus left atrial pressure) only if the tip of the Swan-Ganz catheter lies in zone 3 before balloon inflation. If the balloon is inflated in zone 2, the occluded vessel will then collapse since PA>PV, Without a continuous column of blood between the catheter tip and the left atrium, the wedge pressure cannot reflect left atrial pressure. (Reproduced from reference 45 with permission.) CHEST 1984 85, 537-549DOI: (10.1378/chest.85.4.537) Copyright © 1984 The American College of Chest Physicians Terms and Conditions

Figure 7 Relation of forces governing the fluid flux between the pulmonary capillary microvasculature (mv) and the pulmonary interstitium (is). P refers to hydrostatic pressures, and π refers to oncotic pressures. Kf is the permeability constant of the vessel wall and π is the reflection coefficient. The latter indicates the relative effectiveness of the membrane in preventing the passage of proteins compared to water. In “leaky capillary” edema, the σ value is low and thus hydrostatic forces become much more important than oncotic forces in determining net fluid flux. The pulmonary artery wedge pressure provides an indirect assessment (for important qualifications see text) of both Pmv and left ventricular end-diastolic pressure (LVEDP). (Reproduced from reference 7 with permission.) CHEST 1984 85, 537-549DOI: (10.1378/chest.85.4.537) Copyright © 1984 The American College of Chest Physicians Terms and Conditions

Figure 8 The pulmonary artery wedge pressure is not equivalent to capillary hydrostatic pressure. This figure shows the pressure drop across the pulmonary vessels in experimental studies on dog lungs during infusion of serotonin or histamine, or control conditions. A constant total pressure drop was maintained. Notice that the pulmonary artery wedge pressure would be the same under all conditions, since it measures left atrial pressure (thick arrow). However, the pulmonary capillary hydrostatic pressure (solid circles) at the capillary midpoint (thin arrow) is different in each case. Thus, the relationship between pulmonary artery wedge pressure and pulmonary capillary pressure is influenced by the longitudinal distribution of resistance in the pulmonary circulation. (Reproduced from reference 56 with permission.) CHEST 1984 85, 537-549DOI: (10.1378/chest.85.4.537) Copyright © 1984 The American College of Chest Physicians Terms and Conditions

Figure 9 Estimation of the true capillary hydrostatic filtration pressure from the pulmonary occlusion pressure decay curve. Upper panel represents the pulmonary vasculature according to a simplified electric analog model. PA, PC, and Pv are the pulmonary artery pressure, capillary pressure, and venous pressure, respectively. Resistance to flow exists on the upstream or arterial side (RA) and on the downstream or venous side (Rv). Most vascular capacitance is located in the microvessels (Cv). Occlusion of either the pulmonary artery or the pulmonary veins is equivalent to opening the switches SWA or SWv, respectively. Lower right panel demonstrates that when the pulmonary artery is occluded, PA rapidly equilibrates to Pc. Subsequent pressure change (due to drop across Pv) would occur more slowly since the microvascular capacitor (Cv) “discharges” (accumulates blood). Thus, the Pc will be represented on the decay curve by the point of inflection from rapid to slow pressure change. Lower left panel demonstrates that similar information is obtained by pulmonary venous occlusion. However, unlike pulmonary artery occlusion, pulmonary venous occlusion is not routinely performed in the ICU. (Reproduced from reference 55 with permission.) CHEST 1984 85, 537-549DOI: (10.1378/chest.85.4.537) Copyright © 1984 The American College of Chest Physicians Terms and Conditions

Figure 10 Effect of respiratory pressure variation on displayed wedge pressure. Digital readouts of “systolic,” “mean” or “diastolic” pressures actually represent the highest, average, and lowest pressures recorded during a 3-4-second scanning interval. Thus, during mechanical positive pressure breathing, the digital readout of “diastolic” pressure actually provides a more accurate indication of the wedge pressure at end-expiration than the “mean” pressure. Nevertheless, usually it is preferable to obtain pressure tracings on calibrated paper and visually identify end-expiration (see Fig 11). (Reproduced from reference 55 with permission.) CHEST 1984 85, 537-549DOI: (10.1378/chest.85.4.537) Copyright © 1984 The American College of Chest Physicians Terms and Conditions

Figure 11 Example of how rapid, labored respirations can result in marked fluctuations of the pulmonary artery pressure tracing. The patient's respiratory rate was 40 and the peak pulmonary artery pressure varied from 35-40 to 18 mm Hg. Since the pressures are recorded on calibrated strip chart paper, the pressures corresponding to the brief period of end-expiration can be identified. An electric digital readout would be very misleading, since the value would represent a 3-4second scanning period (see Fig 10). (Reproduced from reference 20 with permission.) CHEST 1984 85, 537-549DOI: (10.1378/chest.85.4.537) Copyright © 1984 The American College of Chest Physicians Terms and Conditions

Figure 12 Illustrated are the effects of respiratory phase on thermodilution right-sided cardiac output determinations. Panel A shows a series of 50 random measurements. Panel B shows the same 50 injections plotted according to respiratory cycle phase. Panel C shows mean determinations plotted against respiratory cycle phase at different levels of PEEP (0, 5, 10, and 15 cm H2O). Notice that increasing PEEP causes a mild “phase-shift” in the effect of respiration upon thermodilution right-sided cardiac output. For instance, at 40 percent of the cycle (near end-inspiration), the cardiac output measurement might be “depressed” (0 PEEP) or “elevated” (15 cm H2O PEEP). At end-expiration (100 percent of cycle), the cardiac outputs are near “normal,” except at high PEEP (⩾ 15 cm H2O). Thus, timing of thermodilution output determinations to a particular phase of respiration may not ensure absolute “comparability” of measurements obtained under different ventilatory conditions. (Reproduced from reference 80 with permission.) CHEST 1984 85, 537-549DOI: (10.1378/chest.85.4.537) Copyright © 1984 The American College of Chest Physicians Terms and Conditions