Chapter 8, cont… (Page 5)

Pulmonary circulation

SUMMARY

In contrast to the systemic circulation, the pulmonary circulation is a low pressure, high capacitance system. Pulmonary hypertension, a common physiologic problem, can be found in many different diseases, including virtually all chronic heart and lung conditions. Mechanisms of pulmonary hypertension include hypoxemia, loss of pulmonary vasculature, increased pulmonary capillary hydrostatic pressure, and pulmonary artery narrowing.

Bedside measurement of pulmonary artery pressures and resistances and measurement of right ventricular cardiac output can be obtained with the balloon­tipped, flow­directed (Swan­Ganz) right heart catheter. In selected patients, Swan­Ganz catheterization can provide useful information about hemodynamic status. The most frequently obtained Swan­Ganz measurement is pulmonary artery wedge pressure (PAWP). Under ideal conditions PAWP reflects the left atrial and the left ventricular filling pressures and the left ventricular preload (left ventricular volume); at such times PAWP is a valid guide to fluid therapy. In some situations, however, such as when positive endexpiratory pressure is being delivered or when left ventricular compliance is reduced, PAWP may not accurately reflect left ventricular preload and may give a false impression of the patient's fluid status. PAWP measurement must be interpreted cautiously and must always be evaluated in conjunction with the full clinical, radiologic, laboratory, and hemodynamic picture.

Apart from the improper interpretation of Swan-Ganz data, another potential pitfall involves leaving the catheter in place beyond its period of clinical usefulness. In addition, many complications can occur with Swan­Ganz catheterization, including venous thrombosis, pulmonary hemorrhage, and cardiac arrhythmias.

REVIEW QUESTIONS

State whether each of the following is true or false .

1. Normal pulmonary artery pressure is one half the systemic artery pressure.

2. Pulmonary artery pressure will increase in the presence of arterial hypoxemia and decrease in the presence of arterial acidosis.

3. Swan­Ganz catheterization allows for direct measurement of left ventricular pressures.

4. Hallmarks of septic shock are elevated cardiac output and reduced systemic vascular resistance.

5. If available, hemodynamic monitoring is indicated for all cases of severe dehydration.

6. The Swan­Ganz catheter can be used to obtain a sample of mixed venous blood from the pulmonary artery.

7. Cor pulmonale is right­sided heart failure caused by pulmonary hypertension.

8. The pulmonary artery wedge pressure is used to calculate pulmonary vascular resistance.

9. In primary pulmonary hypertension, the pulmonary artery diastolic pressure is higher than the pulmonary artery wedge pressure.

10. Pulmonary edema may occur without an elevation of pulmonary artery wedge pressure.

References

Enson, Y., Giuntini, C., Lewis, M.L., et al.: The influence of hydrogen ion concentration and hypoxia on the pulmonary circulation, J. Clin. Invest. 43:1146, 1964.

Forrester, I.S., Diamond, G., McHugh, T.J., et al.: Filling pressures in the right and left sides of the heart in acute myocardial infarction, N. Engl. 1. Med. 285:190, 1971.

Grossman, W.G., editor: Cardiac catheterization and angiography; Philadelphia, 1980, Lea & Febiger.

Matthay, R.A., and Berger, H.J.: Cardiovascular performance in chronic obstructive pulmonary diseases, Med. Clin. North Am. 65(3):489, 1981.

O'Quin, R., and Marini, I.1.: Pulmonary artery occlusion pressure: clinical physiology, measurement, and interpretation, Am. Rev. Respir. Dis. 128:319, 1983.

Swan, H.J.C., Ganz, W., Forrester, I.S., et al.: Catheterization of the heart in man with use of a flow­directed balloon-tipped catheter, N. Engl. 1. Med. 283:447, 1970.

Tooker, 1., Huseby, 1., and Butler, 1.: The effect of Swan­Ganz catheter height on the wedge pressure­left atrial pressure relationship in edema during positive­pressure ventilation, Am. Rev. Respir. Dis. 117:721, 1978.

West, I.B., Dollery, C.T., and Naimark, A.: Distribution of blood flow in isolated lung: relation to vascular and alveolar pressures, 1. Appl. Physiol. 19:713, 1964.

Suggested Readings

Connors, A.F., Castele, R.J., Farhat, N.Z., et al.: Complications of right heart catheterization: a prospective autopsy study, Chest 88:567, 1985.

Connors, A.F., McCaffree, D.R., and Gray, B.A.: Evaluation of right­heart catheterization in the critically ill patient acute myocardial infarction. N. Engl. 1. Med. 308:263, 1983.

Eaton, R.J., Taxman, R.M., and Avioli, L.V.: Cardiovascular evaluation of patients treated with PEEP, Arch. Intern. Med. 143:1958, 1983.

Elliott, C.G., Zimmerman, G.A., and Clemmer, T.P.: Complications of pulmonary artery catheterization in the care of critically ill patients: a prospective study, Chest 76:647, 1979.

Forrester, I.S., Diamond, G., Chatterjee, K., et al.: Medical therapy of acute myocardial infarction by application of hemodynamic subsets, N. Engl. 1. Med. 295:1356, 1976.

Jardin, E., Farcot, I.C., Boisante, 1., et al.: Influence of positive endexpiratory pressure on left ventricular performance, N. Engl. 1. Med. 304:387, 1981.

Raper, R., and Sibbald, W.J. : Misled by the wedge? The Swan-Ganz catheter and left ventricular preload, Chest 89:427, 1986.

Rowley, K.M., Clubb, K.S., Smith, G.J., et. al.: Right­sided infective endocarditis as a consequence of flow­directed pulmonary­artery catheterization, N. Engl. 1. Med. 311:1152, 1984.

Shaver, I.A.: Hemodynamic monitoring in the critically ill patient, N. Engl. 1. Med. 308:277, 1983.

Sprung, C.L., editor: The pulmonary artery catheter: methodology and clinical applications, Baltimore, 1983, University Park Press.

Swan, H.J.C.: The role of hemodynamic monitoring in the management of the critically ill, Crit. Care Med. 3:83,1975.

Timms, R.M., Khaja, F.U., and Williams, G.w. Hemodynamic response to oxygen therapy in chronic obstructive pulmonary disease, Ann. Intern. Med. 102:29, 1985.

Weil, M.H. and Rackow, E.C.: Critical care medicine: caveat emptor, Arch. Intern. Med. 143:1391, 1983.

Wiedemann, H.P., Matthay, M.A., and Matthay, R.A.: 1. Cardiovascular­pulmonary monitoring in the intensive care unit, Chest 85:537, 1984.

Wiedemann, H.P., Matthay, M.A., and Matthay, R.A.: 11. Cardiovascular­pulmonary monitoring in the intensive care unit, Chest 85:656, 1984.

See also General References in Appendix G.

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