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APPt..NDIX 111-8: MECHANICAL VENllLATION 827

which the panent attempts each wean (time of day, activities before and

after the wean, position during the wean) and parameters to be manipulated during the wean (frequency, intensity, duration). Patients should be placed in a position that facilitates the biomechanics of their ventilation.12 For many parients, rhis is seared and may also include the ability ro sir forward with the arms supported.

Biofeedback to increase VT and relaxation has been shown to

improve rhe effecriveness of weaning and reduce time on the ventilaror. n Inspirarory muscle resistive training has also been shown to increase respiratory muscle strength and endurance ro facilitate the

weaning success. 14

References

I. Manno P. The ICU Book (2nd ed). Philadelphia: Lea & Febiger, 1998.

2. Slutsky AS. Mechanical ventilation. American College of Chest Physicians' Consensus Conference Isee commentsJ. Chest 1993; 104: 1833.

3. Howman SF. Mechanical vemilation: a review and update for clinicians.

Hosplt.1 Physician 1999;December:26-36.

4. Sadowsky liS. Thoracic Surgical Procedures, Monitoring, and Support

Equipment. In EA Hillegass, HS Sadowsky (eds), Essentials of Cardiopulmonary PhYSIcal Therapy (2nd ed). Philadelphia: Saunders, 2001; 464-469.

5. Amuero A, Peters JI, Tob," MJ, et al. Effecrs of prolonged mechanical

ventilation on diaphragmatic function in healthy adult baboons. Crit

Care Med 1997;25:1187-1190.

6. Gerold KB. Physical therapists' guide to the principles of mechanical

ventilation. Cardlopul Phys Ther 1992;3:8.

7. Costello ML, Mathieu-Costello 0. West JB. Stress fracture of alveolar

epithelial cells studied by scanning electron microscopy. Am Rev Respir

DIS 1992;145:1446-1455.

8. Mathieu-Costello 0, West JB. Are pulmonary capillaries susceptible to

mechal1lcal stress? Chest 1994;105(Suppl):1025-107S.

9. Heimler R, Huffman RG, Starshak RJ. Chronic lung disease in premature infams: A retrospective evaluation of underlying factors. Crit Care Med 1988;16:1213-1217.

10. Yang KL, Tobin MJ. A prospective study of indexes predicting the outcome of trials of weaning from mechanical vencilation. N Engl J Med 1991 ;324: 1446-1495.

11. Dries DJ. \Veaning from mechanical ventilation. J Trauma 1997;

43:372-384.

12. Shekleron ME. Respiratory muscle condition and the work of breachinga critical balance in [he weaning patient. AACN Clin Issues Crit Care 1991;2:405-414.

828 AC� CARE HANDBOOK FOR PHYSICAL THERAPISTS

13. Holliday JE, Hyers TM. The reduction of wean time frol11 mechanical

ventilation using tidal volume and relaxation biofeedback. Am Rev

Respir Dis 1990;141:1214-1220.

14. Aldrich TK, Karpel JP, Uhrlass RM, et 301. Weaning from mechanical

ventilation: adjunctive use of inspiratory muscle resistive training. Crit

Care Med 1989;17:143-147.

III-C

Circulatory Assist Devices

Jaime C. Paz

The purpose of this appendix is to describe rhe following circulatory

assist devices: (1) intra-aortic balloon pump (IABP), (2) vemricular

assist device (VAD) , and (3 ) extracorporal membrane oxygenarion

(ECMO) . These devices are primarily used wirh a patient who has

severe cardiac pump dysfunction, with or without concurrent pulmonary pump dysfuncrion.

Intra-Aortic Balloon Pump

The main function of rhe IABP is to lessen rhe work (decreased myocardial oxygen demand) of rhe heart by decreasing afrerioad in the proximal aorta. The LABP also improves coronary artery perfusion

(increa ed myocardial oxygen supply) by increasing diasrolic pressure

in the aorta,l,2

The IABP consists of a carheter with a sausage-shaped balloon ar

the end of ir, all of which is connecred to an external pump-controlling device. The catheter is inserted percutaneously or surgically into the femoral artery and is threaded amegrade umil ir reaches the proximal descending thoracic aorta. Figure III-C.! illustrates the balloon 829

830 ACUTE CARE HANDBOOK FOR PHYSICAL TIIFRAPISTS

Balloon

inflated

Figure HI-C. I. Mechanisms of action of imra-aortic balloon pump. A. Diastolic balloon inflation augments coronary blood flolll. B. Systolic balloon deflation decreases afterload. (Reprinted tvith permission from LA Thelan

{edl. Critical Care Nursing: Diagnosis and Management (2nd edJ. St. Louis:

Mosby, 1994.)

inflating during ventricular filling (diastole) and deflating during ventricular contraction (systole). The deflation of the balloon juSt before aortic valve opening decreases afterload and therefore reduces resistance to the ejection of blood during systole. The blood in the aorta is then propelled forward into the systemic circulation. The inflation of

the balloon during diastole assists with the perfusion of the coronary

and cerebral vessels. This process is referred to as counterpulsation,

because the inflation and deflation of the balloon occur opposite to

the contraction and relaxation of the heart. 1.2