The Effects of Obesity on the Cardiopulmonary System: Implications for Critical Care Nursing

Kim Garrett, RN, MS, CNP; Kathy Lauer, RN, PhD; Beth-Anne Christopher, RN, MS

Disclosures

Prog Cardiovasc Nurs. 2004;19(4) 

In This Article

Effects of Obesity on Measurements of Cardiac Performance

Cardiac output is defined as heart rate × stroke volume. The accepted normal parameter is 4−8 L/min. This calculation is based on an average-sized individual and does not take into account the additional tissue mass of an obese individual.[25] Therefore, while a cardiac output of 5 L/min might be sufficient to perfuse the organs of a 75-kg man, the same cardiac output would not be adequate for an individual who weighs 100−200 kg. A more accurate measurement for the obese individual would be the cardiac index, which is based on the standard measurement of cardiac output divided by the patient's body surface area in order to obtain a more accurate indication of cardiac performance individualized to the patient's body mass. The normal cardiac index is 2.5−4.2 L/min/m2.[25] All standard hemodynamic parameters may be indexed to the individual patient.

Blood pressure measurements may be difficult to obtain by the standard cuff method. To obtain an accurate reading, the cuff bladder should be ≥ 80% of the patient's arm circumference and the width of the cuff ≥ 40% of the arm circumference.[26] Even when the appropriate size cuff is obtained, accurate measurement may be difficult because the shape of the arm may prevent a good fit. Comparisons of cuff and intra-arterial readings have shown variations in both directions. If accuracy is important, an arterial line may be necessary.[17]

Heart rate may be increased in obese individuals because of increased demand on the heart to pump an increased blood volume, increased systemic vascular resistance related to hypertension, and general deconditioning related to decreased mobility. It is important to remember that at comparable workloads, obese individuals use more oxygen and energy and have higher heart rates and blood pressure responses than nonobese individuals. Heart rate is an effective indicator of activity tolerance in the obese patient.[17]

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