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Correspondence  |   October 1995
Femororadial Pressure-delta and Thermoregulation
Author Notes
  • Professor, Department of Anesthesia, The Bowman Gray School of Medicine, Medical Center Boulevard, Winston-Salem, North Carolina 27157-1009.
Article Information
Correspondence
Correspondence   |   October 1995
Femororadial Pressure-delta and Thermoregulation
Anesthesiology 10 1995, Vol.83, 875-876.. doi:
Anesthesiology 10 1995, Vol.83, 875-876.. doi:
To the Editor:--Hynson et al. [1] attempted to elucidate the mechanism of the aortoradial pressure difference (A-R delta) sometimes seen at the conclusion of cardiopulmonary bypass (CPB). They measured femoral and radial arterial pressures and finger, skin, and forearm blood flows in six healthy 20-40-yr-old volunteers exposed first to cold temperature (21 degrees Celsius) until shivering; second, to warm air (42 degrees Celsius) until profuse sweating; third, to cold temperature; and fourth, to anesthesia with nitrous oxide-propofol. The authors concluded that thermoregulation and anesthesia produced the post-CPB A-R delta by increasing "upper-extremity blood flow."
Although thermoregulation may play an indirect role in the A-R delta during anesthesia, this study in young, healthy volunteers, does not provide the data needed to suggest that conclusion. The typical patient affected by post-CPB A-R delta is older than 52 yr with various degrees of vascular disease, has undergone coronary artery bypass grafting (CABG), [2-6] and CPB, and, in most instances, has been cooled temporarily to a core temperature of 28 degrees Celsius. In adolescents and young adults, the peripheral (brachial, radial, femoral) arterial pulse pressure is about 50% greater than that measured in the ascending aorta, whereas in elderly subjects, the two measurements are virtually identical. [7] Thus, the two patient populations bear little resemblance to each other.
The authors intended to measure forearm blood flow (FBF) but do not mention whether the circulation to the hand was excluded during the FBF measurement. I suspect that the authors never measured FBF properly. This is supported by their finding that propofol/nitrous oxide anesthesia increased FBF. Other investigators, well acquainted with plethysmography, find that both anesthetics decrease FBF, [8] but that nitrous oxide increases total hand blood flow (HBF). [9] Failure to exclude the hand circulation during the FBF measurement also would explain the large increase in FBF during sweating. Body heating produces a large increase in HBF and only a mild increase in FBF. [10] A second potential problem concerns the authors' technique for assessment of finger blood flow (fbf) with venous occlusion plethysmography. The authors state that the fbf was measured "as previously described." [11] In the study quoted, two requirements to accurately measure flows by venous occlusion plethysmography were ignored: the venous occluding cuff should be in close proximity to the plethysmograph (in the study referred to by Rubinstein and Sessler, [11] the plethysmograph covered the last phalanx, and the venous tourniquet was at the base of the finger, leaving a large venous bed to be filled before blood flow could be detected); and flow should be calculated during the first few seconds after the occlusion. [12,13] Burch [12] demonstrated, using both calculations and real flow measurements, how critical it is to include only the first three pulsations after the occlusion. However, Hynson et al. compared high and slow flows as described by Rubenstein and Sessler. [11] The latter authors traced high flows during the first 5 s after venous occlusion and slow flows after an interval of approximately 7 s after venous occlusion. In Figure 1, I have traced (dotted line) the slope of the high flow in a comparable time scale with the slow flow. It can be seen that any real difference was smaller than what they reported; however, neither tracing reflect real fbfs.
Figure 1. Trace of the volume-time deflection quantifying fbfs: (A) high. (B) slow. (A) The estimated fbf parallels three pulse deflections in the flow slope from the beginning of cuff inflation (arrow down). (B) There is no real flow slope. The flow slope in B would be comparable with one on the same time scale in A. (See text.) (Modified with permission. [11])
Figure 1. Trace of the volume-time deflection quantifying fbfs: (A) high. (B) slow. (A) The estimated fbf parallels three pulse deflections in the flow slope from the beginning of cuff inflation (arrow down). (B) There is no real flow slope. The flow slope in B would be comparable with one on the same time scale in A. (See text.) (Modified with permission. [11])
Figure 1. Trace of the volume-time deflection quantifying fbfs: (A) high. (B) slow. (A) The estimated fbf parallels three pulse deflections in the flow slope from the beginning of cuff inflation (arrow down). (B) There is no real flow slope. The flow slope in B would be comparable with one on the same time scale in A. (See text.) (Modified with permission. [11])
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In conclusion, this study does not provide any useful data by which the cause of the post-CPB A-R delta can be determined, because the wrong population was studied and the wrong measurements were performed.
Alfredo L. Pauca, M.D., Professor, Department of Anesthesia, The Bowman Gray School of Medicine, Medical Center Boulevard, Winston-Salem, North Carolina 27157-1009.
(Accepted for publication July 3, 1995.)
REFERENCES
Hynson JM, Sessler DI, Moayeri A, Katz JA: Thermoregulatory and anesthetic-induced alterations in the differences among femoral, radial, and oscillometric blood pressures. ANESTHESIOLOGY 81:1411-1421, 1994.
Pauca AL, Hudspeth AS, Wallenhaupt SL, Tucker WY, Kon ND, Mills SA, Cordell AR: Radial artery-to-aorta pressure difference after discontinuation of cardiopulmonary bypass. ANESTHESIOLOGY 70:935-941, 1989.
Bazaral MG, Welch M, Golding LAR, Badhwar K: Comparison of brachial and radial arterial pressure monitoring in patients undergoing coronary bypass surgery. ANESTHESIOLOGY 73:38-45, 1990.
Rich GF, Lubanski RE, McLoughlin TM: Differences between aortic and radial artery pressure associated with cardiopulmonary bypass. ANESTHESIOLOGY 77:63-66, 1992.
Mohr R, Lavee J, Goor DA: Inaccuracy of radial artery pressure measurement after cardiac operations. J Thorac Cardiovasc Surg 94:286-290, 1987.
Pauca AL, Wallenhaupt SL, Kon ND: Reliability of the radial arterial pressure during anesthesia: Is wrist compression a possible diagnostic test? Chest 105:69-75, 1994.
O'Rourke MF, Kelly RP, Avolio AP: The Arterial Pulse. Philadelphia, Lea & Febiger, 1992, pp 47-71.
McKeating K, Howe JP, McArdle L: The effects of propofol and thiopentone on forearm circulation. Anaesthesia 45:294-296, 1990.
Pauca AL, Hopkins AM: Acute effects of halothane, nitrous oxide and thiopentone on the upper limb blood flow. Br J Anaesth 43:326-333, 1971.
Shepherd JT: Physiology of the Circulation in Human Limbs in Health and Disease. Philadelphia, WB Saunders, 1963, pp 9-41.
Rubinstein EH, Sessler DI: Skin-surface temperature gradients correlate with fingertip blood flow in humans. ANESTHESIOLOGY 73:541-545, 1990.
Burch GE: Digital Plethysmography. New York, Grune and Stratton, 1954, pp 2-56.
Greenfield ADM, Whitney RJ, Mowbray JF: Methods for the investigation of peripheral blood flow. Br Med Bull 19:101-109, 1963.
Figure 1. Trace of the volume-time deflection quantifying fbfs: (A) high. (B) slow. (A) The estimated fbf parallels three pulse deflections in the flow slope from the beginning of cuff inflation (arrow down). (B) There is no real flow slope. The flow slope in B would be comparable with one on the same time scale in A. (See text.) (Modified with permission. [11])
Figure 1. Trace of the volume-time deflection quantifying fbfs: (A) high. (B) slow. (A) The estimated fbf parallels three pulse deflections in the flow slope from the beginning of cuff inflation (arrow down). (B) There is no real flow slope. The flow slope in B would be comparable with one on the same time scale in A. (See text.) (Modified with permission. [11])
Figure 1. Trace of the volume-time deflection quantifying fbfs: (A) high. (B) slow. (A) The estimated fbf parallels three pulse deflections in the flow slope from the beginning of cuff inflation (arrow down). (B) There is no real flow slope. The flow slope in B would be comparable with one on the same time scale in A. (See text.) (Modified with permission. [11])
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