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March 2000
Two-Lung and One-Lung Ventilation in Patients with Chronic Obstructive Pulmonary Disease: The Effects of Position and F(IO)2
Bardoczky GI, Szegedi LL, d'Hollander AA, et al.
Anesth Analg 2000 Jan;90(1):35-41.
Commentary by Katherine Grichnik, M.D.
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[ see abstract below ]
This is a very interesting article, which addresses a finding that is not well known. The respiratory effects of one lung ventilation (OLV) have been well studied. However, most measurements have been made in the lateral position because surgery that has required OLV has traditionally been done in this position. The authors correctly point out that many approaches to cardiac and thoracic procedures now utilize OLV in the supine position. Examples of procedures which may be done supine with OLV include lung volume reduction surgery, minimally invasive coronary artery bypass surgery, off-pump coronary artery bypass surgery, and some approaches to double lung transplantation. Few other studies have been done to measure the effects of one lung ventilation in the supine position.
The authors examined 24 patients randomly assigned to 3 groups (F(IO)2=0.4, F(IO)2=.6 and F(IO)2=1.0) in both supine and lateral positions. The mode of ventilation was kept constant and the study was done with the chest closed before the start of surgery. Respiratory parameters and arterial blood gases were measured during two-lung ventilation (TLV) and OLV in both the supine and lateral positions. Measurements included peak and plateau airway pressures, intrinsic positive end-expiratory pressure, PaCO2, PaO2, and P(A-a)O2. The authors found that during TLV, position did not influence the respiratory parameters significantly. However, during OLV, PaO2 was always higher in the lateral position as compared to the supine position at all F(IO)2 levels. Similarly P(A-a)O2 was lower in the lateral position as compared to the supine position.
The authors postulate that the gravitational effects of perfusion can partially explain this result. In the lateral position, gravity leads to redistribution of blood flow from the nondependent to the dependent lung. Thus, when the nondependent lung is deflated, some of the obligatory shunt has already been resolved by the diversion of the blood flow to the dependent lung. This is not the situation in the supine position, where gravity leads to greater blood flow in the more posterior portions of BOTH lungs. Thus when one lung is deflated, a greater shunt occurs simply on the basis of position. Further, HPV augments the blood flow reduction in the atelectatic lung. This mechanism is additive to the reduction of blood flow due to gravity in the lateral position but is less effective in the supine position when both lungs are equally affected by gravitational forces.
This is an important paper because it documents a difference in respiratory function between the supine and lateral positions during one lung anesthesia. It was not intuitive to this author that hypoxia would be worse during OLV in the supine position. It is important to both recognize and explain this phenomenon. In this way we can be prepared to recognize, prevent and treat hypoxia during supine procedures requiring OLV.
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ABSTRACT
Two-lung and one-lung ventilation in patients with chronic obstructive pulmonary disease: the effects of position and F(IO)2
Bardoczky GI, Szegedi LL, d'Hollander AA, Moures JM, de Francquen P, Yernault JC
SOURCE:
Anesth Analg 2000 Jan;90(1):35-41
ABSTRACT:
We compared the effects of position and fraction of inspired oxygen (F(IO)2) on oxygenation during thoracic surgery in 24 consenting patients randomly assigned to receive an F(IO)2 of 0.4 (eight patients, Group 0.4), 0.6 (eight patients, Group 0.6), or 1.0 (eight patients, Group 1.0) during the periods of two-lung (TLV) and one-lung ventilation (OLV) in the supine and lateral positions. TLV and OLV were maintained while the patients were first in the supine and then in the lateral position for 15 min each. Thereafter, respiratory mechanical data were obtained, and arterial blood gas samples were drawn. PaO2 decreased during OLV compared with TLV in both the supine and lateral positions. In all three groups, PaO2 was significantly higher during OLV in the lateral than in the supine position: 101 (72-201) vs 63 (57-144) mm Hg in Group 0.4; 268 (162-311) vs 155 (114-235) mm Hg in Group 0.6; and 486 (288-563) vs 301 (216-422) mm Hg in Group 1.0, respectively (P < 0.02, Wilcoxon's signed rank test). We conclude that, compared with the supine position, gravity augments the redistribution of perfusion as a result of hypoxic pulmonary vasoconstriction, when patients in the lateral position, which explains the higher PaO2 during OLV.
IMPLICATIONS:
This study compares oxygenation during thoracic surgery during periods of two-lung and one-lung ventilation with patients in the supine and lateral positions when using three different fractions of inspired oxygen values. Arterial oxygen tension
was decreased in all three groups during one-lung ventilation in comparison with the two-lung ventilation values, but the decrease was significantly less in the lateral, compared with the supine position.
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