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Ventilation‐perfusion relationships and atelectasis formation in the supine and lateral positions during conventional mechanical and differential ventilation
Author(s) -
Klingstedt C.,
Hedenstierna G.,
Baehrendtz S.,
Lundqvist H.,
Strandberg Å.,
Tokics L.,
Brismar B.
Publication year - 1990
Publication title -
acta anaesthesiologica scandinavica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.738
H-Index - 107
eISSN - 1399-6576
pISSN - 0001-5172
DOI - 10.1111/j.1399-6576.1990.tb03117.x
Subject(s) - supine position , medicine , atelectasis , anesthesia , positive end expiratory pressure , ventilation (architecture) , ventilation perfusion mismatch , dead space , mechanical ventilation , perfusion , shunt (medical) , blood flow , lung , cardiology , lung volumes , physics , thermodynamics
Patients without respiratory symptoms were studied awake and during general anesthesia with mechanical ventilation prior to elective surgery. Ventilation‐perfusion (a) relationships, gas exchange and atelectasis formation were studied during five different conditions: 1) supine, awake; 2) supine during anesthesia with conventional mechanical ventilation (CV); 3) in the left lateral position during CV; 4) as 3) but with 10 cm of positive end‐expiratory pressure (PEEP) and 5) as 3) but using differential ventilation with selective PEEP (DV + SPEEP) to the dependent lung. Atelectatic areas and increases of shunt blood flow and blood flow to regions with low a , ratios appeared after induction of anesthesia and CV. With the patients in the lateral position, further a mismatch with a fall in Pao 2 an icreased dead space ventilation was observed. Atelectatic lung areas were still present, although the total atelectatic area was slightly decreased. Some of the effects caused by the lateral position could be counteracted by adding PEEP. Perfusion of regions with low a ratios and venous admixture were then diminished, while Pao 2 was slightly increased; shunt blood flow and dead space ventilation were essentially unchanged. During CV + PEEP, there was a decrease in cardiac output, compared to CV in the lateral position. DV + SPEEP was more effective than CV + PEEP in decreasing shunt flow and increasing Pao 2 in the lateral position; in addition to this, cardiac output was not affected.