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Canadian Journal of Anesthesia 50:863-864 (2003)
© Canadian Anesthesiologists' Society, 2003

Correspondence

The effect of right and left lateral position on PA-aO2 and PA-ETCO2 in thoracic surgery

Michael Vassiliadis, MD and Nikolaos Barbetakis, MD

Thessaloniki, Greece

To the Editor:

A preliminary small-sampled study was conducted to investigate the effect of right and left lateral position on PA-aO2 and PA-ETCO2. After approval from the hospital Ethics Committee, we examined 23 ASA I–III patients undergoing elective exploratory thoracotomy for lung cancer. Exclusion criteria were dyspnea or angina with minimal activity (New York Heart Association classification >= III), clinically important radiological findings in the dependent lung and values of forced expiratory volume in the first second and forced vital capacity below 60% of predicted values. Induction and maintenance of anesthesia were achieved with propofol, remifentanil and 66% N2O in O2 during two-lung ventilation (TLV) and 100% O2 during one-lung ventilation (OLV). Size 39–41 Fr double-lumen tubes were used, according to body weight. Tidal volume was set at 10 mL•kg-1 and respiratory frequency at 8 beats•min-1. After opening of the pleura, arterial blood samples were drawn first during TLV and then during OLV. End-tidal CO2 values were recorded at those moments. PAO2 was calculated according to the equation: PAO2 = FIO2*(Patm-PH2O)- PaCO2/0.8. During OLV, PA-aO2 did not differ significantly in the left or in the right lateral position, but during TLV it was increased in the right lateral compared to the left lateral position (TableGo). In the left lateral position, Pa-ETCO2 was lower than in the right lateral position. These findings were similar during OLV and TLV.1


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  		TABLE A-aO2 and Pa-ETCO2 during OLV and TLV
 
In conclusion, it seems that, during OLV, PA-aO2, which reflects intraoperative shunt, remains unaffected by lateral positioning, contradicting earlier studies,2 while during TLV it is increased in the right lateral position. Pa-ETCO2 is increased in the right lateral position during both types of ventilation. Therefore in the left lateral position, PaCO2 is estimated more accurately from PETCO2 than in the right lateral position.

References

1 Ip Yam PC, Innes PA, Jackson M, Snowdon SL, Russel GN. Variations in the arterial to end-tidal PCO2 difference during one-lung thoracic anaesthesia. Br J Anesth 1994; 72: 21–4.[Abstract/Free Full Text]

2 Slinger P, Suissa S, Triolet W. Predicting arterial oxygenation during one-lung anaesthesia. Can J Anaesth 1992; 39: 1030–5.[Abstract/Free Full Text]


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CJA 2003 50: 864. [Full Text]  




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