Ventilation-Perfusion Relationships During Anaesthesia and Abdominal Surgery

Abstract

Nine patienth, 61-72 yearb old, wcrc stitdied awake anti during halothane anaesthesia Iiclorc and during upper ahdoniinal 5iiIge1 ) . (:cn~ral cii.rulalion Was rvaluated by nieaw (11' pulmonary artery i~athrteci/.a~ioci and ga5 cxc.haiige 1 , ) micltiiile i i c e r~ gas c:limina~ion ~cchnic~uc'. <\Make a i d sicpine, a rathcr wide dis!14~111iori o f \ '~/ Q was observed, with regions of low VA/Qin five patients and a small shunt (I-3%) in three patients. The overall dispersion of blood flow was log s.d. 0.93. With anaesthesia and mechanical ventilation, cardiac output fell by 30%, whereas pulmonary vascular pressures remained unaltered. The dispersion of pulmonary blood Ilow against V~l Q r a t i o s was further increased with a log s.d. of 1.67. Perfusion of regions with a low VA/Qwas significantly increased. With surgery, no significant changes were seen in cardiac output or vascular pressures. True shunt appeared or increased in seven patients, ranging from 1.3 to 17%. Perfusion to regions with low irA/Qdid not change. It is concluded that abdominal surgery interferes with gas exchange, presumably because of a cranial shift of the diaphragm which lowers FRC and thereby promotes airway closure. 39: 573-583. 33. Sybrecht G W, Garret I., Anthonisen N R. Eft'ect of chest strapping on regional lung function. J Appl Physiol39: 707-713. 34. Scheidt M, Hyatt R E, Rehder K. Effects ofrib cage or abdominal restrictiononlungmechanics.JA~plPhy.iiolI981:51: 1115-1121. 35. Klineberg P I,, Rehder K, Hyatt R E. Pulmonary mechanics and gas exchange in seated normal man with chest restriction. 3 Appl Plpiol

The influence of position on ventilation‐perfusion distribution after abdominal surgery

“…Patients at risk to develop postoperative hypoxaemia have been demonstrated to be those with preoperative negative values ofFRC-CC ratio (31). By contrast, no preoperative spirometric tests were shown to predict the extent of V,& mismatching in the study of Lundh & Hedenstierna, although elderly patients with pre-existing ventilation perfusion abnormalities were more at risk to develop postoperative impairment in gas exchange (32,33). In this study pre-and postoperative values of P ( A -~) o ?…”

Optimizing peroperative compliance with PEEP during upper abdominal surgery: effects on perioperative oxygenation and complications in patients without preoperative cardiopulmonary dysfunction

“…The incidence of late postoperative hypoxaemia and complications after upper abdominal non‐laparascopic surgery is between 30%–50% among preoperatively cardiopulmonary healthy patients [1,2]. The development of atelectasis and unequal distribution of perfusion and ventilation during anaesthesia and surgery, and perhaps reappearance of these disturbances after surgery, is one of the main hypotheses to explain postoperative hypoxaemia in cardiopulmonary healthy patients [3–5]. Although recruitment manoeuvres followed by constant positive end‐expiratory pressure (PEEP) have been shown to improve oxygenation during anaesthesia and surgery, as well as in the immediate postoperative period, [6] studies on constant peroperative PEEP have so far been inconclusive with regard to influence on postoperative hypoxaemia [7,8].…”

Persisting concentrating and second gas effects on oxygenation during N2O anaesthesia

“…This prolonged effect is only predicted to be significant in the presence of moderately severe degrees of ventilation‐perfusion (V/Q) inhomogeneity, and is due to ongoing N 2 O uptake in low V/Q lung units [6]. These levels of V/Q inhomogeneity are typical of anaesthetised patients, even those with healthy lungs [7–11]. However, N 2 O accelerates absorption atelectasis in regions of low V/Q [12, 13] and may worsen shunting intra‐operatively.…”