Air Test In Diagnosis Of Postoperative Lung Atelectasis

Overview

Postoperative pulmonary complication represent asignificant source of morbidity and have greater incidence and costs than cardiac complications alone .Atelectasis is the commonest one. Aelectasis may develop in nearly up to 90% of patients after general anaesthesia ,persist up to several days .Oxygen therapy is usually given in the postoperative period to alleviate hypoxemia. However it's usually discontinued before discharge to the ward based on clinical criteria such as patients being awake with normal vital signs and no respiratory distress. Available literatures suggest that it's not valid . Pulse oximetry provide accurate objective measurement of oxygenation,continuous and non invasive.Recently, Fernando etal 2017,used pulse oximetry after 5 minutes of oxygenation to detect postoperative atelectasis, the cut point was 96%.

Although it has been postulated that early hypoxemia lasts approximately two hours after a surgical procedure, the first 20 minutes of the postoperative period seem to be most critical . It is evident that the majority of transport times would fall well within this 20 minute window , thus the potential for postoperative hypoxemia during the transport period does exist. Canet, et al. (1989) found significant differences in oxygen saturation when administering 35% oxygen to adults in the PACU after a 30 second transport while breathing room air.The alveolar shunt induced by atelectasis is the main cause of oxygenation impairment during postoperative period. Witting MD, Lueck CH reported the ability of pulse oximetry at room air to detect hypoxemia based on 513 blood gas analysis. Coincidentially a room air oxygen saturation value \<96% was selected a cut point of hypoxemia ( Po2 \<70 mmhg )and moderate hypercapnia ( Pco2 \>50 mmhg ) . Jones and Jones descriped a digram showing relationship between SPO2 and FiO2 and proved that SPO2 \< 96% correspond to shunt effect of more than 10% and defines alveolar collapse . clark et al 2001determined time required for partial pressure of arterial oxygen to reach equilibrium during mechanical ventilation after a step change in fractional inspired oxygen, they reported that 5-10 minutes will be adequate . Ferrando C 2017 reported The accuracy of postoperative, non-invasive Air-Test to diagnose atelectasis in healthy patients after surgery They found that the air test diagnosed postoperative atelectasis with sensitivity of 82% and specificity of 87% and area uder the curve of 0.9 The presence of atelectasis was confirmed by CT scan in all patients with positive air test and in 5 patients with negative air test .The Air-Test may represent an accurate, simple, inexpensive and non-invasive method for diagnosing postoperative atelectasis.Sonography is a simple, noninvasive, and radiation-free methodology which has gained increasing usage in daily practice for detection of atelectasis. Sonography is a radiation-free methodology which plays an important role in diagnosing pulmonary diseases including obstructive and compressive atelectasis of different origins Furthermore, lung ultrasound has shown reliable sensitivity and specificity for the diagnosis of anaesthesia-induced atelectasis . Telectasis after general anaesthesia is basal and segmental. For this,we designed this trial as a pilot to detect the accuracy (sensitivity and specificity) of Air-Test to detect atelectasis in a homogenous group (elderly patients undergoing orthopedic surgery) using Roc testing.