Computerized tomography of the chest and gas exchange measurements during ketamine anaesthesia

Abstract

The effects of atelectasis on pulmonary gas exchange were studied in eight supine, clinically lung-healthy patients. Atelectasis was studied by computerized tomography (CT), and gas exchange by blood gas analysis. The distribution of ventilation/perfusion ratios was assessed by a multiple inert gas elimination technique. No patient had any signs of atelectasis in the awake state, and gas exchange was normal. During ketamine anaesthesia and spontaneous breathing, lung ventilation and perfusion were well matched in most subjects. In one patient there was perfusion of poorly ventilated regions amounting to 14% of cardiac output, and in another there was a shunt of 4% of cardiac output; this patient was the only one who developed atelectasis in dependent lung regions. After muscular relaxation and commencement of mechanical ventilation, all patients but one developed both shunt (2-6% of cardiac output) and atelectasis. The shunt correlated to the size of atelectasis. It is concluded that the occurrence of shunt during anaesthesia is related to the development of atelectasis in dependent lung region, which is consistent with the hypothesis that it is changes in chest-wall mechanics that cause atelectasis.

Body position does not influence the location of ventilator-induced lung injury

“…Computed tomography provides good evidence of atelectasis in anesthetized patients. It is concentrated in the most dependent parts of both lungs and appears in almost 90 % of patients who are anesthetized [12]. Collapse mostly occurs near the diaphragm in the supine position and lessens towards the apex.…”

Perioperative functional residual capacity

“…76 The FRC is not changed during ketamine anaesthesia 24 with spontaneous breathing but is reduced during ketarnine anaesthesia with controlled ventilation following pancuronium neuromuscular blockade. 75 In this instance, shunt is related to the extent of the atelectasis (Table I1). It is probable that pancuronium abolishes inspiratory tone, leading to FRC reduction and atelectasis.…”

The Comparison of Propofol and Ketofol Side Effects During Sedation with Spinal Anesthesia

“…In the present study, although statistically unimportant, Group KP had slightly better blood oxygen saturation (SpO 2 ) levels. Several studies on ketamine administration report that ketamine decreases pulmonary pressures, preserves functional residual capacity and tidal volume, and increases oxygenation 20,21 . We did not observe any respiratory complications in either group.…”