Correlation of gas exchange impairment to development of atelectasis during anaesthesia and muscle paralysis

Abstract

Pulmonary gas exchange and the development of atelectasis were studied in eight essentially lung-healthy patients, awake and during halothane anaesthesia with mechanical ventilation. Gas exchange was evaluated by a multiple inert-gas elimination technique and conventional blood-gas analysis, and atelectasis was studied by computerized tomography (CT). Ventilation and lung perfusion were well matched in the majority of the patients when awake. In two patients there was low perfusion of poorly ventilated regions (low VA/Q). One patient had a shunt corresponding to 4% of cardiac output. None of the patients showed signs of atelectasis on the CT scans. After 15 min of anaesthesia, shunt had appeared in all patients, ranging from 1% in two patients (unchanged from the awake state) to 17%. The major VA/Q mode was widened and ventilation of poorly perfused regions (high VA/Q) was noted in seven patients. Densities in dependent lung regions (interpreted as atelectasis) were seen on the CT scans in six patients. The extent of atelectasis was significantly correlated both to the magnitude of shunt (r = 0.93, P less than 0.01) and to the impairment of arterial oxygenation (r = 0.99, P less than 0.001). The findings indicate that atelectasis in dependent lung regions during halothane anaesthesia creates shunting of blood flow and that atelectasis is the major or sole cause of impaired gas exchange in the lung-healthy, anaesthetized subject.

Perioperative functional residual capacity

“…Although relatively small, the extent has significant correlations with the magnitude of intraoperative shunt (Qs/0T) and the impairment of P(A-a)O2 . 73 The application of PEEP does decrease the extent of the atelectasis, but oxygenation is not improved. 69 '74 Atelectatic areas do not appear under two conditions: during ketamine anaesthesia with spontaneous breathing 75 and in patients with severe COPD.…”

Prolonged Thoracic Epidural Anesthesia in the Correction of Hypoxia in the Postoperative Period

“…По всей видимости, основной причиной гипоксемии являлось нарушение вентиляционно перфузионных соотношений в легких вследствие микроателектазиро вания. По данным литературы [2], развитие микроате лектазов, которые не выявляются с помощью рутин ных методов рентгенологического исследования, является ведущей причиной гипоксемии в послеопера ционном периоде. Формирование ателектазов сопро вождает практически любую анестезию вне зависимос ти от ее методики [8] и связано с неподвижностью пациентов, проведением ИВЛ, использованием отно сительно высоких концентраций кислорода.…”

“…Частота пневмоний при абдоминальных опе рациях, в особенности при вмешательствах на органах верхнего этажа брюшной полости, может достигать 28% [1]. Еще более частым осложнением является формиро вание ателектазов, которое при целенаправленной диа гностике выявляется с частотой до 87% у всех пациен www.niiorramn.ru тов, перенесших общую анестезию [2]. Механизмы фор мирования послеоперационных респираторных ослож нений достаточно разнообразны и, кроме механических причин, нарушений центральной регуляции дыхания, болевого синдрома, могут включать в себя повышение нагрузки на недыхательные функции легких вследствие развития хирургического стресс ответа.…”

Réplica

“…Estamos de acordo com o que está descrito no consenso. A quase totalidade dos pacientes submetidos à anestesia geral irá desenvolver atelectasias nos primeiros minutos depois do relaxamento da musculatura respiratória [14][15][16] . Contudo, sem a devida prevenção, que deve ser entendida como a utilização de valores de PEEP adequado (não há consenso na literatura sobre esse valor), o uso de FiO 2 de 100% e desconexões freqüentes do tubo traqueal do circuito respiratório, ocorrerá recolapso pulmonar, pois os fatores relacionados com a formação de atelectasias ainda estão presentes e, nesse contexto, a repetição de manobras de recrutamento alveolar está justificada.…”

“…Almost all patients undergoing general anesthesia develop atelectasis in the first minutes after relaxation of the respiratory musculature [14][15][16] . However, without proper prevention in the form of adequate levels of PEEP (the literature does not have a consensus on which level is adequate), use of 100% FiO2, and frequent disconnection of the tracheal tube from the respiratory circuit, the patient will reestablish lung collapse because the factors related to the development of atelectasis are still present and, in this context, repetition of the alveolar recruiting maneuver is justified.…”