Brazilian Journal of Anesthesiology
Brazilian Journal of Anesthesiology
Original Investigation

Effect of seasons on delirium in postoperative critically ill patients: a retrospective analysis

Efeito das estações no delirium em pacientes críticos pós-operatórios: uma análise retrospectiva

Yuwei Qiu, Eva Rivas, Marianne Tanios, Roshni Sreedharan, Guangmei Mao, Ilker Ince, Ahmed Salih, Remie Saab, Jagan Devarajan, Kurt Ruetzler, Alparslan Turan

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Background and objectives
Postoperative delirium is common in critically ill patients and is known to have several predisposing and precipitating factors. Seasonality affects cognitive function which has a more dysfunctional pattern during winter. We, therefore, aimed to test whether seasonal variation is associated with the occurrence of delirium and hospital Length Of Stay (LOS) in critically ill non-cardiac surgical populations.

We conducted a retrospective analysis of adult patients recovering from non-cardiac surgery at the Cleveland Clinic between March 2013 and March 2018 who stayed in Surgical Intensive Care Unit (SICU) for at least 48 hours and had daily Confusion Assessment Method Intensive Care Unit (CAM-ICU) assessments for delirium. The incidence of delirium and LOS were summarized by season and compared using chi-square test and non-parametric tests, respectively. A logistic regression model was used to assess the association between delirium and LOS with seasons, adjusted for potential confounding variables.

Among 2300 patients admitted to SICU after non-cardiac surgeries, 1267 (55%) had postoperative delirium. The incidence of delirium was 55% in spring, 54% in summer, 55% in fall and 57% in winter, which was not significantly different over the four seasons (p = 0.69). The median LOS was 12 days (IQR = [8, 19]) overall. There was a significant difference in LOS across the four seasons (p = 0.018). LOS during summer was 12% longer (95% CI: 1.04, 1.21; p = 0.002) than in winter.

In adult non-cardiac critically ill surgical patients, the incidence of postoperative delirium is not associated with season. Noticeably, LOS was longer in summer than in winter.


Postoperative delirium;  Seasonal;  Surgical Intensive care unit



O delirium pós-operatório é comum em pacientes gravemente enfermos e é conhecido por ter vários fatores predisponentes e precipitantes. A sazonalidade afeta a função cognitiva que tem um padrão mais disfuncional durante o inverno. Nosso objetivo, portanto, foi testar se a variação sazonal está associada à ocorrência de delirium e tempo de permanência hospitalar (TDP) em populações cirúrgicas não cardíacas criticamente doentes.


Realizamos uma análise retrospectiva de pacientes adultos em recuperação de cirurgia não cardíaca na Cleveland Clinic entre março de 2013 e março de 2018, que permaneceram na Unidade de Terapia Intensiva Cirúrgica (UTI) por pelo menos 48 horas e receberam diariamente Confusion Assessment Method Intensive Care Unit (CAM -ICU) para delirium. A incidência de delirium e TDP foram resumidos por estação e comparadas usando o teste qui-quadrado e testes não paramétricos, respectivamente. Um modelo de regressão logística foi usado para avaliar a associação entre delirium e TDP com as estações do ano, ajustado para possíveis variáveis de confusão.


Entre 2.300 pacientes internados na UTI após cirurgias não cardíacas, 1.267 (55%) apresentaram delirium pós-operatório. A incidência de delirium foi de 55% na primavera, 54% no verão, 55% no outono e 57% no inverno, não diferindo significativamente nas quatro estações (p = 0,69). O tempo médio de permanência foi de 12 dias (IQR = [8, 19]) no geral. Houve uma diferença significativa no TDP nas quatro estações (p = 0,018). O tempo de permanência no verão foi 12% maior (IC 95%: 1,04, 1,21; p = 0,002) do que no inverno.


Em pacientes cirúrgicos adultos não cardíacos em estado crítico, a incidência de delirium pós-operatório não está associada à estação do ano. Notavelmente, o TDP foi mais longo no verão do que no inverno.


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