Objective Focused cardiac ultrasound (FCU) and lung ultrasound (LU) are increasingly being used in critically ill patients. This study aimed to investigate the effect of FCU in combination with LU on these patients and to determine if the timing of ultrasound examination was associated with treatment change. Methods This is a multicenter cross-sectional observational study. Consecutive patients admitted to the intensive care unit (ICU) were screened for enrollment. FCU and LU were performed within the first 24 h, and treatment change was proposed by the performer based on the ultrasound results and other clinical conditions. Results Among the 992 patients included, 502 were examined within 6 h of ICU admission (early phase group), and 490 were examined after 6 h of admission (later phase group). The early phase group and the later phase group had similar proportions of treatment change (48.8% vs. 49.0%, χ 2=0.003, P=0.956). In the multivariable analysis, admission for respiratory failure was an independent variable associated with treatment change, with an odds ratio (OR) of 2.357 [95% confidence interval (CI): 1.284-4.326, P=0.006]; the timing of examination was not associated with treatment change (OR=0.725, 95%CI: 0.407-1.291, P=0.275). Conclusions FCU in combination with LU, whether performed during the early phase or later phase, had a significant impact on the treatment of critically ill patients. Patients with respiratory failure were more likely to experience treatment change after the ultrasound examination.