This paper presents an exploratory investigation of how ICUs in Brazil have coped with the pandemic. A resilience engineering perspective is adopted, using a mixed-method research design. The quantitative stage comprised an exploratory survey for assessing the uptake of five work system guidelines that are logically related to resilience. The guidelines are: provide slack resources; give visibility to processes and outcomes; support diversity of perspectives when making decisions; monitor and understand the gap between work-as-imagined and work-as-done; and monitor unintended consequences of improvements and changes. These guidelines were described as statements in the survey, accompanied by ICU examples. There was a sliding bar with two endpoints: fully disagree (zero) and fully agree (100). For example, one of the statements related to the guideline on slack was as follows: there are extra or standby human resources that can be quickly deployed, and these are available in sufficient quantity to cope with unforeseen events. There were 33 valid responses, all from different ICUs. All respondents were invited to be interviewed and seven agreed with that. These interviews shed light on the rationale for the survey responses. The qualitative stage followed with interviews with two public health officials and non-participant observations of the meetings of a municipal COVID-19 crisis management committee in a capital city. Joint data analysis from the quantitative and qualitative stages supported the identification of five lessons learned, each corresponding to one of the aforementioned guidelines. Results indicated the guideline on slack resources as the most relevant as it addressed the key pandemic issue of matching capacity to demand. The provision of sufficient and experienced staff was found to be more challenging than the provision of facilities and supplies.