Our purpose was to determine the intensive care units’ (ICUs) medical staff surge capacity during the Covid-19 outbreak in spring 2020 in Spain. Methods: a multicenter retrospective survey addressing the medical specialties present in the ICUs and the increase in bed capacity during this period. Results: Sixty-seven centers (62.04%) answered the questionnaire. The ICU bed capacity during the pandemic outbreak increased by 160% (95%CI 128.97-191.03%). The average number of beds per intensive care medicine (ICM) specialist was 1.5 ± 0.60 and 3.71 ± 2.44 beds/specialist before and during the Covid-19 outbreak, respectively. Non-ICM specialists and residents were present in 50 (74.63%) and 23 (34.3%) ICUs during the outbreak, respectively. The number of physicians (ICM and non-ICM residents and specialists) in the ICU increased by 89.40% (95%CI 64.26 -114.53%). The increase in ICM specialists was, however, of 4.94% (95%CI -1.35 - 11.23%) Most non-ICM physicians were anesthetists, followed by pediatricians and cardiologists. Conclusion: The majority of ICUs in our study were able to rapidly expand critical care capacity by adapting areas outside of the normal ICU to manage critically ill patients, and by extending the critical care staff with noncritical care physicians working as force multipliers.