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SummaryTo examine the risk factors of early postoperative emergencies that required an intensive care team intervention, a matched nested case-control study (34 cases and 126 controls) was conducted. Over a 17-month period, the incidence of early postoperative emergencies occurring within 48 h of surgery was 0.21% (95% confidence intervals (CI): 0.14%-0.30%). The intensive care team treated two cardiac arrests and three respiratory arrests. The major physiological changes which led to ward staff summoning an intensive care team were hypotension (13 cases) and a decreased level of consciousness (nine cases). Significant associations with early postoperative emergencies were high ASA (Ն IV) physical status grades (odds ratio: 4.51, 95% CI: 1.24-16.40) and surgery performed outside normal working hours (odds ratio: 4.40, 95% CI: 1.41-13.69). High-risk patients may benefit from a visit by a postoperative care team during the early postoperative period but this requires further evaluation.

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Background The optimal level of positive end-expiratory pressure (PEEP) during mechanical ventilation for COVID-19 pneumonia remains debated and should ideally be guided by responses in both lung volume and perfusion. Capnodynamic monitoring allows both end-expiratory lung volume ($${\text{EELV}}_{{{\text{CO}}_{2} }}$$ EELV CO 2 ) and effective pulmonary blood flow (EPBF) to be determined at the bedside with ongoing ventilation. Methods Patients with COVID-19-related moderate to severe respiratory failure underwent capnodynamic monitoring of $${\text{EELV}}_{{{\text{CO}}_{2} }}$$ EELV CO 2 and EPBF during a step increase in PEEP by 50% above the baseline (PEEPlow to PEEPhigh). The primary outcome was a > 20 mm Hg increase in arterial oxygen tension to inspired fraction of oxygen (P/F) ratio to define responders versus non-responders. Secondary outcomes included changes in physiological dead space and correlations with independently determined recruited lung volume and the recruitment-to-inflation ratio at an instantaneous, single breath decrease in PEEP. Mixed factor ANOVA for group mean differences and correlations by Pearson’s correlation coefficient are reported including their 95% confidence intervals. Results Of 27 patients studied, 15 responders increased the P/F ratio by 55 [24–86] mm Hg compared to 12 non-responders (p < 0.01) as PEEPlow (11 ± 2.7 cm H2O) was increased to PEEPhigh (18 ± 3.0 cm H2O). The $${\text{EELV}}_{{{\text{CO}}_{2} }}$$ EELV CO 2 was 461 [82–839] ml less in responders at PEEPlow (p = 0.02) but not statistically different between groups at PEEPhigh. Responders increased both $${\text{EELV}}_{{{\text{CO}}_{2} }}$$ EELV CO 2 and EPBF at PEEPhigh (r = 0.56 [0.18–0.83], p = 0.03). In contrast, non-responders demonstrated a negative correlation (r = − 0.65 [− 0.12 to − 0.89], p = 0.02) with increased lung volume associated with decreased pulmonary perfusion. Decreased (− 0.06 [− 0.02 to − 0.09] %, p < 0.01) dead space was observed in responders. The change in $${\text{EELV}}_{{{\text{CO}}_{2} }}$$ EELV CO 2 correlated with both the recruited lung volume (r = 0.85 [0.69–0.93], p < 0.01) and the recruitment-to-inflation ratio (r = 0.87 [0.74–0.94], p < 0.01). Conclusions In mechanically ventilated patients with moderate to severe COVID-19 respiratory failure, improved oxygenation in response to increased PEEP was associated with increased end-expiratory lung volume and pulmonary perfusion. The change in end-expiratory lung volume was positively correlated with the lung volume recruited and the recruitment-to-inflation ratio. This study demonstrates the feasibility of capnodynamic monitoring to assess physiological responses to PEEP at the bedside to facilitate an individualised setting of PEEP. Trial registration: NCT05082168 (18th October 2021).