An intermediate VT (7-8 ml/kg PBW) ventilation strategy was applied to the first four patients to increase pulmonary efficiency to eliminate CO 2 , and this was used in the next four patients. Gas exchange consists of oxygenation and ventilation. Oxygenation is quantified by the Pa O 2 /FI O 2 ratio, and this method has gained wide acceptance, particularly since publication of the Berlin definition of ARDS (7). However, the Berlin definition does not include additional pathophysiological information about ARDS, such as alveolar ventilation, as measured by pulmonary dead space, which is an important predictor of outcome (8). Increased pulmonary dead space reflects the inefficiency of the lungs to eliminate CO 2 , which may lead to hypercapnia. In our patients with ARDS with COVID-19, hypercapnia was common at ICU admission with low VT ventilation. Assuming the anatomic portion of dead space is constant, increasing VT with constant respiratory rate would effectively increase alveolar ventilation. Any such increase in VT would decrease Pa CO 2 , which would be captured by VR (6). VR, a novel method to monitor ventilatory adequacy at the bedside (4-6), was very high in our patients, reflecting increased pulmonary dead space and inadequacy of ventilation. With an acceptable plateau pressure and driving pressure, titration of VT was performed. Pa CO 2 and VR were significantly decreased when an intermediate VT (7-8 ml/kg PBW) was applied. We suggest that intermediate VT (7-8 ml/kg PBW) is recommended for such patients. Therefore, low VT may not be the best approach for all patients with ARDS, particularly those with a less severe decrease in respiratory system compliance and inadequacy of ventilation. In summary, we found that hypercapnia was common in patients with COVID-19-associated ARDS while using low VT ventilation. VR was increased in these patients, which reflected increased pulmonary dead space and inadequacy of ventilation. An intermediate VT was used to correct hypercapnia efficiently, while not excessively increasing driving pressure. Clinicians must have a high index of suspicion for increased pulmonary dead space when patients with COVID-19-related ARDS present with hypercapnia. n Author disclosures are available with the text of this letter at www.atsjournals.org.

Background: Subtraction CT angiography (sCTA) is a technique used to evaluate pulmonary perfusion based on iodine distribution maps. The aim of this study is to assess lung perfusion changes with sCTA seen in patients with COVID-19 pneumonia, and correlate them with clinical outcomes. Material and Methods: A prospective cohort study was carried out with 45 RT-PCR-con rmed COVID-19 patients that required hospitalization at three different hospitals, between April and May 2020. In all cases, a basic clinical and demographic pro le was obtained. Lung perfusion was assessed using sCTA. Evaluated imaging features included: Predominant type of perfusion abnormality (increased perfusion or hypoperfusion), perfusion abnormality distribution (focal or diffuse), extension of perfusion abnormalities (mild, moderate and severe involvement), presence of vascular dilatation and vascular tortuosity. All participants were followed-up until hospital discharge searching for the development of any of the study endpoints. These endpoints included intensive-care unit (ICU) admission, initiation of invasive mechanical ventilation (IMV) and death. Results: Forty-one patients (55.2 +/-16.5 years, 22 men) with RT-PCR-con rmed SARS-CoV-2 infection and an interpretable iodine map were included. Patients with perfusion anomalies on sCTA in morphologically normal lung parenchyma showed lower Pa/Fi values (294 ± 111.3 vs. 397 ± 37.7, p=0.035), and higher D-dimer levels (1156 ± 1018 vs. 378 ± 60.2, p<0.01). The patterns seen on lung CT were ground-glass opacities, mixed pattern and alveolar consolidation in 51.2%, 41.6% and 7.3%, respectively. Perfusion abnormalities were common (36 patients, 87.8%), mainly hypoperfusion in areas of apparently healthy lung. Patients with severe hypoperfusion in areas of apparently healthy lung parenchyma had an increased probability of being admitted to ICU and to initiate IMV (HR of 11.9% and HR 7.8%, respectively). Conclusion: Perfusion abnormalities evidenced in iodine maps obtained by sCTA are associated with increased admission to ICU and initiation of IMV in COVID-19 patients. Summary Statement Lung perfusion abnormalities in patients with COVID-19 pneumonia were associated with admission to Intensive Care Unit and requirement of invasive mechanical ventilation.

Objectives-To assess the frequency of hyperthermia in a population of acute neurosurgical patients; to assess the relation between brain temperature (ICT) and core temperature (Tc); to investigate the eVect of changes in brain temperature on intracranial pressure (ICP). Methods-The study involved 20 patients (10 severe head injury, eight subarachnoid haemorrhage, two neoplasms) with median Glasgow coma score (GCS) 6. ICP and ICT were monitored by an intraventricular catheter coupled with a thermistor. Internal Tc was measured in the pulmonary artery by a Swan-Ganz catheter. Conclusions-Fever is extremely frequent during acute cerebral damage and ICT is significantly higher than Tc. Moreover, Tc may underestimate ICT during the phases when temperature has the most impact on the intracranial system because of the close association between increases in ICT and ICP. (J Neurol Neurosurg Psychiatry 2001;71:448-454) Results-Mean

Pyrexia is extremely frequent in the acute phase after head injury. Its incidence is higher in more severe cases and is correlated with a longer ICU stay. It may affect ICP, but its contribution is difficult to assess when other major causes of increased intracranial volume are present. Antipyretic therapy is poorly effective for controlling body temperature and may be deleterious for CPP.