Discussion

The main objective of an ACS is to offload overburdened hospitals. This is especially important for small community hospitals in remote areas such as those in Imperial County, where each of the hospitals are licensed for less than 200 beds and there are no tertiary care centers in the county. ^{Reference Breyre, Sloane and Herring3} Kadri et al. found that hospitals experiencing surges were associated with higher mortality rates. ^{Reference Kadri, Sun and Lawandi8}

COVID-19 pneumonia is characterized by a variable clinical course with few reliable predictors of subsequent deterioration. With the paucity of effective treatments other than oxygen and respiratory support available during the time period that this ACS operated, clinical deterioration requiring a higher level of medical treatment is expected for some patients. Because ACS usually cannot match the full capability of a general acute care hospital, judicious patient selection and optimization of care provided within the ACS is important to provide safe and quality care to limit transport of patients back to overwhelmed hospitals.

For the ACS to provide expanded support to the local hospitals, admission criteria were broadened when the Imperial ACS was reopened during the second COVID-19 wave. The oxygen limitation was increased from 2 LPM to 8 LPM. Oxygen concentrators with a maximum flow rate of 10 LPM were used as the primary source of supplemental oxygen, delivered by means of simple nasal cannula, nasal cannula oxymizer, or face mask. ^{Reference Devereaux, Backer and Salami9} All patients had continuous pulse oximetry monitoring. With this oxygen strategy, patients were accepted with up to an 8 LPM initial oxygen requirement, allowing some reserve for escalation of oxygen therapy in case of respiratory deterioration.

Admission criteria were also expanded to include more complex comorbidities. Sanyaolu et al. noted that COVID-19 patients with a history of hypertension, obesity, chronic lung disease, diabetes, and cardiovascular disease are at greatest risk for severe disease and have worse prognosis. ^{Reference Sanyaolu, Okorie and Marinkovic10} Well-controlled chronic diseases were successfully managed, such as those requiring hemodialysis, with active malignancies, and liver cirrhosis. Patients with obstructive sleep apnea could bring their continuous positive airway pressure device from home to be used with entrained supplemental oxygen at nighttime. Obesity was a limitation only if patients could not fit in the bariatric wheelchairs or could not self-prone.

The major care improvements implemented at the ACS-IVC2 to optimize patient treatment and reduce the need to transfer patients back to the hospital included both patient care and staff team support. Patient care optimization included emphasis on incentive spirometry to decrease atelectasis from low lung volume breathing, pulmonary rehabilitation, and gradually progressive physical therapy. ^{Reference Seyller, Gottlieb and Colla11,Reference Zhu, Wang and Zhou12} Continuous pulse oximetry and trending of a patient’s incentive spirometry volume trend also served as a clinical sign for disease progression or improvement. During both time periods, standard treatment for ACS patients included Remdesivir (if not provided during care before transfer), dexamethasone, and anti-thrombotic therapy, encouragement for self-proning, and weaning of supplemental oxygen as tolerated, which were standard of care recommendations at that time. Data on the extent and degree of individual adherence to self-proning recommendations are not available.

Because staff consisted of rotating disaster medical (paid) volunteers with many new program graduates, tools to optimize team function and support decision-making were instituted. These included pre-printed admission orders, protocols for clinical care, regular in-service education, integration of pharmacists into the clinical teams, and establishment of a rapid response team that could evaluate and stabilize a patient with clinical deterioration or signs of distress (Table 2). Active team integration has been demonstrated in other settings to improve care and reduce medical errors. ^{Reference Morey, Simon and Jay13,Reference Risser, Rice and Salisbury14} ACS admission criteria were widely circulated within the hospitals, and clinical liaisons at each hospital had daily calls with ACS staff to determine which patients were suitable for care at the ACS.

Not all patients who required an increase in O2 flow rates were transported back to the hospital. The use of portable chest x-ray permitted ACS clinicians to monitor progression of disease and supported clinical decision making for patients with pulmonary deterioration. Patients who required increased supplemental O2 at the ACS, without significant radiographic change, and remained hemodynamically stable were kept at the ACS and closely monitored. ^{Reference Kohli, Hande and Chugh15}

Efforts also focused on preventing patients from returning to the emergency department after discharge from the ACS. Respiratory therapy and physical therapy aimed to optimize patient functionality and pulmonary rehabilitation. With the establishment of a home oxygen program, patients who were stable on supplemental oxygen less than 5 LPM were discharged home with close monitoring through home health and paramedic visits.

While patients in the 2 time periods were similar in demographics and comorbidities, the transfer rate for new admissions decreased by nearly 60% with no deaths or emergent intubations before or during transport. There are many factors that may affect the transfer rate, but we observed that implementation of process improvement clinical care interventions significantly contributed to this reduction in transfer rate.

Symptomatic patients with COVID-19 tend to have potentially significant underlying comorbidities, which complicate the provision of care in a non-traditional environment. At a similar hospital-level ACS in New York caring for less-severely symptomatic COVID-19 patients with a maximum supplemental oxygen requirement of 4 LPM on admission, Mathews et al. had a transfer rate of 12%. ^{Reference Mathews, Podlog and Greenstein16} At the Imperial County ACS, the transfer rate was 14.5% of admissions for a higher acuity patient population with greater initial oxygen requirements.

Patients within the first week of symptom onset are in the acute infection phase and have a higher probability of deterioration. ^{Reference Datta, Talwar and Lee17} Admitting patients who are more than 1 wk from the onset of symptoms may assure that supplemental O2 requirements can be met and transfer rates further decreased; however, we accepted patients directly from the 2 hospital emergency departments when both the ED and the in-patient services were experiencing major surge.

The relative value of individual clinical care interventions on reduced transfer rates or improved aggregate care cannot be determined from our data. The effects of such clinical changes are likely synergistic and are reflected in overall improvements in care delivery. After a period of 2 wk (Transition period), a 60% reduction in transfer rate was achieved despite a higher acuity patient population and shorter length of stay (Figure 2). There were no dramatic changes in COVID-19 treatments or the virus itself during that time, and staff expertise with a rotating core of volunteer nurses and doctors did not account for the difference.

Figure 2. Percent of patients transferred back to hospital in each time period. n = number of patients admitted in that time period.

The transfer rate provides a useful measure of patient appropriateness and the ability of a hybrid care ACS to provide a safe and effective means to decompress overburdened hospitals. While transfers for patients who deteriorate are expected, a high return rate may reflect an increased health risk to patients, greater costs to the health-care system, increased logistical burden of patient transport, and a lower perceived value of the ACS to the local medical community. The relative impact on health-care surge and cost-effectiveness of ACS versus expanding resources within hospitals is not resolved and likely depends on many factors, including the health resources within a community and region, the nature of the health-care surge, and the capabilities of the ACS. The experience in Imperial County demonstrates the potential value of ACS as well as factors to optimize this value to both patients and health systems.

This observational study has multiple limitations. While the Imperial County ACS was 1 of the highest used ACS locations in the state of California, the overall patient admissions totaled 326, limiting ability to generalize these results. Additionally, this patient population is from a resource-limited and health-care–limited area of the United States, which also limits application to areas with greater resources and enhanced preventative health care. In analyzing the change following this study’s intervention, the local inpatient capacity increased from Period 1 to Period 2. During this time, tents and additional staffing increased the local hospitals’ ability to admit more patients, and this may have altered the patients who presented as candidates for the ACS. Long-term patient follow-up would be useful because 67 of the 79 patients transferred were lost to follow-up. Outcomes for patients discharged on the home oxygen program were not available for this analysis, but maybe evaluated in a subsequent publication. Future studies at other ACS should also look at the application of similar clinical care interventions and validate the use of transfer rate as a metric for ACS.

Given that hospitals experiencing surges are associated with higher mortality, Kadri et al. also suggested ACS should be opened earlier to prevent hospitals from reaching capacity. This topic is especially important as regions across the country experience rising COVID-19 cases and consider instituting crisis standards of care (CSC). California has so far been able to avoid CSC by using multiple other measures, including ACS, to manage the surge.