Mechanical ventilation strategies for patients with Pneumonia Ata Mahmoodpoor.MD.FCCM Associate Professor of Anesthesiology, TBZMed. Summer 2016

HAP or NP Any pneumonia contracted by a patient in a hospital at least 48–72 hours after admission. Usually caused by a bacterial infection, rather than a virus. Is the most frequent hospital acquired infection and along with primary bacteremia, is the leading cause of death from hospital acquired infection

Incidence Depends on the age, with about 5/1000 cases in hospitalized patients aged 65 years of age. Ranges from 4-50 cases per 1,000 admissions in community hospitals and general medical wards of teaching hospitals, and up to cases per 1,000 admissions in some ICU or among patients requiring MV. Death reaches 30±50%,with an estimated attributable mortality of 10±50%

Risk Factors

VAP 48 hours characterized by the presence of a new or progressive infiltrate, signs of systemic infection (fever, altered WBC count), changes in sputum characteristics, and detection of a causative agent. Approximately half of all cases of HAP. Occur in 9–27 % of all MV patients, with the highest risk being early in the course of hospitalization. The second most common nosocomial infection in the ICU and the most common in MV patients. Range from 1.2 to 8.5 per 1,000 ventilator days.

Risk for VAP is greatest during the first 5 days of MV (3 %) with the mean duration between intubation and development of VAP being 3.3 days. This risk declines to 2 %/day between days 5 to 10 of ventilation, and 1 %/day thereafter. Over the years, the attributable risk of death has decreased and is more recently estimated at 9–13 %, largely because of implementation of preventive strategies. Early onset VAP: occurs within 4 days, is usually attributed to antibiotic sensitive pathogens late onset VAP is more likely caused by MDR bacteria and emerges after 4 days of intubation

Ventilator-Associated Events Surveillance Definition Algorithm Uses a tiered approach, moving from measures of VAC, to IVAC, to possible and probable VAP. The first tier of VAE surveillance, VAC, seeks to identify episodes of sustained respiratory deterioration, and will capture both infectious and non-infectious conditions and complications occurring in mechanically ventilated patients. VAC is defined by a sustained period of worsening oxygenation that immediately follows a baseline period of stability or improvement on the ventilator.

VAEs - deterioration in respiratory status after a period of stability or improvement on the ventilator, - evidence of infection or inflammation - laboratory evidence of respiratory infection. To report VAEs Patients must be mechanically ventilated for more than 2 calendar days to be eligible for VAE. The earliest day on which VAE criteria can be fulfilled is day 4 of mechanical ventilation (where the day of intubation and initiation of mechanical ventilation is day 1).

IVAC Attempts to identify the subset of VACs that are potentially infection-related, as evidenced by (an abnormal WBC count or temperature and the initiation of a new antimicrobial agent). The Working Group recognized the low predictive value of an abnormal temperature or WBC count in ICU patients, and showed that the addition of fever or abnormal WBC count to the VAC definition does not substantially enhance the definition’s predictive value for death. The additional required criterion of the start of a new antimicrobial, where the new agent is continued for at least 4 days, may add specificity and clinical credibility to the IVAC definition, although data are needed to clarify this.

Two features of the VAE surveillance definition First, radiographic evidence of pneumonia is not included as a criterion (lack of specificity, and the subjectivity inherent in facilities’ and individual providers’ practices in ordering, performing, interpreting, and reporting the results of chest radiographs). Second, only VAC and IVAC are intended to be possible candidates for future use in public reporting, interfacility comparisons, and pay- for-performance programs.

VAP vs VAT Gradual emergence of VAP, mainly of late onset, is a common condition. Clinicians should be aware of this gradual onset of the infection to establish an early antibiotic treatment, even before the classic diagnostic criteria for VAP are applied.

The hypothesis of a continuum between airway colonization, an intermediate process VAT and VAP. During this developing period, the patient’s immune system will attempt to prevent the spread of the organism, and signs will be observable in the form of fever, leukocytosis, and purulent bronchial secretions. This process is typical in late-onset VAP (inoculate at intubation in early VAP, and due to accidental aspiration of subglottic secretions in late VAP).

In the event of suspected VAP, a mCPIS score higher than 5 could indicate antibiotic initiation. The lack of sensitivity of mCPIS precludes a safe use of this tool to rule out the existence of an ongoing infectious process. Usefulness of CPIS to safely withdraw antibiotics after 72 h of treatment in patients with an initial but incomplete diagnosis of VAP (CPIS ≤6 points at inclusion).

The ventilatory pattern should be selected according to the type of lung disease. Bronchopneumonia: Low RR and low I:E ratio Interstitial or lobar: Low VT, relatively high RR, PEEP and increased I:E ratios In very severe lung disease, controlled hypoventilation and permissive hypercapnia when not contraindicated. Supplemental strategies in patients with refractory hypoxia: recruitment manoeuvres, increasing PEEP level, haemodynamic stabilisation, inhaled NO, prone positioning and ECMO

Adjusting PEEP PEEP/Fio 2 table, is reasonable in patients that respond to PEEP. However, in the nonresponder, tables prevent additional oxygen from being administered without a simultaneous increase in PEEP. Resp mechanics Stress index, needs more trials Driving pressure(Plat-PEEP) in PEEP non responders instead of PEEP/Fio 2 table. Pes, needs more trials (LIP)Incremental PEEP: PEEP,Fio 2 combination to achieve desired level of oxygenation/highest compliance, has not been tested in a RCT in which both patient groups receive lower tidal volumes. Further, the approach is limited by the need to deeply sedate and paralyze patients for accurate curve construction. Even with a relaxed patient, there is significant interobserver and intraobserver variability in identifying the LIP. In some patients, the LIP cannot be accurately identified. (UDP)Decremental PEEP: PEEP decrease from high level in stepwise method until derecruitment occurs

The open lung approach may dramatically improve oxygenation, while minimizing VALI. The potential for alveolar recruitment in the individual patient is unfortunately extremely variable and difficult to estimate a priori. As a general rule, patients with early, diffuse disease are good recruiters, whereas patients with late disease (>1 week) or focal ones are not. In poor recruiters, the open lung approach may induce alveolar hyperinflation and VALI. The stress index could be a valuable tool to monitor open lung approach-induced hyperinflation.

Aerocell therapy

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