Mechanical ventilation is one of the most common interventions implemented in the intensive care unit. More than half of the patients in the ICU are ventilated the first 24 hours after ICU admission; comprised of individuals who have acute respiratory failure, compromised lung function, difficulty in breathing, or failure to protect their airway.  The lungs primary function is to add oxygen and to remove CO2 from the blood passing through the lung’s capillary bed.  The lungs are compromised of a million alveoli (bunches of grapes) clinging to each other and emptying into the bronchiolar tree by the tributary network of airways eventually emptying into main bronchi and trachea. There are multiple modes of  mechanical ventilation support that provide air to the patient  based on pressure, flow and volume.  Although lifesaving, mechanical ventilation can be associated with life threatening complications, including air leaks and  pneumonia. 

Many conditions predispose patients to acute lung injury.  The common feature in acute lung injury is the activation of white blood cells (neutrophils)  and pulmonary inflammation.  Causes of  acute respiratory failure can be  extra pulmonary such as intra abdominal sepsis, pancreatitis, or intracranial hypertension; or the cause can  be intrapulmonary such as pneumonia, pulmonary contusion, or aspiration.  Once the individual no longer need mechanical ventilation, they are ready to be weaned [from the ventilator].   All candidates for weaning must have adequate oxygenation, adequate carbon dioxide elimination, adequate respiratory muscle strength and reserve, and the ability to protect their airway.  Once these conditions are satisfied, a number of easy obtained bedside parameters can be used to predict the likelihood of removing the patient from ventilator support.  The parameters include minute ventilation, spirometry, the PA02/ FI02 ratio and rapid shallow breathing index.  Non-invasive ventilation (CPAP or BIPAP) refers to the provision of ventilator assistance techniques that do not bypass the upper airway.  This may prove very useful in patients in pulmonary edema from heart failure, immunocompromised patients, following aspiration or Chronic Obstructive Pulmonary Disease exacerbation.  Noninvasive ventilation can also serve as  a bridge between extubation and spontaneous ventilation where the patient breathes on their own.  Measurements of adequacy of breathing include use of arterial blood gases, pulse oximetry, and  measurement of end-tidal CO2.   

Facts:

 790,257 hospitalizations involving mechanical ventilation in 2005, representing 2.7 episodes of mechanical ventilation per 1000 population; estimated national costs were 27 billion representing 12% of all hospital costs.

 Acute lung injury and Acute Respiratory Distress Syndrome were estimated at 86.2/100,000 and 64.0/100,000 person years respectively. 

 In 2004, the ICU mortality rate among 49,688 patients from 349 ICUs was 31% overall, where the hospital mortality rate was 37%. 

 In a cohort study using year 2005 hospital discharge records from six states (Massachusetts, Maryland, New Jersey, New York, Texas and Washington) the following statistics were observed:

 -In hospital mortality of ventilated patients was 34.5% and only 30.8% of patients were discharged home from the hospital.

-A total of 44.6% had at least one major co-morbid condition; the most common co-morbidities included diabetes (13.2 %) and pulmonary disease (13.2%)

-Daily incremental cost of mechanical ventilation for ICU patients is estimated at between $600 and $1500 per day

-Mean Length of Stay was 14.1 +/- 16.9 days, accounting for 7.1% of hospital days

-Mean hospital costs were $34,257 dollars (+/- $40,559 dollars) with lower average costs in rural and small hospitals.

 Discontinuing mechanical ventilation continues to be one of the most challenging events in ICU management, and a significant portion of time spent on the ventilator (40%) is dedicated to weaning.. 

Both premature and delayed extubation is associated with adverse outcomes.  The timing of extubation is critical.  The timing and method of weaning varies among clinicians.

Web sites:

http://www.thoracic.org/clinical/critical-care/patient-information/index.php from the American Thoracic Society- it’s got great info although navigation is a little awkward.

http://www.thoracic.org/clinical/critical-care/patient-information/icu-devices-and-procedures/mechanical-ventilator.php

 Section on weaning from the vent:

http://www.thoracic.org/clinical/critical-care/patient-information/icu-devices-and-procedures/weaning-from-mechanical-ventilation.php

 Section on mechanical ventilator

http://www.nhlbi.nih.gov/health/dci/Diseases/vent/vent_what.html

From the National Heart Lung and Blood Institute- about mechanical ventilators

http://www.nlm.nih.gov/medlineplus/criticalcare.html

From MedlinePlus- lots of good links and PDFs

Articles:

The epidemiology of mechanical ventilation in the United States. H Wunsch, W Linde-Zwirble, D Angus, M Hartman, E. Milbrandt, J Kahn. Crit Care Med 2010; 38:1947-1953

Mechanical ventilation : epidemiological insights into current practices. E Goligher, N Ferguson. Curr Opin Crit Care 15:44-51

Epidemiological insights into current practices. E Goligher, N Ferguson. Curr Opin Crit Care. 2009,  15:44-51

Epidemiology of mechanical ventilation: Analysis of the SAPS 3 Database.  P Metnitz, B Metnitz, R Moreno, P Bauer, L Del Sorbo, C Hoermann, S Afonso de Carvalho, V Ranieri. Intensive Care Med 2009 35:816-825

Author: Orlando Kirton, MD (2011)