Mechanical Ventilator Adjustments and Patient Dyspnea

The Influence of Standard Ventilator Setting Adjustments on Dyspnea Experienced in Awake Mechanically-ventilated Patients: A Pilot Study

In the past 5 years, there are increasing data suggesting that patients treated with mechanical ventilation experience shortness of breath, despite appropriate sedation. This adverse experience is believed to contribute to the finding that up to 25% of patients who survive severe respiratory diseases experience mental health problems including post traumatic distress syndrome (PTSD). The purpose of this study is to evaluate if/how sequential changes in the delivery of mechanical ventilation affect shortness of breath sensation in awake patients requiring mechanical ventilation. Improving the knowledge of the impact of the patient-ventilator interaction on shortness of breath sensation may lead to strategies to improve the comfort of non-sedated and sedated ventilated patients, and thereby reduce mental health sequelae in survivors of acute severe respiratory diseases The investigators hypothesize that current ventilator strategies, particularly reduced tidal volume (size of breath given by the ventilator) utilized in managing patients with severe respiratory diseases, contribute to shortness of breath in patients with increased drive to breathe. In this setting, some safe ventilator changes may improve or worsen the shortness of breath sensation in awake patients on mechanical ventilation.

For patients who develop acute respiratory failure, endotracheal tube (ETT) intubation and mechanical ventilation represent a potentially life-saving intervention to provide support for breathing and allow the opportunity for lungs to recover from critical illness. Current standard practice for mechanical ventilation varies, and includes selecting mechanical ventilator mode (including volume-cycled or pressure-cycled), and routine adjustments of ventilator settings [including settings such as flow rate, tidal volume (Vt), positive end-expiratory pressure (PEEP)].

To assess and confirm the choice of mechanical ventilator settings for each patient, current standard practice includes monitoring vital signs, lung mechanics, observed use of accessory respiratory/breathing muscles by the patient, non-invasive measurement of percent oxygen saturation of the blood (SpO2), and direct blood sample analysis (including arterial or venous blood gas tests). However, direct assessment of patient breathing comfort, or the presence of breathing discomfort (i.e. dyspnea), is not routinely performed in mechanically ventilated patients, and represents a significant knowledge gap.

Dyspnea is a common symptom in hospitalized patients, but the incidence, prevalence and severity of dyspnea in mechanically ventilated ICU patients is incompletely understood. Dyspnea is a common symptom among hospitalized patients. It is defined by American Thoracic Society as "a term used to characterize a subjective experience of breathing discomfort that consists of qualitative distinct sensations that may vary in intensity. The experience derives from interaction among multiple physiological, psychological, social and environmental factors, and may induce secondary physiological and behavioral responses".

Limited publications suggest that up to 50% of intubated patients experience moderate-to-severe dyspnea during ICU admission (data limited to patients who are able to communicate), and survivors of critical illness acute respiratory failure report post-traumatic stress disorder (PTSD), and dyspnea symptoms other mental health problems commonly associated with including nightmares and flashbacks.

Dyspnea assessment in intubated and mechanically ventilated patients represents a substantial challenge. For patients with acute critical illness requiring intubation and mechanical ventilation, treatment often also requires a heavy significant level of analgosedation to provide patient comfort, but while rendering the patient non-communicative.

The purpose of this protocol is to perform a pilot investigation, a prospective, single center, multiple ICU, randomized, blinded, clinical study to assess the impact of standard ventilator setting adjustments on breathing discomfort experienced by intubated patients recovering from acute respiratory failure. This study will focus on adults who remain intubated (endotracheal tube; ETT), mechanically ventilated, but are awake and can effectively communicate by non-verbal means.

Data collection will focus on assessment for the presence or absence of patient-reported dyspnea at baseline, and following transitioning to a standard mechanical ventilator mode (VC/AC), and then during various standard adjustments of mechanical ventilator settings (including tidal volume, PEEP, and oxygen flow rate). Adjustments for each setting will include a specified pre-determined number of adjustments that reflect standard-of-care, followed by an assessment of patient-reported dyspnea over the course of 3 minutes at each setting adjustment.

For the purposes of this study, randomization refers to the sequence of changes in ventilator settings for each patient. All ventilator adjustments will be performed in the presence of a physician and respiratory therapist. Dyspnea will be assessed using standard validated tools (including Dyspnea modified multidimensional scale, and Dyspnea Quality Scale). Data will be collected on standardized form. The pilot study plan to enroll a total of 20 patients over a period of 6 months, including patients receiving care in any one of the BIDMC intensive care units, and each patients will be evaluated over the course of "30 minutes to 2 hours" for the purposes of this protocol.

Data from this pilot study will improve understanding of dyspnea associated with intubation and mechanical ventilation, and inform on design of future studies focusing on the management of patients with acute respiratory failure and requiring intubation and mechanical ventilation.

Inclusion Criteria:

• Admitted to a participating ICU at BIDMC

• Requiring mechanical ventilation

• Awake by both of the following criteria

• RASS -2 to +2*

• CAM-ICU negative‡

• Able to communicate/answer dyspnea questionnaire

  • RASS (Richmond Agitation-Sedation Scale) is a validated scale commonly used in the ICU to assess patient's level of sedation and agitation. It ranges from -5 to +4. While -5 means an unarousable coma, +4 means violent patient with immediate self danger. The scale from -2 to +2 ranges from light sedation to agitated.

    • CAM-ICU (Confusion Assessment Method) is an ICU validated scale used to assess the presence of delirium. A negative CAM-ICU scale has good positive and negative predictive value to diagnose or exclude delirium.

Physicians and nurses are trained to evaluate patients using both scales

Exclusion Criteria:

• Age < 18 years old
• Comfort measures only
• Hemodynamic instability (MAP < 65 mmHg) or increasing requirement of vasopressor
• PEEP > 10 cmH2O
• FiO2 > 0.6
• Current Prone position
• Current Pneumothorax
• Bronchopleural fistula
• Neuromuscular conditions that impair responding to the dyspnea scale or expression
• Dementia
• Prisoners
• Pregnant women
• Patients intubated and ventilated for less than 12 hours during the current ventilation episode
• pH < 7.20 or > 7.55
• Presence of chest tube
• Status post thoracotomy
• Treating clinician refusal