Sedation
Observational study of patient-ventilator asynchrony and relationship to sedation level

https://doi.org/10.1016/j.jcrc.2008.08.011Get rights and content

Abstract

Purpose

Clinicians frequently administer sedation to facilitate mechanical ventilation. The purpose of this study was to examine the relationship between sedation level and patient-ventilator asynchrony.

Materials and Methods

Airway pressure and airflow were recorded for 15 minutes. Patient-ventilator asynchrony was assessed by determining the number of breaths demonstrating ineffective triggering, double triggering, short cycling, and prolonged cycling. Ineffective triggering index (ITI) was calculated by dividing the number of ineffectively triggered breaths by the total number of breaths (triggered and ineffectively triggered). Sedation level was assessed by the following 3 methods: Richmond Agitation-Sedation Scale (RASS), awake (yes or no), and delirium (Confusion Assessment Method for the intensive care unit [CAM-ICU]).

Results

Twenty medical ICU patients underwent 35 observations. Ineffective triggering was seen in 17 of 20 patients and was the most frequent asynchrony (88% of all asynchronous breaths), being observed in 9% ± 12% of breaths. Deeper levels of sedation were associated with increasing ITI (awake, yes 2% vs no 11%; P < .05; CAM-ICU, coma [15%] vs delirium [5%] vs no delirium [2%]; P < .05; RASS, 0, 0% vs −5, 15%; P < .05). Diagnosis of chronic obstructive pulmonary disease, sedative type or dose, mechanical ventilation mode, and trigger method had no effect on ITI.

Conclusions

Asynchrony is common, and deeper sedation level is a predictor of ineffective triggering.

Introduction

Patient-ventilator asynchrony is a frequently encountered problem in mechanically ventilated patients. Thille et al [1] found that 24% of patients experienced asynchrony in at least 10% of their breaths, with ineffective triggering and double triggering being the most common asynchronies. Indeed, ineffective triggering is especially common in patients with chronic obstructive pulmonary disease (COPD) occurring in up to 80% of patients [2], [3], [4]. Patient-ventilator asynchrony has also been found to be associated with longer duration of mechanical ventilation and lower rates of successful weaning [1], [5].

A number of mechanisms for poor patient-ventilator interactions have been identified including abnormal respiratory mechanics and ventilator factors [1], [5], [6], [7]. Clinicians cite facilitation of mechanical ventilation and promotion of patient-ventilator synchrony as among the most common reasons for administration of sedation during the course of mechanical ventilation [8], [9]. However, little evidence exists to support this practice. In a study of 8 patients undergoing mechanical ventilation, Grasso et al [10] found increasing sedation depth resulted in incremental decreases in inspiratory muscle effort. Extending these findings, it is possible that increasing sedation depth results in progressively lower maximal inspiratory flow and weaker muscle effort, clinically manifesting as ineffective triggering. However, because these patients appear calm, the asynchrony may not be diagnosed by clinicians and may remain unrecognized. Paradoxically, patient agitation due to asynchrony is often treated with medications that cause respiratory depression that may then lead to ineffective triggering. To our knowledge, other investigators have not accounted for sedation when analyzing the patient-ventilator interaction.

We conducted a pilot study to determine the frequency of asynchrony in medical intensive care unit patients and to evaluate the relationship between asynchrony and sedation level. We postulated that deeper levels of sedation were associated with more frequent asynchrony, particularly ineffective triggering.

Section snippets

Inclusion and exclusion criteria

All patients undergoing invasive mechanical ventilation in the medical intensive care unit at Virginia Commonwealth University Medical Center (Richmond, Va) were eligible for study participation unless they met exclusion criteria. Exclusion criteria were age less than 18 years, positive end-expiratory pressure (PEEP) of at least 9 cm H2O, partial pressure of oxygen divided by fraction of inspired oxygen of less than 150, ventilation through a tracheotomy, and inability to initiate breaths

Statistical analysis

Mixed model repeated measures analysis of variance was used to test the relationship between sedation level (RASS, CAM-ICU, and wakefulness) and the proportion of asynchronous breaths. Mixed model repeated measures analysis of variance allows for multiple observations per patient. Other variables entered in the model were diagnosis of COPD, arterial partial pressure of carbon dioxide, trigger method (pressure vs flow trigger), mode of mechanical ventilation, plateau pressure, amount of pressure

Results

Twenty medical patients underwent 35 observations. Table 1 lists the demographics of the patients. Five patients had COPD and underwent 9 observations. Mechanical ventilation modes were synchronized intermittent mandatory ventilation with pressure support (19 observations), pressure support alone (15 observations), and pressure control (1 observation). Trigger method was flow triggering on 22 occasions (2.6 ± 0.7 L/min) and pressure triggering on 13 occasions (2.1 ± 0.2 cm H2O). Positive

Discussion

The main finding of our pilot study is that (i) asynchrony is common, with ineffective triggering being the most common asynchrony, and that (ii) sedation level affects patient-ventilator interactions, with deeper sedation level associated with more ineffective triggering. In particular, comatose patients, patients who are not awake and those who are more deeply sedated have significantly higher rates of ineffective triggering compared to noncomatose patients who are awake, alert, and

References (21)

  • FabryB. et al.

    An analysis of desynchronization between the spontaneously breathing patient and ventilator during inspiratory pressure support

    Chest

    (1995)
  • ChaoD.C. et al.

    Patient-ventilator trigger asynchrony in prolonged mechanical ventilation

    Chest

    (1997)
  • ThilleA.W. et al.

    Patient-ventilator asynchrony during mechanical ventilation: Prevalence and risk factors

    Intensive Care Med

    (2006)
  • NavaS. et al.

    Patient-ventilator interaction and inspiratory effort during pressure support ventilation in patients with different pathologies

    Eur Respir J

    (1997)
  • PurroA. et al.

    Physiologic determinants of ventilator dependence in long-term mechanically ventilated patients

    Am J Respir Crit Care Med

    (2000)
  • EpsteinS.K.

    Optimizing patient-ventilator synchrony

    Semin Respir Crit Care Med

    (2001)
  • LeungP. et al.

    Comparison of assisted ventilator modes on triggering, patient effort, and dyspnea

    Am J Respir Crit Care Med

    (1997)
  • Hansen-FlaschenJ.H. et al.

    Use of sedating drugs and neuromuscular blocking agents in patients requiring mechanical ventilation for respiratory failure. A national survey

    JAMA

    (1991)
  • RhoneyD.H. et al.

    National survey of the use of sedating drugs, neuromuscular blocking agents, and reversal agents in the intensive care unit

    J Intensive Care Med

    (2003)
  • GrassoS. et al.

    Patient-ventilator interactions during psv at different levels of sedation in ALI patients

    Intensive Care Med

    (2004)
There are more references available in the full text version of this article.

Cited by (123)

  • Attention-based convolutional long short-term memory neural network for detection of patient-ventilator asynchrony from mechanical ventilation

    2022, Biomedical Signal Processing and Control
    Citation Excerpt :

    Table 1 shows the basic information of the patients with approximately 30,000 breath sequences registered per patient. We mainly consider two types of PVAs, namely ineffective expiration as well as double triggering, which account for more than 80% of all PVA types [4,25]. When a patient attempts to breathe but does not reach the trigger threshold, then the breathing is ineffective expiration.

  • Treatment of acute respiratory distress syndrome

    2022, FMC Formacion Medica Continuada en Atencion Primaria
  • Ventilator waveforms

    2022, Small Animal Critical Care Medicine
View all citing articles on Scopus

The study was supported with the following grants: NIH K23 GM068842 and NIH M01 RR00065; Novametrix (Wallingford, Conn) provided equipment and supplies at no cost. The granting institution is the NIH located in Bathesda, Maryland.

View full text