Metabolic Cost of IMT

Mechanical ventilation is a life-saving intervention used worldwide. Despite this, critically ill patients who undergo mechanical ventilation commonly develop muscle weakness; this includes limb muscle weakness and diaphragmatic weakness.

Physiotherapy interventions on critically ill patients include; mobilisation to improve limb muscle strength and function, and inspiratory muscle training which aims to target the diaphragm and accessory inspiratory muscles with the goal of improving endurance and strength. Whilst these interventions are standard practice in intensive care, little is known about the physiological load imposed on patients.

The purpose of this study is to assess the feasibility of using indirect calorimetry (measured using the Beacon Caresystem) to measure the metabolic cost (oxygen consumption \[VO2\] and carbon dioxide production \[VCO2\]) of inspiratory muscle training and physical rehabilitation in mechanically ventilated intensive care patients.

This is an initial cross-sectional study using a non-randomised convenience sample. Patients will be studied during either rehabilitation or Inspiratory Muscle Training.

All participants will have Maximal Inspiratory Pressure (PImax) measured every 5 days. Baseline measurements of VO2 and VCO2 at rest on their baseline ventilation will be measured using the Beacon Caresystem for 1 hour before Inspiratory Muscle Training or physical rehabilitation is initiated.

Inspiratory muscle training will will performed using a resistive device (Philips Respironics ® Threshold PEP device) which is inserted into the participants ventilator tubing 30 minutes before starting inspiratory muscle training. At this point, the device will be set to its lowest setting; the resistance will be overcome by support delivered through the ventilator meaning no additional effort for the participant.

The patient will then perform 12 breaths of inspiratory muscle training at 4cmH20, and at 30%, 50% and 80% PImax with a 30 second rest every 6 breaths and a 10-20 minute rest every 12 breaths

Inspiratory muscle training will normally occur five days per a week. The Beacon Caresystem will be connected for analysis up to 2 days per week.

Participants will receive usual physiotherapy exercise. These will be prescribed by the patient's physiotherapist and may include assisted mobilisation and / or upper and lower limb exercises to help strengthen muscles. Exercises performed will be categorised for analysis in the study according to a scale called the intensive care mobility scale.

When physical rehabilitation begins (i.e when the patient starts to move with the physiotherapist); a time stamp will be activated on the Beacon Caresystem. When physical rehabilitation has ended the time stamp will be deactivated.

Immediately after exercise the patient will be asked to rate their exertion using a simple scale designed to measure physical effort, called the BORG rating scale of perceived exertion.

Physical rehabilitation will normally occur six days per a week. The Beacon Caresystem will be connected for analysis up to 4 days per week.

Eligibility Criteria:
Inclusion Criteria:

* Patient invasively ventilated for ≥ 72 hours
* Have an endotracheal tube or tracheostomy in situ
* Respiratory rate of ≤ 35 breaths/min
* Fraction Inspired Oxygen (Fi02) ≤ 0.50
* Co-operative and able to participate in physical rehabilitation and inspiratory muscle training
* Age ≥ 18 years
* Patient consent or, in the case that the patient is unable, advice from the next of kin and acceptance of oral and written information describing the study.

Exclusion Criteria:

* Undrained pneumothorax/pneumomediastinum
* The absence of an arterial catheter for blood sampling at study start
* Unlikely to survive
* Pregnancy
* Consultant discretion that patient is not appropriate