Ventilation Sedation and Positioning
Patients suffering from many diseases and physiological issues require ventilation and/or ICU admission for varied periods of time whether it be for postoperative care, post MI, pneumonia or Guillain Barre Syndrome or anything in between
There is one huge constant in all of their care which is to be able cease invasive ventilation as soon as it is safely practicable, but why? Surely the process of ventilation is safe and complication free
Essentially the longer your ventilated the greater the risks of complication – the entire process is risk versus benefit
Complications associated with invasive ventilation include pneumothorax, acute lung injury, ventilator associated pneumonia, laryngeal dysfunction, tracheomalachia etc. So we monitor and try to reduce these risk factors and time of ventilation where able
Invasive Ventilation is the mainstay of most ICUs but what decides how long they are ventilated?
- ABG results
- slow neurological recovery
- resolution of admission pathology
- chest Xray
- level of sputum
- coexisting illnesses (returning to Operating Theater etc)
But there is one thing missing from this list;
What is it?
The progressive detoning of the largest respiratory muscle, causing decreased muscular contraction and bulk associated with resultant increased Work Of Breathing through need to use accessory muscles
This atrophy can start to occur in as little as 3 hours but studies show it reaches its peak if therapy is continued unchanged more than 72 hours
OK – While your sitting there try to breath without using your diaphragm, lift your shoulders to increase volume and expand your intercostal muscles to add to than volume. Yes those volumes are tiny
Why is it?
Approximately 40% of patients in medical intensive care units require Mechanical Ventilation (MV), and difficulties in discontinuing MV are encountered in 20-25% of these patients. Multiple studies suggest that MV has an unloading effect on the respiratory muscles leading to diaphragmatic dysfunction, a process called;
Ventilator-Induced Diaphragm Dysfunction (VIDD).
In ICU this may be caused by our actual treatment with antibiotics, corticosteroids, sedatives and neuromuscular agents, all of which can weaken respiratory muscles
Most commonly precipitated by inactivating the muscle though complete ventilation under high sedation, IE totally controlled ventilation with SIMV with a RASS greater than -3
How is it avoided?
- minimising Sedation
- targeting whenever able a RASS score as close to 0 while still ensuring patient comfort, compliance and safety
- unless a Sedation Score other than -1 to -2 has been ordered they should always remain your default
Your patient should be able to spontaneously cough between suctioning and respond to active suctioning to clear secretions, the absence of a strong cough reflex is a clear indication of excess sedation
- minimise Mandatory Ventilation
Targeting whenever able, in consultation with the multidisciplinary team, a move to more spontaneous modes of breathing on the ventilator – CPAP, PSV, APRV
What is the default position of the ICU patient in bed?
- Sitting straight up or as close to it as we can
Most of the pressure exerted by the ventilator on ventilating a patient laying flat is to over come both initial resistance of the airways and then the flow required to overcome splinting of the lungs by the spread of the abdomen up under the diaphragm. Because the pelvis forms an immovable barrier on one side the lungs are by far the easiest organ to force out of the way and compress. By sitting the patient up we cause the abdominal contents to move down away from the diaphragm
This pulls the diaphragm down bringing with it the base of the lungs, increasing thoracic volume
So best way to increase lung volume, diaphragmatic movement and get air into lung bases?
Sit them up or, even better, sit them out (every patient in any ward)
Of course, this works on all types of ventilation – invasive, non-invasive and patients waiting for other processes to resolve – frankly just about everyone (with the added benefit that a patient who feels they are moving forward in their hospital stay usually does move forward)
So who can not sit up?
- spinal patients (including uncleared cervical injuries)
- some complex pelvic orthopaedic (usually externally braced)
- very morbidly obese (may benefit from upright lateral positioning)
- very haemodynamically unstable (rare) (haemorrhage etc)
So who can not sit out?
- as above
- patients at mobilisation risk to themselves (if no restraints allowed)
- Intra Aortic Balloon Pump located in the groin (brachial IABP access patients may mobilise)
NOTE; The obese may find the positioning of a chair far better than a bed
At the start of your shift discuss with your T/L regarding sedation, ventilation and mobilisation, it could well be the most important and beneficial discussion you have all day!
Oh’s Intensive Care Manual 7th Edition 2014 by Andrew Bersten, Neil Soni
Pilbeam’s Mechanical Ventilation: Physiological and Clinical Applications 6th Edition by J M Cairo