Clinical IPPV & NMB Flashcards
When are circumstances where we need to breathe for the patient?
- P is unable to ventilate (Thx Sx, diaphragmatic hernia Sx, NMB)
- inadeq ventilation
- increased ICP
- administration of high dose opioid drugs
- IPPV, only ventilate when indicated
Minute ventilation (MV) =
TV x RR
The efficiency of ventilation is assessed by…
the elimination of CO2
How do you measure the efficiency of ventilation?
By assessing the elimination of CO2 by capnograph or intermittent blood gases
Inadequate ventilation =
hypoventilation
When does hypoventilation occur?
- too deep anaesthesia
- geriatric P
- obesity
- pregnancy, space-occupying masses
- muscle weakness
- laparoscopy
- pain
Hypoventilation increases partial pressure of
CO2 above normal
What are mild systemic effects of hypercarpia/hypercapnia?
Stimulation of the SNS by
- tachycardia
- vasoconstriction
- hypertension
What are the effects on the heart of severe hypercapnia?
- Tachycardia increases myocardial O2 consumption
- Neg inotropy (decreased cardiac contractility) leads to hypotension
- Hypotension decreased myocardial oxygenation
What are the effects of severe hypercapnia on the respiratory system?
- CO2 displaces O2 in alveoli leading to Hypoxaemia if there is no supplemental O2 administered
- respiratory acidosis worsens arrhythmias
What effects are the effects of severe hypercapnia on the CNS?
- CO2 regulates cerebral BV diameter so Low CO2 = constricted BV, High CO2 = dilated BV –> inside skull = increased ICP
- Vasoconstriction –> decrease blood –> loss of consciousness
- EtCO2 > 7.4 kPa (>56 mmHg) –> cerebral vasodilation –> increased ICP
- High CO2 lvls –> anaesthetic effects = decreased consciousness
What is intermittent positive pressure ventilation?
- Manual squeezing of the bag on the breathing system or an ambu bag
- mechanical using a ventilator
What equipment is required for IPPV?
- suitable breathing system (Circle, Bain, T-piece)
- +/- automatic ventilator
- Emergencies: ambu bag (self-inflating)
What do you need to do to carry out IPPV?
- normal RR (10-20 bpm)
- normal TV (10-20 ml/kg)
- normal inspiratory to expiratory ratio (1:2) aka active inspiration faster than expiration (passive recoil of lungs)
- watch pressure gauge on system and do not exceed peak inspiratory pressure of 20 cm H2O
- monitor EtCO2 and aim for normal 4.6-6 kPa (35-45 mmHg) –> over ventilation reduces brain vessels –> hypoxaemia
normal partial pressure of CO2 is required to stimulate
the respiratory centre
When CO2 levels are below the normal, there is no drive to…
breathe, therefore P will stop breathing
Long-term lack of breathing leads to…
brain damage due to cerebral vasoconstriction causing brain hypoxia
My patient is breathing spontaneously, when should I start IPPV?
- If EtCO2 is constantly > 7 kPa (55 mmHg)
- if you have a cardiac P, start if EtCO2 is constantly >/= 6 kPa (45 mmHg)
- if increased ICP, start immediately & maintain around 4.6 kPa (35 mmHg)
IPPV raises… therefore it may reduce…
IPPV raises intrathoracic pressure, therefore it may reduce cardiac output –> drop in BP
If a patient is breathing against a ventilator, what should you be aware of or do in response?
- check depth of anaesthesia
- may feel more pain so give more analgesia
- use RR slightly faster than normal
- increase tidal volume by ventilating so thx wall expansion is slightly greater than normal to reduce CO2 & respiratory drive, do NOT exceed PIP 20 cm H2O
Why might a patient fail to breathe following IPPV?
- deep anaesthesia
- hypothermia
- hypocapnia
- pneumothorax
- pain
- residual NMB/opioids
- hypoxic brain damage
What are clinical methods of providing muscle relaxation?
- deep anaesthesia
- regional nerve blocks
- paralyse the P
- drugs w/ muscle relaxant properties (central action - diazepam, guaifenesin) (peripheral action - at the NMJ = paralysis)
What are the ‘take-home messages’ of a neuromuscular blockade?
- All skeletal muscle in paralysed so the patient cannot breathe or move
- does NOT provide analgesia so P can feel all Sx incl pain & all will be consciously perceived
- does NOT provide hypnosis or sedation so P is awake!
What are potential indications for NMB?
- to relax skeletal muscle
- to facilitate control of respiration
- ocular Sx
- TRUE INDICATIONS ARE RARE AND NONE ARE IN GENERAL PRACTICE!
What are some NMB considerations?
- P must be as stable as possible
- P must have rigorous pre-anaesthetic assessment
- P must be intubated & provided w/ IPPV
- Must ensure analgesia & hypnosis
What signs are used to monitor depth of anaesthesia during NMB?
- RR & depth
- jaw tone
- flexor withdrawal reflex
- palpebral reflex
- position of eye
- ALL ARE OF LITTLE USE WHEN PROFOUND NMB IS PRESENT SO YOU CANNOT USE THESE TO ASSESS YOUR PATIENT!
Under NMB, monitoring depth depends on…
- CV system: BP, HR, Pulse qlty
- pupil dilation, lacrimation, salivation
- twitching of facial muscles/tongue
- capnography to ensure adequacy of IPPV
What are important things to remember about a nerve stimulator?
- does not monitor depth of anaesthesia, just depth of paralysis
- all muscle twitches must return back to normal & at normal strength and working diaphragm to generate adequate tidal volume
What are the patterns of stimul used with a nerve stimulator?
- Train of four
- double burst
- tetanic
Reversal of NMB is…
ESSENTIAL!
What drugs are used to reverse NMB?
Neostigmine, edrophonium (anticholinesterase drugs)
Sugammadex
For adequate reversal of NMB, you MUST CONFIRM…
- adequate ventilation
- adequate oxygenation while breathing air
- airway protection
