Hypoxia
Clinical signs of hypoxia include tachypnea, confusion, anxiety, delirium,
, tachycardia, tremor, restlessness, etc.
-There are 6 things that cause hypoxia, i.e. decreased delivery of
oxygen into the bloodstream:
- Shunt: i.e. Pulmonary edema or congenital causes. Cannot completely correct for this with increased FiO2
- VQ mismatch: airflow obstruction (COPD, asthma), inflammation (pneumonia, sarcoid) or vascular obstruction (PE). Increasing FiO2 will correct for this
- Decreased diffusion: i.e. interstitial lung disease
- Anemia
- Hypoventilation: Will see elevated PCO2…can be caused by oversedation, increased abdominal pressure, neuromuscular disease, paralyzed diaphragm or just a weak diaphragm from profound deconditioning or myasthenia gravis/GBS
- Decreased Fi02: This is almost never relevant unless you are at high altitude
-Supplemental O2: Goal to get SpO2 above 90%/PaO2 of 60mm hg; they
don’t need to be 99% (in fact you don’t want them much above 92% if
they have COPD as they will be a chronic CO2 retainer)
Nasal Cannula
- Make sure both prongs are actually in the nose!
- Keep in mind that this won’t work as well for mouth breathers, but should still get some delivery of oxygen.
- Cannot deliver a specific amount of oxygen; 1L/min is ~ FiO2 of 25%-
- each liter above 1 L increases the FiO2 by about 4% (2L is 29%, etc.)
- oxygenation over 4 L --> use humidifier
- regular NC can support only 5 L. For over 6 L use high flow NC.
- In general, if you need more than 5L via NC, you should consider moving to a different modality
Venturi Mask
- More precise oxygen delivery.
- therefore useful in patients who are CO2 retainers (e.g. COPD), where too much O2 will be troublesome.
- http://en.wikipedia.org/wiki/Venturi_mask
Non-Rebreather
▫ Usually 80-90% oxygen delivery
▫ Contains a one-way valve maximizes oxygen delivery
CPAP (continuous positive airway pressure)
▫ Great for hypoxia; functions as externally applied PEEP
▫ Indications for CPAP: hypoxic respiratory failure (despite 100% oxygen administation), Pneumocystis carinii pneumonia, PE, dense lobar pneumonia, atelectasis, shunt
▫ Initiate CPAP at 3-5cm H2O & increase by 3-5 up to 10-15cm H2O to
achieve PaO2 at 60 (SAT of 90%)
▪ BiPAP (Bi-level positive airway pressure)
▫ Helps with ventilation by preventing alveolar collapse during
expiration (think COPD flare)
▫ Indications for BiPAP: hypercarbic resp. failure, COPD exacerbation, asthma, CHF, flash pulmonary edema
▫ Start at 5-10cm H2O over 3-5cm H20; increase incrementally as with
CPAP
▫ Note that for CPAP & BiPAP the patient has to be alert, able to protect
their airway & clear their secretions; they cannot eat while wearing
these masks otherwise with positive pressure they can aspirate &
the food will get pushed further down the bronchial tree
▫ CHECK Code Status! - Remember to consider CPAP or BiPAP as noninvasive
alternatives! If you are not going to intubate because of
code status, make sure you confirm the code status with the patient
or family member. If you are not sure about the code status,
always err on the side of intubating – as this can always be undone
(but not the other way around!)
Indications for Intubation/Mechanical Ventilation:
▫ Impaired airway protection (no gag; alt. MS)
▫ Inadequate oxygenation with alternative less invasive methods
▫ Prevention of aspiration & adequate suctioning
▫ Hyperventilation needs (i.e. with increased ICP)
▫ Acute hypercapnea
▫ Apnea
▫ Upper airway obstruction (laryngeal edema)