Airway, Breathing and Oxygen Therapy

Oxygen Therapy: When and How Much

In short: give oxygen to correct low oxygen levels, aim for a target SpO2, and set the flow for the job.

When to give it

• Give oxygen for hypoxia (SpO2 below 94%): cardiac arrest/resuscitation, respiratory distress, severe asthma, anaphylaxis, shock, major trauma, drowning.
• Always 100%, whatever the oximeter says:
  • CO poisoning / smoke inhalation — the pulse oximeter counts carboxyhaemoglobin as oxygen, so it gives a falsely normal reading.
  • Decompression illness (divers).

Target SpO2 — two rules you will hear

• Oxygen-therapy rule (BTS oxygen guideline): titrate to 94–98%. Known COPD or CO2-retaining patients: 88–92% — too much oxygen can depress their breathing, so turn the flow down to target.
• Bedside rule of thumb used when taking vital signs: normal SpO2 is 95% or more; below 95% after an injury → act; around 90% → give oxygen. Exception: chronic heart or lung patients who normally sit at 85–90%.
• The two rules agree in practice: below the mid-90s, look for a cause and be ready with oxygen; with COPD, aim lower.

Flow rate and oxygen concentration (face mask)

• Standard therapy: 4–6 L/min by mask.
• Resuscitation: 15 L/min through a bag-valve-mask (BVM, “AMBU”) with reservoir — about 90% O2, the most you can deliver on board.
• Nasal prongs: for non-critical patients, or when the patient will not tolerate a mask (or hold the mask just off the face).

Pocket mask

• Kept in the AED pouch with 2 sets of gloves, scissors, a shaver and a swab.
• Has a one-way valve. It only works with a complete seal: press it down and tilt the head back.
• During CPR, leave it on the face between compressions (see CPR, AED and Choking).

Oxygen Equipment, Cylinders and Hazards

In short: know your cylinder, set it up cleanly, respect the fire risk and know how long your oxygen will last.

Kit and maintenance

• Typical yacht/ship kit: an oxygen D cylinder with a multiflow regulator. Medical stores rules: MSN 1905 (M+F).
• Monthly onboard checks · hydraulic test every 5 years · service every 3 years · oxygen refilled every year.
• Pin Index system (older cylinders): the cylinder valve has gas-specific pin holes and the regulator yoke has two matching pins, so the wrong regulator physically cannot fit. A Bodok seal (sealing washer) sits between valve and yoke. Keep about 6 spare Bodok washers.

Giving oxygen — step by step

1. Confirm the indication (SpO2 below 94%, or always 100% for CO/smoke and decompression illness).
2. Identify the cylinder: medical oxygen is black with white shoulders. Use no other colour. Don’t trust colours abroad — the US and India use different codes.
3. Crack (flush) the valve briefly before fitting the regulator to blow out dirt. Check for dents, rust and leaks.
4. Fit the regulator hand-tight only — no spanners.
5. Set the flow: 4–6 L/min standard · 15 L/min with BVM + reservoir for resuscitation · nasal prongs for mild cases.
6. Titrate to target: SpO2 94–98% (COPD 88–92%).
7. Watch the hazards (below).
8. Defective cylinder: empty it slowly outdoors, never refill it, and store empties apart from full ones.

The four hazards

• 🔥 Fire: oxygen feeds combustion. No oil or grease on fittings, no naked flames, ventilate the space.
• ⏳ Limited supply: work out endurance = cylinder pressure × water volume ÷ flow. Example: a 2.3 L cylinder at 137 bar holds about 315 L → about 21 min at 15 L/min or about 52 min at 6 L/min. Read the figures on your own cylinder label.
• 💨 Dry gas: long use dries the mouth and airway → humidify.
• ❗ Oxygen is not ventilation: if the patient is not breathing, you must breathe for them with a BVM; a mask alone does nothing.

Airway Adjuncts: Guedel (OPA) and Nasal Airway (NPA)

In short: adjuncts hold the tongue away from the back of the throat. They keep the airway open, but they do not protect it from vomit.

What adjuncts do — and don’t do

• They keep the airway patent only. No oxygen connects to them; if they block, suction through them.
• Neither OPA nor NPA prevents aspiration of vomit → an unconscious breathing patient goes in the recovery position with continuous monitoring.
• Supraglottic airways (i-gel type) also exist; some yachts carry them.

Guedel / oropharyngeal airway (OPA)

• A rigid, curved tube in the mouth that keeps the tongue off the back of the throat.
• Only for a completely unconscious patient with no gag reflex.
• If they gag, cough or react → remove it immediately (risk of vomiting, laryngospasm, aspiration). Gagging means they are not fully unconscious; spitting it out means they are waking up.
• On board: usually only 2 sizes — 6 (red) and 7 (yellow), the commonest adult sizes — not the full set.

Insertion

1. Confirm: completely unconscious, no gag reflex.
2. Size it against the cheek: corner of the mouth to the angle of the jaw.
3. Wrong size makes things worse: too short pushes the tongue back; too long can trigger laryngospasm.
4. Insert upside down (curve towards the palate), then rotate 180° as it reaches the soft palate.
5. Children: insert it the right way up straight away, using a tongue depressor — their palate is delicate.
6. Push until the flange rests on the teeth; secure with ribbon tied loosely.
7. Gag or cough → out at once.
8. Recovery position + continuous monitoring.

Nasopharyngeal airway (NPA)

• A soft, flexible tube passed through the nostril to the back of the throat, behind the tongue.
• Big advantage: tolerated by semi-conscious patients who still have a gag reflex — also useful with a clenched jaw (trismus) or mouth injuries, when an OPA cannot go in.
• Choose it when airway swelling is coming — e.g. facial burns or blast injury can swell dramatically within about 10 min.
• Contraindication: suspected basal skull fracture — head injury with CSF or blood from nose or ears, raccoon eyes, Battle’s sign (bruising behind the ear). The tube could enter the skull.
• Caution: nasal fractures, bleeding disorders.

Insertion

1. Rule out a basal skull fracture.
2. Size it: length nostril to ear tragus; width about the patient’s little finger. Average adult male ≈ size 7.
3. Lubricate well (it comes with its own lubricant).
4. Right nostril first, bevel towards the septum. Advance gently with a slight twist, straight back along the floor of the nose — not upwards.
5. Resistance → try the other nostril (they are rarely equal). Never force it. Nosebleed is the commonest complication; too long a tube can cause gagging or vomiting.
6. The flange (or a safety pin through it) stops it sliding into the nose.
7. No aspiration protection → recovery position + continuous monitoring.

The Unconscious Patient: Looking for the Cause

In short: run DRSABC, then a full ABCDE, and at every step look for clues to why the patient lost consciousness (LOC).

Airway and breathing clues — look in the mouth

• Cyanosis → low SpO2? (dark skin: check the inside of the lips / gums)
• Swelling → anaphylaxis?
• Injury → major trauma?
• Froth or bitten tongue → seizure?
• Soot (carbon) in the mouth → smoke inhalation.
• Sweet smell → diabetic emergency (ketones smell like nail-polish remover).
• Almond smell → cyanide (from burning plastics and foams in a fire).

Circulation clues

• Hands and feet cold, clammy and sweaty → hypovolaemic shock? · Warm and red → anaphylaxis / sepsis?
• Pulse: fast? irregular? weak? · Low BP → shock?
• Tender abdomen: peritonitis? bruising? trauma? pelvis?
• Anatomy pointers: right-side pain → liver / gallbladder; the stomach fundus is on the left (reflux eases lying on the left); abdominal pain in a man around 50+ → think of an aortic rupture too.

Exposure clues

• Urticarial rash (hives) → anaphylaxis? · Non-blanching, blood-coloured rash → meningitis?
• Temperature: signs of sepsis or heat stroke.
• Surroundings: possible trauma · injection marks (drug use) · a hot environment.

Common causes of unconsciousness

• Anaphylaxis / asthma / pneumonia
• Peritonitis
• Sepsis / infectious disease
• Heat exhaustion / heat stroke / dehydration
• Drugs / alcohol
• Diabetic collapse
• Faints (low blood pressure)
• Fits (seizures)
• Toxic gases (lack of oxygen)
• Trauma / head injury / external or internal bleeding

Enclosed spaces: H2S smells of rotten eggs at low levels but knocks out your sense of smell at high levels; it is heavier than air, flammable and kills in minutes. Rotting cargo also gives off CO2, and the air may be short of oxygen. Only trained crew go in: space ventilated, atmosphere tested, a person outside in constant contact with a spare BA set ready. Confined spaces still kill about 2 people a day across industry.

Finishing the examination

• Low GCS → recovery position and secure the airway.
• Write down your findings in the patient’s notes.
• Explain them to the patient and say what happens next: treatment, radio medical advice, reassessment.
• Keep reassessing — patients deteriorate.
• Chart the observations, e.g. a NEWS-style chart: respirations, SpO2, air or oxygen, blood pressure over time, with red/orange bands for abnormal values so a decline jumps out.

GCS and Vital Signs Monitoring

In short: score consciousness with AVPU, then GCS for serious head injury; repeat vital signs often enough to stay one step ahead.

Glasgow Coma Scale (SCMG)

• AVPU first (Alert, Voice, Pain, Unresponsive). Use GCS for serious head injuries and repeat it often to track deterioration.
• Eyes (1–4): open spontaneously › to command › to pain › none. Eyes swollen shut cannot be scored.
• Motor (1–6): obeys commands › localises pain (pushes your hand away) › withdraws from pain without localising › decorticate (stiff, arms bent inwards) › decerebrate (arms straight, hands turned outwards — worse, brain damage) › none.
• Verbal (1–5): oriented (date, place, name) › confused › inappropriate words › incomprehensible sounds › none.
• Total 3–15. 8 or less = very serious; 13–15 = best.
• Every unconscious patient gets a blood glucose test — glucose swings after trauma, and the body cannot heal without it.

Vital signs — practical tips

• Blood pressure: a manual cuff is the most accurate. Electronic units need yearly calibration, and a drop can ruin them. Cuff 2 fingers above the elbow crease.
• Beware the white-coat effect: one high reading is not hypertension. Re-check morning and evening for a week, and take more than one reading before you trust a number.
• How often: critical or chest injury → every 15 min, cuff left on. Once stable → every 30 min, then hourly.
• SpO2: normal 95% or more. Cold hands read falsely low → warm them. Slumped posture lowers the reading → sit them up, take a few breaths, measure again.
• Respirations: adult range 12–20/min (a resting ideal is often quoted as 10–12). 25/min is out of range → think shock or low oxygen.

Recovery Position and the Face-Down Casualty

In short: an unconscious patient who is breathing normally goes on their side to keep the airway clear. Choose the side with care.

Recovery position

1. Casualty breathing normally (depending on signs and symptoms) → recovery position.
2. Loosen tight clothing at the neck and waist first.
3. Roll them on their side: head tilted back, airway open, top knee bent to stop them rolling; place the arm so they cannot roll over.
4. Keep the airway secure and monitor continuously.

Which side?

• Pregnant → LEFT: the womb does not press on the vena cava (same reason as the CPR tilt in late pregnancy).
• Seasick → LEFT: the stomach outlet (pylorus) points right, so lying left slows emptying into the gut and reduces reflux and vomiting.
• Swallowed poison → LEFT: the poison stays in the deepest part of the stomach — less vomiting and inhalation, and less passes on to the small intestine, where most is absorbed.
• Bleeding from the mouth or a head wound → bleeding side DOWN, so blood drains out (blood kept inside raises pressure on the brain). If injuries conflict, the head/brain wins.
• Broken femur: never lie them on it.
• Chest injury (exception): sit them up, leaning towards the INJURED side — the good lung can expand and leaning on the sore side eases the pain.

Memory hook — “LEFT is best”: pregnancy, seasickness and swallowed poison all go on the left.

Face-down casualty

1. Don’t roll them straight away. Check breathing from behind (the back rises); the mouth drains on its own; slide your hands underneath to feel for bleeding.
2. Turn them only if you cannot confirm breathing (CPR needed) — roll them towards the side opposite the way the face is pointing.
3. Examine the back when you log-roll them onto the stretcher — don’t roll them back and forth.