Respiratory Alkalosis DDx


  • Stimulated respiratory drive
    • CNS
      • CVA, ICH, psychogenic
    • Hypermetabolic
      • Thyrotoxicosis
      • Pregnancy (Progesterone)(Secondary to reduced FRC)
      • Sepsis (fever) (often before metabolic acidosis)
      • DT, anxiety, pain
      • DKA and aspirin OD
    • Environmental
      • HYPERthermia (Heat tetany)
    • Drugs
      • Aspirin OD
      • Progesterone
    • Liver failure (encephalopathy) with hyperammonaemia (ammonia)
  • Iatrogenic (mechanical ventilation)
  • Hypoxemia induced
    • Pneumonia, PE, asthma
    • Congenital heart disease
    • Chronic altitude compensation
    • Early in altitude acclimatization
  • Compensation for metabolic acidosis


  • Self-perpetuating process: Hyperventilation removes CO2 which causes cerebral acidosis and stimulates further increase in ventilation
  • Chronic respiratory alkalosis is unique in that it CAN have full metabolic compensation (Only acid-base disorder that allows this)


  • Associated changes
    • HYPOcalcaemia, HYPOkalaemia, HYPOphosphatemia
    • Decreased Co2 reduces H+ binding, increases negative charge of proteins and increases binding of calcium to proteins
      • Thus reducing ionised calcium
    • Hypocalcaemia with tetany and carpopedal spasm
  • Shift 02 dissociation curve to the left (Alkalosis) (Increased affinity of Hb for O2)


  • Treat underlying cause
  • Re-breather mask

CCC Differential Diagnosis Series


Anosmia, Ataxia, Blepharospasm, Bulbar and Pseudobulbar palsy, Central Pontine Myelinosis, Cerebellar Disease, Chorea, Cranial nerve lesions, Dementia, Dystonia, Exophthalmos, Eye trauma, Facial twitches, Fixed dilated pupil, Horner syndrome, Loss of vision, Meningism, Movement disorders, Optic disc abnormality, Parkinsonism, Peripheral neuropathy, Radiculopathy, Red eye, Retinal Haemorrhage, Seizures, Sudden severe headache, Tremor, Tunnel vision


Bronchial breath sounds, Bronchiectasis, High airway pressures, Massive haemoptysis, Sore throat, Tracheal displacement


Atrial Fibrillation, Bradycardia, Cardiac Failure, Chest Pain, Murmurs, Post-resuscitation syndrome, Pulseless Electrical Activity (PEA), Pulsus Paradoxus, Shock, Supraventricular tachycardia (SVT), Tachycardia, VT and VF, SVC Obstruction


Abdominal distension, Abdominal mass, Abdominal pain, Asterixis, Dysphagia, Hepatomegaly, Hepatosplenomegaly, Large bowel obstruction, Liver palpation abnormalities, Lower GI haemorrhage, Malabsorption, Medical causes of abdominal pain, Rectal mass, Small bowel obstruction, Upper GI Haemorrhage


Genital ulcers, Groin lump, Scrotal mass, Urine colour, Urine Odour, Urine transparency


Arthritis, Shoulder pain, Wasting of the small muscles of the hand


Palmar erythema, Serious skin signs in sick patients, Thickened Tethered Skin, Leg ulcers, Skin Tumour, Acanthosis Nigricans


Diabetes Insipidus, Diffuse Goitre, Gynaecomastia, Hirsutism, Hypoglycaemia, SIADH, Weight Loss




Floppy infant 


Anaphylaxis, Autoimmune associated diseases, Clubbing, Parotid Swelling, Splinter haemorrhages, Toxic agents and abnormal vitals, Toxicological causes of cardiac arrest


CHEST: Atelectasis, Hilar adenopathy, Hilar enlargement on CXR, Honeycomb lung, Increased interstitial markings, Mediastinal widening on mobile CXR, Pulmonary fibrosis, Pseudoinfiltrates on CXR, Pulmonary opacities on CXR,
Gas on abdominal X-ray, Kidney mass,
Intracranial calcification, Intracranial structures with contrastVentriculomegaly,
OTHER: Pseudofracture on X-Ray


LOW: Anaemia, Hypocalcaemia, hypochloraemia, Hypomagnesaemia

HIGH: Bilirubin and Jaundice, HyperammonaemiaHypercalcaemia, Hyperchloraemia, Hyperkalaemia, Hypermagnesaemia

ACID BASE: Acid base disorders, Resp. acidosis, Resp. alkalosis,

Creatinine, CRP, Dipstick Urinalysis, Laboratory Urinalysis, Liver function tests (LFTs), Pleural fluid analysis, Urea, Urea Creatinine Ratio, Uric acid, Urinalysis, Urine Electrolytes


CCC 700 6

Critical Care


BA MA (Oxon) MBChB (Edin) FACEM FFSEM. Emergency physician, Sir Charles Gairdner Hospital.  Passion for rugby; medical history; medical education; and asynchronous learning #FOAMed evangelist. Co-founder and CTO of Life in the Fast lane | Eponyms | Books | Twitter |

One comment

  1. Also add dysfunctional breathing to the list. Common cause in the asthmatic/COPDer who seems to have dyspnoea symptoms out of keeping with the degree of lung pathology. End up in a self perpetuating state of chronic hyperventilation and usually breathing at higher lung volumes but never fully exhaling out.

    Retraining with Resp Physios familiar with this pathology aims to get the patients brain to reset back to normal CO2/pH targets + getting all the Resp muscles back to normal functioning, but can be a lengthy process.

    I end up doing some immediate intervention regarding trying to do slow but normal sized breaths (not slow deep breaths) – it’s super hard for them but repeatedly trying to & employing distraction therapy helps. Sometimes need a bit of benzos or opioids if really struggling to settle themselves. Plus with these patients I find have to back off on the asthma treatment as the side effects of that are usually making it worse and making the whole thing feed on itself.

    Tricky patients to spot though unless you’re very familiar with severe bronchospasm presentations, their breathing patterns and management as have to spot those ones where it just doesn’t all add up. And most people won’t feel confident backing away from the asthma management in someone who’s probably still got wheeze and high work of breathing.

    A good history and review of previous gases and bicarbs can help get the diagnosis.

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