Immersion pulmonary oedema (IPO / swimming‑induced pulmonary oedema)
What it is
Immersion pulmonary oedema (IPO) is an acute, immersion‑associated pulmonary oedema that usually occurs during or shortly after swimming, snorkelling or diving. Immersion (especially cold water and exertion) shifts blood centrally, raising pulmonary capillary hydrostatic pressure and producing interstitial and alveolar fluid.
Clinically it behaves like cardiogenic pulmonary oedema and is managed using the same emergency principles (see NICE - acute heart failure CG187 and Resuscitation Council UK ABCDE guidance).
Pathophysiology
Immersion and hydrostatic pressure drive peripheral venous blood into the thorax, increasing venous return and cardiac filling pressures. Cold exposure and exertion worsen peripheral vasoconstriction and afterload. The rise in pulmonary capillary pressure causes transudation into the interstitium and alveoli. Tight wetsuits, high exertion and pre‑existing cardiac disease reduce reserve and increase risk.
Risk factors
- Pre‑existing cardiac disease (hypertension, left ventricular hypertrophy, heart failure, valvular disease)
- Cold‑water immersion and sudden or strenuous exertion
- Tight wetsuits or restrictive equipment
- Female sex and older age are over‑represented in series, but IPO can occur in fit individuals
- Acute myocardial ischaemia, sodium/fluid loading or vasoactive drugs may precipitate