Tuesday February 27, 2007
'insensible' water loss

In ICU, total volume status is the key to whole management of patient care. Often ignored aspect is 'insensible' water loss. Most important point to understand: this is loss of pure water without any associated solute loss. 'Insensible' water loss happens via 2 routes.

• Water evaporation via skin (call transepidermal diffusion), which is about 400 ml/day in healthy adult and
  
• Water evaporation loss from the respiratory tract, which is also about 400 ml/day in healthy adult

In ICU patients, 'insensible' water loss is higher due to fever, increase catabolism, surgical status and higher minute ventilation. It is estimated that in hospitalized patient it reaches upto 1200 ml/day or may be higher in sicker or surgical patients. The management should take into consideration of full clinical picture based on blood pressure, heart rate, CVP, urine output etc. In ventilated patients , 'insensible' water loss can be minimized by humidification of inspiried gas at 37°C.

Surgery itself is a big contributor in 'insensible' water loss. Per one study during routine cardiac surgery in adults, insensible losses of 1 litre are to be expected 1. See our previous pearl in this regard - fluid-facts .


Another related previous pearl: Arterial line and volume assessment




References:

1.Insensible fluid loss during cardiac surgery - Critical Care 2001, 5(Suppl 4):2