DRINK AND DIVING

By Dr. Jean Yves Berney, Head of Medicine Consultation and Hyperbaric Therapy, Geneva University Hospitals.

Water, of course, is inseparable from diving as an outdoor environment: but we must not forget that it is also a matter of the indoor environment, which is essential to our safety. Why do we have a strong urge to urinate after diving? Why do we recommend drinking more than usual? What is happening inside the body? I propose to answer these questions by detailing the mechanisms and the consequences of immersion in the diver which, I hope, will shed light on the recommendations in force.

THE EFFECTS OF IMMERSION

During immersion, the hydrostatic pressure exerted on the body, will drive blood from the periphery (the limbs essentially) to the thorax which has a distensible vascular network. This is the famous "blood shift" Anglo-Saxon, that can be translated by displacement of blood. And this blood movement can reach a volume of 1 liter! This can be compared with the closure of secondary roads on the road network: result, an excess of traffic on the main roads and highways. Then stuck in the traffic jams, you may think that far too many people took their car that day. In fact the total number of cars is always the same, but moved and focused. Ditto for your blood during the immersion.

DIURETIC MOLECULES ARE PRODUCED

The reduction in vascular capacity (our "road network") will cause an immediate increase in intravascular and intracardiac pressures (of the order of 12 mm Hg). Pressure-sensitive receptors (called baroreceptors) will react to correct them, and the cardiac atria will produce a small diuretic molecule called the "natriuretic peptide" and the hypothalamus will reduce production by the pituitary gland. an antidiuretic hormone, vasopressin. These mechanisms will trigger a diuresis, ie a urine production, called immersion: your urinary flow is then six times greater than in normal situation. And this diuresis is further increased by the cold (diving in the lake, insufficient thermal protection).

AN INEVITABLE WATER DEFICIT

The immersion therefore significantly modifies the water content of the body. During and after the dive, the diver has a marked water deficit. After immersion, with the disappearance of the hydrostatic pressure, the vascular capacity is initially restored and realizes a table of hypodynamic dehydration (low blood flow due to dehydration in relaxed vessels). To maintain proper blood pressure, intense vasoconstriction is observed which will further reduce this vascular capacity. The degassing of the inert tissue gases is considerably reduced, thus altering the desaturation rates.

MICROCIRCULATION LESS GOOD

At the same time the blood containing less water, the hematocrit (relative percentage of the volume of cells circulating in the blood relative to the total volume of the blood) increases. This is called hyperviscosity of the blood, ie it is less fluid, an unfavorable situation for microcirculation potentially already altered by circulating microbubbles. Dehydration is therefore a critical diving situation and is currently recognized as the first risk factor for developing a decompression sickness (ADD). The analysis of the so-called "undeserved" ADDs, namely without any procedural faults (60% of the ADDs) found in the majority of the cases an insufficient hydration.

DRINK WITHOUT THIRST FOR ITS SAFETY

The height of the diver is therefore to find himself dehydrated even though he is surrounded by billions of liters of water. When practicing diving, it therefore becomes essential to reduce the risk of developing ADD to hydrate properly and to avoid any factor aggravating dehydration. But be careful, you must drink before you are thirsty! In children, the sensation of thirst appears when they have already lost 3% of their water supply, in adults when they have lost 3 to 5%, and in people over 70 years of age the sensation thirst appears when it has already lost 5 to 7% of its water supply. Thirst is therefore a mechanism that appears late, so you should not rely on it to judge your state of hydration. As Captain Haddock ® said, it is recommended to be a drink-without-thirst!

BUT ONLY WATER

Immersion diuresis will create a water deficit of about one liter at each dive. But the compensation must be done with non-diuretic drinks! Hydration is effective only if you drink water. Coffee, tea, herbal teas, sodas are to be avoided because the water balance will be zero (which enters is equal to what comes out). Alcohol, a powerful diuretic, will induce a negative balance, aggravating dehydration. In practice in the hour following the dive, the ideal is to drink a liter of water minimum (flat, mineral or not). We will also eat foods rich in water (dairy products, fruits, vegetables), sodium and potassium (bananas).

HANDLING AFTER BUT ALSO FRONT

You must also start your dive by being well hydrated at the base. A study published in 2009 (Gempp & al. BMSH 2009, vol 19, no 1) demonstrated a beneficial effect of a prehydration of more than one liter on the number of circulating bubbles. The diver can even hydrate himself during the dive thanks to adapted systems, but rather reserved for Tech diving. Some divers avoid drinking so as not to feel the strong need to urinate during the 2nd half of the dive, this is a big mistake.

ALCOHOL REMAINS ENEMY NUMBER 1

Powerful diuretic, alcohol remains the number 1 enemy. It also worsens the risk of developing narcosis of the depths. Alcohol consumption should be moderate, only in the evening and interrupted 8 hours before any dive. So be careful with watered evenings followed by dives the next day at 6:00 am. The practice of physical exercise during the 2 hours following the dive is prohibited, because it contributes to dehydration. The water needs of about 2-3 liters per day (drinks and food included) in normal situation will also increase up to 4-5 liters depending on the climatic conditions of the dive site (sun, wind). Free water on diving cruises or safaris is an excellent incentive for good hydration. Exposure to the sun after diving goes in the same direction. Respecting a sufficient surface interval during successive dives also allows the body to recover and correct the water deficits of the previous dive.

In summary, water, shade, rest and good surface interval are the best allies of the diver to fight against the dehydration inherent in the practice of its activity, major risk factor to develop an ADD.

To dive, you have to have a bottle ...