Wednesday, June 11, 2008

The diving reflex: a little knowledge is a dangerous thing

There is an old saying that "a little knowledge is a dangerous thing" and that is certainly the case in homebirth midwifery. A classic example is the claim that waterbirth is safe because of the "diving reflex". There is, indeed, a diving reflex, but it does not mean what homebirth midwives think it means. Because homebirth midwives do not understand the basic physiology of the diving reflex, they do not understand that it cannot and will not prevent a baby from breathing when born in water.

The scientific paper Respiratory responses to cold water immersion: neural pathways, interactions, and clinical consequences awake and asleep contains an explanation of the diving reflex. The explanation is highly technical, but the basic facts are these:

1. The diving reflex exists to prevent drowning. Its primary purpose is to minimize oxygen consumption in pathological situations. It is elicited by the stress of attempting to avoid death, not as a typical response to normal phenomena.

2. Breath holding is only one aspect of the diving reflex. The others are bradycardia and peripheral vasoconstriction; neither bradycardia (slow heart rate) or peripheral vasoconstriction (diminished blood flow to non-essential organs and tissues) are normal events. Bradycardia can be so profound as to lead to cardiac arrhythmias or cardiac arrest.

3. The diving reflex is elicited by COLD water, not by room temperature or warm water.

These facts raise several important questions about waterbirth:

The diving reflex exists to prevent drowning. Clearly babies are not supposed to be in a situation where they might drown. Why would you deliberately expose a baby to drowning and rely on a reflex to save itself from pathological exposure to water? The diving reflex exists because it is UNNATURAL and HARMFUL for the baby to be submersed.

Why would you deliberately expose a baby to the dangers of bradycardia and peripheral vasoconstriction (both being efforts of the body to decrease oxygen consumption to survive pathological oxygen deprivation)?

Why would you rely on a reflex is not even elicited in the presence of warm water?

The authors specifically address the physiologic response to waterbirth. Discussing the claims of waterbirth proponents, they write:
For some time it has been thought that the vagally mediated triad of responses to trigeminal nerve stimulation (apnea, bradycardia, and selective vasoconstriction) that constitute the oxygen conserving "diving response" provides protection against drowning for babies during underwater birth by conserving oxygen. However, it is known that the response in neonatal animals is markedly diminished in the presence of hypoxemia, as can occur with a difficult delivery, and recently underwater birth has been linked to neonatal distress and mortality as part of a near-drowning scenario with radiological evidence consistent with lung aspiration of birthing pool water. Thus it appears that the apnea associated with the diving response is insufficient in newborn babies to ensure that water is not inhaled during underwater delivery.
In other words, the diving reflex does not prevent neonatal drowning in a birth pool of warm water. Those who understand the diving reflex would not expect it to prevent waterbirth drowning.

The key point is this: anyone with a comprehensive knowledge of the diving reflex would never claim that it could prevent drowning at waterbirth. There is a diving reflex, but it does not work the way midwives claim, its effects are not limited to breathholding, and it is elicited by cold water, not warm water.

Waterbirth is the epitome of an unnatural stunt claiming to be "natural" simply because it ignores scientific evidence.


1 Old Comments:

I wouldn't let you any where near my vagina if I was pregnant.

By Anonymous Anonymous, at 11:32 PM