Figure 3.

Influence of minute ventilation on breathing frequency for two patients of differing body size. Minute ventilation influences on breathing frequency for two patients of differing body size (50 kg and 85 kg). Using the 6 ml/kg predicted body weight guideline, a small patient would be obligated to breathe at an unacceptably high frequency as minute ventilation increases (15 and 20 l/minute). Observing the commonly used upper limit of 30 breaths/minute, tidal volumes far in excess of the 6 ml/kg criterion would be required to ventilate the smaller patient in this higher range (500 and 670 ml, as opposed to 300 ml). br, breaths; pbw, predicted body weight.