Intensive Care Med (2007) 33:203DOI 10.1007/s00134-006-0423-z PEDIATRIC CORRESPONDENCE

Ritesh AgarwalAlok Nath

Peak pressures or plateaupressures in acute asthma

Accepted: 20 September 2006Published online: 26 October 2006© Springer-Verlag 2006

This comment refers to the article availableat: http://dx.doi.org/10.1007/s00134-006-0424-y

Sir: We read with interest the arti-cle “Isoflurane therapy for severerefractory status asthmaticus inchildren” wherein the authors de-scribe the use of inhaled isofluranein a series of children with life-threatening asthma [1]. However,it was surprising to note that inthe algorithm the authors used thepeak inspiratory pressure ratherthan plateau pressure for titrationof tidal volumes and as a surrogatefor lung hyperinflation. Peak inspi-ratory pressure does not reflect peakalveolar pressure or the degree ofoverdistension of alveolar structures,as the high pressures are encoun-tered largely by robust proximalairways.

On the other hand, plateau pres-sures (measured after an inspiratoryhold of 0.5–1.5 s) are most reflectiveof the peak alveolar pressure (alsoused in calculation of transpulmonarypressure and static lung compliance).Plateau pressures of more than30–35 cmH2O risk barotraumaand hemodynamic compromisewithout tangible benefit to gas

exchange or oxygen delivery [2].Ina classical case of acute asthmarequiring mechanical ventilation,the peak inspiratory pressures andplateau pressures are in the range of75–100 cmH2O and 25–35 cmH2Orespectively [3]. Therefore high peakpressures are generally accepted, andin fact recent data have failed to showa relationship between peak pressuresand complications of mechanicalventilation [4]. Also, a strategy aimedat reducing inspiratory time with fastinspiratory flow rates and the squareinspiratory flow waveform is usuallyassociated with high peak inspiratorypressures.

The importance of recognizinghigh peak inspiratory pressures liesin setting the alarms to a level higherthan the peak pressure, otherwise theventilator would cycle with everybreath and would not deliver the settidal volume, leading to hypoventila-tion and worsening gas exchange [5].In addition, the difference betweenthe peak and plateau pressure repre-sents the contribution from airwayresistance to the value of the peakpressure [6].

In conclusion, the measurementof peak pressures has limited clinicalrelevance; because of their impor-tant resistive component, the peakpressures do not reflect the alveolardistension pressure in most of thelung.

References1. Shankar V, Churchwell KB, Desh-

pande JK (2006) Isoflurane therapyfor severe refractory status asthmati-cus in children. Intensive Care Med32:927–933

2. Marini JJ (1991) Monitoring the mech-anics of the respiratory system. In:Tobin MJ (ed) Respiratory monitoring.Churchill Livingstone, New York,pp 163–196

3. Mutlu GM, Factor P, Schwartz DE,Sznajder JI (2002) Severe status asth-maticus: management with permissivehypercapnia and inhalation anesthesia.Crit Care Med 30:477–480

4. Williams TJ, Tuxen DV,Scheinkestel CD, Czarny D, Bowes G(1992) Risk factors for morbidity inmechanically ventilated patients withacute severe asthma. Am Rev RespirDis 146:607–615

5. Hess DR, Kacmarek RM (2002)Asthma. In: Hess DR, Kacmarek RM(eds) Essentials of mechanical ven-tilation. McGraw-Hill, New Delhi,pp 196–204

6. Oddo M, Feihl F, Schaller MD, Perret C(2006) Management of mechanicalventilation in acute severe asthma:practical aspects. Intensive Care Med32:501–510

R. Agarwal (�) · A. NathPostgraduate Institute of Medical Educationand Research, Department of PulmonaryMedicine,Sector-12, Chandigarh160012, Indiae-mail: ritesh@indiachest.org;riteshpgi@gmail.comTel.: +91-172-2784976Fax: +91-172-2745959; +91-172-2748215