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Pressure-Controlled Ventilation in Children with Severe Status Asthmaticus*

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Pressure-Controlled Ventilation in Children with Severe Status Asthmaticus* Feature Articles Pressure-controlled ventilation in children with severe status asthmaticus* Ashok P. Sarnaik, MD, FAAP, FCCM; Kshama M. Daphtary, MD; Kathleen L. Meert, MD, FAAP; Mary W. Lieh-Lai, MD, FAAP; Sabrina M. Heidemann, MD, FAAP Objective: The optimum strategy for mechanical ventilation in trolled ventilation, median pH increased to 7.31 (6.98–7.45, p < a child with status asthmaticus is not established. Volume-con- .005), and PCO2 decreased to 41 torr (21–118 torr, p < .005). For trolled ventilation continues to be the traditional approach in such patients with respiratory acidosis (PCO2 >45 torr) within 1 hr of children. Pressure-controlled ventilation may be theoretically starting pressure-controlled ventilation, the median length of time more advantageous in allowing for more uniform ventilation. We until PCO2 decreased to <45 torr was 5 hrs (1–51 hrs). Oxygen describe our experience with pressure-controlled ventilation in saturation was maintained >95% in all patients. Two patients had children with severe respiratory failure from status asthmaticus. pneumomediastinum before pressure-controlled ventilation. One Design: Retrospective review. patient each developed pneumothorax and subcutaneous emphy- Setting: Pediatric intensive care unit in a university-affiliated sema after initiation of pressure-controlled ventilation. All pa- children’s hospital. tients survived without any neurologic morbidity. Median duration Patients: All patients who received mechanical ventilation for of mechanical ventilation was 29 hrs (4–107 hrs), intensive care status asthmaticus. stay was 56 hrs (17–183 hrs), and hospitalization was 5 days Interventions: Pressure-controlled ventilation was used as the (2–20 days). initial ventilatory strategy. The optimum pressure control, rate, Conclusions: Based on this retrospective study, we suggest and inspiratory and expiratory time were determined based on that pressure-controlled ventilation is an effective ventilatory blood gas values, flow waveform, and exhaled tidal volume. strategy in severe status asthmaticus in children. Pressure-con- Measurement and Main Results: Forty patients were admitted trolled ventilation represents a therapeutic option in the manage- for 51 episodes of severe status asthmaticus requiring mechan- ment of such children. (Pediatr Crit Care Med 2004; 5:133–138) ical ventilation. Before the institution of pressure-controlled ven- KEY WORDS: status asthmaticus; ventilators; mechanical; inten- tilation, median pH and PCO2 were 7.21 (range, 6.65–7.39) and 65 sive care; child; preschool; child; adolescent torr (29–264 torr), respectively. Four hours after pressure-con- sthma remains one of the most mortality rates among patients receiving constant would achieve pressure equili- common causes of hospitaliza- mechanical ventilation can be consider- bration earlier during inspiration com- tion in children despite consid- able. Markedly increased airway resis- pared with more obstructed areas. Thus, erable advances in our under- tance and prolonged time constant are units with shorter time constants would Astanding of its pathophysiology and characteristic features of respiratory me- attain their final volume earlier in inspi- management (1). Severe acute exacerba- chanics in asthma. Traditionally, volume ration whereas those with longer time tions of asthma, which are refractory to control has been the preferred mode of constants would continue to receive ad- pharmacologic interventions, are poten- ventilation (2–4). However, as tidal vol- ditional volume later in inspiration. This tially life threatening and may require ume is delivered with constant flow in would result in more even distribution of mechanical ventilation. Morbidity and traditional volume-controlled ventilation inspired gas, delivery of more tidal vol- (VCV), relatively less obstructed airways ume for the same inflation pressure, and with shorter time constant are likely to improved dynamic compliance compared *See also p. 191. receive more volume throughout inspira- with VCV. A disadvantage of PCV is that From the Division of Critical Care Medicine, De- tion compared with more obstructed air- the delivered tidal volume will vary de- partment of Pediatrics, Children’s Hospital of Michigan, ways with longer time constant. This pending on the respiratory system resis- Wayne State University School of Medicine, Detroit, MI. Presented, in part, at the American College of would result in uneven ventilation, tance. In a disease such as asthma with Chest Physicians Annual Meeting, Philadelphia, PA, higher peak inspiratory pressure, and a potentially rapid changes in airway resis- November 2001. decrease in dynamic compliance. It has tance, the tidal volume received by the Address requests for reprints to: Ashok P. Sarnaik, been suggested that pressure-controlled patient may change dramatically for the MD, Children’s Hospital of Michigan, 3901 Beaubien, Detroit, MI 48201. E-mail: [email protected] mode is better suited for mechanical ven- same amount of inflation pressure. This Copyright © 2004 by the Society of Critical Care tilation in asthma (5, 6). With pressure- would necessitate frequent changes in Medicine and the World Federation of Pediatric Inten- controlled ventilation (PCV), because of a pressure control level to accommodate sive and Critical Care Societies constant inflation pressure, relatively less changes in resistance. Pressure-regulated DOI: 10.1097/01.PCC.0000112374.68746.E8 obstructed lung units with shorter time volume control may be more advanta- Pediatr Crit Care Med 2004 Vol. 5, No. 2 133 geous than PCV because it guarantees as indicated by exhaled tidal volume Ͼ12 episodes in 45 patients received mechan- tidal volume by regulating inflation pres- mL/kg and resolution of respiratory acidosis. ical ventilation. Four patients were rap- sure in the face of changing dynamic Patients were weaned from mechanical venti- idly weaned off mechanical ventilation compliance. However, pressure-regulated lation when their flow waveforms demon- and extubated within 4 hrs of admission volume control is a relatively new mode strated an exhalation phase short enough to and were excluded from the analysis. One allow spontaneous breathing in between ma- of ventilation, not available in most ven- patient sustained cardiorespiratory arrest chine-delivered breaths and their PCO2 values tilators, and therefore not well studied. were Ͻ45 torr. Pharmacologic paralysis was at home, was resuscitated, but was clini- The objective of our study is to describe stopped before weaning. Patients were weaned cally brain dead on arrival to the ICU and our experience using PCV in the initial according to physician preference by decreas- also was excluded from analysis. The re- management of children with status asth- ing PCV synchronized intermittent mandatory maining 40 patients were admitted for 51 maticus according to a predetermined ventilation rate, by providing pressure sup- episodes of status asthmaticus; 34 pa- strategy. port, by changing to VCV, or by combining tients were admitted once, two patients VCV with pressure support. were admitted twice, three patients were MATERIALS AND METHODS Baseline Patient Characteristics. Age, gen- admitted three times, and one patient der, race, past medical history, current home was admitted four times. Twenty-one pa- medications, referral source, and medications Study Population. Medical records of chil- tients (41%) were intubated and mechan- administered before and after mechanical ven- dren receiving mechanical ventilation for sta- ically ventilated for respiratory acidosis, tus asthmaticus, admitted to the intensive tilation were recorded. Reasons for intubation care unit (ICU) of Children’s Hospital of Mich- and mechanical ventilation were categorized 19 (37%) for clinical impression of fa- igan between January 1, 1995, and December as a) cardiorespiratory arrest; b) respiratory tigue, and 11 (22%) for respiratory arrest. 31, 2000, were reviewed. Patients who were arrest (absent or agonal respirations); c) respi- Baseline characteristics of patients are Յ Ն intubated before admission and extubated ratory acidosis (pH 7.32 with PCO2 50 shown in Table 1. The racial distribution within 4 hrs of admission, and those who had torr), with clinical impression of respiratory of patients reflects our referral base for suffered cardiopulmonary arrest and met clin- fatigue (severe retractions, inability to speak a medical/surgical emergencies. ical criteria of brain death on admission, were complete sentence, obtunded sensorium and Medical therapy administered before excluded. The Wayne State University Human diaphoresis); and d) clinical impression of re- and during institution of PCV is shown in spiratory fatigue without documented respira- Investigation Committee approved the study Table 2. All episodes were managed with tory acidosis. and waived the need for informed consent. sedatives and analgesics, and 46 episodes Ventilatory Strategy. All patients were Outcome Measures. Ventilator settings and managed with PCV as the initial ventilatory arterial or capillary blood gas values were re- were managed with neuromuscular mode. Puritan Bennett 7200 (Nellcor Puritan corded before initiation of PCV, within 1 hr of blocking agents from the initiation of Bennett, Pleasanton, CA), VIP Bird (Bird Prod- starting PCV, and at 4, 8, and 12 hrs after PCV. Sedation and analgesia were ucts, Palm Springs, CA), and Siemens 900C initiation of PCV. Duration of mechanical ven- achieved with midazolam
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