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 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 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 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 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 phase short enough to and were excluded from the analysis. One allow spontaneous 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 and morphine. (Siemens-Elma, Solna, Sweden) were used for tilation, intensive care and hospitalization, Ketamine was used as an adjunct sedative mechanical ventilation. All patients received a complications, and mortality also were noted. in six patients. Vecuronium was used for Complications evaluated included pneumo- positive end-expiratory pressure of 4 cm H2O. pharmacologic paralysis. All episodes The level of pressure control (peak inspiratory thorax, pneumomediastinum, subcutaneous were treated with inhaled albuterol and Ϫ emphysema, the need for fluid resuscitation pressure positive end-expiratory pressure) intravenous corticosteroids, and 94% re- and vasopressor agents, and neurologic mor- was initiated at 25–30 cm H2O for patients age Ͼ bidity. Fluid resuscitation was provided for ceived intravenous theophylline (7). So- 1–5 yrs and at 30–35 cm H2O for patients 5 yrs of age. was initially set at hypotension and/or clinical impression of hy- dium bicarbonate or tris-(hydroxy- 12–16 breaths/min for patients age 1–5 yrs povolemia (cold, clammy extremities and de- methyl) aminomethane was administered and at 10–12 breaths/min in patients Ͼ5 yrs. creased urine output). Vasopressor agents in 11 episodes for metabolic acidosis. An- The inspiratory to expiratory ratio was set at were started for hypotension resistant to fluid tibiotics were given in five episodes for 1:4. Exhaled tidal volume and flow-time curve resuscitation. suspected bacterial infection. Arterial on ventilator waveform graphics were contin- Statistical Analysis. Categorical variables catheters were placed in 45 episodes. uously monitored. Pressure control was ad- are represented by the absolute count and Bronchoscopy was performed in five for percentage in each category. Continuous vari- justed by changes of 2–5cmH2O to achieve an management of plugging. ables are represented by the median and exhaled tidal volume of 10–12 mL/kg. In gen- Ventilator settings that achieved the range. Both capillary and arterial blood gas eral, the increase in pressure control was lim- most satisfactory within the values were used for analysis of pH and PCO . ited to 50 cm H2O. Ventilatory rate, inspira- 2 tory time, and expiratory time were selected to Since all patients received albuterol nebuliza- first 8 hrs in age groups 1–5 yrs, 6–10 ensure near-complete return of expiratory tion with 100% oxygen delivered through the yrs, and 11–18 yrs are shown in Table 3. flow to baseline and to achieve the desired inspiratory limb of the ventilator, the actual Blood pH and PCO2 on admission and at 1, exhaled tidal volume. Pressure control, rate, FIO2 delivered to the patient could not be ac- 4, 8, and 12 hrs after institution of PCV inspiratory time, and expiratory time were curately determined. Therefore, PaO2/FIO2 val- are shown in Table 4. Seven patients had Ͼ ues were omitted from statistical interpreta- Ͻ subsequently adjusted to maintain pH 7.3 PCO2 45 torr, 21 patients (41%) had Ͻ tion. Blood gas measurements over time were and PCO2 50 torr or exhaled tidal volume of PCO between 45 and 70 torr, 12 patients compared using Wilcoxon signed ranks test. 2 10–12 mL/kg. The FIO2 was adjusted to main- (24%) had PCO between 71 and 99 torr, Ͼ We considered p Ͻ .05 to be significant. 2 tain SpO2 95%. The optimal settings for Ն and eight patients (16%) had PCO2 100 each patient were defined as the combination torr before initiation of PCV. Blood gases of pressure control, rate, and inspiratory time within the initial 8 hrs that resulted in the RESULTS were not obtained before PCV in three patients because emergent intubation first observed decline in PCO2 that was sus- tained on subsequent blood gas determina- During the study period, 278 patients and mechanical ventilation were clini- tions. Pressure control was reduced by 2–5cm were admitted to the ICU for manage- cally deemed necessary. Of the ten pa- Ͻ H2O with improvement in airway obstruction ment of status asthmaticus. Of these, 56 tients with PCO2 45 torr or nondocu-

134 Pediatr Crit Care Med 2004 Vol. 5, No. 2 Table 1. Baseline characteristics (n ϭ 51) monly used are PCV and VCV. In PCV, a predetermined airway pressure is main- a Age, yrs 9.0 (0.8–17) tained for a set period of inspiratory time. Males 32 (63)b Race The delivered tidal volume depends on African-American 49 (96) and dynamic compli- White 1 (2) ance. In VCV, a predetermined tidal vol- Hispanic 1 (2) ume is delivered throughout the inspira- Reason for intubation Respiratory arrest 11 (22) tory phase. The resultant peak airway Respiratory acidosis 21 (41) pressure is a dependent variable deter- Clinical impression of fatigue 19 (37) mined by airway resistance and dynamic Previous ICU admission for status asthmaticus 26 (51) compliance. Dynamic compliance is Previous mechanical ventilation for status asthmaticus 18 (35) greatly influenced by flow-resistive prop- Home medications Inhaled ␤-agonists 51 (100) erties of the lung. In diseases with in- Inhaled corticosteroids 19 (37) creased airway resistance, dynamic com- Oral corticosteroids 4 (8) pliance can be sharply reduced at higher Theophylline 6 (12) respiratory rates because of an increase in Referral source Emergency room 26 (51) air flow. Another important consider- General ward 5 (10) ation in mechanical ventilation is that of Another hospital 20 (39) time constant, a product of static compli- ance and resistance. Time constant is a ICU, intensive care unit. reflection of the amount of time that is a b Data are median (range); data are absolute counts (%). necessary for equilibration of proximal airway pressure and alveolar pressure. Asthma is a predominantly obstructive Table 2. Medical therapies (n ϭ 51) combining VCV with pressure support in ten episodes. The duration of mechanical airway disease characterized by long time Before During ventilation was 29 hrs (4–107 hrs), inten- constant requiring a relatively long time PCV PCV sive care 56 hrs (17–183 hrs), and hospi- for approximation of pressure at proximal talization 5 days (2–20 days). Complica- airway and alveoli during inspiration and Inhaled expiration. Expiratory time constant is Albuterol 51 (100) 51 (100) tions encountered are shown in Table 5. Of note, fluid resuscitation was provided prolonged even more because of a greater Ipratropium bromide 21 (41) 24 (47) increase in expiratory resistance result- Isoproterenol 8 (16) 0 in 78% of episodes. Two patients had Helium-oxygen 0 25 (49) pneumomediastinum at admission before ing from an upstream (closer to the ter- Intravenous institution of PCV. In both patients, minal airways) displacement of the equal Corticosteroids 51 (100) 51 (100) pneumomediastinum resolved during pressure point and narrowing of airways Theophylline 28 (55) 48 (94) during expiration. As opposed to disor- Isoproterenol 6 (12) 21 (41) PCV. One patient each developed pneu- Magnesium sulfate 7 (14) 9 (18) mothorax and subcutaneous emphysema ders of static compliance with short time Ketamine 0 6 (12) after initiation of PCV. Subcutaneous em- constants such as acute respiratory dis- Terbutaline 3 (6) 0 tress syndrome that can be managed with Subcutaneous physema resolved spontaneously and pneumothorax resolved after insertion of relatively faster respiratory rates, disor- Epinephrine 33 (65) 0 ders of resistance such as asthma require Terbutaline 3 (6) 0 a single chest tube while PCV was con- tinued. All patients survived without neu- relatively slow rates for adequate ventila- PCV, pressure-controlled ventilation. rologic morbidity including polyneurop- tion. Insufficient inspiratory time would Data are absolute counts and percentages. athy associated with the use of steroids result in decreased tidal volume, whereas and neuromuscular blocking agents. incomplete exhalation would result in dy- namic hyperinflation and auto positive mented PCO before PCV, eight were end-expiratory pressure. Ventilator strat- 2 DISCUSSION intubated for clinical impression of respi- egies for patients with asthma should in- ratory fatigue and two for respiratory ar- Despite maximum medical therapy, clude relatively low respiratory rates with rest. Noninvasive ventilation was not mechanical ventilation may be needed to long expiratory times. used in any of these patients. For patients manage respiratory insufficiency result- The degree of airway obstruction is Ͼ with PCO2 45 torr within 1 hr of starting ing from airway obstruction in severe sta- not uniform in asthma and varies in dif- PCV, the median length of time until tus asthmaticus. Mechanical ventilation ferent lung units. Thus, there may be Ͻ PCO2 decreased to 45 torr was 5 hrs in patients with airway obstruction may considerable regional variation in time (1–51 hrs). SpO2 was maintained above be associated with significant morbidity constants. It could be argued that in sta- 95% in all patients throughout the ICU and mortality rates. The goal of mechan- tus asthmaticus, PCV is a better strategy stay. ical ventilation in status asthmaticus is than VCV, which is the traditionally rec- Patients were weaned from mechani- two-fold: to provide sufficient gas ex- ommended mode of ventilation (2–4). cal ventilation by decreasing the PCV syn- change to ensure survival until reversal With VCV, tidal volume is delivered at a chronized intermittent mandatory venti- of airway obstruction is accomplished, relatively constant flow rate so that rela- lation rate in 28 episodes, by providing and to minimize complications associ- tively less obstructed airways with pressure support in eight episodes, by ated with such support. The two modes of shorter time constants are likely to re- changing to VCV in five episodes, and by mechanical ventilation that are com- ceive more volume throughout inspira-

Pediatr Crit Care Med 2004 Vol. 5, No. 2 135 Table 3. Optimal ventilator settings tilation. Mechanical ventilation is most often reserved for children with actual or 1–5 Yrs 6–10 Yrs 11–18 Yrs impending respiratory failure. Of 278 pa- ϭ ϭ ϭ (n 20) (n 13) (n 18) tients with status asthmaticus admitted to the ICU during the study period, only Peak inspiratory pressure, cm H2O 36 (20–45) 38 (26–49) 40 (30–60) Rate, breaths/min 14 (10–20) 12 (10–14) 12 (8–12) 56 (20%) required intubation. These find- Inspiratory time, secs 1.0 (0.6–1.2) 1.0 (1.0–1.25) 1.2 (1.0–1.8) ings are similar to those of Roberts et al. I:E ratio 1:4 (1:3–1:5) 1:4 (1:3–1:5) 1:4 (1:2–1:5) (12), who reported a 17% incidence of PEEP, cm H O 44 4 2 mechanical ventilation in asthmatic chil- I:E, inspiratory/expiratory; PEEP, positive end-expiratory pressure. dren from 11 pediatric ICUs. Little infor- Data are median (range). mation is available in the literature re- garding the specific indications for intubation in patients with asthma. Stein Table 4. Blood gas values over time et al. (13) reported that 10% of asthmatic Within 1 Hr 4 Hrs 8 Hrs 12 Hrs children intubated in the ICU had preced- Before PCV of PCV After PCV After PCV After PCV ing respiratory arrest. Among adult stud- ies, approximately 50% of asthmatics re- pH 7.21 7.22 7.31a 7.34a 7.38a quiring intubation had cardiopulmonary (6.65–7.39) (6.95–7.47) (6.98–7.45) (7.07–7.49) (7.17–7.55) arrest or coma (14, 15). (n ϭ 48) (n ϭ 51) (n ϭ 51) (n ϭ 46) (n ϭ 43) a a a It has been suggested that mechanical PCO2, torr 65 59 41 38 37 (29–264) (24–115) (21–118) (23–98) (16–76) ventilation itself may be a cause of mor- (n ϭ 48) (n ϭ 51) (n ϭ 51) (n ϭ 46) (n ϭ 43) tality and morbidity in patients with acute severe asthma. Studies of patients PCV, pressure-controlled ventilation. with severe asthma who received me- a Ͻ p .01 by Wilcoxon’s signed ranks test compared with values obtained before PCV. Data are chanical ventilation during the 1970s and median and range. 1980s have reported mortality rates as high as 23–38% (16–18). More recent Table 5. Outcomes (n ϭ 51) studies suggest that the mortality rate for ventilated asthmatics may be decreasing Duration of mechanical ventilation, hrs 29 (4–107)a Duration of ICU stay, hrs 56 (17–183) (19, 20). The greatest threats to survival Duration of hospitalization, days 5 (2–20) in such patients are ineffective oxygen- Complications ation and ventilation, and barotrauma. Need for fluid resuscitation 40 (78)b Darioli and Perret (21) proposed using Need for vasopressors 4 (8) permissive to minimize Pneumothorax 1 (2) Pneumomediastinum 0c barotrauma in patients with asthma who Subcutaneous emphysema 1 (2) need mechanical ventilation. Purported Neurologic morbidity 0 benefits of hypercapnia include a reduc- Death 0 tion in lung stretch, dilation of small airways, improvement in collateral venti- aData are median (range); bdata are absolute counts (%); ctwo patients had pneumomediastinum before initiation of pressure-controlled ventilation. lation, and attenuation of inflammatory processes (12). Several authors have re- ported decreased mortality rates with the tion compared with more obstructed air- only study reported that describes the use use of controlled hypoventilation (14, 19, ways with longer time constants. This of PCV exclusively in managing severe 20). However, there are no controlled will result in uneven ventilation, higher respiratory failure from status asthmati- studies demonstrating benefits of permis- peak inspiratory pressure, and decrease cus. It is also the second largest study sive hypercapnia compared with normo- in dynamic compliance. With PCV, be- describing the outcome of children with capnia. Moreover, hypercapnia and the cause of the constant inflation pressure, status asthmaticus who were intubated resultant respiratory acidosis may be as- relatively less obstructed lung units with and mechanically ventilated. sociated with undesirable consequences shorter time constants will achieve pres- Risk factors for intubation in asthmat- such as decreased catecholamine respon- sure equilibration during early inspira- ics include psychosocial problems, family siveness, blunting of the effects of bron- tion and more obstructed areas with dysfunction, low socioeconomic status, chodilators (22, 23), and increased intra- longer time constants will continue to second-hand smoke exposure, parental cranial pressure. We aimed at achieving receive additional volume in late inspira- history of allergy, prior intubation, inter- normocapnia in our patients using the tion. This will result in more even distri- current respiratory infection, prior hos- pressure control, respiratory rate, in- bution of inspired gas, delivery of more pitalization for asthma in the past year, spiratory time, and expiratory time re- ␤ tidal volume for the same inflation pres- excessive use of 2-agonist inhalers, and quired to deliver the necessary tidal vol- sure, and improved dynamic compliance. steroid dependence (9–11). A number of ume and minute alveolar ventilation.

There are isolated case reports of PCV and these risk factors were evident in our More than 80% of our patients had PCO2 pressure support ventilation in patients patients (Table 1). Most children with sta- Ͼ45 torr before the institution of PCV. with status asthmaticus who required tus asthmaticus are medically managed All these patients had a steady decline in mechanical ventilation (6, 8). This is the without intubation and mechanical ven- PCO2 after institution of PCV. All patients

136 Pediatr Crit Care Med 2004 Vol. 5, No. 2 Despite eschewing permissive hyper- positive end-expiratory pressure and de- capnia, the incidence of barotrauma (4%) creased dynamic compliance. Older pa- ur retrospective was relatively low in our patients. It is of tients required higher peak inspiratory study of 51 epi- note that another two (4%) patients had pressure and lower rates. Pressure con- pulmonary airleak before initiation of trol was decreased as exhaled tidal vol- sodes in 40 pa- PCV. Furthermore, the pulmonary air- umes increased and PCO2 decreased. Once O leak in our patients was easily managed sufficiently improved, the patients were tients demonstrates the effi- and still allowed continuation of PCV rapidly weaned off the mechanical sup- port by withdrawing pharmacologic pa- cacy of pressure-controlled mode. In pediatric studies that used VCV without controlled hypoventilation, the ralysis and allowing spontaneous respira- ventilation in treating chil- incidence of barotrauma was 16–33% tions in PCV or VCV modes with or (25, 26). Studies using permissive hyper- without pressure support and decreasing dren with acute respiratory capnia and limited peak inflation pres- the synchronized intermittent mandatory sures reported the incidence of baro- ventilation rate. failure from severe status trauma ranging from zero in one study Our retrospective study of 51 episodes asthmaticus. Pressure-con- (24) to 15–20% in others (4, 13, 27, 32). in 40 patients demonstrates the efficacy The corresponding rates of barotrauma in of PCV in treating children with acute trolled ventilation represents adults who received VCV for asthma, with respiratory failure from severe status and without controlled hypoventilation asthmaticus. PCV represents a therapeu- a therapeutic option in the strategies, were 4–27% (14, 15, 19–21) tic option in the management of such children. Randomized controlled trials management of such and 2–18% (29, 30), respectively. The in- cidence of barotrauma in our study using are needed to compare the efficacy and children. PCV strategy aimed at achieving normo- complications of PCV and VCV. Further- capnia compares favorably with that re- more, the superiority of normocapnic vs. ported in the literature. A large percent- hypercapnic strategy regarding duration age (78%) of patients exhibited of mechanical ventilation and complica- tions needs to be investigated. survived to be discharged from the hos- circulatory compromise manifested by pital. cool, clammy extremities and reduced urine output. 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