Early positive end-expiratory pressure in the adult respiratory distress syndrome.

This prospective study was designed to determine the effect of positive end-expiratory pressure (PEEP) instituted early in the course of adult respiratory distress syndrome (ARDS). Seventy-nine (7%) of 1,200 patients admitted to the surgical intensive care unit were selected because of a high probability that ARDS would develop, and were randomized into two treatment groups. Of the 79 patients, 45 were immediately treated with 5 cm H2O of end-expiratory pressure (early PEEP group), and 34 received PEEP only when severe hypoxemia developed (late PEEP group). The incidence of ARDS was significantly lower in the early PEEP group than in the late PEEP group (20% vs 53%; P less than .002). Fewer pulmonary deaths occurred in this group (11% vs 29%; P = .02), and there was less pulmonary morbidity. This study supports the efficacy of early low-level PEEP in the treatment of patients for whom there is a high probability that ARDS will develop.     

High-level positive end-expiratory pressure management in trauma-associated adult respiratory distress syndrome.

This study evaluated the effect of high-level positive end-expiratory pressure (PEEP) on mortality, barotrauma, intrapulmonary shunt (Qsp/Qt), and oxygen delivery (DO2) in posttraumatic adult respiratory distress syndrome (ARDS). All hypoxemic trauma patients admitted to the surgical intensive care unit (SICU) in 1989-1990 who received PEEP greater than 15 cm H2O were included. The PEEP was titrated to achieve an intrapulmonary shunt (Qsp/Qt) of approximately 0.20, and FIO2 was weaned to less than 0.50. Hemodynamic and pulmonary variables at four distinct intervals were recorded. Fifty-nine patients received PEEP greater than 15 cm H2O. Of these, 19 patients died of severe head injury or uncontrollable hemorrhage (16 within 48 hours). Forty (29 male, 11 female) were evaluated in detail. The PEEP levels ranged from 18-50 cm H2O with a mean of 27. PaO2/FIO2 ratios and Qsp/Qt improved as PEEP therapy was titrated. Cardiac index and oxygen delivery were maintained or improved throughout PEEP therapy by transfusion and fluid resuscitation, with a mean maximum positive fluid balance of 21.1 L and an average of 51 units of blood and blood products transfused per patients during their SICU stay. Twenty-nine (73%) had evidence of barotrauma, the majority being pneumothoraces clearly related to the initial trauma. Only three (7.5%) had evidence of barotrauma not related to trauma or line insertion. Eight of 40 patients (20%) died. Mean ISS and RTS for the entire group were 32 and 5.88, respectively. We conclude that titration of PEEP to achieve a Qsp/Qt of approximately 0.20 is an attainable goal. This was accomplished with minimal hemodynamic effects or barotrauma and a low mortality rate.     

Clinical application of differential ventilation with selective positive end-expiratory pressure in adult respiratory distress syndrome

Differential ventilation in the lateral position with positive end-expiratory pressure (PEEP) selectively applied to the dependent lung (DVSP) has been shown to reduce venous admixture and improve oxygenation without compromizing cardiac output in short term studies of patients with acute respiratory failure. We have applied this ventilation technique as a long-term treatment in severe adult respiratory distress syndrome (ARDS) in an open clinical trial. Eleven patients with ARDS of varying aetiology were treated with DVSP for a total of 34 days.
Median duration of conventional ventilatory therapy before start of DVSP was 5 days (1 to 18 days), inspiratory oxygen fraction (F₁***₂) was 0.61 ±0.16 (mean±s.d.), resulting in a mean arterial oxygen tension (Pao₂) of 7.1±2.1 kPa (Pao₂/F₁o₂= 11 ± 4 kPa). A gradual improvement in gas exchange was seen during the first 24 h of DVSP such that Pao₂ increased to 8.4±1.4 with a decreased F₁o₂ (0.52±0.14) resulting in an increased Pao₂/F₁o₂ (16±5 kPa). Five out of the eleven patients survived. No major complication was noted using DVSP as a method. We found a steady improvement in gas exchange over the first 24 hours in most patients. However, mortality rate was no lower than expected. Drawbacks with DVSP were increased demand on staff and difficulties with adequate endo-bronchial suctioning.     

Continuous positive airway pressure versus positive end-expiratory pressure in respiratory distress syndrome.

The hemodynamic and respiratory effects of spontaneous ventilation with continuous positive airway pressure (CPAP) and mechanical ventilation with positive end-expiratory pressure (PEEP) were compared in nine patients who had adult respiratory distress syndrome. These patients were capable of maintaining spontaneous ventilation (tidal volume above 300 ml. and PaCO2 below 45 torr). Arterial and mixed venous blood gases, cardiac output, oxygen delivery and consumption, pulmonary artery pressure, and pulmonary wedge pressure were measured in 11 instances, with each patient on 5 or 10 cm. H2O CPAP or PEEP, and in nine instances, with each patient on the ventilator but without PEEP (O PEEP). During CPAP, when compared to PEEP at the same level of end-expiratory pressure, mean PaO2 increased significantly (p less than 0.05) and mean physiological shunt decreased (p less than 0.05). In nine of 11 instances, cardiac output was higher on CPAP than on a corresponding level of PEEP. Thus CPAP was more effective than the same amount of PEEP in improving arterial oxygenation by the lung without adversely affecting cardiac output.     

The use of positive end-expiratory pressure in the management of the acute respiratory distress syndrome

Clinical and experimental research on the effects of positive end-expiratory pressure (PEEP) has produced a plethora of information during the last two decades. The application of PEEP is expected to increase PaO2; however, it is generally agreed that simply using increased PaO2 as the end point is inappropriate. Four mechanisms have been proposed to explain the improved pulmonary function and gas exchange with PEEP: 1) increased functional residual capacity; 2) alveolar recruitment; 3) redistribution of extravascular lung water; and 4) improved ventilation-perfusion matching. The optimal method of applying PEEP is still controversial. The main effect of augmenting PEEP is maintain recruitment of alveolar units that were previously collapsed. Thus, since tidal volume is distributed to more alveoli, peak airway pressure is reduced and compliance is increased. During acute lung injury, and depending on the severity of lung disease, PEEP can markedly alter the compliance of the lung by alveolar recruitment. The greater the alveolar collapse and pulmonary edema, the more the compliance curve of the respiratory system shifts downward and to the right. As PEEP is applied and alveoli recruited, the pressure-volume curve shifts upward and to the left. Despite its intuitive benefit, there were very few controlled studies of the effects of PEEP on ARDS outcome and no prospective randomised controlled trial of PEEP has been ever carried out in patients with acute lung injury and/ or ARDS to evaluate its efficacy until recently.     

Pulmonary acute respiratory distress syndrome: positive end-expiratory pressure titration needs stress index

Background

The heterogeneity of lung injury in pulmonary acute respiratory distress syndrome (ARDS) may have contributed to the greater response of hyperinflated area with positive end-expiratory pressure (PEEP). PEEP titrated by stress index can reduce the risk of alveolar hyperinflation in patients with pulmonary ARDS. The authors sought to investigate the effects of PEEP titrated by stress index on lung recruitment and protection after recruitment maneuver (RM) in pulmonary ARDS patients.

Materials and methods

Thirty patients with pulmonary ARDS were enrolled. After RM, PEEP was randomly set according to stress index, oxygenation, static pulmonary compliance (Cst), or lower inflection point (LIP) + 2 cmH₂O strategies. Recruitment volume, gas exchange, respiratory mechanics, and hemodynamic parameters were collected.

Results

PEEP titrated by stress index (15.1 ± 1.8 cmH₂O) was similar to the levels titrated by oxygenation (14.5 ± 2.9 cmH₂O), higher than that titrated by Cst (11.3 ± 2.5 cmH₂O) and LIP (12.9 ± 1.6 cmH₂O) (P < 0.05). Compared with baseline, PaO₂/FiO₂ and recruitment volume were significantly improved after PEEP titration with the four strategies (P < 0.05). PaO₂/FiO₂ and recruitment volume were similar when using PEEP titrated by stress index and oxygenation but higher than that titrated by Cst and LIP. Compared with baseline, lung compliance increased significantly when PEEP determined by Cst, but there was no difference of Cst in these four strategies. There was no influence of PEEP titration with the four strategies on hemodynamic parameters.

Conclusions

PEEP titration by stress index might be more beneficial for pulmonary ARDS patients after RM.     

Recruitment maneuvers after a positive end-expiratory pressure trial do not induce sustained effects in early adult respiratory distress syndrome

BACKGROUND: Recruitment maneuvers performed in early adult respiratory distress syndrome remain a matter of dispute in patients ventilated with low tidal volumes and high levels of positive end-expiratory pressure (PEEP). In this prospective, randomized controlled study the authors evaluated the impact of recruitment maneuvers after a PEEP trial on oxygenation and venous admixture (Qs/Qt) in patients with early extrapulmonary adult respiratory distress syndrome. METHODS: After a PEEP trial 30 consecutive patients ventilated with low tidal volumes and high levels of PEEP were randomly assigned to either undergo a recruitment maneuver or not. Data were recorded at baseline, 3 min after the recruitment maneuver, and 30 min after baseline. Recruitment maneuvers were performed with a sustained inflation of 50 cm H2O maintained for 30 s. RESULTS: Compared with baseline the ratio of the arterial oxygen partial pressure to the fraction of inspired oxygen (Pao2/Fio2) and Qs/Qt improved significantly at 3 min after the recruitment maneuver (Pao2/Fio2, 139 +/- 46 mm Hg versus 246 +/- 111 mm Hg, P < 0.001; Qs/Qt, 30.8 +/- 5.8% versus 21.5 +/- 9.7%, P < 0.005), but baseline values were reached again within 30 min. No significant differences in Pao2/Fio2 and Qs/Qt were detected between the recruitment maneuver group and the control group at baseline and after 30 min (recruitment maneuver group [n = 15]: Pao2/Fio2, 139 +/- 46 mm Hg versus 138 +/- 39 mm Hg; Qs/Qt, 30.8 +/- 5.8% versus 29.2 +/- 7.4%; control group: [n = 15]: Pao2/Fio2, 145 +/- 33 mm Hg versus 155 +/- 52 mm Hg; Qs/Qt, 30.2 +/- 8.5% versus 28.1 +/- 5.4%). CONCLUSION: In patients with early extrapulmonary adult respiratory distress syndrome who underwent a PEEP trial, recruitment maneuvers failed to induce a sustained improvement of oxygenation and venous admixture.     

Spontaneous breathing with continuous positive airway pressure in adult respiratory distress syndrome.

The authors describe three systems of spontaneous respiration with positive end expiratory pressure (P.E.E.P.) : the system of continuous positive airway pressure (C.P.A.P.), the bubble and the intermittent mandatory ventilation with C.P.A.P. (I.M.V.-C.P.A.P.) by Servo-Ventilator 900 B. The results are conclusive with the C.P.A.P. unit used for post-traumatic adult patients in acute respiratory distress and for patients who have been anesthetized for more than three hours. The PaO2 significantly increase in subjects whose PaO2 in the ambient air without P.E.E.P. is lower than 70 mm Hg. The bubble is less used due to its drawbacks. The Servo 900 B offers many possibilities, one of which is reported in this paper.     

Respiratory distress syndrome and its treatment with high positive end-expiratory pressure ventilation

In a 25-month period, nine patients developed a severe, rapidly progressive respiratory distress syndrome (RDS) and did not respond adequately to conventional respiratory therapy despite the application of positive end-expiratory pressure ventilation (PEEP) up to an upper limit of 15 cm H2O. Treatment with high PEEP was instituted up to 35 cm H2O, in order to achieve a PaO2 higher than 70 mmHg. Massive infusion of electrolyte solutions, colloids and red blood cells were necessary to maintain an adequate circulation that could be monitored by simple parameters such as arterial blood pressure, peripheral skin temperature and urine production. Seven patients (78%) survived. Sepsis was the cause of death in two patients. There were no pulmonary functional or radiological abnormalities, one to 14 months after discharge from the hospital. The upper limit for PEEP should be abandoned and PEEP should be administered according to the needs of each individual patient. As an adequate oxygenation can always be achieved with high-PEEP ventilation, in surgical patients there is hardly, if ever, an indication for ECMO.     

Adjusting positive end-expiratory pressure and tidal volume in acute respiratory distress syndrome according to the pressure-volume curve

BACKGROUND: Management of acute respiratory distress syndrome (ARDS) patients implies the selection of the adequate ventilatory parameters, essentially PEEP and tidal volume (Vt), to prevent ventilator-induced lung injury. These parameters should be reset as the lung injury evolves. Among the different methods proposed for the adjustment of the ventilator, the measurement of the P-V curve has emerged as a useful, although debated, tool. Our aim has been to study the relationship between the different inflection points of the P-V curve in ARDS patients, and to assess the changes in the empiric PEEP and Vt (PEEP(emp), V(temp) following its use. METHODS: P-V curves were measured in 27 patients (lung injury score [LIS] >or= 2, 69 measurements) by means of the low-flow continuous inflation method. RESULTS: A lower inflection point (LIP) was found in all patients and, although it correlated with the PEEP(emp), there was only a fair concordance, so the PEEP was modified in 80% of the cases. The expiratory inflection point (EIP) was significantly lower than the LIP (6.3 +/- 1.7 vs. 8.1 +/- 3.2, P = 0.008). An upper inflection point was observed in 16 measurements (23%) and the Vt was reset in 20% of the cases. Both PEEP and Vt were readjusted on 10 occasions (14%). Only the EIP was significantly higher on the first 3 days of mechanical ventilation. The LIS was correlated with all the inflection points. There were no differences for any parameter independent of the cause of the ARDS (pulmonary/extrapulmonary). CONCLUSIONS: The quasi-static measurement of the P-V curve is a simple method, easy to interpret, for objective adjustment of the ventilatory parameters in ARDS patients as the lung injury evolves. The implementation of this strategy may vary the empiric clinical practice. The role of the EIP for the evaluation of the severity of lung injury deserves further investigation.     

肺牵张指数指导不同原因急性呼吸窘迫综合征复张后呼气末正压选择的实验研究

目的研究以肺牵张指数指导不同原因急性呼吸窘迫综合征(ARDS)肺复张后呼气末正压(PEEP)的选择。方法通过静脉注射油酸、生理盐水肺灌洗和盐酸吸入建立三种犬ARDS模型。容量控制通气,回归法计算肺牵张指数(b)。调整PEEP使b=1,肺复张后再次调整PEEP,分别使b=1、<1与>1。稳定通气30 min后测定肺复张容积,同时观察呼吸力学和肺气体交换。结果盐水灌洗组复张后b=1时的PEEP为(12．8±1．8)cm H2O,显著高于盐酸吸入组[(9．2±1．8)cm H2O,P<0．05],但与油酸组比较无显著差异。与复张前b=1相比,三组复张后b=1时的氧合指数均显著升高。复张后b=1时,油酸组氧合指数为(399±61)mm Hg,较b<1[(307±71)mm Hg]时显著增加(P<0．05),与b>1时比较无显著差异。复张后b=1时,盐水灌洗组氧合指数显著高于盐酸吸入组(P<0．05),但与油酸组比较无显著差异(P>0．05)。三组动物复张后b=1时肺复张容积无明显差异,但均显著高于复张前b=1时的复张容积(P<0．05)。与复张后b>1比较,三组动物复张后b=1时均具有较高的肺顺应性和明显较低的气道平台压。结论肺牵张指数可指导不同原因ARDS复张后的PEEP选择。     

Combined effects of inhaled nitric oxide and positive end-expiratory pressure during mechanical ventilation in acute respiratory distress syndrome

We studied the combined effects of inhaled nitric oxide (INO) and positive end expiratory pressure (PEEP) during mechanical ventilation in patients with acute respiratory distress syndrome (ARDS). Eleven patients received 0 and 4 parts per million of INO in random order for 30 min at PEEP levels of 0, 5, and 10 cm H2O. Respiratory and cardiovascular parameters were measured. The addition of INO and PEEP significantly improved arterial oxygenation (p < 0.005 and p < 0.0001, respectively). The combined effect of INO and PEEP on arterial oxygenation was remarkable during 10 cm H2O PEEP. There was synergistic effect on arterial oxygenation by combining INO and 10 cm H2O PEEP. The present study showed that the combination of INO and 10 cm H2O PEEP enhanced arterial oxygenation in patients with ARDS.     

Cavitating lung infarction after bland pulmonary thromboembolism in patients with the adult respiratory distress syndrome.

During one year five patients were observed with the adult respiratory distress syndrome who were found at necropsy to have cavitated lung infarcts following bland (non-infected) pulmonary thromboembolism. There were three instances of bronchopleural fistula and in one person a tension pneumothorax was the immediate cause of death. Four of the five patients had severe lung infections. In all patients airway pressure was raised as a result of positive pressure mechanical ventilation. It is postulated that diffuse microvascular injury, bacterial pneumonia, and high airway pressures may be important factors predisposing patients with adult respiratory distress syndrome to develop lung necrosis, cavitation, and bronchopleural fistula after bland pulmonary thromboembolism. This complication may occur more frequently than has been previously recognised.     

Pathophysiologic significance of lung granulocytes in human adult respiratory distress syndrome induced by septic or traumatic shock

To evaluate the significance of lung granulocytes in the adult respiratory distress syndrome (ARDS), 12 ARDS patients were studied with bronchoalveolar lavage (BAL) within 4-12 hours after clinical diagnosis of the syndrome. The specificity of pulmonary granulocytes in ARDS was investigated in comparison with five patients requiring ventilator treatment for cardiogenic pulmonary oedema and 17 normal patients about to undergo cholecystectomy. The percentage of granulocytes among recovered BAL cells was significantly higher in ARDS (77 +/- 18, M +/- SD) than in the cardiac (7 +/- 4) or the normal (1.5 +/- 1.0) group. In serial BAL (48-hour intervals) in five ARDS patients, significant reduction of granulocytes 86 +/- 11----32 +/- 10%) accompanied clinical improvement. The percentage of granulocyte in BAL correlated significantly and inversely with the PaO2/FiO2 ratio (r = -0.98), and in ARDS it was significantly higher after septic than after traumatic shock (89 +/- 14 vs. 55 +/- 12). Myeloperoxidase, a specific constituent of neutrophils, was significantly and inversely correlated with PaO2/FiO2 ratio (r = -0.62). The findings suggest a role for activated granulocytes in the lung, with release of tissue-damaging substances, in initial ARDS pathogenesis, notably when the syndrome is sepsis-induced.     

Gas exchange and lung morphology after surfactant replacement in experimental adult respiratory distress syndrome induced by repeated lung lavage

Severe respiratory insufficiency was induced in adult guinea pigs by repeated lung lavage. The animals were then ventilated for 75 min with 100% O2, insufflation pressure 28/6-8 cmH2O (2.7/0.6-0.8 kPa), frequency 30/min, and 33% inspiration time. One group of animals (I) was treated with protein-depleted porcine surfactant, prepared by a combination of sucrose-gradient centrifugation, heating to 90 degrees C, and chloroform/methanol extraction. Another group (II) received the phospholipid fraction of porcine surfactant, isolated from minced lungs by chloroform/methanol extraction and liquid-gel chromatography. Surfactant was administered in two 1-ml doses (lipid concentration 90 mg/ml) instilled via the tracheal cannula about 15 and 45 min after the lavage procedure. Non-treated, lavaged animals served as controls. After 75 min of ventilation, control values for PaO2 and PaCO2 were 13.3 +/- 6.8 and 6.8 +/- 2.3 kPa (mean +/- s.d.), respectively. The corresponding values in Group I of surfactant-treated animals were 52.9 +/- 7.7 and 4.4 +/- 1.1 kPa, in Group II 53.5 +/- 7.3 and 4.8 +/- 1.3 kPa (P less than 0.02-0.002). The two groups of surfactant-treated animals also had significantly improved alveolar air expansion in histological sections, as reflected by increased alveolar volume density (0.67 +/- 0.05 and 0.62 +/- 0.11 vs 0.45 +/- 0.08 in controls; P less than 0.002). The benefits of surfactant replacement in this experimental model were thus similar to those previously observed in animal models of neonatal surfactant deficiency as well as in babies with respiratory distress syndrome (RDS). Our data suggest that surfactant replacement might have a therapeutic effect also in clinical adult RDS.     

双相正压通气与持续正压通气对急性呼吸窘迫综合征患者肺复张效果的比较

目的 比较双相正压通气(BIPAP)与持续正压通气(CPAP)对急性呼吸窘迫综合征(ARDS)患者肺复张的效果.方法 选择ARDS患者44例,ASA Ⅲ或Ⅳ级,性别不限,年龄35～63岁,体重52～74 kg,肺复张前基础通气模式为同步间歇指令通气联合压力支持通气,随机分为2组(n=22):CPAP组和BIPAP组.CPAP组10 s内逐渐上升呼气末正压(PEEP)至30 cm H2O,持续30 s,然后在5～10 8内恢复肺复张前通气模式.BIPAP组高水平和低水平压力分别为40、20 cm H2O,持续90 s,然后在5～10 s内恢复肺复张前通气模式.记录肺复张通气前即刻(T1),肺复张通气结束后即刻(T2)、2 min(T3)、5 min(T4)、15 min(T5)、30 min(T6)时HR、MAP、CVP、SpO2和肺动态顺应性(Cdyn).分别于T1、T5、肺复张通气结束后1 h(T7)、2 h(T8)、4 h(T9)时采集桡动脉血样,测定pH值、PaO2和PaCO2,计算PaO2/FiO2比值.结果 与CPAP组比较,BIPAP组SpO2、Cdyn、PaO2和PaO2/FiO2升高,CVP降低(P<0.05),HR和MAP比较差异无统计学意义(P>0.05).与T1时比较,CPAP组T3时MAP升高,T2时CVP升高,Cdyn降低,T3～6时SpO2和Cdyn升高,T7,8时PaO2升高,T5,7,8时PaO2/FiO2升高,BIPAP组T2～6时SpO2升高,T3～6时Cdyn升高,T5,7,8时PaO2和PaO2/FiO2升高(P<0.05).结论 与CPAP比较,BIPAP对ARDS患者行肺复张通气时血液动力学影响小,可进一步提高氧合和肺顺应性,是一种安全有效的肺复张方法 .     

Beneficial effects of high positive end-expiratory pressure in lung respiratory mechanics during laparoscopic surgery

Background: The effect of neuromuscular blockade (NMB) and positive end‐expiratory pressure (PEEP) on the elastic properties of the respiratory system during pneumoperitoneum (PnP) remains a controversial subject. The main objective of the present study was to evaluate the effects of NMB and PEEP on respiratory mechanics. Methods: We performed a dynamic analysis of respiratory mechanics in patients subjected to PnP. Twenty‐one patients underwent cholecystectomy videolaparoscopy and total intravenous anesthesia. The respiratory system resistance (R_RS), pulmonary elastance (E_P), chest wall elastance (E_CW), and respiratory system elastance (E_RS) were computed via the least squares fit technique using an equation describing the motion of the respiratory system, which uses primary signs such as airway pressure, tidal volume, air flow, and esophageal pressures. Measurements were taken after tracheal intubation, PnP, NMB, establishment of PEEP (10 cmH₂O), and PEEP withdrawal [zero end‐expiratory pressure (ZEEP)]. Results: PnP significantly increased E_RS by 27%; both E_P and E_CW increased 21.3 and 64.1%, respectively (P<0.001). NMB did not alter the respiratory mechanic properties. Setting PEEP reduced E_RS by 8.6% (P<0.05), with a reduction of 10.9% in E_P (P<0.01) and a significant decline of 15.7% in R_RS (P<0.05). These transitory changes in elastance disappeared after ZEEP. Conclusions: We concluded that the 10 cmH₂O of PEEP attenuates the effects of PnP in respiratory mechanics, lowering R_RS, E_P, and E_RS. These effects may be useful in the ventilatory approach for patients experiencing a non‐physiological increase in IAP owing to PnP in laparoscopic procedures.     

Pharmacologic alterations in pulmonary artery pressure in the adult respiratory distress syndrome

The progressive hypoxemia of acute respiratory distress syndrome (ARDS) has been associated with increased pulmonary vascular resistance (PVR). Pharmacologic reduction of PVR might improve oxygenation in ARDS patients. To test this hypothesis we administered vasoactive drugs to nine hypoxemic patients (P_aO₂^0.4 < 70 Torr) with increased PVR. Nitroprusside (1–3 μg/kg/min) or glucagon (0.5 mg/min) was administered iv for 15 min. Hemodynamic measurements were obtained before and during each infusion. Thirty-minute stabilization periods were allowed between infusions. Nitroprusside significantly decreased PVR, 175 to 139 dyn · sec/cm⁵, (P < 0.05), yet intrapulmonary shunt (Q_s/Q_t) increased, 34 to 42% (P < 0.05) and arterial PO₂ decreased, 68 to 55 Torr (P < 0.01). O₂ delivery, 615 to 519 ml/min/m², was also significantly decreased (P < 0.05). Glucagon significantly increased arterial PO₂, 67 to 73 Torr (P < 0.05), with little change in Q_s/Q_t) (36.4 to 33.8%). Glucagon also increased PVR (145 to 157 dyn · sec/cm⁵). Nitroprusside-induced vasodilation is nonselective and supercedes protective hypoxic vasoconstriction. Glucagon improves oxygenation, but does not reduce PVR. Neither drug offers the patient with ARDS and pulmonary hypertension any specific benefits. The decrease in O₂ delivery with nitroprusside further indicates that this drug should be used with caution in any hypoxic patient.