Clinical Investigation

Transcription

1 1692 Clinical Investigation Interposed Abdominal Compression Cardiopulmonary Resuscitation and Resuscitation Outcome During Asystole and Electromechanical Dissociation Jeffrey B. Sack, MD; Michael B. Kesselbrenner, MD; and Anwar Jarrad, MD Background. Coronary perfusion pressure has been shown to be a significant determinant of return of spontaneous circulation from cardiac arrest during asystole and electromechanical dissociation. The addition of interposed abdominal compression to otherwise standard cardiopulmonary resuscitation (CPR) increases coronary perfusion pressure in animal and human models. Methods and Results. Accordingly, we conducted a randomized prospective study of 143 consecutive patients experiencing cardiac arrest in a large universityaffiliated teaching hospital in whom the initial arrest rhythm was asystole or electromechanical dissociation. Patients were randomized to receive either interposed abdominal compressioncpr or standard CPR. The two end points studied were return of spontaneous circulation and 24hour survival. In addition, we studied the complications associated with interposed abdominal compressioncpr. Sixtynine men and 74 women with a mean age of 64 years (range, 1997 years) were studied. The overall rate of return of spontaneous circulation was 38%. Return of spontaneous circulation was significantly greater in the group receiving interposed abdominal compressioncpr compared with the group receiving standard CPR (49%o versus 28%o, p=o.ol). At 24 hours, there was a significantly greater number of patients alive in the experimental group than in the control group (33% versus 13%, p=o.oo9). We found no complication directly related to the procedure of interposed abdominal compression in a small subset of patients who died and underwent necropsy. Conclusions. We conclude that the addition of interposed abdominal compression may be a useful adjunct to otherwise standard CPR that can improve resuscitation outcome of patients experiencing inhospital cardiac arrest from asystole and electromechanical dissociation. (Circulation 1992;86: ) KEY WORDs * aortic diastolic pressure * asystole * cardiac arrest * cardiopulmonary resuscitation * coronary perfusion pressure * counterpulsation * electromechanical dissociation epinephrine M aintenance of an adequate coronary perfusion pressure is considered a necessary requirement for the return of spontaneous circulation (ROSC) from cardiac arrest.1'2 However, even during optimally performed cardiopulmonary resuscitation (CPR), myocardial blood flow is only 35% of normal.3 The positive influence of increasing peripheral vascular tone on myocardial blood flow and coronary perfusion pressure during CPR was described by Pear From the Department of Medicine, Seton Hall University School of Graduate Medical Education, St. Joseph's Hospital and Medical Center, Paterson, N.J., and the Department of Medicine, Division of Cardiology, University of California Los Angeles Medical Center. Presented in part before the 40th Annual Scientific Session of the American College of Cardiology, Atlanta, Ga., March 37, Address for correspondence: Jeffrey B. Sack, MD, Division of Cardiology, University of California Los Angeles Medical Center, CHS, Los Angeles, CA Address for reprints: Michael B. Kesselbrenner, MD, Department of Medicine, St. Joseph's Hospital and Medical Center, Paterson, NJ Received November 24, 1991; revision accepted August 13, son and Redding4'5 and others.6 Recent efforts aimed at improving resuscitation outcome have focused on pharmacological measures that increase coronary perfusion pressure.7 The addition of interposed abdominal compression to otherwise standard cardiopulmonary resuscitation (STDCPR) refers to the technique of applying external pressure over the abdomen counter to the rhythm of chest compressions. Interposed abdominal compression is a simple adjunct to STDCPR that can supplement the use of pharmacological measures to increase myocardial blood flow. Interposed abdominal compression during otherwise standard CPR (IACCPR) has been shown to improve coronary perfusion pressure in animal8'9 and human10'1' models of cardiac arrest. Significant increases in cardiac output during CPR have been observed with the addition of interposed abdominal compression.12 Recently, IACCPR was shown to improve resuscitation rates and survival of patients experiencing inhospital cardiac arrest.'3 The most striking outcome advantage was seen in those patients whose initial arrest rhythm was asystole or electromechanical dissociation (EMD). Patients experiencing inhospital cardiac arrest from asystole or EMD have an extremely

2 Sack et al Interposed Abdominal Compression During CPR 1693 grave prognosis.14,15 Successful restoration of spontaneous circulation from asystole and EMD may be more dependent upon the maintenance of an adequate coronary perfusion pressure than ventricular fibrillation and ventricular tachycardia. We undertook this study to determine whether IACCPR could improve resuscitation outcome over STDCPR in humans experiencing inhospital cardiac arrest when the initial arrest rhythm was asystole or EMD. Methods Protocol The study institution is a 740bed tertiary care center affiliated with Seton Hall University School of Graduate Medical Education and the University of Medicine and Dentistry of New Jersey. It is a levelii trauma center, which averages 350 resuscitation attempts yearly. The study protocol was approved by the institutional review board of the hospital. All patients admitted to the medical or surgical service of the hospital were considered eligible for the study. The study included all cardiac arrests occurring in the intensive care units and general medical wards. See p 2011 A code (99) is announced on the overhead page system, and a cardiac arrest team is notified by pocket beeper. The code is supervised by a code team leader, who is a thirdyear internal medicine resident certified in advanced cardiac life support and trained in the technique of IACCPR. In addition to the code team leader, the code team consists of one secondyear and two additional first or secondyear internal medicine residents. An anesthesiology resident is always on call to perform endotracheal intubation during a cardiac arrest. The following exclusion criteria were used: cardiopulmonary arrest secondary to trauma; primary respiratory arrest; history or signs consistent with an abdominal aortic aneurysm; age less than 18 years; recent abdominal surgery (less than 2 weeks); suspected pregnancy; and the return of spontaneous circulation before arrival of the CPR team. In addition, we excluded those patients in whom endotracheal intubation took longer than 5 minutes from the arrival of the code team. Patients experiencing cardiac arrest whose initial arrest rhythm was asystole or EMD were randomized to receive either IACCPR or STDCPR. Randomization of patients was done via computergenerated random numbers on the day of cardiac arrest. All patients included in the study experienced primary cardiac arrest. All patients were unresponsive, apneic, and pulseless when CPR was initiated. Cardiac arrests that occur on the wards may not be witnessed; therefore the exact time before initiation of CPR cannot be accurately determined in all cases. The study commenced after the conclusion of our initial survival study examining 135 resuscitation attempts in 103 patients.'3 The IACCPR and STDCPR groups presented here represent an entirely new patient population with a different randomization scheme than was previously Data Collection We recorded demographic and clinical information for each patient at the time of cardiac arrest. The location of the arrest was noted. The initial arrest rhythm was documented as the first rhythm seen on telemetry at the start of CPR. In patients with previously established cardiac monitors, the initial arrest rhythm may reflect the mechanism of cardiac arrest. However, in patients on the general medical wards without cardiac monitoring, the initial arrest rhythm seen may be significantly different than the mechanism of cardiac arrest. Blood pressure in all cases was measured with a blood pressure cuff placed on an upper extremity and attached to an aneroid sphygmomanometer. Patients in intensive care units with previously inserted arterial lines had continuous arterial pressure recordings made throughout the resuscitation attempt. Blood samples were drawn at the start of CPR, at 15minute intervals, and at the end of CPR for measurement of serum electrolytes, indexes of renal funcreported. Interventions Resuscitation attempts were conducted according to current American Heart Association guidelines.'6 1AC CPR was added after endotracheal intubation in patients randomized to receive IACCPR. All medical residents were trained in the technique of IACCPR by one of the principal investigators. Abdominal compression was performed with open hands, one over the other centered over the umbilicus. Abdominal compression was begun at the start of relaxation of chest compression corresponding to CPR "early diastole." The compression force on the abdomen was maintained until the start of the next chest compression. This corresponds to a 50% duty cycle. The abdominal and chest compression rates were equal at 80100/min. The abdominal compression force was standardized to 100 mm Hg±20 mm Hg. Residents were instructed by placing an airfilled bladder with attached aneroid sphygmomanometer between the hands of the rescuer and the patient's abdomen to monitor the first minute of abdominal compressions. The remainder of IACCPR was performed with the air bladder removed. IACCPR was continued in this fashion until there was a palpable pulse or the CPR team leader determined that further resuscitation efforts would be fruitless, at which time CPR was discontinued. Ventilation was performed with a bagvalvemask apparatus attached to the endotracheal tube. Oxygen was given at a concentration of 100% FiO2 at a rate of five to eight breaths per minute in the IACCPR and STDCPR groups. One of the cardiac arrest team members made frequent clinical assessment of the patient to ensure a patent airway and good airflow in both lungs. Assessment of ventilation was based on the presence of good air entry in both lung fields by auscultation and the analysis of arterial saturation by arterial blood gases. All patients received 1 mg epinephrine intravenously at the start of CPR (i.e., at initiation of advanced cardiac life support) and at 5minute intervals. Higher doses of epinephrine were not used. Other resuscitation medications were given in accordance with current advanced life support guidelines.

3 1694 Circulation Vol 86, No 6 December 1992 tion, and hematological variables. Arterial blood samples were drawn in a similar fashion for determination of blood gas analysis. The dosage of all resuscitation medications given was recorded. End Points Patients experiencing cardiac arrest during the study period were followed for 24 hours after resuscitation. Outcome was recorded at the time of resuscitation and 24 hours after resuscitation. Few people experiencing cardiac arrest from asystole or EMD survive to hospital discharge. Therefore, survival to hospital discharge was not prospectively established as an end point. Patients surviving to hospital discharge were evaluated retrospectively. CPR was considered successful when there was return of spontaneous circulation as defined by the presence of a palpable femoral arterial pulse and systolic blood pressure >80 mm Hg for longer than 3 minutes. Other investigators have used the presence of a systolicl or mean'719 blood pressure >60 mm Hg as a measure of resuscitation success. All postmortem reports completed by the hospital's department of pathology were reviewed for evidence of abdominal trauma. The pathologist performing the autopsy was not aware of the type of CPR the patient received. Statistical Analyses All data were collected and stored on computer with DBASE IV. Statistical procedures were performed using spss Pc+ version 3.1. The two major groups (IACCPR and STDCPR) were analyzed together and separately. Resuscitation outcome and 24hour survival rates for both groups were compared using x2 analysis with Yates's correction.20 Continuous variables were analyzed by Student's twotailed t test. Categorical variables were compared by either Yates's corrected x2 analysis or Fisher's exact test where appropriate. A stepwise logistic regression model was constructed to examine the effect of the following prearrest variables on resuscitation outcome and 24hour survival: age; presence or absence of diabetes, coronary artery disease, renal failure, and sepsis; initial arrest rhythm; location of arrest; initial blood gas analysis; and the duration of CPR. Differences were considered significant when the probability values were less than or equal to Means are expressed as + SEM. Results During the period of July 1, 1990, to June 30, 1991, there were 158 cardiac arrests caused by asystole or EMD (Figure 1). Fifteen resuscitation attempts were excluded from the study. Endotracheal intubation was prolonged in five patients. Three patients had recent abdominal surgery, and three patients had a history of abdominal aortic aneurysm. Two patients experienced the return of spontaneous circulation before the arrival of the cardiac arrest team, and two patients experienced respiratory arrest only. One hundred fortythree patients were randomized to receive either IACCPR or STDCPR and followed for 24 hours. IACCPR was performed during 67 resuscitation attempts, and STD CPR was performed in 76 resuscitation attempts. FIGURE 1. Protocol schema. During the study period, there were 158 cardiac arrests in patients (Pts.) with an initial arrest rhythm of either asystole or electromechanical dissociation (EMD); 15 patients were excluded (see text), 67patients were randomized to receive interposed abdominal compressioncardiopulmonary resuscitation (IACCPR), and 76 patients were randomized to receive standard CPR (STDCPR). Clinical Characteristics of the Study Population Sixtynine men and 74 women were studied. The mean age of the study population was 64 years (range, 1997 years). There was no significant difference in the mean age of the IACCPR and STDCPR groups (64±+2 years versus 63±2 years, respectively,p=). The most common clinical diagnosis in the study group was coronary artery disease (41%). In 23% of patients, it could not be conclusively established from the record whether significant obstructive coronary artery disease existed. Table 1 lists the demographic and clinical characteristics of the IACCPR and STDCPR groups. A comparison of clinical variables revealed no significant differences between treatment groups. The initial blood gas analysis of patients experiencing cardiac arrest was ph 7.17±0.04; Po2, 83±8 mm Hg; Pco2, 36±6 mm Hg; HCO3, 16±2 mmol/l. No significant differences were found in initial arterial blood gas analysis, baseline serum electrolytes, and hematological values between the control and treatment groups. The ending blood gas analysis of the study group was ph 7.10±0.05; Po2, 122± 8 mm Hg; Pco2, 27±3 mm Hg. There was no significant difference in the ending blood gas data between the IACCPR and STDCPR groups. There was significant variation in the duration of the resuscitation attempts (median, 22 minutes; range, 580 minutes); however, there was no difference between the IACCPR and STDCPR groups (24±2 minutes versus 24±2 minutes, p=). There was a high incidence of renal insufficiency in the both the IACCPR and STD CPR groups as indicated by elevation of the serum creatinine and blood urea nitrogen levels (BUN) at the start of CPR (creatinine, 2.6±0.3 mg/dl versus 3.2±0.5 mg/dl, p=; BUN, 51±5 mg/dl versus 49±5 mg/dl, p=). Table 2 lists the principal clinical diagnosis of the study group before cardiac arrest. Seventysix percent of all resuscitation attempts were performed in the intensive care setting and 24% on general medical and surgical wards. There was no significant difference in location of arrest between the

4 Sack et al Interposed Abdominal Compression During CPR 1695 TABLE 1. Baseline Demographic and Clinical Characteristics of IACCPR and STDCPR Groups Age (years) Sex (M/F) HTN (%) DM (%) CAD (%) Duration of CPR (min) Initial ph Initial Po2 (mm Hg) Initial Pco2 (mm Hg) Initial HCO3 (mmol/l) Ending ph Ending Po2 (mm Hg) Ending Pco2 (mm Hg) BUN (mg/dl) Creatinine (mg/dl) Sodium (mmol/l) Potassium (mmol/l) Chloride (mmol/l) Bicarbonate (mmol/l) WBC (x109/l) Hemoglobin (g/dl) Hematocrit (%) Platelet count (x 109/1) IACCPR 64±2 30/ ±2 7.19± ±7 37±3 15±1 7.12± ±9 29±1 51±5 2.6± ±1 4.5± ±1 19±1 13±1 11±1 20±2 234±20 STDCPR 63±2 39/ ±2 7.14± ±11 36±3 17±1 7.09± ±11 25±1 49±5 3.2± ±2 4.3± ±2 19±1 15±2 12±2 31±2 266±29 p Means expressed as +SEM. IACCPR, interposed abdominal compressioncardiopulmonary resuscitation; STDCPR, standard CPR; HTN, hypertension; DM, diabetes mellitus (insulin and noninsulin dependent); CAD, coronary artery disease; BUN, blood urea nitrogen; WBC, white blood cell count. IACCPR and STDCPR groups (intensive care, 81% versus 76% and wards, 13% versus 18%, respectively, p=). There was no significant difference in the frequency of presenting rhythm between the IACCPR and STDCPR groups. Asystole was the initial arrest rhythm in 44 patients (66%) receiving IACCPR and 53 patients (70%) receiving STDCPR (p=). In the remaining patients, the initial arrest rhythm was EMD (Table 3). Return of Spontaneous Circulation ROSC was defined by the presence of a palpable femoral arterial pulse and systolic blood pressure >80 mm Hg for longer than 3 minutes. The overall resuscitation rate for 143 resuscitation attempts was 38%. The IACCPR group had a significantly higher rate of ROSC than the group undergoing CPR by standard methods (49% versus 28%, p=0.01). 24Hour Survival Analysis The overall 24hour survival rate was 22%. There was a significantly greater proportion of patients surviving 24 hours in the IACCPR group than in the STDCPR group (33% versus 13%, respectively,p=0.009). Table 4 compares the resuscitation rate and 24hour survival rate for each initial arrest rhythm. No patient from either group survived to hospital discharge with intact neurological function. TABLE 2. Clinical Diagnosis of IACCPR and STDCPR Groups IACCPR STDCPR Sepsis Bacterial 9 11 Fungal 2 Pneumonia Bacterial 6 6 Fungal 2 1 Other 3 1 Acute renal failure 2 4 Chronic renal failure 7 7 Acute myocardial infarction 3 4 Congestive heart failure 3 7 Atrial arrhythmias 1 1 Ventricular arrhythmias 1 1 Complete heart block 1 Digoxin toxicity 1 2 Acute mitral regurgitation 2 S/P CABG 3 0 S/P PTCA 0 2 IABP 3 2 Tamponade 1 AIDS 4 6 COPD 3 2 Cancer 1 2 Acute pancreatitis 1 Liver failure 2 Alcohol abuse 1 1 GI bleeding 1 Stroke 3 2 Hepatic encephalopathy 1 1 Complete data not available on all patients. Numbers are not mutually exclusive. IACCPR, interposed abdominal compressioncardiopulmonary resuscitation; STDCPR, standard CPR; S/P, status post; CABG, coronary artery bypass grafting; PTCA, percutaneous transluminal coronary angioplasty; IABP, intraaortic balloon pump; AIDS, acquired immune deficiency syndrome; COPD, chronic obstructive pulmonary disease; GI, gastrointestinal. Multivariate Analysis We examined prearrest variables considered predictive of outcome from CPR for their effect on ROSC and 24hour survival. The only variable consistently predictive of ROSC was initial arrest rhythm. The relative risk of not surviving the immediate resuscitation attempt in patients with asystole was 2.7 times (95% confidence level, ) that of patients with EMD (p=0.01). However, this effect was not seen when 24hour survival TABLE 3. Frequency of Presenting Rhythms During 143 Resuscitation Attempts Rhythm IACCPR (n=67) STDCPR (n=76) Asystole 44 (66%) 53 (70%) Electromechanical dissociation 23 (34%) 23 (30%) p=. IACCPR, interposed abdominal compressioncardiopulmonary resuscitation; STDCPR, standard CPR.

5 1696 Circulation Vol 86, No 6 December 1992 TABLE 4. Breakdown of Outcome by Initial Arrest Rhythm Rhythm ROSC Survived 24 hours Asystole 31/97 (32%) 17/97 (18%) IACCPR 18/44(41%) 11/44 (25%) STDCPR 13/53 (25%) 6/53 (11%) Electromechanical dissociation 23/46 (50%) 15/46 (33%) IACCPR 15/23 (65%) 11/23 (48%) STDCPR 8/23 (35%) 4/23 (17%) ROSC, return of spontaneous circulation; IACCPR, interposed abdominal compressioncardiopulmonary resuscitation; STDCPR, standard CPR. was the dependent variable. There was no effect of age (Figures 2A and 2B) or the presence of diabetes (Figure 3) on ROSC or 24hour survival. The coefficients, standard errors, and significance of the variables remaining in the final logistic model are presented in Tables 5 and 6. The interpretation of the equations is that a low Po2 or Pco2 obtained on initial arterial blood gas analysis is associated with a poor outcome. These data must be interpreted with caution, however, as the primary purpose of this study was to compare IACCPR with STDCPR with respect to resuscitation outcome, not to evaluate predictors of resuscitation success. The finding that a low initial Pco2 was associated with a poorer outcome is surprising. However, the time from cardiac arrest to measurement of Pco2 was short. It may be that the lower Pco2 reflects compensation for a metabolic acidosis. Metabolic acidosis has previously been correlated with poor outcome from cardiac arrest. Complications Before intubation, emesis was noted in eight of 67 patients (12%) in the IACCPR group and in eight of 76 patients (11%) in the STDCPR group (p=) (Table 7). After intubation, emesis occurred in five more patients in the IACCPR group and in seven more patients in the STDCPR group. These differences were not statistically significant by x2 analysis. We examined patients for clinical evidence of abdominal trauma, including the presence of hematoma, persistent abdominal pain, or the need for abdominal surgery during the postresuscitation period in patients who survived the resuscitation attempt. We found no evidence of abdominal trauma in this small sample of patients. Postmortem reports were obtained on 11 subjects and reviewed for evidence of abdominal organ damage. There were five patients from the IACCPR group and six patients from the STDCPR group for whom necropsy data were available (Table 8). We found no evidence of abdominal organ damage in the small subset of patients who received IACCPR and underwent necropsy. Discussion The reported outcome of patients experiencing cardiac arrest varies widely. Differences in discharge rates principally depend upon where the cardiac arrest took place (in versus outofhospital) and the initial mechanism of cardiac arrest. Published survival rates for outofhospital cardiac arrest during all cardiac rhythms range from 2% to 25%.2122 Outcome from inhospital cardiac arrest is generally poorer,23 26 and worse outcomes are seen in the elderly27 and in patients whose initial arrest rhythm is asystole or EMDZ8 30 Few patients experiencing inhospital cardiac arrest from asystole or EMD survive to hospital discharge.'s In the present study, we observed a significant improvement in resuscitation rates and 24hour survival with the addition of interposed abdominal compression to otherwise standard CPR in patients with asystole or EMD. Experimental studies of cardiac arrest have shown that the most common rhythms seen after immediate countershock are asystole and EMD.31 Although restoration of electrical activity of the heart may occur, there is no effective mechanical contraction caused by diffuse myocardial ischemia.1,32 Attempts to correct these rhythms must be directed toward the restoration of myocardial perfusion. Several investigators have shown that coronary perfusion pressure is a major determinant of the return of a perfusing cardiac rhythm after cardiac arrest.33 Recent focus has been on the use of highdose catecholamines for augmenting coronary perfusion pressure during CPR. The addition of interposed abdominal compression to otherwise standard CPR has been used by several groups in an attempt to increase coronary perfusion pressure. Studies have demonstrated a significant improvement in aortic diastolic and coronary perfusion pressure during CPR with interposed abdominal compression.34'35 Figure 4 demonstrates the improvement in central arterial pressures seen with the addition of A Age, in decades Age, in decades FIGURE 2. Bargraphs depict no effect ofage on return of spontaneous circulation (ROSC) (panel A) or24hoursurvival (panel B).

6 1697 Sack et al Interposed Abdominal Compression During CPR P =.008 P = T s6 % Pts %x Pts so O f P = P= 40 j ) 10t o Dlaei~fi NOWDIs~sl~c m e 1 De FIGURE 3. Bar graphs depict return of spontaneous circulation and 24hour survival rates in patients (Pts.) with and without diabetes mellitus. IACCPR, interposed abdominal compressioncardiopulmonary resuscitation; STDCPR, standard CPR. interposed abdominal compression to standard CPR in a patient with EMD. In an electrical model of the circulation, Babbs et al36 demonstrated improved myocardial perfusion with interposed abdominal compression at all levels of chest compression pressure by amounts linearly related to peak abdominal pressure. Work by Coletti et al10 demonstrated improved coronary perfusion pressure with the use of IACCPR in a dog model of cardiac arrest. Followup studies by Ralston et a18 and Voorhees et al37 in animals confirmed these findings. There are several possible mechanisms by which IACCPR may facilitate ROSC during resuscitation from cardiac arrest. Interposed abdominal compression may provide hemodynamic augmentation similar to that provided by the use of catecholamines, such as epinephrine. Epinephrine significantly improves coronary perfusion pressure; however, it increases myocardial oxygen consumption (Mvo2) as well. This may be detrimental, especially in the setting of myocardial ischemia. The use of interposed abdominal compression may be an easily applied technique that can supplement the use of exogenous catecholamines during cardiac arrest. The second mechanism by which IACCPR may improve hemodynamics during CPR is priming of the thoracic pump. The thoracic pump hypothesis of blood flow during CPR states that global increases in intrathoracic pressure are equally transmitted to the heart, lung, and pulmonary vessels such that the intrathoracic blood pool is advanced with each compression.38 During CPR diastole, elastic recoil of the thorax refills this reservoir from the extrathoracic veins. Interventions that increase intrathoracic return would be expected to increase cardiac output. We believe there is augmentation of TABLE 5. Coefficients, Standard Errors, and Significance of Individual Predictors for Logistic Regression Model With Return of Spontaneous Circulation as the Dependent Variable Coefficient Standard error X2 df p Variable Rhythm* Initial Po Initial Pco Constant = *Asystole 1, electromechanical dissociation= 1. venous return (socalled "priming the pump") with IACCPR. Additionally, Howard et al39 demonstrated that the same systemic arteriovenous pressure difference on a higher venous pedestal may better overcome capillary closing pressure, especially in the myocardium. This would be expected to improve myocardial perfusion. Although these factors appear to play a significant role in return of spontaneous circulation from cardiac arrest, further study onf blood flow during IACCPR in humans is necessary. The primary goal of this study was to determine whether the addition of interposed abdominal compression to otherwise standard CPR improves resuscitation outcome in patients experiencing inhospital cardiac arrest from asystole and EMD. In our prior study of inhospital cardiac arrest,13 a significant improvement in resuscitation outcome was seen with the use of interposed abdominal compression during all initial arrest rhythms. The most significant resuscitation advantage was seen in those patients with asystole and EMD. However, subgroup analysis did not allow adequate statistical comparison between the IACCPR and STDCPR groups. We undertook this study to examine the effects of IACCPR in patients with asystole and EMD. This study represents an entirely new population with a different randomization scheme than previously reported. Although we demonstrated improved resuscitation outcome with the use of IACCPR, the present study had limited scope and objectives. Because patients with asystole and EMD have a grave prognosis, we elected to study the immediate resuscitation outcome, namely, ROSC and 24hour survival. However, no neurological assessment was made at 24 hours. This significantly limits our findings. Moreover, there were few survivors to hospital discharge, and no patient was discharged from the hospital with intact neurological function. ResuscitaTABLE 6. Coefficients, Standard Errors, and Significance Individual Predictors for Logistic Regression Model With 24Hour Survival as the Dependent Variable Variable Coefficient Standard error x2 df Initial Po Initial Pco Constant of p

7 1698 Circulation Vol 86, No 6 December 1992 TABLE 7. Complications During CPR Complication IACCPR STDCPR Aspiration 13/67 (19%) 13/76 (17%) Before ETT 8/67 (12%) 8/76 (11%) After ETT 5/67 (7%) 5/76 (7%) Abdominal trauma* 0/67 0/76 CPR, cardiopulmonary resuscitation; IACCPR, interposed abdominal compressioncpr; STDCPR, standard CPR; ETT, endotracheal intubation. *Includes abdominal pain, hematoma, or need for abdominal surgery. tion of a patient who is then left with severe neurological deficit may not be appropriate in all instances. The inability to adequately blind the investigators during the resuscitation process is an unavoidable limitation of our study. There may have been significant observer bias in favor of the IACCPR group. In addition, enthusiasm for a new form of CPR may have led to more heroic resuscitative efforts in the IACCPR group. However, if this were the case, one would expect to find extremely poor resuscitation rates in the STD CPR group. In fact, our overall resuscitation rate of 28% for STDCPR is consistent with previously published reports.2426 In addition, the duration of CPR was not significantly different between the IACCPR and STDCPR groups. These findings are also not consistent with prolonged efforts favoring the IACCPR group. Babbs et a140 demonstrated enhanced coronary perfusion pressures with IACCPR by mechanisms completely independent of "investigator enthusiasm." Although investigator enthusiasm was not evident in our study, its potential impact cannot be ignored. We did not standardize chest compressions. There may have been differences in the force of chest compression between the IACCPR and STDCPR groups. Compression rate and force may be critical factors in determining resuscitation outcome. In addition, higher compression forces may be associated with a higher incidence of rib fractures and pulmonary atelectasis. There were no differences in ending Po2 data between the IACCPR and STDCPR groups to reflect a higher incidence of atelectasis. However, we did not systematically look at the incidence of rib fractures between groups. This, too, may limit our findings. Many investigations in both animal and human models of cardiac FaP 1 F (l 1 11 F1SmHgl )ue vi;iiilil sl_r_= 1V TABLE 8. Autopsy Data From IACCPR and STDCPR Groups IACCPR STDCPR (n=5) (n=6) Cardiomegaly 4 4 Pulmonary congestion 5 5 Hepatic congestion 5 4 Hepatic trauma 0 0 Pulmonary embolus 1 1 Sepsis 0 1 Stroke (hemorrhagic) 1 0 Splenic rupture 0 0 Chronic lymphocytic leukemia 0 1 IACCPR, interposed abdominal compressioncardiopulmonary resuscitation; STDCPR, standard CPR. arrest have attempted to standardize both compression rate and compression force with various mechanical devices (i.e., Thumper). However, these devices are not easily transported within a facility. The use of these devices would have prohibited us from initiating CPR in a timely manner. Early studies of continuous abdominal pressure during CPR led to concerns of abdominal organ damage, specifically hepatic rupture during simultaneous chest and abdominal compressions.4143 However, recent studies using abdominal compression techniques have failed to substantiate these concerns.4445 This may be due to the fact that during interposed abdominal compression there is zero or near zero pressure applied to the abdomen during chest compression. The liver is not splinted and trapped beneath the rib cage as occurs with continuous abdominal pressure. In the present study, there was no clinical evidence of abdominal trauma in either the IACCPR or STDCPR groups. However, we used clinical variables that may not have good sensitivity in detecting abdominal trauma. Biochemical markers of hepatic function were not evaluated. Although we found no evidence of abdominal organ damage in a small subset of patients from the IACCPR group who died and underwent necropsy, this small subset of patients may not be representative of the entire study group. There may have been significant abdominal organ damage caused by interposed abdominal compression that was not detected. We found no evidence of increased rates of emesis or aspiration of gastric :: i: :1. T lr T1 A1t FIGURE 4. Femoral arterial tracing (noncontinuous) ofone patient in electromechanical dissociation undergoing cardiopul H monary resuscitation (CPR). The first five V t I beats (A) were recorded during interposed +;+ abdominal compressioncpr. The last seven J J1 beats (B) were recorded during standard CPR. Time _

8 Sack et al Interposed Abdominal Compression During CPR 1699 contents in patients undergoing IACCPR. The absence of a difference between the IACCPR and STDCPR groups is consistent with prior studies in animals46 and humans.45 Previous investigations on the use of IACCPR have varied moderately in the technique. We elected to apply IACCPR with open hands, one over the other, thus more centrally directing the compression force toward the abdominal aorta in an effort to maximize aortic diastolic pressure. There are no data supporting this method of IACCPR as the optimum application of abdominal compression during CPR. In fact, Babbs47 showed that the central arteriovenous pressure difference is maximized when abdominal pressure is applied directly over the abdominal aorta, hence, the recommendation that abdominal compression should be applied just leftward of the umbilicus. However, this may predispose to increased risk of abdominal organ damage and may be more difficult to teach rescuers. We believe that the previous use of folded manometers by other investigators for the duration of CPR may have contributed adversely to the overall effect of interposed abdominal compression by decreasing the pressure force per unit area directly exerted upon the abdominal aorta, thus underestimating the benefit of IACCPR. IACCPR is an easily applied manual technique that is an evolution, not a revolution, in the treatment of cardiac arrest. We observed an improvement in resuscitation outcome in a small sample of patients suffering from inhospital cardiac arrest. The addition of interposed abdominal compression to otherwise standard CPR is an optional adjunct for which asystole and EMD may be future indications. Acknowledgments The authors wish to gratefully acknowledge the residents in internal medicine and nursing personnel of St. Joseph's Hospital and Medical Center whose cooperation made this study possible. We thank Vincent DeBari, PhD, for his generous help and thoughtful comments throughout the design and implementation of the study. We are indebted to Mitchell Finkel, MD, from the University of Pittsburgh, Division of Cardiology, for his critical review of the manuscript and his support. References 1. Paradis NA, Martin GB, Rivers EP, Goetting MG, Appleton TJ, Feingold M, Nowak RM: Coronary perfusion pressure and the return of spontaneous circulation in human cardiopulmonary resuscitation. JAMA 1990;263: Saunders AB, Ewy GA, Taft TV: Prognostic and therapeutic importance of the aortic diastolic pressure in resuscitation from cardiac arrest. Crit Care Med 1984;12: Voorhees WD, Babbs CF, Tacker WA: Regional blood flow during cardiopulmonary resuscitation in dogs. Crit Care Med 1980;8: Pearson JW, Redding JS: The role of epinephrine in cardiac resuscitation. Anesth Analg 1963;42: Pearson JW, Redding JS: Peripheral vascular tone and cardiac resuscitation. Anesth Analg 1965;44: Ralston SH, Voorhees WD, Babbs CF: Intrapulmonary epinephrine during prolonged cardiopulmonary resuscitation: Improved regional blood flow and resuscitation outcome in dogs. Ann Emerg Med 1984;13: Paradis NA, Martin GB, Rosenberg J, Rivers EP, Goetting MG, Appleton TJ, Feingold M, Cryer PE, Wortsman J, Nowak RM: The effect of standard and highdose epinephrine on coronary perfusion pressure during prolonged cardiopulmonary resuscitation. JAMA 1991;265: Ralston SH, Babbs CF, Niebauer MJ: Cardiopulmonary resuscitation with interposed abdominal compression in dogs. Anesth Analg 1982;61: Babbs CF, Tacker WA: Cardiopulmonary resuscitation with interposed abdominal compression. Circulation 1986;74(suppl IV): IV37IV Coletti RH, Kaskel PS, Cohen SR, Bregman D: Abdominal counterpulsation: A new concept in circulatory assistance. Trans Am Soc Artif Intern Organs 1982;28: Bellamy RF, DeGuzman LR, Pedersen DC: Coronary blood flow during cardiopulmonary resuscitation in swine. Circulation 1984; 69: Ward KR, Sullivan RJ, Zelenak RR, Summer WR: A comparison of interposed abdominal compression CPR and standard CPR by monitoring endtidal Pco2. Ann Emerg Med 1989;18: Sack JB, Kesselbrenner MB, Bregman D: Survival from inhospital cardiac arrest with interposed abdominal counterpulsation during cardiopulmonary resuscitation. JAMA 1992;267: Roberts D, Landolfo K, Light BR, Dobson K: Early predictors of mortality for hospitalized patients suffering cardiopulmonary arrest. Chest 1990;97: Vincent JL, Thijs L, Weil MH, Michaels S, Silverberg RA: Clinical and experimental studies on electromechanical dissociation. Circulation 1981;64: American Heart Association: Standards and guidelines for cardiopulmonary resuscitation and emergency cardiac care. JAMA 1986; 255: Kern KB, Carter AB, Showen RL, Voorhees WD, Babbs CF, Tacker WA, Ewy GA: Twentyfour hour survival in a canine model of cardiac arrest comparing three methods of manual cardiopulmonary resuscitation. JAm Coll Cardiol 1986;7: Kern KB, Carter AB, Showen RL, Voorhees WD, Babbs CF, Tacker WA, Ewy GA: Comparison of mechanical techniques of cardiopulmonary resuscitation: Survival and neurologic outcome in dogs. Am J Emerg Med 1987;5: Kette F, Weil MH, Gazmuri RJ: Buffer solutions may compromise cardiac resuscitation by reducing coronary perfusion pressure. JAMA 1991;266: Feinstein AR: Clinical Biostatistics. St Louis, CV Mosby Co, Eisenberg MS, Horwood BT, Cummins RO, ReynoldsHaertle R, Hearne TR: Cardiac arrest and resuscitation: A tale of 29 cities. Ann Emerg Med 1990;19: Eisenberg MS, Hallstrom A, Bergner L: Longterm survival after outofhospital cardiac arrest. N Engl J Med 1982;306: Bedell SE, Delbanco TL, Cook EF, Epstein FH: Survival after cardiopulmonary resuscitation in the hospital. N EnglJ Med 1983; 309: Taffet GE, Teasdale TA, Luchi RJ: Inhospital cardiopulmonary resuscitation. JAMA 1988;260: Tortolani AJ, Riscucci DA, Rosati RJ, Dixon R: Inhospital cardiopulmonary resuscitation: Patient, arrest and resuscitation factors associated with survival. Resuscitation 1990;20: Urberg M, Ways C: Survival after cardiopulmonary resuscitation for an inhospital cardiac arrest. J Fam Pract 1987;25: Murphy DJ, Murray AM, Robinson BE, Campion EW: Outcomes of cardiopulmonary resuscitation in the elderly. Ann Intern Med 1989;111: Peterson MW, Geist LJ, Schwartz DA, Konicek S, Moseley PL: Outcome after cardiopulmonary resuscitation in a medical intensive care unit. Chest 1991;100: Tortolani AJ, Risucci DA, Powell SR, Dixon R: Inhospital cardiopulmonary resuscitation during asystole. Chest 1989;96: Roberts D, Landolfo K, Light RB, Dobson K: Early predictors of mortality for hospitalized patients suffering from cardiopulmonary arrest. Chest 1990;97: Niemann JT, Cairns CB, Sharma J, Lewis RJ: Treatment of prolonged ventricular fibrillation: Immediate countershock versus highdose epinephrine and CPR preceding countershock. Circulation 1992;85: Ewy GA: Defining electromechanical dissociation.ann Emerg Med 1984;13: Saunders AB, Ewy GA, Taft TV: Prognostic and therapeutic importance of the aortic diastolic pressure in resuscitation from cardiac arrest. Crit Care Med 1984;12: Linder KH, Ahnefeld FW, Bowdler IM: Cardiopulmonary resuscitation with interposed abdominal compression after asphyxial fibrillatory cardiac or arrest in pigs. Anesthesiology 1990;72: Walker JW, Bruestle IC, White BC, Evans AT, Indreri R, Bialek H: Perfusion of the cerebral cortex by use of abdominal counter

9 1700 Circulation Vol 86, No 6 December 1992 pulsation during cardiopulmonary resuscitation. Am J Emerg Med 1984;2: Babbs CF, Ralston SH, Geddes LA: Theoretical advantages of abdominal counterpulsation in CPR as demonstrated in a simple electrical model of the circulation. Ann Emerg Med 1984;13: Voorhees WD, Babbs CF, Niebauer MJ: Improved oxygen delivery during cardiopulmonary resuscitation with interposed abdominal compressions. Ann Emerg Med 1983;12: Rudikoff MT, Maughan WL, Effron M, Freund P, Weisfeldt ML: Mechanisms of blood flow during cardiopulmonary resuscitation. Circulation 1980;61: Howard M, Carrubba C, Foss F, Janiak B, Hogan B, Guiness M: Interposed abdominal compressioncpr: Its effects on parameters of coronary perfusion in human subjects. Ann Emerg Med 1987;16: Babbs CF, Weaver JC, Ralston SH, Geddes LA: Cardiac, thoracic, and abdominal pump mechanisms in CPR: Studies in an electrical model of the circulation. Am J Emerg Med 1984;2: Bircher NG, Alifimoff JK, Safar P: Perfusion augmentation during cardiopulmonary resuscitation. Circ Shock 1980;7: Birch LH, Kenney LJ, Doombos F, Kosht DW, Barkalow CE: A study of external cardiac compression. Mich Med 1962;11: Harris LC, Kirimili B, Safar P: Augmentation of artificial circulation during cardiopulmonary resuscitation. Anesthesiology 1967;28: Berryman CR, Phillips GM: Interposed abdominal compression CPR in human subjects. Ann Emerg Med 1984;13: Mateer JR, Stueven HA, Thompson BM, Aprahamian C, Darin JC: Prehospital IACCPR versus standard CPR: Paramedic resuscitation of cardiac arrests. Am J Emerg Med 1985;3: Babbs CF, Schoenlein WE, Lowe MW: Gastric insufflation during IACCPR and standard CPR in a canine model. Am J Emerg Med 1985;3: Babbs CF: Abdominal counterpulsation in cardiopulmonary resuscitation: Animal models and theoretical considerations. J Emerg Med 1985;3:165170