Chest Compression, Medications, and Special Problems in Neonatal Resuscitation

Importance of Effective Ventilation

Effective positive pressure ventilation (PPV) is the most critical action needed to stabilize a newborn infant that is compromised at delivery. This is because the most likely cause of cardiovascular collapse of a newborn is asphyxia (inadequate gas exchange). When effective ventilation is the primary focus of a newborn resuscitation team, chest compressions and medications are rarely needed. Data from a busy intercity delivery service with a highly trained resuscitation team suggests that chest compressions are provided for 0.1% of all deliveries and chest compressions plus medications in 0.05%. Premature newborns have higher rates of receiving chest compressions than their term counterparts.

The most recent Neonatal Resuscitation Program (NRP) guidelines from the American Heart Association and the American Academy of Pediatrics suggest that chest compressions be performed if the heart rate remains less than 60 beats per minute after ventilation that inflates the lungs, as evidenced by chest rise with ventilation breaths. Specific steps to improve ventilation before starting chest compressions should be initiated using the mnemonic algorithm MRSOPA ( Table 34.1 ), which includes checking for a good m ask seal, r epositioning the infant in the open airway position, s uctioning the oropharynx for possible obstructing secretions, o pening the mouth so that ventilation attempts are not just through the higher resistance nasal passages, increasing the peak inspiratory p ressure of the PPV device, and placing an advanced a irway such as a laryngeal mask airway or endotracheal intubation. Thus, if at all possible, the airway should be secured and ventilation provided via an advanced airway before initiation of chest compressions. The increased focus on achieving effective ventilation means that some extra time is allowed to work on the MRSOPA steps before proceeding to chest compressions. Common sense must prevail in the uncommon circumstance when neither a laryngeal mask airway nor endotracheal tube can be placed successfully. In this situation, chest compressions may have to be started while continuing to focus on optimization of mask ventilation. This can be accomplished by observation of adequate chest rise, bilateral auscultation of the lungs, and use of an end-tidal CO ₂ (ETCO ₂ ) detector. A neonatal pig study of asphyxia-induced asystole found no difference in rates of return of spontaneous circulation when the initial steps of resuscitation (dry, position, suction if needed, and stimulation) were followed by 30 versus 60 seconds of ventilation before compressions were started; however, 90 seconds of ventilation before supporting the circulation with compressions decreased rates of return of spontaneous circulation. There is no evidence regarding optimal length of ventilation before compressions in the situation of severe bradycardia rather than asystole. There is no clinical evidence to offer guidance in either circumstance.

Current resuscitation guidelines recommend that initial PPV be provided with 21%-30% oxygen in preterm infants <35 weeks of gestation and with 21% oxygen in the remaining older preterm and term infants. Oxygen supplementation should be guided by pulse oximetry and oxygen saturation per minute-of-life norms; however, when chest compressions are initiated, it is recommended that 100% O ₂ be used until the heart rate is stabilized. This recommendation remains controversial, and clinical data for guidance are lacking. Animal studies of profound cardiovascular collapse caused by asphyxia provide mixed results, with some suggesting a protective effect when 100% O ₂ is avoided. Other studies suggest that 100% O ₂ and 21% O ₂ are equivalent, and still others suggest benefits when 100% O ₂ is used. Two clinical reports suggest that following asphyxia and resuscitation, newborns who demonstrate early hyperoxia in the neonatal intensive care unit (NICU) have worse neurologic outcomes. There are no randomized studies to determine whether hyperoxia is causal for neurologic injury or merely a marker of a more severe asphyxial insult that needed more oxygen for stabilization. The best compromise for the clinician at the present time continues to be to resuscitate with supplemental oxygen when chest compressions are necessary (as ventilation with room air will have already been tried by this point), with weaning of the oxygen as soon as possible once the heart rate is stabilized to limit exposure to hyperoxia.

Chest Compressions

The most common reason for why a newborn fails to successfully transition at birth is lack of gas exchange resulting in simultaneous hypoxia and mixed metabolic and respiratory acidosis, otherwise known as asphyxia. Combined profound hypoxia and acidosis depresses myocardial function and promotes maximal vasodilation. The goal of chest compressions is to mechanically pump the blood through the heart until the myocardium is sufficiently oxygenated to recover spontaneous function. Due to preferential perfusion of the heart and brain during cardiac compressions, greater than 50% of normal cardiac and cerebral blood flow can be achieved through optimized cardiac compressions. Improved myocardial perfusion increases the likelihood of faster return of spontaneous circulation, while improved cerebral perfusion positively impacts neurologic outcome.

Chest compressions should be centered over the lower one-third of the sternum to compress most directly over the heart. Compression of the sternum directly over the heart squeezes it against the spine. This increases intrathoracic pressure, which causes blood to be pumped from the heart into the arteries. When the pressure on the sternum is released, venous blood refills the heart and blood flows into the coronary arteries. Chest radiograph studies demonstrate that the center of the infant heart is positioned under the lower third of the sternum the majority of the time. Ten pediatric patients (between 1 month and 3 years of age) who sustained cardiac arrest and had arterial pressure monitoring lines in place were monitored during external chest compressions performed by medical providers who were blinded to the blood pressure monitoring. Compressions were provided in random order either at the level of the patient's nipples (midsternum) or over the lower one-third of the sternum above the xiphoid. Each patient served as his or her own control with compressions performed at both locations in random sequence. The performance of compressions over the lower one-third of the sternum resulted in significantly better systolic and mean arterial blood pressures. A more recent study of 63 infants confirmed that location of the left ventricle in 90% of cases was under the lower 1/3 of the sternum using infant CT scan measurements. Although there is one report of CT scan measurements for 75 infants with a mean age of 4.4 ± 3.6 months, which found the heart to be located under the lower 1/4 of the sternum, care must be taken to not be too low on the sternum to avoid dislocation of the xiphoid process, which could lead to liver laceration. Similarly, placement of the compressing thumbs must be centered over the sternal bone so as to not cause rib fractures, which could inhibit critical ventilation via pneumothoraces or a flail chest.

The two-thumb technique in which the hands encircle the chest while the thumbs compress the sternum should be used for neonatal chest compressions. The older, less effective two-finger method is no longer recommended. Evidence from animal models of asphyxia-induced asystole demonstrate that the two-thumb technique generates higher blood pressures than the two-finger technique. This has also been shown in a manikin model with a customized artificial arterial system. Manikin studies demonstrate that the two-thumb technique improves depth of compression, lessens fatigue of the compressor, and results in more consistently accurate thumb placement on the sternum than the two-finger technique. Clinical data are limited to a few case reports but also suggest that the two-thumb technique generates better perfusion pressures than the two-finger technique in newborns. In the past, the two-finger technique was used primarily as a means of keeping the compressor's arms out of the way while emergent umbilical venous line placement was obtained. With the implementation of the MRSOPA algorithm and securing an advanced airway before initiation of compressions, the compressor can move to the head of the bed once the tube or laryngeal mask is secured and continue the more effective two-thumb technique even while emergent intravenous access is obtained. It is crucial that compressions from the head of the bed never interfere with adequate ventilation and establishment of an advanced airway.

Optimal compression depth for the newborn is believed to be one-third the anterior-posterior (AP) diameter of the chest and thus varies with the size of the baby. Computed tomography images of the chest of neonates and young infants estimate that a compression depth of half the AP diameter might result in internal organ damage but that one-third the AP diameter would lessen this risk while still resulting in enough compression of the heart to generate blood flow. Clinical data are limited to a report of six infants who had arterial lines in place after cardiac surgery and subsequent cardiac arrest. Chest compressions were given to a depth of one-third the AP diameter and subsequently one-half the AP diameter. Although a compression depth of one-half the AP diameter resulted in higher mean arterial pressures, this was mainly owing to an effect on systolic blood pressure. Diastolic pressures between the two groups were similar. This is an important distinction, because coronary perfusion pressure is determined by aortic diastolic blood pressure minus the right atrial diastolic blood pressure, so it is the diastolic blood pressure that is most critical. It has also been noted that a compression-to-relaxation ratio with a slightly shorter compression than relaxation phase offers theoretical advantages for blood flow in the very young infant. The chest must be allowed to fully recoil before the next compression so that the heart can refill with blood.

The best ratio of compressions to ventilations to optimize perfusion and ventilation during neonatal resuscitation is unknown. It is clear from animal models that ventilations in combination with chest compressions result in better outcomes than if resuscitation proceeds with ventilations or compressions alone, especially during prolonged resuscitation. Physiologic mathematical modeling suggests that higher compression-to-ventilation ratios would result in underventilation of asphyxiated infants. Such models predict that three to five compressions to one ventilation should be most efficient for newborns. The current NRP guidelines recommend a ratio of three compressions to one ventilation breath such that 90 compressions and 30 breaths per minute are achieved. The medical providers performing the compressions and ventilations should communicate by having the compressor count the cadence out loud as “one and two and three and breathe and.” Studies have compared 3 : 1 to 9 : 3 compression-to-ventilation ratios and 3 : 1 to 15 : 2 ratios in newborn pig models of asystole caused by asphyxia. Although the 15 : 2 ratio provided more compressions per minute without compromising ventilation as measured by arterial blood gas and generated statistically higher diastolic blood pressures, the diastolic blood pressure was still inadequate until epinephrine was given, and thus there was no difference in the time to stabilize the heart rate. A manikin study of 3 : 1, 5 : 1, and 15 : 2 compression-to-ventilation ratios using the two-thumb technique compared depth of compressions, decay of compression depth over time, compression rates, and breaths delivered over a 2-minute interval. Providers using the 3 : 1 versus 15 : 2 ratio achieved a greater depth of compressions as well as more consistent depth over time. The 3 : 1 ratio delivered the most breaths and fewest compressions, as would be expected. Thus, there is no evidence from human, animal, manikin, or mathematical modeling studies to warrant a change from the current compression-to-ventilation ratio of 3 : 1. Rescuers may consider using higher ratios (15 : 2) if the arrest is believed to be of cardiac origin.

Concern that simultaneous compressions and ventilation breaths might impede effective ventilation has led to continued emphasis that compressions and ventilations should be coordinated during neonatal cardiopulmonary resuscitation (CPR), so that they do not interfere with each other. Although studies of asynchronous chest compressions and ventilation (CCaV) show improved minute ventilation, there was no improvement in return of spontaneous circulation (ROSC). CCaV is associated with increased rescuer fatigue and poor quality chest compressions as well as increased left ventricular lactate levels, possibly from trauma or anaerobic metabolism. Recently, neonatal animal model studies and a randomized feasibility study in a small number of neonates showed shorter time to ROSC with continuous chest compressions during sustained inflation. A larger clinical trial is underway to determine if continuous chest compressions during a sustained inflation results in increased ROSC in neonates receiving CPR.

Strategies for optimizing the quality of the compressions and ventilations with as few interruptions as possible should be considered. NRP currently recommends that the interval between auscultation pauses be at least 1 minute in an effort to decrease interruptions in perfusion. Once compressions are initiated, cardiac monitoring leads should be placed so that pauses for auscultation of heart rate can be minimized. It can take a team 17 seconds to complete the auscultation process during delivery room resuscitation when using a stethoscope. When the cardiac monitor heart rate is greater than 60 beats per minute, it is important to confirm by auscultation that the displayed heart rate is not just pulseless electrical activity.

Quantitative ETCO ₂ monitoring can serve as a noninvasive tool to eliminate frequent auscultation pauses during CPR. Changes in ETCO ₂ primarily reflect changes in cardiac output during CPR. A piglet model of asphyxia-induced asystole demonstrated that once effective PPV is provided, ETCO ₂ plummets to near zero with loss of pulmonary blood flow and then increases slightly with initiation of chest compressions, reflecting some blood being pumped through the lungs by the chest compressions. ROSC correlates with a sudden rise in ETCO ₂ as the re-established perfusion brings CO ₂ -laden blood back to the lungs. An ETCO ₂ greater than 15 mm Hg correlates well with return of an audible heart rate greater than 60 beats per minute in a newborn pig model. A single case report of CPR in a very preterm infant at birth noted ROSC just after ETCO ₂ reached 12 mm Hg during the resuscitation. Clinical correlate studies are currently underway.

Medications

When to Discontinue Resuscitation Efforts

If an infant still has no heart rate after 10 minutes of what otherwise appears to be effective resuscitation, resuscitation providers may consider discontinuing their efforts. This does not mean that the resuscitation team must stop at 10 minutes after birth, but rather that after 10 minutes of well-coordinated resuscitation efforts if the newborn is still asystolic, it is appropriate to consider discontinuation. The majority of available data indicate that after 10 minutes of asystole, there are few survivors and those who do survive frequently have severe disability. Infants with 10-minute Apgar scores of zero but who survived to be admitted to the NICU and entered into a hypothermia clinical trial had better outcomes than those reported in the systematic review by Harrington; however, there was significant selection bias. Recent cohort studies of infants with 10-minute Apgar scores of zero who were subsequently treated with hypothermia had ~20%-30% survival with normal development on early assessments. Decisions regarding whether to continue or discontinue resuscitative efforts must be individualized. Variables to be considered may include whether the resuscitation was considered optimal; the availability of advanced neonatal care such as therapeutic hypothermia; the specific circumstances before delivery (e.g., known timing of the insult); and the wishes expressed by the family.