# Situation: A 72-year-old woman with chronic obstructive pulmonary disease (COPD) is admitted to the intensive care unit (ICU) with an exacerbation and started on noninvasive ventilation (NIV) by face mask. Her ordered oxygen saturation target is 88–92%. She was intubated when NIV failed. On day 4 she meets readiness criteria and begins a spontaneous breathing trial. Per unit protocol, the trial is stopped for a respiratory rate above 35/min, oxygen saturation below 90%, or a change of more than 20% in heart rate or systolic pressure. Start — respiratory rate 26/min; oxygen saturation 93%; heart rate 96/min; blood pressure 128/74 mmHg 20 minutes — respiratory rate 34/min; oxygen saturation 91%; heart rate 112/min; blood pressure 156/80 mmHg What should the nurse do?

> source: MyMerci (mymerci.kr)  
> url: https://mymerci.kr/pages/nclex_q.php?qn_id=630221  
> language: ko  
> subject: Nursing Practice V — Care of Clients with Maladaptive Patterns of Behavior; Care of Clients with Life-Threatening Conditions, Acute Multi-Organ Problems, High Acuity and Emergency Situations

## 문제

Situation: A 72-year-old woman with chronic obstructive pulmonary disease (COPD) is admitted to the intensive care unit (ICU) with an exacerbation and started on noninvasive ventilation (NIV) by face mask. Her ordered oxygen saturation target is 88–92%.

She was intubated when NIV failed. On day 4 she meets readiness criteria and begins a spontaneous breathing trial. Per unit protocol, the trial is stopped for a respiratory rate above 35/min, oxygen saturation below 90%, or a change of more than 20% in heart rate or systolic pressure.
Start — respiratory rate 26/min; oxygen saturation 93%; heart rate 96/min; blood pressure 128/74 mmHg
20 minutes — respiratory rate 34/min; oxygen saturation 91%; heart rate 112/min; blood pressure 156/80 mmHg
What should the nurse do?

## 보기

1. Continue the trial, since her heart rate changed by less than 20%
2. Continue the trial, since her oxygen saturation stays above 90%
3. Prepare for extubation, since gas exchange stays within target
4. Stop the trial, resume prior support, and notify the physician **✔ 정답**

**정답: 4**

## 해설

Each criterion must be checked. The respiratory rate (34/min) and oxygen saturation (91%) are within limits, and the heart rate rose 16.7% (16 ÷ 96), but systolic pressure rose 21.9% (28 ÷ 128), above the 20% limit. One failed criterion is enough to stop the trial, return her to the previous ventilator support, and report.

## 심화 해설

Why the trial must stop

The spontaneous breathing trial (SBT) is a structured stress test. It asks whether the patient can sustain the work of breathing without excessive cardiovascular or respiratory compensation. In this patient, three of the four parameters remain within protocol limits, but one failed criterion is sufficient to terminate the trial. The systolic blood pressure rose from 128 mmHg to 156 mmHg, an increase of 28 mmHg. Calculated as a percentage change, that is 21.9% (28 ÷ 128), which exceeds the 20% threshold specified in the unit protocol.

Watch out! The heart rate increase of 16.7% (16 ÷ 96) is below the 20% cutoff, so it does not independently stop the trial. The respiratory rate of 34/min is below the 35/min limit, and the oxygen saturation of 91% is above the 90% threshold. The trial fails on blood pressure alone.

Physiologic meaning of the blood pressure rise

During an SBT, the patient transitions from positive-pressure ventilator support to spontaneous breathing. This shift increases venous return and left ventricular afterload because intrathoracic pressure becomes less positive during inspiration. In a patient with limited cardiopulmonary reserve, the left ventricle may struggle against the increased afterload, triggering a sympathetically mediated rise in systolic pressure. A systolic pressure change greater than 20% signals that the cardiovascular system is under excessive stress, even when gas exchange and respiratory rate appear acceptable. The rise from 128 to 156 mmHg suggests that the patient is not yet ready to sustain the work of breathing independently.

Why extubation is not appropriate now

Meeting gas exchange targets during the trial does not equal readiness for extubation. The SBT is designed to detect failure across multiple domains: respiratory drive, oxygenation, and hemodynamic stability. A patient who passes oxygenation but fails hemodynamic tolerance is still at high risk for post-extubation failure. Extubation failure is associated with longer ICU stays, higher mortality, and increased need for reintubation. The correct action is to return the patient to the previous ventilator settings, allow recovery, and notify the physician so the weaning plan can be reassessed.

Role of structured protocols in weaning

Standardized SBT criteria reduce reliance on subjective clinical judgment. The protocol in this scenario defines objective stopping points, which supports consistent decision-making among nurses and physicians. A nurse-led or protocol-driven approach to weaning assessment is feasible and supports safe liberation from mechanical ventilation when clear thresholds are applied. The nurse's responsibility is to monitor each parameter, calculate percentage changes accurately, and act immediately when any single criterion is breached.

Key point! The percentage change formula is (new value − baseline value) ÷ baseline value × 100. For systolic pressure: (156 − 128) ÷ 128 = 0.21875, or 21.9%. For heart rate: (112 − 96) ÷ 96 = 0.1667, or 16.7%. Only the systolic pressure crosses the 20% threshold.

| Parameter | Baseline | 20 min | Change | Limit | Pass/Fail |
| --- | --- | --- | --- | --- | --- |
| Respiratory rate | 26/min | 34/min | +8/min | above 35/min stops | Pass |
| Oxygen saturation | 93% | 91% | −2% | below 90% stops | Pass |
| Heart rate | 96/min | 112/min | 16.7% | over 20% stops | Pass |
| Systolic pressure | 128 mmHg | 156 mmHg | 21.9% | over 20% stops | Fail |

Immediate nursing actions

The nurse should stop the SBT, resume the previous mode and settings of mechanical ventilation, and notify the physician. The patient should be monitored closely for continued hemodynamic instability or respiratory distress after returning to ventilator support. Documentation should include the exact values at each time point, the calculated percentage changes, and the specific criterion that triggered termination. This information guides the next weaning attempt and helps identify whether the failure was primarily cardiovascular rather than respiratory.

## 임상 시나리오

SBT Failure: One Criterion Is EnoughStop the trial when any single parameter exceeds the protocol limit
During a spontaneous breathing trial, evaluate every parameter against the unit protocol. A trial is failed if any one criterion is breached, even if all others remain acceptable.

In this case, systolic pressure rose from 128 mmHg to 156 mmHg, a change of 28 mmHg or 21.9%, exceeding the 20% limit. Heart rate increased only 16.7%, respiratory rate 34/min was below 35/min, and SpO2 91% was above 90%, but these do not override the blood pressure failure.

The blood pressure rise reflects increased left ventricular afterload as the patient shifts from positive-pressure support to spontaneous breathing. A systolic change over 20% signals excessive cardiovascular stress, even when gas exchange appears stable.

CautionNever continue an SBT or prepare for extubation when any single failure criterion is met. Stop the trial, resume the previous ventilator settings, and notify the physician immediately.

## 핵심 개념

- **Spontaneous breathing trial** — A structured test to determine whether a mechanically ventilated patient can sustain spontaneous breathing without excessive cardiovascular or respiratory compensation.
- **SBT failure criteria** — Predetermined limits such as respiratory rate >35/min, SpO2 20% change in heart rate or systolic pressure that indicate the trial should be stopped.
- **Percentage change calculation** — The difference between two values divided by the starting value, multiplied by 100; used to assess hemodynamic changes during an SBT.
- **Systolic pressure threshold** — A rise of more than 20% from baseline during an SBT signals excessive cardiovascular stress and requires termination of the trial.
- **Ventilator weaning readiness** — The process of assessing whether a patient can transition from full ventilatory support to spontaneous breathing and eventual extubation.

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