diff --git a/src/main/java/reactor/rabbitmq/Sender.java b/src/main/java/reactor/rabbitmq/Sender.java
index 5af3394..b3ce4af 100644
--- a/src/main/java/reactor/rabbitmq/Sender.java
+++ b/src/main/java/reactor/rabbitmq/Sender.java
@@ -35,11 +35,9 @@
 import java.util.Iterator;
 import java.util.Map;
 import java.util.Objects;
-import java.util.concurrent.ConcurrentNavigableMap;
-import java.util.concurrent.ConcurrentSkipListMap;
-import java.util.concurrent.ExecutorService;
-import java.util.concurrent.Executors;
+import java.util.concurrent.*;
 import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicLong;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.BiConsumer;
 import java.util.function.Function;
@@ -526,7 +524,10 @@ private static class PublishConfirmSubscriber implements
 
         private final AtomicReference<Throwable> firstException = new AtomicReference<Throwable>();
 
-        private final ConcurrentNavigableMap<Long, OutboundMessage> unconfirmed = new ConcurrentSkipListMap<>();
+//        private final ConcurrentNavigableMap<Long, OutboundMessage> unconfirmed = new ConcurrentSkipListMap<>();
+
+        private final Map<Long, OutboundMessage> unconfirmed = new ConcurrentHashMap<>();
+        private final AtomicLong lowerBoundOfMultiple = new AtomicLong(1);
 
         private final Channel channel;
 
@@ -555,24 +556,48 @@ public void handleNack(long deliveryTag, boolean multiple) {
                 }
 
                 private void handleAckNack(long deliveryTag, boolean multiple, boolean ack) {
+//                    if (multiple) {
+//                        try {
+//                            ConcurrentNavigableMap<Long, OutboundMessage> unconfirmedToSend = unconfirmed.headMap(deliveryTag, true);
+//                            Iterator<Map.Entry<Long, OutboundMessage>> iterator = unconfirmedToSend.entrySet().iterator();
+//                            while (iterator.hasNext()) {
+//                                subscriber.onNext(new OutboundMessageResult(iterator.next().getValue(), ack));
+//                                iterator.remove();
+//                            }
+//                        } catch (Exception e) {
+//                            handleError(e, null);
+//                        }
+//                    } else {
+//                        OutboundMessage outboundMessage = unconfirmed.get(deliveryTag);
+//                        try {
+//                            unconfirmed.remove(deliveryTag);
+//                            subscriber.onNext(new OutboundMessageResult(outboundMessage, ack));
+//                        } catch (Exception e) {
+//                            handleError(e, new OutboundMessageResult(outboundMessage, ack));
+//                        }
+//                    }
+                    Long lowerBound = lowerBoundOfMultiple.get();
                     if (multiple) {
                         try {
-                            ConcurrentNavigableMap<Long, OutboundMessage> unconfirmedToSend = unconfirmed.headMap(deliveryTag, true);
-                            Iterator<Map.Entry<Long, OutboundMessage>> iterator = unconfirmedToSend.entrySet().iterator();
-                            while (iterator.hasNext()) {
-                                subscriber.onNext(new OutboundMessageResult(iterator.next().getValue(), ack));
-                                iterator.remove();
+                            for (long i = lowerBound; i <= deliveryTag; i++) {
+                                OutboundMessage message = unconfirmed.remove(i);
+                                if (message != null) {
+                                    subscriber.onNext(new OutboundMessageResult(message, ack));
+                                }
                             }
                         } catch (Exception e) {
                             handleError(e, null);
                         }
+                        lowerBoundOfMultiple.compareAndSet(lowerBound, deliveryTag);
                     } else {
-                        OutboundMessage outboundMessage = unconfirmed.get(deliveryTag);
+                        OutboundMessage message = unconfirmed.remove(deliveryTag);
                         try {
-                            unconfirmed.remove(deliveryTag);
-                            subscriber.onNext(new OutboundMessageResult(outboundMessage, ack));
+                            subscriber.onNext(new OutboundMessageResult(message, ack));
                         } catch (Exception e) {
-                            handleError(e, new OutboundMessageResult(outboundMessage, ack));
+                            handleError(e, new OutboundMessageResult(message, ack));
+                        }
+                        if (deliveryTag == lowerBound + 1) {
+                            lowerBoundOfMultiple.compareAndSet(lowerBound, deliveryTag);
                         }
                     }
                     if (unconfirmed.size() == 0) {